Chemical derivatives of a small molecule deubiquitinase inhibitor have antiviral activity against several RNA viruses

Cellular takeover: How new world alphaviruses impact host organelle function

Alphavirus replication is dependent on host cell organelles to facilitate multiple steps of the viral life cycle. New world alphaviruses (NWA) consisting of eastern, western and Venezuelan equine encephalitis viruses are a subgroup of alphaviruses associated with central nervous system disease. Despite differing morbidity and mortality amongst these viruses, all are important human pathogens due to their transmission through viral aerosolization and mosquito transmission. In this review, we summarize the utilization of host organelles for NWA replication and the subversion of the host innate immune responses. The impact of viral proteins and replication processes on organelle function is also discussed. Literature involving old world alphaviruses (OWA), such as chikungunya virus and Sindbis virus, is included to compare and contrast between OWA and NWA and highlight gaps in knowledge for NWA. Finally, potential targets for therapeutics or vaccine candidates are highlighted with a focus on host-directed therapeutics.

Chemical tools to define and manipulate interferon-inducible Ubl protease USP18

Ubiquitin-specific protease 18 (USP18) is a multifunctional cysteine protease primarily responsible for deconjugating the interferon-inducible ubiquitin-like modifier ISG15 from protein substrates. Here, we report the design and synthesis of activity-based probes (ABPs) that incorporate unnatural amino acids into the C-terminal tail of ISG15, enabling the selective detection of USP18 activity over other ISG15 cross-reactive deubiquitinases (DUBs) such as USP5 and USP14. Combined with a ubiquitin-based DUB ABP, the USP18 ABP is employed in a chemoproteomics screening platform to identify and assess inhibitors of DUBs including USP18. We further demonstrate that USP18 ABPs can be utilized to profile differential activities of USP18 in lung cancer cell lines, providing a strategy that will help define the activity-related landscape of USP18 in different disease states and unravel important (de)ISGylation-dependent biological processes.

Viral deubiquitinating proteases and the promising strategies of their inhibition

Several viruses are now known to code for deubiquitinating proteases in their genomes. Ubiquitination is an essential post-translational modification of cellular substrates involved in many processes in the cell, including in innate immune signalling. This post-translational modification is regulated by the ubiquitin conjugation machinery, as well as various host deubiquitinating enzymes. The conjugation of ubiquitin chains to several innate immune related factors is often needed to induce downstream signalling, shaping the antiviral response. Viral deubiquitinating proteins, besides often having a primary function in the viral replication cycle by cleaving the viral polyprotein, are also able to cleave ubiquitin chains from such host substrates, in that way exerting a function in innate immune evasion. The presence of viral deubiquitinating enzymes has been firmly established for numerous animal-infecting viruses, such as some well-researched and clinically important nidoviruses, and their presence has now been confirmed in several plant viruses as well. Viral proteases in general have long been highlighted as promising drug targets, with a current focus on small molecule inhibitors. In this review, we will discuss the range of viral deubiquitinating proteases known to date, summarise the various avenues explored to inhibit such proteases and discuss novel strategies and models intended to inhibit and study these specific viral enzymes.

Host Cell Targets for Unconventional Antivirals against RNA Viruses

The recent COVID-19 crisis has highlighted the importance of RNA-based viruses. The most prominent members of this group are SARS-CoV-2 (coronavirus), HIV (human immunodeficiency virus), EBOV (Ebola virus), DENV (dengue virus), HCV (hepatitis C virus), ZIKV (Zika virus), CHIKV (chikungunya virus), and influenza A virus. With the exception of retroviruses which produce reverse transcriptase, the majority of RNA viruses encode RNA-dependent RNA polymerases which do not include molecular proofreading tools, underlying the high mutation capacity of these viruses as they multiply in the host cells. Together with their ability to manipulate the immune system of the host in different ways, their high mutation frequency poses a challenge to develop effective and durable vaccination and/or treatments. Consequently, the use of antiviral targeting agents, while an important part of the therapeutic strategy against infection, may lead to the selection of drug-resistant variants. The crucial role of the host cell replicative and processing machinery is essential for the replicative cycle of the viruses and has driven attention to the potential use of drugs directed to the host machinery as therapeutic alternatives to treat viral infections. In this review, we discuss small molecules with antiviral effects that target cellular factors in different steps of the infectious cycle of many RNA viruses. We emphasize the repurposing of FDA-approved drugs with broad-spectrum antiviral activity. Finally, we postulate that the ferruginol analog (18-(phthalimide-2-yl) ferruginol) is a potential host-targeted antiviral.

