• Rabi Tawil, Kathryn R Wagner, Johanna I Hamel, Doris G Leung, Jeffrey M Statland, Leo H Wang, Angela Genge, Sabrina Sacconi, Hanns Lochmüller, David Reyes-Leiva, Jordi Diaz-Manera, Jorge Alonso-Perez, Nuria Muelas, Juan J Vilchez, Alan Pestronk, Summer Gibson, Namita A Goyal, Lawrence J Hayward, Nicholas Johnson, Samantha LoRusso, Miriam Freimer, Perry B Shieh, S H Subramony, Baziel van Engelen, Joost Kools, Olof Dahlqvist Leinhard, Per Widholm, Christopher Morabito, Christopher M Moxham, Diego Cadavid, Michelle L Mellion, Adefowope Odueyungbo, William G Tracewell, Anthony Accorsi, Lucienne Ronco, Robert J Gould, Jennifer Shoskes, Luis Alejandro Rojas, and John G Jiang.
• Department of Neurology, University of Rochester Medical Center, Rochester, NY, USA.
• Lancet Neurol. 2024 May 1; 23 (5): 477486477-486.

BackgroundFacioscapulohumeral muscular dystrophy is a hereditary progressive myopathy caused by aberrant expression of the transcription factor DUX4 in skeletal muscle. No approved disease-modifying treatments are available for this disorder. We aimed to assess the safety and efficacy of losmapimod (a small molecule that inhibits p38α MAPK, a regulator of DUX4 expression, and p38β MAPK) for the treatment of facioscapulohumeral muscular dystrophy.MethodsWe did a randomised, double-blind, placebo-controlled phase 2b trial at 17 neurology centres in Canada, France, Spain, and the USA. We included adults aged 18-65 years with type 1 facioscapulohumeral muscular dystrophy (ie, with loss of repression of DUX4 expression, as ascertained by genotyping), a Ricci clinical severity score of 2-4, and at least one skeletal muscle judged using MRI to be suitable for biopsy. Participants were randomly allocated (1:1) to either oral losmapimod (15 mg twice a day) or matching placebo for 48 weeks, via an interactive response technology system. The investigator, study staff, participants, sponsor, primary outcome assessors, and study monitor were masked to the treatment allocation until study closure. The primary endpoint was change from baseline to either week 16 or 36 in DUX4-driven gene expression in skeletal muscle biopsy samples, as measured by quantitative RT-PCR. The primary efficacy analysis was done in all participants who were randomly assigned and who had available data for assessment, according to the modified intention-to-treat principle. Safety and tolerability were assessed as secondary endpoints. This study is registered at ClinicalTrials.gov, number NCT04003974. The phase 2b trial is complete; an open-label extension is ongoing.FindingsBetween Aug 27, 2019, and Feb 27, 2020, 80 people were enrolled. 40 were randomly allocated to losmapimod and 40 to placebo. 54 (68%) participants were male and 26 (33%) were female, 70 (88%) were White, and mean age was 45·7 (SD 12·5) years. Least squares mean changes from baseline in DUX4-driven gene expression did not differ significantly between the losmapimod (0·83 [SE 0·61]) and placebo (0·40 [0·65]) groups (difference 0·43 [SE 0·56; 95% CI -1·04 to 1·89]; p=0·56). Losmapimod was well tolerated. 29 treatment-emergent adverse events (nine drug-related) were reported in the losmapimod group compared with 23 (two drug-related) in the placebo group. Two participants in the losmapimod group had serious adverse events that were deemed unrelated to losmapimod by the investigators (alcohol poisoning and suicide attempt; postoperative wound infection) compared with none in the placebo group. No treatment discontinuations due to adverse events occurred and no participants died during the study.InterpretationAlthough losmapimod did not significantly change DUX4-driven gene expression, it was associated with potential improvements in prespecified structural outcomes (muscle fat infiltration), functional outcomes (reachable workspace, a measure of shoulder girdle function), and patient-reported global impression of change compared with placebo. These findings have informed the design and choice of efficacy endpoints for a phase 3 study of losmapimod in adults with facioscapulohumeral muscular dystrophy.FundingFulcrum Therapeutics.Copyright © 2024 Elsevier Ltd. All rights reserved.

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