With Monday’s data from SAPPHIRE, Scholar Rock is building toward regulatory submissions for apitegromab in spinal muscular atrophy in the first quarter of 2025.
Scholar Rock on Monday announced that its investigational myostatin blocker apitegromab aced the Phase III SAPPHIRE trial in spinal muscular atrophy, demonstrating significant improvement in motor function.
At 52 weeks, patients aged two to 12 years who were treated with either 10-mg/kg and 20-mg/kg doses of apitegromab saw a 1.8-point improvement on the Hammersmith Functional Motor Scale Expanded (HFMSE) tool versus placebo, an effect that was “statistically significant and clinically meaningful,” with a p-value of 0.0192, according to the company’s announcement.
According to Scholar Rock, the HFMSE is the “gold standard” metric for motor function in spinal muscular atrophy. In the trial, 30% of apitegromab-treated patients saw at least a 3-point improvement in HFMSE, versus 12.5% of placebo comparators. Apitegromab’s motor function benefits were apparent as early as 8 weeks into treatment and expanded through 52 weeks.
Scholar Rock’s stock surged as much as 335% on Monday in reaction to the readout, according to Seeking Alpha.
CEO Jay Backstrom said in a statement that the company is “thrilled” by SAPPHIRE’s data, which “clearly demonstrate robust and clinically meaningful improvement in motor function in patients with SMA (spinal muscular atrophy).” The company is “working with urgency” to make apitegromab available to patients around the world, according to Backstrom, with regulatory submissions planned for the first quarter of 2025.
In an investor note, Jefferies analyst Michael Yee said that Monday’s readout from SAPPHIRE was “an upside surprise to the market,” given that many investors expected apitegromab to fail. The strong Phase III data will also help “de-risk” Scholar Rock’s pipeline and platform, according to Yee.
Trust Securities’ Srikripa Devarakonda agrees, noting that Scholar Rock now has a strong regulatory case for apitegromab. “In our view, Ph3 SAPPHIRE data support Apitegromab approval with possibility of a broad labe,” covering patients ages two to 21.
Afflicting around 30,000 to 35,000 people in the U.S. and Europe, SMA is a rare genetic disease characterized by loss of motor neurons and the atrophy of voluntary muscles, particularly in the limbs and the trunk. Patients with SMA suffer from progressive weakness and in its severe forms, the disease can also lead to difficulties in breathing.
Apitegromab, a fully human monoclonal antibody, works by targeting and inhibiting the activation of myostatin, a growth factor that is largely expressed in skeletal muscle cells. According to Scholar Rock, the absence of the myostatin gene has been linked with more muscle mass and strength, which in turn could lead to better motor function in SMA patients.
