Hypoxia alters the response to anti-EGFR therapy by regulating EGFR expression and downstream signaling in a DNA methylation-specific and HIF-dependent manner.

Intratumoral hypoxia occurs in 90% of solid tumors and is associated with a poor prognosis for patients. Cancer cells respond to hypoxic microenvironments by activating the transcription factors hypoxia-inducible factor 1 (HIF-1) and HIF-2. Here we studied the unique gene expression patterns of 31 different breast cancer cell lines exposed to hypoxic conditions. The epidermal growth factor receptor (EGFR), a member of the ErbB (avian erythroblastosis oncogene B) family of receptors that play a role in cell proliferation, invasion, metastasis, and apoptosis, was induced in 7 of the 31 breast cancer cell lines by hypoxia. A functional hypoxia response element (HRE) was identified, which is activated upon HIF-1 binding to intron 18 of the EGFR gene in cell lines in which EGFR was induced by hypoxia. CpG methylation of the EGFR HRE prevented induction under hypoxic conditions. The HRE of EGFR was methylated in normal breast tissue and some breast cancer cell lines and could be reversed by treatment with DNA methyltransferase inhibitors. Induction of EGFR under hypoxia led to an increase in AKT, ERK, and Rb phosphorylation as well as increased levels of cyclin D1, A, B1, E2F, and repression of p21 in a HIF-1α-dependent manner, leading to cell proliferation and migration. Increased expression of EGFR sensitized cells to EGFR inhibitors. Collectively, our data suggest that patients with hypoxic breast tumors and hypomethylated EGFR status may benefit from EGFR inhibitors currently used in the clinic.