[WP1130 relieves septic shock in mice by inhibiting NLRP3 inflammasome activation]

OBJECTIVE

To investigate the mechanism by which the small molecule compound WP1130 inhibits NLRP3 inflammasome activation and alleviates septic shock.

METHODS

Mouse bone marrow-derived macrophages (BMDM) and human THP-1 cells were pre-treated with WP1130 before stimulation with different NLRP3 inflammasome agonists (Nigericin, ATP, MSU and intracellular LPS transfection), and AIM2 inflammasomes were activated with poly A: T. The levels of caspase-1 and IL-1β in the cell culture supernatant were determined using Western blotting and ELISA, and mitochondrial damage in the cells was observed using confocal microscopy. In the animal experiment, male C57BL/6 mice were randomized into blank control group, septic shock group (LPS group) and WP1130 treatment group (WP1130+LPS group), and the levels of IL-1β and TNF-α in the serum and peritoneal cavity were detected using ELISA.

RESULTS

In murine BMDM and human THP-1 cells, WP1130 significantly inhibited NLRP3 agonists-induced caspase-1 and IL-1β secretion in a dose-dependent manner (P < 0.05) but did not obviously affect the secretion of such inflammatory factors as IL-6 and TNF-α that were not associated with inflammasomes (P>0.05). Treatment with WP1130 did not significantly affect poly A: T-induced activation of AIM2 inflammasomes (P>0.05) or induce obvious changes in mitochondrial damage, an upstream signal of NLRP3 inflammasome activation. In the mouse model of LPS-induced septic shock, WP1130 treatment significantly reduced the level of IL-1β (P < 0.05) without obviously affecting TNF-α level either in the serum or in the peritoneal cavity (P>0.05).

CONCLUSION

WP1130 specifically inhibits NLRP3 inflammasome activation to alleviate LPS-induced septic shock in mice.

Inhibitors of Deubiquitinating Enzymes Interfere with the SARS-CoV-2 Papain-like Protease and Block Virus Replication In Vitro

The ubiquitin proteasome system (UPS), particularly its deubiquitinating enzymes (DUBs), play a key role in the replication cycle of coronaviruses. The SARS-CoV-2 papain-like protease (Plpro) is known to process the viral polyproteins to form the replicase transcriptase complex and to counteract the host viral response. Recently, it was shown that this viral protease can also act as a deubiquitinating enzyme. In this study, we demonstrate that certain DUB-Inhibitors (DIs) interfere with SARS-CoV-2 replication. The DIs PR-619 and HBX41108 restrict SARS-CoV-2 in both Vero B4 and human Calu-3 lung cells where cells were infected with a Multiplicity of Infection (MOI) of 0.02. An in vitro protease assay using recombinant Plpro and Amido-4-methylcoumarin (AMC)-conjugated substrate revealed that PR-619 and HBX41108 are able to block the protease at concentrations where the interventions restricted virus replication. In contrast, DIs that do not inhibit Plpro had no influence on virus replication, which indicated that the protease might be at least one major target. Future vertical studies that would gain more insights into the mechanisms of how DUBs effect the replication of SARS-CoV-2 will further validate them as a potential therapeutic target.

