Acceleration of MRP-associated efflux of rhodamine 123 by genistein and related compounds.

Multidrug resistance (MDR), caused by overexpression of either P-glycoprotein or the multidrug resistance protein (MRP), is characterised by a decreased cellular drug accumulation due to an enhanced drug efflux. In this study, we examined the effects of genistein and structurally related (iso)flavonoids on the transport of rhodamine 123 (Rh123) and daunorubicin in the MRP-overexpressing MDR lung cancer cell lines COR-L23/R and MOR/R. Genistein, genistin, daidzein and quercetin showed major differences in effects on Rh123 vs daunorubicin transport in the MRP-mediated MDR cell lines: the accumulation of daunorubicin was increased, whereas the accumulation of Rh123 was decreased by the flavonoids. The depolarisation of the membrane potential caused by genistein might be involved in the acceleration of the efflux of Rh123 measured in the MRP-overexpressing cell lines. These observations should be taken into account when using fluorescent dyes as probes for determination of transporter activity as a measure of MDR.