Hepatitis C drug discovery: in vitro and in vivo systems and drugs in the pipeline

New acridone-4-carboxylic acid derivatives as potential inhibitors of hepatitis C virus infection

A new class of compounds--acridone derivatives--was tested using the direct fluorometric helicase activity assay to determine the inhibitory properties of the derivatives towards the NS3 helicase of Hepatitis C virus (HCV). The compounds were also tested as putative transcription inhibitors of in vitro transcription based on the DNA-dependent T7 RNA polymerase. Most of the acridone derivatives tested were transcription inhibitors; however, only four of them inhibited the NS3 helicase at low concentrations (IC(50) from 3 microM to 20 microM) and were therefore selected for further studies on the mechanism of inhibition. The acridone derivatives probably act via intercalation into double-stranded nucleic acids but they may also interact directly with viral enzymes. Selected carboxamides were tested in the subgenomic HCV replicon system. Two of the compounds: N-(pyridin-4-yl)-amide and N-(pyridin-2-yl)-amide of acridone-4-carboxylic acid are efficient RNA replication inhibitors with selectivity indexes of 19.4 and 40.5, respectively, proving that the acridone derivatives may be regarded as potential antiviral agents.

Discovery of novel dialkyl substituted thiophene inhibitors of HCV by in silico screening of the NS5B RdRp

A novel 5,4-dialkyl substituted thiophene was discovered by in silico screening of the 3D polymerase crystal structure (1GX6) that demonstrated single digit micromolar HCV inhibition activity in the replicon assay and dose-dependent inhibition in the replicase complex assay. Subsequently, SAR was explored with a small set of dialkyl and tetrahydro-benzo thiophenes. Since these thiophenes inhibit synthesis of both, single- and double-stranded RNAs, their mechanism of action is distinct from other known HCV inhibitors.