ACE-031.
ACE-031 (ramatercept) is not a peptide but a recombinant fusion protein that joins the extracellular domain of the human activin receptor type IIB (ActRIIB) to the Fc region of IgG1.
ACE-031 (ramatercept) is not a peptide but a recombinant fusion protein that joins the extracellular domain of the human activin receptor type IIB (ActRIIB) to the Fc region of IgG1. ACE-031 is in human trials, and PepCue grades its published evidence D tier (49/100). Also known as ramatercept · ActRIIB-Fc. This is a research reference, not medical or dosing advice.
What it is
ACE-031 (ramatercept) is not a peptide but a recombinant fusion protein that joins the extracellular domain of the human activin receptor type IIB (ActRIIB) to the Fc region of IgG1. Developed by Acceleron Pharma, it works as a ligand trap that soaks up myostatin and related TGF-beta-family proteins that normally restrain muscle growth. It was engineered as a candidate therapy for muscle-wasting conditions, most prominently Duchenne muscular dystrophy (DMD). Unlike most compounds grouped with muscle peptides, it genuinely reached human clinical trials before its development was stopped.
How it works
ActRIIB is a receptor through which myostatin (GDF-8), activins, and several other TGF-beta-superfamily ligands signal to limit skeletal muscle mass. By presenting a soluble decoy receptor, ACE-031 binds these ligands in the circulation and prevents them from activating ActRIIB on muscle, releasing the brake on muscle growth. Because the trap captures multiple ligands beyond myostatin, including some that act on blood vessels, it produces effects outside muscle as well. This mechanism was established in animal models and then probed directly in humans.
Mechanism pathways
Removing the biological brake that limits skeletal muscle growth.
Skeletal muscle mass is actively restrained, not merely permitted. Myostatin, also called GDF-8, is a member of the TGF-beta superfamily secreted by muscle itself, and it signals through activin type II receptors, principally ActRIIB, partnered with a type I receptor. Activation phosphorylates SMAD2 and SMAD3, which enter the nucleus and suppress the transcriptional programme for muscle growth while promoting protein degradation pathways. The biology is unusually well demonstrated: naturally occurring loss-of-function mutations in myostatin produce dramatic muscle overgrowth in cattle, dogs, mice, and at least one documented human case. Few pathways have that quality of natural experiment behind them. Removing the brake therefore promotes satellite cell activation, myofibre hypertrophy, and reduced fibrosis. Two strategies are represented here. One uses a soluble decoy receptor: the extracellular ligand-binding portion of ActRIIB fused to an antibody fragment, which circulates and captures ligands before they can reach receptors on muscle. The other uses a naturally occurring binding protein that neutralises myostatin along with activin A, GDF-11, and several bone morphogenetic proteins, preventing them from engaging the type II receptors at all. The crucial difference between them is breadth, and breadth is a double-edged property. Neutralising more ligands produces larger effects on muscle than blocking myostatin alone, which is why broader inhibition is attractive. But ActRIIB and the related receptors serve ligands with jobs elsewhere in the body, including in blood vessels, bone, and reproductive tissue. Capturing those ligands produces effects well outside muscle, and this is not a theoretical concern: clinical development of the decoy receptor approach for muscle-wasting conditions was halted after non-muscle effects including nosebleeds and gum bleeding emerged in human studies, attributed to interference with vascular-related ligands. Honest position: the pathway is real and important, and it remains a legitimate target under active pharmaceutical development. What has not been achieved is a clean separation between the muscle benefit and the off-target consequences of blocking a receptor family with broad physiological responsibilities. No agent in this group is approved for any indication. The gene-therapy-adjacent versions of this approach raise entirely separate and more serious issues. Material sold under these names is unregulated, and for the binding-protein approach in particular, whether an injected peptide fragment reproduces the biology of the full protein at all is uncertain.
