UPDATE: Pfizer's phase 3 gene therapy trial fails to improve function for boys with Duchenne muscular dystrophy

Pfizer’s phase 3 gene therapy trial has failed to demonstrate significant improvement in motor function for boys with Duchenne muscular dystrophy (DMD).

The late-stage miss comes a little more than a month after the Big Pharma reported the death of a young boy participating in a related phase 2 trial called DAYLIGHT, which included boys with DMD ages 2 to 3 years. The boy had received the gene therapy in early 2023 and died from cardiac arrest on May 3 of this year.  

The phase 3 DMD trial, dubbed CIFFREO, is a double-blind study evaluating an investigational recombinant adeno-associated virus gene therapy called fordadistrogene movaparvovec among ambulatory boys ages 4 to 7 years. The late-stage trial uses a crossover trial design with DAYLIGHT, but Pfizer paused dosing associated with the CIFFREO crossover after the death occurred.

Now, the pharma has revealed that CIFFREO failed to hit its primary goal of improving motor function when compared to placebo at one year of treatment, as assessed by a movement scale known as the North Star Ambulatory Assessment. Key secondary endpoints, such as 10-meter run/walk velocity and time to rise, also failed to demonstrate a significant difference between fordadistrogene movaparvovec and placebo.

The gene therapy’s overall safety profile in the phase 3 trial was manageable, with mostly mild to moderate adverse events occurring, according to Pfizer. Treatment-related serious adverse events were generally responsive to clinical management, the company said in a June 12 release.

The Big Pharma will continue to monitor all participants in the study and is evaluating what the appropriate next steps for the program are.

“We are extremely disappointed that these results did not demonstrate the relative improvement in motor function that we had hoped,” Dan Levy, M.D., Ph.D., Pfizer’s development head for DMD, said in the release. “We plan to share more detailed results from the study at upcoming medical and patient advocacy meetings, with the goal of ensuring that learnings from this trial can help improve future clinical research and development of treatment options that can improve care for boys living with Duchenne muscular dystrophy. We are grateful for the boys, their families, advocates and the investigators who have participated in this research and the continuing effort to advance treatment options for this debilitating disease.”

Pfizer Chief Scientific Officer and President of R&D Mikael Dolsten, M.D., Ph.D., had previously touted the gene therapy as "the main game in town" after Sarepta Therapeutics’ confirmatory DMD trial ended in failure in October 2023. Sarepta had also been testing out a gene therapy—sold under the name Elevidys—and evaluated it using the North Star Ambulatory Assessment, a primary endpoint measure that failed to reach statistical significance in a phase 3 study. 

However, Sarepta's trial did score statistically significant results on all key prespecified endpoints, including time to rise and 10-meter walk test. 

Elevidys, which currently has accelerated approval for patients with DMD aged 4 and 5 years old, awaits a full FDA approval and label expansion decision. The gene therapy was granted priority review and a decision is expected by June 21. 

"Given the proximity to the PDUFA goal date, we do not expect today's news to impact any decision by the agency," William Blair analysts wrote June 13 about the pending Elevidys determination. The firm believes the gene therapy will be approved in full, but is less confident about a label expansion for non-ambulatory patients.  

Fordadistrogene movaparvovec was never a competitive threat to Elevidys given the safety concerns tied to the therapy's development, according to William Blair. The phase 3 fail is just the cherry on top, with William Blair writing that the news "all but removes" the asset from the competitive landscape.