Rare Daily Staff

Shares of Stealth Biotherapeutics tumbled more than 60 percent as the company reported its experimental therapy elamipretide for treatment of patients with primary mitochondrial myopathy failed to meet the primary endpoints of a late-stage study.

Primary mitochondrial myopathy (PMM) is characterized by debilitating skeletal muscle weakness, chronic fatigue, and exercise intolerance. Investigators used changes in the six-minute walk test and Primary Mitochondrial Myopathy Symptom Assessment (PMMSA) Total Fatigue Score as endpoints in the study. Safety results showed that treatment with elamipretide was well tolerated with most adverse events mild to moderate in severity.

Elamipretide targets the inner mitochondrial membrane where it associates with cardiolipin—the signature phospholipid of the inner mitochondrial membrane, which plays a role in many mitochondrial processes, including respiration and energy conversion. In preclinical and clinical studies, elamipretide was shown to increase mitochondrial respiration, improve the electron transport chain function and ATP production, and reduce formation of pathogenic reactive oxygen species levels.

In October 2019, Alexion Pharmaceuticals paid Stealth $30 million for an option to co-develop and commercialize elamipretide for mitochondrial diseases.

The company said it plans to review its operational resources to align them with its near-term priorities of progressing its other programs. It expects to provide further guidance next month.

“We remain confident in the promise of our platform and committed to our mission of improving the lives of people living with diseases involving mitochondrial dysfunction,” said CEO Reenie McCarthy.

McCarthy said the company plans to meet with the U.S. Food and Drug Administration in early 2020 regarding its Barth syndrome program, where the company observed significant improvement in cardiac stroke volume during open-label extension. It continues to enroll patients in a phase 2b clinical trial in geographic atrophy associated with dry age-related macular degeneration, in which it observed improvement in visual function during an earlier phase 1 study. The company is also progressing its pipeline of second-generation mitochondrial therapeutics, with its lead pipeline compound SBT-272 entering the clinic.

Photo: Reenie McCarthy, CEO of Stealth Biotherapeutics

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