ACE-031

ACE-031, also designated ramatercept, is a recombinant fusion protein consisting of the extracellular ligand-binding domain of human activin receptor type IIB (ActRIIB, encoded by ACVR2B) fused to the Fc region of human immunoglobulin G1. The resulting molecule circulates as a soluble decoy receptor, sequestering members of the TGF-beta superfamily before they can engage cell-surface receptors on muscle and other tissues.

The principal target is myostatin (GDF-8), the dominant negative regulator of skeletal muscle mass. Myostatin normally binds ActRIIB on myocytes, recruits co-receptors ALK4 or ALK5, and activates Smad2/Smad3 signaling, which drives transcription of atrophy-associated genes and suppresses satellite-cell proliferation and differentiation. ACE-031 intercepts myostatin in circulation before this interaction occurs, relieving the brake on hypertrophic and regenerative programs.

In addition to myostatin, ActRIIB binds GDF-11, multiple activins, and the bone morphogenetic proteins BMP9 and BMP10. ACE-031 captures all of these ligands without selectivity. This broad promiscuity augments anabolic potency beyond what myostatin-selective inhibitors achieve, but simultaneously disrupts BMP9/BMP10-dependent vascular homeostasis, producing the off-target endothelial toxicity that ultimately terminated clinical development. Plasma half-life after subcutaneous administration is approximately 10 to 15 days, yielding prolonged pharmacodynamic activity from infrequent dosing.

The strongest human evidence comes from two prospective randomized controlled trials conducted by Acceleron Pharma before development was discontinued.

A Phase 1 randomized, double-blind, placebo-controlled single ascending-dose study (Attie et al., Muscle & Nerve, 2013; PMID 23169607; DOI 10.1002/mus.23539) enrolled 48 healthy postmenopausal women receiving a single subcutaneous dose of ACE-031 at levels from 0.02 to 3 mg/kg, allocated 3:1 against placebo. At the highest dose of 3 mg/kg, statistically significant increases were observed at day 29: total lean body mass rose 3.3 percent (p = 0.03 by DXA) and thigh muscle volume 5.1 percent (p = 0.03 by MRI). Bone formation markers and fat-mass biomarkers also changed favorably. Pharmacokinetics were linear with a half-life of 10 to 15 days.

A Phase 2 randomized, double-blind, placebo-controlled dose-escalation trial (NCT01099761; Campbell et al., Muscle & Nerve, 2017; PMID 27462804) enrolled 24 ambulatory boys with Duchenne muscular dystrophy: 18 received ACE-031 subcutaneously every 2 to 4 weeks at escalating doses and 6 received placebo. The trial was halted after the second dosing regimen because of epistaxis and telangiectasias in treated participants. Non-significant trends favored the treatment group for maintained 6-minute walk test distance, increased lean body mass, and higher bone mineral density; none reached statistical significance in the abbreviated cohort.

A 2026 preclinical study in common marmosets (Cadena et al., PLOS ONE; PMID 41686840; DOI 10.1371/journal.pone.0342666; n = 12) found that weekly subcutaneous ACE-031 at 3 mg/kg for 14 weeks produced significant lean body mass gains, biceps Type I fiber hypertrophy of 34 percent and Type II of 20 percent, and improved specific muscle force, with no observed adverse effects in that preclinical cohort.

Acceleron Pharma, in collaboration with Shire PLC, permanently discontinued clinical development in May 2013 following nonclinical toxicology studies that did not support continuation.

Typical dosage: Research only (research).

The only formally documented human doses derive from Acceleron's terminated clinical program. In the Phase 1 single-dose trial (Attie et al., 2013), doses ranged from 0.02 to 3 mg/kg as a single subcutaneous injection; the highest dose of 3 mg/kg produced the meaningful body-composition changes noted at day 29. The Phase 2 Duchenne muscular dystrophy trial (NCT01099761) used ascending subcutaneous schedules of 0.5 mg/kg every four weeks and 1.0 mg/kg every two weeks. Neither a maximum tolerated dose nor an optimal therapeutic dose was established before the program was abandoned.

No approved dosing protocol exists for any indication. ACE-031 is currently sold through unregulated online vendors as a research chemical. Anecdotal reports from performance and fitness communities describe doses of approximately 1 to 3 mg/kg subcutaneously every one to two weeks, loosely mirroring the Phase 2 escalation schedule. The biological activity of commercially available material is uncertain; a 2025 gel electrophoresis study (Reichel et al., Drug Testing and Analysis, DOI 10.1002/dta.3898) found that none of 12 tested black market products contained the authentic ACVR2B-Fc fusion protein, meaning the actual composition and biological activity of street-sourced material is unknown.

This content is provided for educational reference only and does not constitute medical advice. ACE-031 carries no approved therapeutic indication, is prohibited by the World Anti-Doping Agency under the S4 Hormone and Metabolic Modulators category (in- and out-of-competition), and its clinical development was abandoned owing to vascular safety findings.

No compound-specific stability data has been identified for this peptide. The general lyophilized-peptide handling framework applies — see Storage & handling for temperature, reconstitution diluent, and beyond-use dating principles.

No peer-reviewed clinical or preclinical data exists on combining ACE-031 with other peptides or anabolic agents. All combination use described in fitness and research-chemical communities is anecdotal and uncontrolled.

• Growth hormone and IGF-1: the theoretical rationale holds that removing a negative regulator of muscle growth (myostatin) while simultaneously activating a hypertrophic promoter (the GH/IGF-1 axis) could yield additive lean-mass gains. No controlled evidence supports this, and the combination has not been studied.

• BPC-157 or TB-500: some anecdotal commentary suggests these peptides' reported pro-angiogenic and tissue-repair properties could theoretically offset ACE-031's vascular liability. There is no scientific evidence for or against this claim, and it is entirely speculative.

Given ACE-031's documented vascular adverse-event profile arising from BMP9/BMP10 inhibition, any combination that further amplifies systemic anabolic signaling carries additional and wholly uncharacterized risk.

ACE-031 is not currently FDA-approved for any indication. It is generally classified as a research compound. Regulatory status varies by country.

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Reported side effects: Research compound, not for human use

The principal safety liability is vascular toxicity arising from off-target inhibition of BMP9 and BMP10. These ligands are essential regulators of endothelial cell maintenance and vascular homeostasis; their blockade produces a phenotype resembling hereditary hemorrhagic telangiectasia (HHT), a genetic condition caused by loss-of-function mutations in ALK1 or endoglin.

In the Phase 2 Duchenne muscular dystrophy trial, treated boys developed epistaxis (nosebleeds), gingival bleeding, and telangiectasias (dilated small vessels visible in the skin). All adverse events resolved upon treatment discontinuation and were not classified as serious at the time of occurrence. Nevertheless, they triggered halting of the trial in April 2011. Subsequent nonclinical and toxicology studies led Acceleron and Shire to permanently discontinue the program in May 2013, with the companies stating that findings did not support further development.

In the Phase 1 single-dose healthy-volunteer trial, injection-site erythema was the most common adverse event; no vascular effects were observed. This pattern is consistent with the hypothesis that dose accumulation from repeated dosing drives the vascular phenotype rather than any single exposure.

A 2025 gel electrophoresis analysis found that commercially available black market products did not contain the authentic ACVR2B-Fc fusion protein, making the actual toxicology of street-sourced material wholly unpredictable.

ACE-031 has no regulatory approval in any jurisdiction and is WADA-prohibited (S4 category, in- and out-of-competition). Individuals with vascular malformations, coagulation disorders, hereditary hemorrhagic telangiectasia, or related conditions face particular risk. No long-term human safety data exists.