Scholar Rock Outlines Pivotal Apitegromab Trial Design In Spinal Muscular Atrophy Patients

Scholar Rock Holding Corp SRRK announced the study design for the SAPPHIRE Phase 3 trial of apitegromab, a selective inhibitor of the activation of latent myostatin. The trial will evaluate the efficacy and safety of apitegromab in patients with non-ambulatory Type 2 and Type 3 spinal muscular atrophy (SMA). 

• Study start-up activities for SAPPHIRE have commenced.
• Approximately 156 patients aged 2-12 years old with non-ambulatory Type 2/3 SMA will be enrolled in the primary efficacy population. 
• Patients will be randomized 1:1:1 to receive for 12 months either apitegromab 10 mg/kg, apitegromab 20 mg/kg, or placebo by intravenous infusion every four weeks added on top of background SMN treatment. 
• Patients receiving the background SMN treatment of nusinersen or risdiplam will be eligible for enrollment.
• The primary efficacy endpoint will evaluate the mean change from baseline in the Expanded Hammersmith Functional Motor Scale (HFMSE) total score after 12 months of treatment.
• An exploratory population of 48 patients aged 13-21 years old with non-ambulatory Type 2/3 SMA will be evaluated separately. 
• These patients will be randomized 2:1 to receive either apitegromab 20 mg/kg or placebo added to background SMN treatment with nusinersen or risdiplam. 
• To further characterize apitegromab, upon completion of the 12-month treatment period, all patients will be offered the option of enrolling in an open-label extension study. 
•  In addition, the TOPAZ Phase 2 extension continues to follow patients and evaluate the longer-term efficacy and safety of apitegromab. 
• Related Link: Why Did Scholar Rock Shares Drop Despite Positive Apitegromab Data In Spinal Muscular Atrophy.
• Price Action: SRRK shares closed 4.23% higher at $26.55 on Tuesday.