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 two specific strategies for modifying this barrier to improve drug delivery, but also potentially important complications of polypharmacy related to xenobiotic upregulation of efflux transporter expression. One strategy for improving CNS delivery of drugs that are P-glycoprotein substrates involves activating protein kinase C (PKC) isoform beta1 or sphingolipid signaling at the blood-brain barrier. This causes a rapid and reversible reduction in basal P-glycoprotein transport activity in isolated brain capillaries and in intact rats. We have now identified a drug, Fingolimod (FTY720) currently in use in the clinic, that will target this signaling system and reduced P-glycoprotein tranport activity in vitro and in vivo. In vivo, such signaling increases brain uptake of drugs that are P-glycoprotein substrates. Thus, targeting signals that regulate basal activity of this transporter increases delivery of therapeutic drugs to the brain, including HIV protease inhibitors. A second strategy to improve HIV drug delivery to the CNS involves use of an innovative chemical strategy with the P-gp substrate and anti-viral agent, abacavir, in conjunction with a traceless tether. Dimeric prodrugs of abacavir were designed to have two functions: inhibit P-gp efflux at the BBB and revert to monomeric therapeutic within cellular reducing environments. The prodrug dimers are potent P-gp inhibitors in cell culture and in a brain capillary model of the BBB. Significantly, these agents demonstrate anti-HIV activity in two T-cell-based HIV assays, a result that is linked to cellular reversion of the prodrug to abacavir. This strategy represents a platform technology that may be applied to other therapies with limited brain penetration due to P-glycoprotein.

Project Start
Project End
Budget Start
Budget End
Support Year
13
Fiscal Year
2012
Total Cost
$207,729
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
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
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

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