METABOLISM OF CARBOVIR, A POTENT INHIBITOR OF HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1, AND ITS EFFECTS ON CELLULAR-METABOLISM

Carbovir (CBV) [the (-)-enantiomer of the carbocyclic analog of 2',3'- dideoxy-2',3'-didehydroguanosine] is a potent inhibitor of human immun odeficiency virus type 1 (HIV) replication in vitro. We have character ized the metabolism of CBV and its effect on cellular metabolism in an effort to better understand its mechanism of action. CBV was primaril y metabolized to the 5'-triphosphate of CBV (CBV-TP) to concentrations sufficient to inhibit HIV reverse transcriptase. Infection of CEM cel ls with HIV did not affect the metabolism of CBV. In CEM cells, there was no evidence of the degradation of CBV by purine nucleoside phospho rylase. The half-life of CBV-TP in CEM cells was 2.5 h, similar to tha t of the 5'-triphosphate of zidovudine (AZT). However, unlike the leve ls of the 5'-triphosphate of AZT, CBV-TP levels declined without evide nce of a plateau. CBV did not affect the metabolism of AZT, and AZT di d not affect the metabolism of CBV. A small amount of CBV was incorpor ated into DNA in intact CEM cells, and this incorporation was increase d by incubation with mycophenolic acid, an inhibitor of IMP dehydrogen ase. CBV specifically inhibited the incorporation of nucleic acid prec ursors into DNA but had no effect on the incorporation of radiolabeled precursors into RNA or protein. CBV did not decrease the level of TTP , dGTP, dCTP, or dATP. These results suggested that the cytotoxicity o f CBV was due to the inhibition of DNA synthesis. Further studies are necessary to identify the target(s) responsible for growth inhibition.