Pfizer is shutting down two clinical studies assessing the anti-myostatin monoclonal antibody domagrozumab (PF-06252616) for the treatment of Duchenne muscular dystrophy (DMD).

A Phase II safety and efficacy study (B5161002) and an open-label extension study (B5161004) are being terminated, following a primary analysis of data.

The Phase II study B5161002 - investigating the efficacy and safety of domagrozumab, administered in monthly IV doses, in 121 boys aged 6 to 15 with DMD, regardless of underlying mutation - failed to meet its primary efficacy endpoint of demonstrating a difference in the mean change from baseline in 4 Stair Climb (in seconds) following one year of treatment.

“Further evaluation of the totality of evidence including secondary endpoints did not support a significant treatment effect,” Pfizer said, further stressing that the studies were not terminated for safety reasons.

“We are disappointed by these results and while we are not progressing with the studies, the data will contribute to a greater understanding of this disease and we will evaluate the total data set to see if there is a place for this medicine in muscular diseases,” said Seng Cheng, senior vice president and chief scientific officer, Pfizer Rare Disease Research Unit.

DMD is a rare, serious, debilitating childhood genetic disease characterised by progressive muscle degeneration and weakness and significantly shortened life expectancy. It is the most common form of muscular dystrophy worldwide and primarily affects boys, with incidence of 1 in every 3500 to 5000 live male births each year.

The drug giant Pfizer has one ongoing clinical trial in DMD with a gene therapy, PF-06939926, which is an investigational, recombinant AAV9 capsid carrying a truncated or shortened version of the human dystrophin gene (mini-dystrophin) under the control of a human muscle specific promotor.