PF-06939926, developed by Pfizer, is an investigational gene therapy for the treatment of Duchenne muscular dystrophy (DMD).

How PF-06939926 works

PF-06939926 uses a modified virus called an adeno-associated virus serotype 9 (AAV9) capsid to deliver a shortened version of the human DMD gene that encodes for a so-called mini-dystrophin protein. DMD is caused by a mutation in the DMD gene, which is the largest human gene. Because the gene is too long to fit into the adenoviral vector, a shorter but still functional version of the gene is used for the therapy. The AAV9 capsid lets the therapy specifically target the muscles.

PF-06939926 in clinical trials

A Phase 1b open-label clinical trial (NCT03362502) assessing the safety and tolerability of a single intravenous infusion of PF-06939926 in boys ages 5–12 with DMD who can still walk is ongoing and still recruiting patients at sites across the United States. Six study participants have already received the treatment. The most common adverse events recorded so far were nausea, vomiting, decreased appetite, tiredness, or fever. Immune responses occurred in all participants, and one of the six had to be admitted to a pediatric intensive care unit as a result. He was discharged from the hospital after 11 days.

Mini-dystrophin was detected in the muscle fibers of the boys two months after dosing. One-year follow-up data from two participants showed a 4.5-point increase in the NorthStar ambulatory assessment score (a score to assess motor function). While the scores are highly variable, they are usually stable or decline over time in DMD patients.

Pfizer is planning a second, randomized, placebo-controlled Phase 3 study to further test PF-06939926. The trial is expected to start in the first half of 2020.

Additional information

PF-06939926 received orphan drug designation by the U.S. Food and Drug Administration (FDA) and an orphan medicinal product designation by the European Medicines Agency (EMA) in May 2017.

 

Last updated: 07/14/2019

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