The evidence
ACE-031 has genuine human data. Attie et al. reported a single ascending-dose study in healthy postmenopausal women in Muscle & Nerve (2013, PMID 23169607), observing increases in lean mass and biomarker changes consistent with myostatin inhibition. That was a phase 1 design: a small, single-administration, dose-escalating study in a narrowly selected healthy population, sponsored by the developer Acceleron Pharma, with imaging and biomarker endpoints rather than measures of function, and without the duration needed to detect anything that emerges over months. Campbell et al. published the randomized, placebo-controlled trial in ambulatory boys with DMD in Muscle & Nerve (2017, PMID 27462804), which showed trends toward preserved 6-minute-walk distance, higher lean mass and bone mineral density, and lower fat mass, but was stopped early. Because the trial was terminated before completing enrollment and follow-up, the walking-distance result remained a trend rather than a demonstrated benefit, the study lost the statistical power it had been designed with, and no confirmatory trial was ever run. Every efficacy statement about ACE-031 therefore rests on an interrupted study. This places ACE-031 well beyond the preclinical status of most muscle compounds, even though it never demonstrated confirmed clinical efficacy. The wider myostatin-pathway field has repeated the same pattern. Domagrozumab, an anti-myostatin antibody, failed its primary endpoint in Duchenne muscular dystrophy. Bimagrumab, an ActRII-blocking antibody, has produced consistent increases in lean mass without delivering the functional outcomes originally sought, and its cardiac safety has been examined separately in older adults (PMID 41873146). Increasing muscle mass has proven considerably easier than improving what patients can actually do. For ACE-031 specifically there is no chronic exposure data, no published long-term follow-up of the participants who were treated, no completed outcome trial, and no development activity after the early 2010s from which to draw further evidence.
The evidence, in brief
A recombinant ActRIIB-Fc fusion protein (ramatercept) that traps myostatin and related TGF-beta ligands, not a peptide. It reached genuine human trials, including a randomized placebo-controlled study in ambulatory boys with Duchenne muscular dystrophy, with lean-mass and bone-density signals but no confirmed clinical efficacy. The program was halted in 2011 for safety after dose-related vascular effects (nosebleeds, gum bleeding, telangiectasias), and development was never restarted.
- Single ascending-dose study of muscle regulator ACE-031 in healthy volunteersMuscle Nerve, 2013 (PMID 23169607)
- ACE-031 in ambulatory boys with DMD: randomized, placebo-controlled trialMuscle Nerve, 2017 (PMID 27462804)
Evidence maturity
An evidence-only reading: approval status, human vs preclinical data, mechanism and safety. Popularity never raises it. Research file #002
Some human signal atop preclinical work; gaps remain.
Studied in human clinical trials; evidence is meaningful.
Claim receipts
Popular claims about ACE-031, checked against the state of the evidence. The verdict describes evidence maturity, never an invented study result.
An early-phase human study reported lean-mass increases and biomarkers consistent with myostatin-pathway inhibition.
The randomized trial showed trends toward preserved walking distance but was stopped early, leaving the functional result unconfirmed.
The Duchenne program was halted over dose-related vascular effects including nosebleeds, gum bleeding and telangiectasias.
Development was terminated in the early 2010s and no confirmatory trial was ever run.
It is an unapproved recombinant protein made outside pharmaceutical controls, with identity, aggregation and endotoxin unverified.
Safety profile
The DMD program was halted in 2011 for safety reasons. Investigators observed dose-related, non-muscle vascular effects, specifically epistaxis (nosebleeds), gum bleeding, and telangiectasias (small dilated skin vessels), attributed to the trap's activity on additional TGF-beta-family ligands. The mechanistic explanation is that a soluble ActRIIB decoy does not bind myostatin alone: it also sequesters activins and bone morphogenetic proteins that help maintain vascular integrity, so the bleeding signal is a predictable consequence of the trap's breadth rather than an idiosyncratic reaction. These events appeared in children being treated for a serious progressive disease, the population most willing to accept risk for benefit, and they were still judged unacceptable. Acceleron and its partner Shire ended the collaboration and did not restart development. Short-term human exposure is documented, but the compound was discontinued precisely because of these off-target vascular signals, and long-term safety was never established. There is no chronic dosing data, no published long-term follow-up of the boys who were exposed, and no immunogenicity or reproductive toxicology in the public record. Later programs targeting the same pathway were deliberately engineered for narrower ligand selectivity in order to avoid this exact problem. Anything sold online under the ACE-031 name is an unapproved recombinant protein produced outside pharmaceutical manufacturing controls, where identity, glycosylation, aggregation state, and endotoxin content are all unverified, and aggregated Fc-fusion proteins carry their own immunogenicity risk. The monitoring a real trial would demand, including vascular and bleeding assessment, dermatologic examination, and anti-drug antibody testing, does not exist outside a clinical setting.
