5. Stockholders’ equity

The total number of shares of all classes of capital stock that the Company is authorized to issue is 440,000,000 shares, consisting of 400,000,000 shares of common stock, par value $0.001 per share and 40,000,000 shares of preferred stock, par value $0.001 per share.

Series A Preferred Stock

As of March 31, 2026 and December 31, 2025, a total of 31,194 shares of Series A Preferred Stock remained outstanding, which are convertible into 15,596 shares of common stock. In April 2025, a total of 25,033 shares of Series A Preferred stock were converted into 12,516 shares of common stock.

Common Stock

The holders of common stock are entitled to one vote for each share of common stock. In the event of any voluntary or involuntary liquidation, dissolution or winding up of the Company, after the payment or provision for payment of all debts and liabilities of the Company, the holders of common stock shall be entitled to share in the remaining assets of the Company available for distribution, if any.

Shelf Registration Statement

On January 26, 2024, the Company filed a shelf registration statement (the “2024 Shelf Registration Statement”) with the SEC for issuance of common stock, preferred stock, warrants, rights, debt securities and units up to an aggregate of $150 million, including a prospectus for the sale of $1.0 million of shares of our common stock under the At The Market Offering Agreement by and between the Company and H.C. Wainwright & Co., LLC (“HCW”) dated as of January 26, 2024 (the “January 2024 ATM Agreement), which was declared effective on February 2, 2024. The Company subsequently filed a prospectus supplement to the 2024 Shelf Registration Statement for the sale of up to $2.0 million of shares of common stock pursuant to the January 2024 ATM Agreement. The Company did not make any sales under the January 2024 ATM Agreement and in March 2024, the Company terminated the January 2024 ATM Agreement.

On November 8, 2024, the Company entered into an At the Market Offering Agreement (the “November 2024 ATM Agreement”) with HCW. On November 8, 2024, the Company filed a prospectus supplement to the 2024 Shelf Registration Statement with the SEC for the sale of up to $3.0 million pursuant to the November 2024 ATM Agreement,

as discussed below. Pursuant to the November 2024 ATM Agreement and the prospectus supplement filed in connection therewith, the Company may, from time to time, in its sole discretion, issue and sell through HCW, acting as sales agent and/or principal, up to $3.0 million of shares of common stock. During the year ended December 31, 2025, the Company issued and sold 1,337,948 shares of common stock under the November 2024 ATM Agreement resulting in net proceeds to the Company of approximately $1.9 million after deducting approximately $76,000 in issuance costs. During the three months ended March 31, 2026, the Company did not issue and sell shares of common stock under the November 2024 ATM Agreement.

March 2024 Private Placement

On March 11, 2024, the Company entered into a securities purchase agreement with certain purchasers (the “March 2024 Purchasers”) pursuant to which the Company agreed to issue and sell to the March 2024 Purchasers in a private placement offering exempt from registration under the Securities Act of 1933, as amended, or the Securities Act, and the Purchasers agreed to purchase from the Company (i) 1,687,712 shares of the Company’s common stock at a purchase price of $7.29 per share (the “March 2024 Shares”), (ii) pre-funded common stock purchase warrants to purchase an aggregate of up to 507,076 shares of the Company’s common stock at an exercise price of $0.001 per share (the “March 2024 Pre-Funded Shares”), (iii) tranche A common stock purchase warrants to purchase up to 1,097,394 shares of the Company’s common stock at an exercise price of $7.29 per share (the “Tranche A Warrants”), and (iv) tranche B common stock purchase warrants to purchase up to 1,097,394 shares of the Company’s common stock at an exercise price of $9.1125 per share (the “Tranche B Warrants”). The Tranche A Warrants will be exercisable until the earlier of (i) the three-year anniversary of issuance and (ii) 30 days after the Company announces the recommended Phase 2 dose for ATRN-119, and, following such announcement, the daily volume weighted average price of the Company’s common stock equals or exceeds $14.58 for 30 consecutive trading days. The Tranche B Warrants will be exercisable until the earlier of (i) the five-year anniversary of issuance and (ii) 30 days after the Company announces the recommended Phase 2 dose for APR-1051 and, following such announcement, the daily volume weighted average price of the Company’s common stock equals or exceeds $18.225 for 30 consecutive trading days. The aggregate upfront gross proceeds from the issuance of common stock and pre-funded common stock purchase warrants totaled approximately $16.0 million, before deducting placement agent fees and offering costs of approximately $1.3 million. The gross proceeds from potential future warrant cash exercises are expected to be up to approximately $18.0 million, before deducting placement agent fees. In April 2024, the Company registered on Form S-3 the resale of the March 2024 Shares, the March 2024 Pre-Funded Shares and the shares underlying the Tranche A Warrants and Tranche B Warrants.

