Mechanism of action of 1-beta-D-2,6-diaminopurine dioxolane, a prodrug of the human immunodeficiency virus type 1 inhibitor 1-beta-D-dioxolane guanosine

(-)-beta -D-2,6-Diaminopurine dioxolane (DAPD), is a nucleoside reverse tra nscriptase (RT) inhibitor with activity against human immunodeficiency viru s type 1 (HIV-1). DAPD, which nas designed as a water-soluble prodrug, is d eaminated 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 dete rmined 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, on ly the 5'-triphosphate of DXG (DXG-TP) was detected. DXG-TP is a potent alt ernative substrate inhibitor of HIV-1 RT. Rapid transient kinetic studies s how the efficiency of incorporation for DXG-TP to be lower than that measur ed 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 d etermined for DXG-TP. DXG showed little or no cytotoxicity and no mitochond rial toxicity at the concentrations tested.