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Sarepta, in shadow of FDA setback, marks gene therapy progress

Three patients with a type of limb-girdle muscular dystrophy were able to stand up, walk and run faster after treatment with Sarepta Therapeutics’ gene therapy SRP-9003, which is on track to begin testing with a higher dose.SRP-9003 is one of three gene therapies Sarepta is developing for limb-girdle muscular dystrophies that target a type of the protein sarcogylcan, which protects muscles from damage. The data will be formally presented to physicians Saturday at a conference of the World Muscle Society.Shares rose about 7% following the data release Friday morning. Sarepta has been buffeted by the Food and Drug Administration’s rejection of golodirsen and the submission of a competing candidate from NS Pharma to the agency.

Behind its marketed Duchenne muscular dystrophy product Exondys 51 (eteplirsen), Sarepta has built a broad pipeline of treatments for different types of muscular dystrophy.

In limb-girdle muscular dystrophy, three are in the clinic. Two stimulate production of a type of sarcoglycan, and a third focuses on another protein called dysferlin. Meanwhile, another sarcoglycan-stimulating candidate is in pre-clinical research.

Sarepta is testing SRP-9003 in patients with limb-girdle muscular dystrophy type 2E, where absence of beta-sarcoglycan leads to progressive weakness in the arms and legs. The first three patients received a dose of 50 trillion vector genomes per kilogram of body weight carrying a transgene encoding for beta sarcoglycan. So far the three have been followed for more than 270 days.

At that time point, the patients showed an improvement of one, six and six points on a functional test called the North Star Assessment, along with registering faster times standing up, running, walking and climbing stairs. By comparison, analysis of data from similar, but untreated, muscular dystrophy patients showed a decline in almost every case.

Two of the patients had elevated liver enzymes, one case of which was classified as a serious adverse event. In both cases, steroid treatment — taken to prevent an immune response to the viral vectors used to deliver the therapy — had been previously reduced. Enzyme counts returned to normal after resumption of steroid treatment.

RBC Analyst Brian Abraham wrote in a note to clients today that the data suggest Sarepta might succeed in an “underappreciated, $2.5B opportunity” in limb-girdle muscular dystrophy.

The data are a bright spot after a disappointing few weeks for Sarepta, in which shares tumbled from an all-time high of $156.91 in mid-July.

In August, the FDA delivered a Complete Response Letter for the experimental DMD drug Vyondys 53 (golodirsen) due to infection risk and preclinical kidney toxicity, according to the company.

Meanwhile, competitor Nippon Shinyaku this week announced it had submitted to the FDA a Vyondys competitor called viltolarsen, which aims to treat DMD amenable to exon 53 skipping. The timing of the viltolarsen submission suggests that Nippon Shinyaku could launch it before Vyondys.