STEALTH BIOTHERAPEUTICS ANNOUNCES FDA ACCEPTANCE OF ELAMIPRETIDE NDA RESUBMISSION

NEEDHAM, Mass., Aug. 21, 2025 /PRNewswire/ -- Stealth BioTherapeutics, a clinical-stage biotechnology company focused on the discovery, development and commercialization of novel therapies for diseases involving mitochondrial dysfunction, announced today that the U.S. Food and Drug Administration (FDA) has accepted for review the resubmission of the New Drug Application (NDA) for elamipretide for the treatment of Barth syndrome. While the FDA considers the resubmission a complete, class 2 response with a six-month user fee goal date of February 15, 2026, the agency has advised the Company that its planned goal date is September 26, 2025.

"We appreciate the FDA's timely acceptance and commitment to expeditiously review our NDA resubmission," said Reenie McCarthy, Chief Executive Officer. "We are sharing this news in the spirit of transparency with families living with Barth syndrome and their many champions, and with gratitude to the FDA for recognizing the urgency of the unmet need."

Stealth resubmitted its NDA to the FDA on August 15, 2025, following its receipt of a May 2025 complete response (CR). As recommended by the FDA in the CR, the resubmission seeks accelerated approval of elamipretide on the basis of improvements in knee extensor muscle strength, an intermediate clinical endpoint, which improved by >45% in the TAZPOWER Phase 2 open-label clinical trial. Stealth's resubmission included a protocol for a post-marketing trial to confirm clinical benefit.

If approved, this would be the first marketing authorization for elamipretide, a first-in-class mitochondria-targeted therapeutic. Elamipretide is also in development for primary mitochondrial myopathy and dry age-related macular degeneration.

About Barth Syndrome
Barth syndrome is an ultra-rare genetic condition characterized by exercise intolerance, muscle weakness, debilitating fatigue, heart failure, recurrent infections, and delayed growth. The disease is associated with reduced life expectancy, with 85% of early deaths occurring by age 5. Barth syndrome occurs almost exclusively in males and is estimated to affect one in 1,000,000 males worldwide or around 150 individuals in the United States. There are currently no FDA- or EMA-approved therapies for patients with Barth syndrome. Elamipretide has Orphan Drug, Fast Track and Rare Pediatric Designation from the FDA and Orphan Drug Designation from the EMA for the treatment of Barth syndrome. The Barth syndrome NDA was granted priority review.

About Stealth BioTherapeutics
Stealth BioTherapeutics is a clinical-stage biotechnology company focused on the discovery, development, and commercialization of novel therapies for diseases involving mitochondrial dysfunction. Mitochondria, found in nearly every cell in the body, are the body's main source of energy production and are critical for normal organ function. Dysfunctional mitochondria characterize a number of rare genetic diseases and are involved in many common age-related diseases, typically involving organ systems with high energy demands such as the heart, the eye, and the brain. The Company believes its lead product candidate, elamipretide, has the potential to treat rare diseases including Barth syndrome and primary mitochondrial myopathy and common age-related diseases including dry age-related macular degeneration. The Company is also evaluating a topical ophthalmic formulation of bevemipretide, its second-generation clinical-stage candidate, for dry age-related macular degeneration. The Company has a deep pipeline of novel compounds under evaluation for rare neurological and cardiac disease indications following promising preclinical data.

Media Contact
Anna Stallmann
Ascent Strategic Communications
[email protected]

Investor Relations Contact
Austin Murtagh
Precision AQ
[email protected]

SOURCE Stealth BioTherapeutics Inc.