Alterations in gene expression and DNA methylation profiles in gastric cancer cells obtained from ascitic fluids collected before and after chemotherapy

Resistance to anticancer drugs is a critical issue in cancer treatment. Alterations in gene expression and DNA methylation profiles that accompany the acquisition of drug resistance are associated with resistance mechanisms. To analyze chemotherapy-associated alterations in gene expression and DNA methylation in gastric cancer cells obtained from ascites, ascitic fluids were collected from a patient with gastric cancer before chemotherapy with capecitabine and oxaliplatin (CapeOX), and after the disease had progressed. The fluids were cultured for 10 days, passaged into new flasks, and cultured for an additional 2 weeks. Normal cells, including white blood cells and mesothelial cells, were removed. The expression and DNA methylation profiles of 18,185 genes were analyzed using microarray, and compared between cells in ascitic fluids collected before and after the chemotherapy with CapeOX. In addition, fluorouracil- and oxaliplatin-resistant AGS cells were established and analyzed. Pathways having genes with expression profiles altered by CapeOX included those associated with signaling by G-protein-coupled receptor' and the immune system'. Genes that were commonly expressed at higher levels in CapeOX-resistant ascitic cells, fluorouracil-resistant AGS cells. and oxaliplatin-resistant AGS cells compared with those in untreated cells included telomerase reverse transcriptase (TERT), apolipoprotein C1 (APOC1) and serine/threonine/tyrosine kinase 1 (STYK1), whereas genes commonly expressed at lower levels in the three drug-resistant cell types compared with the untreated cells included defensin beta 4A (DEFB4A). A comparatively large number of genes exhibited altered methylation levels in drug-resistant AGS cells compared with the CapeOX-resistant cells. In addition, among the genes expressed at higher levels in decitabine-treated AGS cells, the majority were expressed at higher levels in fluorouracil-resistant AGS cells, and exhibited lower methylation levels. Taken together, the present study has demonstrated that comparing the expression profiles of gastric cancer cells obtained from ascitic fluids before and after chemotherapy with the expression profiles of drug-resistant cultured cells is a useful method for analyzing the molecular mechanisms underlying chemotherapy resistance.