Scholar Rock’s spinal muscular atrophy (SMA) therapy has shown benefit in muscle function in children under 12 in a pivotal study, but investors are not impressed.
The Phase III SAPPHIRE trial (NCT05156320) evaluated the safety and efficacy of apitegromab, a monoclonal antibody that inhibits myostatin activation by selectively binding the proforms and latent forms of myostatin in the skeletal muscle.
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Scholar Rock said the therapy met secondary endpoints in predefined subgroups, including patients aged two to 12. Patients on the study drug benefitted from a consistent improvement in motor function as per the Hammersmith Functional Motor Scale Expanded (HFMSE) versus placebo across all five-point thresholds after one year.
Efficacy was also consistent across patient outcome measures of motor function, according to the Revised Upper Limb Module (RULM) and World Health Organization (WHO) motor development milestones.
Scholar Rock president and CEO Dr Jay Backstrom said: “Progressive muscle weakness robs many people with SMA of the motor function needed for the most basic activities, despite current SMN-targeted treatments, and the SMA community has clearly been asking for more.
“We are thrilled with the consistency of clinical benefit demonstrated across important outcome measures in all patient subgroups and now are urgently preparing to commercialise apitegromab in the US, Europe and additional countries where patients with SMA can benefit from therapy.”
Despite Scholar Rock hailing the data as positive, the company’s stock, listed on the Nasdaq exchange, is set to drop by 7.49% (correct at 6am EDT) at market open today (17 March), according to the pre-market estimates.
The new data is set to be presented at the 2025 Muscular Dystrophy Association (MDA) Clinical & Scientific Conference in Dallas, Texas.
The company previously announced the Phase III study met the primary endpoint of statistically and clinically meaningful improvement on the Hammersmith Functional Motor Scale Expanded (HFMSE). This update caused a 362% increase in the company’s stock price which has remained relatively stable since.
The new analysis, published alongside secondary endpoint data, has shown clinically meaningful and consistent improvement in HFMSE across pre-specified subgroups and geographic regions.
The therapy remained well-tolerated and serious adverse events (SAEs) were consistent with underlying disease and SMN-targeted therapy. There were no SAEs assessed as related to apitegromab.
According to GlobalData analysis, the SMA market across the seven major markets (7MM: US, France, Germany, Italy, Spain, UK, and Japan) is set to grow from $2.7bn in 2023 to $3bn in 2033. GlobalData anticipates that this growth will be driven in part by the approval of three SMA therapies, including Scholar Rock’s apitegromab. Other impactful therapies are set to be Roche’s RG-6237 and Biohaven’s talditercept alfa which also aim to improve muscle strength and function in patients with SMA.
GlobalData is the parent company of Clinical Trials Arena.
Novartis is also targeting the SMA market with its gene therapy Zolgensma (onasemnogene abeparvovec) which reached its primary endpoint in a Phase III study (NCT05089656) in paediatric patients aged two to 17 years with type II SMA.
