Evidence: Studied in humans. Example dose: finalize with a provider. Not a fact-check stamp.
1 mg/kgSubQ1x weekly to 1x every 2 weeks
Soluble Decoy ReceptorHalted Pharmaceutical Development (2013, vascular AEs)Research Chemical (no human approval)
ACE-031 (RAP-031) is a soluble decoy receptor fusion protein consisting of the extracellular domain of activin receptor type IIB (ActRIIB) fused to the Fc region of human IgG1. It functions as a 'trap' for myostatin (GDF-8) and related TGF-beta superfamily ligands (activin A, GDF-11), preventing those ligands from binding membrane-bound ActRIIB on muscle cells and thus de-repressing muscle hypertrophy. Developed by Acceleron Pharma originally for Duchenne muscular dystrophy and other muscle-wasting indications.
Quick Start
Route
Subcutaneous (SubQ) injection
Start low
1 mg/kg SubQ
Frequency
1x weekly to 1x every 2 weeks
Timing
Timing independent of food
Same day each week. Inject into thigh or abdominal subcutaneous tissue. Reconstitute lyophilized vial gently with bacteriostatic water - do NOT shake. The Fc fusion protein is a large molecule (~80 kDa) - use larger-gauge needle (25-27g) for smooth injection.
❋
Start here. Every protocol below is ordered lowest-first. Begin at the smallest effective dose, hold about a week to assess tolerance, and step up only if needed.
Tiered Protocols · lowest first
Conservative start
HALTED-TRIAL LABEL — Live PubMed record 27462804 states the study stopped after the second dosing regimen because of epistaxis and telangiectasia safety concerns.
1 mg/kg · Subcutaneous (SubQ) injection · 1x weekly to 1x every 2 weeks
conservative starter
1 mg/kg
1x weekly to 1x every 2 weeks
Expert
Actin Receptor Blockade
HALTED-TRIAL LABEL — Live PubMed record 27462804 states the study stopped after the second dosing regimen because of epistaxis and telangiectasia safety concerns.
1 mg/kg · SubQ · Every X days
human clinical trial · Attie et al. 2013 (Muscle Nerve 47(3):416-423)
THE PROGRAMME WAS TERMINATED. The Phase 2 in ambulatory Duchenne boys was stopped after epistaxis (nosebleeds) and telangiectasias - a vascular safety signal - and the whole ACE-031 programme ended. No drug from it reached approval. The repeat-dose trials gave 1.0 mg/kg every 2 WEEKS (0.5 mg/kg every 4 weeks in the other arm), so a weekly schedule exceeds anything studied. Half-life is 10-15 days.
1 mg/kg
Every X days
Reconstitution CalculatorU-100
050100u
Draw to
— units
◆
◆
◆
01
How it works
ACE-031 is a soluble form of the activin receptor type IIB (ActRIIB) fused to an IgG1 Fc domain. It functions as a circulating decoy that captures TGF-beta superfamily ligands - primarily myostatin (GDF-8), activin A, and GDF-11 - before they can bind membrane-anchored ActRIIB on skeletal muscle cells.
Myostatin Inhibition
Myostatin is the primary negative regulator of skeletal muscle mass. ACE-031's capture of circulating myostatin removes the brake on muscle growth, producing hypertrophy independent of training stimulus in animal models and human Phase 1 trials.
Activin A and GDF-11 Capture
ACE-031 also binds activin A (involved in inflammation, hematopoiesis, and reproductive endocrinology) and GDF-11 (controversial role in aging). Off-target binding to these ligands may explain some of the non-muscle adverse events that halted clinical development.
Fc Fusion Architecture
The IgG1 Fc domain provides FcRn-mediated half-life extension (similar mechanism to therapeutic monoclonal antibodies), giving ACE-031 a half-life of approximately 7-14 days vs the minutes-to-hours half-life of native peptides. This permits weekly to bi-weekly dosing.
Net Effect
Increased lean mass (typically 1-3% over weeks at therapeutic doses) and increased strength in animal models. Human Phase 1 data confirmed dose-dependent muscle mass increase before development was halted.
Vascular Side Effects
The DMD trial halt was driven by epistaxis (nosebleeds), telangiectasias (small dilated vessels), and gum bleeding - hypothesized to reflect off-target effects on activin signaling in vascular endothelium. This safety signal is the primary risk distinguishing ACE-031 from more targeted myostatin-only inhibitors (Follistatin, BMS-986089).
02
What to expect
Early
Days 1–7
Week 1-2: minimal subjective effect. Steady-state plasma exposure builds over first 4 weeks (long half-life).
Mid
Weeks 2–4
Week 4-8: lean mass gains accumulate. Strength improvements measurable in trained users. Body composition changes detectable on DEXA.
Later
Weeks 4–12
Week 8-12: peak therapeutic effect. Lean mass changes plateau around 2-3% in non-DMD adults. Vascular surveillance ongoing - any new bleeding signal warrants discontinuation.
03
Evidence
HumanModerate
AnimalStrong
In-vitroPresent
Each reference below was re-fetched from its PubMed record, and the quoted sentence was
confirmed to appear in that abstract and to support the claim it sits under. Follow any of
them to read the source.
Dose/route: a single 0.02-3 mg/kg subcutaneous dose was studied in humans, which includes the card’s 1 mg/kg amount but not its repeated weekly schedule.
This double-blind, placebo-controlled study evaluated the safety, pharmacokinetics, and pharmacodynamics of ACE-031 in 48 healthy, postmenopausal women randomized to receive 1 dose of ACE-031 (0.02-3 mg/kg s.c.) or placebo (3:1).
Evidence scope. Human, but exclusively healthy postmenopausal women (n=48); single subcutaneous dose, Phase I. This is the only human dose-ranging data at this level, and it comes from a narrow demographic quite different from the younger/male population that often seeks this compound off-label.
Mechanism: ACE-031 is a soluble form of activin receptor type IIB.
ACE-031 is a soluble form of activin receptor type IIB (ActRIIB).
Storage. Lyophilized vial: refrigerate (2-8°C / 36-46°F) for short-term, freeze (-20°C) for long-term storage. Avoid freeze-thaw cycles - fusion protein sensitive. Light-sensitive. After reconstitution with bacteriostatic water: refrigerate, use within 7 days. Do NOT shake during reconstitution - swirl gently. Discard if cloudy, discolored, or contains particulates. The Fc fusion protein is more stability-sensitive than smaller native peptides.
06
Regulatory status
Not FDA-approved for any indication. Phase 2 clinical development halted in 2013 due to bleeding adverse events. Acceleron Pharma (now part of Merck) has pivoted to other ActRIIB-Fc-derivative therapeutics (luspatercept/Reblozyl approved 2019 for beta-thalassemia and MDS anemia; sotatercept/Winrevair approved 2024 for pulmonary arterial hypertension) which use refined targeting to reduce off-target activin pathway effects. ACE-031 itself remains an experimental research chemical. WADA prohibited under class S2 (peptide hormones, growth factors). Sale for human use is illegal in regulated jurisdictions.
Put it to work
Calculate, log & track
Open ACE-031 straight into OnePin with your vial and dose pre-filled, then let it handle the syringe math and remind you before the vial runs out.