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Pfizer's DMD Gene Therapy Fails to Meet Phase III Trial Endpoints

NEW YORK – Pfizer on Thursday said that the CIFFREO trial failed to meet its primary endpoint and that the study did not show that an investigational Duchenne muscular dystrophy (DMD) gene therapy significantly improved motor functions compared to placebo in young boys.

In the double-blind Phase III trial, Pfizer was comparing the activity of its mini-dystrophin gene therapy fordadistrogene movaparvovec against placebo in boys 4 to 7 years old with ambulatory DMD. As the primary endpoint, Pfizer used the North Star Ambulatory Assessment score to measure the change in patients' motor functions from baseline to one year after receiving treatment. Secondary endpoints included patients' velocity running or walking 10 meters, as well their velocity rising from the floor.

According to Pfizer, there were no significant differences in primary or secondary outcomes measures between patients on the gene therapy and those on a placebo. "Pfizer will continue to closely monitor all participants enrolled in the study and is evaluating appropriate next steps for the program," the company said in a statement.

Last month, after a young boy on fordadistrogene movaparvovec died suddenly of cardiac arrest in a different trial, dubbed DAYLIGHT, Pfizer said that as it investigated what happened, it would stop giving patients the gene therapy in the crossover portion of the CIFFREO trial, where patients were still receiving the gene therapy.

Now, with CIFFREO failing to meet its primary endpoint, Dan Levy, head of development for DMD at Pfizer, expressed disappointment in the results but added in a statement that the drug giant will share more detailed analysis at future medical and patient advocacy meetings so that the field can apply the learnings from the trial to future DMD therapy trials.

If Pfizer's gene therapy had been successful in clinical trials, it would have competed with Sarepta Therapeutics' Elevidys (delandistrogene moxeparvovec-rokl). The US Food and Drug Administration granted accelerated approval to Sarepta's DMD gene therapy last year for treating patients who are 4 or 5 years old, even though the company had sought approval in all ages in its original biologics license application (BLA). The agency relied on Phase II trial data showing Elevidys increased microdystrophin expression after 12 weeks to grant accelerated approval.

Sarepta is hoping that data from the placebo-controlled EMBARK study will allow it to prove that its gene therapy improves DMD patients' physical functions and mobility, allowing it to expand the treatment's indication to patients of all ages, and convert the accelerated approval into full approval. However, the EMBARK trial also failed to meet its primary endpoint and show that Elevidys-treated patients had significantly better North Star Ambulatory Assessment scores than those in the placebo arm, but unlike Pfizer's drug, it has shown that patients on the gene therapy did significantly better on other types of secondary mobility endpoints.

In February, the FDA accepted this additional efficacy data as part of Sarepta's supplementary BLA seeking approval for Elevidys in DMD patients of all ages. The agency has agreed to evaluate this application under priority review and expects to issue a decision by June 21.