ACE-031 (also known as Ramatercept or ActRIIB-IgG1) is a recombinant fusion protein, not a traditional small peptide. It consists of the extracellular domain of the activin type IIB receptor (ActRIIB or ACVR2B) fused to the Fc portion of human IgG1.1
How It Works (Mechanism)
ACE-031 functions as a soluble decoy receptor. It binds to and sequesters myostatin (GDF-8) and other related TGF-β superfamily ligands (such as activin A, activin B, and certain BMPs) that circulate in the blood. This prevents them from binding to natural ActRIIB receptors on muscle cells, thereby removing a key “brake” on muscle growth. The result is increased muscle protein synthesis, satellite cell activity, muscle fiber hypertrophy, and overall lean mass. It has also shown effects on bone metabolism and fat mass reduction in studies.2
Research Description and Benefits
Preclinical and Phase 1 studies: In animal models and a Phase 1 single-ascending-dose trial in healthy postmenopausal women (doses 0.02–3 mg/kg subcutaneous), ACE-031 demonstrated clear biological activity. A single 3 mg/kg dose led to statistically significant increases in total body lean mass (3.3%) and thigh muscle volume (5.1%) by day 29, along with favorable changes in bone formation biomarkers and fat metabolism markers. It was generally well-tolerated, with a half-life of ~10–15 days. The main reported adverse event was mild injection-site erythema (redness).2
Phase 2 in Duchenne Muscular Dystrophy (DMD): In ambulatory boys with DMD, multiple ascending doses every 2–4 weeks produced trends toward maintained 6-minute walk test distance (vs. decline in placebo), increased lean body mass, higher bone mineral density, and reduced fat mass. No serious or severe adverse events directly linked to muscle function were reported.3
Research interest centers on muscle-wasting conditions (e.g., DMD, sarcopenia, cachexia), potential improvements in muscle strength, bone density, and metabolic health. It is widely studied in non-human laboratory research and sold by peptide suppliers strictly for research use only.
