ACE-031 (Ramatercept): The Complete Guide

StackTrax does not endorse ACE-031 use. This guide exists because the compound is in gray-market circulation and users deserve the actual record.

Three load-bearing facts:

1. Phase 2 was halted in February 2011 after the second cohort of DMD boys developed vascular adverse events — epistaxis (nosebleeds), telangiectasias (small dilated cutaneous vessels), gingival bleeding, and skin erythema. Acceleron and Shire formally announced trials would not resume on April 21, 2011. Program terminated 2013.
2. The vascular-leak signal is mechanistically explained, not stochastic. Off-target inhibition of BMP9/10 produces a phenotype indistinguishable from drug-induced hereditary hemorrhagic telangiectasia (HHT). This is intrinsic to the ActRIIB-Fc design.
3. Vendor "ACE-031" identity confidence is near zero. The legitimate molecule is a glycosylated dimeric Fc fusion produced in CHO cells — this is materially incompatible with the small-batch peptide CDMOs supplying the research-chemical market. What you receive in a vial labeled "ACE-031" almost certainly is not the clinical molecule.

Existing peptide-knowledge content frames the trial halt as “minor nosebleeds and gum bleeding.” That language understates the reality. Trials in DMD do not stop for trivial findings.

ACE-031 (also known as ramatercept) is a recombinant fusion protein, not a peptide. The exact construct:

• Extracellular ligand-binding domain of human activin receptor type IIB (ActRIIB / ACVR2B), the receptor subunit through which myostatin and several activins initiate signaling.
• Fused at its C-terminus to the hinge–CH2–CH3 region of human IgG1 Fc.
• Produced as a glycosylated homodimer in mammalian (CHO) cells.
• Apparent molecular weight ~110–115 kDa (each monomer ~55–58 kDa).

This is two to three orders of magnitude larger than a typical research peptide (BPC-157 is ~1.4 kDa). The disulfide architecture and glycosylation are required for activity and PK. Recombinant production at clinically relevant purity is meaningfully harder than producing a 30-residue peptide.

Originator and partners:

• Acceleron Pharma, Inc. (originator).
• Shire plc (partner, ended 2013).
• The Acceleron pipeline subsequently shifted: sotatercept (Winrevair, ACE-011) — ActRIIA-Fc — reached FDA approval March 26, 2024 for pulmonary arterial hypertension. The activin-trap class is not categorically unsafe; ACE-031’s specific failure mode reflects ActRIIB’s specific promiscuity for BMP9/10.

Regulatory status:

• FDA (US): not approved. Never licensed. Phase 2 halted; program terminated 2013.
• EMA (EU): not approved.
• Other agencies: not approved anywhere.
• WADA 2026: myostatin inhibitors and activin/myostatin pathway antagonists are prohibited at all times under S4 Hormone and Metabolic Modulators. Use by a tested athlete is sanctionable.

Clinical development timeline:

• 2008–2010: Phase 1 SAD in 48 healthy postmenopausal women (NCT00709904).
• 2010–2011: Phase 2 multiple-dose study in DMD boys (NCT01099761), 24-week SC dosing.
• February 2011: Trial paused after vascular AEs in cohort C2 (1 mg/kg q2w).
• April 21, 2011: Acceleron + Shire announce trials will not resume.
• 2013: Acceleron + Shire end collaboration. ACE-031 program terminated.
• 2013–present: No sponsor has restarted ACE-031 development.

ActRIIB is the principal type II receptor for myostatin (GDF-8). It also binds activin A, activin B, GDF-11, and — critically for the safety signal — has measurable affinity for several BMPs including BMP9 and BMP10.

Intended mechanism:

1. ACE-031 (soluble ActRIIB-Fc) circulates in the bloodstream as a decoy.
2. Sequesters myostatin before it can engage cell-surface ActRIIB on muscle.
3. Reduces SMAD2/3 phosphorylation downstream of ActRIIB.
4. Derepresses muscle protein synthesis → muscle hypertrophy.

Off-target mechanism (the safety failure):

The same ActRIIB-Fc trap also sequesters BMP9 and BMP10. These ligands signal through endothelial ALK1 with ENG (endoglin) as co-receptor, driving SMAD1/5/8 activation. This pathway is essential for vascular quiescence and capillary integrity.

Loss-of-function mutations in ENG, ACVRL1 (ALK1), or SMAD4 cause hereditary hemorrhagic telangiectasia (HHT) — characterized by recurrent epistaxis, mucocutaneous telangiectasias, and arteriovenous malformations.

ACE-031’s pharmacologic depletion of BMP9/10 produces a phenotype indistinguishable from drug-induced HHT. The signal is predictable from the binding-promiscuity profile of ActRIIB-Fc — not a stochastic or idiosyncratic toxicity.

