As filed with the Securities and Exchange Commission on July 9, 2026

Registration No. 333-        

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM S-4

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933

PULMATRIX, INC.

(Exact name of registrant as specified in its charter)

945 Concord Street, Suite 1217

Framingham, MA 01701

(888) 355-4440

(Address, including zip code, and telephone number, including area code, of registrant’s principal executive offices)

Peter Ludlum

Interim Chief Executive Officer

Pulmatrix, Inc.

945 Concord Street, Suite 1217

Framingham, MA 01701

(888) 355-4440

(Name, address, including zip code, and telephone number, including area code, of agent for service)

Copies of all communications, including communications sent to agent for service, should be sent to:

Approximate date of commencement of proposed sale of the securities to the public: As soon as practicable after the effective date of this registration statement and the satisfaction or waiver of all other conditions under the Merger Agreement described herein.

If the securities being registered on this Form are being offered in connection with the formation of a holding company and there is compliance with General Instruction G, check the following box: ☐

If this Form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. ☐

If this Form is a post-effective amendment filed pursuant to Rule 462(d) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. ☐

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company, or emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company,” and “emerging growth company” in Rule 12b-2 of the Exchange Act.

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 7(a)(2)(B) of the Securities Act. ☐

If applicable, place an X in the box to designate the appropriate rule provision relied upon in conducting this transaction:

Exchange Act Rule 13e-4(i) (Cross-Border Issuer Tender Offer) ☐

Exchange Act Rule 14d-1(d) (Cross-Border Third-Party Tender Offer) ☐

The Registrant hereby amends this registration statement on such date or dates as may be necessary to delay its effective date until the Registrant shall file a further amendment which specifically states that this registration statement shall thereafter become effective in accordance with Section 8(a) of the Securities Act of 1933, as amended, or until the registration statement shall become effective on such date as the Securities and Exchange Commission, acting pursuant to said Section 8(a), may determine.

The information in this preliminary proxy statement/prospectus is not complete and may be changed. Pulmatrix may not sell the securities described in this preliminary proxy statement/prospectus until the registration statement filed with the Securities and Exchange Commission, of which this preliminary proxy statement/prospectus is a part, is effective. This preliminary proxy statement/prospectus is not an offer to sell and it is not soliciting an offer to buy these securities in any jurisdiction where the offer or sale is not permitted.

PRELIMINARY PROXY STATEMENT/PROSPECTUS

SUBJECT TO COMPLETION, DATED JULY 9, 2026

PROXY STATEMENT FOR THE SPECIAL MEETING OF STOCKHOLDERS IN LIEU OF ANNUUAL MEETING OF PULMATRIX, INC. AND PROSPECTUS FOR 75,245,366 SHARES OF COMMON STOCK OF PULMATRIX, INC.

PROPOSED MERGER -

YOUR VOTE IS VERY IMPORTANT

To the Stockholders of Pulmatrix, Inc. and Eos SENOLYTIX, Inc.,

Pulmatrix, Inc., a Delaware corporation (“Pulmatrix”) and Eos SENOLYTIX Inc., a Delaware corporation (“Eos”), entered into an Agreement and Plan of Merger and Reorganization on March 26, 2026 (the “Merger Agreement”), pursuant to which, among other matters, PUOS Merger Sub, Inc., a direct, wholly owned subsidiary of Pulmatrix (“Merger Sub”), will merge with and into Eos, with Eos surviving as a wholly owned subsidiary of Pulmatrix, and the surviving corporation of the merger (the “Merger”). Pulmatrix following the Merger is referred to herein as the “Combined Company.”

At the effective time of the Merger (the “Effective Time”), Pulmatrix expects to issue 54,911,207 shares of common stock to the stockholders of Eos and investors in concurrent financings, plus 20,334,159 in additional securities for new warrants, options and restricted stock units for a total of 75,245,366 shares of common stock, to be determined as follows:

In connection with the Merger: (i) each share of Pulmatrix common stock that is issued and outstanding at the Effective Time will remain issued and outstanding and such shares, subject to the proposed Pulmatrix reverse stock split, will be unaffected by the Merger, (ii) each warrant to acquire shares of Pulmatrix common stock that is outstanding and unexercised immediately prior to the Effective Time (the “Pulmatrix Warrants”) shall survive the closing of the Merger (the “Closing”) and remain outstanding in accordance with its terms and (iii) each option to acquire shares of Pulmatrix common stock that is outstanding and unexercised immediately prior to the Effective Time (the “Pulmatrix Options”) shall survive the Closing and remain outstanding in accordance with its terms. See the sections titled “The Merger Agreement-Treatment of Pulmatrix Common Stock,” The Merger Agreement-Treatment of Pulmatrix Options,” and “The Merger Agreement-Treatment of Pulmatrix Warrants” beginning on pages 106, 106 and 106 of the accompanying proxy statement/prospectus, respectively.

Based on Pulmatrix’s and Eos’s capitalization, each as of March 26, 2026, each share of Eos capital stock is currently estimated to be entitled to receive approximately 8.64 shares of Pulmatrix common stock. This estimated exchange ratio does not give effect to the proposed Pulmatrix reverse stock split and is subject to adjustment if there is a change to the number of shares underlying Pulmatrix’s stock options or warrants that are outstanding immediately prior to the Effective Time as described in more detail in the section titled “The Merger Agreement-Exchange Ratio” beginning on page 104 of the accompanying proxy statement/prospectus.

Upon entering into the Merger Agreement, approximately 4.0 million shares of Pulmatrix securities were outstanding, including approximately 3.7 million shares of common stock and approximately 0.3 million shares underlying outstanding options and warrants. Immediately after the Merger, based solely on the estimated exchange ratio as described in the accompanying proxy statement/prospectus, these securityholders are expected to own approximately 6% of the Combined Company on a fully-diluted basis excluding the CEO RSUs, with the remaining 94% expected to be owned by Eos securityholders, including shares issued related to merger fees and shares issued or related to Pulmatrix Series B Preferred Stock. For purposes of the valuation analysis, the equity ownership of the combined company was allocated as follows: (i) 6% to the holders of Pulmatrix common stock, (ii) 3% to Palladium Capital Group, LLC as compensation in connection with the Merger, and (iii) 91% to Eos, in each case, calculated without giving effect to the issuance of the CEO RSUs. Eos’ ownership percentage was derived from a pre-money valuation of $100.0 million, plus $18.0 million of anticipated capital raising proceeds and $1.0 million invested in shares of Pulmatrix Series B Preferred Stock. Based on these assumptions, the implied value attributable to Pulmatrix’s 6% equity interest in the Combined Company is approximately $7.85 million.

Immediately following the Merger, SENOTHERAPEUTIX, Inc. is expected to beneficially own more than 50% of the voting power of the Combined Company’s outstanding common stock. SENOTHERAPEUTIX, Inc., as of March 26, 2026, is the sole stockholder of Eos. Kevin Slawin, who is expected to serve as Chief Executive Officer of the Combined Company, holds a majority of the voting power of shares of SENOTHERAPEUTIX, Inc. Under the Nasdaq listing rules, a company of which more than 50% of the voting power for the election of directors is held by an individual, group, or another company is a “controlled company” and is exempt from certain corporate governance requirements. The Combined Company will be a controlled company. Although Eos does not currently intend for the Combined Company to rely on the controlled company exemptions, the Combined Company could elect to rely on one or more of these exemptions in the future. If the Combined Company relies on any such exemptions, its investors will not have the same protections afforded to stockholders of companies that are subject to these corporate governance requirements. See “Risk Factors – The Combined Company will be a “controlled company” within the meaning of Nasdaq rules and qualifies for exemptions from certain corporate governance requirements. As a result, stockholders may not have the same protections afforded to stockholders of companies that are not exempt from such corporate governance requirements” and the sections entitled “Principal Stockholders of the Combined Company” and “Management Following the Merger – Controlled Company Exemption.” 

Shares of Pulmatrix common stock are currently listed on Nasdaq under the symbol “PULM.” Pulmatrix has filed an initial listing application for the Combined Company with Nasdaq. After completion of the Merger, Pulmatrix will be renamed “Eos SENOLYTIX Inc.” and it is expected that the common stock of the Combined Company will trade on Nasdaq under the symbol “EOSX.” On                     , 2026, the last trading day before the date of the accompanying proxy statement/prospectus, the closing sale price of Pulmatrix common stock was $              per share.

Pulmatrix stockholders are cordially invited to attend the special meeting in lieu of the annual meeting of Pulmatrix stockholders. Pulmatrix is holding its special meeting in lieu of the annual meeting of stockholders (the “Pulmatrix Special Meeting”), on                           , 2026, at                               a.m. Eastern Time, unless postponed or adjourned to a later date, in order to obtain the stockholder approvals necessary to complete the Merger and related matters. The Pulmatrix Special Meeting will be conducted exclusively online. Pulmatrix stockholders will be able to attend and participate in the Pulmatrix Special Meeting online by visiting                                                                                   , where they will be able to listen to the meeting live, submit questions and vote. At the Pulmatrix Special Meeting, Pulmatrix will ask its stockholders to:

Following the effectiveness of the registration statement of which the accompanying proxy statement/prospectus forms a part and pursuant to the Merger Agreement, Eos stockholders holding a sufficient number of shares of Eos capital stock to adopt the Merger Agreement and approve the Merger and related transactions will be asked to execute written consents providing for such adoption and approval.

After careful consideration, each of the Pulmatrix and Eos boards of directors has approved the Merger Agreement and the transactions contemplated by the Merger Agreement and have determined that it is advisable to consummate the Merger. The Pulmatrix board of directors has approved the proposals described in the accompanying proxy statement/prospectus and recommends that its stockholders vote “FOR” the applicable proposals described in the accompanying proxy statement/prospectus and “EVERY THREE YEARS” as related to the Say-On-Frequency Proposal.

YOUR VOTE IS IMPORTANT. Even if you plan to attend the Pulmatrix Special Meeting virtually, Pulmatrix requests that you sign and return the enclosed proxy or vote by mail or online to ensure that your shares will be represented at the Pulmatrix Special Meeting if you are unable to attend. You may change or revoke your proxy at any time before it is voted at the Pulmatrix Special Meeting.

More information about Pulmatrix, Eos, the Merger Agreement and transactions contemplated thereby and the foregoing proposals is contained in the accompanying proxy statement/prospectus. Pulmatrix urges you to read the accompanying proxy statement/prospectus carefully and in its entirety. IN PARTICULAR, YOU SHOULD CAREFULLY CONSIDER THE MATTERS DISCUSSED UNDER “RISK FACTORS” BEGINNING ON PAGE 24 OF THE ACCOMPANYING PROXY STATEMENT/PROSPECTUS.

Pulmatrix and Eos are excited about the opportunities the Merger brings to Pulmatrix and Eos stockholders and thank you for your consideration and continued support.

Sincerely,

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of the Merger, the issuance of Pulmatrix securities in connection with the Merger or the other transactions described in the accompanying proxy statement/prospectus or passed upon the adequacy or accuracy of the accompanying proxy statement/prospectus. Any representation to the contrary is a criminal offense.

The accompanying proxy statement/prospectus is dated              , 2026, and is first being mailed to Pulmatrix stockholders on or about                    , 2026.

PULMATRIX, INC.

945 Concord Street, Suite 1217

Framingham, MA 01701

(888) 355-4440

NOTICE OF SPECIAL MEETING OF STOCKHOLDERS IN LIEU OF

ANNUAL MEETING OF STOCKHOLDERS

To the stockholders of Pulmatrix, Inc.:

NOTICE IS HEREBY GIVEN that a virtual special meeting in lieu of the annual meeting of stockholders of Pulmatrix, Inc. (the “Pulmatrix Special Meeting”), will be held on                   , 2026, at                  a.m., Eastern Time, unless postponed or adjourned to a later date. The Pulmatrix Special Meeting will be held exclusively online. You will be able to attend and participate in the Pulmatrix Special Meeting online by visiting                                                                      , where you will be able to listen to the meeting live, submit questions and vote.

You are cordially invited to attend the Pulmatrix Special Meeting to be held for the following purposes:

Record Date: The Pulmatrix board of directors has fixed                    , 2026, as the record date (the “Record Date”) for the determination of stockholders entitled to notice of, and to vote at, the Pulmatrix Special Meeting and any adjournment or postponement thereof. Only holders of record of shares of Pulmatrix common stock at the close of business on the Record Date are entitled to notice of, and to vote at, the Pulmatrix Special Meeting. At the close of business on the Record Date, Pulmatrix had                shares of common stock and 1,000 shares of Series B Convertible Preferred Stock, par value $0.0001 per share (the “Series B Preferred Stock”), outstanding and entitled to vote.

As further described in this proxy statement/prospectus, subject to the terms and conditions of the Merger Agreement: Merger Sub will merge with and into Eos, with Eos surviving as a wholly owned subsidiary of Pulmatrix, and the surviving corporation of the merger (the “Merger”). At the effective time of the Merger (the “Effective Time”):

In connection with the Merger: (i) each share of Pulmatrix common stock that is issued and outstanding at the Effective Time will remain issued and outstanding and such shares, subject to the proposed Pulmatrix reverse stock split, will be unaffected by the Merger, (ii) each warrant to acquire shares of Pulmatrix common stock that is outstanding and unexercised immediately prior to the Effective Time shall survive the Closing and remain outstanding in accordance with its terms and (iii) each option to acquire shares of Pulmatrix common stock that is outstanding and unexercised immediately prior to the Effective Time (the “Pulmatrix Options”) shall survive the Closing and remain outstanding in accordance with its terms. See the sections titled “The Merger Agreement-Treatment of Pulmatrix Common Stock,” “The Merger Agreement-Treatment of Pulmatrix Options,” and “The Merger Agreement-Treatment of Pulmatrix Warrants” beginning on pages 106, 106 and 106 of the accompanying proxy statement/prospectus, respectively.

The above matters are more fully described in this proxy statement/prospectus, which also includes, as Annex A, a copy of the Merger Agreement. You are urged to read carefully this proxy statement/prospectus in its entirety, including each of the Annexes hereto and the accompanying financial statements provided herein.

Your vote is important. The affirmative vote of a majority of the votes cast by the holders of Pulmatrix common stock and Pulmatrix Series B Preferred Stock present in person or represented by proxy at the Pulmatrix Special Meeting and entitled to vote on such matters, voting affirmatively or negatively (excluding abstentions and broker non-votes), assuming a quorum is present, is required for approval of Proposal Nos. 1, 2, 3, 4, 6, 7, 8 and 9. A plurality of the votes cast “FOR” their election by the holders of Pulmatrix common stock present in person or represented by proxy at the Pulmatrix Special Meeting and entitled to vote on such election is required for the election of directors pursuant to Proposal No. 5. Approval of each of Proposal Nos. 1, 2 and 3 is a condition to the completion of the Merger. Therefore, the Merger cannot be consummated without the approval of Proposal Nos. 1, 2 and 3.

In addition, as of the closing of the Merger, Eos shall have received, or shall receive substantially simultaneously with the closing, aggregate gross cash proceeds of at least $13,000,000 from one or more Eos financing transactions; provided, however, that any proceeds received by Eos from bridge financing transactions (including, without limitation, any bridge loans, bridge notes, or other interim financing arrangements entered into by Eos in respect of operations of Eos during the pre-closing period) with an aggregate amount of $5,000,000 or less shall be excluded from the foregoing calculation of aggregate gross cash proceeds received and shall not count towards the satisfaction of this condition.

