Scholar Rock is developing Apitegromab, formerly known as SRK-015, a drug that specifically blocks the latent form of myostatin in order to increase muscle mass and potentially treat spinal muscular atrophy (SMA). Myostatin is a member of the TGF-beta superfamily of growth factors, and the specificity of Apitegromab is intended to prevent the drug from blocking the myostatin receptor, activated myostatin, or any other member of this superfamily, thus greatly reducing the risk of side effects.
Apitegromab is currently in an extension period of a Phase 2 clinical trial for Type 2 and Type 3 SMA, and while this drug is being developed for a specific disorder, its application for other, age-related disorders is obvious. It could potentially be used to combat sarcopenia, the age-related loss of muscle mass and strength that many older people experience and that leads to frailty and increased risk of falls and injury.
In April 2021, Scholar Rock announced via a press release positive 12-month top-line results of its Phase 2 trial of Apitegromab. A majority of patients had meaningful motor function improvements with a ≥1-point increase in Hammersmith Functional Motor Scale Expanded (HFMSE). The company has received Fast Track designation from the FDA and is planning a Phase 3 trial in patients with Type 2 and Type 3 SMA by the end of 2021.
Phase 1 trial results for Apitegromab
A Phase 3 Double-Blind, Placebo-Controlled Trial to Evaluate the Efficacy and Safety of Apitegromab (SRK-015) in Patients With Later-Onset Spinal Muscular Atrophy was completed in December 2024. As of March 2025, the U.S. Food and Drug Administration (FDA) has accepted the Biologics License Application (BLA) for Apitegromab under priority review, with a target action date of September 22, 2025. Similarly, the European Medicines Agency (EMA) has validated the Marketing Authorization Application (MAA) for Apitegromab, initiating the formal review process in Europe.
References: Pirruccello-Straub, M., Jackson, J., Wawersik, S., Webster, M. T., Salta, L., Long, K., … & Mahanthappa, N. K. (2018). Blocking extracellular activation of myostatin as a strategy for treating muscle wasting. Scientific
reports, 8(1), 2292.
