Biochemical characterization of the inhibition of the dengue virus RNA polymerase by beta-d-2'-ethynyl-7-deaza-adenosine triphosphate.

Dengue virus (DENV), an emerging pathogen from the Flaviviridae family with neither vaccine nor antiviral treatment available, causes a serious worldwide public health threat. In theory, there are several ways by which small molecules could inhibit the replication cycle of DENV. Here, we show that the nucleoside analogue beta-d-2'-ethynyl-7-deaza-adenosine inhibits representative strains of all four serotypes of DENV with an EC(50) around or below 1microM. Using membrane-associated native replicase complex as well as recombinant RNA polymerase from each DENV serotype in enzymatic assays, we provide evidence that beta-d-2'-ethynyl-7-deaza-adenosine triphosphate (2'E-7D-ATP) targets viral replication at the polymerase active site by competing with the natural nucleotide substrate with an apparent K(i) of 0.060+/-0.016microM. In single-nucleotide incorporation experiments, the catalytic efficiency of 2'E-7D-ATP is 10-fold lower than for natural ATP, and the incorporated nucleotide analogue causes immediate chain termination. A combination of bioinformatics and site-directed mutagenesis demonstrates that 2'E-7D-ATP is equipotent across all serotypes because the nucleotide binding site residues are conserved in dengue virus. Overall, beta-d-2'-ethynyl-7-deaza-adenosine provides a promising scaffold for the development of inhibitors of dengue virus polymerase.

Synthesis and biological activity of 7-deaza-7-ethynyl-2'-deoxy-2'-fluoro-2'-C-methyladenosine and its 2'-C-methyl-ribo analogue.

In our search for improved therapeutic agents against HCV we synthesized 7-deaza-7-ethynyl-2'-C-methyladenosine (1) and its 2'-deoxy-2'-fluoro analogue 2. The corresponding nucleoside triphosphates were efficient chain terminators of the HCV NS5b polymerase with IC(50)'s of 0.75 microM and 0.4 microM respectively. However, only the ribo-nucleoside 1 exhibited activity in a Huh7 cell based replicon assay with an EC(50) of 0.09 microM. In order to overcome the lack of activity of the fluoro analogue 2 we synthesised several phosphoroamidate prodrugs.