title: Use of cassette dosing approach to examine the effects of P-glycoprotein on the brain and cerebrospinal fluid concentrations in wild-type and P-glycoprotein knockout rats.
abstract: The study objectives were 1) to test the hypothesis that the lack of P-glycoprotein (P-gp) and the inhibition of breast cancer resistance protein (Bcrp) at the blood-brain barrier after cassette dosing of potent P-gp and Bcrp inhibitors were due to low plasma concentrations of those inhibitors and 2) to examine the effects of P-gp on the unbound brain (C(u,brain)) and cerebrospinal fluid (CSF) concentrations (C(u,CSF)) of P-gp substrates in rats. In vitro inhibition of 11 compounds (amprenavir, citalopram, digoxin, elacridar, imatinib, Ko143 [(3S,6S,12aS)-1,2,3,4,6,7,12,12a-octahydro-9-methoxy-6-(2-methylpropyl)-1,4-dioxopyrazino[1',2':1,6]pyrido[3,4-b]indole-3-propanoic acid 1,1-dimethylethyl ester], loperamide, prazosin, quinidine, sulfasalazine, and verapamil) on P-gp and Bcrp was examined in P-gp- and Bcrp-expressing Madin-Darby canine kidney cells, respectively. An in vivo study was conducted in wild-type and Mdr1a(-/-) rats after subcutaneous cassette dosing of the 11 compounds at 1-3 mg/kg, and the brain, CSF, and plasma concentrations of these compounds were determined. At the maximal unbound concentrations observed in rats at 1-3 mg/kg, P-gp and Bcrp were not inhibited by a cassette of the 11 compounds. For non-P-gp/Bcrp substrates, similar C(u,brain), C(u,CSF), and unbound plasma concentrations (C(u,plasma)) were observed in wild-type and P-gp knockout rats. For P-gp/Bcrp substrates, C(u,brain) ≤ C(u,CSF) ≤ C(u,plasma) in wild-type rats, but C(u,brain) and C(u,CSF) increased in the P-gp knockout rats and were within 3-fold of C(u,plasma) for six of the seven P-gp substrates. These results indicate that P-gp and Bcrp inhibition at the blood-brain barrier is unlikely in cassette dosing and also suggest that P-gp and Bcrp activity at the blood-CSF barrier is functionally not important in determination of the CSF concentration for their substrates.
authors.affiliation: Genentech, Inc., South San Francisco, California.
authors.forename: Xingrong
authors.initials: X
authors.lastname: Liu
authors.forename: Jonathan
authors.initials: J
authors.lastname: Cheong
authors.forename: Xiao
authors.initials: X
authors.lastname: Ding
authors.forename: Gauri
authors.initials: G
authors.lastname: Deshmukh
mesh_terms: D018435:ATP Binding Cassette Transporter, Subfamily B / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D000818:Animals; D030801:Animals, Genetically Modified; D001812:Blood-Brain Barrier / Q000187:drug effects / Q000378:metabolism; D001921:Brain / Q000187:drug effects / Q000378:metabolism*; D018929:Cell Culture Techniques; D004285:Dogs; D055786:Gene Knockout Techniques; D061985:Madin Darby Canine Kidney Cells; D008297:Male; D004364:Pharmaceutical Preparations / Q000008:administration & dosage / Q000097:blood / Q000134:cerebrospinal fluid; D051381:Rats; D017207:Rats, Sprague-Dawley; D013379:Substrate Specificity
chemical_list: D018435:ATP Binding Cassette Transporter, Subfamily B; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D004364:Pharmaceutical Preparations; C095122:multidrug resistance protein 3