2026 Registered Offering

On February 2, 2026, the Company entered into an underwriting agreement with Piper Sandler & Co. and UBS Securities LLC, as representatives of the underwriters named therein, in connection with its previously announced underwritten offering (2026 Offering) of 39,576,088 shares (2026 Offering Shares) of the Company’s Common Stock, and, in lieu of 2026 Offering Shares to certain investors, pre-funded warrants (2026 Pre-funded Warrants) to purchase 6,598,046 shares of Common Stock. The price to the investors for the 2026 Offering Shares was $3.79 per 2026 Offering Share, and the price to the investors for the 2026 Pre-funded Warrants was $3.789 per 2026 Pre-funded Warrant, which represents the per share price for the 2026 Offering Shares less the $0.001 per share exercise price for each such 2026 Pre-funded Warrant. The 2026 Offering closed on February 3, 2026.

The gross proceeds to the Company from the 2026 Offering were approximately $175.0 million, before underwriting discounts and commissions and other offering-related expenses.

The exercise price and the number of shares of Common Stock issuable upon exercise of each 2026 Pre-funded Warrant are subject to appropriate adjustment in the event of certain stock dividends and distributions, stock splits, stock combinations, reclassifications or similar events affecting the Common Stock as well as upon any distribution of assets, including cash, stock or other property, to the Company’s stockholders. The 2026 Pre-funded Warrants will not expire and are exercisable in cash or by means of a cashless exercise. A holder of the 2026 Pre-funded Warrants may not exercise such 2026 Pre-funded Warrants if the aggregate number of shares of Common Stock beneficially owned by such holder, together with its affiliates, would be more than 4.99% or 9.99%, as elected by such holder, of the issued and outstanding shares of Common Stock following such exercise, as such percentage ownership is determined in accordance with the terms of the 2026 Pre-funded Warrants. A holder of the 2026 Pre-funded Warrants may increase or decrease this percentage not in excess of 19.99% by providing at least 61 days’ prior notice to the Company.

The 2026 Offering was made pursuant to the Company’s shelf registration statement on Form S-3 (File No. 333-279692), as amended, which was most recently declared effective on April 8, 2025, a related base prospectus dated April 8, 2025, and a free writing prospectus and prospectus supplement each dated February 2, 2026.

2024 At-the-Market (ATM) Agreement

On August 13, 2024, the Company entered into a Controlled Equity OfferingSM Sales Agreement (2024 ATM Agreement) with Cantor Fitzgerald & Co. and RBC Capital Markets, LLC (each, an ATM Agent, and together, the ATM Agents) pursuant to which the Company from time to time may offer and sell shares (2024 ATM Shares) of its Common Stock, through or to the ATM Agents having an aggregate sales price of up to $250.0 million.

Subject to the terms and conditions of the 2024 ATM Agreement, each ATM Agent is required to use its commercially reasonable efforts to sell the ATM Shares from time to time, based upon the Company’s instructions. The Company has provided the ATM Agents with customary indemnification rights, and the ATM Agents will be entitled to a commission of up to 3.0% of the gross proceeds from each sale of the ATM Shares effectuated through or to the applicable ATM Agent selling the ATM Shares.

Sales of the 2024 ATM Shares under the 2024 ATM Agreement may be made in transactions that are deemed to be “at the market offerings” as defined in Rule 415 under the Securities Act of 1933, as amended. The Company has no obligation to sell any of the 2024 ATM Shares and may at any time suspend offers under the 2024 ATM Agreement or terminate the 2024 ATM Agreement.

Any Common Stock sold under the 2024 ATM Agreement will be issued and sold pursuant to the Company’s shelf registration statement on Form S-3 (File No. 333-279692) (the May 2024 Registration Statement), which initially became effective on May 24, 2024 and which was subsequently amended on March 26, 2025 and April 4, 2025, with Post-Effective Amendment #3 being declared effective by the SEC on April 8, 2025. On August 13, 2024, the Company initially filed a prospectus supplement to the May 2024 Registration Statement with the SEC in connection with the offer and sale of up to $250.0 million of the 2024 ATM Shares pursuant to the 2024 ATM Agreement. The Company re-filed the ATM prospectus supplement with each of the post-effective amendments to the May 2024 Registration Statement.

On February 18, 2025, the Company sold 3,379,377 shares of its Common Stock under the 2024 ATM Agreement at an average price of approximately $3.02 per share of Common Stock, resulting in gross proceeds of approximately $10.2 million.