Even if you plan to attend the Pulmatrix Special Meeting virtually, Pulmatrix requests that you sign and return the enclosed proxy or vote by mail or online to ensure that your shares will be represented at the Pulmatrix Special Meeting if you are unable to attend. You may change or revoke your proxy at any time before it is voted at the Pulmatrix Special Meeting.

THE PULMATRIX BOARD OF DIRECTORS HAS DETERMINED AND BELIEVES THAT EACH OF THE PROPOSALS OUTLINED ABOVE IS FAIR TO, IN THE BEST INTERESTS OF, AND ADVISABLE TO PULMATRIX AND ITS STOCKHOLDERS AND HAS APPROVED EACH SUCH PROPOSAL. THE PULMATRIX BOARD OF DIRECTORS UNANIMOUSLY RECOMMENDS THAT PULMATRIX STOCKHOLDERS VOTE “FOR” EACH OF PROPOSAL NOS. 1, 2, 3, 4, 6, 7, 8 AND 9, “FOR” EACH OF THE DIRECTOR NOMINEES IN PROPOSAL NO. 5 AND “EVERY THREE YEARS” FOR PROPOSAL NO. 7.

Important Notice Regarding the Availability of Proxy Materials for the Stockholders’ Meeting to Be Held on                  , 2026, at               a.m., Eastern Time via the internet.

The proxy statement/prospectus, which also serves as the annual report to stockholders in connection with the special meeting in lieu of annual meeting, is available to stockholders at www.pulmatrix.com.

By Order of the Pulmatrix Board of Directors,

Peter Ludlum

Interim Chief Executive Officer

       , 2026

REFERENCES TO ADDITIONAL INFORMATION

This proxy statement/prospectus incorporates important business and financial information about Pulmatrix that is not included in or delivered with this document. You may obtain this information without charge through the Securities and Exchange Commission (“SEC”) website (www.sec.gov) or upon your written or oral request by contacting the Pulmatrix’s Corporate Secretary at 945 Concord Street, Suite 1217, Framingham, MA 01701 or by calling (888) 355-4440.

To ensure timely delivery of these documents, any request should be made no later than                       , 2026, to receive them before the Pulmatrix Special Meeting.

For additional details about where you can find information about Pulmatrix, please see the section titled “Where You Can Find More Information” beginning on page 235 of this proxy statement/prospectus.

ABOUT THIS PROXY STATEMENT/PROSPECTUS

This document, which forms part of a registration statement on Form S-4 filed with the SEC by Pulmatrix, constitutes a prospectus of Pulmatrix under Section 5 of the Securities Act of 1933, as amended (the “Securities Act”), with respect to the shares of Pulmatrix common stock to be issued to Eos equity holders pursuant to the Merger Agreement. This document also constitutes a proxy statement of Pulmatrix under Section 14(a) of the Securities Exchange Act of 1934, as amended (the “Exchange Act”). It also constitutes a Notice of Special Meeting of Stockholders in Lieu of Annual Meeting of Stockholders of Pulmatrix.

Pulmatrix has supplied all information contained in this proxy statement/prospectus relating to Pulmatrix, and Eos has supplied all such information relating to Eos. Pulmatrix and Eos have both contributed to the information related to the Merger contained in this proxy statement/prospectus.

You should rely only on the information contained in this proxy statement/prospectus. Pulmatrix and Eos have not authorized anyone to provide you with information that is different from that contained in this proxy statement/prospectus. This proxy statement/prospectus is dated                     , 2026, and you should not assume that the information contained in this proxy statement/prospectus is accurate as of any date other than such date unless otherwise specifically provided herein.

Further, you should not assume that the information contained in this proxy statement/prospectus is accurate as of any date other than the stated date. Neither the mailing of this proxy statement/prospectus to Pulmatrix stockholders nor the issuance by Pulmatrix of shares of its common stock pursuant to the Merger Agreement will create any implication to the contrary.

This proxy statement/prospectus does not constitute an offer to sell, or a solicitation of an offer to buy, any securities, or the solicitation of a proxy, in any jurisdiction to or from any person to whom it is unlawful to make any such offer or solicitation in such jurisdiction.

TABLE OF CONTENTS

*To be filed by amendment.

QUESTIONS AND ANSWERS ABOUT THE MERGER

Except where specifically noted, the following information and all other information contained in this proxy statement/prospectus does not give effect to the proposed reverse stock split described in Proposal No. 2 of this proxy statement/prospectus.

The following section provides answers to frequently asked questions about the Merger and the Pulmatrix Special Meeting. This section, however, provides only summary information. For a more complete response to these questions and for additional information, please refer to the cross-referenced sections.

Information about the Pulmatrix Special Meeting, the Merger, the Merger Agreement and the other business to be considered by Pulmatrix stockholders at the Pulmatrix Special Meeting is contained in this proxy statement/prospectus. Pulmatrix stockholders should read this information carefully and in its entirety, including the annexes and the documents incorporated by reference. You are invited to participate in the Pulmatrix Special Meeting and to vote on the proposals described in this proxy statement/prospectus. The proxy materials are being mailed to Pulmatrix stockholders on or about    , 2026.

At the Effective Time, upon the terms and subject to the conditions set forth in the Merger Agreement:

For a more complete description of the treatment of Eos securities in the Merger, please see the sections titled “The Merger Agreement-Merger Consideration,” and “The Merger Agreement-Exchange Ratio” beginning on pages 103 and 104, respectively, of this proxy statement/prospectus.

For a more complete description of the treatment of Pulmatrix securities in the Merger, please see the sections titled “The Merger Agreement-Treatment of Pulmatrix Common Stock,” “The Merger Agreement-Treatment of Pulmatrix Options” and “The Merger Agreement-Treatment of Pulmatrix Warrants” beginning on pages 106, 106 and 106 of the accompanying proxy statement/prospectus, respectively. Upon entering into the Merger Agreement, approximately 4.0 million shares of Pulmatrix securities were outstanding, including approximately 3.7 million shares of common stock and approximately 0.3 million shares underlying outstanding options and warrants. Immediately after the Merger, based solely on the estimated Exchange Ratio as described in this proxy statement/prospectus, Pulmatrix securityholders as of immediately prior to the Merger are expected to own approximately 6% of the Combined Company on a fully-diluted basis, excluding the CEO RSUs, with the remaining 94% expected to be owned by Eos securityholders, including the shares issued related to merger fees and shares issued or related to Pulmatrix Series B Preferred Stock.

For a more complete description of the treatment of Pulmatrix securities in the Merger, please see the sections titled “Comparative Market Price and Dividend Information,” “The Merger Agreement-Merger Consideration” and “The Merger Agreement-Exchange Ratio” beginning on pages 23, 103 and 104 respectively, of this proxy statement/prospectus.

Approval of each of Proposal Nos. 1, 2 and 3 is a condition to completion of the Merger. The issuance of Pulmatrix common stock in connection with the Merger and the change of control resulting from the Merger will not take place unless Proposal No. 1 is approved by the Pulmatrix stockholders and the Merger is consummated. The amendment to the Pulmatrix Charter to effect a reverse stock split of Pulmatrix’s issued and outstanding common stock will not take place unless Proposal No. 2 is approved by the requisite Pulmatrix stockholders and the Merger is consummated. The amendment to the Pulmatrix Charter to increase the number of authorized shares of Pulmatrix common stock will not take place unless Proposal No. 3 is approved by the requisite Pulmatrix stockholders and the Merger is consummated. The Pulmatrix board of directors may determine to effect a reverse stock split if the Reverse Stock Split Proposal is approved by the Pulmatrix stockholders, even if the other proposals to be acted upon at the meeting are not approved, including the Nasdaq Stock Issuance Proposal. However, if Pulmatrix stockholders do not approve the Nasdaq Stock Issuance Proposal, the Pulmatrix board of directors is not permitted to effect the increase in the number of shares of Pulmatrix common stock that Pulmatrix is authorized to issue, even if the Authorized Share Increase Proposal is approved by the Pulmatrix stockholders.

In addition to the requirement of obtaining Pulmatrix stockholder approval, the Closing is subject to the satisfaction or waiver of each of the other closing conditions set forth in the Merger Agreement. For a more complete description of the closing conditions under the Merger Agreement, please see the section titled “The Merger Agreement-Conditions to the Completion of the Merger” beginning on page 113 of this proxy statement/prospectus.

The approvals of Proposal Nos. 4, 5, 6, 7, 8 and 9, are not conditions to the Merger.

Your shares will be counted toward the quorum only if you submit a valid proxy (or a valid proxy is submitted on your behalf by your broker, bank or other agent) or if you attend the Pulmatrix Special Meeting virtually and vote. Abstentions and broker non-votes, if any, will be counted toward the quorum requirement. If there is no quorum, the chair of the Special Meeting or the holders of a majority of shares of common stock present at the Special Meeting, either virtually or represented by proxy, may adjourn the Special Meeting to another time or date.

The affirmative vote of a majority of the votes cast by the holders of Pulmatrix common stock present in person or represented by proxy at the Pulmatrix Special Meeting and entitled to vote on the Nasdaq Stock Issuance Proposal, voting affirmatively or negatively (excluding abstentions and broker non-votes), is required to approve the Nasdaq Stock Issuance Proposal. Abstentions and broker-non votes, if any, will have no effect on the Nasdaq Stock Issuance Proposal.

Proposal No. 2 - The Reverse Stock Split Proposal

The affirmative vote of a majority of the votes cast by the holders of Pulmatrix common stock present in person or represented by proxy at the Pulmatrix Special Meeting and entitled to vote on the Reverse Stock Split Proposal, voting affirmatively or negatively (excluding abstentions and broker non-votes), is required to approve the Reverse Stock Split Proposal. Abstentions and broker non-votes, if any, will have no effect on the Reverse Stock Split Proposal.

Proposal No. 3 - The Authorized Share Increase Proposal

The affirmative vote of a majority of the votes cast by the holders of Pulmatrix common stock present in person or represented by proxy at the Pulmatrix Special Meeting and entitled to vote on the Authorized Share Increase Proposal, voting affirmatively or negatively (excluding abstentions and broker non-votes), is required to approve the Authorized Share Increase Proposal. Abstentions and broker non-votes, if any, will have no effect on the Authorized Share Increase Proposal.

Proposal No. 4 - The Auditor Ratification Proposal

The affirmative vote of a majority of the votes cast by the holders of Pulmatrix common stock present in person or represented by proxy at the Pulmatrix Special Meeting and entitled to vote on the Auditor Ratification Proposal, voting affirmatively or negatively (excluding abstentions and broker non-votes), is required to approve the Auditor Ratification Proposal. Abstentions and broker non-votes, if any, will have no effect on the Auditor Ratification Proposal.

Proposal No. 5 - The Director Election Proposal

A nominee will be elected as a director at the Pulmatrix Special Meeting if the nominee receives a plurality of the votes cast “FOR” their election by the holders of Pulmatrix common stock present in person or represented by proxy at the Pulmatrix Special Meeting and entitled to vote on the Director Election Proposal. “Plurality” means that the individual who receives the highest number of votes cast “FOR” is elected as a director. Broker non-votes, if any, and votes that are withheld will not be counted as votes cast on the matter and will have no effect on the outcome of the election. Stockholders do not have cumulative voting rights for the election of directors.

Proposal No. 6 - The Say-on-Pay Proposal

The affirmative vote of a majority of the votes cast by the holders of Pulmatrix common stock present in person or represented by proxy at the Pulmatrix Special Meeting and entitled to vote on the Say-on-Pay Proposal, voting affirmatively or negatively (excluding abstentions and broker non-votes), is required to approve the Say-on-Pay Proposal. Abstentions and broker non-votes, if any, will have no effect on the Say-on-Pay Proposal. The Say-on-Pay Proposal is a non-binding, advisory vote.

Proposal No. 7 - The Say-on-Frequency Proposal

The affirmative vote of a majority of the votes cast by the holders of Pulmatrix common stock present in person or represented by proxy at the Pulmatrix Special Meeting and entitled to vote on the Say-on-Frequency Proposal, voting affirmatively or negatively (excluding abstentions and broker non-votes), is required to approve the Say-on-Frequency Proposal. Abstentions and broker non-votes, if any, will have no effect on the Say-on-Pay Proposal. The Say-on-Frequency Proposal is a non-binding, advisory vote.

Proposal No. 8 – The Incentive Plan Proposal

The affirmative vote of a majority of the votes cast by the holders of Pulmatrix common stock present in person or represented by proxy at the Pulmatrix Special Meeting and entitled to vote on the Incentive Plan Proposal, voting affirmatively or negatively (excluding abstentions and broker non-votes), is required to approve the Incentive Plan Proposal. Abstentions and broker non-votes, if any, will have no effect on the Incentive Plan Proposal.

Proposal No. 9 - The Adjournment Proposal

The affirmative vote of a majority of the votes cast by the holders of Pulmatrix common stock present in person or represented by proxy at the Pulmatrix Special Meeting and entitled to vote on the Adjournment Proposal, voting affirmatively or negatively (excluding abstentions and broker non-votes), is required to approve the Adjournment Proposal. Abstentions and broker non-votes, if any, will have no effect on the Adjournment Proposal.

In the case of the Merger, Pulmatrix expects to issue approximately 43.7 million shares of Pulmatrix common stock (not including any shares of Pulmatrix common stock issuable upon conversion of Eos notes, Eos Series A Preferred Stock, warrants, options, Series B Preferred Stock, the CEO RSUs and shares issuable to Palladium as compensation in connection with the Merger), and Pulmatrix common stock to be issued pursuant to the Merger Agreement will represent greater than 20% of its voting stock outstanding before the issuance. Accordingly, Pulmatrix is seeking stockholder approval of the issuance pursuant to the Merger under the Nasdaq rules.

On                    , 2026 the last trading day before the date of this proxy statement/prospectus, the closing sale price of Pulmatrix common stock was $                        per share.

The Pulmatrix board of directors also recommends that Pulmatrix stockholders vote “FOR” the director nominees in Proposal 5 and “FOR” Proposal Nos. 4, 6, 8 and 9 and “EVERY THREE YEARS” for Proposal No. 7.

Stockholder of Record: Shares Registered in Your Name

If you are a stockholder of record, you may vote at the Pulmatrix Special Meeting, vote by proxy over the telephone, vote by proxy through the Internet or vote by proxy using a proxy card, the form of which is attached as Annex J. Whether or not you plan to attend the meeting, Pulmatrix urges you to vote by proxy to ensure your vote is counted. You may still attend the meeting and vote even if you have already voted by proxy.

Your signed proxy card, telephonic proxy instructions or internet proxy instructions must be received by 11:59 p.m. Eastern Time on                , 2026, to be counted.

Beneficial Owner: Shares Registered in the Name of Broker, Bank or Other Agent

If you are a beneficial owner of shares registered in the name of your broker, bank, or other agent, you should have received voting instructions from that organization rather than from Pulmatrix. Simply follow the voting instructions provided to ensure that your vote is counted. You may vote by telephone or over the Internet as instructed by your broker, bank or other agent. To vote at the Pulmatrix Special Meeting, you must contact your broker, bank, or other agent and obtain a valid legal proxy in order to attend, participate in and vote at the Pulmatrix Special Meeting. Follow the voting instructions from your broker, bank or other agent, or contact your broker, bank or other agent for instructions.

Pulmatrix will endeavor to answer as many stockholder-submitted questions as time permits that comply with the Pulmatrix Special Meeting rules of conduct. Pulmatrix reserves the right to edit profanity or other inappropriate language and to exclude questions regarding topics that are not pertinent to meeting matters or Pulmatrix’s business. If Pulmatrix receives substantially similar questions, it may group such questions together and provide a single response to avoid repetition.