Why subsequent generations of the chemistry escaped this:

Acceleron’s next-generation ligand traps explicitly addressed binding promiscuity:

• Luspatercept (Reblozyl) — engineered ActRIIB-Fc shifted toward GDF11 over myostatin/activin A. FDA-approved for transfusion-dependent anemias.
• Sotatercept (Winrevair, ACE-011) — uses ActRIIA, not ActRIIB. FDA-approved March 2024 for PAH.

The class can succeed; ACE-031 specifically failed.

Phase 1 SAD — Attie 2013

Attie KM, Borgstein NG, Yang Y, et al. Muscle Nerve 2013;47(3):416–423. PMID 23169607. Title: “A single ascending-dose study of muscle regulator ACE-031 in healthy volunteers.”

• Randomized, double-blind, placebo-controlled, single ascending dose.
• 48 healthy postmenopausal women.
• Doses: ACE-031 0.02, 0.06, 0.2, 0.6, 1, 2, or 3 mg/kg subcutaneously.
• Day 29: 3 mg/kg cohort showed statistically significant increases in lean body mass (DXA) and thigh muscle volume (MRI). Bone-formation markers up; bone-resorption markers down.
• Adverse events at single dose: generally mild/moderate. Vascular bleeding signal was not dominant at single dose — emerged with repeat dosing.

Citation correction: the existing StackTrax peptide-knowledge entry cited "Attie KM et al. (2013) Neuromuscular Disorders. DOI:10.1016/j.nmd.2013.02.015." That DOI / PMID resolves to an unrelated 2013 paper on ovarian-cell lipid content in IVF patients. The correct anchor is PMID 23169607 in Muscle & Nerve.

Phase 2 in DMD — Campbell 2017 (halted)

Campbell C, McMillan HJ, Mah JK, et al. Muscle Nerve 2017;55(4):458–464. PMID 27462804. Title: “Myostatin inhibitor ACE-031 treatment of ambulatory boys with Duchenne muscular dystrophy: Results of a randomized, placebo-controlled clinical trial.”

• Randomized, double-blind, placebo-controlled, multiple-dose, two sequential cohorts (C1, C2).
• Ambulatory boys with DMD, ages 4–11.
• SC dosing every 2–4 weeks for 24 weeks. C1: 0.5 mg/kg q4w. C2: 1.0 mg/kg q2w.
• Trial terminated early after the second cohort due to safety.
• Reported vascular AEs: epistaxis, telangiectasias, gingival bleeding, skin erythema.
• Trends toward lean-body-mass increase and stable/slightly improved 6MWT — in the truncated dataset, not statistically conclusive.

The total human dataset:

~48 healthy postmenopausal women (Phase 1 SAD) plus the truncated DMD cohort (Phase 2). No Phase 3. No extension study. No real-world registry. No long-term safety data.

Conflation with structurally and mechanistically different agents is widespread in gray-market literature. The distinctions matter.

Molecule	What it is	Status
ACE-031 (this guide)	ActRIIB-Fc decoy receptor	Halted 2011; terminated 2013
Sotatercept (Winrevair)	ActRIIA-Fc decoy receptor (different receptor)	FDA-approved March 2024 for PAH
Luspatercept (Reblozyl)	Engineered ActRIIB-Fc biased toward GDF11	FDA-approved for transfusion-dependent anemias
Bimagrumab (BYM338)	Anti-ActRIIB monoclonal antibody (different modality)	Failed Phase 2b/3 in sIBM 2016; later ZEPBOUND combination terminated
Follistatin / FS344	Direct ligand-binding glycoprotein (extracellular ligand sequestration, not receptor decoy)	Gene-therapy program (Sarepta SRP-9003) ongoing; vendor protein injection unvalidated
Domagrozumab	Anti-myostatin antibody (Pfizer)	Failed Phase 2 in DMD
Stamulumab (MYO-029)	Anti-myostatin antibody (Wyeth)	Failed Phase 1/2 in dystrophies
Trevogrumab (Regeneron)	Anti-myostatin antibody	Halted
Landogrozumab (Lilly)	Anti-myostatin antibody	Halted
ACE-083 (Acceleron)	Modified follistatin-Fc fusion (locally administered)	Halted across FSHD and CMT 2019–2022

Big Pharma anti-myostatin class graveyard: multiple Phase 2/3 programs have produced lean-mass gains without functional improvement, with various safety signals across the class. The consistent pattern is the most underused calibration point for any "myostatin pathway" claim.

ACE-031 is administered subcutaneously. As an IgG1-Fc-fused biologic recycled by the neonatal Fc receptor (FcRn), it has a long terminal half-life — on the order of weeks.

