Pfizer is developing the AAV9 gene therapy, PF-06939926, to provide children with the progressive muscle degenerative disease DMD with a form of the dystrophin gene behind the condition. The goal is to enable patients to make more of the muscle-building dystrophin protein, thereby freeing them from some of the negative outcomes associated with of DMD.
A Phase III trial of the gene therapy is due to start in the first half of 2020. In working toward that goal, Pfizer is putting manufacturing capacity in place to support the larger product volumes that will be needed for the late-phase study.
Talking on a second-quarter results conference call with investors, Mikael Dolsten, president of worldwide research and development at Pfizer, said, “Our manufacturing, including large-scale 2,000-liter bioprocessors, are on track.”
Pfizer is pushing forward on the strength of data from the first six patients dosed in a Phase Ib trial of the gene therapy. Dolsten said “the integrated data set are sufficiently encouraging to support the continued development of the investigational therapy” but people outside of Pfizer have questioned whether PF-06939926 will be competitive.
After Pfizer shared early data from the trial in late June, William Blair analyst Tim Lugo said Sarepta Therapeutics is the “clear leader in DMD with no close No. 2.” The comment reflected safety data shared to date by Pfizer, Sarepta and Solid Biosciences, the three most advanced companies in the race to bring a DMD gene therapy to market.
Pfizer’s June data drop was marred by the hospitalization of one of the six patients treated with its gene therapy. The patient suffered a rapid antibody response with activation of the complement system associated with acute kidney injury, hemolysis and reduced platelet count, resulting in them spending 11 days in hospital. Pfizer stopped the trial to enact additional safety monitoring.
Safety issues, including serious adverse events and a clinical hold, have dampened hopes for Solid’s DMD gene therapy, leaving Sarepta as the current frontrunner in the field. Pfizer, Solid and a pack of earlier-stage rivals including Vertex Pharma hope to supplant Sarepta at the front of the pack.
PF-06939926 is part of a broader push into gene therapies at Pfizer. On the second-quarter results conference call, Pfizer CEO Albert Bourla also highlighted the progress of SB-525, a haemophilia A gene therapy that the company is developing with Sangamo Therapeutics.
Pfizer and Sangamo presented Phase I/II data on the gene therapy in July. The update provided more evidence that SB-525 can raise levels of the blood-clotting protein Factor VIII into the normal range, although more follow-up is needed to show the durability of the gene therapy.