The meeting webcast will begin promptly at                                a.m., Eastern Time. Online check-in will begin approximately 15 minutes before then, and Pulmatrix encourages you to allow ample time for check-in procedures. If you experience technical difficulties during the check-in process or during the meeting, please call the number listed on the meeting website for technical support. Additional information regarding the rules and procedures for participating in the Pulmatrix Special Meeting will be set forth in Pulmatrix’s meeting rules of conduct, which stockholders can view during the meeting at the meeting website.

If your shares of Pulmatrix common stock are registered directly in your name with Pulmatrix’s transfer agent, VStock Transfer, LLC, you are considered to be, with respect to those shares of Pulmatrix common stock, the registered stockholder, and these proxy materials are being sent directly to you by Pulmatrix.

Beneficial Owner: Shares Registered in the Name of Broker, Bank or Other Agent

If your shares of Pulmatrix common stock are held by a broker, bank or other agent, you are considered the beneficial owner of shares of Pulmatrix common stock held in street name, and these proxy materials are being forwarded to you from that broker, bank or other agent.

If you are the registered stockholder and do not vote in one of the ways described above, your shares will not be voted at the Pulmatrix Special Meeting and will not be counted toward the quorum requirement.

Beneficial Owner: Shares Registered in the Name of Broker, Bank or Other Agent

If you are the beneficial owner and do not direct your broker, bank or other agent how to vote your shares, your broker, bank or other agent will only be able to vote your shares with respect to proposals considered to be “routine.” Your broker, bank or other agent is not entitled to vote your shares with respect to “non-routine” proposals, which Pulmatrix refers to as a “broker non-vote.” Whether a proposal is considered routine or non-routine is subject to stock exchange rules and final determination by the stock exchange. Even with respect to routine matters, some brokers are choosing not to exercise discretionary voting authority. As a result, Pulmatrix urges you to direct your broker, bank or other agent how to vote your shares on all proposals to ensure that your vote is counted.

The shares represented by each signed and returned proxy will be voted at the Pulmatrix Special Meeting by the persons named as proxies in the proxy card in accordance with the instructions indicated on the proxy card.

However, if you are the registered stockholder and sign and return your proxy card without giving specific instructions, the persons named as proxies in the proxy card will vote your shares in accordance with the recommendations of the Pulmatrix board of directors. Your shares will be counted toward the quorum requirement.

Beneficial Owner: Shares Registered in the Name of Broker, Bank or Other Agent

If you are the beneficial owner and do not direct your broker, bank or other agent how to vote your shares, your broker, bank or other agent will only be able to vote your shares with respect to proposals considered to be “routine.” Your broker, bank or other agent is not entitled to vote your shares with respect to “non-routine” proposals, resulting in a broker non-vote with respect to such proposals. Accordingly, if you hold your shares beneficially in street name please be sure to instruct your broker, bank or other agent how to vote to ensure that your vote is counted on each of the proposals, following the procedures provided by your broker, bank or other agent.

Pulmatrix stockholders of record may revoke and/or change their vote at any time before their proxy is voted at the Pulmatrix Special Meeting in one of four ways:

Your signed proxy card, telephonic proxy instructions, internet proxy instructions, or written notice must be received by                                     , 2026, 11:59 p.m. Eastern Time to be counted.

Beneficial Owner: Shares Registered in the Name of Broker, Bank or Other Agent

If a Pulmatrix stockholder who beneficially owns Pulmatrix shares in street name has instructed a broker, bank or other agent to vote its shares of Pulmatrix common stock, the stockholder must follow directions received from its broker, bank or other agent to change and/or revoke those instructions.

North American Toll-Free Phone: +1 (855) 434-5243

Email: info@campaign-mgmt.com

Call Collect Outside North America: +1 (212) 632-8422

PROSPECTUS SUMMARY

This summary highlights selected information from this proxy statement/prospectus and may not contain all of the information that is important to you. To better understand the Merger and the proposals being considered at the Pulmatrix Special Meeting, you should read this entire proxy statement/prospectus carefully, including the Merger Agreement and the other annexes to which you are referred in this proxy statement/prospectus, and the documents incorporated by reference therein. For more information, please see the section titled “Where You Can Find More Information” beginning on page 235 of this proxy statement/prospectus. Except where specifically noted, the following information and all other information contained in this proxy statement/prospectus does not give effect to the proposed reverse stock split described in Proposal No. 2 of this proxy statement/prospectus.

The Companies

Pulmatrix, Inc.

945 Concord Street, Suite 1217

Framingham, MA 01701

(888) 355-4440

Pulmatrix is a biopharmaceutical company that has focused on the development of novel inhaled therapeutic products intended to prevent and treat migraine and respiratory diseases with important unmet medical needs using Pulmatrix’s patented iSPERSE™ technology. Pulmatrix’s proprietary product pipeline includes treatments for central nervous system (“CNS”) disorders such as acute migraine and serious lung diseases such as Chronic Obstructive Pulmonary Disease (“COPD”) and allergic bronchopulmonary aspergillosis (“ABPA”). Pulmatrix’s product candidates are based on its proprietary engineered dry powder delivery platform, iSPERSE™, which seeks to improve therapeutic delivery to the lungs by optimizing pharmacokinetics and reducing systemic side effects to improve patient outcomes.

Pulmatrix designs and develops inhaled therapeutic products based on its proprietary dry powder delivery technology, iSPERSE™, which enables delivery of small or large molecule drugs to the lungs by inhalation for local or systemic applications. The iSPERSE™ powders are engineered to be small, dense particles with highly efficient dispersibility and delivery to airways. iSPERSE™ powders can be used with an array of dry powder inhaler technologies and can be formulated with a broad range of drug substances including small molecules, biologics, drug combinations, peptides, proteins and nucleic acids. Pulmatrix believes the iSPERSE™ dry powder technology offers enhanced drug loading and delivery efficiency that outperforms traditional lactose-blend inhaled dry powder therapies.

Eos SENOLYTIX Inc.

2710 Reed Road, Suite 160

Houston, TX 77051

Phone Number: (305) 809-6920

Eos is a biotechnology company focused on the clinical development of novel therapeutics targeting biological mechanisms associated with aging. Eos’s approach is based on the hypothesis that addressing fundamental drivers of cellular dysfunction associated with aging may improve physiological function and mitigate the progression of a broad range of age-related conditions.

Eos is developing specific members of a novel class of peptide-based therapeutics, which are referred to as MitoXcel™ geropeptides, that range in size from 18 to 30 amino acids and are designed to both modulate mitochondrial function and selectively target senescent cells for self-elimination via a single target, the lower and declining Mitochondrial Membrane Potential (“MMP” or “ΔΨm”) that universally develops in every living organism with aging. Eos’s lead product candidate, PTC-2105, an 18 amino acid MitoXcel™ geropeptide licensed from SENOTHERAPEUTIX, Inc., is in clinical development for the treatment of sarcopenia and sarcopenic obesity, conditions characterized by loss of muscle mass, impaired physical function, and increased morbidity in a large proportion of aging populations. Eos’s next generation mitochondria-targeted therapeutic candidates seek to build on the science behind Stealth Bio’s Forzinity™ (elamipretide), a tetrapeptide (4 amino acids) recently granted accelerated approval by the FDA for the treatment of Barth syndrome, a rare, serious and life-threatening disease condition characterized by muscle weakness, chronic fatigue, and low muscle mass. Forzinity was granted accelerated approval based on improvement in knee extensor muscle strength. While Stealth Bio, recently renamed Mighty Therapeutics, is still required to conduct post-approval trials to confirm Forzinity’s long term clinical effectiveness, Forzinity remains the first FDA-approved therapy that directly targets mitochondria. While no relationship exists between the two companies, Eos’s programs are designed to advance the inner mitochondrial membrane as a target through next-generation compounds. 

Eos is in the preclinical stage of development and is conducting IND-enabling studies to support the initiation of first-in-human clinical trials.

PUOS Merger Sub, Inc.

945 Concord Street, Suite 1217

Framingham, MA 01701

(888) 355-4440

Merger Sub is a direct, wholly owned subsidiary of Pulmatrix and was formed solely for the purpose of carrying out the Merger.

The Merger (see page 73)

Pursuant to the Merger Agreement, subject to the satisfaction or waiver of the conditions to closing set forth in the Merger Agreement, Merger Sub will merge with and into Eos, with Eos continuing as a wholly owned subsidiary of Pulmatrix and the surviving corporation of the Merger.

If the Merger is completed, it is expected the Combined Company will prioritize developing Eos’s product candidates, however, the legacy Pulmatrix business will continue to operate as a business stream of the Combined Company. In addition, Eos will potentially explore the possibility of delivering certain Eos pipeline follow-on indications candidate MitoXcel geropeptides via the pulmonary route using Pulmatrix’s iSPERSE™ technology.

Pulmatrix’s PUR3100 has received the FDA acceptance of an IND application and receipt of a “study may proceed” letter for a Phase 2 study. Pulmatrix has also internally explored a direct-to-Phase 3 pathway. Pulmatrix is seeking a licensing partner for this product. Pulmatrix’s partner for PUR1900, Cipla, has been approved to commence a Phase 3 trial in India. Pulmatrix will receive 2% royalties on any potential future net sales by Cipla outside the United States. Within the United States, Pulmatrix and Cipla share a 50%/50% interest in any future U.S based development. Pulmatrix’s PUR1800 has completed Phase 1 and is dependent on a license from a third party.

Pulmatrix is seeking to consummate a strategic transaction and in particular this merger, in part because it was unable to obtain funding or a partnership to further pursue its product candidates and in part due to the 2022-2025 decrease in U.S. biotechnology funding transactions. There were no clinical or regulatory challenges associated with further developing our product candidates other than the time and costs required for clinical trials.

Pulmatrix’s Reasons for the Merger (see pages 82 to 85)

In reaching its decision to approve the Merger Agreement and the transactions contemplated by the Merger Agreement, the Pulmatrix board of directors considered a number of factors that it viewed as supporting its decision to approve the Merger Agreement, including the following (which factors are not necessarily presented in any order of relative importance):

Eos’s Reasons for the Merger (see pages 85 to 86)

In reaching its decision to approve the Merger Agreement and the transactions contemplated by the Merger Agreement, the Eos board of directors considered a number of factors that it viewed as supporting its decision to approve the Merger Agreement, including the following (which factors are not necessarily presented in any order of relative importance):

Interests of Pulmatrix Directors, Officers and Affiliates in the Merger (see pages 94 and 95)

In considering the recommendation of the Pulmatrix board of directors with respect to issuing shares of Pulmatrix common stock in the Merger and the other matters to be acted upon by the Pulmatrix stockholders at the Pulmatrix Special Meeting, the Pulmatrix stockholders should be aware that Pulmatrix directors and executive officers have interests in the Merger that are different from, or in addition to, the interests of Pulmatrix stockholders generally. These interests may present Pulmatrix directors and executive officers with actual or potential conflicts of interest. These interests include the following:

Interests of Eos Directors, Officers and Affiliates in the Merger (see pages 95 and 96)

In considering the recommendation of the Eos board of directors with respect to approving the Merger, stockholders should be aware that Eos’s directors and executive officers have interests in the Merger that are different from, or in addition to, the interests of Eos stockholders generally. These interests may present them with actual or potential conflicts of interest. These interests include the following:

The Eos board of directors was aware of these potential conflicts of interest and considered them, among other matters, in reaching its decision to approve the Merger Agreement and the Merger, and to recommend that the Eos stockholders approve the Merger as contemplated by this proxy statement/prospectus.

Opinion of Pulmatrix’s Financial Advisor (see page 86)

On March 22, 2026, Gemini Valuation Services, LLC (“Gemini” or “GVS”) rendered its opinion to the Pulmatrix board of directors that, as of such date and based upon and subject to the various assumptions and limitations made, and such other factors Gemini deemed relevant upon the review undertaken by Gemini in preparing its opinion, the exchange ratio proposed to be paid by Pulmatrix pursuant to the terms of the Merger Agreement was fair, from a financial point of view, to the holders of Pulmatrix common stock.

The full text of the written opinion of Gemini, dated March 22, 2026, which describes the assumptions made and the qualifications and limitations upon the review undertaken by Gemini in preparing its opinion, is attached as Annex D to this proxy statement/prospectus and is incorporated herein by reference. Gemini’s financial advisory services and opinion were provided for the information and assistance of the Pulmatrix board of directors (in their capacity as directors and not in any other capacity) in connection with and for purposes of the Pulmatrix board of directors’ consideration of the Merger and the opinion of Gemini addressed only the fairness, from a financial point of view, as of the date thereof, to the holders of Pulmatrix common stock of the exchange ratio proposed to be paid by Pulmatrix pursuant to the terms of the Merger Agreement. The opinion of Gemini did not address any other term or aspect of the Merger Agreement or the Merger and does not constitute a recommendation to any stockholder of Pulmatrix or Eos as to whether or how such holder should vote with respect to the Merger or otherwise act with respect to the Merger or any other matter.

The full text of the written opinion of Gemini should be read carefully in its entirety for a description of the assumptions made and qualifications and limitations upon the review undertaken by Gemini in preparing its opinion.

Overview of the Merger Agreement and Agreements Related to the Merger Agreement

Merger Consideration and Adjustment (see page 97)

Treatment of Eos Capital Stock

At the Effective Time, upon the terms and subject to the conditions set forth in the Merger Agreement, each then-outstanding share of Eos Capital Stock will be converted into the right to receive a number of shares of Pulmatrix common stock calculated in accordance with the Merger Agreement.

Upon entering into the Merger Agreement, approximately 4.0 million shares of Pulmatrix securities were outstanding, including approximately 3.7 million shares of common stock and approximately 0.3 million shares underlying outstanding options and warrants. Immediately after the Merger, based solely on the estimated Exchange Ratio as described in this proxy statement/prospectus, Pulmatrix securityholders as of immediately prior to the Merger are expected to own approximately 6% of the Combined Company on a fully-diluted basis, excluding the CEO RSUs, with the remaining 94% expected to be owned by Eos securityholders, including the shares issued related to merger fees and shares issued or related to Pulmatrix Series B Preferred Stock.

Treatment of Eos Options (see page 105)

At the Effective Time, Pulmatrix shall assume each Eos Equity Incentive Plan and each stock option of Eos, whether vested or unvested, that is outstanding immediately prior to the Effective Time, which shall, at the Effective Time, cease to represent a right to acquire shares of Eos Common Stock and shall be converted, at the Effective Time, into an option to purchase shares of Pulmatrix Common Stock (an “Assumed Option”), on the same terms and conditions (including any vesting provisions and any provisions providing for accelerated vesting upon certain events) as were applicable under such Eos Option as of immediately prior to the Effective Time, except for administrative or ministerial changes as determined by the Company Board (or, following the Effective Time, the Pulmatrix Board or compensation committee thereof).

The number of shares subject to each such Assumed Option shall be equal to (i) the number of shares of Eos common stock subject to the respective Eos Option immediately prior to the Effective Time multiplied by (ii) the Exchange Ratio, rounded down, if necessary, to the nearest whole share of Pulmatrix Common Stock, and such Assumed Option shall have an exercise price per share (rounded up to the nearest whole cent) equal to (A) the exercise price per share of the Eos Common Stock otherwise purchasable pursuant to the respective Eos Option immediately prior to the Effective Time divided by (B) the Exchange Ratio; provided, that in the case of any Eos Option to which Section 421 of the Code applies as of immediately prior to the Effective Time (taking into account the effect of any accelerated vesting thereof, if applicable) by reason of its qualification under Section 422 of the Code, the exercise price, the number of shares of Pulmatrix common stock subject to such option and the terms and conditions of exercise of such option shall be determined in a manner consistent with the requirements of Section 424(a) of the Code; provided further, that in the case of any Assumed Option to which Section 409A of the Code applies as of the Effective Time, the exercise price, the number of shares of Pulmatrix common stock subject to such option and the terms and conditions of exercise of such option shall be determined in a manner consistent with the requirements of Section 409A of the Code in order to avoid the imposition of any additional taxes thereunder.

