2',3'-Didehydro-3'-deoxythymidine: regulation of its metabolic activation by modulators of thymidine-5'-triphosphate biosynthesis

GS Ahluwalia, WY Gao, H Mitsuya and DG Johns

Laboratory of Medicinal Chemistry, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892-4255, USA.

The anti-human immunodeficiency virus (anti-HIV) agent 2',3'-didehydro- 3'-deoxythymidine (D4T), like other 2',3'-dideoxynucleosides, requires conversion to its 5'-triphosphate to exert its pharmacological effect. Although D4T-triphosphate is unusually potent as an inhibitor of HIV-1 reverse transcriptase, the phosphorylation of the drug at low dose levels is inefficient because of its low affinity as an alternate substrate for the initial phosphorylation enzyme thymidine kinase. Because thymidine kinase is under feedback regulatory control by the physiological deoxynucleoside-5'-triphosphate dTTP, we examined the effect on D4T phosphorylation and thus, potentially, on its antiviral activity, of a variety of agents that lower intracellular dTTP pools. We found that agents that inhibit the de novo pyrimidine biosynthetic pathway have the ability to increase D4T phosphorylation, the most effective being two inhibitors of thymidylate formation, methotrexate and 5-fluoro-2'-deoxyuridine, compounds that block the enzymes dihydrofolate reductase and thymidylate synthetase, respectively. Because HIV itself lacks the capacity to synthesize dTTP and the other deoxynucleoside triphosphates essential for viral replication, combinations of D4T with modulatory agents that deplete host-cell dTTP, unlike conventional anti-HIV drug monotherapy directed solely at viral enzymes, have the ability to inhibit replication of mutant HIV strains as well as of wild-type virus.

Volume 50, Issue 1, pp. 160-165, 07/01/1996
Copyright © 1996 by American Society for Pharmacology and Experimental Therapeutics

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