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5th International Workshop on HIV Drug Resistance & Treatment Strategies4-8 June 2001, Scottsdale, Arizona |
Amdoxovir [DAPD (–)-β-D-2,6-diaminopurine dioxolane] is a selective inhibitor of HIV-1 replication in vitro. DAPD is deaminated in vivo by adenosine deaminase to yield (–)-β-D-dioxolane guanine (DXG), which is subsequently converted to the corresponding 5'- triphosphate (DXG-TP). DXG-TP is a potent inhibitor of the HIV reverse transcriptase (RT) with a Ki of 0.019 μM. Mycophenolic acid (MPA) and ribavirin inhibit the de novo synthesis of guanosine nucleotides by inhibition of inosine monophosphate dehydrogenase (IMPDH). Reduction of intracellular dGTP levels through inhibition of IMPDH may effectively increase the intracellular concentration of DXG-TP thereby augmenting inhibition HIV replication. The effects of MPA and ribavirin on the antiviral activity of DAPD and DXG against wild-type and mutant strains of HIV- 1 were analysed in peripheral blood mononuclear cells (PBMCs) using a p24-based ELISA assay. Similar analyses were conducted in the laboratory adapted Tcell line MT2 using an XTT based cytotoxicity assay. When tested against wild-type HIV-1 in MT2 cells, both MPA and ribavirin decreased the apparent EC50 for DXG by 1 log. By contrast, MPA and ribavirin increased the EC50 for zidovudine and had no effect on the activity of abacavir or emtricitabine in this cell line. Combination assays performed in PBMCs demonstrated that addition of 0.25 μM MPA or 20 μM ribavirin completely inhibited virus replication at all concentrations of DXG tested. HIV-1 isolates containing the L74V, K65R or Q151M mutations are 4- to 10-fold less sensitive to inhibition by DXG than wild-type virus. Addition of 0.25 μM MPA or 20 μM ribavirin completely reversed the DXG resistance observed with these isolates. Similarly, when tested against a virus fully resistant to inhibition by DXG (K65R/Q151M, EC50=80 μM), MPA and ribavirin decreased the apparent EC50 for DXG to within five-fold of wild-type. The combination of 0.25 μM MPA or 20 μM ribavirin was not cytotoxic to the cells in these assays. In addition, when tested at physiologically relevant concentrations, neither compound demonstrated mitochondrial toxicity, alone or in combination with DAPD or DXG. These data suggest a potential role for the use of IMPDH inhibitors in combination therapy with amdoxovir in the treatment of HIV.
PRESENTING AUTHOR: K Borroto-Esoda
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