Regeneron paused the phase 2 trial of its rare bone disease drug after multiple patients died in the extension part of the study. The company is reviewing the data “to better understand” the drug’s benefit-risk profile and has alerted regulators and the study’s independent data monitoring committee to the deaths.
The patients died in the open-label extension of the trial, in which all patients received the drug, garetosmab, Regeneron said in a statement Friday. This part of the study followed a 28-week period in which patients received either garetosmab or placebo. No patients died in the placebo-controlled portion of the study, the company said.
The company did not specify how many patients had died, nor did it say whether those patients had been in the garetosmab or placebo arms in the first part of the study.
Regeneron is developing garetosmab for patients with the inherited disorder fibrodysplasia ossificans progressiva (FOP), whose muscles and soft tissue gradually transform into bone, making movement difficult or impossible. This transformation sometimes happens spontaneously, but often follows an injury or illness. There is no treatment for FOP, but doctors may prescribe drugs to relieve pain and swelling.
The drug is designed to reduce the formation of heterotopic bone—or bone in the wrong place—by neutralizing the Activin A protein.
The phase 2 study, LUMINA-1, pitted garetosmab against placebo in 44 patients with FOP of varying severity, aged 18 to 60. Some patients in the study had difficulty moving specific parts of their body, while others had “near-total immobility.” Regeneron had planned to discuss a filing with regulators based on results from the first part of the study it unveiled in January.
After 28 weeks of treatment, patients taking garetosmab saw a 25% reduction in the number of bone lesions and a 90% drop in new bone lesions, Regeneron announced in January. The drug also beat placebo at preventing flare-ups, or episodes of localized inflammation, with a flare-up rate of 10% for the garetosmab arm compared to 42% for placebo.
As for safety, patients in both treatment arms experienced side effects, with all 24 placebo patients and 19 out of 20 garetosmab patients finishing the 28 weeks of treatment. Most side effects were mild to moderate, but two patients developed serious abscesses that required hospitalization during the open-label extension. Both continued on garetosmab.