The U.S. Food and Drug Administration on Friday approved Atebrioz (zilurgisertib) tablets, giving patients with fibrodysplasia ossificans progressiva (FOP) a new once-daily oral treatment. Mirum Pharmaceuticals Inc. (MIRM) and Incyte Corporation (INCY) announced the regulatory milestone, noting the medication helps reduce the volume of new abnormal bone formation in adults and children aged 12 and older.

Targeting the Root Cause

Incyte originally developed Atebrioz, while Mirum Pharmaceuticals holds the exclusive license for its global development and commercialization. The drug functions as an activin receptor-like kinase 2 (ALK2) inhibitor.

FOP patients possess mutations in the ACVR1 gene, which abnormally activates ALK2. This activation drives heterotopic ossification (HO), a process where bone develops in muscles, ligaments, and tendons. Because HO progressively restricts movement and causes severe disability, Atebrioz aims to directly block this underlying biological pathway.

Clinical Efficacy and Safety Profile

The FDA based its approval on Cohort 1 of the PROGRESS clinical study. Researchers measured efficacy by tracking the total new HO lesion volume over a 24-week double-blind period.

Patients taking zilurgisertib saw a mean decrease of 3.2 cubic centimeters in total new HO lesion volume. In contrast, patients receiving a placebo experienced a 24.6 cubic centimeter increase. The medication maintained these positive treatment effects through a 48-week open-label extension.

Global Regulatory Steps and Pediatric Vouchers

Alongside the approval, the FDA awarded a Rare Pediatric Disease Priority Review Voucher to Incyte. The company can apply this voucher to expedite the review of a future, unrelated drug application.

The European Medicines Agency is currently reviewing a marketing authorization application for zilurgisertib for patients 12 and older.

Meanwhile, the PROGRESS study continues evaluating younger patients. Researchers finished enrolling children aged six to under 12 in Cohort 2 and are actively enrolling children aged two to under 12 in Cohort 3.

Price Action: Mirum Pharmaceuticals shares were up 2.00% at $91.49 and Incyte shares were unchanged 0.00% at $123.89 during premarket trading on Monday, according to market data.