Treatment of Investor Financing Warrants

At the Effective Time, each Investor Financing Warrant, whether vested or unvested, that is outstanding and unexercised immediately prior to the Effective Time, will be converted into and become a warrant to purchase Pulmatrix common stock (each, an “Assumed Warrant”), and Pulmatrix shall assume the terms of the Investor Financing Warrant by which such Investor Financing Warrant is evidenced (but with changes to such documents as Pulmatrix and Eos mutually agree are appropriate to reflect the substitution of the Investor Financing Warrant by Pulmatrix to purchase shares of Pulmatrix common stock). All rights with respect to Eos Common Stock under the Investor Financing Warrant assumed by Pulmatrix will thereupon be converted into rights with respect to Pulmatrix common stock.

Accordingly, from and after the Effective Time: (i) each Investor Financing Warrant assumed by Pulmatrix may be exercised solely for shares of Pulmatrix common stock; (ii) the number of shares of Pulmatrix common stock subject to each Investor Financing Warrant assumed by Pulmatrix will be determined by multiplying (x) the number of shares of Eos common stock that were subject to such Investor Financing Warrant, as in effect immediately prior to the Effective Time by (y) the Exchange Ratio and rounding the resulting number down to the nearest whole number of shares of Pulmatrix common stock; (iii) the per share exercise price for the Pulmatrix common stock issuable upon exercise of each Investor Financing Warrant assumed by Pulmatrix will be determined by dividing (x) the per share exercise price of Eos common stock subject to such Investor Financing Warrant, as in effect immediately prior to the Effective Time, by (y) the Exchange Ratio and rounding the resulting exercise price up to the nearest thousandth of a cent; and (iv) any restriction on the exercise of any Investor Financing Warrant assumed by Parent will continue in full force and effect, and the term, exercisability, method of exercise, vesting schedule, and other provisions of such Investor Financing Warrant will otherwise remain unchanged; provided, however, that to the extent provided under the terms of an Investor Financing Warrant assumed by Pulmatrix in accordance with the Merger Agreement will, in accordance with its terms, be subject to further adjustment as appropriate to reflect any stock split, division or subdivision of shares, stock dividend, reverse stock split, consolidation of shares, reclassification, recapitalization or other similar transaction with respect to Pulmatrix common stock subsequent to the Effective Time.

Treatment of Eos CEO RSUs

At the Effective Time, the restricted stock units with respect to up to the equivalent of 13,000,000 shares of Pulmatrix common stock in the Combined Company that Eos issued to RCM Eos RSU HOLDINGS, LLC on July 7, 2026, an entity that was established by the Chief Executive Officer of Eos (the form of which is attached hereto as Annex I, the “CEO RSUs”), whether vested or unvested, that are outstanding immediately prior to the Effective Time, will be converted into and become restricted stock units with respect to Pulmatrix common stock (the “Assumed CEO RSUs”), and Pulmatrix shall assume the terms of the CEO RSUs by which such CEO RSUs is evidenced by the form of CEO RSU attached hereto as Annex I, which was consented to by Pulmatrix on July 2, 2026. All rights with respect to Eos common stock under the CEO RSUs assumed by Pulmatrix will thereupon be converted into rights with respect to Pulmatrix common stock. The shares of common stock underlying the CEO RSUs may only be delivered to the grantee or a personal representative thereof during calendar year 2029.

Accordingly, from and after the Effective Time: (i) the number of shares of Pulmatrix common stock subject to each CEO RSUs assumed by Pulmatrix will be determined by multiplying (x) the number of shares of Eos common stock that were subject to such CEO RSUs, as in effect immediately prior to the Effective Time by (y) the Exchange Ratio and rounding the resulting number down to the nearest whole number of shares of Pulmatrix common stock; and (ii) any restriction on the exercise (if applicable) of any CEO RSUs assumed by Pulmatrix will continue in full force and effect, and the term, exercisability, method of exercise, vesting schedule, and other provisions of such CEO RSUs will otherwise remain unchanged; provided, however, that to the extent provided under the terms of a CEO RSUs assumed by Pulmatrix in accordance with the terms of the Merger Agreement, such Assumed CEO RSUs will, in accordance with its terms, be subject to further adjustment as appropriate to reflect any stock split, division or subdivision of shares, stock dividend, reverse stock split, consolidation of shares, reclassification, recapitalization or other similar transaction with respect to Pulmatrix common stock subsequent to the Effective Time.

Treatment of Eos Convertible Notes

Each Eos Convertible Note that is outstanding and unconverted as of immediately prior to the Effective Time shall be converted solely into the right to receive a number of shares of Pulmatrix common stock equal to (x) the number of Eos capital stock that the holder of such Eos Convertible Note would have been entitled to had the Eos Convertible Note converted into Eos capital stock prior to the Effective Time, multiplied by (y) the Exchange Ratio.

Treatment of Pulmatrix Common Stock (see page 106)

Except as contemplated by the proposed increase in the number of authorized shares of Pulmatrix common stock described in Proposal No. 3 of this proxy statement/prospectus and the proposed reverse stock split of issued and outstanding Pulmatrix common stock described in Proposal No. 2 of this proxy statement/prospectus, Pulmatrix common stock will remain unaffected by the Merger.

Treatment of Pulmatrix Warrants (see page 106)

Under the terms of the Merger Agreement, each warrant to acquire shares of Pulmatrix common stock that is outstanding and unexercised immediately prior to the Effective Time shall survive the Closing and remain outstanding in accordance with its terms.

Treatment of Pulmatrix Options (see page 106)

Each outstanding option to acquire shares of Pulmatrix common stock that is outstanding and unexercised immediately prior to the Effective Time shall survive the Closing and remain outstanding in accordance with its terms.

Regulatory Approvals (see page 112)

Pulmatrix must comply with applicable federal and state securities laws and the rules and regulations of Nasdaq in connection with the issuance of shares of Pulmatrix common stock, to Eos stockholders in connection with the transactions contemplated by the Merger Agreement and the filing of this proxy statement/prospectus with the SEC. Pulmatrix and Eos do not intend to seek any regulatory approval from antitrust authorities to consummate the transactions.

Conditions to the Completion of the Merger (see page 113)

To complete the Merger, Pulmatrix stockholders must approve Proposal Nos. 1, 2 and 3, and Eos stockholders must adopt the Merger Agreement and approve the Merger and the related transactions contemplated by the Merger Agreement. In addition, each of the other closing conditions set forth in the Merger Agreement must be satisfied or waived.

In addition, as of the closing of the Merger, Eos shall have received, or shall receive substantially simultaneously with the closing, aggregate gross cash proceeds of at least $13,000,000 from one or more Eos financing transactions; provided, however, that any proceeds received by the Eos from bridge financing transactions (including, without limitation, any bridge loans, bridge notes, or other interim financing arrangements entered into by Eos in respect of operations of Eos during the pre-closing period) with an aggregate amount of $5,000,000 or less shall be excluded from the foregoing calculation of aggregate gross cash proceeds received and shall not count towards the satisfaction of this condition.

Non-Solicitation (see page 110)

Each of Pulmatrix and Eos have agreed that, except as described below, Pulmatrix and Eos and any of their respective subsidiaries will not, nor will either party or any of its subsidiaries authorize any of the directors, officers, employees, investment bankers, financial advisors, attorneys, accountants or other advisors, agents or representatives retained by it or any of its subsidiaries to, directly or indirectly:

An “Acquisition Inquiry” means, with respect to a party, an inquiry, indication of interest or request for non-public information (other than an inquiry, indication of interest or request for information made or submitted by Eos, on the one hand, or Pulmatrix on the other hand, to the other party) that would reasonably be expected to lead to an Acquisition Proposal.

An “Acquisition Proposal” means, with respect to a party, any offer or proposal, whether written or oral (other than an offer or proposal made or submitted by or on behalf of Eos or any of its affiliates, on the one hand, or by or on behalf of Pulmatrix or any of its affiliates, on the other hand, to the other party) contemplating or otherwise relating to an Acquisition Transaction with such party.

An “Acquisition Transaction” means any transaction or series of related transactions involving:

Notwithstanding the foregoing or anything to the contrary herein, in the event that the initial End Date has passed (without taking into account extensions thereto set forth in the Merger Agreement), Pulmatrix and Eos shall be, without further action on the part of any party, released from any and all of its obligations with respect to the foregoing, and each of Pulmatrix and Eos shall be free to pursue, solicit or otherwise participate in, without liability hereunder, any offer or transaction, whether or not it would constitute a Superior Offer or an Acquisition Proposal, without providing notice to or seeking consent or a waiver from the other party.

Board Recommendation Change (see page 111)

Under the Merger Agreement, subject to certain exceptions described below, both Eos and Pulmatrix agreed that their respective board of directors may not withhold, amend, withdraw or modify (or publicly propose to withhold, amend, withdraw or modify) the recommendation of such party’s board of directors in a manner adverse to the other party except if, at any time prior to the approval of the Merger by each party’s respective stockholders, and subject to the conditions described below, (i) such party has received a bona fide written Acquisition Proposal that such party’s board of directors determines, following consultation with its outside legal counsel and financial advisor, to be a Superior Offer, or (ii) a material development or change in circumstances (other than any such event, development or change to the extent related to any Acquisition Proposal, Acquisition Inquiry, Acquisition Transaction or the consequences thereof) that affects the business, assets or operations of such party and occurs or arises after the date the Merger Agreement was executed.

In the case of a change recommendation due to a material development or change in circumstance, such party’s board of directors must first promptly notify the other party, in writing, at least four business days before making a change in its recommendation, stating the material facts and circumstances related to the applicable material development or change in circumstance and that such party’s board of directors intends to make a change in its recommendation.

In the case of a change its recommendation due to a Superior Offer, such party’s board of directors must first:

A “Superior Offer” means an unsolicited bona fide written Acquisition Proposal (with all references to 20% in the definition of Acquisition Transaction being treated as references to 50% for these purposes) that (a) was not obtained or made as a direct or indirect result of a breach of the Merger Agreement, (b) is on terms and conditions that the board of directors of the party receiving the offer determines in good faith, based on such matters that it deems relevant (including the likelihood of consummation thereof and the financing terms thereof), as well as any written offer by the other party to the Merger Agreement to amend the terms of the Merger Agreement, and following consultation with its outside legal counsel and financial advisors, if any, are more favorable, from a financial point of view, to that party’s stockholders than the terms of the transactions contemplated by the Merger Agreement, (c) with respect to which any required financing is fully committed pursuant to customary debt or equity commitment letters that contain only customary conditions, or is reasonably capable of being obtained on a timely basis and (d) is reasonably capable of being completed on the terms proposed.

In addition, in the event of a material amendment to a Superior Offer, the applicable notice period shall be extended to ensure that at least three (3) business days remain following notification of such amendment, during which the parties shall comply again with the foregoing requirements.

In the event that the initial End Date (the date that is the six (6) month anniversary of the date of the Merger Agreement) has passed (without taking into account extensions thereto set forth in the Merger Agreement), Pulmatrix and Eos shall be, without further action on the part of any party, released from any and all of its obligations with respect to the foregoing and the Eos shall be free to pursue, solicit or otherwise participate in, without liability under the Merger Agreement, any offer or transaction, whether or not it would constitute a Superior Offer, without providing notice to or seeking consent or a waiver from Pulmatrix or Merger Sub.

Termination of the Merger Agreement (see page 114)

Either Pulmatrix or Eos may terminate the Merger Agreement under certain circumstances, which would prevent the Merger from being consummated.

Lock-Up Agreements (see page 113)

SENOTHERAPEUTIX, Inc. has entered into, each person who is expected to serve on the Combined Company board of directors will enter into, lock-up agreements, pursuant to which such parties have agreed or will agree, as applicable, not to, except in limited circumstances, offer, pledge, sell, contract to sell,

sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, or otherwise transfer or dispose of, directly or indirectly, any shares of Pulmatrix common stock or any securities convertible into or exercisable or exchangeable for Pulmatrix common stock, currently or thereafter owned until 180 days after the effective time in the case of certain stockholders and until up to 24 months after the effective time subject to a tiered release schedule in the case of executive officers, directors and certain institutional investors.

Voting Agreement

In connection with the Pulmatrix Financing (as defined herein), Pulmatrix and the Buyer (as defined herein) entered into the Voting Agreement (as defined herein), pursuant to which the Buyer has agreed to vote, at any annual or special meeting of Pulmatrix called with respect to matters the Board of Directors of Pulmatrix has recommended the stockholders of Pulmatrix to vote in favor of, including but not limited to, any matters as related to the proposals to be put forth at the Special Meeting, and at every adjournment or postponement thereof, and on every action or approval by written consent or consents of Pulmatrix stockholders with respect to such matter, to vote or cause the holder of record to vote its shares of Series B Preferred Stock, or any shares of Pulmatrix common stock, in favor of providing the requisite stockholder approval. Additionally, pursuant to the terms of the Voting Agreement, the Buyer has agreed that for a period commencing upon the execution of the Pulmatrix Purchase Agreement and ending at the date of termination of the Voting Agreement, the Buyer will not, directly or indirectly transfer, sell, offer, exchange, assign, pledge, convey any legal or beneficial ownership interest in or otherwise dispose of (by merger (including by conversion into securities or other consideration), by tendering into any tender or exchange offer), or encumber any of the shares of Series B Preferred Stock or shares of Pulmatrix common stock, or enter into any contract, option, or other agreement with respect to, or consent to, a transfer of, any such shares or the Buyer’s voting or economic interest.

Organizational Structure

As of June 30, 2026, SENOTHERAPEUTIX, Inc. owned approximately 99.8% of Eos and Eos has no subsidiaries. Following the consummation of the Merger, Eos will continue as the surviving corporation and will be a wholly-owned subsidiary of Pulmatrix (which will be renamed).

Management Following the Merger (see page 204)

The following table sets forth the name, age as of June 30, 2026, and position of each of the individuals who are expected to serve as executives and directors of the Combined Company following completion of the Merger:

Material U.S. Federal Income Tax Considerations (see page 99)

As discussed in detail in the section titled “The Merger-U.S. Federal Income Tax Considerations-The Merger,” subject to the limitations and qualification described therein, Pulmatrix and Eos intend that the Merger qualifies as a “reorganization” within the meaning of Section 368(a) of the Code for U.S. federal income tax purposes. Assuming the Merger so qualifies, a U.S. Holder of Eos stock (as defined therein) will not recognize gain or loss upon the exchange of its Eos stock for Pulmatrix stock. For a more detailed discussion of the U.S. federal income tax considerations of the Merger, please see the section titled “The Merger-U.S. Federal Income Tax Considerations-The Merger” beginning on page 100 of this proxy statement/prospectus.

