ACE-031 (Fusion Protein — Not a True Peptide)

Mechanism of action: Acts as a soluble decoy receptor for myostatin; Acts as a soluble decoy receptor for activin A; Blocks ActRIIB pathway signaling that normally limits muscle growth

Proposed indications: Muscle mass (early clinical trials); Muscle-wasting disorders; Duchenne muscular dystrophy (research)

Typical clinical dosing schedule: No approved dosing regimen exists; clinical development has not progressed to an approved product.

Administration: Injection (clinical research settings only) — No approved dosing regimen exists

Compare with: Follistatin 344IGF-1 LR3 (Long R3 IGF-1)

An "emerging / limited evidence" rating means rigorous research hasn't caught up yet -- not that this peptide doesn't work. Many peptides in this category are newer or simply understudied rather than proven ineffective.

Evidence rating: ⭐⭐⭐☆☆ — Evaluated in a randomized, placebo-controlled Phase II trial in ambulatory boys with Duchenne muscular dystrophy (Campbell et al., 2017); documented vascular adverse events contributed to discontinuation of clinical development. This is the best-supported historical safety statement among this round's newer entries — directly observed in human trial participants, not a class-effect inference.

Landmark trials: Campbell C, McMillan HJ, Mah JK, et al. (2017) — Randomized, placebo-controlled Phase II trial of ACE-031 in ambulatory boys with Duchenne muscular dystrophy; reported reversible epistaxis, gingival bleeding, and skin telangiectasias, contributing to early termination of the trial.

Common side effects: Reversible epistaxis (nosebleeds), Gingival bleeding, Skin telangiectasias (small dilated blood vessels), particularly at higher doses

Serious risks: Vascular adverse events (epistaxis, gingival bleeding, skin telangiectasias) were directly observed in ACE-031-treated participants in a randomized Phase II trial and contributed to discontinuation of clinical development — this is a documented finding, not a theoretical or class-level inference.; Long-term safety in humans has not been established; clinical development has not progressed to regulatory approval.

Monitoring: Clinical monitoring for vascular adverse effects in trial settings.

Legal status: Not a true peptide — this is a larger engineered soluble-receptor fusion protein, included here for discoverability since it's often searched alongside peptides. Investigational; not FDA-approved and not available by prescription. Clinical development has been limited — verify current status independently before considering use.

Regulatory status: Investigational • Not FDA Approved • Fusion protein, not a peptide

Contraindications: No approved labeling exists. Not established for use outside clinical trials.

Pregnancy & breastfeeding: Avoid.

Campbell C, McMillan HJ, Mah JK, et al. (2017). Myostatin inhibitor ACE-031 treatment of ambulatory boys with Duchenne muscular dystrophy: results of a randomized, placebo-controlled clinical trial. Muscle & Nerve, 55(4), 458–464. https://doi.org/10.1002/mus.25268 Lee SJ, Bhasin S, Klickstein L, et al. (2023). Challenges and future prospects of targeting myostatin/activin A signaling to treat diseases of muscle loss and metabolic dysfunction. The Journals of Gerontology: Series A, 78(Suppl 1), 32–37. Suh J, Lee YS. (2020). Myostatin inhibitors: panacea or predicament for musculoskeletal disorders? Journal of Bone Metabolism, 27(3), 151–165. Lee SJ. (2021). Targeting the myostatin signaling pathway to treat muscle loss and metabolic dysfunction. Journal of Clinical Investigation, 131.