Incyte and Mirum Pharmaceuticals are taking a step closer to approval of their investigational pill for fibrodysplasia ossificans progressiva despite having no statistical difference in abnormal bone lesions between their drug candidate and the placebo in the mid-stage study.
The companies published results from the Phase 2 PROGRESS trial in over 60 patients on the oral drug zilurgisertib versus placebo on Sunday. One patient in the zilurgisertib arm developed new HO lesions (abnormal bone formation inside soft tissues) at the 24-week point. By the 24-week mark, there was one patient in the zilurgisertib arm who developed new HO lesions (abnormal bone formation inside soft tissues). Five placebo comparators experienced such “anomalous bone lesions” as compared to GSP.
Incyte and Mirum said the treatment effect was 81%, but not statistically significant (p-value of 0.0986) against zilurgisertib.
After the 24-week placebo-controlled period of PROGRESS, the trial was followed by an open-label extension in which patients who had started in the placebo arm were re-randomized to zilurgisertib. At a 24-week follow-up examination, in this subset of the study, the number of participants with new abnormal bone lesions remained unchanged.
“Despite a primary endpoint failure,” wrote Leerink Partners in a note to the investing public on Monday, “these data place ZGB in a good position to gain approval in September with a clear benefit of reducing/preventing new HO lesions.”
Last month, Mirum announced the FDA had accepted its drug package for zilurgisertib, which is expected to be available for action by September 26.
Zilurgisertib “improved several clinical measurements,” the analysts added. Indeed, aside from reducing abnormal bone formation, Incyte and Mirum on Sunday touted reductions in mean total lesion volume and the average number of new flares for patients on zilurgisertib versus placebo.
Leerink forecasts peak sales of around $200 million for zilurgisertib, which the firm concedes is “modest” for Mirum, which at present is valued at over $6 billion. Incyte is considerably larger at over $20 billion in market cap. But, for Mirum, the firm believes zilurgisertib offers a “greater upside than downside risk” due to the biotech’s experience in rare disease therapeutics and the unmet need in the indication.
Fibrodysplasia ossificans progressiva (FOP) is a rare genetic condition that causes bone to grow in soft tissues like muscles, tendons and ligaments. Those who have the condition experience greatly limited movement, eventually losing all mobility, and experience other complications such as eating, speaking, and breathing difficulties. Inhibiting the ALK2 receptor, Zilurgisertib works by blocking the abnormal activity of the receptor in patients with FOP that leads to the abnormal bone formation.
Mirum and Incyte are reinforcing the case for regulatory approval of their investigational therapy for an uncommon bone disease, despite a disappointing outcome in a mid-stage clinical trial. The latest developments suggest that Mirum remains confident in the broader body of evidence supporting the treatment’s potential benefits for patients with limited therapeutic options.
Mirum and Incyte Navigate a Mid-Stage Setback
While the mid-stage study did not achieve all of its intended objectives, Mirum and its partner continue to emphasize positive findings from other clinical assessments. The companies believe that the overall dataset provides meaningful insights into the therapy’s effectiveness and supports continued discussions with regulatory authorities.
The outcome illustrates the challenges often associated with developing treatments for rare diseases, where patient populations are small and clinical endpoints can be difficult to measure.
Mirum Continues to Build Clinical Evidence
A key component of the strategy involves presenting a comprehensive package of clinical evidence. Mirum has highlighted data related to patient outcomes, safety observations, and disease-specific markers that may help demonstrate the therapy’s value.
By combining results from multiple studies, Mirum aims to create a stronger scientific foundation that supports future approval considerations and broader clinical adoption.
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