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Sarepta’s Stocks Drop 50% Following Middling Trial Data for Gene Therapy
On January 7th, Sarepta Therapeutics reported the first part results of its Phase 2 clinical trial that evaluated the gene transfer therapy, SRP-9001. Although the delivery of the therapy increased the target protein, the candidate failed to significantly improve patients’ motor skills. The news resulted in the stock of the company falling over 50%.
Duchenne Muscular Dystrophy (DMD) is a rare genetic, progressive, and potentially deadly neuromuscular disease that affects over 16,000 people in the US. DMD is caused by mutations in the DMD gene responsible, which codes for a protein key to muscle health known as dystrophin. Lack of this protein results in muscle weakness and atrophy. The symptoms are first noticeable in early childhood and when the atrophy extends to the heart muscles, which results in life-threatening complications.
There are few FDA approved treatments, including corticosteroids such as Emflaza and exon skipping therapies such as Exondys 51, Vyondys 53, and Viltepso. Only Emflaza can be used to treat most patients, while exon skipping therapies can only be used with a small subpopulation of patients. More treatments are necessary that can be used to slow down or cure DMD.
Phase 2 Trial of SRP-9001
SRP-9001 is a gene therapy that delivers a shortened version of the DMD gene into the patient’s cells. SRP-9001 gives the cells the instructions to produce mini-dystrophin, which could compensate for the lack of normal protein and slow down the disease.
The efficacy of SRP-9001 was tested on a double-blind, randomized, placebo-controlled Phase 2 clinical trial known as Study 102. For the study, 41 patients between the ages of 4-7 years old were given a single dose of SRP-9001. The levels of mini-dystrophin were determined 12-weeks after injection, and the total change on the North Star Ambulatory Assessment (NSAA), which measures motor skills, was determined at 48 weeks post injections. Treatment with SRP-9001 resulted in significantly higher expression mini-dystrophin.
However, the treatment failed to significantly improve the NSAA score compared to the placebo group. Although, the company shows data claiming that the lack of significance could be explained by an imbalance in the starting NSAA score of patients. The company claims that patients with better scores were randomly assigned to the placebo group than to the treatment group. This possible explanation, however, did not prevent the company’s stock from crashing more than 50%.
The company still plans to continue with the second part of the clinical trial and expressed confidence in the treatment. Doug Ingram, President, and Chief Executive Officer of Sarepta, said, “Study 102 remains blinded, and we will analyze the functional results for all patients, including cross-over participants, once they have achieved the 48-week timepoint in Part 2. We have already enrolled and dosed 11 participants in Study 103, using our commercial process material, and we will have biomarker and safety results from that cohort in the second quarter. And very importantly, Study 102 has provided us with a wealth of information and insight, which we will use to refine and complete the protocol for our upcoming trial using commercial process material. We intend to continue to move forward with diligence and urgency to generate the evidence necessary to bring SRP-9001 to waiting Duchenne patients around the world.”
By Daniel Ojeda, Ph.D.
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