Abstract LB-313: Precancerous keratinocytes promote neighboring HNSCC cancer stem cell-like properties and PI3K inhibitor insensitivity via EGFR

Abstract

Head and neck squamous cell carcinoma (HNSCC) is the sixth most common cancer in the world and HNSCC patients have relatively few effective treatment options. Genomic analyses of HNSCCs have demonstrated that genes encoding components of the phosphoinositide 3-kinase (PI3K) signaling pathway are amongst the most frequently mutated and amplified. Because PI3K drives cancer cell proliferation and survival, PI3K inhibitors are being evaluated as anti-cancer therapeutic agents. However, the preclinical effectiveness of PI3K inhibitors has not necessarily translated to remarkable benefit in cancer patients. A large proportion of HNSCC is associated with tobacco and alcohol consumption that induce genetic lesions in a field of mucosa, the “precancerous field”. Carcinomas often arise from this precancerous field. Thus, we sought to determine how precancerous keratinocytes influence HNSCC proliferation, cancer stem cell (CSC) maintenance and response to PI3K inhibitors. The keratinocyte cell line NOK harbors CDKN2A promoter methylation and TP53 mutation (two frequent genetic events in HNSCC), but does not form tumors. Thus, we used NOK cells as a model of precancerous keratinocytes and examined their effect on two different HNSCC cell lines, CAL27 and UMSCC1. NOK cells promoted HNSCC proliferation and PI3K inhibitor resistance in co-culture assays. Similarly, NOK cell conditioned media applied to recipient HNSCC cells promoted proliferation, PI3K inhibitor resistance and CSC phenotypes. We utilized SOMAscan, a targeted proteomics platform, to determine the relative levels of >1,300 analytes in the media conditioned by NOK cells and control cells in the presence and absence of PI3K inhibitor. These results demonstrated that NOK cells release abundant levels of ligands that activate EGFR and FGFR, two receptor tyrosine kinases with oncogenic activity. Inhibition of EGFR, but not FGFR, blunted PI3K inhibitor resistance and CSC phenotypes induced by NOK cells. Our results demonstrate that precancerous keratinocytes directly support neighboring HNSCC by activating EGFR. Importantly, PI3K inhibitor sensitivity is not necessarily a cancer cell-intrinsic property and the tumor microenvironment impacts therapeutic response and supports CSCs. Additionally, combined inhibition of EGFR with PI3K inhibitor diminishes EGFR activation induced by PI3K inhibitor and potently inhibits cancer cell proliferation and CSC maintenance. We are currently establishing mouse models of the oral precancerous field and testing its influence on HNSCC and immune cell function. Citation Format: Khoa A. Nguyen, Madison J. Keith, Xiao-Jing Wang, Christian D. Young. Precancerous keratinocytes promote neighboring HNSCC cancer stem cell-like properties and PI3K inhibitor insensitivity via EGFR [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr LB-313.