Pfizer's DMD Gene Therapy Shows Severe Side Effects in Study

Pfizer, Inc. PFE announced promising data from an early-stage study on its investigational gene therapy for the treatment of Duchenne muscular dystrophy (DMD), a rare muscular degenerative disease. However, further dosing in the study has been stopped as serious side effects were observed in two participants in the study.

The phase Ib study is an open-label, non-randomized, ascending dose assessment, to be conducted on approximately 12 boys with DMD. The study is designed to evaluate the safety and tolerability of PF-06939926 and assess muscle strength, quality and function in the given patient population.

In the phase Ib study, two doses of PF-06939926 were tested in six boys with DMD aged 6 to 12 years. Preliminary safety data from the study showed that one of the six boys was hospitalized for two days for severe nausea and vomiting. Moreover, one of the boys also developed a severe immune response, which led to renal complications. Pfizer said that no other participants will be dosed until specific additional safety monitoring obtains all appropriate approvals.

The data also showed that two months after being administered one-time intravenous dose of PF-06939926, mini-dystrophin expression levels ranged from 10% to 60% of normal. The data was promising enough for Pfizer to announce plans to begin a phase III study in the first half of 2020.

Pfizer’s shares have declined 0.8% this year so far against an increase of 2.2% for the industry.



Duchenne muscular dystrophy is a rare genetic disease and a severe form of muscular dystrophy, primarily affecting males. It progressively weakens and degenerates skeletal and heart muscles. DMD is caused by the absence of a particular gene, dystrophin, which the body uses to keep the muscle cells intact. Sarepta Therapeutics, Inc.'s SRPT Exondys 51 and PTC Therapeutics, Inc.’s PTCT Emflaza are among the approved treatments of DMD in the United States. However, the focus for DMD treatment is currently shifting to development of gene therapies. Gene therapies deliver a functional copy of the dystrophin to muscle cells to restore its production

In response to the safety concerns observed in Pfizer’s study, shares of Sarepta rose more than 17%. Sarepta is also conducting studies to evaluate gene therapies for DMD. Solid Biosciences Inc. SLDB also has an early-stage gene therapy candidate, SGT-001, which is being developed for DMD. Solid Biosciences’ shares were up around 14% on Friday.

Pfizer currently carries a Zacks Rank #2 (Buy). You can see the complete list of today’s Zacks #1 Rank (Strong Buy) stocks here.

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