Spontaneous mitochondrial membrane potential change during apoptotic induction by quercetin in K562 and K562/adr cells

Natural products from plants such as flavonoids are potential drugs to overcome multidrug resistance (MDR) in cancer treatments. However, their modes of action are still unclear. In this study, the effects of quercetin on mitochondrial membrane potential (DeltaPsi(m)) change as well as quercetin's ability to induce apoptosis and inhibit Pgp-mediated efflux of Tc-99m-MIBI in K562/adr cells were investigated. Quercetin exhibits cytotoxicity against erythroleukemic cells: IC50 are 11.0 +/- 2.0 mumol/L and 5.0 +/- 0.4 mumol/L for K562 and K562/adr, respectively. Quercetin induces cell death via apoptosis in both K562 and K562/adr cells and does not inhibit Pgp-mediated efflux of Tc-99m-MIBI. Quercetin (10 mumol/L, 3 h) and etoposide (100 mumol/L, 24 h) induce similar levels of apoptosis in K562 and K562/adr cells. Quercetin induces an increase followed by a decrease in \DeltaPsi(m)\ value depending on its concentration. A decrease in the \DeltaPsi(m)\ value is associated with an increase in the percentage of early apoptotic cells. It is clearly shown that quercetin results in a spontaneous DeltaPsi(m) change during apoptotic induction. Therefore, quercetin is potentially an apoptotic-inducing agent, which reacts at the mitochondrial level.