Stealth BioTherapeutics Announces Positive Results From Study to Evaluate Efficacy of Elamipretide in Barth Patients Compared to Natural History Control

Date : February 18, 2020

BOSTON, Feb. 18, 2020 /PRNewswire/ -- Stealth BioTherapeutics (Nasdaq: MITO), a clinical-stage biotechnology company focused on the discovery, development and commercialization of novel therapies for diseases involving mitochondrial dysfunction, today announced positive results from its retrospective natural history study, clinical protocol SPIBA-001, evaluating the efficacy of subcutaneous injections of elamipretide relative to a natural history control comprised of 19 propensity score matched subjects with Barth syndrome (Barth).  Subjects receiving elamipretide for up to one year during the TAZPOWER trial and open-label extension showed a mean improvement of greater than 80 meters on their six-minute walk test (6MWT), the primary efficacy endpoint, compared to less than one meter for subjects in the natural history group evaluated over the same time period (p=0.0005).  Patients also showed statistically significant improvements in several key secondary endpoints, including muscle strength and sit-to-stand evaluations. Additional analysis of these data will be presented at an upcoming medical meeting. 

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"We are grateful to have access to such recent and carefully collected natural history data to serve as a control for our TAZPOWER open-label extension, demonstrating the tremendous potential of elamipretide as a treatment for patients suffering from Barth," said Reenie McCarthy, Chief Executive Officer of Stealth. "Thanks to the foresight and commitment of our investigators at Johns Hopkins and the Barth Syndrome Foundation, we have been able to show that elamipretide's effect on important functional parameters associated with Barth is not only striking but well-beyond what would be expected based on the natural course of disease progression. We look forward to meeting with the FDA later this quarter to discuss these encouraging findings.  We will also introduce data from our TAZPOWER open label extension, demonstrating improvements in surrogate endpoints of cardiac dysfunction, which is the leading cause of early mortality in this disease."

"Our patient community is in dire need of a therapy that addresses the complex, multi-system challenges that occur as a result of Barth syndrome," said Emily Milligan, Executive Director of the Barth Syndrome Foundation. "In our meetings with FDA, the Agency has emphasized the importance of natural history data to support therapeutic development in this ultra-rare disease, and we are optimistic to see elamipretide demonstrate such measurable improvements in several key markers of disease that have otherwise been shown to persist over time."  

Barth syndrome is an ultra-rare mitochondrial disease in which reduced levels of the mitochondrial phospholipid cardiolipin are associated with skeletal muscle weakness, debilitating fatigue, cardiac abnormalities, recurrent infections, delayed growth and reduced life expectancy. This observational study, SPIBA-001, compared findings on assessments collected throughout the open-label extension portion of the TAZPOWER Phase 2/3 crossover study of elamipretide in 12 patients with Barth syndrome with findings on the same assessments for up to 19 natural history control subjects collected longitudinally between 2012 and 2019 by investigators at Johns Hopkins Kennedy-Krieger Institute. To protect from potential bias, Stealth was blinded from the natural history data while the trial was ongoing, and separate statistical teams were assigned to derive the propensity model and conduct the study. 

The U.S. Food and Drug Administration (FDA) has granted Fast Track and Orphan Drug designations for elamipretide for the treatment of Barth syndrome. In 2018, the Barth Syndrome Foundation hosted a patient focused drug development meeting with the FDA, resulting in a published Voice of the Patient Report, which it shared with the FDA during a Professional Affairs and Stakeholder Engagement meeting.

For additional information on the TAZPOWER study or elamipretide, please refer to Stealth's website and

Conference Call Information

Stealth will host a conference call and webcast today at 8:30 a.m. ET to discuss the Barth syndrome efficacy study using natural history data as a control. The call can be accessed by dialing 877-407-0989 (domestic) or 201-389-0921 (international) and referencing conference ID 13699341. A live audio webcast of the event can be accessed at or by visiting the Investors & News section of Stealth's Investor website, A replay of the webcast will be archived on Stealth's website for 30 days following the event.

About the TAZPOWER Study

TAZPOWER is a Phase 2/3 crossover study evaluating the effects of daily subcutaneous (SC) treatment with elamipretide in 12 patients with genetically confirmed Barth syndrome followed by an open-label treatment extension. Part 1 was a 28-week crossover trial of patients randomized to elamipretide 40 mg SC daily for 12 weeks, followed by SC placebo daily for 12 weeks, or vice versa, separated by a 4-week washout. Part 2 was an open-label assessment for up to 168 weeks of functional, patient-reported outcomes, and safety/tolerability.

The primary endpoints included change in distance walked during the 6MWT and change in the BTHS-SA Total Fatigue score. Secondary endpoints included additional functional assessments, patient-reported outcomes, echocardiographic parameters of cardiac function, and safety/tolerability.

