Abstract
ABSTRACT Aim: With targeted therapy improving the survival of advanced stage epidermal growth factor receptor (EGFR)-mutant non-small cell lung cancer (NSCLC) patients, resistannce remains a major issue in the application of EGFR tyrosine kinase inhibitors (TKIs). Bim, a Bcl-2 family pro-apoptotic protein, has been intensively studied for its role in various targeted therapies. Hence we investigated the epigenetic regulation of Bim in NSCLC cell lines and patients in the hope of identifying its relationship with EGFR TKI resistance. Methods: Methylation specific PCR, pyrosequencing and nested quantitative MSP (nested q-MSP) were applied to study the methylation status of BIM in NSCLC cell lines and the BIM methylation profile in NSCLC patients was assessed by nested q-MSP. PC9 and its gefitinib-resistant cell lines were treated with methylation inhibitor 5-aza-2′-deoxycytidine (AZA) and histone deacetylation inhibitor trichostatin A (TSA) before gefitinib treatment. Bim RNA level, cell survival and resistance to gefitinib were examined. The distribution of various levels of methylated BIM and their relationship with EGFR TKI efficacy was statistically analyzed. Results: 8 NSCLC cell lines all carried hypo-methylated BIM. AZA did not increase the expression of Bim in PC9 and its gefitinib-resistant cell lines, nor did it reverse their resistance to gefitinib. Instead, cells experienced less apoptosis from gefitinib when pre-treated with AZA. TSA on the other hand, not only increased the expression of Bim RNA significantly in the three cell lines, but also reversed their resistance to gefitinib. 25 (78.1%) patients with hypo-methylated BIM and 7 (21.9%) with partial or hyper-methylated BIM were identified. Hypo-methylated BIM distributed randomly in different clinicalpathological charcteristics. In both the entire study group and EGFR mutant group, hypo-methylated BIM carriers experienced no significant PFS difference compared with patients with partial or hyper-methylated BIM. Conclusions: All cell lines in the study and the majority of patients were with hypo-methylated BIM. AZA didn't reverse the resistance to EGFR TKI in acquired resistant cell lines PC9/R and PC9/G2, while HDACi TSA did. Thus histone deacetylation, rather than promoter methylation, may play a major role in the epigenetic silencing of BIM and leads to EGFR TKI resistance in NSCLC. Disclosure: All authors have declared no conflicts of interest.
Published Version
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