RELATIONSHIP BETWEEN EXPRESSION LEVEL OF P-GLYCOPROTEIN AND DAUNORUBICIN TRANSPORT IN LLC-PK1 CELLS TRANSFECTED WITH HUMAN MDR1 GENE

P-Glycoprotein-mediated transcellular transport and intracellular accu mulation of [H-3]daunorubicin were examined in cell monolayers with di fferent levels of P-glycoprotein. The porcine kidney epithelial cell l ine LLC-PK1 was transfected with MDR1 cDNA, and four sublines, LLC-GA5 , LLC-GA5-VLB4, LLC-GA5-COL10, and LLC-GA5-COL150, were obtained by cu lturing the cells in the absence or in the presence of 4 ng/mL vinblas tine, 10 ng/mL colchicine, and 150 ng/mL colchicine, respectively. Wes tern blot analysis showed a large difference in P-glycoprotein express ion within these sublines. The degree of drug resistance was dependent on the expression level of P-glycoprotein. The amount of the unidirec tional transport of [H-3]daunorubicin by P-glycoprotein corresponded t o the expression level of P-glycoprotein, which was followed by the de crease in intracellular accumulation of the agent. The concentration o f cyclosporin A required for the inhibition of P-glycoprotein-mediated transport of [3H]daunorubicin was higher in cells with a high express ion of P-glycoprotein. These findings suggest that the transport of da unorubicin by P-glycoprotein and its inhibition by cyclosporin A corre spond to the expression level of P-glycoprotein. (C) 1997 Elsevier Sci ence Inc.