2′,4′-Dihydroxy-6′-methoxy-3′,5′-dimethylchalcone, a potent Nrf2/ARE pathway inhibitor, reverses drug resistance by decreasing glutathione synthesis and drug efflux in BEL-7402/5-FU cells

2',4'-Dihydroxy-6'-methoxy-3',5'-dimethylchalcone (DMC) is a major active constituent of the buds of Cleistocalyx operculatus (Roxb.) Merr. et Perry (Myrtaceae), a main ingredient of herbal tea in tropical zones. DMC has been reported to significantly reverse drug resistance in BEL-7402/5-FU cells. Glutathione (GSH) and glutathione S-transferase (GST) play important roles in an efflux system that protects the cells from anticancer drugs. In this study, DMC remarkably decreased the intracellular GSH content and GST activity. Furthermore, DMC suppressed the expression of factor erythroid 2-related factor 2 (Nrf2), prevented Nrf2 nuclear translocation, and inhibited the binding of Nrf2 to the antioxidant response element (ARE). The glutamate-cysteine ligase catalytic subunit (GCLC) and glutamate-cysteine ligase modifier subunit (GCLM) were down-regulated by inhibiting Nrf2 with DMC treatment. These results suggested that DMC reduced drug efflux to reverse drug resistance by suppressing the Nrf2/ARE signaling pathway in human hepatocellular carcinoma BEL-7402/5-FU cells.