Garetosmab

ID: garetosmab

Aliases: REGN2477, anti-activin A antibody, ActA antibody

Type: compound

Route/form: intravenous infusion in COURAGE Part B and FOP clinical studies

Status: investigational

Evidence level: human RCT

Best data tier: human controlled/review; exact-use indirect

Support scope: human, non-human/mechanistic, context

Source types: clinical_trial_registry, company, company_regulatory, human_rct, preclinical

Linked sources: 9

Broad outcomes: Fat loss / metabolic health, Muscle growth / performance / recovery, PEDs / AAS / thermogenics

Reading note: These are curation notes anchored to linked sources, not a clinical recommendation or protocol.

Targets / mechanism

• activin A neutralization
• ActRIIA/ActRIIB ligand-pathway modulation
• dual myostatin/activin lean-mass preservation concept

Optimization domains

• metabolic
• obesity
• body composition
• muscle
• myostatin
• activin signaling
• fat loss
• GLP-1 adjunct
• bone
• FOP

Research basis

• Peer-reviewed phase 1 human data support activin A as a second negative regulator of muscle mass, with stronger body-composition effects when garetosmab is combined with trevogrumab than with either antibody alone.
• In COURAGE sponsor/conference results, adding garetosmab to semaglutide plus high-dose trevogrumab produced the largest reported shift toward fat-mass loss at week 26.
• The FOP program gives separate human trial context for IV activin A blockade, although that disease mechanism is not the same as obesity or performance optimization.

Limits, risks, and missing evidence

• FOP evidence should not be treated as proof of healthy-user muscle or fat-loss benefit; it is a different disease biology.
• The COURAGE triplet had a substantially higher discontinuation burden and two deaths in the triplet group; Regeneron did not identify causality, but the safety signal belongs on the page.
• Activin/TGF-beta-family signaling is broad, so long-term connective-tissue, endocrine, reproductive, and off-target consequences need trial-level scrutiny.

Risk flags

• investigational
• monoclonal antibody
• activin A blockade
• IV infusion
• muscle spasms
• tolerability discontinuation
• deaths reported in triplet group
• FOP context not performance
• medical supervision
• doping

Linked papers, labels, and reviews

1. GDF8 and activin A are the key negative regulators of muscle mass in postmenopausal females: a randomized phase I trial
   human_rct / nature_trevogrumab_garetosmab_phase1_2025
   Peer-reviewed randomized phase 1 human pharmacodynamic study of trevogrumab and garetosmab, alone and together, with MRI/DXA body-composition endpoints and safety signals including muscle spasms.
2. Results from Phase 2 COURAGE Trial Demonstrating Potential to Improve Quality of GLP-1 receptor agonist-induced Weight Loss by Preserving Lean Mass, Presented at EASD
   company / regeneron_courage_easd_2025
   Sponsor-reported 26-week COURAGE phase 2 obesity results: semaglutide 2.4 mg plus trevogrumab with or without garetosmab shifted weight-loss composition toward fat mass; not a peer-reviewed paper at this curation point.
3. COURAGE: Trevogrumab or Trevogrumab With Garetosmab in Addition to Semaglutide in Patients With Obesity
   clinical_trial_registry / clinicaltrials_courage_trevogrumab_garetosmab_semaglutide
   ClinicalTrials.gov registry for COURAGE; useful for design, enrollment, active-not-recruiting status, endpoints, and route details: trevogrumab SC in Parts B/C, garetosmab IV in Part B, semaglutide SC.
4. Garetosmab in fibrodysplasia ossificans progressiva: a randomized, double-blind, placebo-controlled phase 2 trial
   human_rct / pubmed_garetosmab_fop_phase2_2023
   Peer-reviewed LUMINA-1 FOP trial of IV garetosmab 10 mg/kg every 4 weeks; relevant for activin A blockade and safety, but not an obesity or performance trial.
5. Regeneron Announces Positive Phase 3 Trial in Adults with Fibrodysplasia Ossificans Progressiva, Demonstrating that Garetosmab Prevents Greater than 99% of Abnormal Bone Formation
   company_regulatory / regeneron_garetosmab_optima_phase3_2025
   Sponsor/regulatory context for garetosmab in FOP, including investigational status and planned submissions; useful safety and development context, not a body-composition source.
6. GDF8 and activin A blockade protects against GLP-1-induced muscle loss while enhancing fat loss in obese male mice and non-human primates
   preclinical / nature_gdf8_activin_glp1_animals_2025
   Mechanism-adjacent mouse and non-human-primate study supporting the COURAGE logic: GDF8 plus activin A blockade during semaglutide exposure preserved or increased lean mass while increasing fat loss.
7. Pharmacokinetics and Pharmacodynamics of Garetosmab (Anti-Activin A): Results From a First-in-Human Phase 1 Study
   human_rct / pubmed_garetosmab_phase1_2020
   First-in-human garetosmab phase 1 study in healthy women; supports IV/SC exposure, total activin A target engagement, PK/PD, and early safety context.
8. Garetosmab in Fibrodysplasia Ossificans Progressiva: Clinical Pharmacology Results from the Phase 2 LUMINA-1 Trial
   human_rct / pubmed_garetosmab_lumina_clinpharm_2023
   Clinical pharmacology from phase 2 LUMINA-1; supports IV dosing, PK/PD, BMP9, immunogenicity, and exposure-response context for activin A blockade.
9. Characterization of flare-ups and impact of garetosmab in adults with fibrodysplasia ossificans progressiva: a post hoc analysis of the randomized, double-blind, placebo-controlled LUMINA-1 trial
   human_rct / pubmed_garetosmab_lumina_flareups_2024
   Post hoc phase 2 LUMINA-1 FOP analysis; disease-specific context for garetosmab effects on flare-ups and heterotopic ossification biology.