Exposure–Response-Based Product Profile–Driven Clinical Utility Index for Ipatasertib Dose Selection in Prostate Cancer

Abstract

The aims of this work were to characterize ipatasertib exposure–response (E-R) relationships in a phase II study and to quantitatively assess benefit-risk using a clinical utility index approach to support ipatasertib phase III dose selection in patients with metastatic castration-resistant prostate cancer. Logistic regression and Cox proportional-hazards models characterized E-R relationships for safety and efficacy endpoints, respectively. Exposure metrics with and without considering dose interruptions/reductions (modifications) were tested in the E-R models. Despite a steeper E-R relationship when accounting for dose modifications, similar dose-response projections were generated. The clinical utility index analysis assessed important attributes, weights, and clinically meaningful cutoff/tradeoff values based on predefined minimal, target, and optimistic product profiles. Ipatasertib 400 mg daily, showing the highest probability of achieving the minimal product profiles and better benefit-risk balance than other doses (200–500 mg daily), was selected for further development in metastatic castration-resistant prostate cancer.