Risk Factors (see page 24)

Both Pulmatrix and Eos are subject to various risks associated with their businesses and their industries. In addition, the Merger, including the possibility that the Merger may not be completed, poses a number of risks to each company and its respective securityholders, including the following risks:

Risks Related to the Merger:

Risks Related to the Proposed Reverse Stock Split:

Risks Related to Pulmatrix:

Risks Related to Eos:

Risks Related to the Combined Company:

These risks and other risks are discussed in greater detail under the section titled “Risk Factors” beginning on page 24 of this proxy statement/prospectus. Pulmatrix and Eos both encourage you to read and consider all of these risks carefully.

Regulatory Approvals (see page 112)

Each of Pulmatrix and Eos will use commercially reasonable efforts to file or otherwise submit, as soon as practicable after the date of the Merger Agreement, all applications, notices, reports and other documents reasonably required to be filed by such party with or otherwise submitted by such party to any governmental authority with respect to the transactions contemplated by the Merger Agreement, if any, and to submit promptly any additional information requested by any such governmental authority.

Nasdaq Stock Market Listing (see page 101)

Pulmatrix has filed an initial listing application for the Combined Company common stock with Nasdaq. If such application is accepted, Pulmatrix anticipates that the common stock of the Combined Company will be listed on Nasdaq following the Closing under the trading symbol “EOSX.” It is a condition to the consummation of the Merger that Pulmatrix will receive confirmation from Nasdaq that the Combined Company has been approved for listing on Nasdaq, but there can be no assurance such listing condition will be met or that Pulmatrix will obtain such confirmation from Nasdaq. If such listing condition is not met or if such confirmation is not obtained, the Merger will not be consummated unless the condition is waived. The Nasdaq condition set forth in the Merger Agreement is not expected to be waived by the applicable parties.

Controlled Company Exemption

Immediately following the Merger, SENOTHERAPEUTIX, Inc. is expected to beneficially own more than 50% of the voting power of the Combined Company’s outstanding common stock. SENOTHERAPEUTIX, Inc., as of March 26, 2026, is the sole stockholder of Eos. Kevin Slawin, who is expected to serve as Chief Executive Officer of the Combined Company, holds a majority of the voting power of shares of SENOTHERAPEUTIX, Inc. Under the Nasdaq listing rules, a company of which more than 50% of the voting power for the election of directors is held by an individual, group, or another company is a “controlled company” and is exempt from certain corporate governance requirements. The Combined Company will be a controlled company. Although Eos does not currently intend for the Combined Company to rely on the controlled company exemptions, the Combined Company could elect to rely on one or more of these exemptions in the future. If the Combined Company relies on any such exemptions, its investors will not have the same protections afforded to stockholders of companies that are subject to these corporate governance requirements. See “Risk Factors – The Combined Company will be a “controlled company” within the meaning of Nasdaq rules and qualifies for exemptions from certain corporate governance requirements. As a result, stockholders may not have the same protections afforded to stockholders of companies that are not exempt from such corporate governance requirements” and the sections entitled “Principal Stockholders of the Combined Company” and “Management Following the Merger – Controlled Company Exemption.”

Anticipated Accounting Treatment (see page 102)

The Merger is expected to be accounted for as a reverse asset acquisition in accordance with U.S. GAAP. Under this method of accounting, Eos is considered to be the accounting acquirer for financial reporting purposes since immediately following the Merger: (i) Eos’s equity holders will own a substantial majority of the voting rights in the Combined Company; (ii) Eos’s largest stockholder will retain the largest interest in the Combined Company; (iii) Eos will designate all but one of the initial members of the Combined Company board of directors; and (iv) Eos’s executive management team will become the management of the Combined Company.

Management expects that this transaction will be accounted for as a reverse asset acquisition because Pulmatrix is not expected to meet the definition of a business under ASC 805 as of Closing, but it does represent a group of assets. Accordingly, the Merger is expected to be treated for accounting purposes as the equivalent of Eos issuing stock to acquire the net assets of Pulmatrix. The net assets of Pulmatrix will be allocated a portion of the purchase price and recorded based on their relative fair values at the time of Closing. Upon completion of the Merger, as a result of Eos being treated as the accounting acquirer, Eos’s assets and liabilities will be recorded at their pre-combination carrying amounts and the historical financial statements of Eos will become the historical consolidated financial statements of Pulmatrix.

Please see the section titled “Unaudited Pro Forma Condensed Combined Financial Information” beginning on page 211 of this proxy statement/prospectus for additional information.

Appraisal Rights and Dissenters’ Rights (see page 102)

Holders of Pulmatrix common stock are not entitled to appraisal rights in connection with the Merger under Delaware law. Holders of Eos capital stock are entitled to appraisal rights in connection with the Merger under Delaware law.

Comparison of Stockholder Rights (see page 224)

Both Pulmatrix and Eos are incorporated under the laws of the State of Delaware and, accordingly, the rights of the stockholders of each are currently, and will continue to be, governed by the Delaware General Corporation Law (“DGCL”). If the Merger is completed, Eos stockholders will become Pulmatrix stockholders, and their rights will be governed by the DGCL, the Pulmatrix Bylaws and the Pulmatrix Charter, as may be further amended by Proposal Nos. 2 and 3 if approved by the Pulmatrix stockholders at the Pulmatrix Special Meeting. The rights of Pulmatrix stockholders contained in the Pulmatrix Charter and Pulmatrix Bylaws differ from the rights of Eos stockholders under the Eos Charter and Eos Bylaws, as more fully described under the section titled “Comparison of Rights of Holders of Pulmatrix Capital Stock and Eos Capital Stock” beginning on page 224 of this proxy statement/prospectus.

COMPARATIVE MARKET PRICE AND DIVIDEND INFORMATION

The Pulmatrix common stock has been listed on the Nasdaq Capital Market under the symbol “PULM” since June 16, 2015.

Eos is a privately held company, and there is no established public trading market for its securities.

The following table sets forth the closing sale prices per share of Pulmatrix common stock on March 25, 2026, the last full trading day immediately preceding the public announcement of the Merger Agreement, and on June 30, 2026, the latest practicable date prior to the date of this proxy statement/prospectus:

Stockholders of Pulmatrix and Eos are urged to obtain current market quotations for Pulmatrix common stock and to review carefully the other information contained in this proxy statement/prospectus or documents filed with the SEC. See the section titled “Where You Can Find More Information” beginning on page 235 of this proxy statement/prospectus.

Holders

As of June 30, 2026, the latest practicable date prior to the date of this proxy statement/prospectus, there were 43 holders of record of Pulmatrix common stock.

As of June 30, 2026, the latest practicable date prior to the date of this proxy statement/prospectus, there was one (1) holder of record of Eos common stock.

Dividends

Pulmatrix has never declared or paid any cash dividends on the Pulmatrix common stock and does not anticipate paying cash dividends on the Pulmatrix common stock for the foreseeable future. Any determination to pay cash dividends subsequent to the Merger will be at the discretion of the Combined Company then-current board of directors and will depend upon a number of factors, including the Combined Company’s results of operations, financial condition, future prospects, contractual restrictions, restrictions imposed by applicable law and other factors the then-current board of directors deems relevant.

Eos has never paid or declared any cash dividends on Eos capital stock. If the Merger does not occur, Eos does not anticipate paying any cash dividends on the Eos capital stock in the foreseeable future, and Eos intends to retain all available funds and any future earnings to fund the development and expansion of its business. Any future determination to pay dividends will be at the discretion of the Eos board of directors and will depend upon a number of factors, including its results of operations, financial condition, future prospects, contractual restrictions, and restrictions imposed by applicable laws and other factors the Eos board of directors deems relevant.

RISK FACTORS

In evaluating the business of the Combined Company, you should carefully consider the following discussion of material risks, events and uncertainties that make an investment in the Combined Company speculative or risky in addition to the other information included in this proxy statement/prospectus and additional information about Pulmatrix set forth in its Annual Report on Form 10-K for the fiscal year ended December 31, 2025, which is filed with the SEC, incorporated by reference into this proxy statement/prospectus. Please see the section titled “Where You Can Find More Information” beginning on page 235 of this proxy statement/prospectus for further information regarding the documents incorporated by reference into this proxy statement/prospectus. A manifestation of any of the following risks and uncertainties could, in circumstances Pulmatrix or Eos may or may not be able to accurately predict, materially and adversely affect the business and operations, growth, reputation, prospects, operating and financial results, financial condition, cash flows, liquidity and stock price of Pulmatrix, Eos or the Combined Company. Some of the factors, events and contingencies discussed below may have occurred in the past, but the disclosures below are not representations as to whether or not the factors, events or contingencies have occurred in the past and instead reflect Pulmatrix and Eos’s beliefs and opinions as to the factors, events, or contingencies that could materially and adversely affect Pulmatrix, Eos or the Combined Company in the future. The risks and uncertainties described below are not the only ones Pulmatrix or Eos face or the Combined Company may face. The operations of Pulmatrix, Eos or the Combined Company could also be affected by factors, events or uncertainties that are not presently known to Pulmatrix or Eos or that Pulmatrix or Eos currently do not consider to present significant risks to the business of Pulmatrix, Eos or the Combined Company. Therefore, you should not consider the following risks to be a complete statement of all the potential risks or uncertainties that Pulmatrix, Eos or the Combined Company face.

Risks Related to the Merger

There is no assurance when or if the Merger will be completed. Any delay in completing the Merger may substantially reduce the potential benefits that Pulmatrix and Eos expect to obtain from the Merger.

Completion of the Merger is subject to the satisfaction or waiver of a number of conditions, as set forth in the Merger Agreement, including the approval by Pulmatrix stockholders, approval by Nasdaq of Pulmatrix’s application for the listing of Pulmatrix common stock to be issued in connection with the Merger, and other customary closing conditions. There can be no assurance that Pulmatrix and Eos will be able to satisfy the closing conditions or that closing conditions beyond their control will be satisfied or waived. For a discussion of the conditions to the completion of the Merger, see the section titled “The Merger Agreement-Conditions to the Completion of the Merger” beginning on page 113 of this proxy statement/prospectus. If the conditions are not satisfied or waived, the Merger may not occur or may not be completed within the expected timeframe, and Pulmatrix and Eos each may materially and adversely lose some or all of the potential benefits that Pulmatrix and Eos expect to achieve as a result of the Merger and could result in additional transaction costs or other effects associated with uncertainty about the Merger. In addition, pursuant to the Merger Agreement, each of Pulmatrix and Eos may extend the originally scheduled End Date (defined in the Merger Agreement) by up to 60 calendar days. Moreover, each of Pulmatrix and Eos has incurred and expects to continue to incur significant expenses related to the Merger, such as legal and accounting fees, some of which must be paid even if the Merger is not completed.

Pulmatrix and Eos can agree at any time to terminate the Merger Agreement, even if Pulmatrix stockholders and/or Eos securityholders have already adopted the Merger Agreement and thereby approved the Merger and the other transactions contemplated by the Merger Agreement. Pulmatrix and Eos can also terminate the Merger Agreement under other specified circumstances.

In addition, if the Merger Agreement is terminated and the Pulmatrix or the Eos board of directors determines to seek another business combination, it may not be able to find a third party willing to provide equivalent or more attractive consideration than the consideration to be provided by each party in the Merger. In such circumstances, the Pulmatrix board of directors may elect to, among other things, divest all or a portion of Pulmatrix’s business, or take the steps necessary to liquidate all of Pulmatrix’s business and assets, and in either such case, the consideration that Pulmatrix receives may be less attractive than the consideration to be received by Pulmatrix pursuant to the Merger Agreement.

If the Merger Agreement is not consummated, it is anticipated that Pulmatrix will be delisted from The Nasdaq Capital Market and may need to consider whether to remain a public company. For risks related to a delisting from The Nasdaq Capital Market, see “In the event that the Combined Company fails to satisfy any of the listing requirements of The Nasdaq Capital Market, its common stock may be delisted, which could affect its market price and liquidity.”

The issuance of shares of Pulmatrix common stock to Eos stockholders in the Merger will substantially dilute the voting power of current Pulmatrix stockholders. Having a minority share position will reduce the influence that current stockholders have on the management of Pulmatrix.

Pursuant to the terms of the Merger Agreement, at the Effective Time, Pulmatrix will issue (or reserve for future issuance) approximately 43.7 million shares of its common stock using the assumed Exchange Ratio of 8.64 (which is subject to change depending on the number of outstanding securities of Pulmatrix and Eos at the Effective Time and which such figure does not include any shares of Pulmatrix common stock issuable upon conversion of Eos notes, Eos Series A Preferred Stock, warrants, options, Series B Preferred Stock, the CEO RSUs and shares issuable to Palladium as compensation in connection with the Merger), without giving effect to the proposed reverse stock split contemplated by the Reverse Stock Split Proposal, to Eos stockholders as merger consideration. As a result, upon completion of the Merger, the Pulmatrix securityholders as of immediately prior to the Merger are expected to own approximately 6.1856% of the outstanding shares of the Combined Company on a fully-diluted basis before payment of Palladium’s fee in the form of a 3.0% ownership in the Combined Company, as further described under “The Merger-Exchange Ratio” in this proxy statement/prospectus. Accordingly, the issuance of the shares of Pulmatrix common stock to Eos stockholders in the Merger will significantly reduce the ownership stake and relative voting power of each share of Pulmatrix common stock held by current Pulmatrix stockholders. Consequently, following the Merger, the ability of current Pulmatrix stockholders to influence Combined Company management will be substantially reduced.

The issuance, or expected issuance, of Pulmatrix common stock in connection with the Merger could decrease the market price of Pulmatrix common stock.

In connection with the Merger and as part of the merger consideration, Pulmatrix expects to issue shares of Pulmatrix common stock to Eos stockholders. The anticipated issuance of Pulmatrix common stock in the Merger may result in fluctuations in the market price of Pulmatrix common stock, including a stock price decrease. In addition, the perception in the market that the holders of a large number of shares of Pulmatrix common stock may intend to sell shares could reduce the market price of Pulmatrix common stock.

The intended benefits of the Merger may not be realized.

The Merger poses risks for Pulmatrix’s and Eos’s ongoing operations, including, among others:

As a result of the foregoing, the Combined Company may be unable to realize the full strategic and financial benefits currently anticipated from the Merger, and Pulmatrix or Eos cannot assure you that the Merger will be accretive to Pulmatrix or Eos in the near term or at all. Furthermore, if Pulmatrix or Eos fails to realize the intended benefits of the Merger, the market price of the Combined Company’s common stock could decline to the extent that the market price reflects those benefits. In such case, Pulmatrix stockholders will have experienced substantial dilution of their ownership interests in Pulmatrix without receiving any commensurate benefit, or only receiving part of the commensurate benefit to the extent the Combined Company is able to realize only part of the strategic and financial benefits currently anticipated from the Merger.

Because the lack of a public market for Eos common stock makes it difficult to evaluate the fairness of the Merger, Eos stockholders may receive consideration in the Merger that is greater than or less than the fair market value of Eos common stock.

The outstanding Eos common stock is privately held and is not traded in any public market. The lack of a public market makes it extremely difficult to determine the fair market value of Eos shares. Since the percentage of Pulmatrix common stock to be issued to Eos stockholders was determined based on negotiations between the parties, it is possible that the value of the Pulmatrix common stock to be issued in connection with the Merger will be greater than the fair market value of Eos shares. Alternatively, it is possible that the value of the shares of Pulmatrix common stock to be issued in connection with the Merger will be less than the fair market value of Eos shares.

Directors and officers of Pulmatrix and Eos may have interests in the Merger that are different from, or in addition to, those of Pulmatrix stockholders and Eos stockholders generally that may influence them to support or approve the Merger.

