Long-term efficacy and safety of osilodrostat in Cushing’s disease: final results from a Phase II study with an optional extension phase (LINC 2)

Background: Many patients with Cushing’s disease (CD) require long-term medical therapy to control their hypercortisolism. In the core phase of a Phase II study (LINC 2; NCT01331239), osilodrostat normalized mean urinary free cortisol (mUFC) in 78.9% of patients with CD. Here, we report long-term efficacy and safety data for osilodrostat following completion of an optional extension to LINC 2. Methods: Adult patients with CD were enrolled in a 22-week prospective Phase II study. Patients with mUFC ≤ upper limit of normal (ULN) or receiving clinical benefit at week 22 could enter the optional extension. The proportion of complete (mUFC ≤ ULN) or partial (mUFC > ULN but ≥ 50% decrease from baseline) mUFC responders was assessed over time. Results: Sixteen of 19 enrolled patients entered the extension. Median (range) osilodrostat exposure from baseline to study end was 5.4 years (0.04–6.7); median (range) average dose was 10.6 mg/day (1.1–47.9). Overall response rate (complete and partial mUFC responders) was consistently ≥ 50%. Sustained control of most cardiovascular-related parameters was observed during the extension. The long-term safety profile was consistent with that reported during the core phase. Testosterone levels (females) decreased towards baseline levels during long-term follow-up, with no new or worsening cases of hirsutism during the extension. Conclusions: In the longest prospective study of a steroidogenesis inhibitor to date, osilodrostat provided sustained reductions in mUFC for up to 6.7 years of treatment, with no new safety signals emerging during the extension. These findings support osilodrostat as an effective long-term treatment for patients with CD.