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Terminus Peptides
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Research profile · Peptide

SS-31

Also known as Elamipretide, MTP-131, Forzinity

Clinical — evidence level 4 of 4: Established clinical evidenceExperimental — UK regulatory status: Experimental — not authorised for human use in the UK

Overview

A mitochondria-targeting tetrapeptide holding a US accelerated approval for one ultra-rare condition, and no UK authorisation.

Category
Peptide
Highest evidence level identified
Established clinical evidence
Last scientifically reviewed
20 August 2026
Last regulatory review
20 August 2026

Mechanism under investigation

Elamipretide is a mitochondria-targeting tetrapeptide that binds cardiolipin in the inner mitochondrial membrane. It is proposed to stabilise mitochondrial cristae architecture and improve electron transport chain efficiency, thereby supporting energy production and reducing reactive oxygen species. This is the best-characterised mechanism of any compound in this dataset, and mechanism is not the limiting factor for it.

Research areas

  • Mitochondrial biology
  • Rare disease research

These are fields in which the compound has been investigated. Listing a field is not a statement that anything was demonstrated within it.

Current evidence

In-vitro evidence

Cells, tissues or biochemical systems outside a living organism.

Extensive. Cardiolipin binding and effects on mitochondrial membrane structure and respiration are well characterised, and the mechanistic base is developed rather than speculative.

Animal evidence

Studies in living non-human animals.

Extensive, across heart failure, renal ischaemia, mitochondrial myopathy and ageing models. This is also not the weak link.

Human observational evidence

Studies observing people without assigning an intervention.

Includes open-label extension data. A 168-week extension in Barth syndrome reported cumulative improvement in a walking test from the extension baseline — but this is an uncontrolled within-subject comparison, in which placebo response, expectancy and natural history cannot be separated out.

Clinical-trial evidence

Studies assigning an intervention to human participants.

Substantial, and largely negative on primary endpoints. The pivotal phase 3 in primary mitochondrial myopathy, with 218 participants over 24 weeks, missed both co-primary endpoints; a post-hoc subgroup suggested benefit in one genetic subset, which is hypothesis-generating only. In Barth syndrome the randomised double-blind portion also failed to meet either primary endpoint, with significance appearing only in the subsequent open-label extension. The compound has additionally been trialled in heart failure, hereditary optic neuropathy and renal artery stenosis.

Study limitations

  • The evidence level reflects the stage the research programme reached — completed phase 3 trials and a regulatory approval — and is emphatically not a statement that benefit is demonstrated. The pivotal phase 3 missed both of its co-primary endpoints.
  • In Barth syndrome the randomised, blinded phase also failed. The positive results come from an uncontrolled open-label extension.
  • The US accelerated approval rests on an intermediate endpoint — muscle strength rather than a direct patient benefit — in a trial of twelve patients, and the regulator has mandated a confirmatory randomised controlled trial. Approval may be withdrawn if benefit is not verified.
  • Barth syndrome is ultra-rare, with perhaps 150 affected individuals in the United States, so trials are inherently tiny and estimates imprecise.
  • Findings in one rare mitochondrial condition do not generalise to other mitochondrial conditions, and certainly not to healthy people.

UK regulatory context

Experimental — not authorised for human use in the UK

A compound appearing in research literature that holds no UK authorisation for human use in any indication.

Source: Elamipretide for treating Barth syndrome — Health Technology Briefing (opens io.nihr.ac.uk in a new tab) (NIHR Innovation Observatory)

Regulatory classification is jurisdiction-specific. A compound authorised elsewhere is not thereby authorised in the UK, and a supplier’s description of a substance does not determine how it is classified in law. See safety and regulation for the framework and the authoritative sources.

Safety and interpretation

In trials the most common adverse effects were mild to moderate injection-site reactions, with increased eosinophil counts seen on longer exposure that generally resolved. The US label carries warnings for hypersensitivity, including serious reactions requiring emergency intervention arising from minutes to months after starting, and for a formulation component unsuitable for neonates. Long-term safety beyond trial durations, and safety in populations other than the approved indication, remain uncharacterised.

References