Adavosertib in Combination with Olaparib in Patients with Refractory Solid Tumors: An Open-Label, Dose-Finding, and Dose-Expansion Phase Ib Trial.

Background: Adavosertib is a first-in-class, selective small-molecule inhibitor of Wee1. Olaparib is an inhibitor of poly(ADP-ribose) polymerase (PARP). Preclinical data suggest that adavosertib enhances the antitumor effect of PARP inhibitors.

Objective: The safety, tolerability, and efficacy of adavosertib plus olaparib were evaluated in patients with refractory solid tumors to define the maximum tolerated dose (MTD) and recommended phase II dose (RP2D).

Patients and methods: Eligible patients in part A (dose finding) had a refractory solid tumor for which there is no established treatment and had received ≥ 1 prior course of systemic therapy; in part B (dose expansion), patients had platinum-sensitive extensive-stage or relapsed small-cell lung cancer (SCLC). Patients received adavosertib [once (qd) or twice daily (bid)] for 3 consecutive days with 4 days off treatment (3/4), or 5 consecutive days with 2 days off (5/2), plus olaparib (bid) for 14 or 21 days of a 21-day cycle.

Results: A total of 130 patients were enrolled in the study, 120 in part A and 10 in part B. The MTD for adavosertib bid was 175 mg (days 1-3, 8-10/21-day cycle) plus continuous olaparib 200 mg bid; the once-daily MTD (and RP2D) was adavosertib 200 mg (days 1-3, 8-10/21-day cycle) plus continuous olaparib 200 mg bid. In the MTD/RP2D cohort, one patient (7%) experienced a dose-limiting toxicity (DLT) of thrombocytopenia. The most common treatment-related adverse events (TRAEs) in the cohorts in which MTD/RP2D for bid dosing and RP2D for qd dosing were determined were fatigue (64.3% and 15.4%, respectively), diarrhea (42.9% and 30.8%), decreased appetite (35.7% and 23.1%), nausea (35.7% and 15.4%), and anemia (35.7% and 38.5%). In the SCLC dose-expansion cohort, TRAEs occurred in eight patients (88.9%), including thrombocytopenia (66.7%) and anemia (55.6%). In part A, objective response rate (ORR) was 14.8% [95% confidence interval (CI) 8.7-22.9] overall; for the cohorts in which MTD/RP2D for bid dosing and RP2D for qd dosing were determined, ORR was 30.8% (9.1-61.4) and 9.1% (0.2-41.3), respectively. ORR was 11.1% [95% CI 0.3-48.2; one partial response (PR)], disease control rate was 22.2% (2.8-60.0; one PR, one stable disease), and median progression-free survival was 1.5 months (1.3-4.2) in the SCLC dose-expansion cohort.

Conclusions: Adverse events and DLTs observed in the bid MTD and once-daily MTD/RP2D dosing schedules were manageable and consistent with known adavosertib and olaparib safety profiles. Limited antitumor activity was observed with adavosertib plus olaparib combination therapy.

Trial registration: ClinicalTrials.gov, NCT02511795 (registration: 28 July 2015).