Abstract
Transporter gene knockout rat models are attracting increasing interest for mechanistic studies of new drugs as transporter substrates or inhibitors in vivo. However, limited data are available on the functional validity of such models at the blood-brain barrier. Therefore, the present study evaluated Mdr1a (P-gp), Bcrp and combined Mdr1a/Bcrp knockout rat strains for the influence of P-gp and BCRP transport proteins on brain penetration of the selective test substrates [14C]WEB 2086 (apafant) for P-gp, and dantrolene for BCRP. Brain-to-plasma ratios (BPR) were measured after intravenous co-infusions of 5.5 μmol/kg/h [14C]WEB 2086 and 2 μmol/kg/h dantrolene for 2h in groups of knockout or wildtype rats. Compared to wildtype controls, mean BPR of [14C]WEB 2086 increased 8-fold in Mdr1a knockouts, 9.5-fold in double Mdr1a/Bcrp knockouts and 7.3fold in Zosuquidar-treated wildtype rats, but was unchanged in Bcrp knockout rats. Mean BPR of dantrolene increased 3.3fold in Bcrp-knockouts and and 3.9-fold in double Mdr1a/Bcrp knockouts compared to wildtype, but was unchanged in the Mdr1a knockouts. The human intestinal CaCo-2 cell bidirectional transport system in vitro confirmed the in vivo finding that [14C]WEB 2086 is a substrate of P-gp but not of BCRP. Therefore, Mdr1a, Bcrp and combined Mdr1a/Bcrp knockout rats provide functional absence of these efflux transporters at the blood-brain barrier and are a suitable model for mechanistic studies on the brain penetration of drug candidates.
- ABC transporters
- active transport
- blood-brain barrier
- CNS pharmacokinetics
- distribution
- drug interactions
- p-glycoprotein
- pharmacokinetics
- transgenic models
- The American Society for Pharmacology and Experimental Therapeutics