Knockdown of the Epidermal Growth Factor Receptor Gene to Investigate Its Therapeutic Potential for the Treatment of Non–Small-Cell Lung Cancers

BackgroundEpidermal growth factor receptor (EGFR) is often overexpressed in non–small-cell lung cancer (NSCLC). Anti-EGFR agents, including EGFR-tyrosine kinase inhibitors are considered to be effective when a drug-sensitive EGFR mutation is present. However, inherent and acquired resistances are major problems of EGFR-targeting therapies. In this study, we performed EGFR knockdown by using small interfering RNAs in NSCLC cell lines to examine the significance of targeting EGFR for NSCLC therapy.MethodsWe treated 13 NSCLC cell lines, including 8 EGFR mutant and 5 EGFR wild type by using gefitinib or small interfering RNAs against EGFR (siEGFR). Three cell lines (PC-9-GR1, RPC-9, and HCC827-ER) were experimentally established with acquired resistance to EGFR-tyrosine kinase inhibitors. The antitumor effect was determined by using an 3-[4,5-dimethylthiazol-2-yl]-5-[3-carboxymethoxyphenyl]-2-[4-sulfophenyl]-2H-tetrazolium, inner salt (MTS) or colony formation assay. The protein expression was evaluated by using Western blotting.ResultsAll 13 cell lines expressed EGFR protein, and siEGFR downregulated EGFR protein expression in all. The cell viability was suppressed by siEGFR in 6 of 8 EGFR-mutant cell lines (suppressed 57%-92% of control cells), including PC-9-GR1 and RPC-9. The NCI-H1650 and HCC827-ER harbored EGFR mutations but were not suppressed. Of note, PTEN (phosphatase and tensin homolog) was deleted in NCI-H1650, and c-MET was amplified in HCC827-ER. It was not suppressed in any of the EGFR wild-type cells except in the NCI-H411, in which EGFR is phosphorylated, which indicates its activation. Conclusions: Analysis of the results indicated that EGFR can be a therapeutic target in NSCLCs with EGFR activation. In contrast, targeting EGFR is not appropriate for tumors in which EGFR is not activated, even if EGFR is expressed.