The Pulmatrix and Eos officers and directors may have interests in the Merger that are different from, or are in addition to, those of Pulmatrix stockholders and Eos stockholders generally. Effective upon the Closing, Kevin Slawin is expected to be employed as an executive officer by the Combined Company. It is expected that six directors designated by Eos, and one director designated by Pulmatrix and agreed to by Eos, are to be appointed as Combined Company directors after the completion of the Merger and will receive cash and equity compensation in consideration for such service as described in more detail in the section titled “Management Following the Merger” beginning on page 204 of this proxy statement/prospectus. Each outstanding option to acquire shares of Eos common stock held by Eos executive officers and directors will be converted into an option to acquire shares of Pulmatrix common stock. In addition, the Pulmatrix and Eos directors and executive officers also have certain rights to indemnification or to directors’ and officers’ liability insurance that will survive the completion of the Merger. These interests may have influenced the Pulmatrix and Eos directors and executive officers to support or recommend the proposals presented to Pulmatrix and Eos stockholders. See the sections titled “The Merger-Interests of Pulmatrix Directors and Executive Officers in the Merger” beginning on page 94 and “The Merger-Interests of Eos Directors and Executive Officers in the Merger” beginning on page 95 of this proxy statement/prospectus.

If the Merger is completed, Eos executive officers and Eos appointees to the Combined Company board of directors will have the ability to significantly influence the Combined Company’s management and business affairs, as well as matters submitted to the Combined Company board of directors or stockholders for approval, especially if they decide to act together with the current Eos stockholders.

Upon completion of the Merger, the former Eos securityholders are expected to own approximately 93.8144% of the outstanding shares of the Combined Company on a fully diluted basis, before payment of Palladium’s fee in the form of a 3.0% ownership in the Combined Company. If the Merger is completed, the Combined Company is expected to be led by Eos executive officers. Furthermore, the Combined Company’s anticipated board of directors will consist of seven members, six of which will be designated by Eos pursuant to the terms of the Merger Agreement and one of which will be designated by Pulmatrix and agreed to by Eos. As a result, such persons, if they choose to act together, will have the ability to significantly influence the Combined Company’s management and business affairs, as well as matters submitted to the Combined Company board of directors or stockholders for approval.

The announcement and pendency of the Merger could have an adverse effect on Pulmatrix’s or Eos’s business, financial condition, results of operations or business prospects.

The announcement and pendency of the Merger could disrupt Pulmatrix’s and/or Eos’s businesses in the following ways, among others:

Should they occur, any of these matters could adversely affect the businesses of, or harm the financial condition, results of operations or business prospects of, Pulmatrix or Eos.

During the pendency of the Merger, Pulmatrix or Eos may not be able to enter into a business combination with another party and will be subject to contractual limitations on certain actions because of restrictions in the Merger Agreement.

Covenants in the Merger Agreement impede the ability of Pulmatrix or Eos to make dispositions or acquisitions or complete other transactions that are not in the ordinary course of business pending completion of the Merger, potential spin-off of all or a portion of Pulmatrix’s assets prior to the consummation of the Merger and certain permitted financings as set forth in the Merger Agreement. As a result, if the Merger is not completed, the parties may be at a disadvantage to their competitors. In addition, while the Merger Agreement is in effect and subject to limited exceptions, each party is prohibited from soliciting, initiating, encouraging or taking actions designed to facilitate any inquiries or the making of any proposal or offer that could lead to the entering into certain extraordinary transactions with any third party, such as a sale of assets, an acquisition, a tender offer, a merger or other business combination outside the ordinary course of business. These restrictions may prevent each of Pulmatrix and Eos from pursuing otherwise attractive business opportunities or other capital structure alternatives and making other changes to their business or executing certain of their business strategies prior to the completion of the Merger, which could be favorable to Pulmatrix stockholders or Eos stockholders. See the section titled “The Merger Agreement-Non-Solicitation” beginning on page 110 of this proxy statement/prospectus.

Certain provisions of the Merger Agreement may discourage third parties from submitting competing proposals, including proposals that may be superior to the arrangements contemplated by the Merger Agreement.

The terms of the Merger Agreement prohibit each of Pulmatrix and Eos from soliciting competing proposals or cooperating with persons making unsolicited takeover proposals, except in limited circumstances if the Pulmatrix board of directors determines in good faith, after consultation with its financial advisor and outside counsel, that an unsolicited competing proposal constitutes, or would reasonably be expected to result in, a superior competing proposal and that failure to take such action would be reasonably likely to result in a breach of the fiduciary duties of the Pulmatrix board of directors. In the event that the Pulmatrix board of directors withdraws or modifies its recommendation for Nasdaq Stock Issuance Proposal based on such superior competing proposal, Eos may terminate the Merger Agreement. See the section titled “The Merger Agreement-Termination and Termination Fees” beginning on page 114 of this proxy statement/prospectus.

The rights of Eos stockholders who become Pulmatrix stockholders in the Merger and Pulmatrix stockholders following the Merger will be governed by the Pulmatrix Charter, as amended.

Upon consummation of the Merger, outstanding shares of Eos common stock will be converted into the right to receive shares of Pulmatrix common stock. Eos stockholders who receive shares of Pulmatrix common stock in the Merger will become Pulmatrix stockholders. As a result, Eos stockholders who become stockholders in Pulmatrix will be governed by the Pulmatrix Charter, rather than being governed by the Eos Charter. Pursuant to the Merger Agreement, the Pulmatrix Charter will be amended, subject to Pulmatrix stockholders’ approval of Proposal Nos. 2 and 3, substantially contemporaneously to the effective time of the Merger. See the section titled “Comparison of Rights of Holders of Pulmatrix Capital Stock and Eos Capital Stock” beginning on page 224 of this proxy statement/prospectus.

The Exchange Ratio is not adjustable based on the market price of Pulmatrix common stock, so the Merger consideration at the Closing may have a greater or lesser value than at the time the Merger Agreement was signed.

The Merger Agreement has set the Exchange Ratio formula for the Eos common stock, and the Exchange Ratio is only adjustable upward or downward to reflect Pulmatrix’s and Eos’s equity capitalization as of immediately prior to the effective time of the Merger and the excess cash Pulmatrix has at the effective time of the Merger. Any changes in the market price of common stock before the completion of the Merger will not affect the number of shares Eos securityholders will be entitled to receive pursuant to the Merger Agreement. Therefore, if before the completion of the Merger, the market price of Pulmatrix common stock declines from the market price on the date of the Merger Agreement, then Eos securityholders could receive merger consideration with substantially lower value. Similarly, if before the completion of the Merger, the market price of Pulmatrix common stock increases from the market price on the date of the Merger Agreement, then Eos securityholders could receive merger consideration with substantially more value for their shares of Eos common stock than the parties had negotiated for in the establishment of the Exchange Ratio. For a discussion of the Exchange Ratio, see the section titled “The Merger Agreement-Exchange Ratio” beginning on page 104 of this proxy statement/prospectus.

Pulmatrix is expected to incur substantial expenses related to the Merger with Eos.

Pulmatrix has incurred, and expects to continue to incur, substantial expenses in connection with the Merger, as well as operating as a public company. Pulmatrix will incur significant fees and expenses relating to legal, accounting, financial advisory and other transaction fees and costs associated with the Merger. Actual transaction costs may substantially exceed Pulmatrix’s estimates and may have an adverse effect on the Combined Company’s financial condition and operating results.

Failure to complete the Merger could negatively affect the value of Pulmatrix common stock and the future business and financial results of both Pulmatrix and Eos.

If the Merger is not completed, the ongoing businesses of Pulmatrix and Eos could be adversely affected. Moreover, each of Pulmatrix and Eos will be subject to a variety of risks associated with the failure to complete the Merger, including without limitation the following:

If the Merger is not completed, the market price of Pulmatrix common stock and the business and financial results of both Pulmatrix (including the cessation of its operations) and Eos could be materially affected.

The Merger is expected to result in a limitation on the Combined Company’s ability to utilize its net operating loss carryforward.

Under Section 382 of the Code, use of Pulmatrix’s net operating loss carryforwards (“NOLs”) will be limited if Pulmatrix experiences a cumulative change in ownership of greater than 50% in a moving three-year period. As of December 31, 2025, Pulmatrix had federal net operating loss carryforwards of approximately $81.7 million available to reduce future taxable income, of which $3.8 million is subject to expiration between 2026 and 2037 and $77.9 million may be carried forward indefinitely. Pulmatrix may experience an ownership change as a result of the Merger and therefore its ability to utilize its NOLs and certain credit carryforwards remaining at the effective time of the Merger may be limited. The limitation would be determined by the fair market value of Pulmatrix common stock outstanding prior to the ownership change, multiplied by the applicable federal rate. Limitations imposed on Pulmatrix’s ability to utilize NOLs could cause U.S. federal and state income taxes to be paid earlier than would be paid if such limitations were not in effect and could cause such NOLs to expire unused, in each case reducing or eliminating the benefit of such NOLs.

The analysis received by the Pulmatrix board of directors from Gemini has not been, and is not expected to be, updated to reflect changes in circumstances that may have occurred since the date of the analysis.

Such analysis was one of many factors considered by the Pulmatrix board of directors in approving the Merger. The analysis does not speak as of the time the Merger will be completed or any date other than the date of such analysis. Subsequent changes in the operation and prospects of Pulmatrix or Eos, general market and economic conditions and other factors that may be beyond the control of Pulmatrix or Eos, may significantly alter the value of Pulmatrix or Eos or the prices of the shares of Pulmatrix common stock by the time the Merger is to be completed. The analysis does not address the fairness of the merger consideration from a financial point of view to Pulmatrix at the time the Merger is to be completed, or as of any other date other than the date of such analysis, and the Merger Agreement does not require that the analysis be updated, revised or reaffirmed prior to the Closing to reflect any changes in circumstances between the date of the signing of the Merger Agreement and the completion of the Merger as a condition to closing the Merger. See the section titled “The Merger-Opinion of Pulmatrix’s Financial Advisor” beginning on page 86 to this proxy statement/prospectus.

The Merger may be completed even though material adverse changes may result from the announcement of the Merger, industry-wide changes or other causes.

In general, either party can refuse to complete the Merger if there is a material adverse effect affecting the other party between March 26, 2026, the date of the Merger Agreement, and the Closing of the Merger. However, some types of changes do not permit either party to refuse to complete the Merger, even if such changes would have a material adverse effect on Pulmatrix or Eos, as the case may be:

If adverse changes occur but Pulmatrix and Eos must still complete the Merger, the market price of Pulmatrix common stock may suffer. For a more complete discussion of what constitutes a material adverse effect on Pulmatrix or Eos under the Merger Agreement, see the section titled “The Merger Agreement-Representations and Warranties” beginning on page 107 of this proxy statement/prospectus.

Pulmatrix, the Pulmatrix Board of Directors, Eos, and/or Eos’s Board of Directors may become involved in securities litigation or stockholder derivative litigation in connection with the Merger, and this could divert the attention of Pulmatrix and Eos management and harm Pulmatrix, Eos, and/or the Combined Company’s business, and insurance coverage may not be available or sufficient to cover all related costs, expenses and damages.

Securities litigation or stockholder derivative litigation frequently follows the announcement of certain significant business transactions, such as the sale of a business division or announcement of a business combination transaction. Pulmatrix, the Pulmatrix Board of Directors, Eos, and/or the Eos Board of Directors may become involved in this type of litigation in connection with the Merger, and the Combined Company may become involved in this type of litigation in the future. Litigation often is expensive and diverts management’s attention and resources, which could adversely affect the business of Pulmatrix, Eos and the Combined Company.

Pulmatrix has never paid and does not intend to pay any cash dividends in the foreseeable future.

Pulmatrix has never paid cash dividends on any of its capital stock. Pulmatrix does not currently anticipate declaring or paying any cash dividends on its capital stock in the foreseeable future.

Pulmatrix is substantially dependent on Pulmatrix’s remaining employees, key contractors and consultants to facilitate the consummation of the Merger.

Pulmatrix’s ability to successfully complete the Merger depends in large part on Pulmatrix’s ability to retain certain remaining personnel, in addition to key contractors and consultants. Despite Pulmatrix’s efforts to retain these employees, as well as key contractors and consultants, one or more may terminate their employment or services with Pulmatrix on short notice. The loss of the service of certain employees, key contractors or consultants could potentially harm Pulmatrix’s ability to consummate the Merger and run Pulmatrix’s day-to-day business operations, as well as fulfill Pulmatrix’s reporting obligations as a public company.

Pursuant to the Merger Agreement, as a condition to the closing of the Merger, Eos shall have received, or will receive substantially simultaneously with the closing of the Merger, aggregate gross cash proceeds of at least $13,000,000 from one or more Eos financing transactions.

Pursuant to the Merger Agreement, as a condition to the closing of the Merger, Eos shall have received, or will receive substantially simultaneously with the closing of the Merger, aggregate gross cash proceeds of at least $13,000,000 from one or more Eos financing transactions; provided, however, that any proceeds received by the Eos from bridge financing transactions (including, without limitation, any bridge loans, bridge notes, or other interim financing arrangements entered into by Eos in respect of operations of Eos during the pre-closing period) with an aggregate amount of $5,000,000 or less shall be excluded from the foregoing calculation of aggregate gross cash proceeds received and shall not count towards the satisfaction of this condition. We can provide no assurances that Eos will have received such financing, in which case, Eos will draw from the Backstop Financing Agreement. As such, the consummation of the Merger may be delayed or not occur.

Risks Related to the Proposed Reverse Stock Split

The proposed reverse stock split may not increase the Combined Company’s common stock price over the long term.

If the Reverse Stock Split Proposal is approved, the Combined Company anticipates effecting a reverse stock split with a ratio between 1-for-2 and 1-for-10 substantially contemporaneously in connection with the Merger in order to cause its stock price to increase.  While it is expected that the reduction in the number of outstanding shares of common stock will proportionally increase the market price of the Combined Company common stock upon effectiveness of the proposed reverse stock split, it cannot be assured that the proposed reverse stock split will result in any sustained proportionate increase in the market price of the Combined Company common stock, which is dependent upon many factors, including the business and financial performance of the Combined Company, general market conditions, and prospects for future success, which are unrelated to the number of shares of the Combined Company common stock outstanding. While the Combined Company common stock price might meet the initial listing requirements for Nasdaq initially, it cannot be assured that it will continue to do so.

The proposed reverse stock split would have the effect of increasing the amount of common stock that the Combined Company is authorized to issue without further approval by the Combined Company stockholders.

As a result of the reverse stock split, and after giving effect to the Merger, the Combined Company expects that it will have between approximately                       shares and                      shares of common stock outstanding, excluding shares underlying options, compared to approximately                       shares of common stock outstanding of the Combined Company after giving effect to the Merger and without giving effect to the proposed reverse stock split, based on the assumed Exchange Ratio of                       The proposed amendment to the Pulmatrix Charter in connection with the Authorized Share Increase Proposal is anticipated to authorize the Combined Company to issue up to 250,000,000 shares of common stock and does not anticipate reducing this amount in connection with the proposed reverse stock split. As a result, it is anticipated that, following the reverse stock split, the Combined Company will have the ability to issue between approximately                        and                       additional shares of common stock, excluding shares that may be issued pursuant to awards that have been granted and shares reserved for equity incentive plans and the employee stock purchase plan, if approved. Except in certain instances, as required by law or by the rules of the securities exchange that lists the Combined Company common stock, these additional shares may be issued by the Combined Company without further vote of the Combined Company stockholders. If the Combined Company board of directors chooses to issue additional shares of the Combined Company common stock, such issuance could have a dilutive effect on the equity, earnings and voting interests of the Combined Company stockholders.

