FDA Puts Investigational FSHD Therapy Losmapimod on Fast Track

The U.S. Food and Drug Administration (FDA) has granted fast track designation to losmapimod, a potential treatment for facioscapulohumeral muscular dystrophy (FSHD) being developed by Fulcrum Therapeutics.

The designation is intended to help bring effective treatments for serious conditions to market more quickly. It grants Fulcrum, as the therapy’s developer, access to more frequent communications with the FDA throughout the drug development process. Fast track status also makes losmapimod eligible for other potential FDA designations, such as priority review and accelerated approval.

“We are pleased that the FDA has granted Fast Track designation, which we believe demonstrates the potential for losmapimod to address unmet medical needs for people living with FSHD,” Judith Dunn, PhD, president of research and development at Fulcrum, said in a press release.

“There are no approved therapies to treat patients with FSHD, and losmapimod is currently the only drug in clinical development for this serious and debilitating disease,” Dunn added.

Losmapimod is an oral medication that works by blocking the activity of the proteins p38 alpha and p38 beta, which help regulate the activity of the DUX4 gene.

More than 90% of FSHD cases are caused by mutations that lead to abnormally high activity of the DUX4 gene. By blocking p38 alpha and p38 beta, losmapimod aims to stop this disease-causing hyperactivity.

Results from a Phase 1 clinical trial, reported last year, indicated that the investigational medication has an acceptable safety profile in FSHD patients. There were no serious adverse events reported.

Full results from a Phase 2b clinical trial called ReDUX4 (NCT04003974) are on track to be presented at the virtual FSHD International Research Congress taking place this June 24-25. ReDUX4 was designed to further assess the therapy’s safety and effectiveness as a treatment for FSHD.

Conducted in North America and Europe, ReDUX4 is a double-blind study, meaning that neither researchers nor participants know which patients are given the therapy and which a placebo. A total of 80 participants received losmapimod — four 7.5 mg tablets, taken two at a time, twice a day — or the placebo for 24 weeks (nearly 6 months). Those who completed the trial could enroll in a Phase 2 extension study (NCT04264442), where they continued receiving the therapy.

The reported data will include the trial’s main efficacy measurement — reduced activity of the DUX4 gene — as well as muscle imaging data, muscle function data, and patient-reported outcomes.

Losmapimod was designated an orphan drug by the FDA early last year. Orphan drug status offers Fulcrum financial support, including fee waivers, in developing the therapy, as well as seven years market exclusivity in the U.S. if regulatory approval is granted.