[Cetuximab in combination with icotinib overcomes the acquired resistance caused by EGFR T790M mutation in non-small cell lung cancer].

Objective The aim of this study was to investigate the effects of combination of icotinib and cetuximab on the acquired drug resistance caused by T790M mutation of EGFR in NSCLC,and provide experimental evidence for rational treatment of NSCLC.Methods The effects of these two agents on cell proliferation,apoptosis,and EGFR-dependent signaling were evaluated using 3-(4,5-dimethylthiazol-2-yl)-5-diphenyltetrazolium bromide (MTT) assay,annexin V staining,and Western blotting.The expression of molecular markers of tumor proliferation PCNA and Ki-67 protein was further examined by immunohistochemistry,and the expression of EGFR-signaling-related proteins in tissue sections taken fromH1975 tumor xenografts was assessed by Western blot assay.Sensitivity to EGFR inhibitors was detected in human H1975 tumor xenograft in nude mice.Results The in vitro experiment showed that the proliferative ability of H1975 cells was inhibited in a dose-dependent manner,along with the increasing doses of cetuximab and icotinib,and the combination of cetuximab with icotinib resulted in a more pronounced growth inhibition of the H1975 cells.The apoptosis rate of H1975 cells after treatment with 0.5 μmol/L icotinib and 1μg/ml cetuximab was (22.03 ± 2.41)％ and that after treatment with 5 μmol/L icotinib and 10 μg/ml cetuximab was (42.75 ± 2.49) ％,both were significantly higher than that after treatment with the same dose of icotinib or cetuximab alone (P ＜ 0.05).The nude mouse experiment showed that the transplanted tumor was growing to (614.5 ± 10.8)mm3 in the blank control group and to (611.2 ± 8.7)mm3 at 28 days after icotinib treatment,but (30.8 ± 2.0) mm3 in the cetuximab treatment group and 0 mm3 in the cetuximab combined with icotinib group.There was a significantly decreased expression of Ki-67 and PCNA proteins and down-regulation of phosphorylation of EGFR signaling-related proteins in the cetuximab combined with icotinib group.Conclusions The combination of icotinib with cetuximab can exert synergistic inhibitory effect on the acquired drug resistance caused by T790M mutation of EGFR in NSCLC H1975 cells,interrupts the EGFR-downstream signaling pathway,and enhances the anticancer activity of chemotherapeutic drugs.Our results provide further experimental evidence for the clinical studies of combination of icotinib with cetuximab in the treatment of NSCLC patients associated with secondary drug resistance caused by T790M mutation of EGFR. Key words: Carcinoma, non-small-cell lung;  H1975 cell line;  Epidermal growth factor receptor;  Epidermal growth factor receptor tyrosine kinase inhibitor;  Cetuximab;  Mice