The biochemical basis for the differential anti-human immunodeficiency virus activity of two cis enantiomers of 2',3'-dideoxy-3'-thiacytidine.
Two cis stereoisomers of 2',3'-dideoxy-3'-thiacytidine (SddC) were investigated for their activity against human immunodeficiency virus type 1 (HIV-1) in human acute lymphoblastic leukemia H-9 cells. (-)-SddC is six times more potent against HIV-1 and at least 1.7-fold less cytotoxic than (+)-SddC. Metabolism studies showed that the intracellular accumulation of the active triphosphate form of (-)-SddC is more than 2-fold greater than that of (+)-SddCTP in H-9 cells. In contrast, (+)-SddCTP is approximately 1.5 times more potent than (-)-SddCTP as an inhibitor of HIV-1 reverse transcriptase using a rRNA template (Ki = 0.22 and 0.034 microM, respectively) and gapped DNA (Ki = 0.53 and 1.02 microM, respectively). The enantiomers are comparable as substrates for incorporation into DNA by the RNA-dependent HIV-1 reverse transcriptase; however, neither analog is incorporated as readily as dCTP. The above observations do not explain the difference in the anti-HIV potency between the enantiomers. A novel 3'-5' exonuclease was partially purified from the cytosol of H-9 cells and assayed for the removal of (+)- and (-)-SddCMP-terminated DNA. Removal of (+)-SddCMP was approximately two to three times faster from 3'-terminals of single-stranded and double-stranded DNA, whereas on DNA/RNA substrates, the exonucleolytic cleavage of (+)-SddCMP proceeded approximately six times faster than that of (-)-SddCMP. This result correlates with the observed difference in the anti-HIV effect between the two compounds and suggests that this novel enzyme may be an important determinant of their antiviral activities.
Skalski
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Department of Pharmacology, Yale University School of Medicine, New Haven, Connecticut 06510.
Chang
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CN
Dutschman
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Cheng
Y C
YC
D000998:Antiviral Agents; D001483:Base Sequence; D005092:Exonucleases / Q000378:metabolism; D054303:HIV Reverse Transcriptase; D015497:HIV-1 / Q000187:drug effects* / Q000254:growth & development; D006801:Humans; D066298:In Vitro Techniques; D019259:Lamivudine; D008969:Molecular Sequence Data; D009843:Oligoribonucleotides / Q000737:chemistry; D010766:Phosphorylation; D018894:Reverse Transcriptase Inhibitors; D013237:Stereoisomerism; D013329:Structure-Activity Relationship; D016047:Zalcitabine / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism
D000998:Antiviral Agents; D009843:Oligoribonucleotides; D018894:Reverse Transcriptase Inhibitors; D019259:Lamivudine; D016047:Zalcitabine; D054303:HIV Reverse Transcriptase; D005092:Exonucleases