Stealth BioTherapeutics Announces MRC Business Engagement Fund Grant to Advance Mitochondrial Disease Research

-- Award to support the Company's preclinical evaluation of SBT-589 in Leigh syndrome --

NEEDHAM, Mass. and HARWELL, England, March 23, 2026 /PRNewswire/ -- Stealth BioTherapeutics (the "Company"), a commercial-stage biotechnology company focused on the discovery, development, and commercialization of novel therapies for diseases involving mitochondrial dysfunction, announced an award from the Business Engagement Fund from the UK Research and Innovation Medical Research Council (MRC) to support a new collaborative research project among the Mary Lyon Centre at MRC Harwell (MLC), the MRC National Mouse Genetics Network (NMGN), and academic leaders from University College London (UCL).

The research collaboration funded by this award will evaluate the effects of SBT-589, one of the Company's lead pipeline compounds, on survival rates, motor function, and biomarkers of disease in a mouse model of Leigh syndrome. Mitochondrial dysfunction is central to Leigh syndrome pathology, affecting cells that supply energy to the brain, nerves, and muscles. Previous preclinical studies have shown that SBT-589 improved bioenergetics in Leigh syndrome patient-derived cells, and ameliorated pathology associated with mitochondrial dysfunction and neurodegeneration across animal models of disease.

The funding builds on the Company's established collaboration with investigators within the NMGN MitoCluster, including Professor Robert Pitceathly of UCL, and on prior clinical research in primary mitochondrial myopathy including multiple MitoCluster members.

"I'm excited to support the preclinical evaluation of SBT-589, leveraging our NMGN MitoCluster platform at the MLC to deeply characterize mitochondrial dysfunction in disease models. Combined with the extensive clinical and non-clinical expertise in mitochondrial pathology contained within our consortium, we aim to accelerate the development of therapeutics, such as SBT-589, towards clinical applications," said Professor Pitceathly.

The MRC Business Engagement Fund is designed to foster meaningful partnerships between industry and the global research community, accelerating the translation of scientific discovery into real-world patient impact.

"This collaboration represents an important step forward for our pipeline and our long-standing engagement with the mitochondrial research community," said David A. Brown, Ph.D., the Company's Chief Scientific Officer. "Testing promising assets in disease-relevant animal models has historically been a barrier to progress in mitochondrial drug development. This project helps address that gap and strengthens our ability to translate innovative science and advance potential therapies into the clinic."

"The Business Engagement Fund is designed to bring the expertise of the MRC National Mouse Genetics Network together with the innovation capacity of industry partners. By supporting early-stage collaborations, we can help accelerate the translation of discoveries from advanced model systems into new approaches for understanding and treating disease, including in important areas such as mitochondrial biology," said Professor Owen Sansom, Director of the MRC National Mouse Genetics Network.

By strengthening ties between industry and academia, the project is expected to accelerate the progression of promising mitochondrial therapies toward clinical development and future regulatory milestones, supporting shared goals to address the significant unmet needs faced by individuals living with diseases of mitochondrial dysfunction.

About Stealth BioTherapeutics
The Company's mission is to develop novel therapies to improve the lives of patients living with diseases of mitochondrial dysfunction.  The Company's first commercial product was granted accelerated approval by the U.S. Food & Drug Administration (FDA) in September 2025. The Company is studying elamipretide in additional indications, including dry age-related macular degeneration and primary mitochondrial disease due to nuclear DNA mutations, including in polymerase gamma, and is developing its next-in-class clinical-stage candidate, bevemipretide, for ophthalmic and neurological disease indications. The Company's preclinical pipeline candidates include SBT-589 and SBT-255, which are both progressing through developmental milestones.

About the Mary Lyon Centre at MRC Harwell
The MLC is the UK's national facility for mouse genetics and the use of mouse models for the preclinical study of human disease. The MLC is based at Harwell, a research and innovation super campus home to cutting-edge scientific instruments, institutes, businesses, and expert teams advancing knowledge and finding solutions. The MLC functions as the central hub of the NMGN, providing research clusters with access to resources, tools, and services, as well as coordinating many cross-cluster interactions. Learn more at www.har.mrc.ac.uk/.

About the MRC National Mouse Genetics Network
The MRC National Mouse Genetics Network is a UK-wide research initiative funded by the Medical Research Council that brings together leading centers to investigate the genetic and molecular basis of human disease. By combining advanced preclinical models with cutting-edge technologies and partnerships with academia and industry, the Network aims to accelerate the translation of biological discoveries into new approaches for diagnosis and treatment. Learn more at https://nmgn.mrc.ukri.org/

Stealth Media Contact
Ascent Strategic Communications
Anna Stallmann
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Stealth Investor Contact
Precision AQ
Austin Murtagh
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Stealth Patient Advocacy
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Mary Lyon Centre at MRC Harwell
Debora Bogani
[email protected]

SOURCE Stealth BioTherapeutics Inc.