Scholar Rock’s investigational spinal muscular atrophy drug helped patients taking Eli Lilly’s obesity blockbuster Zepbound maintain muscle mass, offering another avenue to reach a key goal for the obesity market.
The FDA is currently considering whether to approve apitegromab, an inhibitor of myostatin activation, to treat SMA by September. But today’s phase 2 readout suggests the drug could have wider applications.
The midstage study of patients with obesity showed that 30.2% of total weight loss with tirzepatide, the ingredient in Zepbound, was due to lean mass loss. Adding 10 mg/kg apitegromab therapy to the tirzepatide regimen resulted in halving the proportion of lean mass lost to 14.6%, according to 24-week data shared in Scholar Rock’s June 18 press release.
The company described the apitegromab-tirzepatide combo as resulting in “higher quality of weight loss.” Specifically, these patients lost 85% and 15% of their fat mass and lean mass, respectively, while the ratio for the tirzepatide-placebo cohort was 70% and 30%.
When it came to total weight lost, patients on apitegromab-tirzepatide saw their weight drop by 12.3% compared to 13.4% for those on tirzepatide-placebo.
Apitegromab was “generally well tolerated,” said Scholar Rock, which noted that none of the patients suffered serious adverse events or discontinuations related to apitegromab treatment.
Scholar Rock’s stock was up 5% to $32.80 in premarket trading Wednesday from a Tuesday closing price of $31.15.
Muscle preservation is increasingly seen as key way for rival weight-loss-focused biopharmas to carve out their own niche. Roche and Regeneron have both acquired obesity assets to pair with their existing muscle drug candidates, while Lilly penned a deal with Juvena Therapeutics last week centered on improving muscle health and body composition.
“GLP therapies have been an effective and important innovation for individuals living with obesity and cardiometabolic disorders; however, these treatments can result in substantial loss of lean muscle mass for patients, leading to unwanted health risks,” Akshay Vaishnaw, M.D., Ph.D., president of R&D at Scholar Rock, said in this morning’s release.
“We are pleased that the EMBRAZE trial accomplished its objective by achieving its primary endpoint,” Vaishnaw added. “The results validated our hypothesis that our platform of highly selective myostatin inhibitors has the potential to support healthier weight loss for millions of patients on GLP therapies by safely preserving lean mass.”
Despite this “exciting development,” Vaishnaw said Scholar Rock remains focused on preparing for the launch of apitegromab in SMA, assuming the FDA gives it the green light at the decision date in September.
The approval filing for apitegromab followed a phase 3 win in October 2024 that showed a 1.8-point improvement in motor function for SMA patients compared with placebo after 52 weeks.