Regeneron’s rare bone disorder drug succeeds in late-stage trial

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(Reuters) – Regeneron Pharmaceuticals said on Wednesday its experimental treatment for a rare genetic disorder affecting soft tissue significantly reduced abnormal bone formation, meeting the main goal of a late-stage study.

The company was testing its drug, garetosmab, in adults with fibrodysplasia ossificans progressiva — a condition where muscle, tendon and ligament tissue gradually turn into bone, leading to a “second skeleton” that causes progressive loss of mobility and reduced life expectancy.

The condition affects about one in 1.14 million people in the United States, according to data from the National Institutes of Health. Its only approved treatment is French drugmaker Ipsen’s Sohonos, which gained the U.S. Food and Drug Administration’s nod in 2023.

Garetosmab works by blocking a protein called activin A, which can trigger abnormal bone formation in muscles and soft tissues in people with the disorder.

In a 56-week trial involving 63 participants, garetosmab reduced the development of new bone abnormalities by 94% at a 3 milligram/kilogram dose and by 90% at a 10 mg/kg dose, when compared to placebo.

Based on the trial data, a panel of experts, called the independent data monitoring committee, recommended patients who were on placebo to be transitioned to garetosmab as soon as possible.

Regeneron said it plans to file a U.S. marketing application for the drug by the end of 2025, with global regulatory submissions slated for 2026.

If approved, the drug could compete with Sohonos, which brought in sales of 20.8 million euros for Ipsen in 2024.

($1 = 0.8443 euros)

(Reporting by Christy Santhosh in Bengaluru; Editing by Shilpi Majumdar)