Sarepta shares rally on early DMD data that also reveal 2 serious, 79 mild side effects

Two weeks after Sarepta reported new safety concerns in a Duchenne muscular dystrophy (DMD) clinical trial, the company says another gene therapy candidate has shown some early success and will be brought to the FDA for permission to kick off further testing.

Sarepta again noted some serious side effects, this time in two patients. In all, investigators tallied 79 side effects among the small trial population of 11 patients.

In a conference call with investors Tuesday morning, the company dubbed the side effects mostly mild, including vomiting that came on in the first week and was resolved quickly. The side effects were consistent with earlier testing, executives said. 

Forever the cheerleader for Sarepta’s mixed clinical research results, CEO Doug Ingram added that SRP-9001 worked “with no new or unexpected safety signals.”

Investors seemed to agree, pushing the price of Sarepta’s shares over 11% to $83.50 as of 12:35 p.m. ET.

SRP-9001 is a gene therapy designed to deliver the microdystrophin-encoding gene into the muscle tissue to prompt production of the microdystrophin protein. Patients with DMD have a mutation in the DMD gene and can’t make the protein on their own, leading to a progressive loss of muscle strength.

RELATED: Sarepta thinks it may have a more effective DMD drug, but new side effects could be a problem

The gene therapy is being tested in a phase 1 clinical trial called ENDEAVOR, or Study 103, conducted in partnership with Roche. After 12 weeks, the study found that SRP-9001 demonstrated “robust” expression of microdystrophin with no new safety signals flagged in the 11 patients for whom data were available. The study has a total of 20 people enrolled.

Of the two patients who suffered serious adverse events, one had heightened levels of a liver enzyme called transaminases, which can signal problems with the liver. Another patient had nausea and vomiting. Sarepta said there were no signs of liver function impairment in any patients.

Increased transaminases is a known side effect of AAV-based gene therapies, a spokesperson for Sarepta said. Both of the serious adverse events were fully resolved. 

Sarepta said the early efficacy evidence suggests SRP-9001 could have a differentiated profile for DMD treatment compared to its other therapies. SRP-5051, for example, spurs a process called exon-skipping to jump-start production of the dystrophin protein.

“We are delighted by these seminal results from the Endeavor Study, our first trial results with SRP-9001 made by our commercial-scale manufacturing process,” Ingram said in a statement.

Cambridge, Massachusetts-based Sarepta reported earlier in May that new serious adverse events had been discovered in a phase 2 clinical trial testing SRP-5051. Two patients suffered a critical drop in magnesium levels, called hypomagnesemia, and another patient’s potassium levels plummeted. All the patients were treated, and the concerns were resolved quickly, Sarepta said at the time.

The Sarepta spokesperson said hypomagnesemia is something they will now track and treat with oral supplements to prevent any future events—a statement RBC Capital Markets analysts agreed would resolve concerns. The same concern has not cropped up in studies of SRP-9001.

The next steps for SRP-9001 will be for Sarepta to meet with the FDA and other regulatory agencies, starting midyear, to move forward with Study 301. The company will also expand Study 103 to include older ambulant and non-ambulant patients.