Head and neck squamous cell carcinoma (
HNSCC) is commonly associated with tobacco and alcohol consumption that induce a "precancerous field," with
phosphoinositide 3-kinase (PI3K) signaling being a common driver. However, the preclinical effectiveness of PI3K inhibitors has not necessarily translated to remarkable benefit in
HNSCC patients. Thus, we sought to determine how precancerous keratinocytes influence
HNSCC proliferation, cancer stem cell (CSC) maintenance, and response to PI3K inhibitors. We used the NOK keratinocyte cell line as a model of preneoplastic keratinocytes because it harbors two frequent genetic events in
HNSCC, CDKN2A promoter methylation and TP53 mutation, but does not form
tumors. NOK cell coculture or NOK cell-
conditioned media promoted
HNSCC proliferation, PI3K inhibitor resistance, and CSC phenotypes. SOMAscan-targeted proteomics determined the relative levels of >1300 analytes in the
media conditioned by NOK cells and
HNSCC cells ± PI3K inhibitor. These results demonstrated that NOK cells release abundant levels of
ligands that activate
epidermal growth factor receptor (EGFR) and
fibroblast growth factor receptor (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 can directly support neighboring
HNSCC by activating EGFR. Importantly, PI3K inhibitor sensitivity was 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 diminished EGFR activation induced by PI3K inhibitor and potently inhibited
cancer cell proliferation and CSC maintenance.