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December 2025 Private Placement

On December 8, 2025, the Company entered into a securities purchase agreement with certain purchasers (the “December Purchasers”) pursuant to which the Company agreed to issue and sell to the December Purchasers in a private placement offering exempt from registration under the Securities Act of 1933, as amended, or the Securities Act, and the December Purchasers agreed to purchase from the Company (i) 26,459 shares of the Company’s common stock at a purchase price of $1.165 per share (the “December 2025 Shares”), (ii) pre-funded common stock purchase warrants (the “December 2025 Pre-Funded Warrants”), at a purchase price of $1.164 to purchase an aggregate of up to 2,596,564 shares of the Company’s common stock at an exercise price of $0.001 per share (the “December 2025 Pre-Funded Shares”), (iii) common stock purchase warrants to purchase up to 2,880,533 shares of the Company’s common stock at an exercise price of $1.04 per share (the “December 2025 Warrants”), and (iv) a warrant to purchase up to 257,510 shares of the Company’s common stock to the placement agent (the “Placement Agent Warrant”). The December 2025 Warrants and the Placement Agent Warrant will be exercisable until the five-year anniversary of issuance. The aggregate upfront gross proceeds from the issuance of the December 2025 Shares and December 2025 Pre-Funded Warrants totaled approximately $3.1 million, before deducting placement agent fees and offering costs of approximately $0.4 million. In December 2025, the Company registered on Form S-3 the resale of the December 2025 Shares, the December 2025 Pre-Funded Shares and the shares underlying the December 2025 Warrants and the Placement Agent Warrant.

January 2026 Private Placement

On January 28, 2026, the Company entered into a securities purchase agreement with certain purchasers (the “January Purchasers”) pursuant to which the Company agreed to issue and sell to the January Purchasers in a private placement offering exempt from registration under the Securities Act of 1933, as amended, or the Securities Act, and the January Purchasers agreed to purchase from the Company (i) 1,877,677 shares of the Company’s common stock at a purchase price of $0.8891 per share (the “January 2026 Shares”), (ii) pre-funded common stock purchase warrants (the “January 2026 Pre-Funded Warrants”) at a purchase price of $0.8881 to purchase an aggregate of up to 4,411,180 shares of the Company’s common stock at an exercise price of $0.001 per share (the “January 2026 Pre-Funded Shares”) and (iii) common stock purchase warrants to purchase up to 6,288,857 shares of the Company’s common stock at an exercise price of $0.765 per share (the “January 2026 Warrants”). The January 2026 Warrants will be exercisable until the two-year anniversary of issuance. The aggregate upfront gross proceeds from the issuance of January 2026 Shares and January 2026 Pre-Funded Warrants totaled approximately $5.6 million, before deducting placement agent fees and offering costs of approximately $0.5 million. In February 2026, the Company registered on Form S-3 the resale of the January 2026 Shares, the January 2026 Pre-Funded Shares and the shares underlying the January 2026 Warrants.

March 2026 Private Placement

On March 30, 2026, the Company entered into a securities purchase agreement with certain purchasers (the “March Purchasers”) pursuant to which the Company agreed to issue and sell to the Purchasers in a private placement offering exempt from registration under the Securities Act of 1933, as amended, or the Securities Act, and the March Purchasers agreed to purchase from the Company (i)  pre-funded common stock purchase warrants (the “March 2026 Pre-Funded Warrants”) at a purchase price of $0.807 to purchase an aggregate of up to 37,174,713 shares of the Company’s common stock at an exercise price of $0.001 per share (the “March 2026 Pre-Funded Shares”) and (ii) common stock purchase warrants to purchase up to 37,174,713 shares of the Company’s common stock at an exercise price of $0.683 per share (the “March 2026 Warrants”). The March 2026 Warrants will be exercisable until December 31, 2029. However, if a holder exercises all or a portion of a March 2026 Pre-Funded Warrant then the termination date shall be the 30^th calendar day after the holder exercises such March 2026 Pre-Funded Warrant with respect to the number of shares exercised under such March 2026 Pre-Funded Warrant. The aggregate upfront gross proceeds from the issuance of the March 2026 Pre-Funded Warrants totaled approximately $30.0 million, before deducting placement agent fees and offering costs of approximately $2.3 million. At March 31, 2026, approximately $0.5 million of the proceeds had not yet been received by the Company. The unpaid amount was recorded as a subscription receivable and presented as a reduction of stockholders’ equity. The full amount was received by the Company on April 1, 2026. In April 2026, the Company registered on Form S-3 the resale of the March 2026 Pre-Funded Shares and the shares underlying the March 2026 Warrants.

The Company evaluated the terms of the warrants issued in the December 2025, January 2026 and March 2026 Private Placements and determined that they should be classified as equity instruments within additional paid-in capital. As of March 31, 2026 and December 31, 2025, none of the Tranche A Warrants or Tranche B Warrants have been exercised. During 2025, 91,206 warrants to purchase March 2024 Pre-Funded Shares were exercised for proceeds of $91 and 1,198,700 December 2025 Pre-Funded Warrants to purchase December 2025 Pre-Funded Shares were exercised for no proceeds. For the three months ended March 31, 2026, 1,376,405 December 2025 Pre-Funded Warrants to purchase December 2025 Pre-Funded Shares and 523,596 January 2026 Pre-Funded Warrants to purchase January 2026 Pre-Funded Shares were exercised for no proceeds.

A summary of warrants outstanding as of March 31, 2026 is as follows:

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Stock-Based Compensation Expense

The Company recorded stock-based compensation expense of $0.1 million for each of the three months ended March 31, 2026 and 2025.