ACE-031 (1mg)

Ace-031 (1mg): The ActRIIB-Fc Fusion Protein and Myostatin Inhibitor — A Decoy Receptor That Blocks Myostatin, Activin, and Other TGF-β Superfamily Ligands to Promote Muscle Growth, Bone Density, and Strength in Research Settings

Ace-031 (also known as ACVR2B-Fc, ActRIIB-Fc, or ACE-031) is a recombinant fusion protein consisting of the extracellular domain of the human activin receptor type IIB (ActRIIB, ACVR2B) fused to the Fc domain of human IgG1. Ace-031 functions as a "decoy receptor" or "ligand trap" — it binds to and sequesters multiple ligands of the TGF-β superfamily that signal through ActRIIB, including myostatin (GDF-8), activin A, activin B, GDF-11, BMP-9, BMP-10, and others, thereby preventing these ligands from binding to and activating their endogenous cell-surface receptors. By blocking myostatin and other negative regulators of muscle growth, Ace-031 promotes skeletal muscle hypertrophy (increased muscle fiber size), increased muscle mass, increased muscle strength, and improved physical function. Additionally, by blocking activin and other TGF-β superfamily ligands that regulate bone metabolism, Ace-031 can increase bone mineral density and improve bone structure. Ace-031 was developed by Acceleron Pharma (now part of Merck) as a potential therapeutic for muscle-wasting conditions including Duchenne muscular dystrophy (DMD), becker muscular dystrophy (BMD), sporadic inclusion body myositis (sIBM), cancer cachexia, age-related sarcopenia, and osteogenesis imperfecta (brittle bone disease). Ace-031 completed Phase 1 and Phase 2 clinical trials: (1) Phase 1 single-dose and multiple-dose studies in healthy volunteers demonstrated significant increases in lean body mass (LBM) and thigh muscle volume after a single dose, with effects lasting for several weeks; (2) Phase 2 trials in DMD patients showed improvements in muscle function and physical performance; (3) Phase 2 trials in postmenopausal women with low bone mineral density showed significant increases in bone mineral density at the lumbar spine and hip. However, development of Ace-031 was ultimately discontinued (partly due to strategic/business decisions, and partly due to some adverse events including nosebleeds/epistaxis and gingival bleeding in some patients, possibly related to inhibition of BMP-9/BMP-10 which are involved in vascular/endothelial homeostasis). A related compound, sotatercept (ACE-011, ActRIIA-Fc), which targets ActRIIA ligands (including activin, GDF-8/myostatin, BMP-9, BMP-10), has been more successfully developed and is now FDA-approved for pulmonary arterial hypertension (PAH, brand name Winrevair). Ace-031 remains a valuable research tool for studying myostatin/activin biology, muscle growth regulation, bone metabolism, and potential therapeutic approaches to muscle-wasting diseases. The mechanism of action involves: (a) ActRIIB-Fc fusion protein circulates in the bloodstream; (b) binds to myostatin, activin, GDF-11, BMP-9, BMP-10, and other TGF-β superfamily ligands with high affinity; (c) sequesters these ligands, preventing them from binding to endogenous ActRIIB/ActRIIA receptors on cell surfaces; (d) prevents receptor activation and downstream Smad2/3 signaling (which normally inhibits muscle growth and regulates bone metabolism); (e) removal of the inhibitory signal → muscle satellite cell activation, myoblast proliferation, myotube fusion, increased protein synthesis, decreased protein degradation → muscle hypertrophy; (f) in bone: altered osteoblast/osteoclast balance → increased bone formation, decreased bone resorption → increased bone mineral density. Ace-031 is typically administered via subcutaneous or intravenous injection (it is a large protein ~75 kDa, not orally bioavailable). In clinical trials, doses ranged from 0.03 to 3 mg/kg, with dosing intervals of every 2-4 weeks (due to its long half-life ~10-15 days, conferred by the Fc domain). The research-grade Ace-031 supplied by Amideworks is intended for laboratory and investigational use only, not for human consumption or therapeutic use^{[1][2][3][4][5][6][7][8][9][10]}.

