Use of Pharmacokinetic and Pharmacodynamic Data to Develop the CDK4/6 Inhibitor Ribociclib for Patients with Advanced Breast Cancer

Ribociclib is an orally bioavailable, selective cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitor. CDK4/6 inhibition by ribociclib leads to retinoblastoma tumor suppressor protein (Rb) reactivation, thereby restoring Rb-mediated cell cycle arrest. Ribociclib is approved for the treatment of patients with hormone receptor-positive/human epidermal growth factor receptor-2-negative (HR+/HER2-) advanced breast cancer (ABC), at the dose of 600 mg once daily (QD) during cycles of 21 days on/7 days off, with optional dose reduction to 400 mg and 200 mg. Ribociclib is rapidly absorbed with a median time to reach maximum plasma concentration of 2.4 h, mean half-life of 32.0 h and oral bioavailability of 65.8% at 600 mg. It is eliminated mainly by hepatic metabolism (~ 84% of total elimination), mostly by cytochrome P450 (CYP) 3A4. Age, body weight, race, baseline Eastern Cooperative Oncology Group status, food, mild hepatic impairment, mild-to-moderate renal impairment, proton pump inhibitors, and combination partners (non-steroidal aromatase inhibitors or fulvestrant) have no clinically relevant impact on ribociclib exposure. Ribociclib inhibits CYP3A at 600 mg leading to increased exposure of CYP3A substrates. Strong CYP3A inhibitors or inducers increase or decrease, respectively, ribociclib exposure. Exposure-safety and exposure-efficacy analyses support the clinical benefit of the 600 mg QD starting dose, with potential individualized dose reductions to 400 mg and 200 mg for effective management of the adverse events neutropenia and QTcF interval prolongation, while maintaining efficacy, in patients with HR+/HER2- ABC. Overall, these clinical pharmacology data informed ribociclib dose justification and clinical development, as well as its prescribing information for clinical use in advanced breast cancer patients.