ACE-083

ACE-083 is studied for its ability to selectively add muscle volume at the site of injection, without a systemic effect on the rest of the body. Chemically it is a recombinant fusion protein — a modified form of human follistatin linked to the Fc domain of human IgG2. Rather than acting as a peptide or an antibody, it works as a ligand trap: it intercepts extracellular ligands of the TGF-β superfamily that normally restrain muscle growth — myostatin (GDF8), activin A, activin B and GDF11.

What sets ACE-083 apart from systemic ActRII blockers is locality. The follistatin domain has high affinity for heparin and the extracellular matrix, so after intramuscular injection the protein is retained in the muscle it was injected into and is rapidly inactivated once it reaches the circulation. In preclinical models this produced hypertrophy of the injected muscle only, with no systemic muscle effect and no endocrine perturbation. This is precisely what distinguishes ACE-083 from bimagrumab (a systemic monoclonal antibody against the ActRII receptor) and from ACE-031 (soluble ActRIIB-Fc — also an Acceleron programme, but systemic).

The research history of ACE-083 is effectively closed. Acceleron took the molecule into phase 2 in facioscapulohumeral muscular dystrophy (FSHD) and Charcot-Marie-Tooth disease, where ACE-083 reliably increased the volume of the targeted muscle but did not improve function — development was discontinued in 2020 and the relevant studies are listed as terminated. ACE-083 is not approved as a medicine anywhere.

The full account of the mechanism, trial results and the limits of the evidence is in the monograph.