Safety and pharmacokinetics of DS-6051b in Japanese patients with non-small cell lung cancer harboring ROS1 fusions: a phase I study

Oncogenic ROS1 and NTRK fusions were reported in solid tumors, including non-small cell lung cancer (NSCLC). DS-6051b is an oral, potent selective small molecule tyrosine kinase inhibitor. We report the safety, tolerability, efficacy, and pharmacokinetics of DS-6051b in 15 Japanese patients with NSCLC harboring ROS1 fusions. Patients received DS-6051b once daily (400 mg n = 6; 600 mg n = 6; or 800 mg n = 3) for cycles of 3 weeks. Safety, tolerability, maximum-tolerated dose, pharmacokinetics, and recommended dose for phase II were determined. Common treatment-related adverse events were increased: aspartate aminotransferase and alanine aminotransferase (80.0% each), diarrhea (53.3%), and nausea (46.7%). Dose-limiting toxicities (two grade-3 alanine aminotransferase increases) were seen in the 800 mg cohort. The maximum-tolerated dose and recommended phase II dose was 600 mg once daily. Plasma concentrations of free DS-6051b and DS-6051a increased with dose. Compared with a US phase I study, AUC(0–24 h) on day 15 was higher but narrowed after body weight correction. Objective response rate was 58.3% in patients with target lesions (n = 12) and 66.7% in crizotinib-naïve patients (n = 9). Disease control rate was 100%. DS-6051b is well tolerated and effective in Japanese patients with NSCLC harboring ROS1 fusions and might be a targeted therapy for advanced NSCLC.