FDA Prioritizes Review of Apitegromab BLA for Spinal Muscular Atrophy Treatment

CAMBRIDGE, Mass.—Scholar Rock, a biopharmaceutical organization known for its cutting-edge treatments for severe illnesses such as neuromuscular and cardiometabolic disorders, reported that the U.S. Food and Drug Administration (FDA) has accepted its Biologics License Application (BLA) for apitegromab. This investigational therapy targets muscle improvement in patients with spinal muscular atrophy (SMA) who are already undergoing treatment aimed at SMN (survival motor neuron). The FDA has decided to evaluate the application under a priority review, setting a Prescription Drug User Fee Act (PDUFA) target action date for September 22, 2025. A priority review suggests that, pending approval, apitegromab could mark a significant advancement in the treatment of SMA, a serious disorder.

In parallel, Scholar Rock has also filed for a Marketing Authorisation Application (MAA) with the European Medicines Agency (EMA) for apitegromab, which has been validated, paving the way for a formal review process to commence. Jay Backstrom, M.D., MPH, President and CEO of Scholar Rock, expressed optimism about the priority review designation, which reflects the potential impact of apitegromab as a groundbreaking therapy for SMA patients. He also highlighted the positive reception of the application by the EMA and the company's readiness to collaborate with regulatory bodies to introduce apitegromab to the SMA community, while preparing for a commercial rollout in the U.S.

The BLA submission for apitegromab draws upon successful efficacy and safety findings from the pivotal Phase 3 SAPPHIRE trial, in addition to supportive data from the Phase 2 TOPAZ trial and the long-term ONYX extension study. Earlier this year, the promising results were shared during the 2025 Muscular Dystrophy Association (MDA) Clinical & Scientific Conference. The SAPPHIRE trial's primary endpoint was achieved, showing a substantial and meaningful improvement in motor function among SMA patients treated with apitegromab alongside standard SMN-targeted therapies (nusinersen or risdiplam), compared to a placebo control. This was determined using the Hammersmith Functional Motor Scale Expanded (HFMSE), a widely recognized measurement for motor function.

In anticipation of potential regulatory approvals, Scholar Rock is preparing for a U.S. commercial launch of apitegromab in 2025, with an expected European launch the following year.

Apitegromab is a novel fully human monoclonal antibody that inhibits the activation of myostatin by binding selectively to its pro- and latent forms in skeletal muscle. It is the first muscle-focused treatment for SMA that has demonstrated clinical efficacy in a pivotal Phase 3 trial. Myostatin, part of the TGFβ superfamily, is predominantly produced by skeletal muscle cells, and its gene's absence is linked to increased muscle mass and strength in various species, including humans. Scholar Rock's precise targeting of myostatin with apitegromab may lead to notable motor function improvements in SMA patients. The FDA has awarded Fast Track, Orphan Drug, and Rare Pediatric Disease designations to apitegromab for SMA treatment, while the EMA has granted it Priority Medicines (PRIME) and Orphan Medicinal Product designations. However, apitegromab has not yet received approval for any use by the FDA or any other regulatory bodies.

The SAPPHIRE clinical trial was a Phase 3 study, designed as a randomized, double-blind, placebo-controlled experiment to assess apitegromab's safety and efficacy in nonambulatory patients with Types 2 and 3 SMA, who were already receiving standard treatments like nusinersen or risdiplam. Enrolling 156 patients aged 2-12 as the main efficacy cohort, participants were randomized to receive varying doses of apitegromab or a placebo by intravenous infusion over 12 months. An exploratory cohort of older patients was also included. The trial met its primary endpoint, showing a statistically significant improvement in motor function.

Scholar Rock continues to lead in the development of therapies for diseases with high unmet needs, driven by a proprietary platform that offers selective monoclonal antibody solutions targeting growth factors. This innovative approach has the potential to reshape treatment standards across multiple serious conditions.