Exposure–Response Analyses for Belzutifan to Inform Dosing Considerations and Labeling

Belzutifan (Welireg, Merck & Co., Inc., Rahway, NJ, USA) is an oral, potent hypoxia-inducible factor-2α inhibitor, recently approved in the United States for the treatment of von Hippel–Lindau (VHL) disease-associated renal cell carcinoma (RCC) and other VHL disease-associated neoplasms. Safety and efficacy were investigated in two clinical studies: a Phase 1 dose escalation/expansion study in solid tumors and RCC and a Phase 2 study in VHL-RCC. A population pharmacokinetic model was used to estimate belzutifan exposures to facilitate exposure–response (E-R) analyses for efficacy and safety endpoints. Relationships between exposure and efficacy (overall response rate, disease control rate, progression-free survival, best overall tumor size response, and other endpoints), safety outcomes (Grade ≥3 anemia, Grade ≥3 hypoxia, and time to first dose reduction/dose interruption), and pharmacodynamic biomarkers (erythropoietin [EPO] and hemoglobin [Hgb]) were evaluated using various regression techniques and time-to-event analyses. Efficacy E-R was generally flat with non-significant positive trends with exposure. The safety E-R analyses demonstrated a lack of relationship for Grade ≥3 hypoxia and a positive relationship for Grade ≥3 anemia, with incidences also significantly dependent on baseline Hgb. Exposure-dependent reductions in EPO and Hgb were observed. Based on the cumulative benefit–risk assessment in VHL disease-associated neoplasms using E-R, no a priori dose adjustment is recommended for any subpopulation. These analyses supported the benefit–risk profile of belzutifan 120 mg once daily dosing in patients with VHL-RCC for labeling and the overall development program.