[Relationship between EGFR Promoter Region Methylation and Secondary Resistance Which may be Induced by Gefitinib].

BACKGROUND Nowadays the secondary resistance of gefitinib in the treatment of lung adenocarcinoma is an outstanding problem. This research is to explore whether the gefitinib secondary resistance can be induced by gefitinib, to explore whether epidermal growth factor receptor (EGFR) promotor methylation correlate with the gefitinib-resistance in PC9/GR cell lines and to find a new therapeutic target to overcome the gefitinib secondary resistance in lung adenocarcinoma. METHODS In vitro cultivation of lung adenocarcinoma PC9 cell lines, apply gefitinib on lung adenocarcinoma PC9 cell lines, and improve drug concentration. MTT for test of gefitinib resistance index in PC9 cell and PC9/GR cell. Bisulfite sequencing polymerase chain reaction (BSP) and Reverse transcription-polymerase chain reaction (RT-PCR) for detection of EGFR promoter methylation status and mRNA expression. In vitro cultivation of lung adenocarcinoma PC9 cell lines, apply 1 μmol/L 5-Aza-dc on lung adenocarcinoma PC9/GR cell lines for 72 h. MTT method for test of gefitinib resistance index in PC9/GR cell. RESULTS After improving the gefitinib concentration, MTT results showed that half maximal inhibitory concentration (IC50) of PC9 cell lines increase from (0.01 ± 0.002) μmol/L to (3.95 ± 0.23) μmol/L (P<0.05). BSP results showed that abnormal methylation sites compared the degree of methylation change: PC9: 59%; PC9/GR: 74% (P<0.05). RT-PCR results showed in PC9/GR cell lines, EGFR mRNA expression quantity increased (P<0.05). After applying 5-Aza-dc on PC9 cell lines, IC50 of PC9/GR decrease from (3.87 ± 0.034) μmol/L to (2.55 ± 0.14) μmol/L. CONCLUSIONS The PC9 cell line which is induced by improving gefitinib concentration will be resistant to gefitinib, and the gefitinib-resistant cell line PC9/GR could be built. EGFR gene promoter methylation may be one of the mechanisms for the secondary resistance to gefitinib.