DNA repair gene promoter methylation in non-small cell lung cancer (NSCLC) patients treated with DNA damaging agents.

Abstract

e22130 Background: Approximately 75% of NSCLC patients are advanced at time of diagnosis. Treatments include regimens of DNA-damaging and alkylating agents. Previous in vitro studies have shown that loss of BRCA1 and BRCA2 function through promoter methylation increases sensitivity to sapacitabine, suggesting that tumor cells may be protected by repair systems including BRCA-RAD50 and MGMT pathways induced by DNA damage. The purpose of this study is to investigate the effect of DNA repair gene promoter methylation on outcome of NSCLC patients treated with DNA damaging agents. DNA repair gene promoter hypermethylation may sensitize tumor cells to DNA damaging agents. Methods: The patient group of 240 patients included 135 early stage and 105 late stage (III/IV) cases. Chemotherapy regimens of late stage patients included carboplatin, cisplatin and gemcitabine, as well as other non-DNA damaging agents. Mean overall survival (OS) was 43.7 months. DNA was extracted from micro-dissected primary tumor, bisulfite converted and assessed by pyrosequencing to quantify methylation of cytosine nucleotides along the MGMT, BRCA1 and BRCA2 promoters. Results: Overall average methylation values were 8.4%, 7.3% and 8.3% for MGMT, BRCA1, BRCA2 respectively (compared to 3.2%, 3.6% and 7.3%, respectively, in nonmalignant lung tissue). Percent promoter methylation levels were not significantly correlated with age, gender, smoking status nor histology, with the exception of higher MGMT promoter methylation in smokers. Hypermethylation (greater than 10%) of BRCA1 and BRCA2 promoter was not significantly associated with survival in late stage patients (6.6 mos vs 6.8 mos; p=0.533) in this patient group, however, superior survival was observed with BRCA2 promoter hypermethylation when early stage patients were included (29.3 mos vs median not reached; p=0.045). Promoter hypermethylation of MGMTwas significantly associated with lower five-year survival rate in early stage patients (p=0.022). Conclusions: These data suggest epigenetic control of DNA repair gene expression can affect response to therapy. Further studies on specific treatment regimens will be required to definitively assess these effects.