Safety, anti-tumor activity, and biomarker analysis in a phase 1 trial of the once-daily Wee1 inhibitor adavosertib (AZD1775) in patients with advanced solid tumors.

Purpose The Wee1 kinase inhibitor adavosertib abrogates cell cycle arrest, leading to cell death. Prior testing of twice-daily adavosertib in patients with advanced solid tumors determined the recommended phase 2 dose (RPh2D). Here, we report results for once-daily adavosertib. Patients and methods A 3 + 3 dose escalation design was used, with adavosertib given once daily on days 1-5 and 8-12 in 21-day cycles. Molecular biomarkers of Wee1 activity, including tyrosine 15-phosphorylated Cdk1/2 [pY15-Cdk]), were assessed in paired tumor biopsies. Whole-exome sequencing and RNA sequencing of remaining tumor tissue identified potential predictive biomarkers. Results Among the 42 patients enrolled, the most common toxicities were gastrointestinal and hematological; dose-limiting toxicities were grade 4 hematological toxicity and grade 3 fatigue. The once-daily RPh2D was 300 mg. Six patients (14%) had confirmed partial responses (PR): 4 ovarian, 2 endometrial. Adavosertib plasma exposures were similar to those from twice-daily dosing. On cycle 1 day 8 (pre-dose), tumor pY15-Cdk levels were higher than baseline in 4 of 8 patients, suggesting target rebound during the day 5-8 dosing break. One patient who progressed rapidly had a tumor WEE1 mutation and potentially compensatory PKMYT1 overexpression. Baseline CCNE1 overexpression occurred in both of 2 responding patients, only 1 of whom had CCNE1 amplification, and in 0 of 3 non-responding patients. Conclusions We determined the once-daily adavosertib RPh2D and observed activity in patients with ovarian or endometrial carcinoma, including 2 with baseline CCNE1 mRNA overexpression. Future studies will determine whether CCNE1 overexpression is a predictive biomarker for adavosertib.