Genetic or chemical knock-out of P-glycoprotein (P-gp;MDR1) at the rodent blood-brain barrier (BBB) significantly increases (by 10 to 30-fold) the distribution of P-gp substrate drugs into the brain. Based on these data, it has been widely postulated that P-gp plays a vital role in limiting drug distribution at the human BBB and that P-gp based drug interactions at the human BBB are likely to be profound. Our hypothesis challenges this well-established paradigm and claims that such interactions will be modest because therapeutic plasma concentrations of potential P-gp inhibitor drugs will be insufficient to profoundly inhibit Pgp at the human BBB. Moreover, we hypothesize that such drug interactions can be quantitatively predicted by in vitro cell models and in vivo studies in the rat. The development by our laboratory of a novel and innovative non-invasive, Positron Emission Tomography (PET) imaging method to measure P-gp activity at the human BBB will allow us to test these hypotheses. Since P-gp can demonstrate allosteric activation and multiple binding sites, predictions of P-gp based drug interactions can be complicated by these phenomena. Therefore, our specific aims will be: 1. In vitro studies: We will determine the potency of a variety of drugs (EC50) to inhibit P-gp efflux of verapamil-bodipy by LLCPK1 cells expressing the MDR1 gene or an empty vector (control cells). 2. In vivo rodent studies: For the drugs studied (aim 1), we will determine the ratio of the therapeutic maximum plasma concentration (Cmax) and EC50 (Cmax/ECso) as well as the unbound maximum plasma concentration (Cmaxu) and EC5o(Cmaxu/EC5o). For those drugs (n=4) that are potent inhibitors of P-gp at their therapeutic concentrations (highest ratios), we will determine their in vivo EC50 at the rat BBB using [3H]-verapamil as the P-gp substrate. In vivo human studies: The two most potent inhibitors identified from the rat studies will be tested (at Cmax) for their ability to inhibit P-gp activity at the human BBB by measuring, using PET, their effect on the distribution of [11C]-verapamil into the brain. 4. In vitro-vivo correlation: We will determine (a) if the above in vitro EC50 and in vivo ECso values in the rat are correlated;and (b) whether the in vitro and in vivo rodent data are predictive of the magnitude of interaction observed at the human BBB at the Cmax of the inhibitor. 5. P-QD allosterism and multiple binding sites: We will determine if the interaction of P-gp with its drug substrates demonstrates allosterism and multiple binding sites. If it does, these phenomena will need to be taken into consideration when predicting in vivo P-gp based drug interactions.

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Program Projects (P01)
Project #
5P01GM032165-30
Application #
8380469
Study Section
Special Emphasis Panel (ZGM1-PPBC-6)
Project Start
Project End
2014-07-31
Budget Start
2012-08-01
Budget End
2013-07-31
Support Year
30
Fiscal Year
2012
Total Cost
$283,705
Indirect Cost
$101,884
Name
University of Washington
Department
Type
DUNS #
605799469
City
Seattle
State
WA
Country
United States
Zip Code
98195
Wong, Timothy; Wang, Zhican; Chapron, Brian D et al. (2018) Polymorphic Human Sulfotransferase 2A1 Mediates the Formation of 25-Hydroxyvitamin D3-3-O-Sulfate, a Major Circulating Vitamin D Metabolite in Humans. Drug Metab Dispos 46:367-379
Shirasaka, Y; Chaudhry, A S; McDonald, M et al. (2016) Interindividual variability of CYP2C19-catalyzed drug metabolism due to differences in gene diplotypes and cytochrome P450 oxidoreductase content. Pharmacogenomics J 16:375-87
Manoj, Kelath Murali; Parashar, Abhinav; Gade, Sudeep K et al. (2016) Functioning of Microsomal Cytochrome P450s: Murburn Concept Explains the Metabolism of Xenobiotics in Hepatocytes. Front Pharmacol 7:161
Stamper, Brendan D; Garcia, Michael L; Nguyen, Duy Q et al. (2015) p53 Contributes to Differentiating Gene Expression Following Exposure to Acetaminophen and Its Less Hepatotoxic Regioisomer Both In Vitro and In Vivo. Gene Regul Syst Bio 9:1-14
McDonald, Matthew G; Au, Nicholas T; Rettie, Allan E (2015) P450-Based Drug-Drug Interactions of Amiodarone and its Metabolites: Diversity of Inhibitory Mechanisms. Drug Metab Dispos 43:1661-9
Chaudhry, Amarjit S; Prasad, Bhagwat; Shirasaka, Yoshiyuki et al. (2015) The CYP2C19 Intron 2 Branch Point SNP is the Ancestral Polymorphism Contributing to the Poor Metabolizer Phenotype in Livers with CYP2C19*35 and CYP2C19*2 Alleles. Drug Metab Dispos 43:1226-35
Liu, Li; Collier, Ann C; Link, Jeanne M et al. (2015) Modulation of P-glycoprotein at the Human Blood-Brain Barrier by Quinidine or Rifampin Treatment: A Positron Emission Tomography Imaging Study. Drug Metab Dispos 43:1795-804
Ho, Han Kiat; Chan, James Chun Yip; Hardy, Klarissa D et al. (2015) Mechanism-based inactivation of CYP450 enzymes: a case study of lapatinib. Drug Metab Rev 47:21-8
Chapron, Brian; Risler, Linda; Phillips, Brian et al. (2015) Reversible, time-dependent inhibition of CYP3A-mediated metabolism of midazolam and tacrolimus by telaprevir in human liver microsomes. J Pharm Pharm Sci 18:101-11
Caudle, K E; Rettie, A E; Whirl-Carrillo, M et al. (2014) Clinical pharmacogenetics implementation consortium guidelines for CYP2C9 and HLA-B genotypes and phenytoin dosing. Clin Pharmacol Ther 96:542-8

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