Antiviral activity and intracellular metabolism of Bis(tButyISATE) phosphotriester of beta -L-2',3' dideoxyadenosine, a potent inhibitor of HIV and HBV replication

The beta -L-nucleoside analogue beta -L-2',3'-dideoxy adenosine ( beta -L-ddA) has been shown to exhibit limited antiviral activities. This was attributed to its rapid catabolism through cleavage of the glycosidic bond and poor phosphorylation to the nucleotide beta -L-2',3'-dideoxyadenosine-5'-mono phosphate ( beta -L-ddAMP) (Placidi et al., 2000). However, the nucleotide beta -L-2',3'-dideoxyadenosine-5'-triphosphate ( beta -L-ddATP) inhibited the activity of both HIV-1 reverse transcriptase (RT) and viral DNA polymerase isolated from woodchuck hepatitis virus-infected serum (a model of hepatitis B) with an inhibitory concentration (IC sub(50)) of 2.0 mu M without inhibiting human DNA polymerases alpha , beta , or gamma up to a concentration of 100 mu M. These results suggested that prodrugs of beta -L-ddAMP may bypass the poor metabolic activation of beta -L-ddA and lead to more potent and selective antiviral activity. Therefore, the mononucleoside phosphotriester derivative of beta -L-ddAMP incorporating the S-pivaloyl-2-thioethyl (tButyISATE) groups, beta -L-ddAMP-bis(tButyISATE) was synthesized. beta -L-ddAMP-bis(tButyISATE) inhibited HIV replication in human peripheral blood mononuclear cells (PBMCs) and HBV replication in 2.2.15 cells with effective concentrations (EC sub(50)s) of 2 and 80 nM, respectively. Intracellular metabolism of beta -L-ddAMP-bis(tButyISATE) demonstrated that beta -L-ddATP was the predominant intracellular metabolite in PBMC and liver cells. The intracellular half-life of beta -L-ddATP was 5.4 and 9.2 h in HepG2 and PBMCs, respectively. The intracellular concentrations of beta -L-ddATP were maintained above the EC sub(50) for the inhibition of HIV RT and hepatitis B virus (HBV) for as long as 24 h after removal of the drug.