Involvement of DNA methyltransferase 1 (DNMT1) and multidrug resistance-associated proteins in 2-methoxyestradiol-induced cytotoxicity in EC109/Taxol cells

BACKGROUND: Due to acquired drug resistance, paclitaxel-based chemotherapy has limited clinical effects in the treatment of various tumors including esophageal cancer. This study analyzes the hypothesis that paclitaxel resistance is related to changes in the expression of DNA methyltransferase 1 (DNMT1). The thesis also studies multidrug resistance-related proteins and the mechanism underlying 2-methoxyestradiol (2-ME)-induced cytotoxicity in EC109/Taxol cells was examined. METHODS: In this study, the mechanisms of 2-ME-induced cytotoxicity in EC109/Taxol cells was determined by a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, flow cytometry, DNA ladder assay, DNMT activity assay, and Western blotting. The result of 2-ME-induced cytotoxicity EC109/Taxol cells is compared with that of EC109 parental cells. RESULTS: The results show that low concentrations of 2-ME (0.5–10 µM) inhibited cell growth, with IC50 values of 2.04 and 5.38 µmol/L in EC109/Taxol cells and EC109 parental cells after 72 hours of treatment, respectively. Exposure to 2-ME could increase G2/M cell cycle arrest and could increase apoptosis more effectively in EC109/Taxol cells than that observed in the EC109 parental cells. Furthermore, it is observed that paclitaxel resistance is associated with decreased DNMT activity. This study shows that 2-ME decreases DNMT1-mediated paclitaxel resistance by simultaneously reducing the expression of ATP-binding cassette (ABC) transporters, including phosphoglycoprotein (P-gp), breast cancer resistance protein (BCRP), and multi-drug resistance protein 1 (MRP1), in EC109/Taxol cells. CONCLUSIONS: In this study, the co-treatment of Taxol and 2-ME to EC109 could significantly induce cytotoxic effects, whose mechanism might be associated with DNMT1 and multidrug resistance-associated proteins.