Fulcrum Therapeutics has started a Phase IIb clinical trial of losmapimod in patients suffering from facioscapulohumeral muscular dystrophy (FSHD).
Losmapimod is a selective inhibitor of p38α/β mitogen-activated protein kinase (MAPK).
Fulcrum in-licensed the drug based on its finding that p38α/β inhibition decreases expression of the DUX4 gene in muscle cells extracted from FSHD patients.
FSHD develops due to DUX4 genetic mutation in skeletal muscles, leading to the production of DUX4 proteins that are toxic to muscle tissue.
The rare disorder leads to progressive skeletal muscle loss, which causes weakness of muscles in the face, shoulders, arms, and trunk. As the disease progresses it causes weakness throughout the lower body.
Named ReDUX4, the Phase IIb study will investigate the safety and efficacy of losmapimod in addressing the underlying cause of FSHD over 24 weeks.
Fulcrum Therapeutics president and CEO Robert Gould said: “Initiating ReDUX4 is a significant milestone that brings us a step closer to our goal of improving the lives of patients and families who are impacted by FSHD.
“Losmapimod, a p38α/β mitogen-activated protein kinase (MAPK) inhibitor identified through our proprietary product engine, reduced expression of the DUX4 gene in patient-derived muscle cells, which is the root cause of FSHD.”
The primary endpoint of the randomised, double-blind, placebo-controlled, multi-centre ReDUX4 trial is the efficacy of losmapimod in blocking or mitigating DUX4-driven gene expression.
Skeletal muscle biopsies will be carried out to measure DUX4 expression as a subset of DUX4-regulated gene transcripts. Data from the Phase IIb study will be available in the third quarter of next year.
The company also plans to begin a 52-week open-label study involving interim analyses.