After an FDA rejection in May, Stealth BioTherapeutics has resubmitted a new drug application for its investigational treatment designed to treat an ultra-rare genetic disease.
This is the biotech’s third application for elamipretide, a peptide that targets mitochondria and takes aim at Barth syndrome, an X-linked genetic disorder that weakens the heart and other muscles.
“As directed by the FDA in its May 2025 complete response and subsequent correspondence, the resubmission contains no new clinical efficacy data, a minor safety update, and confirmation that previously cited manufacturing deficiencies were resolved by FDA, which determined in July that the facility remains in compliance,” the biotech said in an Aug. 18 release.
The resubmission also includes—at the FDA’s request—information about post-marketing commitments such as a potential trial to confirm elamipretide’s clinical benefit, according to Stealth Bio.
This spring, the federal agency issued a complete response letter for elamipretide after the drug had been under priority review for more than 16 months. The rejection followed several FDA delays and a split advisory committee vote that ultimately favored approval.
After elamipretide failed to meet a six-minute walk test endpoint in a clinical trial, the FDA said certain Stealth data were “exploratory and uninterpretable.”
The agency recommended that Stealth resubmit the data for accelerated approval based on improvements in knee extensor muscle strength, an intermediate clinical endpoint.
According to Stealth, knee extensor muscle strength improved by more than 45% in a phase 2 open-label study and was significantly correlated with improvements in the six-minute walk test, according to Stealth.
Now, the FDA has signaled a likely Class 2 review for the resubmission, a process that takes six months, the biotech said. Stealth has requested a Class 1 review, which typically takes two months.
Elamipretide has secured orphan, fast track and rare pediatric tags for Barth syndrome, a disease that is thought to impact around one male out of every million born.
Just last week, the Massachusetts biotech said the FDA had denied its request to reconsider its complete response letter, prompting Stealth to question its own viability.
“We have repeatedly sought urgency from the FDA on a viable path forward and have been met with prolonged and consistent delays,” Stealth said in a statement to Fierce at the time. The FDA never responded to Fierce’s request for comment on the matter.
“Without more immediate action from the FDA, we cannot ensure continued drug availability to this vulnerable community or our sustainability as a company,” the biotech said last week. “At this time, we are evaluating all options.”
Earlier on, the agency’s rejection had prompted the biotech to lay off 30% of its staff to save cash.