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Non-enveloped viruses require cell lysis to release new virions from infected cells, suggesting that these viruses require mechanisms to induce cell death. Noroviruses are one such group of viruses, but there is no known mechanism that causes norovirus infection-triggered cell death and lysis 1 – 3 . Here we identify a molecular mechanism of norovirus-induced cell death. We found that the norovirus-encoded NTPase NS3 contains an N-terminal four-helix bundle domain homologous to the membrane-disruption domain of the pseudokinase mixed lineage kinase domain-like (MLKL). NS3 has a mitochondrial localization signal and thus induces cell death by targeting mitochondria. Full-length NS3 and an N-terminal fragment of the protein bound the mitochondrial membrane lipid cardiolipin, permeabilized the mitochondrial membrane and induced mitochondrial dysfunction. Both the N-terminal region and the mitochondrial localization motif of NS3 were essential for cell death, viral egress from cells and viral replication in mice. These findings suggest that noroviruses have acquired a host MLKL-like pore-forming domain to facilitate viral egress by inducing mitochondrial dysfunction. The murine norovirus NTPase NS3 induces mitochondrial disruption, resulting in cell death, which is required for viral egress.

Human noroviruses (HuNoVs) are the leading cause of non-bacterial gastroenteritis worldwide, exhibiting extensive genetic diversity driven by recombination and mutation. The norovirus RNA-dependent RNA polymerase (RdRp), encoded by the NS7 gene, is the main driver of virus evolution by determining the mutation and recombination rates, and impacting viral fitness. Herein, we conducted spatiotemporal phylodynamic analysis on 1,094 complete RdRp amino acid sequences from genogroups GI and GII collected between 1972 and 2024 to investigate molecular evolution, amino acid variation, evolutionary rates, and selection pressures. Time-scaled phylogenetic analysis revealed that GI polymerases diverged into three major lineages since the year ~ 1630, while GII polymerases formed four lineages, including a distinct cluster for P16. Genotype distribution was dominated by GII.P16 (43%) and GII.P31 (20%), both historically associated with GII.4 capsids. Amino acid substitutions were rare to non-existent within conserved motifs (A–G), indicating strong structural and functional constraints. Evolutionary rate estimates showed GII polymerases evolve faster (mean 1.5 × 10⁻³ substitutions/site/year) than GI (mean 3.8 × 10⁻⁴ substitutions/site/year), though overall RdRp evolves more slowly than the major capsid protein VP1. Selection analyses demonstrated pervasive purifying selection, with limited evidence of positive selection at codons outside of the conserved motifs. These findings highlight the high conservation of RdRp, its slower evolutionary dynamics compared to capsid gene, and its role in norovirus diversification, supporting its relevance as a target for antiviral development.

Background Human norovirus (HNV) is the predominant pathogen causing outbreaks of acute gastroenteritis globally. Despite significant efforts to combat norovirus infections, there is currently no FDA approved vaccine or antiviral drug available. Consequently, the development of effective antiviral agents is of critical importance. Methods and results In this study, a series of 41 5-cyano-2-thiacetyl aromatic pyrimidinone compounds were designed and synthesized. A cell viability-based screening for anti-murine norovirus (MNV) compounds was conducted, revealing that compound 29 (hereafter used as Co-29) exhibited antiviral activity against MNV. Co-29 demonstrated effective inhibition of MNV CW3 RNA replication, exhibiting an EC 50 of 58.22 μM. An RdRp enzyme activity assay indicated that Co-29 directly inhibits RdRp activity to both MNV and HNV. Molecular docking studies suggested that Co-29 interacts with the palm region of RdRp via hydrogen bonding with specific residues, which are conserved in RdRps across MNV and HNV norovirus variants. Conclusions In conclusion, our study suggests that the newly synthesized Co-29 may serve as a potential antiviral candidate or lead compound for future studies.

Human noroviruses (HuNoVs) are the primary cause of acute viral gastroenteritis. There are no antivirals or vaccines available to treat and/or prevent HuNoV. Norovirus 3C-like protease (3CLpro) is essential for viral replication; consequently, the inhibition of this enzyme is a fruitful avenue for antinorovirus therapeutics. To discover novel 3CLpro inhibitors with diverse scaffolds, a multi-stage virtual screening approach was performed by docking >10 million compounds into the 3CLpro catalytic site. An initial subset of 18 compounds was selected, and compounds YY-1029 and YY-4204 were identified as the best two molecules. Molecular dynamics (MD) simulations and binding free energy calculations (MM/GBSA) of YY-1029 and YY-4204 were performed to elucidate the binding mechanisms. The ADMET properties were also estimated to predict the potential druggability of representative molecules. All 18 compounds were evaluated for their antinorovirus activity and cytotoxicity in a cell-based replicon system. This work could provide information for the development of 3CL pro inhibitors.

Human noroviruses (HuNoVs) are the most common cause of viral gastroenteritis resulting annually in ~219,000 deaths and a societal cost of ~USD 60 billion, and no antivirals or vaccines are available. Here, we assess the anti-norovirus activity of new peptidomimetic aldehydes related to the protease inhibitor rupintrivir. The early hit compound 4 inhibited the replication of murine norovirus (MNV) and the HuNoV GI.1 replicon in vitro (EC50 ~1 µM) and swiftly cleared the HuNoV GI.1 replicon from the cells. Compound 4 still inhibits the proteolytic activity. We selected a resistant GI.1 replicon, with a mutation (I109V) in a highly conserved region of the viral protease, conferring a low yield of resistance against compound 4 and rupintrivir. After testing new derivatives, compound 10d was the most potent (EC50 nanomolar range). Molecular docking indicated that the aldehyde group of compounds 4 and 10d bind with Cys139 in the HuNoV 3CL protease by a covalent linkage. Finally, compound 10d inhibited the replication of HuNoV GII.4 in infected zebrafish larvae, and PK studies in mice showed an adequate profile.

