A Phase 1b Trial of Prexasertib in Combination with Standard-of-Care Agents in Advanced or Metastatic Cancer

Background The checkpoint kinase 1 (CHK1) inhibitor prexasertib exhibited modest monotherapy antitumor activity in prior trials, suggesting that combination with chemotherapy or other targeted agents may be needed to maximize efficacy. Objectives The aim of this study was to determine the recommended phase II dose and schedule of prexasertib in combination with either cisplatin, cetuximab, pemetrexed, or 5-fluorouracil in patients with advanced and/or metastatic cancer, and to summarize preliminary antitumor activity of these combinations. Patients and Methods This phase Ib, nonrandomized, open-label study comprised dose-escalation phase(s) with multiple sub-arms evaluating different prexasertib-drug combinations: Part A, prexasertib + cisplatin (n = 63); Part B, prexasertib + cetuximab (n = 41); Part C, prexasertib + pemetrexed (n = 3); Part D, prexasertib + 5-fluorouracil (n =8). Alternate dose schedules/regimens intended to mitigate toxicity and maximize dose exposure and efficacy were also explored in sub-parts. Results In Part A, the maximum tolerated dose (MTD) of prexasertib in combination with cisplatin (75 mg/m(2)) was declared at 80 mg/m(2), with cisplatin administered on Day 1 and prexasertib on Day 2 of a 21-day cycle. The overall objective response rate (ORR) in Part A was 12.7%, and 28 of 55 evaluable patients (50.9%) had a decrease in target lesions from baseline. The most frequent treatment-related adverse events (AEs) in Part A were hematologic, with the most common being white blood cell count decreased/neutrophil count decreased, experienced by 73.0% (any grade) and 66.7% (grade 3 or higher) of patients. In Part B, an MTD of 70 mg/m(2) was established for prexasertib administered in combination with cetuximab (500 mg /m(2)), both administered on Day 1 of a 14-day cycle. The overall ORR in Part B was 4.9%, and 7 of 31 evaluable patients (22.6%) had decreased target lesions compared with baseline. White blood cell count decreased/neutrophil count decreased was also the most common treatment-related AE (56.1% any grade; 53.7% grade 3 or higher). In Parts A and B, hematologic toxicities, even with the addition of prophylactic granulocyte colony-stimulating factor, resulted in frequent dose adjustments (> 60% of patients). In Part C, evaluation of prexasertib + pemetrexed was halted due to dose-limiting toxicities in two of the first three patients; MTD was not established. In Part D, the MTD of prexasertib in combination with 5-fluorouracil (label dose) was declared at 40 mg /m(2), both administered on Day 1 of a 14-day cycle. In Part D, overall ORR was 12.5%. Conclusions This study demonstrated the proof-of-concept that prexasertib can be combined with cisplatin, cetuximab, and 5-fluorouracil. Schedule was a key determinant of the tolerability and feasibility of combining prexasertib with these standard-of-care agents. Reversible hematologic toxicity was the most frequent AE and was dose-limiting. Insights gleaned from this study will inform future combination strategies for the development of prexasertib and next-generation CHK1 inhibitors. ClinicalTrials.gov Identifier NCT02124148 (date of registration 28 April 2014).

Automated summary

This study demonstrated that prexasertib can be effectively combined with cisplatin, cetuximab, and 5-fluorouracil. The schedule of administration is crucial in determining the tolerability and feasibility of combining prexasertib with these standard agents. Hematologic toxicity was the most common adverse event and dose-limiting factor in these combinations. Insights gained from this study will guide future combination strategies for the development of prexasertib and next-generation CHK1 inhibitors.