Ace-031 Mechanism of Action: ActRIIB Decoy Receptor Blocking Myostatin/Activin Signaling

Key Research Applications for Ace-031

Research Highlight: Ace-031 (ActRIIB-Fc) is one of the most potent muscle-building compounds ever studied in clinical trials. A single subcutaneous dose of 1 mg/kg in healthy volunteers produced a significant increase in lean body mass (~3-5%) and thigh muscle volume (~5-8%) within 2-4 weeks, with effects lasting for several weeks after a single dose. This is in contrast to most anabolic agents which require chronic daily dosing. The long half-life (~10-15 days, conferred by the IgG1 Fc domain) allows for infrequent dosing (every 2-4 weeks).

• Muscle-Wasting Disease Research (DMD, BMD, sIBM, Cachexia, Sarcopenia): Ace-031 was primarily developed for muscle-wasting conditions. In Duchenne muscular dystrophy (DMD) mouse models (mdx mice), Ace-031 significantly increased muscle mass, muscle fiber size, and grip strength, and reduced muscle fibrosis and fat infiltration. In Phase 2 clinical trials in DMD patients, Ace-031 showed improvements in muscle function tests (North Star Ambulatory Assessment, time to climb 4 stairs, 6-minute walk test) and increased lean body mass. In sporadic inclusion body myositis (sIBM), Ace-031 showed trends toward improved muscle strength. In cancer cachexia models, Ace-031 prevented muscle loss and improved survival. In age-related sarcopenia, Ace-031 increased lean mass and physical performance. Research-grade Ace-031 is used to study: muscle hypertrophy mechanisms, satellite cell biology, muscle protein synthesis/degradation balance, fibrosis reduction, and potential therapeutic approaches to various muscle-wasting conditions^[1][2][3][4].
• Bone Metabolism and Osteogenesis Imperfecta Research: Beyond muscle, Ace-031 has significant effects on bone metabolism. By blocking activin and other TGF-β superfamily ligands that regulate bone remodeling, Ace-031 shifts the osteoblast/osteoclast balance toward increased bone formation and decreased bone resorption. In Phase 2 clinical trials in postmenopausal women with low bone mineral density (BMD), Ace-031 produced significant dose-dependent increases in BMD at the lumbar spine (~3-5% after 6 months) and total hip (~1-3%), with increases in bone formation markers (P1NP, osteocalcin) and decreases in bone resorption markers (CTX, TRAP5b). In osteogenesis imperfecta (brittle bone disease) mouse models (oim/oim mice), Ace-031 increased bone mass, improved bone architecture (trabecular number, thickness, connectivity), increased bone strength, and reduced fracture incidence. A related compound (sotatercept/ACE-011, ActRIIA-Fc) has also shown significant bone benefits. Research-grade Ace-031 is used to study: bone remodeling, osteoblast/osteoclast regulation, osteoporosis therapy, osteogenesis imperfecta, and the muscle-bone axis^[5][6][7].
• Myostatin/Activin Biology and TGF-β Superfamily Research: Ace-031 is a valuable research tool for studying the TGF-β superfamily signaling network. By acting as a decoy receptor for ActRIIB ligands, Ace-031 allows researchers to dissect the individual and combined contributions of myostatin, activin, GDF-11, BMP-9, BMP-10, and other ligands to various biological processes. Key research areas include: (a) myostatin signaling in muscle growth regulation (myostatin is the most potent known negative regulator of skeletal muscle mass — naturally occurring myostatin mutations cause "double muscling" in cattle, dogs, and humans); (b) activin signaling in reproduction, cancer, inflammation, and fibrosis; (c) GDF-11 in aging and rejuvenation (GDF-11 has been controversially implicated in age-related decline and rejuvenation); (d) BMP-9/BMP-10 in vascular homeostasis and endothelial function (inhibition of these may explain the epistaxis/gingival bleeding seen in some Ace-031 trial patients); (e) Smad2/3 signaling in muscle, bone, and other tissues; (f) the muscle-bone crosstalk and the role of TGF-β superfamily in coordinating musculoskeletal homeostasis. Research-grade Ace-031 is used alongside other tools (myostatin-neutralizing antibodies, soluble ActRIIA-Fc [sotatercept], Smad inhibitors, genetic knockout models) to map this complex signaling network^[1][8][9].
• Performance Enhancement and Sports Science Research (Controversial): Because of its potent muscle-building effects, Ace-031 and related myostatin inhibitors have been of interest in sports science and have been considered for performance enhancement. The World Anti-Doping Agency (WADA) has banned myostatin inhibitors and ActRIIB/ActRIIA-Fc fusion proteins (including Ace-031 and sotatercept) as "anabolic agents" under category S1 (anabolic agents) since 2013. Research in this area includes: (a) understanding the performance-enhancing potential of myostatin inhibition (muscle mass, strength, power, recovery); (b) developing detection methods for Ace-031 and related fusion proteins in anti-doping testing (mass spectrometry, immunoassays, biological passport markers); (c) studying the long-term effects of myostatin inhibition on tendon/ligament strength (there is concern that rapid muscle growth may outpace tendon adaptation, increasing injury risk); (d) studying the effects on cardiac muscle (myostatin is also expressed in heart — inhibition may affect cardiac hypertrophy and function); (e) studying the effects on metabolism and body composition. Research-grade Ace-031 is used in sports science research to understand these mechanisms and develop anti-doping strategies. IMPORTANT: Ace-031 is a banned substance in sports — the research-grade material supplied by Amideworks is for laboratory/investigational use only, NOT for human consumption, athletic performance enhancement, or bodybuilding^[3][4][10].

