Toward eradicating HIV reservoirs in the brain: inhibiting P-glycoprotein at the blood-brain barrier with prodrug abacavir dimers

Abstract

Eradication of HIV reservoirs in the brain necessitates penetration of antiviral agents across the blood-brain barrier (BBB), a process limited by drug efflux proteins such as P-glycoprotein (P-gp) at the membrane of brain capillary endothelial cells. We present an innovative chemical strategy toward the goal of therapeutic brain penetration of the P-gp substrate and antiviral 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.

Figures

Figure 1

Design of P-gp inhibitors: dimeric prodrugs containing a traceless linker. These novel dimeric prodrug P-gp inhibitors also revert to the monomeric drugs within the reducing environment of the cell (inset) using a traceless linker strategy.

Figure 2

Structures of abacavir and abacavir prodrug homodimers: AbaS2, AbaS2Me2 and AbaS2Me4.

Figure 3

P-gp efflux is inhibited by prodrug abacavir homodimers in rat brain capillaries. (a) Rat brain capillaries were incubated in the presence or absence of 5 µM AbaS2 or AbaS2Me4 in PBS (pH 7.4), followed by the addition of 2 µM NBD-abacavir in PBS (pH 7.4). Analysis was made by confocal scanning microscopy at 40X magnification. (b and c) Concentration dependent inhibition of P-gp transport of NBD-abacavir in rat brain capillaries by (b) AbaS2 and (c) AbaS2Me4 using 5 µM PSC833 as the positive control.

Figure 4

(a) Inhibition of HIV-1 replication in the presence or absence of increasing concentrations of abacavir or AbaS2Me4. IC50 values of approximately 0.6 and 2.5 µM were obtained for abacavir and AbaS2Me4, respectively (b) Inhibition of HIV-induced cell death with increasing concentrations of abacavir or AbaS2Me4. IC50 values of approximately 2.5 and 6.5 µM were obtained for abacavir and AbaS2Me4, respectively.