Evaluation of Prexasertib, a Checkpoint Kinase 1 Inhibitor, in a Phase Ib Study of Patients with Squamous Cell...

Purpose: Prexasertib, a checkpoint kinase 1 inhibitor, demonstrated single-agent activity in patients with advanced squamous cell carcinoma (SCC) in the dose-escalation portion of a phase I study (NCT01115790). Monotherapy prexasertib was further evaluated in patients with advanced SCC.Patients and Methods: Patients were given prexasertib 105 mg/m² as a 1-hour infusion on day 1 of a 14-day cycle. Expansion cohorts were defined by tumor and treatment line. Safety, tolerability, efficacy, and exploratory biomarkers were analyzed.Results: Prexasertib was given to 101 patients, including 26 with SCC of the anus, 57 with SCC of the head and neck (SCCHN), and 16 with squamous cell non-small cell lung cancer (sqNSCLC). Patients were heavily pretreated (49% ≥3 prior regimens). The most common treatment-related adverse event was grade 4 neutropenia (71%); 12% of patients had febrile neutropenia. Median progression-free survival was 2.8 months [90% confidence interval (CI), 1.9-4.2] for SCC of the anus, 1.6 months (90% CI, 1.4-2.8) for SCCHN, and 3.0 months (90% CI, 1.4-3.9) for sqNSCLC. The clinical benefit rate at 3 months (complete response + partial response + stable disease) across tumors was 29% (23% SCC of the anus, 28% SCCHN, 44% sqNSCLC). Four patients with SCC of the anus had partial or complete response [overall response rate (ORR) = 15%], and three patients with SCCHN had partial response (ORR = 5%). Biomarker analyses focused on genes that altered DNA damage response or increased replication stress.Conclusions: Prexasertib demonstrated an acceptable safety profile and single-agent activity in patients with advanced SCC. The prexasertib maximum-tolerated dose of 105 mg/m² was confirmed as the recommended phase II dose. Clin Cancer Res; 24(14); 3263-72. ©2018 AACR.