Head and neck squamous cell carcinoma (HNSCC) associated with high-risk human papilloma virus (HPV) infection is a growing clinical problem. The WEE1 kinase inhibitor AZD1775 (WEE1i) overrides cell cycle checkpoints and is being studied in HNSCC regimens. We show that the HPV16 E6/E7 oncoproteins sensitize HNSCC cells to single-agent WEE1i treatment through activation of a FOXM1-CDK1 circuit that drives mitotic gene expression and DNA damage. An isogenic cell system indicated that E6 largely accounts for these phenotypes in ways that extend beyond p53 inactivation. A targeted genomic analysis implicated FOXM1 signaling downstream of E6/E7 expression and analyses of primary tumors and The Cancer Genome Atlas (TCGA) data revealed an activated FOXM1-directed promitotic transcriptional signature in HPV+ versus HPV- HNSCCs. Finally, we demonstrate the causality of FOXM1 in driving WEE1i sensitivity. These data suggest that elevated basal FOXM1 activity predisposes HPV+ HNSCC to WEE1i-induced toxicity and provide mechanistic insights into WEE1i and HPV+ HNSCC therapies.

Inhibition of the protein kinase WEE1 induces cancer cell death by forcing cells arrested in S-phase directly into mitosis. However, in the absence of S-phase perturbations, WEE1 inhibition is typically insufficient to trigger premature mitosis. Here, we show that WEE1 inhibition alone drives premature mitotic entry in HPV+ head and neck cancer cells. We also observed unscheduled mitotic entry in E6- and E6E7-expressing HPV-negative UMSCC74a cells upon WEE1 inhibition, but not in empty vector controls. Unlike E6 expression, p53 depletion alone was not sufficient to cooperate with WEE1 inhibition to effect forced mitotic entry. In vitro kinase assays showed elevated CDK1 activity in E6 and E6E7 cells compared to empty vector controls, particularly after WEE1 inhibition. We find that addiction of E6E7 cells to cell cycle inhibitor p21 causes the AZD1775-mediated CDK hyperactivation, therefore intensifying genotoxic replication stress. WEE1 inhibition therefore exacerbates E6E7-associated replication stress leading to slowing of replication forks, excess single-stranded DNA, and elevated RPA loading. RPA depletion further sensitized E6E7 cells to WEE1 inhibition-induced ssDNA accumulation, DNA damage, and cell death, implying a role for RPA in limiting WEE1i-induced replication stress in E6E7-expressing cells. Hallmarks of replication stress and DNA damage persisted in E6E7-expressing cells after recovery from WEE1 inhibition. These observations collectively explain the unique hypersensitivity of HPV+ head and neck tumors to WEE1i. Citation Format: Ahmed Diab, Jherek Swanger, Hakan Gem, Denise Galloway, Eduardo Mendez, Julia Sidorova, Bruce Clurman. WEE1 inhibition triggers premature mitotic entry in HPV16-E6-expressing cells independent of p53 inactivation [abstract]. In: Proceedings of the AACR-AHNS Head and Neck Cancer Conference: Optimizing Survival and Quality of Life through Basic, Clinical, and Translational Research; 2019 Apr 29-30; Austin, TX. Philadelphia (PA): AACR; Clin Cancer Res 2020;26(12_Suppl_2):Abstract nr PR07.