ACE-031
ACE-031 (ramatercept) is a soluble activin receptor type IIB-Fc fusion protein that binds and neutralizes myostatin and related ligands, with research applications in muscle-wasting disorders, bone density enhancement, and cancer-related cachexia.
ACE-031 is a recombinant fusion protein consisting of the extracellular domain of activin receptor type IIB (ACVR2B) linked to the Fc portion of human IgG1. By acting as a decoy receptor, it sequesters myostatin and other TGF-beta superfamily ligands, preventing their signaling through endogenous receptors and thereby promoting muscle growth, bone formation, and favorable metabolic changes.
Overview
ACE-031 functions as a soluble form of ACVR2B, one of the most potent regulators of muscle growth in vivo. Myostatin, a negative regulator of skeletal muscle mass, is bound by ACE-031 and subsequently prevented from signaling through membrane-bound activin receptors. Research in mouse models has demonstrated that disrupting activin receptor signaling leads to substantial increases in muscle mass across all skeletal muscle groups.
As a result of this mechanism, ACE-031 has been investigated in clinical trials as a potential treatment for muscle-wasting diseases including Duchenne muscular dystrophy (DMD). Beyond muscle, activin receptors play roles in gametocyte development, bone metabolism, and tumor biology — the receptor is frequently found to be inactivated in prostate cancer and is damaged or dysfunctional in several forms of colorectal cancer.
Mechanism of Action
ACE-031 acts as a ligand trap for myostatin and other members of the TGF-beta superfamily, including activins and GDF-11. By binding these ligands in the extracellular space, ACE-031 prevents their interaction with membrane-bound type II activin receptors. This blockade removes the inhibitory brake on muscle growth normally imposed by myostatin signaling, while also influencing bone remodeling (via osteoclast suppression), fat metabolism, and oxidative capacity of muscle tissue.
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Research
Clinical Trial in Duchenne Muscular Dystrophy
In a randomized, placebo-controlled clinical trial in ambulatory boys with DMD, subcutaneous injection of ACE-031 every 2–4 weeks resulted in a trend toward maintenance of the 6-minute walk test, indicating preservation of muscle function. Trends toward increased lean body mass, improved bone mineral density, and reduced fat mass were also observed, consistent with findings from other ACE-031 studies. (Campbell et al., 2017)
Muscle Preservation in Postmenopausal Women
ACE-031 was evaluated in a placebo-controlled, single ascending-dose clinical trial in healthy postmenopausal women. A single subcutaneous dose produced significant increases in both lean body mass and thigh muscle volume at day 29. As a secondary finding, participants receiving ACE-031 also showed improvement in serum biomarkers of bone and fat metabolism, suggesting effects beyond muscle growth alone. (Attie et al., 2013)
Requirement for Multi-Pathway Myostatin Blockade
Research in mice indicates that maximal skeletal muscle hypertrophy can only be achieved through simultaneous blockade of multiple activin receptor pathways. Dual inhibition of ActRIIA and ActRIIB produced greater muscle growth than inhibition of either receptor alone, suggesting that optimal muscle protection in wasting conditions may require a multifaceted therapeutic approach combining growth-promoting agents (e.g., growth hormone, IGF-1) with myostatin pathway inhibitors. (Morvan et al., 2017)
Bone Density Enhancement
In a DMD mouse model, weekly ACE-031 administration for seven weeks significantly increased total body weight, muscle mass, and bone mineral density. The bone effects appeared to result from decreased osteoclast numbers, and biomechanical testing confirmed that the enhanced mineralization improved both maximum tolerable force and bone stiffness. ACE-031 increased bone mass by up to 30% in treated mice. (Puolakkainen et al., 2017)
