Scholar Rock Holding Corp. SRRK, -9.77% shares dropped 11% in active Thursday trade after Pfizer Inc. PFE, +0.00% announced it plans to stop two ongoing clinical trials for a similar rare-disease drug. The Pfizer drug in question, domagrozumab, was designed to block a protein that is involved in muscle growth called myostatin; the therapy was being developed for the rare disease Duchenne muscular dystrophy but the company decided there wasn't evidence of a "significant treatment effect." Scholar Rock's lead therapy, SRK-015, also targets myostatin but for other disorders, including a rare disease called spinal muscular atrophy. SRK-015, currently in a phase 1 trial for SMA, is the furthest-along product in Scholar Rock's pipeline; the medication is also in preclinical development for other myostatin-related disorders. But Wedbush analyst David Nierengarten described the development as a buying opportunity, since a myostatin inhibitor would likely need to be paired with another therapy to substantively show improvement in a disease like DMD. "Although SRRK has not formally announced its strategy in DMD, we see the setting as ideal for lead candidate SRK-015, which could complement the gene therapies that are in development from Sarepta SRPT, +0.18% Solid Bio SLDB, +5.40% and Pfizer...Neither SRPT and SLDB have anti-myostatin programs of their own," he said, adding that SRK-015 "should be more selective and provide an improved therapeutic window relative to programs like doma which target mature myostatin." Phase 1 safety data for the therapy could be available before the end of the year, providing a catalyst for Scholar Rock shares, according to Nierengarten. Solid Biosciences had shares rise 7% in Thursday trade, while Sarepta shares lifted 1.2%. Scholar Rock shares have still gained 8.7% since May 24, the day they went public, while the S&P 500 SPX, -0.45% has gained 6.6% over the same time.
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