Scholar Rock's SMA Drug Shows Promise in Obesity Treatment, Preserving Muscle Mass

Scholar Rock's investigational spinal muscular atrophy (SMA) drug, apitegromab, has demonstrated potential in addressing a key challenge in obesity treatment: muscle mass preservation. In a recent phase 2 trial, the drug helped patients taking Eli Lilly's obesity medication Zepbound (tirzepatide) maintain muscle mass, offering a new approach to achieving higher quality weight loss.

Apitegromab's Impact on Lean Mass Retention

The midstage study revealed that patients taking Zepbound alone experienced a 30.2% loss in lean mass as part of their total weight loss. However, when 10 mg/kg of apitegromab was added to the tirzepatide regimen, the proportion of lean mass lost was reduced to 14.6% over 24 weeks.

Patients receiving the apitegromab-tirzepatide combination achieved what Scholar Rock describes as "higher quality of weight loss." These patients lost 85% fat mass and 15% lean mass, compared to a 70% fat mass and 30% lean mass ratio in the tirzepatide-placebo group.

Total weight loss was comparable between the two groups, with apitegromab-tirzepatide patients losing 12.3% of their weight versus 13.4% for those on tirzepatide-placebo.

Safety Profile and Market Implications

Apitegromab, an inhibitor of myostatin activation, was reported to be "generally well tolerated" in the trial. No serious adverse events or treatment discontinuations related to apitegromab were observed.

The positive results from this study have potential implications beyond SMA treatment, for which apitegromab is currently under FDA review with a decision expected by September. The findings suggest broader applications in the rapidly growing obesity market, where muscle preservation is becoming a key differentiator among competing therapies.

Industry Landscape and Future Prospects

The focus on muscle preservation in obesity treatment is gaining traction across the pharmaceutical industry. Companies like Roche and Regeneron have acquired obesity assets to pair with their existing muscle drug candidates. Eli Lilly recently partnered with Juvena Therapeutics to improve muscle health and body composition in obesity treatment.

Akshay Vaishnaw, M.D., Ph.D., president of R&D at Scholar Rock, emphasized the importance of addressing muscle loss in GLP-1 therapies: "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."

While expressing excitement about the potential applications in obesity treatment, Scholar Rock remains focused on the potential launch of apitegromab for SMA, pending FDA approval. The company's stock saw a 5% increase in premarket trading following the announcement of these results.