ACE-031 (research generic name: ramatercept) is a soluble activin receptor type IIB–IgG1 Fc fusion protein — an "ActRIIB-Fc" decoy receptor. Although it is grouped with research peptides, it is technically a recombinant biologic (~110 kDa fusion protein), not a synthetic peptide. ChEMBL: CHEMBL2108674; highest clinical phase reached: 2.
Myostatin/activin inhibitor — a soluble ActRIIB-IgG1 Fc fusion protein (decoy receptor). Single compound.
ACE-031 is the extracellular domain of the activin receptor type IIB (ActRIIB) fused to the Fc region of human IgG1. It works as a soluble decoy: it binds and sequesters ActRIIB ligands — myostatin (GDF-8), activin A, and GDF-11 — before they can reach the membrane-bound receptor. Because myostatin is a negative regulator of skeletal muscle, trapping it de-represses muscle growth, producing gains in muscle mass and strength. The same ligand family also influences bone turnover (research showed reduced resorption and increased bone-formation markers). Critically, ActRIIB ligands also help regulate the vasculature — and off-target inhibition of those ligands is the mechanistic basis for the program's defining safety problem.
ACE-031 is unusually well-documented for a research compound, with real registered human-trial data rather than animal work alone:
In the phase 1 single ascending-dose study by Attie and colleagues (2012), 48 healthy postmenopausal women were randomized to receive 1 dose of ACE-031 (0.02-3 mg/kg s.c.) or placebo (3:1) (PubMed). In the randomized, placebo-controlled trial by Campbell and colleagues (2016) in boys with Duchenne muscular dystrophy, ACE-031 was administered subcutaneously every 2-4 weeks in an ascending-dose design; the study was stopped after the second dosing regimen (PubMed). These describe what was studied in registered trials; ACE-031 was never approved and no label exists.
Development was discontinued (~2013) and ACE-031 was never approved for any indication. The defining finding of the whole program is a safety signal: off-target inhibition of vascular-regulating ligands caused telangiectasia (spider veins), epistaxis (nosebleeds), and gum bleeding. This is the single most important thing the research record establishes about the compound.
Far better documented than most research peptides (multiple registered human trials plus recent non-human-primate data), but the human studies were small, Phase 2 was halted, efficacy was never proven, and there is no long-term safety data. The strongest, most actionable conclusion the literature supports is the vascular safety risk — not a muscle-growth efficacy claim.
ACE-031 is a recombinant Fc-fusion protein, not a synthetic peptide — it behaves like a biologic (large, cell-culture produced, long half-life). "ActRIIB-Fc" and "ramatercept" refer to the same molecule; do not confuse it with luspatercept or sotatercept. Expect it supplied as a lyophilized research protein.
