SS-31 (Elamipretide / MTP-131): A Mitochondria-Targeted Cardiolipin-Binding Peptide

Research summary. SS-31, also known by its INN elamipretide and the developmental codes MTP-131 and Bendavia, is a synthetic aromatic-cationic tetrapeptide developed at Cornell University in the laboratory of Hazel Szeto. It is the prototype of the "Szeto-Schiller" peptide family, designed to selectively accumulate in the inner mitochondrial membrane and bind cardiolipin — a mitochondria-specific phospholipid critical for cristae structure and electron-transport-chain organisation. Unlike most peptides, SS-31's intracellular localisation is mitochondrion-targeted by virtue of its structure rather than via a conventional receptor or transporter. It has progressed through Phase 3 clinical trials for primary mitochondrial myopathy and has been studied across a wide range of mitochondrial-dysfunction indications.

Molecular profile

• Sequence: D-Arg-Tyr(2,6-diMe)-Lys-Phe-NH₂ (a tetrapeptide with a 2,6-dimethyl-modified tyrosine and a D-arginine)
• Molecular formula: C₃₂H₄₉N₉O₅
• Molecular weight: ~639.8 g/mol
• PubChem CID: 11764719
• CAS number: 736992-21-5
• Class: Mitochondria-targeted aromatic-cationic tetrapeptide; cardiolipin-binding
• Synonyms: Elamipretide; MTP-131; Bendavia; SS-31

Mechanism of action

SS-31 is fundamentally distinct from receptor-binding or enzyme-inhibiting peptides:

• Mitochondrial inner-membrane targeting. The alternating aromatic-cationic-aromatic-cationic structure produces a peptide that selectively accumulates in the inner mitochondrial membrane via the negative inner-membrane potential, without requiring a transporter.
• Cardiolipin binding. SS-31 binds cardiolipin and is reported to stabilise cardiolipin-protein interactions critical to cristae architecture and to electron-transport-chain supercomplex assembly.
• ATP synthase efficiency. Stabilisation of cardiolipin-protein interactions is reported to improve electron-transport-chain efficiency, increase ATP production per oxygen consumed, and reduce mitochondrial reactive-oxygen-species (ROS) leak.
• No interference with normal mitochondrial function. Reported across in-vitro work, SS-31 binds cardiolipin without disrupting normal cardiolipin-mediated functions, distinguishing it from cardiolipin-disrupting agents.

The result is a pharmacological intervention that improves mitochondrial efficiency rather than altering a specific signalling pathway.

Preclinical and clinical research highlights

FDA orphan-drug designation. SS-31 received FDA orphan-drug designation for primary mitochondrial myopathy and other mitochondrial-disease indications.

Primary mitochondrial myopathy. Phase 2 (MMPOWER series) and Phase 3 (MMPOWER-3) clinical trials evaluated elamipretide in adults with primary mitochondrial myopathy. The Phase 3 trial's primary endpoint (six-minute walk test) did not achieve statistical significance, although secondary patient-reported endpoints were positive in some analyses.

Barth syndrome. TAZPOWER and follow-on studies in Barth syndrome — a cardiolipin-remodelling-deficient disorder — have reported improvements in muscle strength and cardiac endpoints with elamipretide administration, supported by FDA orphan-drug designation.

Heart failure / cardiac ischaemia-reperfusion. Earlier development as Bendavia evaluated SS-31 in acute myocardial infarction reperfusion (EMBRACE-STEMI) and heart failure, with mixed results. Preclinical models reported substantial protection against ischaemia-reperfusion injury, but clinical translation in acute coronary syndrome was unsuccessful.

Age-related mitochondrial dysfunction. Preclinical research has reported that SS-31 reverses age-related declines in muscle mitochondrial function, exercise tolerance, and cardiac function in aged rodent models.

Macular degeneration and dry eye. Elamipretide topical and systemic formulations have been evaluated in age-related macular degeneration and dry-eye disease, with reported improvements in some subgroups.

Current research status

Elamipretide is an investigational drug. It is not currently FDA-approved as a marketed drug. Stealth BioTherapeutics (the developer) has pursued ongoing engagement with FDA on Barth syndrome and primary mitochondrial myopathy. Research-grade SS-31 is supplied for laboratory use only.

For research-supplier contexts, SS-31 is supplied as a research-grade investigational peptide and is not intended for self-administration.

Key takeaways for researchers

• SS-31 / elamipretide is a synthetic aromatic-cationic tetrapeptide that selectively accumulates in the inner mitochondrial membrane and binds cardiolipin.
• The mechanism is mitochondrion-targeted cardiolipin stabilisation, supporting electron-transport-chain efficiency and reducing ROS leak.
• It has been studied in primary mitochondrial myopathy, Barth syndrome, heart failure, ischaemia-reperfusion, age-related mitochondrial dysfunction, and macular degeneration.
• Phase 3 results in primary mitochondrial myopathy missed the primary endpoint; orphan-drug designations exist for several rare-disease indications.
• SS-31 is not currently FDA-approved as a marketed drug; research-grade material is for laboratory use only.

References

1. Szeto HH. First-in-class cardiolipin-protective compound as a therapeutic agent to restore mitochondrial bioenergetics. Br J Pharmacol. 2014;171(8):2029–2050.
2. Karaa A, Haas R, Goldstein A, Vockley J, Weaver WD, Cohen BH. Randomized dose-escalation trial of elamipretide in adults with primary mitochondrial myopathy. Neurology. 2018;90(14):e1212–e1221.

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This article is provided for educational and research purposes only. SS-31 / elamipretide is a research peptide. It is not currently an FDA-approved drug and is not intended for human consumption, diagnosis, treatment, cure, or prevention of any disease or condition. All work involving this peptide should be conducted by qualified personnel within an appropriate research setting and in compliance with applicable institutional and regulatory requirements.