Atossa Therapeutics Announces Closing of Registered Direct Offering of up to $16.5 Million in Gross Proceeds

$4.5 million upfront with up to an additional $12 million of potential aggregate gross proceeds upon exercise in full of warrants

SEATTLE,June 12, 2026/PRNewswire/ -- Atossa Therapeutics, Inc. (Nasdaq:ATOS) ("Atossa" or the "Company"), a clinical-stage biopharmaceutical company developing novel therapies in oncology and other areas of high unmet clinical need, today announced the closing of its previously announced registered direct offering of 1,363,637 shares (the "Shares") of its common stock, par value $0.18 per share ("Common Stock") (or common stock equivalents in lieu thereof), Series A warrants to purchase up to 1,363,637 shares of Common Stock and short-term Series B warrants to purchase up to 1,363,637 shares of Common Stock (such warrants, collectively, the "Series Warrants") and accompanying Series Warrants. The Series Warrants are exercisable six months following the date of issuance. The Series A warrants expire on the five and one-half (5.5) year anniversary of the date of issuance. The short-term Series B warrants expire on the two (2) year anniversary of the date of issuance.

Rodman & Renshaw LLC acted as the exclusive placement agent for the offering.

The aggregate gross proceeds to the Company from the offering were approximately $4.5 million before deducting the placement agent's fees and other estimated offering expenses payable by the Company. The potential additional gross proceeds to the Company from the Series Warrants, if fully exercised on a cash basis, will be approximately $12 million. No assurance can be given that any of the Series Warrants will be exercised, or that the Company will receive cash proceeds from the exercise of the Series Warrants. The Company currently intends to use the net proceeds from the offering for clinical development of its product candidates, working capital and general corporate purposes.

The securities described above were offered and sold by the Company in a registered direct offering pursuant to a "shelf" registration statement on Form S-3 (File No. 333-279367) that was filed with the Securities and Exchange Commission (the "SEC"), on May 13, 2024, and declared effective by the SEC on May 23, 2024. The securities offered in the registered direct offering were offered only by means of a prospectus, including a prospectus supplement, forming a part of the effective registration statement. A prospectus supplement and the accompanying base prospectus relating to the registered direct offering were filed with the SEC and are available on the SEC's website atwww.sec.gov. Electronic copies of the prospectus supplement and the accompanying base prospectus may also be obtained from Rodman & Renshaw LLC at 600 Lexington Avenue, 32nd Floor, New York, NY 10022, by telephone at (212) 540-4414, or by email at[email protected].

This press release shall not constitute an offer to sell or the solicitation of an offer to buy any of the securities described herein, nor shall there be any sale of these securities in any state or jurisdiction in which such offer, solicitation or sale would be unlawful prior to the registration or qualification under the securities laws of any such state or jurisdiction.

Atossa Therapeutics, Inc. (Nasdaq:ATOS) is a clinical-stage biopharmaceutical company developing innovative medicines in oncology and other areas of significant unmet need. The Company's lead product candidate, (Z)-endoxifen, is currently in development across several clinical settings. More information is available athttps://atossatherapeutics.com.

This press release contains certain "forward-looking statements" within the meaning of the Private Litigation Reform Act of 1995, including but not limited to, the timing and completion of the offering, the satisfaction of customary closing conditions related to the offering, and the intended use of proceeds therefrom. Words such as "expect," "potential," "continue," "may," "will," "should," "could," "would," "seek," "intend," "plan," "estimate," "anticipate," "believe," "design," "predict," "future," or other similar expressions or statements regarding intent, belief or current expectations, are forward-looking statements.

Forward-looking statements in this press release, including those regarding the expected closing date of the offering, the satisfaction of customary closing conditions related to the offering, the intended use of proceeds from the offering, the potential exercise of the Series Warrants and potential proceeds therefrom, are subject to risks and uncertainties that may cause actual results, outcomes, or the timing of actual results or outcomes to differ materially from those projected or anticipated, including, without limitation, risks and uncertainties associated with: market and other conditions, our ability to successfully execute our strategy to shorten our clinical development timelines and pursue a Duchenne Muscular Dystrophy or McCune-Albright Syndrome indication, or other indications for our lead program, (Z)-endoxifen; expected timing, completion and results of our preclinical studies, clinical trials and research and development programs; the unpredictable relationship between preclinical study results and clinical study results; the timing or likelihood of regulatory filings and approvals; the outcome or timing of necessary regulatory approvals; our ability to maintain compliance with Nasdaq listing requirements; our ability to establish and maintain intellectual property rights covering our products; the impact of general macroeconomic conditions on our business; our ability to raise capital; and other risks and uncertainties detailed from time to time in Atossa's filings with the SEC, including, without limitation, its Annual Reports on Form 10-K and Quarterly Reports on Form 10-Q.

Forward-looking statements are presented as of the date of this press release. Except as required by law, we do not intend to update any forward-looking statements.