Overview
ACE-031 is a recombinant fusion protein consisting of the extracellular domain of the human activin receptor type IIB (ACVR2B) linked to the Fc portion of human IgG1. Developed by Acceleron Pharma in collaboration with Shire, ACE-031 functions as a decoy receptor that binds and neutralizes myostatin and other members of the TGF-β superfamily that negatively regulate muscle growth.
The compound was initially developed for Duchenne muscular dystrophy (DMD) and entered Phase 2 clinical trials in 2011. Results demonstrated significant increases in lean body mass and reductions in fat mass, validating the myostatin inhibition approach. However, the clinical program was voluntarily suspended due to minor nosebleeds and gum bleeding observed in some trial participants, possibly related to effects on vascular remodeling pathways.
Despite the clinical hold, ACE-031 generated significant scientific interest as a proof-of-concept for myostatin pathway inhibition. The data from its trials informed the development of next-generation myostatin inhibitors and continues to be referenced in muscle biology research. The compound demonstrated that systemic myostatin inhibition could produce measurable anabolic effects in humans within weeks of treatment.
This guide examines ACE-031's mechanism, clinical trial data, safety profile, and its significance in the broader context of myostatin biology and muscle-wasting therapeutics.
Quick facts
- Mechanism
- Soluble decoy receptor that traps myostatin and activins
- Primary use
- Muscle Wasting & Body Composition
- Evidence
- moderate
- FDA
- Not approved
- Route
- Subcutaneous injection
- Typical results
- Increased lean mass and decreased fat mass observed in Phase 2 trials over 4–12 weeks
Chemical information
ACE-031 is a large fusion protein with a molecular mass of approximately 2,956 g/mol for the receptor domain portion (C₁₂₂H₂₂₇N₄₂O₂₂ for the core peptide). The full construct includes the ACVR2B extracellular domain (residues 19–134) fused to the Fc region of human IgG1 via a minimal linker, producing a homodimeric protein of ~130 kDa total mass. The dimeric structure enhances ligand-binding avidity.
How ACE-031 works
ACE-031 works by acting as a molecular 'trap' for myostatin and related ligands in the TGF-β superfamily. Myostatin (GDF-8) is a potent negative regulator of skeletal muscle mass—it signals through the activin type IIB receptor (ACVR2B) to activate Smad2/3 transcription factors that suppress muscle protein synthesis and promote muscle protein degradation.
By flooding the circulation with soluble ACVR2B-Fc, ACE-031 intercepts myostatin before it can bind to cell-surface receptors on muscle fibers. This effectively removes the 'brake' on muscle growth, allowing the Akt/mTOR anabolic pathway to proceed without TGF-β-mediated suppression. The result is increased muscle fiber hypertrophy and hyperplasia.
Importantly, ACE-031 does not selectively bind myostatin alone. It also binds activin A, activin B, GDF-11, and BMP-9/BMP-10 with varying affinities. This broad ligand-trapping profile explains both its potent anabolic effects and some of the off-target effects observed in clinical trials, particularly those related to vascular biology (BMP-9/10 are critical for vascular integrity).
Preclinical studies in mdx mice (a model for DMD) showed that ACE-031 treatment increased muscle mass by 20–30%, improved grip strength, and reduced markers of muscle damage including serum creatine kinase levels. These effects were dose-dependent and observed within 4 weeks of treatment initiation.
- Myostatin sequestration: Binds circulating myostatin (GDF-8) with high affinity, preventing receptor activation
- Activin neutralization: Also traps activin A/B, removing additional negative regulators of muscle growth
- Smad2/3 suppression: Reduces intracellular Smad signaling that would otherwise inhibit protein synthesis
- Akt/mTOR disinhibition: Allows anabolic signaling to proceed without TGF-β pathway suppression
- Satellite cell activation: May promote muscle stem cell proliferation and differentiation
- Adipose regulation: Myostatin inhibition shifts energy partitioning away from fat storage toward lean tissue
Pharmacokinetics
Pharmacokinetic data is available from Phase 1 and Phase 2 clinical trials in humans.
| Parameter | Value | Significance |
|---|---|---|
| Bioavailability (SC) | ~60–80% (estimated) | Good absorption for a large fusion protein |
| Half-life | ~10–15 days | Supports dosing every 2–4 weeks |
| Tmax | 3–7 days post-injection | Gradual absorption from SC depot |
| Distribution | Primarily extracellular | Functions in circulation to trap ligands |
| Metabolism | Proteolytic degradation (Fc-mediated) | Standard antibody-like clearance |
| Onset of effects | 2–4 weeks (lean mass changes) | Measurable body composition shifts within first month |
Dosing & administration
In clinical trials, ACE-031 was administered subcutaneously at doses ranging from 0.02 to 3 mg/kg every two weeks. The Phase 2 DMD trial used escalating doses of 1 mg/kg and 2.5 mg/kg administered every two weeks for 12 weeks. The 1 mg/kg dose showed the best benefit-risk profile in preliminary analyses.
