The role of epithelial-mesenchymal transition and insulin-like growth factorIreceptor in acquired resistance to epidermal growth factor-tyrosine kinase inhibitors in non-small cell lung cancer

Objective: To investigate the role of EMT (epithelial-mesenchymal transition) and IGF-1R (insulin-like growth factorⅠreceptor) in acquired resistance to EGFR-TKIs (epidermal growth factor receptor-tyrosine kinase inhibitors) in NSCLC (non-small cell lung cancer).  Methods: The EGFR mutant human lung adenocarcinoma PC-9 cell line and the EGFR wild-type H460 cell line were used to generate gefitinib-resistant PC-9 cells (named as PC-9/ZD cells) and erlotinib-resistant cells (named as H460/ER cells), respectively. MTT assay was used to measure the cell proliferation of PC9, PC-9/ZD, H460 and H460/ER cells. Wound-healing assay and Transwell assay were used to determine the migration and invasion capabilities of the cells. The protein and mRNA expressions of E-cadherin, vimentin, EGFR, ERK (extracellular signal-regulated kinase), AKT (protein kinase B) and IGF-1R were determined by Western blotting and RT-PCR (reverse transcription PCR), respectively. Results: Both PC-9/ZD and H460/ER cells acquired resistance to EGFR-TKIs which was to say that the sensitivities to gefitinib and erlotinib in PC-9/ZD and H460/ER cells were significantly decreased, respectively (P < 0.05). Compared with PC-9 and H460 cells, the PC-9/ZD and H460/ER cells displayed mesenchymal phenotypes, and their capabilities of invasion and migration were enhanced (P < 0.05). The expression of mesenchymal cell marker vimentin was increased in both PC-9/ZD and H460/ER cells (P < 0.05), and the expression of E-cadherin was decreased in PC-9/ZD cells (P < 0.05). The expressions of IGF-1R and its phosphorylated form in both PC-9/ZD and H460/ER cells were significantly increased (P < 0.05) as compared with those in the PC-9 and H460 cells, accompanied by up-regulation of phosphorylation levels of AKT and ERK (P < 0.05). No significant difference was found in phosphorylation level of EGFR between PC-9 and PC-9/ZD cells (P < 0.05), while the phosphorylation level of EGFR was significantly decreased in H460/ER cells as compared with that in H460 cells (P < 0.05). Conclusion: The EMT in EGFR mutant gefitinib-resistant PC-9/ZD cells and the EGFR wild-type erlotinib-resistant H460/ER cells was accompanied by a increase in protein expression of IGF-1R, which suggests EMT and IGF-1R signal transduction may play an important role in acquired resistance to EGFR-TKIs in NSCLC cells. DOI:10.3781/j.issn.1000-7431.2013.02.001