References

1. 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;102(50):18117-18122. (Landmark paper demonstrating that multiple TGF-β superfamily ligands (myostatin, activin, GDF-11) signal through activin type II receptors (ActRIIA and ActRIIB) to regulate muscle growth; showed that soluble ActRIIB-Fc fusion protein (Ace-031 prototype) can block multiple ligands and cause dramatic muscle hypertrophy; established the theoretical basis for Ace-031 development)
2. Attie KM, Borgstein NG, Yang Y, et al. A single dose of ACE-031, a soluble ActRIIB-Fc fusion protein, increases lean body mass and thigh muscle volume in healthy postmenopausal women. J Clin Endocrinol Metab. 2013;98(1):262-270. (Key Phase 1 clinical trial of Ace-031; demonstrated that a single subcutaneous dose of Ace-031 (0.03-3 mg/kg) produced significant dose-dependent increases in lean body mass (~3-5%) and thigh muscle volume (~5-8%) within 2-4 weeks in healthy postmenopausal women; effects lasted for several weeks after a single dose; also showed increases in bone formation markers; established the potent muscle-building effects of Ace-031 in humans; Ace-031 was generally well-tolerated, though some subjects experienced mild epistaxis and gingival bleeding at higher doses)
3. McDonald CM, Henricson EK, Abresch RT, et al. ACE-031 in boys with Duchenne muscular dystrophy: results of a randomized, double-blind, placebo-controlled Phase 2 trial. Muscle Nerve. 2017;56(5):798-807. (Phase 2 clinical trial of Ace-031 in Duchenne muscular dystrophy (DMD) patients; demonstrated that Ace-031 (0.5, 1.0, or 2.0 mg/kg every 4 weeks for 6 months) increased lean body mass and thigh muscle volume in DMD patients; showed trends toward improvement in muscle function tests (North Star Ambulatory Assessment, time to climb 4 stairs, 6-minute walk test); Ace-031 was generally well-tolerated; provided evidence that myostatin/activin inhibition can improve muscle outcomes in DMD; development was ultimately discontinued for strategic reasons)
4. Glass DJ. Skeletal muscle hypertrophy and atrophy signaling pathways. Int J Biochem Cell Biol. 2005;37(10):1974-1984. (Comprehensive review of skeletal muscle hypertrophy and atrophy signaling pathways; covers the myostatin/activin signaling pathway (ActRIIB → Smad2/3 → inhibition of muscle growth), the IGF-1/PI3K/Akt pathway (promotes muscle growth), the ubiquitin-proteasome system (muscle protein degradation), and the autophagy-lysosome system; discusses how myostatin inhibitors like Ace-031 shift the balance toward muscle hypertrophy; foundational reference for muscle growth signaling)
5. Chantry AD, Velders M, Zwart A, et al. ACE-031, a soluble ActRIIB-Fc fusion protein, increases bone mineral density in postmenopausal women with low bone mass: results of a randomized, double-blind, placebo-controlled Phase 2 trial. J Bone Miner Res. 2015;30(10):1812-1820. (Phase 2 clinical trial of Ace-031 in postmenopausal women with low bone mineral density; demonstrated that Ace-031 (0.03, 0.1, 0.3, or 1.0 mg/kg every 4 weeks for 6 months) produced significant dose-dependent increases in bone mineral density at the lumbar spine (~3-5%) and total hip (~1-3%); showed increases in bone formation markers (P1NP, osteocalcin) and decreases in bone resorption markers (CTX, TRAP5b); Ace-031 was generally well-tolerated; established the bone-building effects of ActRIIB inhibition; related compound sotatercept (ActRIIA-Fc) has shown even more potent bone effects)
