Transport of new non-cross-resistant antitumor compounds of the benzoperimidine family in multidrug resistant cells

Multidrug resistance (MDR) phenotype in mammalian cells is often correlated with overexpression of P-glycoprotein or multidrug resistance-associated p rotein (MRP1). Both proteins are energy-dependent drug efflux pumps that ef ficiently reduce the intracellular accumulation and hence the cytotoxicity of many natural cytotoxins. The influx and efflux of drugs across the cell membrane are in large part responsible for their intracellular concentratio ns, and in the search for new compounds able to overcome MDR, it is of prim e importance to determine the molecular parameters whose modification would lead to an increase in the kinetics of uptake and/or to a decrease in the pump-mediated efflux. Here, we studied three members of a new family of ben zoperimidine antitumor compounds which exhibit comparable cytotoxicity towa rds resistant cells expressing P-glycoprotein, or MRP1, and sensitive cells . We used spectrofluorometric methods to determine the kinetics of the upta ke and release of these three drugs in different cell lines: the erythroleu kemia cell line K562 and the resistant K562/Adr expressing P-glycoprotein, the small-cell lung cancer cell line GLC4 and resistant GLC4/Adr expressing MRP1. We also studied, using confocal microscopy, the intracellular distri bution of these drugs in NIH/3T3 cells. Our data show that (i) the kinetics for the uptake of these drugs is very rapid, higher than 2 x 10(-17) mole cell(-1) s(-1), (ii) the drugs are strongly accumulated in the nucleus and lysosomes, (iii) the three drugs are recognized and pumped out by both tran sporters, as shown by the inhibition of P-glycoprotein- and MRP1-mediated e fflux of pirarubicin by benzoperimidine, with inhibitory constants of 1.5 a nd 2.1 muM for P-glycoprotein and MRP1, respectively, suggesting that benzo perimidine is transported by the two transporters with K-m similar to 2 muM . In conclusion, the fast uptake kinetics of the benzoperimidines counterba lance their efflux by P-glycoprotein and MRP1. (C) 2001 Elsevier Science B. V. All rights reserved.