Abstract
Multidrug resistance (MDR) has become a significant challenge in chemotherapeutic treatment of cancer. Quercetin, a naturally occurring flavonoid, has been found to possess anti-proliferative, anti-inflammatory and immunoregulatory bioactivities. The present study was performed to examine the effect of quercetin on human leukemic MDR K562/adriamycin (ADR) cells. Treatment of K562/ADR cells with a combination of quercetin and ADR resulted in potentiation of cytotoxicity, which was measured using a cell counting kit-8 assay. Flow cytometric analysis revealed that quercetin dose-dependently promoted cell apoptosis and treatment with a combination of quercetin and ADR caused synergistic enhancement of the apoptotic effect. In addition, treatment of K562/ADR cells with quercetin alone or in combination with ADR resulted in loss of mitochondrial membrane potential, activation of caspase-8, -9 and -3, reduced expression of the anti-apoptotic proteins B-cell lymphoma (Bcl)-2 and Bcl-extra large and enhanced expression of the pro-apoptotic proteins Bcl-2-interacting mediator of cell death, Bcl-2-associated death promoter and Bcl-2-associated X protein in the cells. Furthermore, the combined treatment of quercetin and ADR synergistically increased the expression of phosphorylated (p-)c-Jun N-terminal kinase and p-p38 mitogen-activated protein kinase and decreased the expression of p-extracellular signal-regulated kinase in the K562/ADR cells. In addition, the expression of P-glycoprotein was significantly decreased following treatment with quercetin alone or in combination with ADR. These findings demonstrated that quercetin is important in MDR and may be developed into a new reversal agent for cancer chemotherapy.