The Role of Deubiquitinases in Virus Replication and Host Innate Immune Response

As a critical post-translational modification, ubiquitination is known to affect almost all the cellular processes including immunity, signaling pathways, cell death, cancer development, and viral infection by controlling protein stability. Deubiquitinases (DUBs) cleave ubiquitin from proteins and reverse the process of ubiquitination. Thus, DUBs play an important role in the deubiquitination process and serve as therapeutic targets for various diseases. DUBs are found in eukaryotes, bacteria, and viruses and influence various biological processes. Here, we summarize recent findings on the function of DUBs in modulating viral infection, the mechanism by which viral DUBs regulate host innate immune response, and highlight those DUBs that have recently been discovered as antiviral therapeutic targets.

Norovirus Protease Structure and Antivirals Development

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.

Design and synthesis of new 4-(2-nitrophenoxy)benzamide derivatives as potential antiviral agents: molecular modeling and in vitro antiviral screening

Novel benzamide derivatives as anti adenovirus, HSV-1, coxsackievirus, and SARS-CoV-2: in vitro and in silico study.

The Functional Deubiquitinating Enzymes in Control of Innate Antiviral Immunity

Innate antiviral immunity is the first line of host defense against invading viral pathogens. Immunity activation primarily relies on the recognition of pathogen-associated molecular patterns (PAMPs) by pattern recognition receptors (PRRs). Viral proteins or nucleic acids mainly engage three classes of PRRs: Toll-like receptors (TLRs), retinoic acid-inducible gene I (RIG-I)-like receptors (RLRs), and DNA sensor cyclic GMP-AMP (cGAMP) synthase (cGAS). These receptors initiate a series of signaling cascades that lead to the production of proinflammatory cytokines and type I interferon (IFN-I) in response to viral infection. This system requires precise regulation to avoid aberrant activation. Emerging evidence has unveiled the crucial roles that the ubiquitin system, especially deubiquitinating enzymes (DUBs), play in controlling immune responses. In this review, an overview of the most current findings on the function of DUBs in the innate antiviral immune pathways is provided. Insights into the role of viral DUBs in counteracting host immune responses are also provided. Furthermore, the prospects and challenges of utilizing DUBs as therapeutic targets for infectious diseases are discussed.

ISG15 overexpression compensates the defect of Crimean-Congo hemorrhagic fever virus polymerase bearing a protease-inactive ovarian tumor domain

Crimean-Congo Hemorrhagic Fever virus (CCHFV; family Nairoviridae) is an extremely pathogenic member of the Bunyavirales order. Previous studies have shown that the N-terminal domain of the CCHFV polymerase (L) contains an ovarian tumor-type protease (OTU) domain with the capability to remove both ubiquitin and ISG15 molecules from proteins. The approximately 200 amino acids-long OTU domain, if ectopically expressed, can interfere with both the induction of antiviral type I interferons (IFN) as well as the IFN-stimulated signaling. A OTU protease mutant (C40A), by contrast, was inactive in that respect. However, the effect of the OTU protease activity in the context of the full-length L protein (approximately 4000 amino acids) is only poorly characterized, and recombinant CCHFV with the C40A mutation could not be rescued. Here, we employed transcriptionally active virus-like particles (tc-VLPs) to investigate the interaction between the L-embedded OTU protease and the IFN system. Our data show a cis requirement of the OTU protease for optimal CCHFV polymerase activity in human HuH-7 cells. The L-embedded OTU did not influence IFN signaling, the sensitivity to IFN, or IFN induction. Moreover, the attenuation of OTU C40A-mutated L could not be relieved by inactivating the IFN response, but after overexpression of conjugation-competent ISG15 the polymerase activity recovered to wild-type levels. Consequently, ISG15 was used to produce OTU-deficient tc-VLPs, a potential vaccine candidate. Our data thus indicate that in the context of full-length L the OTU domain is important for the regulation of CCHFV polymerase by ISG15.

