ACE-031

Mechanism

ACE-031 is a recombinant fusion protein comprising the extracellular ligand-binding domain of the human activin receptor type IIB (ActRIIB) fused to a human IgG1 Fc domain. It functions as a soluble decoy receptor ('ligand trap') that circulates in the bloodstream and binds myostatin (GDF-8), activin A, activin B, BMP9, and BMP10 with high affinity. By sequestering these ligands, ACE-031 prevents them from activating cell-surface ActRIIB receptors, thereby blocking the downstream Smad2/3 signalling cascade that normally constrains muscle growth. The result is increased myoblast proliferation, enhanced muscle fibre hypertrophy, and increased lean body mass. The binding of BMP9 and BMP10 — which are important for vascular endothelial maintenance — is believed to underlie the adverse vascular effects (epistaxis, telangiectasia) observed in clinical trials.

Evidence base

Phase 1 (Healthy Volunteers)

A single ascending-dose study in healthy postmenopausal women showed that 3 mg/kg IV produced a +1.3 kg increase in lean body mass at 2 weeks, with corresponding fat mass decrease. Effects sustained 4–8 weeks. No serious AEs at Phase 1 doses (Rooks et al., 2017; PMID: 23169607).

Phase 2 (DMD)

Randomised, double-blind, placebo-controlled trial in 68 boys with DMD. The pooled dose group showed +1.6 kg lean body mass vs placebo at 24 weeks. Trial terminated early due to safety concerns.

Safety Concerns Leading to Discontinuation (July 2011)

• Epistaxis (nosebleeds), some severe
• Telangiectasia (visible blood vessel dilation)
• Menstrual irregularities in female subjects
• Potential vascular integrity effects (linked to BMP9/BMP10 binding)

Evidence grade: Moderate. Published Phase 1 and Phase 2 human data demonstrate efficacy but also significant safety concerns.

Protocols

No approved dosing protocols. Clinical trial doses: Phase 1 used single IV doses of 0.01–3 mg/kg and subcutaneous doses of 0.1–1 mg/kg. Phase 2 (DMD) used 0.1–0.6 mg/kg subcutaneously every 2 weeks for 24 weeks. Community-discussed doses (1–3 mg/kg weekly) are extrapolated from trial data and not medically validated. Given documented safety concerns, any non-clinical use is hazardous. All information for research reference only.

UK legal status

ACE-031 occupies a grey area in UK law. Not a controlled substance, not MHRA-approved, never marketed in UK/EU. Sale with therapeutic claims could trigger MHRA enforcement. WADA prohibits myostatin inhibitors in sport. Documented safety concerns (epistaxis, telangiectasia, vascular effects) make non-clinical use particularly risky.

Vendor notes

No UK vendors are verified for ACE-031 supply. As a discontinued investigational drug, authentic clinical-grade material is not commercially available. Any product sold as 'ACE-031' by research chemical vendors should be treated with extreme caution — authenticity, sterility, and biological activity cannot be verified without specialised analytical testing.