title: Reversal of MRP-mediated multidrug resistance in human lung cancer cells by the antiprogestatin drug RU486.
abstract: Multidrug resistance-associated protein (MRP) and P-glycoprotein (P-gp) are drug efflux pumps conferring multidrug resistance to tumor cells. RU486, an antiprogestatin drug known to inhibit P-gp function, was examined for its effect on MRP activity in MRP-overexpressing lung tumor GLC4/Sb30 cells. In such cells, the antihormone compound was found to increase intracellular accumulation of calcein, a fluorescent compound transported by MRP, in a dose-dependent manner, through inhibition of cellular export of the dye; in contrast, it did not alter calcein levels in parental GLC4 cells. RU486, when used at 10 microM, a concentration close to plasma concentrations achievable in humans, strongly enhanced the sensitivity of GLC4/Sb30 cells towards two known cytotoxic substrates of MRP, the anticancer drug vincristine and the heavy metal salt potassium antimonyl tartrate. Vincristine accumulation levels were moreover up-regulated in RU486-treated GLC4/Sb30 cells. In addition, such cells were demonstrated to display reduced cellular levels of glutathione which is required for MRP-mediated transport of some anticancer drugs. These findings therefore demonstrate that RU486 can down-modulate MRP-mediated drug resistance, in addition to that linked to P-gp, through inhibition of MRP function.
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000037:antagonists & inhibitors*; D003907:Dexamethasone / Q000494:pharmacology; D018432:Drug Resistance, Multiple; D019008:Drug Resistance, Neoplasm; D004958:Estradiol / Q000494:pharmacology; D005452:Fluoresceins / Q000378:metabolism; D006727:Hormone Antagonists / Q000494:pharmacology*; D006801:Humans; D008175:Lung Neoplasms / Q000378:metabolism / Q000473:pathology*; D015735:Mifepristone / Q000494:pharmacology*; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D011374:Progesterone / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D014407:Tumor Cells, Cultured