Screening of multidrug-resistance sensitive drugs by in situ brain perfusion in P-glycoprotein-deficient mice

Purpose. This study was conducted to assess the influence of P-glycoprotein (P-gp) on brain uptake of multidrug resistance sensitive drugs using an in situ brain perfusion technique in P-gp-deficient (mdr1a[-/-]) and wild-typ e mice. Methods. The blood-brain transport of radiolabeled vinblastine, vincristine , doxorubicin, colchicine, and morphine was evaluated in mdr1a(-/-) and wil d-type CF-1. mice with the in situ brain perfusion technique. Brain uptake of drugs after intravenous pretreatment with P-gp reversal agents, (PSC 833 , GF 120918, or (+/-)-verapamil), or vehicle also was studied in wild-type mice. In all experiments, cerebral Vascular volume was determined by co-per fusion of sucrose. Results. Cerebral vascular volume was preserved during perfusion, indicatin g maintenance of blood-brain barrier integrity in both types of mice within the concentration range of substrates in the perfusate. The apparent brain transport of colchicine, vinblastine, doxorubicin, and morphine was increa sed 3.0, 2.7, 1.5, and 1.4-fold, respectively, in mdr1a(-/-) mice compared with the wild-type; the brain uptake of vincristine was not affected by P-g p. Preadministration of PSC 833 or GF 120918 in wild-type mice led to a sim ilar to3-fold increase in the brain transport of colchicine and vinblastine , but no effect was observed for the other compounds. Intravenous verapamil enhanced colchicine brain transport (1.8-fold), but failed to increase the brain uptake of vinblastine and morphine. Conclusion. The in situ brain perfusion technique appears to be a sensitive and powerful tool for medium throughput screening of the brain uptake of m ultidrug resistance sensitive drugs. The effect of P-gp is characterized mo re efficiently with mdr1a(-/-) mice than by using modulators of P-gp in wil d-type mice.