Xenopus laevis oocytes expressing human P-glycoprotein: Probing trans- and cis-inhibitory effects on [H-3]vinblastine and [H-3]digoxin efflux

P-glycoprotein (P-gp; MDR1) recognizes and actively transports many structurally diverse compounds (hydrophobic neutral and cationic). We studied MDR1-mediated drug transport using a high-throughput (96-well) oocyte expression system. MDR1-expressing oocytes contained sufficient ATP levels to conduct fundamental efflux studies; the optimal experimental temperature was 25 degrees C. [H-3]Vinblastine efflux by MDR1-expressing oocytes was detectable and afforded a K-m of 145.5 +/- 25.4 mu M. [H-3]Vinblastine (5.6 +/- 0.3 mu M) and [H-3]digoxin (1.0 +/- 0.1 mu M) were individually injected into MDR1-expressing oocytes and their efflux monitored. Quinidine and verapamil, known MDR1 substrates/inhibitors, showed trans-inhibition on MDR1-mediated [H-3]vinblastine and [H-3]digoxin efflux. Conversely, doxorubicin demonstrated cis-inhibition without trans-inhibition on MDR1-mediated [H-3]vinblastine efflux. The MDR1-expressing oocyte system offers researchers with an alternative in vitro method to screen compounds and may allow one to probe P-gp drug-drug and/or drug-inhibitor interactions. (C) 2010 Elsevier Ltd. All rights reserved.