Assessment of the anti-norovirus activity in cell culture using the mouse norovirus: Identification of active compounds

Discovery of a Novel Class of Norovirus Inhibitors with High Barrier of Resistance

Human noroviruses (HuNoVs) are the most common cause of viral gastroenteritis resulting in ~219,000 deaths annually and a societal cost of ~USD60 billion. There are no antivirals or vaccines available to treat and/or prevent HuNoV. In this study, we performed a large-scale phenotypical antiviral screening using the mouse norovirus (MNV), which included ~1000 drug-like small molecules from the Drug Design and Synthesis Centre (Sapienza University, Rome). Compound 3-((3,5-dimethylphenyl)sulfonyl)-5-chloroindole-N-(phenylmethanol-4-yl)-2.carboxamide (compound 1) was identified as an inhibitor of MNV replication with an EC₅₀ of 0.5 ± 0.1 µM. A series of 10 analogs were synthesized of which compound 6 showed an improved potency/selectivity (EC₅₀ 0.2 ± 0.1 µM) against MNV; good activity was also observed against the HuNoV GI replicon (EC₅₀ 1.2 ± 0.6 µM). Time-of-drug-addition studies revealed that analog 6 acts at a time point that coincides with the onset of viral RNA replication. After six months of selective pressure, two compound 6^res variants were independently selected, both harboring one mutation in VPg and three mutations in the RdRp. After reverse engineering S131T and Y154F as single mutations into the MNV backbone, we did not find a markedly compound 6^res phenotype. In this study, we present a class of novel norovirus inhibitors with a high barrier to resistance and in vitro antiviral activity.

Assessment of the anti-norovirus activity in cell culture using the mouse norovirus: Early mechanistic studies

Human norovirus is the main cause of viral gastroenteritis, resulting annually in ∼ 700 million infections and 200,000 deaths, of whom most are children <5 years. Mouse norovirus-infected macrophages are the most widely used in vitro system to screen and characterize the antiviral effect of norovirus-targeting small molecules. We have previously established antiviral assays using this system, identified novel inhibitors and performed additional studies in order to have a first insight into their mechanism of action. After the identification of novel small molecules with anti-norovirus activity (part 1 of this protocol), we here describe the logical next step which entails the generation of early information of their mode of action. This information together with a continuous improvement of the potency of compounds will contribute to the optimization of a compound class towards in vivo efficacy and a successful preclinical development.

Assessment of the anti-norovirus activity in cell culture using the mouse norovirus: Identification of active compounds

Human norovirus is the main cause of viral gastroenteritis, resulting annually in ∼ 700 million infections and 200,000 deaths, of whom most are children <5 years. Mouse norovirus-infected macrophages are the most widely used in vitro system to screen and characterize the antiviral effect of norovirus-targeting small molecules. We have previously established antiviral assays using this system, identified novel inhibitors and performed additional studies in order to have a first insight into their mechanism of action. As potent and safe anti-norovirus small molecules are urgently needed, we here describe the detailed protocol for a set of assays that will allow the identification of novel norovirus inhibitors.