Insights into the Molecular Mechanism of Inhibition and Drug Resistance for HIV-1 RT with Carbovir Triphosphate

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• 作者：Adrian S. Ray ; Zhenjun Yang ; Junxing Shi ; Ann Hobbs ; Raymond F. Schinazi ; Chung K. Chu ; and Karen S. Anderson
• 刊名：Biochemistry
• 出版年：2002
• 出版时间：April 23, 2002
• 年：2002
• 卷：41
• 期：16
• 页码：5150 - 5162
• 全文大小：204K
• 年卷期：v.41,no.16(April 23, 2002)
• ISSN：1520-4995

文摘

Abacavir (1592U89, or Ziagen) is a powerful and selective inhibitor of HIV-1 viral replicationthat has been approved by the FDA for treatment of acquired immunodeficiency syndrome. Abacavir ismetabolized to the active compound carbovir triphosphate (CBVTP). This compound is a guanosineanalogue containing a 2',3'-unsaturation in its planar carbocyclic deoxyribose ring that acts on HIV-1reverse transcriptase (RT^WT) as a molecular target, resulting in chain termination of DNA synthesis. Asingle amino acid change from methionine 184 to valine in HIV-1 RT (RT^M184V) has been observedclinically in response to abacavir treatment. The ability of the natural substrate, dGTP, or CBVTP to beutilized during DNA- and RNA-directed polymerization by RT^WT and RT^M184V was defined by pre-steady-state kinetic parameters. In the case of RT^WT, CBVTP was found to be a surprisingly poor substraterelative to dGTP. In both DNA- and RNA-directed polymerization, a decrease in the efficiency of CBVTPutilization with respect to dGTP was found with RT^M184V, suggesting that this mutation confers resistanceat the level of CBVMP incorporation. The relatively low incorporation efficiency for RT^WT wasunanticipated considering earlier studies showing that the triphosphate form of a thymidine nucleosideanalogue containing a planar 2',3'-unsaturated ribose ring, D4TTP, was incorporated with high efficiencyrelative to the natural substrate, dTTP. The difference may be related to the isosteric replacement ofoxygen in the deoxyribose ring with carbon. This hypothesis was tested by synthesizing and evaluatingD4GTP (the planar 2',3'-unsaturated deoxyribose guanosine analogue that is complementary to D4TTP).In contrast to CBVTP, D4GTP was found to be an excellent substrate for RT^WT and no resistance wasconferred by the M184V mutation, thus providing novel insight into structure-activity relationships fornucleoside-based inhibitors. In this work, we illustrate how an understanding of the molecular mechanismof inhibition and drug resistance led to the discovery of a novel prodrug of D4G. This compound showspromise as a potent antiviral especially with the drug resistant M184V HIV-1 RT that is so often encounteredin a clinical setting.