ACE-031

also known as: Ramatercept, ActRIIB-Fc, Activin type IIB receptor-Fc fusion

Acceleron's first-generation myostatin trap — Phase 2 development in Duchenne muscular dystrophy was halted in 2013 after epistaxis and telangiectasia adverse events, but the same scaffold concept led to successor programs at Acceleron, Regeneron, and Lilly.

A recombinant fusion protein combining the extracellular ligand-binding domain of activin receptor type IIB (ActRIIB) with a human IgG1 Fc, engineered by Acceleron Pharma to act as a circulating decoy that traps myostatin and related activin/TGF-β family ligands before they can activate endogenous ActRIIB on muscle.

Mechanism of action

Acts as a soluble ligand trap: the extracellular ActRIIB domain binds myostatin, activin A, activin B, GDF-11, and — problematically — BMP9 and BMP10, sequestering them from their membrane receptors. Myostatin blockade drives muscle hypertrophy; BMP9/10 blockade appears to cause the vascular side effects that stopped development.

Primary uses

Historical: Duchenne muscular dystrophy (suspended)
Precursor molecule for understanding activin-Fc decoy pharmacology
Not in current community use due to discontinued development

Typical dosing

discontinued historical: monthly SC (subcutaneous)

Phase 2 DMD trial dosed 1–3 mg/kg SC monthly before suspension.

Regulatory status

Not approved. Phase 2 development in Duchenne muscular dystrophy was suspended by Acceleron in April 2013 after two boys in the trial developed epistaxis and gum bleeding, with telangiectasias observed on examination — adverse events attributed to off-target inhibition of BMP9/BMP10 signaling (critical for vascular integrity). Acceleron pivoted to the more selective successor bimagrumab/luspatercept family.

References

[pubmed] Attie KM, et al. "A single ascending-dose study of muscle regulator ACE-031 in healthy volunteers." Muscle Nerve, 2013;47:416-423.
[news-release] Acceleron Pharma. "Acceleron suspends ACE-031 clinical development program in Duchenne muscular dystrophy." Press release, April 2013.

Related peptides

Follistatin-344

The longer of the two principal follistatin splice variants — binds tissues less avidly than FS-315 and therefore has broader systemic distribution, making it the form used in most gene-therapy and myostatin-inhibition research.

Follistatin-315

The dominant circulating follistatin isoform in human serum — binds heparan sulfate proteoglycans avidly, concentrating at tissue surfaces rather than circulating freely, which limits its systemic reach compared to FS-344.

Bimagrumab

⚠ Monoclonal antibody — not a classical peptide. A first-in-class muscle-sparing antibody (fully human IgG1, ~150 kDa) against activin type II receptors. Combined with semaglutide in the BELIEVE Phase 2b trial (Nature Medicine, March 2026), it produced greater fat loss than semaglutide alone while preserving lean mass. Not approved; Lilly developer. Included here because it's widely discussed alongside peptides in the muscle-sparing and myostatin conversations.

Disclaimer

This entry is for educational purposes only and does not constitute medical advice. Dosing information reflects published regulatory or research data and is not a recommendation. Many compounds described here are not approved for human use in the United States. Consult a licensed medical professional before considering any peptide therapy.