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DECH-box proteins are a subset of DExH/D-box superfamily 2 helicases possessing a conserved Asp-Glu-Cys-His motif in their ATP binding site. The conserved His helps position the Asp and Glu residues, which coordinate the divalent metal cation that connects the protein to ATP and activate the water molecule needed for ATP hydrolysis, but the role of the Cys is still unclear. This study uses site-directed mutants of the model DECH-box helicase encoded by the hepatitis C virus (HCV) to examine the role of the Cys in helicase action. Proteins lacking a Cys unwound DNA less efficiently than wild-type proteins did. For example, at low protein concentrations, a helicase harboring a Gly instead of the DECH-box Cys unwound DNA more slowly than the wild-type helicase did, but at higher protein concentrations, the two proteins unwound DNA at similar rates. All HCV proteins analyzed had similar affinities for ATP and nucleic acids and hydrolyzed ATP in the presence of RNA at similar rates. However, in the absence of RNA, all proteins lacking a DECH-box cysteine hydrolyzed ATP 10–15 times faster with higher K(m) values, and lower apparent affinities for metal ions, compared to those observed with wild-type proteins. These differences were observed with proteins isolated from HCV genotypes 2a and 1b, suggesting that this role is conserved. These data suggest the helicase needs Cys292 to bind ATP in a state where ATP is not hydrolyzed until RNA binds.

A ligand-based approach was applied to screen in silico a library of commercially available compounds, with the aim to find novel inhibitors of the HCV replication starting from the study of the viral NS3 helicase. Six structures were selected for evaluation in the HCV subgenomic replicon assay and one hit was found to inhibit the HCV replicon replication in the low micromolar range. A small series of new pyrrolone compounds was designed and synthesised, and novel structures were identified with improved antiviral activity.

A structure-based virtual screening of commercial compounds was carried out on the HCV NS3 helicase structure, with the aim to identify novel inhibitors of HCV replication. Among a selection of 13 commercial structures, one compound was found to inhibit the subgenomic HCV replicon in the low micromolar range. Different series of new piperazine-based analogues were designed and synthesised, and among them, several novel structures exhibited antiviral activity in the HCV replicon assay. Some of the new compounds were also found to inhibit HCV NS3 helicase function in vitro, and one directly bound NS3 with a dissociation constant of 570 ± 270 nM.

We report the discovery of the bicyclic octahydrocyclohepta[b]pyrrol-4(1H)-one scaffold as a new chemotype with anti-HCV activity on genotype 1b and 2a subgenomic replicons. The most potent compound 34 displayed EC50 values of 1.8 μM and 4.5 μM in genotype 1b and 2a, respectively, coupled with the absence of any antimetabolic effect (gt 1b SI = 112.4; gt 2a SI = 44.2) in a cell-based assay. Compound 34 did not target HCV NS5B, IRES, NS3 helicase, or selected host factors, and thus future work will involve the unique mechanism of action of these new antiviral compounds.

A structure-based virtual screening technique was applied to the study of the HCV NS3 helicase, with the aim to find novel inhibitors of the HCV replication. A library of ∼450000 commercially available compounds was analysed in silico and 21 structures were selected for biological evaluation in the HCV replicon assay. One hit characterized by a substituted thieno-pyrimidine scaffold was found to inhibit the viral replication with an EC50 value in the sub-micromolar range and a good selectivity index. Different series of novel thieno-pyrimidine derivatives were designed and synthesised; several new structures showed antiviral activity in the low or sub-micromolar range.

Background Despite the great progress made in the last 10 years, alternative strategies might help improving definitive treatment options against hepatitis C virus infection. Methods With the aim of identifying novel inhibitors of the hepatitis C virus-1b replication targeting the viral NS3 helicase, the structures of previously reported symmetrical inhibitors of this enzyme were rationally modified, and according to docking-based studies, four novel scaffolds were selected for synthesis and evaluation in the hepatitis C virus-1b subgenomic replicon assay. Results Among the newly designed compounds, one new structural family was found to inhibit the hepatitis C virus-1b replication in the micromolar range. This scaffold was chosen for further exploration and different novel analogues were synthesised and evaluated. Conclusions Different new inhibitors of the hepatitis C virus genotype 1b replication were identified. Some of the new compounds show mild inhibition of the NS3 helicase enzyme.