The proposed reverse stock split may decrease the liquidity of Pulmatrix common stock.

Although the Pulmatrix board of directors believes that the anticipated increase in the market price of Pulmatrix common stock could encourage interest in its common stock and possibly promote greater liquidity for its stockholders, such liquidity could also be adversely affected by the reduced number of shares outstanding after the reverse stock split. The reduction in the number of outstanding shares may lead to reduced trading and a smaller number of market makers for Pulmatrix common stock.

The proposed reverse stock split may lead to a decrease in overall market capitalization of the Combined Company.

Should the market price of Pulmatrix common stock decline after the proposed reverse stock split, the percentage decline may be greater, due to the smaller number of shares outstanding, than it would have been prior to the reverse stock split. A reverse stock split is often viewed negatively by the market and, consequently, can lead to a decrease in the overall market capitalization of the Combined Company. If the per share market price does not increase in proportion to the reverse stock split ratio, then the value of the Combined Company, as measured by its stock capitalization, will be reduced. In some cases, the per-share stock price of companies that have effected reverse stock splits subsequently declined back to pre-reverse split levels and, accordingly, it cannot be assured that the total market value of Pulmatrix common stock will remain the same after the reverse stock split is effected, or that the proposed reverse stock split will not have an adverse effect on Pulmatrix common stock price due to the reduced number of shares outstanding after the proposed reverse stock split.

Risks Related to Pulmatrix

Risks Related to Pulmatrix’s Business

Pulmatrix has a history of net losses and may experience future losses. Pulmatrix’s consolidated financial statements have been prepared on a going concern basis, and do not include adjustments that might be necessary if Pulmatrix is unable to continue as a going concern.

Pulmatrix has yet to establish any history of profitable operations. Pulmatrix reported a net loss of $5.2 million and $9.6 million for the years ended December 31, 2025, and 2024, respectively. As of December 31, 2025, Pulmatrix had an accumulated deficit of $302.3 million. As of March 31, 2026, our cash and cash equivalents balance was approximately $3.3 million, with an additional $0.7 million in restricted cash. Pulmatrix expects to incur additional operating losses for the foreseeable future. There can be no assurance that Pulmatrix will be able to achieve sufficient revenues throughout the year or be profitable in the future.

Pulmatrix’s future operations are highly dependent on the success of the Merger and there can be no assurances that the Merger will be successfully consummated. If the Merger is not consummated, Pulmatrix may seek other strategic alternatives or pursue a dissolution and liquidation.

Pulmatrix anticipates that its cash position is sufficient to fund its operations at least through the anticipated closing of the Merger. However, Pulmatrix believes that without the closing of the Merger, given its current cash position and forecasted negative cash flows from operating activities over the next twelve months, there is substantial doubt about the ability for Pulmatrix to continue as a going concern after the date that is one year from the date of this proxy statement/prospectus. The consolidated financial statements of Pulmatrix do not include any adjustments relating to the recoverability and classification of asset amounts or the classification of liabilities that might be necessary should Pulmatrix be unable to continue as a going concern.

Pulmatrix will need to raise additional capital to meet its business requirements in the future and such capital raises may be costly or difficult to obtain and could dilute its stockholders’ ownership interests.

In order to continue its operations and to fully realize all of its business objectives, absent any non-dilutive funding from a strategic partner or some other strategic transactions, Pulmatrix will need to raise additional capital, which may not be available on reasonable terms, or at all. For instance, Pulmatrix will need to raise additional funds to accomplish the following:

Any additional capital raised through the sale of equity or equity backed securities will dilute Pulmatrix stockholders’ ownership percentages and could also result in a decrease in the market value of its equity securities.

The terms of any securities issued by Pulmatrix in future financing transactions may be more favorable to new investors, and may include preferences, superior voting rights and the issuance of warrants or other derivative securities, which may have a further dilutive effect on the holders of any of Pulmatrix’s securities then outstanding.

Furthermore, any additional capital financing that Pulmatrix may need in the future may not be available on terms favorable to it, or at all. If Pulmatrix is unable to obtain such additional financing on a timely basis, it may have to curtail its development activities and growth plans and/or be forced to sell assets, perhaps on unfavorable terms, which would have a material adverse effect on its business, financial condition and results of operations, and ultimately could be forced to discontinue its operations and liquidate, in which event it is unlikely that stockholders would receive any distribution on their shares. Further, Pulmatrix may not be able to continue operating if it does not generate sufficient revenues from operations needed to stay in business.

In addition, Pulmatrix may incur substantial costs in pursuing future capital financing, including investment banking fees, legal fees, accounting fees, securities law compliance fees, printing and distribution expenses and other costs. Pulmatrix may also be required to recognize non-cash expenses in connection with certain securities it issues, such as convertible notes and warrants, which may adversely impact its financial condition and cause further dilution to its stockholders.

Pulmatrix has historically been a clinical development stage biopharmaceutical company and has never been profitable. Pulmatrix expects to incur additional losses in the future and may never be profitable.

Pulmatrix has historically been a clinical development stage biopharmaceutical company. Pulmatrix has not commercialized any product candidates or recognized any revenues from its product sales. All of Pulmatrix’s product candidates are still in the preclinical or clinical development stage, and none have been approved for marketing or are currently being marketed or commercialized. Pulmatrix’s product candidates will require substantial additional development, clinical studies, regulatory clearances, and additional investments of time and capital before they can be commercialized. Pulmatrix cannot be certain when or if any of its product candidates will obtain the required regulatory approval.

Pulmatrix has never been profitable and has incurred net losses each year since its inception. Pulmatrix’s losses are principally a result of research and development and general administrative expenses in support of its operations. Pulmatrix may incur substantial additional losses as it continues to focus its resources on prioritizing, selecting and advancing its product candidates. Pulmatrix’s ability to generate revenue and achieve profitability depends mainly upon its ability, alone or with others, to successfully develop its product candidates, obtain the required regulatory approvals in various territories and commercialize its product candidates. Pulmatrix may be unable to achieve any or all of these goals with regard to its product candidates. As a result, Pulmatrix may never be profitable or achieve significant and/or sustained revenues.

All of Pulmatrix’s product candidates are still under development, and there can be no assurance of successful commercialization of any of its products.

All of Pulmatrix’s research and development programs are in developmental stages. One or more of Pulmatrix’s product candidates may fail to meet safety and efficacy standards in human testing, even if those product candidates are found to be effective in animal studies. To develop and commercialize inhaled therapeutic treatment for allergic bronchopulmonary aspergillosis (“ABPA”), acute migraine, and other iSPERSE™-based product candidates, Pulmatrix must provide the Food and Drug Administration (“FDA”) and foreign regulatory authorities with human clinical and non-clinical animal data that demonstrate adequate safety and effectiveness. To generate these data, Pulmatrix will have to subject its product candidates to substantial additional research and development efforts, including extensive non-clinical studies and clinical testing. Pulmatrix’s approach to drug development may not be effective or may not result in the development of any drug. Currently Pulmatrix’s development efforts are primarily focused on PUR3100, PUR1800 and PUR1900. Even if PUR3100, PUR1800 and PUR1900 or Pulmatrix’s other product candidates are successful when tested in animals, such success would not be a guarantee of the safety or effectiveness of such product candidates in humans. It can take several years for a product to be approved and Pulmatrix may not be successful in bringing any therapeutic candidates to the market. A new drug may appear promising at an early stage of development or after clinical trials and never reach the market, or it may reach the market and not sell, for a variety of reasons. For example, the drug may:

If Pulmatrix’s delivery platform technologies or product development efforts fail to generate product candidates that lead to the successful development and commercialization of products, its business and financial condition will be materially adversely affected.

Drug development is a long, expensive and inherently uncertain process with a high risk of failure at every stage of development, and results of earlier studies and trials may not be predictive of future trial results.

Pulmatrix has a number of proprietary drug candidates in research and development ranging from the early research phase through preclinical testing and clinical trials. Preclinical testing and clinical trials are long, expensive and highly uncertain processes. It will take Pulmatrix several years to complete clinical trials and it may not have the resources to complete the development and commercialization of any of its proposed drug candidates. The start or end of a clinical trial, such as Pulmatrix’s Phase 2b trial for PUR1900 and future trials, can often be delayed or halted due to changing regulatory requirements, manufacturing challenges, required clinical trial administrative actions, slower than anticipated patient enrollment, changing standards of care, availability or prevalence of use of a competitor drug or required prior therapy, clinical outcomes, or financial constraints of Pulmatrix and its partners.

Drug development is a highly uncertain scientific and medical endeavor, and failure can unexpectedly occur at any stage of preclinical and clinical development. Typically, there is a high rate of attrition for drug candidates in preclinical and clinical trials due to scientific feasibility, safety, efficacy, changing standards of medical care and other variables. The risk of failure is heightened for Pulmatrix’s drug candidates that are based on new technologies, such as the application of Pulmatrix’s dry powder delivery platform, iSPERSE™, including PUR3100, PUR1800, PUR1900 and other iSPERSE™-based drug candidates currently in research or preclinical development. The failure of one or more of Pulmatrix’s iSPERSE™-based drug candidates could have a material adverse effect on its business, financial condition, and results of operations.

In addition, the results of preclinical studies and clinical trials of previously published iSPERSE™-based products may not necessarily be indicative of the results of Pulmatrix’s future clinical trials. The design of Pulmatrix’s clinical trials is based on many assumptions about the expected effects of inhaled drugs used historically in the industry and if those assumptions are incorrect, the trials may not produce statistically significant results. Preliminary results may not be confirmed upon full analysis of the detailed results of an early clinical trial. Product candidates in later stages of clinical trials may fail to show safety and efficacy sufficient to support intended use claims despite having progressed through initial clinical trials. The data collected from clinical trials of Pulmatrix’s product candidates may not be sufficient to obtain regulatory approval in the United States or elsewhere. Because of the uncertainties associated with drug development and regulatory approval, Pulmatrix cannot determine if, or when, it may have an approved product for commercialization or whether it will ever achieve sales of or profits on its product candidates or those it may pursue in the future.

If Pulmatrix’s collaborators are not successful, or breach their agreements with it, Pulmatrix may not effectively develop and market some of its therapeutic candidates.

At this time, Pulmatrix has entered into a co-development agreement regarding one of its therapeutic candidates and, as a result, it no longer has complete control over the development of this candidate. Pulmatrix may also enter into co-development agreements for its other therapeutic candidates in the future. If Pulmatrix’s collaborators do not successfully carry out their contractual duties or meet expected deadlines, or they otherwise breach their contractual obligations to it, Pulmatrix may be delayed or may not obtain regulatory approval for, or commercialize, its product candidates. Pulmatrix is also subject to the terms of such co-development agreements that may affect its ability to develop and manufacture its therapeutic candidates. As a result of such limitations, Pulmatrix may be unable to pursue the most efficient or profitable path in developing its therapeutic candidates.

If Pulmatrix’s relationships with these collaborators terminate, Pulmatrix believes that it would be able to enter into arrangements with alternative third parties. However, replacing any collaborator could delay Pulmatrix’s clinical trials and could jeopardize its ability to obtain regulatory approvals and commercialize its product candidates on a timely basis, if at all.

Pulmatrix may not be able to attract, retain, or manage highly qualified personnel, which could adversely impact its business.

Pulmatrix’s future success and ability to compete in the biopharmaceutical industry is substantially dependent on its ability to identify, attract, and retain highly qualified key managerial, scientific, medical, and operations personnel. The market for key employees in the biopharmaceutical, pharmaceutical and biotechnology industries is competitive. The loss of the services of any of Pulmatrix’s principal members of management or key employees without an adequate replacement or its inability to hire new employees as needed could delay its product development efforts, harm Pulmatrix’s ability to sell its products or otherwise negatively impact its business.

The scientific, research and development personnel upon whom Pulmatrix has historically relied to operate its business have expertise in certain aspects of drug development and clinical development, and it may be difficult to retain or replace these individuals. Pulmatrix has previously conducted its operations within the greater Boston area, and this region is headquarters to many other biopharmaceutical, biotechnology, pharmaceutical, and medical technology companies, as well as many academic and research institutions, and, therefore, Pulmatrix faces increased competition for technical and managerial personnel in this region.

In addition, Pulmatrix has scientific, medical and clinical advisors who assist it in designing and formulating its products and with development and clinical strategies. These advisors are not Pulmatrix’s employees and may have commitments to, or consulting or advisory contracts with, other entities that may limit their availability to Pulmatrix, or may have arrangements with other companies to assist in the development of products that may compete with Pulmatrix’s.

Despite Pulmatrix’s efforts to retain valuable employees, members of its management and scientific and development teams may terminate their employment with it at any time. Although Pulmatrix has written employment offer letter agreements with its executive officers, its executive officers can leave their employment at any time, for any reason, with 30 days’ notice. A sustained labor shortage or increased turnover rates within Pulmatrix’s employee base could lead to increased costs, such as increased overtime to meet demand and increased wage rates to attract and retain employees, and could negatively affect its ability to efficiently operate its manufacturing and distribution facilities and overall business. If Pulmatrix is unable to hire and retain employees capable of performing at a high-level, or if mitigation measures it may take to respond to a decrease in labor availability, such as overtime and third-party outsourcing, have unintended negative effects, its business could be adversely affected. An overall labor shortage, lack of skilled labor, increased turnover or labor inflation could have a material adverse impact on Pulmatrix’s operations, results of operations, liquidity or cash flows. The loss of the services of any of Pulmatrix’s executive officers or its other key employees and its inability to find suitable replacements could potentially harm its business, financial condition and prospects. Pulmatrix does not maintain “key man” insurance policies on the lives of these individuals or the lives of any of its other employees.

Pulmatrix faces substantial competition in the development of its product candidates and may not be able to compete successfully, and its product candidates may be rendered obsolete by rapid technological change.

The pharmaceutical and biotechnology industry is highly competitive, and Pulmatrix faces substantial competition from many pharmaceutical, biopharmaceutical and biotechnology companies that are researching and marketing products designed to address the indications for which Pulmatrix is currently developing therapeutic candidates or for which it may develop product candidates in the future.

Many of Pulmatrix’s existing or potential competitors have, or have access to, substantially greater financial, research and development, production, and sales and marketing resources than Pulmatrix does and have a greater depth and number of experienced managers. As a result, Pulmatrix’s competitors may be better equipped than it to develop, manufacture, market and sell competing products. In addition, gaining favorable reimbursement is critical to the success of Pulmatrix’s product candidates. Pulmatrix is aware of many established pharmaceutical companies in the United States and other parts of the world that have or are developing technologies for inhaled drug delivery for the prevention and treatment of respiratory diseases, including GlaxoSmithKline, Mereo BioPharma, Mylan, Savara, Insmed, Satsuma, Bristol-Meyers, TFF Pharmaceuticals, Zambon Pharma and Pulmocide, which Pulmatrix considers its potential competitors in this regard. If Pulmatrix is unable to compete successfully with these and other potential future competitors, it may be unable to grow or generate revenue.

The rapid rate of scientific discoveries and technological changes could result in one or more of Pulmatrix’s product candidates becoming obsolete or noncompetitive. Pulmatrix’s competitors may develop or introduce new products that render its iSPERSE™ delivery technology and other product candidates less competitive, uneconomical or obsolete. Some of these technologies may have an entirely different approach or means of accomplishing similar therapeutic effects compared to Pulmatrix’s drug candidates. Pulmatrix’s future success will depend not only on its ability to develop its product candidates but to improve them and keep pace with emerging industry developments. Pulmatrix cannot assure you that it will be able to do so.

