# Garetosmab > An anti-activin-A antibody (Regeneron) — closest to approval of the axis (FOP), and a partner in obesity muscle-preservation combinations. - Also known as: REGN2477 - Class: Growth Hormone, Metabolic - FDA approved: No - Canonical page: https://www.americanpeptide.com/catalog/garetosmab ## Overview Garetosmab is a monoclonal antibody from Regeneron that neutralizes activin A — a TGF-β-superfamily ligand that, like myostatin, signals through the activin type II receptors. Blocking activin A widens the axis beyond myostatin alone, and garetosmab plays two roles in this catalog: it is the most clinically advanced agent here, and it is the third leg of the triple obesity combination. Garetosmab’s lead indication is fibrodysplasia ossificans progressiva (FOP) — an ultra-rare disease in which soft tissue turns to bone, driven by activin A. Its Phase 3 OPTIMA trial was positive (roughly 90–94% reduction in new heterotopic bone lesions), and its FDA Biologics License Application was accepted for Priority Review with a decision target around August 2026 — making it the closest-to-approval molecule on this axis, albeit for a rare bone disease rather than obesity. Its metabolic role is as the activin-A arm of the semaglutide + trevogrumab + garetosmab triple combination, which produced the best body-composition profile in early data. As an anti-activin-A antibody (~150 kDa), it illustrates that the "myostatin axis" is really a broader activin/ActRII network with multiple blockable nodes. ## Mechanism Binds and neutralizes activin A, blocking its signaling through ActRII. In bone disease this prevents activin-A-driven abnormal ossification; in the metabolic setting, adding activin-A blockade to myostatin blockade and incretin therapy further shifts body composition toward fat loss with preserved muscle. ## Chemistry | Property | Value | | --- | --- | | Molecular weight | 150000 Da | ## Research areas Studied in: Fibrodysplasia ossificans progressiva, Obesity, Body composition, Muscle preservation. Guides on this site: - [Weight Loss & Metabolic Health](https://www.americanpeptide.com/research-areas/weight-loss): Incretin and metabolic peptides studied for glycemic control and fat loss. - [Growth Hormone & Body Composition](https://www.americanpeptide.com/research-areas/growth-hormone-axis): Secretagogues studied for GH release, IGF-1, and body composition. ## Key research - FOP — positive Phase 3 OPTIMA (~90–94% reduction in new abnormal bone lesions); the lead indication. - Regulatory status — BLA accepted for FDA Priority Review (target decision ~Aug 2026), the most advanced agent on this axis. - Anti-activin A — widens muscle/fat modulation beyond myostatin by blocking a related ActRII ligand. - Triple combination — the activin-A leg of semaglutide + trevogrumab + garetosmab for body composition. - Investigational in obesity — its metabolic use is not approved. ## Storage, handling & synthesis **Storage.** Stored refrigerated (2–8 °C), protected from light and freezing, not shaken; investigational handling per trial protocol. **Handling.** A large glycosylated antibody sensitive to freezing, heat, and agitation, which can cause aggregation. **Synthesis.** Garetosmab is a recombinant monoclonal antibody (~150 kDa) produced in mammalian cell culture, characterized with antibody-grade analytics (glycan/charge-variant profiling, mass spectrometry, binding/potency bioassay) — not a synthetic peptide. ## FAQs ### What is garetosmab? A Regeneron monoclonal antibody that neutralizes activin A. Its lead use is the rare bone disease FOP, and it is also a component of an obesity triple-combination aimed at preserving muscle. ### Why does an FOP drug appear alongside obesity compounds? Activin A signals through the same ActRII receptors as myostatin. Blocking it both prevents abnormal bone formation in FOP and, combined with myostatin blockade and a GLP-1 drug, shifts weight loss toward fat while sparing muscle. ### Is this medical advice? No — this is a research and educational reference. Garetosmab’s obesity use is investigational; its FOP application was under FDA review. ## Latest research Recent trials and publications mentioning Garetosmab, pulled automatically from ClinicalTrials.gov and PubMed (unfiltered search results, refreshed daily). ### Recent trials - [A Study to Test if Trevogrumab or Trevogrumab With Garetosmab When Taken With Semaglutide is Safe and How Well They Work in Adult Patients With Obesity for Weight Loss, Fat Loss, and Lean Mass Preservation](https://clinicaltrials.gov/study/NCT06299098) — ACTIVE_NOT_RECRUITING · PHASE2 · NCT06299098 - [A Study to Investigate the Safety, Pharmacokinetics (PK), and Efficacy of Garetosmab in Children and Adolescents With Fibrodysplasia Ossificans Progressiva (FOP)](https://clinicaltrials.gov/study/NCT07559513) — NOT_YET_RECRUITING · PHASE3 · NCT07559513 - [A Study to Assess Safety, Tolerability and Efficacy of Garetosmab Versus Placebo Administered Intravenously (IV) in Adult Participants With Fibrodysplasia Ossificans Progressiva (FOP)](https://clinicaltrials.gov/study/NCT05394116) — ACTIVE_NOT_RECRUITING · PHASE3 · NCT05394116 - [An Expanded Access Program of Garetosmab in Adult Patients With Fibrodysplasia Ossificans Progressiva (FOP)](https://clinicaltrials.gov/study/NCT07301450) — TEMPORARILY_NOT_AVAILABLE · NCT07301450 - [Study of Safety and Effects of Garetosmab in Healthy Obese Men and Post-Menopausal Women](https://clinicaltrials.gov/study/NCT06970405) — WITHDRAWN · PHASE1 · NCT06970405 - [Study to Assess the Efficacy and Safety of Garetosmab in Japanese Adult Patients With Fibrodysplasia Ossificans Progressiva (FOP)](https://clinicaltrials.gov/study/NCT04577820) — WITHDRAWN · PHASE3 · NCT04577820 --- Source: AmericanPeptide.com — https://www.americanpeptide.com/catalog/garetosmab Data license: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Attribution: AmericanPeptide.com. Research reference only — computational and educational content, not medical advice.