Intratumor heterogeneity of EGFR expression mediates targeted therapy resistance and formation of drug tolerant microenvironment

Epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors are commonly used to treat non-small cell lung cancers with EGFR mutations, but drug resistance often emerges. Intratumor heterogeneity is a known cause of targeted therapy resistance and is considered a major factor in treatment failure. This study identified clones of EGFR-mutant non-small cell lung tumors expressing low levels of both wild-type and mutant EGFR protein. These EGFR-low cells were found to be intrinsically more tolerant to EGFR inhibitors, more invasive, and exhibited an epithelial-to-mesenchymal-like phenotype compared to their EGFR-high counterparts. The EGFR-low cells secrete TGFβ-family cytokines, leading to increased recruitment of cancer-associated fibroblasts and immune suppression, thus contributing to the drug-tolerant tumor microenvironment. Notably, pharmacological induction of EGFR using epigenetic inhibitors sensitized the resistant cells to EGFR inhibition. These findings suggest that intrinsic drug resistance could be prevented or reversed using combination therapies. PC-9 cells were stained with EGFR antibody and sorted 6 sequential rounds for 5-10% highest("EGFR-high") and 5-10% lowest ("EGFR-low") expressing cells. Bulk mRNA sequencing was conducted for PC-9 Parental cells, PC-9 EGFR-high cells and PC-9 EGFR-low cells.