A separate mouse study comparing ACE-031 with a strict myostatin-only inhibitor confirmed that while both increased muscle mass, only ACE-031 improved bone density — with a 132% increase in femoral bone density and a 27% increase in vertebral density. These results indicate that ACE-031 binds ligands beyond myostatin that are relevant to bone metabolism. (Bialek et al., 2014)
Effects on Energy Metabolism
Mouse studies indicate that myostatin negatively affects muscle energy metabolism, with excess myostatin leading to severe muscle fatigue. Blocking endogenous ActRIIB signaling in mice results in elevated serum lactate and metabolic damage to muscle, along with reduced vascularization of muscle tissue. Supplementing with exogenous ACE-031 not only promotes muscle growth through myostatin inhibition but also improves oxidative capacity, which protects against fatigue and free radical-mediated damage. (Relizani et al., 2014)
Muscle Strength and Contractile Function
ACE-031 appears to improve muscle function beyond what would be expected from myostatin inhibition alone. In a mouse model of DMD, ACE-031 administration improved maximum and total contractile force by 40% and 25% respectively, while preserving energy supply and shifting muscle thermodynamics toward oxidative respiration. No changes in ATP homeostasis or contractile efficiency were observed, indicating that ACE-031 enhances force-generating capacity without altering fundamental energy dynamics. (Bechir et al., 2016)
Cancer Cachexia and Chemotherapy-Induced Muscle Loss
Cancer and chemotherapy both activate signaling pathways leading to muscle cell death and metabolic stress. In cell culture models, ACE-031 prevents activation of the ERK1/2 pathway in muscle cells, blocking muscle fiber atrophy via programmed cell death. ACE-031 also preserves mitochondrial function and improves muscle fiber energy efficiency, helping offset the metabolic burden of cancer and chemotherapy. (Barreto et al., 2016)
Some cancers directly produce myostatin as a mechanism to induce cachexia. Research in cell culture demonstrates that ACE-031 prevents myostatin-mediated muscle wasting in this context, with cancer cells appearing to exert multiple direct effects on muscle function including inactivation of endogenous activin receptors and reduction of mitochondrial numbers. (Lokireddy et al., 2012)
Beyond muscle composition, inactivating myostatin in the setting of cancer improves insulin sensitivity, reduces fat deposition, decreases inflammation, and enhances bone strength and fracture healing rates. (Han et al., 2013)
Safety Profile
In clinical trials, ACE-031 was generally well tolerated at lower doses. In the DMD trial, the study was halted early due to minor safety signals including epistaxis (nosebleeds) and gingival bleeding, as well as telangiectasias (dilated small blood vessels). These effects may be related to the broad ligand-trapping activity of ACE-031, which affects not only myostatin but also other TGF-beta superfamily members involved in angiogenesis. No serious adverse events were attributed to ACE-031 in the healthy volunteer study.
Pharmacokinetic Profile
ACE-031 — Pharmacokinetic Curve
Subcutaneous injectionQuick Start
- Route
- Subcutaneous injection
Research Indications
Muscular Dystrophy
Phase 2 RCT showed trends toward maintenance of 6-minute walk distance (vs. decline in placebo) and increased lean body mass and BMD. Trial halted due to epistaxis and telangiectasias from off-target TGF-beta family inhibition. Program discontinued in 2013.
Phase 1 study in healthy postmenopausal women showed 3.3% increase in lean mass and 5.1% increase in thigh muscle volume at day 29 with single 3 mg/kg dose. Demonstrates proof-of-concept for ActRIIB ligand trapping.
Bone Health
Secondary endpoints in DMD trial showed trends toward increased bone mineral density. Myostatin and activin inhibition via ActRIIB pathway has known positive effects on bone formation in preclinical models.
Research Protocols
subcutaneous Injection
A single subcutaneous dose produced significant increases in both lean body mass and thigh muscle volume at day 29. The protocol used single subcutaneous doses of ACE-031 at 0.02, 0.05, 0.1, 0.3, 1, and 3 mg/kg, with follow-up through day 113.
