US Phase I First-in-human Study of Taletrectinib (DS-6051b/AB-106), a ROS1/TRK Inhibitor, in Patients with Advanced Solid Tumors

Purpose: Taletrectinib ( DS-6051b/AB-106) is an oral, tyrosine kinase inhibitor of ROS1 and NTRK with potent preclinical activity against ROS1 G2032R solvent-front mutation among others. We report the first-in-human U.S. phase I results of taletrectinib. Patients and Methods: Patients >= 18 years old with neuroendocrine tumors, with tumor-induced pain, or tumors harboring ROS1/NTRK rearrangements were eligible. Accelerated titration followed by modified continuous reassessment method and escalation with overdose control was used (50-1,200 mg once daily or 400 mg twice daily). Primary objectives were safety/tolerability, and MTD determination. Secondary objectives were food-effect pharmacokinetics and antitumor activity. Results: A total of 46 patients were enrolled. Steady-state peak concentration (C-max) and exposure (AUC0-8) increased dose dependently from 50-mg to 800-mg once-daily doses. The ratio of the geometric mean of AUC0- 24 between low-fat-diet-fed/fasted state was 123% (90% confidence interval, 104%-149%). Doselimiting toxicities (grade 3 transaminases increase) occurred in two patients (1,200-mg once-daily dose). MTD was 800 mg once daily. Most common treatment-related adverse events were nausea (47.8%), diarrhea (43.5%), and vomiting (32.6%). Pain score reductions were observed in the 800-mg once-daily dose cohort. Confirmed objective response rate was 33.3% among the six patients with RECIST-evaluable crizotinib-refractory ROS1+ NSCLC. One patient with TPM3-NTRK1 differentiated thyroid cancer achieving a confirmed partial response of 27 months at data cutoff. We identified a cabozantinib-sensitive ROS1 L2086F as an acquired taletrectinib-resistance mutation. Conclusions: Taletrectinib has manageable toxicities at the MTD of 800 mg daily. Preliminary efficacy was observed in patients with crizotinib-refractory ROS1(+) NSCLC.