Human norovirus is the first cause of foodborne disease worldwide, leading to extensive outbreaks of acute gastroenteritis, and causing around 200,000 children to die annually in developing countries. No specific vaccines or antiviral agents are currently available, with therapeutic options limited to supportive care to prevent dehydration. The infection can become severe and lead to life-threatening complications in young children, the elderly and immunocompromised individuals, leading to a clear need for antiviral agents, to be used as treatments and as prophylactic measures in case of outbreaks. Due to the key role played by the viral RNA-dependent RNA polymerase (RdRp) in the virus life cycle, this enzyme is a promising target for antiviral drug discovery. In previous studies, following in silico investigations, we identified different small-molecule inhibitors of this enzyme. In this study, we rationally modified five identified scaffolds, to further explore structure–activity relationships, and to enhance binding to the RdRp. The newly designed compounds were synthesized according to multiple-step synthetic routes and evaluated for their inhibition of the enzyme in vitro. New inhibitors with low micromolar inhibitory activity of the RdRp were identified, which provide a promising basis for further hit-to-lead optimization.

Viral gastroenteritis is an important cause of morbidity and mortality worldwide, being particularly severe for children under the age of five. The most common viral agents of gastroenteritis are noroviruses, rotaviruses, sapoviruses, astroviruses and adenoviruses, however, no specific antiviral treatment exists today against any of these pathogens. We here discuss the feasibility of developing a broad-spectrum antiviral treatment against these diarrhea-causing viruses. This review focuses on the viral polymerase as an antiviral target, as this is the most conserved viral protein among the diverse viral families to which these viruses belong to. We describe the functional and structural similarities of the different viral polymerases, the antiviral effect of reported polymerase inhibitors and highlight common features that might be exploited in an attempt of designing such pan-polymerase inhibitor.

Human norovirus is the leading cause of acute gastroenteritis worldwide, affecting every year 685 million people. In about one third of cases, this virus affects children under five years of age, causing each year up to 200,000 child deaths, mainly in the developing countries. Norovirus outbreaks are associated with very significant economic losses, with an estimated societal cost of 60 billion dollars per year. Despite the marked socio-economic consequences associated, no therapeutic options or vaccines are currently available to treat or prevent this infection. One promising target to identify new antiviral agents for norovirus is the viral polymerase, which has a pivotal role for the viral replication and lacks closely homologous structures in the host. Starting from the scaffold of a novel class of norovirus polymerase inhibitors recently discovered in our research group with a computer-aided method, different new chemical modifications were designed and carried out, with the aim to identify improved agents effective against norovirus replication in cell-based assays. While different new inhibitors of the viral polymerase were found, a further computer-aided ligand optimisation approach led to the identification of a new antiviral scaffold for norovirus, which inhibits human norovirus replication at low-micromolar concentrations.

Human norovirus (HuNoV) infection is a global health and economic burden. Currently, there are no licensed HuNoV vaccines or antiviral drugs available. The protease encoded by the HuNoV genome plays a critical role in virus replication by cleaving the polyprotein and is an excellent target for developing small-molecule inhibitors. The current strategy for developing HuNoV protease inhibitors is by targeting the enzyme’s active site and designing inhibitors that bind to the substrate-binding pockets located near the active site. However, subtle differential conformational flexibility in response to the different substrates in the polyprotein and structural differences in the active site and substrate-binding pockets across different genogroups, hamper the development of effective broad-spectrum inhibitors. A comparative analysis of the available HuNoV protease structures may provide valuable insight for identifying novel strategies for the design and development of such inhibitors. The goal of this review is to provide such analysis together with an overview of the current status of the design and development of HuNoV protease inhibitors.

Proteases are a major enzyme group playing important roles in a wide variety of biological processes in life forms ranging from viruses to mammalians. The aberrant activity of proteases can lead to various diseases; consequently, host proteases have been the focus of intense investigation as potential therapeutic targets. A wide range of viruses encode proteases which play an essential role in viral replication and, therefore, constitute attractive targets for the development of antiviral therapeutics. There are numerous examples of successful drug development targeting cellular and viral proteases, including antivirals against human immunodeficiency virus and hepatitis C virus. Most FDA-approved antiviral agents are peptidomimetics and macrocyclic compounds that interact with the active site of a targeted protease. Norovirus proteases are cysteine proteases that contain a chymotrypsin-like fold in their 3D structures. This review focuses on our group’s efforts related to the development of norovirus protease inhibitors as potential anti-norovirus therapeutics. These protease inhibitors are rationally designed transition-state inhibitors encompassing dipeptidyl, tripeptidyl and macrocyclic compounds. Highly effective inhibitors validated in X-ray co-crystallization, enzyme and cell-based assays, as well as an animal model, were generated by launching an optimization campaign utilizing the initial hit compounds. A prodrug approach was also explored to improve the pharmacokinetics (PK) of the identified inhibitors.