HIV protease inhibitors, such as, ritonavir and saquinavir, are substrates for xenobiotic efflux pumps, e.g., P-glycoprotein and Mrp2 and thus penetrate the blood-brain barrier poorly. To map the extracellular and intracellular signals that regulate these transporters, we use 1) pharmacological tools, 2) intact brain capillaries from rats and mice (including transgenics and knockouts), 2) fluorescent substrates, 3) confocal imaging to measure transport function, 4) Western blotting to measure transporter expression, and 5) brain perfusion in rats and mice to validate signaling-based changes in blood-brain barrier transporter function in vivo. Our recent studies have focused on identifying signals that modify pump activity in the barrier. These in vitro and in vivo experiments with animal models suggest multiple strategies for specifically modifying this barrier, but also potentially important complications of polypharmacy. 
 Strategies for improving drug delivery of drugs that are P-glycoprotein substrates include: activating VEGF signaling through src kinase and specifically activating protein kinase C (PKC) isoform beta1. Both strategies cause rapid and reversible loss of P-glycoprotein transport activity in isolated brain capillaries. In rats in vivo, such signaling increases brain uptake of drugs that are P-glycoprotein substrates. Thus, targeting signals that regulate basal activity of this transporter has the potential to increase delivery of therapeutic drugs, including HIV protease inhibitors, to the brain. Complications related to polypharmacy involve increased expression of multiple blood-brain barrier drug efflux pumps after exposure to therapeutic drugs, dietary constituents and environmental toxicants that specifically activate nuclear receptors, including, Pregnane-X Receptor (PXR), Constitutive Androstane Receptor (CAR) or Aryl hydrocarbon Receptor (AhR). Once activated by ligand, these receptors translocate to the nucleus, targeting the promoter regions of genes coding for xenobiotic metabolizing enzymes and efflux transporters. In brain capillaries in vitro, exposure to ligands for PXR, CAR or AhR more than doubles expression and transport activity of P-glycoprotein, Mrp2 and BCRP. in vivo, such signaling reduces brain uptake of drugs that are P-glycoprotein substrates. These findings raise the possibility of further tightening of the blood-brain barrier to many therapeutic drugs in patients undergoing polypharmacy.

Project Start
Project End
Budget Start
Budget End
Support Year
11
Fiscal Year
2010
Total Cost
$68,244
Indirect Cost
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Miller, D S (2015) Regulation of ABC transporters at the blood-brain barrier. Clin Pharmacol Ther 97:395-403
Wang, Xueqian; Campos, Christopher R; Peart, John C et al. (2014) Nrf2 upregulates ATP binding cassette transporter expression and activity at the blood-brain and blood-spinal cord barriers. J Neurosci 34:8585-93
Miller, David S (2014) Sphingolipid signaling reduces basal P-glycoprotein activity in renal proximal tubule. J Pharmacol Exp Ther 348:459-64
Emmert, Dana; Campos, Christopher R; Ward, David et al. (2014) Reversible dimers of the atypical antipsychotic quetiapine inhibit p-glycoprotein-mediated efflux in vitro with increased binding affinity and in situ at the blood-brain barrier. ACS Chem Neurosci 5:305-17
Cartwright, Tara A; Campos, Christopher R; Cannon, Ronald E et al. (2013) Mrp1 is essential for sphingolipid signaling to p-glycoprotein in mouse blood-brain and blood-spinal cord barriers. J Cereb Blood Flow Metab 33:381-8
Dallas, Shannon; Block, Michelle L; Thompson, Deborah M et al. (2013) Microglial activation decreases retention of the protease inhibitor saquinavir: implications for HIV treatment. J Neuroinflammation 10:58
Miller, David S; Cannon, Ronald E (2013) Signaling Pathways that Regulate Basal ABC Transporter Activity at the Blood-Brain Barrier. Curr Pharm Des :
Namanja, Hilda A; Emmert, Dana; Davis, David A et al. (2012) Toward eradicating HIV reservoirs in the brain: inhibiting P-glycoprotein at the blood-brain barrier with prodrug abacavir dimers. J Am Chem Soc 134:2976-80
Zhang, Dan; Hu, Xiaoming; Qian, Li et al. (2011) Microglial MAC1 receptor and PI3K are essential in mediating ýý-amyloid peptide-induced microglial activation and subsequent neurotoxicity. J Neuroinflammation 8:3
Wang, Xueqian; Hawkins, Brian T; Miller, David S (2011) Activating PKC-ýý1 at the blood-brain barrier reverses induction of P-glycoprotein activity by dioxin and restores drug delivery to the CNS. J Cereb Blood Flow Metab 31:1371-5

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