Mechanism of Action of 1-β- d -2,6-Diaminopurine Dioxolane, a Prodrug of the Human Immunodeficiency Virus Type 1 Inhibitor 1-β- d -Dioxolane Guanosine

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Abstract
(−)-β- d -2,6-Diaminopurine dioxolane (DAPD), is a nucleoside reverse transcriptase (RT) inhibitor with activity against human immunodeficiency virus type 1 (HIV-1). DAPD, which was designed as a water-soluble prodrug, is deaminated by adenosine deaminase to give (−)-β- d -dioxolane guanine (DXG). By using calf adenosine deaminase a K m value of 15 ± 0.7 μM was determined for DAPD, which was similar to the K m value for adenosine. However, the k cat for DAPD was 540-fold slower than the k cat for adenosine. In CEM cells and peripheral blood mononuclear cells exposed to DAPD or DXG, only the 5′-triphosphate of DXG (DXG-TP) was detected. DXG-TP is a potent alternative substrate inhibitor of HIV-1 RT. Rapid transient kinetic studies show the efficiency of incorporation for DXG-TP to be lower than that measured for the natural substrate, 2′-deoxyguanosine 5′-triphosphate. DXG-TP is a weak inhibitor of human DNA polymerases α and β. Against the large subunit of human DNA polymerase γ a K i value of 4.3 ± 0.4 μM was determined for DXG-TP. DXG showed little or no cytotoxicity and no mitochondrial toxicity at the concentrations tested.

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