Pulmatrix also expects to face increasing competition from universities and other non-profit research organizations. These institutions carry out substantial research and development in the areas of respiratory diseases. These institutions are becoming increasingly aware of the commercial value of their findings and are more active in seeking patent and other proprietary rights as well as licensing revenues.

The potential acceptance of therapeutics that are alternatives to Pulmatrix’s may limit market acceptance of its product candidates, even if commercialized. Respiratory diseases, including Pulmatrix’s targeted diseases and conditions, can also be treated by other medication or drug delivery technologies. These treatments may be widely accepted in medical communities and have a longer history of use. The established use of these competitive drugs may limit the potential for Pulmatrix’s product candidates to receive widespread acceptance if commercialized.

If the third parties on which Pulmatrix relies to conduct its clinical trials and to assist it with preclinical development do not perform as contractually required or expected, it may not be able to obtain regulatory clearance or approval for, or to commercialize, its products.

Pulmatrix does not have the ability to independently conduct its preclinical and clinical trials for its products and it must rely on third parties, such as contract research organizations, medical institutions, clinical investigators and contract laboratories to conduct such trials. If these third parties do not successfully carry out their contractual duties or regulatory obligations or meet expected deadlines, if these third parties need to be replaced, or if the quality or accuracy of the data they obtain is compromised due to the failure to adhere to Pulmatrix’s clinical protocols or regulatory requirements or for other reasons, Pulmatrix’s preclinical development activities or clinical trials may be extended, delayed, suspended or terminated, and it may not be able to obtain regulatory approval for, or successfully commercialize, its products on a timely basis, if at all, and its business, operating results and prospects may be adversely affected. Furthermore, Pulmatrix’s third-party clinical trial investigators may be delayed in conducting its clinical trials for reasons outside of its control, such as, but not limited to, patient enrollment.

Pulmatrix relies on third-party contract vendors to manufacture and supply it with high quality active pharmaceutical ingredients and manufacture its therapeutic candidates in the quantities it requires on a timely basis.

Pulmatrix currently does not manufacture any active pharmaceutical ingredients (“APIs”). Instead, Pulmatrix relies on third-party vendors for the manufacture and supply of its APIs that are used to formulate its therapeutic candidates. Pulmatrix also does not currently own or operate manufacturing facilities and therefore relies, and expect to continue to rely, on third parties to manufacture clinical and commercial quantities of its therapeutic candidates and for quality assurance related to regulatory compliance. If these suppliers or manufacturers are incapable or unwilling to meet Pulmatrix’s current or future needs at its standards or on acceptable terms, if at all, it may be unable to locate alternative suppliers or manufacturers on acceptable terms, if at all, or produce necessary materials or components on its own.

While there may be several alternative suppliers of API in the market, changing API suppliers or finding and qualifying new API suppliers can be costly and can take a significant amount of time. Many APIs require significant lead time to manufacture. There can also be challenges in maintaining similar quality or technical standards from one manufacturing batch to the next. Pulmatrix could experience a delay in conducting clinical trials of or obtaining regulatory approval for PUR3100, PUR1800, PUR1900 or its other drug candidates and incur additional costs if it changed API suppliers for any reason. Similarly, replacing Pulmatrix’s manufacturers could cause it to incur added costs and experience delays in identifying, engaging, qualifying and training any such replacements.

If Pulmatrix is not able to find stable, affordable, high quality, or reliable supplies of the APIs, or if it is unable to maintain its existing or future third-party manufacturing arrangements, it may not be able to produce enough supply of its therapeutic candidates or commercialize any therapeutic candidates on a timely and competitive basis, which could adversely affect Pulmatrix’s business, financial condition or results of operations.

Supply chain and shipping disruptions may result in shipping delays, a significant increase in shipping costs, and could increase product costs and result in lost sales and reputational damage, which may have a material adverse effect on Pulmatrix’s business, operating results and financial condition.

Pulmatrix’s third-party manufacturers and suppliers have experienced, and may continue to experience, supply chain disruption and shipping disruptions, including disruptions or delays in loading container cargo in ports of origin or off-loading cargo at ports of destination, as a result of congestion in port terminal facilities, labor supply and shipping container shortages, inadequate equipment and persons to load, dock and offload container vessels and for other reasons. These disruptions may impact Pulmatrix’s ability to receive its raw materials and certain components required for the manufacture of its clinical trial materials or products in the future, to distribute its products in a cost-effective and timely manner and to meet demand, all of which could have an adverse effect on its financial condition and results of operations. There can be no assurance that further unforeseen events impacting the supply chain will not have a material adverse effect on Pulmatrix in the future. Additionally, the impacts that supply chain disruptions have on Pulmatrix’s third-party manufacturers and suppliers are not within its control. It is not currently possible to predict how long it will take for these supply chain disruptions to cease or ease. Prolonged supply chain disruption that may impact Pulmatrix or its manufacturers and suppliers could interrupt or delay its clinical trials, product manufacturing, increase raw material and product lead times, increase raw material and product costs, impact its ability to meet customer demand and result in lost sales and reputational damage, all of which could have a material adverse effect on its business, financial condition and results of operations.

Pulmatrix may not be successful in negotiating for an appropriate price in a future sale or assignment of its rights related to its current drug candidates.

Pulmatrix may seek to sell or assign its rights related to its current drug candidates. If completed, any such sale or assignment may be at a substantial discount, the consideration received may not accurately represent the value of the assets sold or assigned and its stockholders may not be entitled to participate in the future prospects of such drug candidates and such sale or assignment may not contribute materially to the planned dividend.

Pulmatrix’s failure to successfully acquire, develop and market additional drug candidates or approved drug products could impair its ability to grow.

As part of Pulmatrix’s growth strategy, it may evaluate, acquire, license, develop and/or market additional product candidates and technologies, subject to the availability of adequate financing. However, Pulmatrix’s internal research capabilities are limited, and it may be dependent upon pharmaceutical and biotechnology companies, academic scientists and other researchers to sell or license products or technology to it. The success of this strategy depends partly upon Pulmatrix’s ability to identify, select and acquire promising pharmaceutical product candidates and products. The process of proposing, negotiating and implementing a license or acquisition of a product candidate or approved product is lengthy and complex. Other companies, including some with substantially greater financial, marketing and sales resources, may compete with Pulmatrix for the license or acquisition of product candidates and approved products. Pulmatrix has limited resources to identify and execute the acquisition or in-licensing of third-party products, businesses and technologies and integrate them into its current infrastructure. Moreover, Pulmatrix may devote resources to potential acquisitions or in-licensing opportunities that are never completed, or it may fail to realize the anticipated benefits of such efforts. Pulmatrix may not be able to acquire the rights to additional product candidates on terms that it finds acceptable, or at all.

Any product candidate that Pulmatrix acquires may require additional development efforts prior to commercial sale, including extensive clinical testing and approval by the FDA and applicable foreign regulatory authorities. All product candidates are prone to risks of failure typical of pharmaceutical product development, including the possibility that a product candidate will not be shown to be sufficiently safe and effective for approval by regulatory authorities. In addition, Pulmatrix cannot provide assurance that any products that it develops or approved products that it acquires will be manufactured profitably or achieve market acceptance. Pulmatrix cannot guarantee that it will be able to successfully conduct the preclinical studies of the identified potential product candidates as anticipated.

Pulmatrix’s business strategy may include entry into additional collaborative or license agreements. Pulmatrix may not be able to enter into collaborative or license agreements or may not be able to negotiate commercially acceptable terms for these agreements.

Pulmatrix’s current business strategy may include the entry into additional collaborative or license agreements for the development and commercialization of its product candidates and technologies. The negotiation and consummation of these types of agreements typically involve simultaneous discussions with multiple potential collaborators or licensees and require significant time and resources. In addition, in attracting the attention of pharmaceutical and biotechnology company collaborators or licensees, Pulmatrix competes with numerous other third parties with product opportunities as well as the collaborators’ or licensees’ own internal product opportunities. Pulmatrix may not be able to consummate collaborative or license agreements, or it may not be able to negotiate commercially acceptable terms for these agreements.

If Pulmatrix does enter into such arrangements, it could be dependent upon the subsequent success of these other parties in performing their respective responsibilities and the cooperation of its partners. Pulmatrix’s collaborators may not cooperate with it or perform their obligations under Pulmatrix’s agreements with them. Pulmatrix cannot control the amount and timing of its collaborators’ resources that will be devoted to researching its product candidates pursuant to its collaborative agreements with them. Pulmatrix’s collaborators may choose to pursue existing or alternative technologies in preference to those being developed in collaboration with it. If Pulmatrix does not consummate collaborative or license agreements, it may use its financial resources more rapidly on its product development efforts, continue to defer certain development activities or forego the exploitation of certain geographic territories, any of which could have a material adverse effect on its business prospects. Further, Pulmatrix may not be successful in overseeing any such collaborative arrangements. If Pulmatrix fails to establish and maintain necessary collaborative or license relationships, its business prospects could suffer.

Pulmatrix may be subject to claims that its employees, independent consultants or agencies have wrongfully used or inadvertently disclosed confidential information of third parties.

Pulmatrix employs individuals and contracts with independent consultants and agencies that may have previously worked at or conducted business with third parties; and, it may be subject to claims that it or its employees, consultants or agencies have inadvertently or otherwise used or disclosed confidential information of its employees’ former employers or other third parties. Pulmatrix may also be subject to claims that its employees’ former employers or other third parties have an ownership interest in its patents. Litigation may be necessary to defend against these claims. There is no guarantee of success in defending these claims, and if Pulmatrix is successful, litigation could result in substantial cost and be a distraction to its management and other employees.

Market and economic conditions may negatively impact Pulmatrix’s business, financial condition and share price.

Concerns over inflation, geopolitical issues, the United States financial markets and a declining real estate market, unstable global credit markets and financial conditions, and volatile oil prices have led to periods of significant economic instability, diminished liquidity and credit availability, declines in consumer confidence and discretionary spending, diminished expectations for the global economy and expectations of slower global economic growth going forward, increased unemployment rates, and increased credit defaults in recent years. Pulmatrix’s general business strategy may be adversely affected by any such economic downturns, volatile business environments and continued unstable or unpredictable economic and market conditions. If these conditions continue to deteriorate or do not improve, it may make any necessary debt or equity financing more difficult to complete, more costly, and more dilutive. In addition, there is a risk that one or more of Pulmatrix’s current and future service providers, manufacturers, suppliers, hospitals and other medical facilities, its third-party payors, and other partners could be negatively affected by difficult economic times, which could adversely affect its ability to attain its operating goals on schedule and on budget or meet its business and financial objectives.

Global economic and political instability and conflicts, such as the conflicts in Venezuela, between Russia and Ukraine or in the Middle East, could adversely affect Pulmatrix’s business, financial condition or results of operations.

Pulmatrix’s business could be adversely affected by unstable economic and political conditions within the United States and foreign jurisdictions and geopolitical conflicts, such as the conflicts in Venezuela, between Russia and Ukraine or in the Middle East. While Pulmatrix does not have any customer or direct supplier relationships in impacted areas at this time, the current military conflict, and related sanctions, as well as export controls or actions that may be initiated by nations including the United States, the European Union or Russia (e.g., potential cyberattacks, disruption of energy flows, etc.) and other potential uncertainties could adversely affect its business and/or its supply chain, business partners, employees or customers, and interrupt its ability to supply products, or otherwise adversely impact its business.

If Pulmatrix fails to maintain proper and effective internal controls, its ability to produce accurate and timely financial statements could be impaired, which could harm its operating results, its ability to operate its business and investors’ views of it.

Ensuring that Pulmatrix has adequate internal financial and accounting controls and procedures in place so that it can produce accurate financial statements on a timely basis is a costly and time-consuming effort that will need to be evaluated frequently. Section 404 of the Sarbanes-Oxley Act of 2002 (the “Sarbanes-Oxley Act”) requires public companies to conduct an annual review and evaluation of their internal controls. Pulmatrix’s failure to maintain the effectiveness of its internal controls in accordance with the requirements of the Sarbanes-Oxley Act could have a material adverse effect on its business. Pulmatrix could lose investor confidence in the accuracy and completeness of its financial reports, which could have an adverse effect on the price of its common stock.

Pulmatrix’s ability to use its net operating loss carryforwards to offset future taxable income may be subject to certain limitations.

Pulmatrix’s ability to use its net operating loss carryforwards to offset future taxable income may be subject to certain limitations. In general, under Section 382 of the Internal Revenue Code of 1986, as amended (the “Code”) a corporation that undergoes an “ownership change” is subject to annual limitations on its ability to use its pre-change net operating loss carryforwards or other tax attributes (“NOLs”), to offset future taxable income or reduce taxes. Pulmatrix’s past issuances of stock and other changes in its stock ownership may have resulted in ownership changes within the meaning of Section 382 of the Code; accordingly, Pulmatrix’s pre-change NOLs may be subject to limitation under Section 382. If Pulmatrix determines that it has not undergone an ownership change, the Internal Revenue Service could challenge its analysis, and Pulmatrix’s ability to use its NOLs to offset taxable income could be limited by Section 382 of the Code. Future changes in Pulmatrix’s stock ownership, some of which are outside of Pulmatrix’s control, could result in ownership changes under Section 382 of the Code further limiting Pulmatrix’s ability to utilize its NOLs. Furthermore, Pulmatrix’s ability to use NOLs of companies that it may acquire in the future may be subject to limitations. For these reasons, Pulmatrix may not be able to use a material portion of the NOLs, even if it attains profitability.

Pulmatrix’s business is subject to cybersecurity risks.

Pulmatrix’s operations are increasingly dependent on information technologies and services. Threats to information technology systems associated with cybersecurity risks and cyber incidents or attacks continue to grow, and include, among other things, storms and natural disasters, terrorist attacks, utility outages, theft, viruses, phishing, malware, design defects, human error, and complications encountered as existing systems are maintained, repaired, replaced, or upgraded. Risks associated with these threats include, among other things:

Although Pulmatrix utilizes various procedures and controls to mitigate its exposure to such risk, cybersecurity attacks and other cyber events are evolving and unpredictable. Moreover, Pulmatrix has no control over the information technology systems of third parties conducting its clinical trials, its suppliers, and others with which its systems may connect and communicate. As a result, the occurrence of a cyber incident could go unnoticed for a period of time.

Pulmatrix has cybersecurity insurance coverage in the event it becomes subject to various cybersecurity attacks, however, it cannot ensure that it will be sufficient to cover any particular losses it may experience as a result of such cyberattacks. Any cyber incident could have a material adverse effect on Pulmatrix’s business, financial condition and results of operations.

Risks Related to Pulmatrix Regulatory Matters

Pulmatrix’s product candidates must undergo rigorous nonclinical and clinical testing, and it must obtain regulatory approvals, which could be costly and time-consuming and subject it to unanticipated delays or prevent it from marketing any products. Pulmatrix cannot be certain that any of its current and future product candidates will receive regulatory approval, and without regulatory approval it will not be able to market its product candidates.

Pulmatrix’s ability to generate revenue related to product sales, if ever, will depend on the successful development and regulatory approval of its product candidates. Pulmatrix currently has no products approved for sale, and it cannot guarantee that it will ever have marketable products. The development of a product candidate and issues relating to its approval and marketing are subject to extensive regulation, including regulation for safety, efficacy and quality, by the FDA in the United States and comparable regulatory authorities in other countries, with regulations differing from country to country. The FDA regulations and the regulations of comparable foreign regulatory authorities are wide-ranging and govern, among other things: