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

(-)-beta -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 nas designed as a water-soluble prodrug, is deaminated by adenosine deaminase to give (-)-beta -D-dioxolane guanine (DXG). By using calf adenosine deaminase a K-m value of 15 +/- 0.7 muM 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 alpha and beta. Against the large subunit of human DNA polymerase gamma a K-i value of 4.3 +/- 0.4 muM was determined for DXG-TP. DXG showed little or no cytotoxicity and no mitochondrial toxicity at the concentrations tested.