Tick-transmitted Crimean-Congo Hemorrhagic Fever virus (CCHFV) causes a serious and potentially fatal disease in humans. The CCHFV polymerase possesses an N-terminal ovarian tumor-type protease (OTU) domain that cleaves ubiquitin and ISG15 modifiers from target proteins. Previous studies demonstrated that the ectopically expressed OTU domain can inhibit antiviral type I interferon responses. Hence, cleavage-negative OTU mutants of virus or transcriptionally active virus-like particles (tc-VLPs) are expected to exhibit elevated immunogenicity and would be candidates for a live vaccine. For unknown reasons, however, recombinant virus with just the OTU minus mutation cannot be generated. Using tc-VLPs, we show that in human HuH-7 cells the activity of the OTU minus polymerase is reduced by more than 80%. Curiously, the attenuation could not be compensated by inactivating the interferon system or by adding the OTU domain in trans. However, a complete reversion of the OTU minus phenotype was achieved by transcomplementation with ISG15, whereas the other OTU substrate, ubiquitin, had no such positive influence. Our data thus indicate a role of cis OTU in CCHFV polymerase regulation that is independent of an anti-interferon activity but connected to ISG15. Transcomplementation with ISG15 may be a means to rescue the OTU minus CCHV vaccine candidate.

Norovirus antivirals: Where are we now?

Human noroviruses inflict a significant health burden on society and are responsible for approximately 699 million infections and over 200 000 estimated deaths worldwide each year. Yet despite significant research efforts, approved vaccines or antivirals to combat this pathogen are still lacking. Safe and effective antivirals are not available, particularly for chronically infected immunocompromised individuals, and for prophylactic applications to protect high-risk and vulnerable populations in outbreak settings. Since the discovery of human norovirus in 1972, the lack of a cell culture system has hindered biological research and antiviral studies for many years. Recent breakthroughs in culturing human norovirus have been encouraging, however, further development and optimization of these novel methodologies are required to facilitate more robust replication levels, that will enable reliable serological and replication studies, as well as advances in antiviral development. In the last few years, considerable progress has been made toward the development of norovirus antivirals, inviting an updated review. This review focuses on potential therapeutics that have been reported since 2010, which were examined across at least two model systems used for studying human norovirus or its enzymes. In addition, we have placed emphasis on antiviral compounds with a defined chemical structure. We include a comprehensive outline of direct-acting antivirals and offer a discussion of host-modulating compounds, a rapidly expanding and promising area of antiviral research.

A compendium of small molecule direct-acting and host-targeting inhibitors as therapies against alphaviruses

Alphaviruses were amongst the first arboviruses to be isolated, characterized and assigned a taxonomic status. They are globally widespread, infecting a large variety of terrestrial animals, birds, insects and even fish. Moreover, they are capable of surviving and circulating in both sylvatic and urban environments, causing considerable human morbidity and mortality. The re-emergence of Chikungunya virus (CHIKV) in almost every part of the world has caused alarm to many health agencies throughout the world. The mosquito vector for this virus, Aedes, is globally distributed in tropical and temperate regions and capable of thriving in both rural and urban landscapes, giving the opportunity for CHIKV to continue expanding into new geographical regions. Despite the importance of alphaviruses as human pathogens, there is currently no targeted antiviral treatment available for alphavirus infection. This mini-review discusses some of the major features in the replication cycle of alphaviruses, highlighting the key viral targets and host components that participate in alphavirus replication and the molecular functions that were used in drug design. Together with describing the importance of these targets, we review the various direct-acting and host-targeting inhibitors, specifically small molecules that have been discovered and developed as potential therapeutics as well as their reported in vitro and in vivo efficacies.