Practical implications:

• Any adverse event will persist for weeks regardless of dose discontinuation, because the molecule is not rapidly cleared.
• Steady-state accumulation over multi-dose dosing is non-trivial; the vascular signal in the Phase 2 DMD trial appeared at and after the second cohort’s dosing as exposure accumulated, not after a single dose.
• Off-label or gray-market “trial” dosing has no experimental basis for cycling, washout, or safety monitoring.

No published mass-balance, metabolism, or hepatic-impairment studies. No published interaction studies. No pediatric PK data outside the truncated DMD trial.

This is the central audit finding and the central correction to the existing peptide-knowledge entry. The previous framing of “minor nosebleeds and gum bleeding” understates the picture in three ways:

1. The events were severe enough to halt a pediatric trial in a fatal disease. Trials in DMD do not stop for trivial findings.
2. They reflect a pharmacology-driven systemic vascular signal, not a local irritation.
3. They cluster mechanistically with HHT, a known genetic disease with documented serious sequelae including pulmonary and cerebral arteriovenous malformations. The trial duration was too short to know whether longer exposure would have produced these.

What was observed clinically:

• Epistaxis (nosebleeds) — recurrent, sometimes spontaneous, in multiple subjects in cohort C2. Most readily-recognizable consumer-facing symptom.
• Telangiectasias — visible cutaneous and mucocutaneous small dilated vessels (the hallmark lesion of HHT). Appearing on face, hands, oral mucosa.
• Gingival bleeding — with brushing and spontaneously.
• Skin erythema — diffuse and at injection sites.

Theoretical / unobserved-but-plausible additional risks (off-label use):

• Reproductive: ActRIIB inhibition perturbs activin signaling in the gonadal axis (FSH regulation). No human reproductive-tox data exist for ACE-031.
• Cardiac: GDF-11 has been implicated in cardiac aging; ActRIIB-Fc traps capture GDF-11. Clinical relevance debated.
• Tendon: aggressive muscle hypertrophy without commensurate tendon adaptation is a documented concern across the myostatin-inhibitor class in animal models.
• Immunogenicity: anti-drug antibodies to a recombinant Fc fusion are a routine concern with any biologic. Detailed ACE-031 immunogenicity data not in peer-reviewed literature.

The molecule described in this guide and the vial sold under the same name on research-chemical sites are not necessarily the same thing.

The legitimate clinical molecule:

• Glycosylated dimeric Fc fusion produced in CHO cells.
• Disulfide-bonded structure and post-translational modifications required for activity and PK.
• ~110–115 kDa.
• Materially incompatible with synthesis by the small-batch peptide CDMOs that supply the research-chemical market.

Vendor "ACE-031":

• Typically sold as a lyophilized vial in the 1–3 mg range at peptide-vendor pricing.
• Independent identity testing of vendor product is not publicly published.
• Mass-spec, SDS-PAGE, and SEC profiles compatible with a ~115 kDa glycosylated Fc fusion are not characteristic of what these vendors typically deliver.

Plausible vendor realities (none currently rule-out-able for any specific lot):

• Empty / excipient-only vials.
• Unrelated recombinant protein at low purity.
• An unrelated peptide labeled "ACE-031."
• Bacterial-expressed unglycosylated ActRIIB ECD without Fc — would have neither the half-life nor the activity profile of the clinical molecule.
• Rarely, a low-purity Fc fusion of indeterminate activity.

For ACE-031 specifically, vendor identity confidence should be treated as near zero by default. A user reporting "I tried ACE-031 and felt nothing" or "I tried it and got nosebleeds" has no way to know what was actually injected. Both outcomes are consistent with the gray-market identity-uncertainty problem and provide no information about the legitimate molecule.

• Anyone — the rational conclusion from the public record is do not use. Halted trial, no current sponsor, no monitored supply, no way to authenticate gray-market product.
• Pregnancy / breastfeeding / planning pregnancy — absolute. ActRIIB inhibition perturbs gonadal-axis activin signaling.
• Personal or family history of HHT, AVMs, or unexplained recurrent epistaxis — absolute. The pharmacologic phenotype recapitulates this disease.
• Bleeding disorders (von Willebrand, hemophilia, etc.) — absolute.
• Active cardiovascular disease — class concern; GDF-11 capture has cardiac implications.
• Concurrent anticoagulant or antiplatelet therapy — bleeding risk amplification.
• Athletes subject to anti-doping testing — do not use. WADA S4; sanctionable.
• Anyone unwilling to accept that the only Phase 2 trial was halted for safety in children with a fatal disease.

If you've already used vendor "ACE-031":

• Stop.
• Document any nasal, oral, or skin bleeding/erythema with photos and dates.
• See a physician — bring the trial halt summary and the Campbell 2017 paper (PMID 27462804).
• Do not redose.
• Be aware the half-life is on the order of weeks — symptoms may persist after stopping.