Plasma Cell-free DNA Concentration And LINE-1 Methylation In Non-small Cell Lung Cancer Before And After Operation

Background and ObjectiveLung cancer is the leading cause of cancer death.Lung adenocarcinoma accounts for the largest proportion.There is no relatively non-invasive early diagnosis and dynamic monitoring of blood biomarkers for surgically resected lung cancer.Circulating cell-free(cfDNA)have the advantages of reflecting the heterogeneity of tumors and real-time changes.CfDNA may become a method of supplemental screening and early diagnosis of lung cancer.Concentrations and epigenetic variations(such as DNA methylation)of cfDNA may provide useful monitoring of treatment efficacy or diagnostic information.CfDNA contains circulating tumor(ctDNA)released from the tumor cells into the blood,but most of cfDNA are not of cancer origin.Therefore,it has been difficult to detect cancer-related alleles in cfDNA containing a large amount of non-tumorigenicity.Long interspersed nuclear elements-1(LINE-1),is a repetitive sequence accounts for about 17%of genomic DNA which facilitates detection and is associated with tumorigenesis.Previous studies have confirmed LINE-1 Studies have confirmed the hypomethylation of LINE-1 in lung cancer tissues and hypermethylation in healthy individuals.However,the methylation of LINE-1 in cfDNA has not been studied yet.The purpose of this thesis is to study the difference of plasma cfDNA concentration and LINE-1 methylation level between healthy and resectable lung adenocarcinoma patients before and after surgery.To explore the potential clinical application value of plasma cfDNA concentration and LINE-1 methylation level in patients with lung adenocarcinoma,such as early diagnosis of lung cancer and treatment efficacy.MethodsThe cfDNA concentration was measured by ultra-high sensitivity QuantusTM Fluorometer(Promega,America).Taqman probe-labeled real-time quantitative PCR(qPCR)was used to detect LINE-1 methylation levels in plasma cfDNA for a total of 50 blood samples,including 40 blood samples collecting from 20 cases of lung adenocarcinoma patient pre-and postoperatition,10 blood samples collecting from healthy controls.Retrograde transposon LINE-1 methylation levels were analyzed by a relatively quantitative method.ResultsThe cfDNA concentration and LINE-1 methylation levels in patients with lung adenocarcinoma were significantly different before and after surgery.Pre-and postoperative plasma cfDNA concentrations were significantly higher than heathy subjects and preoperative levels were lower than postoperative levels.The LINE-1 methylation level of plasma cfDNA in the preoperative group was lower than that in the postoperative group and the healthy group.No significant difference in plasma circulating free DNA concentration was found associated with the clinical pathological parameters.The level of methylation of LINE-1 in plasma circulating free DNA was significantly different in gender and body mass index(BMI)groups.However,there was no significant difference in other clinicopathological groups.ConclusionThis study investigated the possibility of cfDNA concentration for early screening of lung cancer and found that cfDNA concentration was not associated with tumor resection.The further detection of specific LINE-1 methylation in plasma was negatively correlated with surgical resection of lung adenocarcinoma.The experimental results suggest that LINE-1 methylation changes in cfDNA are potential clinical blood biomarkers.