Abstract: Objective To explore the role of epithelial-mesenchymal transition（EMT） in the acquired resistance to epidermal growth factor receptor-tyrosine kinase inhibitors（EGFR-TKIs） in nonsmall cell lung cancer（NSCLC）.
Methods The EGFR del E746-A750-mutated human lung adenocarcinoma PC9／AB cell line and the EGFR wild-type H460/ER cell line were used in this study. The role of EMT in the acquired resistance to EGFR-TKIs was investigated by establishing stable E-cadherin over-expression cell lines（PC9／AB-CDH1 and H460/ER-CDH1） by transforming gene-CDH1 with lentivirus. MTT assay was used to measure the cell proliferation. Wound-healing assay and Transwell assay were adopted to determine the migration and invasion ability of the cells. The mRNA and protein expressions of E-cadherin， Vimentin， Snail， β-catenin and EGFR were determined by the real-time fluorescence quantitative PCR（qRT-PCR） and Western blotting，respectively.
Results EMT（low E-cadherin and high Vimentin）was found in H460／ER and PC9／AB cells， neither T790M mutation nor c-Met amplification were detected. Over-expression of E-cadherin in both PC9／AB-CDH1 and H460／ER-CDH1 cells reversed morphological signature of EMT. Reversing of EMT remarkably increased the sensitivity to EGFR-TKIs in PC9／AB-CDH1and H460／ER-CDH1 cells. Compared with PC9／AB cells， the sensitivity to gefitinib in PC9/ABCDH1 cells increased 11.4 folds. The half-inhibition concentration（IC50）of PC9／AB-CDH1 and PC9/AB cells was （0.70±0.22）μmol／L and （8.68±0.44）μmol/L with statistical significance（P＜0.05）. Compared with H460/ER cells, the sensitivity to erlotinib in H460/ERCDH1 cells increased 6.1 folds. The IC50 of H460/ER-CDH1 and H460/ER cells was （7.51±1.12） μmol/L and （53.72±12.95） μmol/L with statistical significance（P＜0.05）. The expressions of EGFR and its phosphorylation form in both PC9／ABCDH1and H460／ER-CDH1 cells were significantly increased（P＜0.05）.
ConclusionIt demonstrates that reversing of EMT can reverse the acquired gefitinib／erlotinib-resistance in NSCLC， which suggests that EMT plays an important role in the acquired resistance to EGFR-TKIs in NSCLC， possibly through down-regulating the phosphorylation of EGFR.