Long-term exposure to gefitinib induces acquired resistance through DNA methylation changes in the EGFR-mutant PC9 lung cancer cell line

This study was designed to identify epigenetically regulated genes and to clarify the contribution of epigenetic alteration to acquired resistance to epidermal growth factor receptor-tyrosine kinase inhibitors (EGFR-T KIs). We established a gefitinib-resistant lung cancer cell line, PC9, which was originally gefitinib-sensitive, by serial long-term exposure to gefitinib. RNA and DNA were collected from both gefitinib-sensitive and -resistant PC9 cells, and comprehensive DNA methylation and mRNA expression analyses were performed using Infinium HumanMethylation27 Bead Arrays and Agilent SurePrint G3 Human Gene Expression 8x60K Array, respectively. DNA methylation was increased in 640 genes in gefitinib-resistant cells compared to parental cells. Among them, we selected 29 candidate genes that presented a decrease in mRNA expression in resistant PC9. We further studied four of the selected genes (C10orf116, IGFBP3, KL, and S100P) and found that KL or S100P silencing by siRNA induced a decrease in gefitinib sensitivity compared to that in the negative control in PC9. In conclusion, KL and S100P could be potential targets to overcome resistance to EGFR-TKIs.