Establishment and biological characteristics of acquired gefitinib resistance in cell line NCI-H1975/gefinitib-resistant with epidermal growth factor receptor T790M mutation.

Non­small cell lung cancer (NSCLC) cells harboring mutations in the epidermal growth factor receptor (EGFR) gene initially respond well to EGFR tyrosine kinase inhibitors (TKI), including gefitinib. However the tumor cells will invariably develop acquired resistance to the drug. The EGFR T790M mutation is generally considered to be the molecular genetic basis of acquired TKI resistance. The present study aimed to explore how the T790M mutation induces tumor cells to escape inhibition by TKI treatment. An acquired gefitinib­resistant cell line (NCI­H1975/GR) was generated from the NCI­H1975 human NSCLC cell line, which harbors the sensitive L858R and resistant T790M mutations of EGFR. The resistant cell line was established by exposing the cells intermittently to increasing concentrations of gefitinib. The mechanisms by which NSCLC acquires resistance to TKIs based on the T790M mutation, were investigated by detecting the protein expression levels of the EGFR/Kirsten rat sarcoma viral oncogene homolog (KRAS)/v­Raf murine sarcoma viral oncogene homolog B (BRAF) transduction pathway, and epithelial­mesenchymal transition (EMT) with immunocytochemistry. The resistance of the NCI­H1975/GR cells to gefitinib was 2.009­fold, as compared with the parent cells; however, the protein expression levels of EGFR, KRAS and BRAF were lower in the resistant cells. Some mesenchymal morphology was observed in the NCI­H1975/GR cells, alongside a decreasing E­cadherin expression and increasing vimentin expression. These results suggest that the reactivation of the EGFR/KRAS/BRAF transduction pathway was not detected in the NCI­H1975/GR cells. EMT may have an important role in the development of acquired resistance to EGFR­TKIs in NSCLC cells with sensitivity and resistance mutations.