Abstract
P-glycoprotein (P-gp)-mediated efflux at the blood-brain barrier has been implicated in limiting the brain distribution of many anti-HIV1 drugs, primarily protease inhibitors, resulting in suboptimal concentrations in this important sanctuary site. The objective of this study was to characterize the interaction of abacavir with P-gp and determine whether P-gp is an important mechanism in limiting abacavir delivery to the central nervous system (CNS). In vitro and in vivo techniques were employed to characterize this interaction. Abacavir stimulated P-gp ATPase activity at high concentrations. The cellular accumulation of abacavir was significantly decreased by ∼70% in Madin-Darby canine kidney II (MDCKII)-MDR1 monolayers compared with wild-type cells and was completely restored by the P-gp inhibitors ((R)-4-((1aR,6R,10bS)-1,2-difluoro-1,1a,6,10b-tetrahydrodibenzo(a,e)cyclopropa(c)cycloheptan-6-yl)-α-((5-quinoloyloxy)methyl)-1-piperazineethanol, trihydrochloride) (LY335979) and N-[4-[2-(6,7-dimethoxy-3,4-dihydro-1H-isoquinolin-2-yl)ethyl]phenyl]-5-methoxy-9-oxo-10H-acridine-4-carboxamide (GF120918). Directional flux experiments indicated that abacavir had greater permeability in the basolateral-to-apical direction (1.58E-05 cm/s) than in the apical-to-basolateral direction (3.44E-06 cm/s) in MDR1-transfected monolayers. The directionality in net flux was abolished by both LY335979 and GF120918. In vivo brain distribution studies showed that the AUCplasma in mdr1a(-/-) CF-1 mutant mice was ∼2-fold greater than the AUCplasma in the wild type, whereas the AUCbrain in the mutant was 20-fold higher than that in the wild type. Therefore, the CNS drug targeting index, defined as the ratio of AUC brain-to-plasma for mutant over wild type, was greater than 10. These data are the first in vitro and in vivo evidence that a nucleoside reverse transcriptase inhibitor is a P-gp substrate. The remarkable increase in abacavir brain distribution in P-gp-deficient mutant mice over wild-type mice suggests that P-gp may play a significant role in restricting the abacavir distribution to the CNS.
Footnotes
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This project was supported by National Institutes of Health Grant NS42549.
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doi:10.1124/dmd.107.017723.
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ABBREVIATIONS: NRTI, nucleoside reverse transcriptase inhibitor; CNS, central nervous system; ART, active retroviral therapy; P-gp, P-glycoprotein; ABC, ATP-binding cassette; AUC, area under the concentration-time curve; HPLC, high performance liquid chromatography; BBB, blood-brain barrier; ER, efflux ratio; Bcrp1, breast cancer resistance protein 1; AZT, zidovudine (3′-azido-3′-deoxythymidine); FTC, fumitremorgin C; LY335979, (R)-4-((1aR,6R,10bS)-1,2-difluoro-1,1a,6,10b-tetrahydrodibenzo(a,e)cyclopropa(c)cycloheptan-6-yl)-α-((5-quinoloyloxy)methyl)-1-piperazineethanol, trihydrochloride; WT, wild-type; MDCKII, Madin-Darby canine kidney II; GF120918, N-(4-[2-(1,2,3,4-tetrahydro-6,7-dimethoxy-2-isoquinolinyl)ethyl]-phenyl)-9,10-dihydro-5-methoxy-9-oxo-4-acridine carboxamide; A-to-B, apical-to-basolateral; B-to-A, basolateral-to-apical; B/P, brain-to-plasma concentration ratio.
- Received July 19, 2007.
- Accepted August 17, 2007.
- The American Society for Pharmacology and Experimental Therapeutics
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