| Goal | Dose | Frequency | Duration |
|---|---|---|---|
| General Research Protocol | See literature | Every 2-4 weeks | 2–4 weeks(Route: Subcutaneous Injection) |
| Phase 1 — Single Ascending Dose in Healthy Postmenopausal Women | 3 mg, 1 mg | Single dose | —(Route: Subcutaneous Injection) |
| Phase 2 — Duchenne Muscular Dystrophy Trial | See literature | Every 2-4 weeks | 2-4 weeks(Route: Subcutaneous Injection) |
| Dose Escalation Design | 3 mg | Every 2-4 weeks | 4 weeks(Route: Subcutaneous Injection) |
What to Expect
What to Expect
Levels begin building after first administration; half-life of ~25–32 days means steady state reached over month 4-6
In a randomized, placebo-controlled clinical trial in ambulatory boys with DMD, subcutaneous injection of ACE-031 every 2–4 weeks resulted in a trend...
A single subcutaneous dose produced significant increases in both lean body mass and thigh muscle volume at day 29.
The protocol used single subcutaneous doses of ACE-031 at 0.02, 0.05, 0.1, 0.3, 1, and 3 mg/kg, with follow-up through day 113.
Continued use as directed
Safety Profile
Common Side Effects
- Injection Site Reactions:: Commonly reported injection site erythema in clinical trials
- Development Discontinued:: Clinical trials were halted due to unspecified safety concerns in DMD patient population
- Limited Long-term Data:: No extensive human safety data exists beyond short-term single or multiple dose studies
- Generally Well-Tolerated:: In healthy volunteers, acute side effects were minimal at lower to moderate doses
Quality Indicators
What to look for
- Human clinical trials conducted
- Well-established safety profile
- Extensive peer-reviewed research base
Caution
- Short half-life may require frequent dosing
Red flags
- Significant side effect risk noted
Frequently Asked Questions
References (14)
- [7]Bechir N et al ActRIIB blockade increases force-generating capacity and preserves energy supply in exercising mdx mouse muscle in vivo FASEB J (2016)
- [6]Relizani K et al Blockade of ActRIIB signaling triggers muscle fatigability and metabolic myopathy Mol Ther (2014)
- [5]
- [1]A single ascending-dose study of muscle regulator ACE-031 in healthy volunteers
→ Single-dose ACE-031 treatment in healthy postmenopausal women resulted in statistically significant increases in total body lean mass (3.3%) and thigh muscle volume (5.1%) at day 29, with mean half-life of 10-15 days and generally well-tolerated side effects.
- [2]Myostatin inhibitor ACE-031 treatment of ambulatory boys with Duchenne muscular dystrophy: Results of a randomized, placebo-controlled clinical trial
→ Randomized, double-blind trial of ACE-031 in boys with Duchenne muscular dystrophy evaluated safety as primary objective with secondary objectives including efficacy measurements, administered subcutaneously every 2-4 weeks.
- [3]Administration of a soluble activin type IIB receptor promotes skeletal muscle growth independent of fiber type
→ ACE-031 treatment in mice for 28 days increased body weight by 16% and muscle wet weights by 26-46%, with fiber cross-sectional area increases of 22-28% in both type I and type II fibers, demonstrating fiber-type independent muscle growth.
- [8]Puolakkainen T et al Treatment with soluble activin type IIB-receptor improves bone mass and strength in a mouse model of Duchenne muscular dystrophy BMC Musculoskelet Disord (2017)
- [4]Emerging drugs affecting skeletal muscle function and mitochondrial biogenesis - Potential implications for sports drug testing programs
→ Review identifying ACE-031 among compounds under preclinical and clinical investigation for skeletal muscle function that could potentially be misused by athletes for performance enhancement, necessitating anti-doping monitoring.
- [9]
- [10]Barreto R et al Chemotherapy-related cachexia is associated with mitochondrial depletion and the activation of ERK1/2 and p38 MAPKs Oncotarget (2016)
- [11]
- [12]Han HQ et al Myostatin/activin pathway antagonism: molecular basis and therapeutic potential Int J Biochem Cell Biol (2013)
- [13]Pirruccello JP et al — Analysis of cardiac magnetic resonance imaging in 36,000 individuals yields genetic insights into dilated cardiomyopathy Nat Commun (2022)
- [14]
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