Pfizer on Friday presented promising results from a tiny early study of its experimental gene therapy for a rare muscle disease, but two of the six patients in the trial experienced side effects that landed them in the hospital.
Duchenne muscular dystrophy (DMD) is a genetic degenerative disease that affects one in 3,500 to 5,000 males.
People with the condition lack the protein dystrophin needed to keep muscle cells intact. That can lead to life-threatening damage to the heart, and over time, death, often at a young age.
The study tested two different dosages of the gene therapy in boys ranging in age from 6 to 12-years old. Two months after receiving the one-time therapy, mini-dystrophin expression levels ranged from 10% to 60% of normal, Pfizer said.
Gene therapies use engineered viruses to carry healthy genetic material into a person’s cells to replace faulty or mutated genes that cause a disease or condition.
The higher tested dose appeared to be more effective, according to data presented at the Parent Project Muscular Dystrophy conference in Orlando, Florida.
Pfizer said future trials will use the higher dose, which had triple the concentration of virus with genetic material. The U.S. drugmaker said it also may test an intermediate dose.
Both of the boys who required hospital treatment had received the higher dose.
One had developed a kidney injury. He was hospitalized for 11 days and received two doses of Alexion’s Soliris, but left the hospital with normal kidney function.
The other suffered nausea and vomiting after the treatment and spent two days in a hospital.
Pfizer is racing Sarepta Therapeutics Inc to be first to market with a gene therapy for DMD.
So far, there are just two approved gene therapies in the United States, even though pharmaceutical companies have been pouring money into potentially lucrative treatments that could offer patients with deadly or debilitating conditions a possible one-time cure.
In October, Sarepta said a study of its gene therapy in four patients showed mean micro-dystrophin levels of 74% of normal. But Sarepta and Pfizer used different techniques to measure dystrophin, so the data are not immediately comparable.
Evercore ISI analysts said an investor survey the brokerage conducted indicated dystrophin levels of greater than 40% would likely mean Pfizer’s drug could be competitive.
Sarepta’s older drug, Exondys 51, won U.S. approval to treat some forms of DMD in 2016.