Scholar Rock is looking to file for regulatory approval in the US and EU after the positive data. Image credit: Shutterstock / eamesBot

Scholar Rock’s stock has soared off the back of positive Phase III results from its spinal muscular atrophy (SMA) candidate.

The Phase III SAPPHIRE trial (NCT05156320) evaluating Scholar Rock’s lead pipeline candidate apitegromab, met its primary endpoint of statistically significant and clinically meaningful improvement in motor function, as measured by the Hammersmith Functional Motor Scale Expanded (HFMSE).

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The company’s stock price rocketed by 362% after the news dropped, from a 4 October close of $7.42 to a close of $34.28 yesterday (7 October).

The company said it will look to file a Biologics License Application (BLA) to the US Food and Drug Administration (FDA) and a marketing authorisation application (MAA) to the European Union in Q1 2025.

Apitegromab is a monoclonal antibody that inhibits myostatin activation by selectively binding the pro- and latent forms of myostatin in the skeletal muscle. It is the first muscle-targeted treatment candidate to demonstrate clinical proof-of-concept in SMA.

Kenneth Hobby, President of Cure SMA, said: “It’s a great day for people living with SMA and their families. These encouraging trial results mark a critical milestone for the SMA community. Declining motor function and hopes for reversing losses associated with muscle weakness are significant unmet needs, impacting activities of daily living, from breathing, eating, self-care, to working and social interactions. We need an approved therapy that can support motor function and further improve daily activities for people with SMA.”

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In the main population, aged 2-12, the mean difference in change from baseline in HFMSE was 1.8 points for all patients receiving apitegromab, compared to placebo, with improvement measured as early as eight weeks. Patients receiving 20mg/kg of apitegromab showed a 1.4-point difference while the 10mg/kg cohort showed an improvement of 2.2 points.

The exploratory population, aged 13-21, also favoured apitegromab compared to placebo in motor function improvement.

There was more than a three-point improvement in HFMSE in 30% of apitegromab patients versus 12.5% of patients on placebo.

Treatment was well tolerated, and the safety profile was consistent with previous studies. Following trial completion, 98% of SAPPHIRE patients enrolled in the ongoing ONYX open-label expansion study.

President and Chief Executive Officer of Scholar Rock, Dr. Jay Backstrom said: “We are thrilled that apitegromab met the primary endpoint in our Phase III SAPPHIRE clinical study. The results clearly demonstrate robust and clinically meaningful improvement in motor function in patients with SMA. At Scholar Rock, we are working with urgency to deliver the potentially transformative benefits of apitegromab to children and adults with SMA in the US, Europe, and around the world.”

The FDA granted Fast Track, Orphan Drug, and Rare Paediatric Disease designations to apitegromab while the European Medicines Agency (EMA) has granted Priority Medicines (PRIME) and Orphan Medicinal Product designations.

Analyses of the full Phase III SAPPHIRE data are ongoing, with a detailed presentation to take place at a 2025 medical conference. Scholar Rock is also investigating apitegromab alongside a glucagon-like peptide-1 receptor agonist (GLP-1ra) in patients with obesity in a Phase II trial.

SMA is a rare neuromuscular disorder that results in the loss of motor neurons and progressive muscle wasting. It is usually diagnosed in infancy or early childhood. Current treatments include Spinraza (nusinersen), Evrysdi (risdiplam) and Zolgensma (onasemnogene abeparvovec).

According to GlobalData, 50 drugs are currently being developed for SMA. GlobalData is the parent company of the Clinical Trials Arena.