Mirum Pharmaceuticals and Incyte announced positive pivotal Phase 2 results from Cohort 1 of the PROGRESS study evaluating zilurgisertib in adolescents and adults with fibrodysplasia ossificans progressiva (FOP). The data, presented at ENDO 2026, demonstrated a 99.9% reduction in total volume of new heterotopic ossification (HO) lesions compared to placebo at Week 24. The U.S. Food and Drug Administration (FDA) has accepted the New Drug Application (NDA) for zilurgisertib under Priority Review, with a target action date of September 26, 2026.

The PROGRESS study evaluated zilurgisertib 100 mg once-daily in 63 patients randomized 1:1 to receive either the drug or placebo during a 24-week double-blind period, followed by an open-label extension. Results showed a consistent treatment effect across measures of disease activity and durability through Week 48. No new HO lesions were observed among patients who continued to receive zilurgisertib or among placebo-treated patients who crossed over to active treatment at Week 24.

"The findings presented at ENDO represent an important milestone for the zilurgisertib program and further strengthen the growing body of clinical evidence supporting its potential as a treatment for FOP," said Steven Stein, M.D., Executive Vice President, Chief Medical Officer and Head of Late-Stage Development at Incyte.

Key Efficacy Findings

Key efficacy findings included an 81% reduction in the number of patients developing new HO lesions versus placebo at Week 24. Additionally, the treatment resulted in a reduction in total existing HO lesion volume compared with an increase observed in placebo-treated patients. Flare activity was also lower in the zilurgisertib group compared to placebo.

Safety and Tolerability

Zilurgisertib was generally well-tolerated during the 24-week placebo-controlled period. Most adverse events were mild or moderate, and no adverse events led to treatment discontinuation or dose reduction. Serious adverse events and Grade ≥3 adverse events occurred at low rates in both treatment groups. The most commonly reported adverse events among patients receiving zilurgisertib were FOP flare-up or aching/pain due to FOP (25%), headache (21.9%), upper respiratory tract infection (21.9%), arthralgia (18.8%), epistaxis (12.5%), and nausea (12.5%).

"People living with FOP and their families urgently need additional treatment options," said Joanne Quan, M.D., Chief Medical Officer at Mirum Pharmaceuticals. "These results reinforce our confidence in the potential of zilurgisertib and our commitment to working with Incyte to bring this important program forward."

Mirum Pharmaceuticals licensed zilurgisertib from Incyte for worldwide development and commercialization. The PROGRESS study is a global, randomized, double-blind, placebo-controlled Phase 2 study. Additional cohorts will evaluate the efficacy and safety of zilurgisertib in younger patient populations.

Mirum Pharmaceuticals, Inc. granted inducement awards to 8 new employees on June 10, 2026, consisting of non-qualified stock options to purchase 10,100 shares of common stock and 13,350 restricted stock units (RSUs). The awards were approved by the Compensation Committee of Mirum's Board of Directors as an employment inducement material to the new employees, in accordance with Nasdaq Listing Rule 5635(c)(4). The grants were issued under Mirum's 2020 Inducement Plan.

Award Details

Each stock option carries an exercise price of $94.00 per share, matching the closing price of Mirum's common stock on June 10, 2026. The options will vest over four years, with 25% of the underlying shares vesting on the one-year anniversary of the applicable vesting commencement date. The remaining shares will vest monthly over the subsequent 36 months, contingent on the new employees' continued service with Mirum through the applicable vesting dates.

The RSUs will vest over three years, with 33% of the underlying shares vesting on each anniversary of the applicable initial vesting date. These vesting schedules are also subject to the new employees' continued service relationship with Mirum through the applicable vesting dates. All awards are subject to the terms and conditions of Mirum's 2020 Inducement Plan and the respective award agreements.

Mirum Pharmaceuticals focuses on rare liver and rare genetic diseases, with a commercial portfolio including LIVMARLI, CHOLBAM, and CTEXLI. The company's clinical-stage pipeline features volixibat, brelovitug, zilurgisertib, and MRM-3379.