# Apitegromab

> A monoclonal antibody that selectively blocks pro/latent myostatin — the muscle brake — studied to preserve lean mass during GLP-1 weight loss.

- Also known as: SRK-015, SRK-439
- Class: Growth Hormone, Metabolic
- FDA approved: No
- Canonical page: https://www.americanpeptide.com/catalog/apitegromab

## Overview

Apitegromab is a fully human monoclonal antibody (Scholar Rock) and the first of the anti-myostatin biologics in this catalog. Where myostatin is the growth factor that brakes muscle and follistatin is the body’s natural antagonist, apitegromab is an engineered antagonist: an antibody that binds the inactive precursor forms of myostatin (pro- and latent myostatin) and prevents their activation. Its selectivity for those precursors — rather than mature myostatin or the related GDF11/activins — is its defining design feature.

Apitegromab’s lead program is in spinal muscular atrophy (SMA), where it is added on top of SMN-targeted therapy to build motor-relevant muscle. The same mechanism underlies its forward-looking metabolic use: in the Phase 2 EMBRAZE study, adding apitegromab to tirzepatide preserved lean mass during weight loss compared with tirzepatide alone, and its precursor-selectivity was framed as a potential tolerability advantage over broader myostatin/activin blockers.

As a biologic it sits a full step beyond the protein hormones elsewhere in this catalog: it is an antibody (~150 kDa), produced in mammalian cells, designed to deplete a specific target. It is investigational — not an approved drug — and is included here as the antibody arm of the myostatin axis that myostatin and follistatin introduce.

## Mechanism

Binds pro-myostatin and latent myostatin, blocking the proteolytic activation that releases mature, active myostatin. Lowering active myostatin disinhibits muscle growth via the ActRIIB/Smad pathway.

## Chemistry

| Property | Value |
| --- | --- |
| Molecular weight | 150000 Da |

## Research areas

Studied in: Spinal muscular atrophy, Muscle preservation, GLP-1 muscle preservation, Body composition.

Guides on this site:

- [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

- Precursor-selective — binds pro/latent myostatin rather than mature myostatin or GDF11/activins, the basis of its selectivity claim.
- SMA — the lead clinical program, building muscle on top of SMN-directed therapy.
- GLP-1 muscle preservation — Phase 2 EMBRAZE preserved lean mass when added to tirzepatide.
- Antibody biologic — a ~150 kDa monoclonal antibody, the far end of the biologic spectrum from synthetic peptides.
- Investigational — not FDA-approved.

## Storage, handling & synthesis

**Storage.** Monoclonal antibodies are stored refrigerated (2–8 °C), protected from light and freezing, and never shaken. Investigational handling follows the trial protocol.

**Handling.** A large folded, glycosylated antibody — sensitive to freezing, heat, and agitation, which can aggregate it. Aggregation is an immunogenicity concern.

**Synthesis.** Apitegromab is a recombinant monoclonal antibody (~150 kDa) produced in mammalian cell culture — the most complex biologic class in this catalog, far removed from solid-phase peptide synthesis. Characterization is antibody-grade: glycan and charge-variant profiling, identity by mass spectrometry, and target-binding/cell-based potency, with host-cell-protein and endotoxin limits.

## FAQs

### What is apitegromab?

A monoclonal antibody that selectively blocks the precursor forms of myostatin, the growth factor that limits muscle. It is studied in spinal muscular atrophy and, in combination with GLP-1/GIP drugs, to preserve muscle during weight loss.

### How is it different from blocking mature myostatin?

Apitegromab targets pro- and latent (inactive) myostatin before it is activated, rather than the mature protein — a selectivity intended to avoid hitting related factors and improve tolerability.

### Is this medical advice?

No — this is a research and educational reference. Apitegromab is an investigational antibody, not an approved drug.

## Latest research

Recent trials and publications mentioning Apitegromab, pulled automatically from ClinicalTrials.gov and PubMed (unfiltered search results, refreshed daily).

### Recent trials

- [A Study to Evaluate How Apitegromab Works in Subjects Who Are Less Than 2 Years Old and Have Spinal Muscular Atrophy](https://clinicaltrials.gov/study/NCT07047144) — RECRUITING · PHASE2 · NCT07047144
- [EAP of Apitegromab for Patients With Spinal Muscular Atrophy](https://clinicaltrials.gov/study/NCT06877689) — NO_LONGER_AVAILABLE · NCT06877689
- [Phase 2 Study Evaluating Apitegromab for the Treatment of FSHD](https://clinicaltrials.gov/study/NCT07435129) — NOT_YET_RECRUITING · PHASE2 · NCT07435129
- [Efficacy and Safety of Apitegromab for the Treatment of Adults Who Are Overweight or Obese](https://clinicaltrials.gov/study/NCT06445075) — COMPLETED · PHASE2 · NCT06445075
- [Efficacy and Safety of Apitegromab in Patients With Later-Onset Spinal Muscular Atrophy Treated With Nusinersen or Risdiplam](https://clinicaltrials.gov/study/NCT05156320) — COMPLETED · PHASE3 · NCT05156320
- [Long-Term Safety & Efficacy of Apitegromab in Patients With SMA Who Completed Previous Trials of Apitegromab](https://clinicaltrials.gov/study/NCT05626855) — ACTIVE_NOT_RECRUITING · PHASE3 · NCT05626855

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Source: AmericanPeptide.com — https://www.americanpeptide.com/catalog/apitegromab
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.