Epigenome-wide Association Study On Early-stage Non-small Cell Lung Cancer

Lung cancer is the leading cause of cancer death worldwide,with non-small cell lung cancer(NSCLC)accounting for approximately 85%,mainly including lung adenocarcinoma(LUAD)and lung squamous cell carcinoma(LUSC).NSCLC has poor survival and exhibits histological heterogeneity requiring individualized treatment.DNA methylation as a heritable reversible epigenetic modification is an innovative cancer biomarker and therapeutic target.Objective:We performed a two-stage,epigenome-wide association study of DNA methylation of NSCLC patients and overall survival to explore possible epigenetic mechanisms affecting the prognosis of early NSCLC patients and to identify potential methylation biomarkers.Methods: The methylation data of 1230 early NSCLC patients from 5 international cooperation centers were integrated and divided into discovery set and validation set for a two-stage analysis.Meanwhile,we also combined the gene expression data from the Cancer Gene Atlas(TCGA)for related analysis.We conducted prognostic association studies from three perspectives: global,epigenome-smoking cessation interaction and candidate genes.Methods we used include relative entropy,cubic spline function,Cox proportional hazard model,stratified analysis,sensitivity analysis,random forests,and classification and regression trees.Results:(1)From a global perspective,we integrated information of all differential methylated CpG probes by relative entropy to calculate the methylation distribution difference between tumor tissues and adjacent normal tissues,and there was a nonlinear relationship between the distribution difference and overall survival of LUAD patients.(2)Based on epigenome-wide DNA methylation-smoking cessation interaction analysis,a LUAD-specific CpG probe(cg02268510)was identified that significantly modified the effect of smoking cessation on survival in LUAD patients.(3)By analyzing the methylation of CpG probes located in the candidate gene family EGLN1-3,we identified that DNA methylation at cg25923056 was significantly associated with survival of LUAD patients and was correlated with EGLN2 expression.Meanwhile,expression of EGLN2 and HIF1 A were significantly interacted on overall survival of LUAD patients.Conclusions: Both individual CpG analysis and global analysis showed that DNA methylation affects the prognosis of early NSCLC under different mechanisms.(1)The underlying mechanism of the nonlinear relationship between global methylation differences and overall survival of LUAD still needs further studies.Our research provides a new strategy for epigenetic research by detecting the relationship between methylation and prognosis from a global perspective.(2)Smoking cessation benefited survival of LUAD patients with low methylation at cg02268510.The results have implications for not only smoking cessation after diagnosis,but also possible methylation-specific drug targeting.(3)DNA methylation of EGLN2-HIF1 A is a potential marker for LUAD prognosis and these genes are potential treatment targets for further development of HIF-1α inhibitors in lung cancer therapy.