About SPIBA-001: an Efficacy Study Using Natural History Data as a Control

This retrospective efficacy study compared findings on assessments collected through weeks 36 and 48 of the open-label extension portion of the TAZPOWER trial with findings on the same assessments for up to 19 propensity score matched natural history control subjects, for whom data was collected longitudinally between 2012 and 2019 by investigators at Johns Hopkins Kennedy-Krieger Institute.  The primary endpoint was the change in distance walked during the 6MWT.  Secondary endpoints included all additional functional assessments for which there was natural history data, which were measurements of muscle strength, balance, and the time to complete an assessment requiring patients to sit and stand five times in succession (5XSST).  A multi-domain responder analysis was also conducted to assess the percentage of patients experiencing at least a 10% clinically meaningful gain (or loss) on these endpoints. Data from these endpoints will be presented at an upcoming medical meeting.

About Barth Syndrome

Barth syndrome is an ultra-rare genetic condition characterized by muscle weakness, cardiac abnormalities often leading to heart failure, recurrent infections, delayed growth, and reduced life expectancy. Barth syndrome occurs almost exclusively in males and is estimated to affect one in 200,000 to 400,000 individuals worldwide at birth. There are currently no FDA-approved therapies for patients with Barth syndrome.

About Stealth

We are 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 also involved in many common age-related diseases, typically involving organ systems with high energy demands such as the heart, the eye, and the brain. We believe our lead product candidate, elamipretide, has the potential to treat both rare genetic cardiomyopathic diseases, such as Barth, as well as ophthalmic diseases entailing mitochondrial dysfunction, such as Leber's hereditary optic neuropathy and dry age-related macular degeneration. Our second-generation clinical stage candidate, SBT-272, is being evaluated for rare neurodegenerative disease indications. Our pipeline compounds include SBT-259, which we are evaluating for rare peripheral neuropathies, and the SBT-550 series of compounds, which we plan to evaluate for rare neurodegenerative and ophthalmic disease indications. We have optimized our discovery platform to identify novel mitochondria-targeted compounds, which may be nominated as therapeutic product candidates or utilized as scaffolds to deliver other compounds to mitochondria. We have assembled a highly experienced management team, board of directors and group of scientific advisors to help us achieve our mission of leading mitochondrial medicine.

Forward-Looking Statements

This press release contains forward-looking statements within the meaning of The Private Securities Litigation Reform Act of 1995. Such forward-looking statements include those regarding Stealth BioTherapeutics' plans, strategies and expectations for its advancement of its drug development programs, including its ongoing clinical trials of elamipretide; the potential benefits of Stealth BioTherapeutics' product candidates; its key milestones for 2020; its plans regarding future data presentations; and its financial guidance regarding the period in which it will have capital available to fund its operations.  Statements that are not historical facts, including statements about Stealth BioTherapeutics' beliefs, plans and expectations, are forward-looking statements. The words "anticipate," "expect," "hope," "plan," "potential," "possible," "will," "believe," "estimate," "intend," "may," "predict," "project," "would" and similar expressions are intended to identify forward-looking statements, although not all forward-looking statements contain these identifying words. Stealth BioTherapeutics may not actually achieve the plans, intentions or expectations disclosed in these forward-looking statements, and you should not place undue reliance on these forward-looking statements. Actual results or events could differ materially from the plans, intentions and expectations disclosed in the forward-looking statements as a result of known and unknown risks, uncertainties and other important factors, including: Stealth BioTherapeutics' ability to obtain additional funding; the ability to successfully demonstrate the efficacy and safety of Stealth BioTherapeutics' product candidates and future product candidates; the preclinical and clinical results for Stealth BioTherapeutics' product candidates, which may not support further development and marketing approval; the potential advantages of Stealth BioTherapeutics' product candidates; the content and timing of decisions made by the U.S. FDA, the EMA or other regulatory authorities, investigational review boards at clinical trial sites and publication review bodies, which may affect the initiation, timing and progress of preclinical studies and clinical trials of Stealth BioTherapeutics product candidates; Stealth BioTherapeutics' ability to obtain and maintain requisite regulatory approvals and to enroll patients in its planned clinical trials; unplanned cash requirements and expenditures; competitive factors; Stealth BioTherapeutics' ability to obtain, maintain and enforce patent and other intellectual property protection for any product candidates it is developing; and general economic and market conditions. These and other risks are described in greater detail under the caption "Risk Factors" included in Stealth BioTherapeutics' most recent Annual Report on Form 20-F filed with the Securities and Exchange Commission ("SEC"), as well as in any future filings with the SEC. Forward-looking statements represent management's current expectations and are inherently uncertain. Except as required by law, Stealth BioTherapeutics does not undertake any obligation to update forward-looking statements made by us to reflect subsequent events or circumstances. 

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