Sex-dependent expression and activity of the ATP-binding cassette transporter breast cancer resistance protein (BCRP/ABCG2) in liver

The breast cancer resistance protein (BCRP/ABCG2) is an ATP-binding cassette drug efflux transporter present in the liver and other tissues that affects the pharmacological behavior of many compounds. To assess the possible role of BCRP in sex-dependent pharmacokinetics, we studied the in vivo disposition of several murine Bcrp1 substrates in male and female wild-type and Bcrp1 knockout mice. After oral administration of the antibiotic nitrofurantoin, the area under the plasma concentrationtime curve in wild-type female mice was approximately 2-fold higher than in wild-type male mice. Moreover, after i.v. administration of nitrofurantoin, the antiulcerative cimetidine, the anticancer drug topotecan, and the carcinogen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), the plasma levels in wild-type female mice were all significantly higher than those in wild- type male mice. Analysis of the expression of murine Bcrp1 in several pharmacokinetically important tissues showed that only the hepatic Bcrp1 expression was higher in male mice compared with female mice. In line with this difference, the hepatobiliary excretion for nitrofurantoin and PhIP was, respectively, 9-fold higher and approximately 2-fold higher in male compared with female wild-type mice. No significant sex differences were observed in plasma levels or hepatobiliary excretion for any of the tested compounds in Bcrp1(-/-) mice, indicating that Bcrp1 was the main cause of the sex difference in wild-type mice. Analysis of hepatic expression of human BCRP also indicated a higher expression in men compared with women. In conclusion, sex-dependent expression of BCRP/Bcrp1 in the liver may be a cause of sex-specific variability in the pharmacokinetics of BCRP substrates, with potential impact on the clinical-therapeutic applications and toxicity risks of drugs.