Lantheus Agreements

Investment Agreement

On January 8, 2024, the Company entered into an investment agreement (Lantheus Investment Agreement) with Lantheus Alpha Therapy, LLC, a Delaware limited liability company and wholly owned subsidiary of Lantheus Holdings, Inc. (Lantheus), pursuant to which the Company agreed to sell and issue to Lantheus in a private placement transaction certain shares (Lantheus Shares) of Common Stock. The closing of the purchase and sale of the Lantheus Shares to Lantheus by the Company (the Lantheus Closing) was subject to the Company raising at least $50.0 million of gross proceeds (excluding Lantheus’ investment) in a qualifying third-party financing transaction, which occurred on January 22, 2024.

The number of Lantheus Shares sold was 5,634,235, representing 19.99% of the outstanding shares of Common Stock as of January 8, 2024. Pursuant to the Lantheus Investment Agreement, the Company agreed to cooperate in good faith to negotiate and enter into a registration rights agreement with Lantheus, obligating the Company to file a registration statement on Form S-3 with the SEC to register for resale the Lantheus Shares issued at the Lantheus Closing. The Company filed such Form S-3 on March 29, 2024, and the SEC declared it effective on April 9, 2024 (File No. 333-278362).

The Lantheus Investment Agreement also contains agreements of the Company and Lantheus whereby Lantheus is provided certain board observer and information rights of the Company, subject to certain exceptions.

The Lantheus Investment Agreement also provides Lantheus with certain pro rata participation rights to maintain its ownership position in the Company in the event that the Company makes any public or non-public offering of any equity or voting interests in the Company or any securities that are convertible or exchangeable into (or exercisable for) equity or voting interests in the Company, subject to certain exceptions.

Pursuant to the Lantheus Investment Agreement, the Company is required to notify Lantheus within 10 business days of the end of a fiscal quarter in which the Company issued shares of Common Stock pursuant to at-the-market programs, including the 2024 ATM Agreement, of (i) the number of shares of Common Stock issued during such fiscal quarter pursuant to the 2024 ATM Agreement and (ii) the average price per share received by the Company before commissions (ATM Average Price). Upon receipt of such notice, Lantheus may elect, at its option, to purchase all or a portion of its Pro Rata Portion (as defined in the Lantheus Investment Agreement) of such shares at an aggregate price equal to the number of shares purchased multiplied by the ATM Average Price for such quarter (ATM Participation Right). Pursuant to the Lantheus Investment Agreement, Lantheus may not exercise the ATM Participation Right more than two times per calendar year.

Option Agreement

On January 8, 2024, the Company entered into an option agreement (Option Agreement) with Lantheus whereby Lantheus was granted an exclusive option to negotiate an exclusive, worldwide, royalty- and milestone-bearing right and license to [212Pb]VMT-α-NET, the Company’s clinical-stage alpha therapy developed for the treatment of neuroendocrine tumors. If good-faith negotiations fail, Lantheus has a one-year right to reenter negotiations if a third party offers to purchase or license the [212Pb]VMT-α-NET program. Additionally, Lantheus has a right to co-fund the Investigational New Drug (IND) application, enabling studies for early-stage therapeutic candidates targeting prostate-specific membrane antigen and gastrin-releasing peptide receptor and, prior to IND filing, a right to negotiate for an exclusive license to such candidates. In consideration of the rights granted by the Company to Lantheus pursuant to the Option Agreement, Lantheus paid to the Company a one-time payment of $28.0 million, subject to certain withholding provisions.

Under the terms of the Option Agreement, Lantheus also had a right of first offer and last look protections for any third-party merger and acquisition transactions involving the Company for a 12-month period which expired on January 8, 2025.

The Company determined that the Option Agreement should be accounted for as a research and development arrangement in accordance with Accounting Standards Codification (ASC) 730-20, Research and Development Arrangements, as Lantheus held approximately 19.9% of the Company’s outstanding Common Stock at March 31, 2024. The Option Agreement contains no repayment provisions, does not create any obligation to enter into any license, transfer or sale agreements with Lantheus, and does not restrict the use of the funds in any way.

Accordingly, the Condensed Consolidated Balance Sheets report long-term liabilities related to these options under the caption, “Deferred Income.” The values for each distinct option within the Option Agreement were determined by estimating the fair value of each distinct option by a third-party valuation firm and the liabilities will be recognized as income in the Condensed Consolidated Statements of Operations and Comprehensive Loss as the various options expire. In connection with the January 8, 2025 expiration of the right of first offer and last look provisions provided under the Option Agreement, the Company recognized $1.4 million in the Condensed Consolidated Statements of Operations and Comprehensive Loss as “Other income from a related party.”