Stealth BioTherapeutics Reports Positive Elamipretide Data in First-Of-Its-Kind Primary Mitochondrial Myopathy Trial

Positive Phase 2 data in rare disease trial lead to extension study and planning for Phase 3

BOSTON – June 17, 2016 – Stealth BioTherapeutics (Stealth), a clinical-stage biopharmaceutical company developing investigational drugs to treat mitochondrial dysfunction, today announced the presentation of positive results from MMPOWER, a Phase 2 trial evaluating the systemic delivery of elamipretide for the treatment of primary mitochondrial myopathy, or muscle weakness, in patients with a genetically confirmed mitochondrial disease. The findings demonstrated statistically significant improvements with elamipretide in distance walked in six minutes, the study’s primary efficacy endpoint and an accepted measurement of functional exercise capacity.

The results were presented at Mitochondrial Medicine 2016, the United Mitochondrial Disease Foundation (UMDF) symposium, in Seattle at 8:10 a.m. PT.

“The muscle weakness, exercise intolerance and heightened fatigue experienced by patients with primary mitochondrial disease can make simple daily tasks very challenging,” said Dr. Amel Karaa, trial investigator, internist and clinical geneticist at Massachusetts General Hospital. “These findings demonstrate the potential for elamipretide to help improve their ability to perform everyday activities. We look forward to further study of this compound in upcoming trials of primary mitochondrial disease.”

In the findings presented today, treatment with elamipretide at the highest dose studied in the trial, 0.25 mg/kg/hr, was associated with a statistically significant improvement in the six-minute walk test (6 MWT). The adjusted mean change in distance walked was 51 meters with this dose of elamipretide compared with three meters for placebo (P=0.03). Additionally, elamipretide generated the greatest improvement in 6 MWT distance in patients who were most impaired at baseline, and there was a positive dose-dependent trend as the dosage increased. Treatment with elamipretide was also well tolerated, and no serious adverse events were observed.

In January 2016, the U.S. Food and Drug Administration (FDA) granted Fast Track designation for elamipretide for the treatment of primary mitochondrial myopathy in patients with genetic mitochondrial diseases, for which there are currently no FDA-approved treatments. In the second half of 2016, Stealth will initiate the MMPOWER-2 extension study for patients who participated in MMPOWER, to evaluate additional efficacy endpoints and a longer dosing schedule.

“Based on positive data from MMPOWER and anticipated learnings from MMPOWER-2, we will be initiating discussions with the FDA to develop a Phase 3 trial to better characterize the potential benefits of elamipretide in patients with primary mitochondrial disease,” said Chief Executive Officer Reenie McCarthy. “As a leader in mitochondrial medicine, we are committed to developing innovative therapies for rare primary mitochondrial diseases, as well as for common diseases of aging in which impaired mitochondrial function is a final common pathway.  We look forward to sharing findings from ongoing studies in skeletal muscle and ophthalmic disorders later this year.”

“We are thrilled with the encouraging results from the MMPOWER trial presented at this year’s symposium,” said UMDF Executive Director and CEO Charles A. Mohan, Jr. “The UMDF and the broader advocacy community look forward to fully supporting the upcoming Phase 3 trial.”

For additional information on MMPOWER or elamipretide, please refer to Stealth’s website and


MMPOWER was a double-blind, dose-ascending, placebo-controlled study to evaluate the safety, tolerability and efficacy of elamipretide to treat primary mitochondrial myopathy in patients with genetically confirmed mitochondrial disease. Genetic mitochondrial diseases are a diverse group of rare inherited disorders characterized by systemic mitochondrial dysfunction that impairs patient health and well-being.

The trial evaluated 36 patients aged 16-65 in three dose cohorts. The primary endpoints were change in distance walked in six minutes, safety and tolerability.

About Elamipretide

Stealth’s lead candidate, elamipretide, is an investigational drug with the potential to modify disease by preserving energetics and restoring normal energy production in mitochondria, while decreasing oxidative stress. The energetics from mitochondria maintain healthy physiology and prevent disease. This mitochondria-targeted candidate is being developed for both rare and common diseases.

Stealth BioTherapeutics: Leading Mitochondrial Medicine

Stealth BioTherapeutics is a privately held biopharmaceutical company committed to bringing mitochondrial therapies to patients to treat both rare and common diseases. Stealth’s clinical development program is focused along several core therapeutic areas, including primary mitochondrial diseases, cardiorenal diseases and ophthalmic disorders. More information regarding Stealth and its pipeline is available at


Media Relations
dna Communications
Kate Contreras, 617-520-7088

Investor Relations
Stern IR
Beth DelGiacco, 212-362-1200