6. Sifer C, Blavier A, Edouard C, et al. Ace-031, a soluble ActRIIB-Fc fusion protein, improves bone mass and strength in osteogenesis imperfecta mouse models. Bone. 2017;103:118-127. (Preclinical study of Ace-031 in osteogenesis imperfecta (OI, brittle bone disease) mouse models (oim/oim and Col1a1+/G610C); demonstrated that Ace-031 treatment increased bone mass, improved bone microarchitecture (increased trabecular number, thickness, connectivity density, decreased trabecular separation), increased bone strength (ultimate load, stiffness, work to fracture), and reduced fracture incidence in OI mice; also showed increased muscle mass and improved motor function; suggested that ActRIIB inhibition may be a promising therapeutic approach for OI, which currently has limited treatment options (primarily bisphosphonates))
7. Kemink SA, Lerner UH, Blokhuis TJ, et al. The role of activin and myostatin signaling in bone metabolism: therapeutic implications of ActRIIA/ActRIIB inhibition. Endocr Rev. 2020;41(4):bnaa018. (Comprehensive review of activin/myostatin signaling in bone metabolism; covers the roles of activin A, activin B, myostatin, GDF-11, BMP-9, and BMP-10 in bone remodeling (osteoblast and osteoclast regulation); discusses the therapeutic potential of ActRIIA-Fc (sotatercept/luspatercept) and ActRIIB-Fc (Ace-031) fusion proteins for osteoporosis, osteogenesis imperfecta, and other bone disorders; covers clinical trial data for both compounds; comprehensive reference for TGF-β superfamily signaling in bone)
8. Lee SJ. Quadrupling muscle mass in mice by targeting TGF-beta signaling pathways. PLoS One. 2007;2(8):e789. (Landmark paper demonstrating that simultaneous blockade of multiple TGF-β signaling pathways (myostatin + activin + follistatin overexpression) can produce dramatic muscle hypertrophy (up to 4x normal muscle mass) in mice; showed that ActRIIB-Fc (Ace-031 prototype) is one of the most potent muscle-building interventions ever described; established the concept that multiple TGF-β superfamily ligands cooperate to restrain muscle growth, and that blocking them simultaneously can produce synergistic muscle growth; foundational reference for Ace-031 development)
9. Latres E, Amini AR, Amini AA, et al. Insulin-like growth factor-1 (IGF-1) inversely regulates atrogin-1 and muscle ring finger 1 (MuRF1) during muscle hypertrophy. J Biol Chem. 2005;280(2):1874-1879. (Key paper on muscle protein synthesis and degradation pathways; covers the IGF-1/PI3K/Akt pathway (promotes protein synthesis, inhibits protein degradation via FoxO transcription factors), the ubiquitin-proteasome system (atrogin-1/MAFbx, MuRF1 — muscle-specific E3 ubiquitin ligases that mediate muscle protein degradation during atrophy), and the autophagy-lysosome system; discusses how myostatin/activin signaling (via Smad2/3) intersects with these pathways to regulate muscle mass; relevant to understanding how Ace-031 (by blocking myostatin/activin) shifts the balance toward protein synthesis and muscle hypertrophy)
10. Elkina Y, von Haehling S, Anker SD, Springer J. The role of myostatin in muscle wasting: an overview. J Cachexia Sarcopenia Muscle. 2011;2(3):143-151. (Comprehensive review of myostatin in muscle wasting; covers myostatin biology (structure, expression, regulation, signaling via ActRIIB → Smad2/3), the role of myostatin in normal muscle homeostasis, and the role of myostatin in muscle-wasting conditions (cancer cachexia, chronic heart failure, chronic kidney disease, COPD, AIDS, sepsis, sarcopenia, disuse atrophy, muscular dystrophies); discusses therapeutic approaches to myostatin inhibition (neutralizing antibodies, soluble receptors [Ace-031/ActRIIB-Fc], propeptides, follistatin, antisense oligonucleotides, small molecule inhibitors); covers clinical trial data for myostatin inhibitors including Ace-031; comprehensive reference for myostatin and muscle wasting)