Phase I study of GDC-0425, a checkpoint kinase 1 inhibitor, in combination with gemcitabine in patients with refractory solid tumors

Purpose: Chk1 inhibition potentiates DNA-damaging chemotherapy by overriding cell-cycle arrest and genome repair. This phase I study evaluated the Chk1 inhibitor GDC-0425 given in combination with gemcitabine to patients with advanced solid tumors. Experimental Design: Patients received GDC-0425 alone for a 1-week lead-in followed by 21-day cycles of gemcitabine plus GDC-0425. Gemcitabine was initially administered at 750 mg/m² (Arm A), then increased to 1,000 mg/m² (Arm B), on days 1 and 8 in a 3 + 3 + 3 dose escalation to establish maximum tolerated dose (MTD). GDC-0425 was initially administered daily for three consecutive days; however, dosing was abbreviated to a single day on the basis of pharmacokinetics and tolerability. TP53 mutations were evaluated in archival tumor tissue. On-treatment tumor biopsies underwent pharmacodynamic biomarker analyses. Results: Forty patients were treated with GDC-0425. The MTD of GDC-0425 was 60 mg when administered approximately 24 hours after gemcitabine 1,000 mg/m². Dose-limiting toxicities included thrombocytopenia (n = 5), neutropenia (n = 4), dyspnea, nausea, pyrexia, syncope, and increased alanine aminotransferase (n = 1 each). Common related adverse events were nausea (48%); anemia, neutropenia, vomiting (45% each); fatigue (43%); pyrexia (40%); and thrombocytopenia (35%). The GDC-0425 half-life was approximately 15 hours. There were two confirmed partial responses in patients with triple-negative breast cancer (TP53-mutated) and melanoma (n = 1 each) and one unconfirmed partial response in a patient with cancer of unknown primary origin. Conclusions: Chk1 inhibition with GDC-0425 in combination with gemcitabine was tolerated with manageable bone marrow suppression. The observed preliminary clinical activity warrants further investigation of this chemopotentiation strategy.