title: Impact of P-glycoprotein (ABCB1) and breast cancer resistance protein (ABCG2) on the brain distribution of a novel BRAF inhibitor: vemurafenib (PLX4032).
abstract: Vemurafenib [N-(3-{[5-(4-chlorophenyl)-1H-pyrrolo[2,3-b]pyridin-3-yl]carbonyl}-2,4-difluorophenyl)propane-1-sulfonamide(PLX4032)] is a novel small-molecule BRAF inhibitor, recently approved by the Food and Drug Administration for the treatment of patients with metastatic melanoma with a BRAF(V600E) mutation. The objective of this study was to investigate the role of P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP) in the distribution of vemurafenib to the central nervous system. In vitro studies conducted in transfected Madin-Darby canine kidney II cells show that the intracellular accumulation of vemurafenib is significantly restricted because of active efflux by P-gp and BCRP. Bidirectional flux studies indicated greater transport in the basolateral-to-apical direction than the apical-to-basolateral direction because of active efflux by P-gp and BCRP. The selective P-gp and BCRP inhibitors zosuquidar and (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 (Ko143) were able to restore the intracellular accumulation and bidirectional net flux of vemurafenib. The in vivo studies revealed that the brain distribution coefficient (area under the concentration time profile of brain/area under the concentration time profile of plasma) of vemurafenib was 0.004 in wild-type mice. The steady-state brain-to-plasma ratio of vemurafenib was 0.035 ± 0.009 in Mdr1a/b(-/-) mice, 0.009 ± 0.006 in Bcrp1(-/-) mice, and 1.00 ± 0.19 in Mdr1a/b(-/-)Bcrp1(-/-) mice compared with 0.012 ± 0.004 in wild-type mice. These data indicate that the brain distribution of vemurafenib is severely restricted at the blood-brain barrier because of active efflux by both P-gp and BCRP. This finding has important clinical significance given the ongoing trials examining the efficacy of vemurafenib in brain metastases of melanoma.
authors.affiliation: Department of Pharmaceutics, Brain Barriers Research Center, University of Minnesota, Minneapolis, Minnesota 55455, USA.
authors.forename: Rajendar K
authors.initials: RK
authors.lastname: Mittapalli
authors.forename: Shruthi
authors.initials: S
authors.lastname: Vaidhyanathan
authors.forename: Ramola
authors.initials: R
authors.lastname: Sane
authors.forename: William F
authors.initials: WF
authors.lastname: Elmquist
mesh_terms: D018435:ATP Binding Cassette Transporter, Subfamily B; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000378:metabolism*; D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport; D001812:Blood-Brain Barrier / Q000187:drug effects / Q000378:metabolism; D001921:Brain / Q000378:metabolism*; D002478:Cells, Cultured; D004285:Dogs; D007211:Indoles / Q000493:pharmacokinetics*; D061985:Madin Darby Canine Kidney Cells; D008545:Melanoma / Q000188:drug therapy / Q000235:genetics / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D047428:Protein Kinase Inhibitors / Q000493:pharmacokinetics; D048493:Proto-Oncogene Proteins B-raf / Q000037:antagonists & inhibitors* / Q000378:metabolism; D013449:Sulfonamides / Q000493:pharmacokinetics*; D014018:Tissue Distribution; D000077484:Vemurafenib
chemical_list: D018435:ATP Binding Cassette Transporter, Subfamily B; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters; C501412:Abcg2 protein, mouse; D007211:Indoles; D047428:Protein Kinase Inhibitors; D013449:Sulfonamides; D000077484:Vemurafenib; C482120:Braf protein, mouse; D048493:Proto-Oncogene Proteins B-raf; C507084:Abcb1b protein, mouse