Compound notes
- ACE-031 (ramatercept) is not a peptide but a recombinant fusion protein joining the extracellular domain of activin receptor type IIB (ActRIIB) to an IgG1 Fc region.
- It works as a decoy ligand trap, binding myostatin and related TGF-beta-family proteins in the circulation so they cannot activate ActRIIB and restrain muscle growth.
- Developed by Acceleron Pharma, it reached randomized human trials, including a placebo-controlled study in ambulatory boys with Duchenne muscular dystrophy.
- That program was halted in 2011 and development was never restarted.
ACE-031 releases a brake on muscle by removing myostatin signaling. GH secretagogues instead push the GH/IGF-1 accelerator. Different targets, different risk profiles.
- Development was discontinued for safety: investigators observed dose-related vascular effects including nosebleeds, gum bleeding, and telangiectasias, attributed to the trap catching ligands beyond myostatin.
- Never approved by any regulator, and long-term safety was never established.
- Anything sold online as ACE-031 is unapproved research-grade material.
Regulatory status
ACE-031 was never approved by the FDA or any other regulator, and its clinical development was terminated in the early 2010s after the DMD trial was stopped for safety. It is not a marketed drug and is not legitimately available for human use. Any product sold online as ACE-031 is unapproved research-grade material.
Investigational, currently in registered human clinical trials.
By the numbers
- 01Recombinant ActRIIB-IgG1-Fc fusion protein, not a small peptide
- 02Acts as a decoy ligand trap for myostatin and related TGF-beta ligands
- 03Developed by Acceleron Pharma; also known as ramatercept
- 04Reached randomized human trials in Duchenne muscular dystrophy
- 05DMD program halted in 2011 over vascular effects (nosebleeds, telangiectasias)
- 06Never approved; development discontinued, now research-only
ACE-031: research formats
Choose the format you are researching to see route-specific notes.
Given by injection inside trials that were stopped in 2011. No legitimate administration format exists today.
ACE-031 is not a peptide but a recombinant ActRIIB-IgG1-Fc fusion protein, and unlike most compounds in this category it genuinely reached randomized human trials. Those trials were run under clinical supervision by Acceleron and its partner, and the Duchenne muscular dystrophy program was halted in 2011 over dose-related vascular effects. Development was never restarted, so there is no marketed product, no labeled route, and no established administration format outside those terminated studies. This page therefore presents no example schedule or concentration math.
The reason the program stopped is the reason no format is reproduced here: investigators observed nosebleeds, gum bleeding, and telangiectasias attributed to the trap's activity on TGF-beta-family ligands beyond myostatin.
Anything sold online as ACE-031 is unapproved research-grade material of unverified identity, produced outside the manufacturing controls the trial product had.
Sources
Every factual claim above resolves to a real, published source.
- Single ascending-dose study of muscle regulator ACE-031 in healthy volunteersMuscle Nerve, 2013 (PMID 23169607)
- ACE-031 in ambulatory boys with DMD: randomized, placebo-controlled trialMuscle Nerve, 2017 (PMID 27462804)
- Cardiac safety of chronic inhibition of the myostatin-activin pathway with bimagrumab in healthy older adultsJ Clin Endocrinol Metab, 2026 (PMID 41873146)
- ClinicalTrials.gov search: ACE-031ClinicalTrials.gov registry
- PubMed search: myostatin inhibition ActRIIB Duchenne muscular dystrophy trialPubMed / NCBI
Cite this page
PepCue. “ACE-031: the evidence.” PepCue, reviewed June 1, 2026. https://www.pepcue.app/p/ace-031.
Log your doses, run the vial math, and keep a provider-ready record in PepCue.