Transport of lamivudine [(-)-/β-L-2′,3′-dideoxy-3′- thiacytidine] and high-affinity interaction of nucleoside reverse transcriptase inhibitors with human organic cation transporters 1, 2, and 3

Nucleoside reverse transcriptase inhibitors (NRTIs) need to enter cells to act against the HIV-1. Human organic cation transporters (hOCT1-3) are expressed and active in CD4+ T cells, the main target of HIV-1, and have been associated with antiviral uptake in different tissues. In this study, we examined whether NRTIs interact and are substrates of hOCT in cells stably expressing these transporters. Using [3H]/V-methyl- 4-phenylpyridinium, we found a high-affinity interaction among abacavir [[(1S,4R)-4-[2-amino-6- (cyclopropylamino)purin-9-yl]- cyclopent-2-enyl]methanol sulfate] (ABC); <0.08 nM], azidothymidine [3′-azido-3′-deoxythymidine (AZT); lt;0.4 nM], tenofovir disoproxil fumarate (lt;1.0 nM), and emtricitabine (<2.5 nM) and hOCTs. Using a wide range of concentrations of lamivudine [(-)-β-L-2′,3′-dideoxy-3′-thiacyitidine (3TC)], we determined two different binding sites for hOCTs: a high-affinity site (K d1 = 12.3-15.4 pM) and a low-affinity site (Kd2 = 1.9-3.4 mM). Measuring direct uptake of [3H]3TC and inhibition with hOCT substrates, we identified 3TC as a novel substrate for hOCT1, 2, and 3, with hOCT1 as the most efficient transporter (Km = 1.25 ± 0.1 mM; Vmax = 10.40 ± 0.32 nmol/mg protein/ min; V max/Km = 8.32 ± 0.40 uμl/mg protein/min). In drug-drug interaction experiments, we analyzed cis-inhibition of [ 3H]3TC uptake by ABC and AZT and found that 40 to 50% was inhibited at low concentrations of the drugs (Ki = 22-500 pM). These data reveal that NRTIs experience a high-affinity interaction with hOCTs, suggesting a putative role for these drugs as modulators of hOCT activity. Finally, 3TC is a novel substrate for hOCTs and the inhibition of its uptake at low concentrations of ABC and AZT could have implications for the pharmacokinetics of 3TC. Copyright © 2009 by The American Society for Pharmacology and Experimental Therapeutics.