Phase 1 healthy volunteer studies showed dose-dependent increases in thigh muscle volume (+3.2% at highest doses) and decreases in subcutaneous fat volume. Effects on lean mass were detectable by MRI within 29 days of a single dose, demonstrating rapid pharmacodynamic activity.
ACE-031 is not currently available for clinical use, and the development program was suspended. Any future dosing recommendations would need to be established through new clinical trials with improved selectivity profiles.
Important: These dosing ranges are not FDA-approved. Any use should be under qualified medical supervision.
Side effects & safety
ACE-031's clinical development was voluntarily suspended in 2013 after Phase 2 trials in DMD patients revealed minor bleeding events (epistaxis and gum bleeding) and telangiectasias. These effects were attributed to the compound's inhibition of BMP-9 and BMP-10, which play important roles in vascular endothelial integrity. The events were not life-threatening, but prompted a pause for further evaluation.
Common
- • Minor nosebleeds (epistaxis)
- • Gum bleeding
- • Injection site reactions
- • Mild headache
- • Skin telangiectasias (dilated small blood vessels)
- • Fatigue
Serious / potential risks
- • Potential vascular effects due to BMP-9/10 inhibition
- • Theoretical risk of pulmonary arterial hypertension with chronic use
- • Unknown long-term effects on cardiac muscle remodeling
- • Potential effects on bone metabolism (activin involvement in bone turnover)
- • Clinical program suspended due to safety signals—long-term data unavailable
Drug interactions
Limited drug interaction data exists from clinical trials. The following are based on known pharmacology.
| Medication | Interaction | Recommendation |
|---|---|---|
| Anticoagulants (Warfarin, DOACs) | ACE-031 may increase bleeding risk due to vascular effects | Contraindicated or use extreme caution |
| Anti-platelet agents (Aspirin, Clopidogrel) | Additive bleeding risk with BMP-9/10 inhibition | Avoid concomitant use |
| Corticosteroids | Both affect muscle metabolism; steroids are standard DMD therapy | Was used concomitantly in trials; monitor carefully |
| Other myostatin inhibitors | Excessive myostatin inhibition theoretically possible | Do not combine; redundant mechanism |
| TGF-β pathway modulators | Overlapping signaling pathway targets | Avoid combination; monitor for excessive pathway inhibition |
Storage & handling
Lyophilized Powder
- • Store at -20°C to -80°C for long-term stability
- • Protect from light and moisture
- • Stable for 12+ months when properly stored
- • Allow to reach room temperature before reconstitution
Reconstituted Solution
- • Use sterile water for injection for reconstitution
- • Store at 2–8°C after reconstitution
- • Use within 24 hours of reconstitution
- • Do not freeze reconstituted solution
Cost & availability
| Source | Cost | Notes |
|---|---|---|
| Clinical trials | Not commercially available | Was only available through clinical trial participation |
| Research supply (historical) | $500–$2,000+ per mg | Limited availability; research-grade only |
| Next-generation alternatives | Varies | Newer selective myostatin inhibitors may become available |
The bottom line
ACE-031 is a anabolic compound with research interest in muscle growth, myostatin inhibition, muscular dystrophy. While preclinical evidence is encouraging, it remains investigational and is not FDA-approved. Any use should be under qualified medical supervision.
Best for
- • Researchers studying anabolic processes and muscle development
- • Individuals interested in muscle growth under medical guidance
Not for
- • Self-administration without medical supervision
- • Pregnant or breastfeeding individuals
- • Individuals with contraindicated conditions
Related compounds
Frequently asked questions
References
- [1] Attie KM, Borgstein NG, Yang Y, et al.. A single ascending-dose study of muscle regulator ACE-031 in healthy volunteers. Muscle Nerve (2013). doi: 10.1002/mus.23539 PMID: 23553570
- [2] Campbell C, McMillan HJ, Mah JK, et al.. Myostatin inhibitor ACE-031 treatment of ambulatory boys with Duchenne muscular dystrophy: results of a randomized, placebo-controlled clinical trial. Muscle Nerve (2017). doi: 10.1002/mus.25268 PMID: 27462804
- [3] Lee SJ, Reed LA, Davies MV, et al.. Regulation of muscle growth by multiple ligands signaling through activin type II receptors. Proc Natl Acad Sci USA (2005). doi: 10.1073/pnas.0505996102 PMID: 16352722
- [4] Cadena SM, Tomkinson KN, Monnell TE, et al.. Administration of a soluble activin type IIB receptor promotes skeletal muscle growth independent of fiber type. J Appl Physiol (2010). doi: 10.1152/japplphysiol.00866.2009 PMID: 20044472
- [5] Sako D, Grinberg AV, Liu J, et al.. Characterization of the ligand binding functionality of the extracellular domain of activin receptor type IIb. J Biol Chem (2010). doi: 10.1074/jbc.M110.114959 PMID: 20576610