Secretion of high amounts of hepatocyte growth factor is a characteristic feature of cancer‐associated fibroblasts with EGFR‐TKI resistance‐promoting phenotype: A study of 18 cases of cancer‐associated fibroblasts

Humoral factors from cancer‐associated fibroblasts (CAFs) reportedly affect epidermal growth factor receptor tyrosine kinase inhibitor (EGFR‐TKI) resistance in cancer cells with EGFR mutations. The aim of this study was to identify the robust humoral factors secreted from CAFs that induce the primary resistance to EGFR‐TKI. We evaluated the EGFR‐TKI sensitivity of EGFR‐mutant lung adenocarcinoma cell line (PC‐9) treated with condition media (CM) from 18 cases of CAFs and matched non‐cancerous‐tissue‐associated fibroblasts (NCAFs). We measured the expression levels of hepatocyte growth factor (HGF), interleukin‐6, fibroblast growth factor‐2, insulin‐like growth factor‐1, and vascular endothelial growth factor‐A in CAFs and NCAFs. We examined whether HGF neutralizing antibody could annul the EGFR‐TKI resistance induced by CM from CAFs. Compared to CM from NCAFs, CM from CAFs increased the resistance of PC‐9 cells to EGFR‐TKI in five out of 18 cases. Relative expression ratio of HGF messenger RNA was significantly higher in these five CAFs compared to others ( P = 0.0013), whereas other cytokines were not. In four of these five cases, the addition of HGF neutralizing antibody significantly decreased the survival ratio of PC‐9 cells. This study suggests that the secretion of higher amounts of HGF is the robust feature of EGFR‐TKI resistance‐promoting CAFs.