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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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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