Epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs) are effective against non-small cell lung cancer (NSCLC) with EGFR-activating mutations. The mechanisms underlying EGFR-TKI resistance are not fully understood. Several studies have revealed that ligand-dependent activation of the EGFR signaling pathway is a putative mechanism for EGFR-TKI resistance. However, the specific effects remain unclear. This study analyzed the effects of seven EGFR ligands on EGFR-TKI sensitivity of NSCLC cells and patients, and demonstrated Epiregulin as a possible promoter for EGFR-TKI resistance.
Cells with EGFRE746-A750 delmutation were treated with seven recombinant EGFR ligands, we systemically assessed the response of EGFR-mutant cells to EGFR-TKIs in the presence of different EGFR ligands in vitro. The results revealed that epiregulin (EREG) showed the most significant inhibitory effect on TKI response. Furthermore, high expression of EREG was correlated with low clinical response and poor progression-free survival (PFS) in NSCLC patients receiving TKI treatment. However, the expression levels of the other six EGFR ligands were not correlated with erlotinib response or PFS of patients.
Mechanistically we have shown that EREG induced AKT phosphorylation and promoted TKI resistance by preventing apoptosis rather than promoting cell proliferation possibly through the EGFR/ErbB2 heterodimer. However, overexpression or knockdown of EREG in cancer cells had little impact on TKI sensitivity. Single-cell RNA sequencing data revealed that EREG was predominantly expressed in macrophages in the tumor microenvironment. In addition, EREG-enriched macrophage conditional medium induced EGFR-TKI resistance. We conclude that EREG expressed by macrophages in the tumor microenvironment induced TKI resistance by preventing apoptosis through the EGFR/ErbB2 heterodimer.
These results shed new light on the mechanism underlying EGFR-TKI resistance, and suggest macrophage-produced intratumoral EREG as a novel regulator and biomarker for EGFR-TKI therapy in NSCLC. These new findings lead patients to choose the proper EGFR-TKI treatment and provide a new way to overcome EGFR-TKI resistance, which may benefit NSCLC patients.