Phase I Study of the Plk1 Inhibitor BI 2536 Administered Intravenously on Three Consecutive Days in Advanced Solid Tumours

Background: This open-label phase i study with an accelerated titration design was performed to determine the maximum tolerated dose of BI 2536, a potent, highly selective small-molecule polo-like kinase 1 (Plk1) inhibitor. Methods: Patients with advanced solid tumours received a single 60-minute intravenous infusion of BI 2536 (50–70 mg) on days 1–3 of each 21-day treatment course. Recipients without disease progression or untenable toxicity could receive additional treatment courses. The maximum tolerated dose was determined based on dose-limiting toxicities. Other assessments included safety, pharmacokinetic profile, and antitumour activity according to the Response Evaluation Criteria in Solid Tumors. Results: The study enrolled 21 patients. The maximum tolerated dose for BI 2536 was determined to be 60 mg for the study schedule. Dose-limiting toxicities included hematologic events, hypertension, elevated liver enzymes, and fatigue. The most frequently reported drug-related adverse events were mild-to-moderate fatigue, leukopenia, constipation, nausea, mucosal inflammation, anorexia, and alopecia. The pharmacokinetics of BI 2536 were linear within the dose range tested. Plasma concentration profiles exhibited multi-compartmental pharmacokinetic behaviour, with a terminal elimination half-life of 20–30 hours. Conclusions: In the present study, BI 2536 showed an acceptable safety profile warranting further investigation of Plk1 inhibitors in this patient population.