Review article accepted for publication in Degenerative Neurological and Neuromuscular Disease and builds on Atossa’s previously published Duchenne Muscular Dystrophy (DMD) research

SEATTLE, May 20, 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 significant unmet clinical need, today announced that the manuscript titled, “(Z)-Endoxifen as a Potential Modulator of Utrophin Pathways in Duchenne Muscular Dystrophy: A Mechanistic and Transcriptomic Perspective,” has been accepted for publication in Degenerative Neurological and Neuromuscular Disease.

The review centers on utrophin, a structural and functional homolog of dystrophin. Utrophin may partially compensate for dystrophin deficiency by supporting sarcolemmal and muscle-cell membrane stability when dystrophin is absent or deficient. The manuscript describes how (Z)-endoxifen, the primary active metabolite of tamoxifen, could create a cellular environment that favors utrophin expression, localization, and function, which could potentially influence disease-relevant processes, such as protein kinase C beta-1 signaling, estrogen receptor signaling, calcium homeostasis, inflammation, fibrosis, mitochondrial function, and muscle regeneration. The authors describe (Z)-endoxifen as a compelling mechanistic candidate in treating DMD and identified next steps including preclinical evaluation in dystrophin-deficient models and biomarker development focused on utrophin expression and localization, calcium handling, PKC activity, developmental myosin, transcriptomic signatures, and muscle composition imaging.

“This publication advances our scientific rationale for studying (Z)-endoxifen through the lens of utrophin biology, one of the most compelling mutation-agnostic strategies in DMD,” said Dr. Steven C. Quay, M.D., Ph.D., President and Chief Executive Officer of Atossa Therapeutics. “DMD remains a devastating disease with significant unmet need, and we are encouraged by the mechanistic and transcriptomic evidence suggesting that (Z)-endoxifen may help support pathways involved in utrophin-mediated muscle stabilization and repair.”

The new article builds on Atossa’s previously published DMD manuscript in Degenerative Neurological and Neuromuscular Disease, “A Hypothesized Therapeutic Role of (Z)-Endoxifen in Duchenne Muscular Dystrophy” (L. Remmel, 2025), which introduced the broader rationale for evaluating (Z)-endoxifen in DMD. The accepted manuscript builds upon that work by placing greater emphasis on utrophin pathway biology as a potential unifying mechanism for (Z)-endoxifen’s multi-pathway effects.

The manuscript was authored by H. Lawrence Remmel, Sandra S. Hammer, Scott M. Blackburn, and Steven C. Quay. The authors also acknowledge input from Dame Professor Kay E. Davies, CBE FRS FMedSci, Emeritus Fellow of Hertford College, Oxford.

About Duchenne Muscular Dystrophy

DMD is a rare, progressive neuromuscular disease caused by mutations in the DMD gene, which encodes dystrophin, a protein essential for maintaining muscle-cell structural integrity. Loss of functional dystrophin causes muscle fibers to become fragile and susceptible to contraction-induced damage, leading over time to progressive weakness, fibrosis, loss of ambulation, cardiomyopathy, respiratory failure, and premature death.

About Atossa Therapeutics

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.

(Z)-Endoxifen is a potent Selective Estrogen Receptor Modulator/Degrader (SERM/D) with demonstrated activity across multiple mechanisms of interest. Atossa is evaluating its potential applications in oncology and rare diseases. The Company’s proprietary oral formulation has shown a favorable safety profile and pharmacology distinct from tamoxifen, including ER-targeted effects and PKC inhibition. Atossa’s (Z)-endoxifen is not approved for any indication.

Atossa has previously received Orphan Drug and Rare Pediatric Disease (RPD) designations for (Z)-endoxifen for the treatment of DMD from the FDA. Upon approval of a qualifying marketing application, drugs with RPD designation may be eligible for a Priority Review Voucher (PRV), which can be used to obtain priority review for a future application or may be sold or transferred to another sponsor. In the last 18-24 months, disclosed PRV sales have ranged from $100-$205 million.

Atossa’s (Z)-endoxifen program is supported by a growing global intellectual property portfolio, including multiple recently issued U.S. patents and numerous pending applications worldwide.

More information is available at https://atossatherapeutics.com.

Forward-Looking Statements

This press release contains certain “forward-looking statements” within the meaning of applicable securities laws, including, but not limited to, our expectations regarding the Company’s development and regulatory strategy and related milestones, including the potential indications that the Company may pursue for (Z)-endoxifen, the potential role of (Z)-endoxifen in utrophin pathway modulation, expectations regarding the design, enrollment, data, timing, results and outcomes of the Company’s clinical studies, the potential for (Z)-endoxifen to receive regulatory approval and the timing thereof, the Company’s potential eligibility for and the value of a Rare Pediatric Disease Priority Review Voucher, and the potential market and growth opportunities for the Company. 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 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: our ability to successfully execute our strategy to shorten our clinical development timelines and pursue a DMD 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.

The market value of a PRV is variable and subject to a number of factors beyond our control and reported past PRV sale amounts are not necessarily indicative of PRV sale amounts in the future.

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.

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