Apitegromab Shows ‘Robust’ Motor Improvement in Phase 3 SMA Trial Update

Experimental spinal muscular atrophy (SMA) drug apitegromab showed promising results in a large, late-stage clinical trial, positioning the therapy for regulatory approval early next year.

The phase 3 SAPPHIRE trial tested apitegromab in 188 patients with SMA who were already taking approved treatments, according to a press release by the drug’s maker, Scholar Rock. The study met its primary endpoint and demonstrated statistical significance, with approximately 30% of patients on apitegromab achieving a 3-point or greater improvement in a motor function score, compared to about 13% of patients in the placebo arm.

"The results clearly demonstrate robust and clinically meaningful improvement in motor function in patients with SMA," said Jay Backstrom, CEO of Scholar Rock, in the company's press release. “We look forward to submitting our applications to the FDA and the [European Medicines Agency (EMA)] in Q1 2025,” the company’s Chief Medical Officer, Jing Marantz, M.D., Ph.D., said in the statement.

Apitegromab works by targeting a protein called myostatin that limits muscle growth. It's designed to be used alongside existing SMA treatments Spinraza (nusinersen), Evrysdi (risdiplam) and Zolgensma (onasemnogene abeparvovec-xioi) to further improve muscle strength. The drug has already received Fast Track, Orphan Drug and Rare Pediatric Disease designations from the FDA, and Priority Medicines (PRIME) and Orphan Medicinal Product designations from the EMA.

Most patients in the study were children aged 2-12, but an exploratory arm included patients aged 13-21, a population that isn’t typically included in trials, given the progressive loss of motor function with the disease. Patients in this expanded arm also saw motor function outcomes consistent with the younger patient group, the company said. Patients received either apitegromab or a placebo through IV infusions every four weeks for a year. The drug appeared to be safe, with side effects similar to previous studies. Common issues included fever, cough, and upper respiratory infections.

“It’s a great day for people living with SMA and their families,” said Kenneth Hobby, President of Cure SMA, in Scholar Rock’s press release. “These encouraging trial results mark a critical milestone for the SMA community.”

The company plans to present preliminary baseline characteristics of the trial at the Annual Congress of the World Muscle Society on Friday, October 11, being held in Prague, Czech Republic.