Also known as: SRK-015, SRK015
Motor function improvement in spinal muscular atrophy (SMA)
Amount
10-20 mg/kg
Frequency
Every 4 weeks (Q4W)
Duration
12 months (pivotal study)
Route
IVTiming
Administered as IV infusion at clinical sites under medical supervision. Background SMN-targeted therapy (nusinersen or risdiplam) required in all patients.
Duration
12 months (extendable based on response)
Repeatable
Yes
CBC with differential
When: Baseline
Why: Baseline blood cell counts
CMP (Comprehensive Metabolic Panel)
When: Baseline
Why: Baseline liver and kidney function
Anti-drug antibody testing
When: Periodic
Why: Monitor for immunogenicity
Serum latent myostatin
When: Periodic
Why: Confirm pharmacodynamic target engagement
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Apitegromab (SRK-015) is a fully human monoclonal antibody of the IgG4-lambda subclass that selectively targets the pro- and latent forms of myostatin (promyostatin and latent myostatin), preventing myostatin activation in skeletal muscle. Unlike other myostatin pathway inhibitors that neutralize the active mature form, apitegromab works upstream by blocking the conversion of inactive myostatin to its active signaling form.
Developed by Scholar Rock (now partnered with Novo Nordisk for SMA), apitegromab has become the first muscle-targeted therapy to demonstrate clinical benefit in spinal muscular atrophy (SMA) in a Phase 3 trial. The compound has also shown promise for lean mass preservation during obesity treatment.
Apitegromab's mechanism is distinct from other myostatin inhibitors:
This upstream targeting approach differs fundamentally from:
SMA is a rare genetic neuromuscular disease caused by mutations in the SMN1 gene, leading to motor neuron degeneration and progressive muscle weakness. While SMN-targeted therapies (nusinersen/Spinraza, risdiplam/Evrysdi, onasemnogene abeparvovec/Zolgensma) address the genetic cause, patients often continue to experience muscle limitations because:
Apitegromab addresses this unmet need by reducing myostatin-mediated muscle suppression as an adjunct to ongoing SMN therapy.
The pivotal SAPPHIRE trial enrolled 188 nonambulatory patients with Types 2 and 3 SMA aged 2-21 years across 48 sites globally. All participants received ongoing SMN-targeted therapy (nusinersen or risdiplam).
| Outcome (12 months) | Apitegromab | Placebo |
|---|---|---|
| HFMSE change from baseline | +0.6 points | -1.2 points |
| Difference vs placebo | +1.8 points (p=0.019) | -- |
| Patients with >=3-point improvement | 30.4% | 12.5% |
| Patients with >=4-point improvement | 19.6% | 6.3% |
Scholar Rock also evaluated apitegromab in combination with tirzepatide for lean mass preservation in 100 adults with overweight or obesity:
| Outcome (24 weeks) | Apitegromab + Tirzepatide | Placebo + Tirzepatide |
|---|---|---|
| Total weight loss | -12.3% | -13.4% |
| Weight loss composition | 85% fat / 15% lean | 70% fat / 30% lean |
| Lean mass preserved | 54.9% (p=0.001) | Reference |
Apitegromab is not yet approved by any regulatory agency. The FDA CRL was related to manufacturing issues, not clinical concerns, and a BLA resubmission is planned. As a monoclonal antibody (~150 kDa), apitegromab cannot be obtained from peptide suppliers or compounding pharmacies and is only accessible through clinical trials or, upon approval, prescription.
A randomized phase 1 safety, pharmacokinetic and pharmacodynamic study of the novel myostatin inhibitor apitegromab (SRK-015): a potential treatment for spinal muscular atrophy, published in Advances in Therapy (Barrett D et al., 2021; PMID: 33963971):
Safety and efficacy of apitegromab in patients with spinal muscular atrophy types 2 and 3: the phase 2 TOPAZ study, published in Neurology (Crawford TO et al., 2024; PMID: 38330285):
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See real-world usage patterns alongside the clinical evidence above. Community-sourced, not clinically verified.
Based on 20+ community reports
View community protocolsApitegromab (SRK-015) is a fully human IgG4-lambda monoclonal antibody that selectively binds to the pro- and latent forms of myostatin, preventing its activation in skeletal muscle. Developed by Scholar Rock, it is the first muscle-targeted therapy to demonstrate clinical benefit in spinal muscular atrophy (SMA), achieving its primary endpoint in the Phase 3 SAPPHIRE trial with a statistically significant 1.8-point HFMSE improvement over placebo. It is also being explored for lean mass preservation during obesity treatment, with the Phase 2 EMBRAZE trial showing 54.9% lean mass preservation when combined with tirzepatide.
Research suggests the following potential benefits of Apitegromab: First muscle-targeted therapy with Phase 3 proof of concept in SMA. Selectively blocks myostatin activation without affecting GDF-11 or activin A. Demonstrated statistically significant motor function improvement in SAPPHIRE. Well-tolerated with safety profile comparable to placebo in SMA trials. Expanding into obesity/lean mass preservation (EMBRAZE trial with tirzepatide). These findings are based on available studies and the evidence level varies across different applications.
Apitegromab is primarily studied for: Motor function improvement in Types 2 and 3 spinal muscular atrophy, Adjunct to SMN-targeted therapies (nusinersen, risdiplam) in SMA, Lean mass preservation during GLP-1/GIP agonist-induced weight loss. Research is ongoing and the evidence base continues to develop. Not all potential applications have been validated in human clinical trials.
Reported side effects of Apitegromab include pyrexia (fever), nasopharyngitis, upper respiratory tract infection, cough, vomiting. Most reported side effects are mild and transient. Comprehensive human safety data may be limited. Consult the detailed side effects profile for full information.
Apitegromab is currently in the phase3 stage. In the United States, it is classified as Investigational. Regulations vary by country and may change.
Enobosarm (Ostarine/GTx-024): oral SARM for muscle preservation during GLP-1 weight loss. QUALITY Phase 2b positive. PLATEAU trial with tirzepatide planned.
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Bimagrumab (BYM338): activin type II receptor antibody for muscle preservation and fat loss. BELIEVE trial showed 22.1% weight loss with semaglutide combo.
This website is for educational and informational purposes only. The information provided is not intended to diagnose, treat, cure, or prevent any disease. Always consult with a qualified healthcare professional before using any peptide or supplement.
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Comprehensive guide to peptides for muscle growth and preservation — myostatin inhibitors (follistatin, bimagrumab, trevogrumab, apitegromab), IGF-1 pathway (IGF-1 LR3, MGF), and growth hormone secretagogues (ibutamoren, HGH) with clinical evidence and body recomp strategies.
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