ACE-031 at a glance
A fast read for beginners, with evidence strength, route context, safety depth, and community activity surfaced before the deeper sections.
ACE-031 is a fusion protein consisting of the extracellular domain of activin receptor type IIB (ActRIIB) fused to an IgG1-Fc region. By acting as a decoy receptor, it sequesters myostatin, GDF-11, activins, and other TGF-β superfamily ligands that limit muscle growth - effectively releasing the body's natural brake on skeletal muscle mass.
In Phase 1 and Phase 2 trials for Duchenne Muscular Dystrophy and healthy postmenopausal women, ACE-031 produced significant lean mass increases of 3-5% within 1-3 months - representing some of the most dramatic muscle gains observed in a clinical setting. However, Phase 2 trials were halted due to adverse events including telangiectasias (dilated blood vessels), epistaxis (nosebleeds), and gum bleeding, attributed to the broad inhibition of multiple ActRIIB ligands beyond myostatin alone.
Bimagrumab (a monoclonal antibody targeting ActRIIB with more selectivity) subsequently advanced further in trials with a somewhat better tolerability profile, demonstrating that the mechanism remains therapeutically relevant. ACE-031 itself is no longer in active development. Its use in performance contexts carries significant unknown risk given the halted trials.
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