TLR7 Agonists Display Potent Antiviral Effects against Norovirus Infection via Innate Stimulation

Norovirus infections are a significant health and economic burden globally, accounting for hundreds of millions of cases of acute gastroenteritis every year. In the absence of an approved norovirus vaccine, there is an urgent need to develop antivirals to treat chronic infections and provide prophylactic therapy to limit viral spread during epidemics and pandemics. Toll-like receptor (TLR) agonists have been explored widely for their antiviral potential, and several are progressing through clinical trials for the treatment of human immunodeficiency virus (HIV) and hepatitis B virus (HBV) and as adjuvants for norovirus viruslike particle (VLP) vaccines. However, norovirus therapies in development are largely direct-acting antivirals (DAAs) with fewer compounds that target the host. Our aim was to assess the antiviral potential of TLR7 agonist immunomodulators on norovirus infection using the murine norovirus (MNV) and human Norwalk replicon models. TLR7 agonists R-848, Gardiquimod, GS-9620, R-837, and loxoribine were screened using a plaque reduction assay, and each displayed inhibition of MNV replication (50% effective concentrations [EC₅₀s], 23.5 nM, 134.4 nM, 0.59 μM, 1.5 μM, and 79.4 μM, respectively). RNA sequencing of TLR7-stimulated cells revealed a predominant upregulation of innate immune response genes and interferon (IFN)-stimulated genes (ISGs) that are known to drive an antiviral state. Furthermore, the combination of R-848 and the nucleoside analogue (NA) 2'C-methylcytidine elicited a synergistic antiviral effect against MNV, demonstrating that combinational therapy of host modulators and DAAs might be used to reduce drug cytotoxicity. In summary, we have identified that TLR7 agonists display potent inhibition of norovirus replication and are a therapeutic option to combat norovirus infections.

Inhibitors of Deubiquitinating Enzymes Block HIV-1 Replication and Augment the Presentation of Gag-Derived MHC-I Epitopes

In recent years it has been well established that two major constituent parts of the ubiquitin proteasome system (UPS)—the proteasome holoenzymes and a number of ubiquitin ligases—play a crucial role, not only in virus replication but also in the regulation of the immunogenicity of human immunodeficiency virus type 1 (HIV-1). However, the role in HIV-1 replication of the third major component, the deubiquitinating enzymes (DUBs), has remained largely unknown. In this study, we show that the DUB-inhibitors (DIs) P22077 and PR-619, specific for the DUBs USP7 and USP47, impair Gag processing and thereby reduce the infectivity of released virions without affecting viral protease activity. Furthermore, the replication capacity of X4- and R5-tropic HIV-1_NL4-3 in human lymphatic tissue is decreased upon treatment with these inhibitors without affecting cell viability. Most strikingly, combinatory treatment with DIs and proteasome inhibitors synergistically blocks virus replication at concentrations where mono-treatment was ineffective, indicating that DIs can boost the therapeutic effect of proteasome inhibitors. In addition, P22077 and PR-619 increase the polyubiquitination of Gag and thus its entry into the UPS and the major histocompatibility complex (MHC)-I pathway. In summary, our data point towards a model in which specific inhibitors of DUBs not only interfere with virus spread but also increase the immune recognition of HIV-1 expressing cells.

Manipulation of viral infection by deubiquitinating enzymes: new players in host-virus interactions

Ubiquitination regulates gene expression post-translationally through the well-characterized ubiquitin system, which has been clearly established to have important functions in the regulation of many intracellular biological activities. Being obligate intracellular microbes, viruses inevitably co-opt this conserved host cytosolic machinery to accomplish their own life cycle, from entry into host cells to the release of progeny viral particles. Deubiquitinating enzymes (DUBs) remove ubiquitins from target proteins to reverse the modification of ubiquitination, and thusly affect a great number of signaling pathways, as well as viral infections. This review presents what is known about how viruses bypass or employ DUBs to evade host immune defenses and discusses new therapeutic strategies targeting DUBs for diseases treatment.

Anti-infective Activity of 2-Cyano-3-Acrylamide Inhibitors with Improved Drug-Like Properties against Two Intracellular Pathogens

Due to the rise of antibiotic resistance and the small number of effective antiviral drugs, new approaches for treating infectious diseases are urgently needed. Identifying targets for host-based therapies represents an emerging strategy for drug discovery. The ubiquitin-proteasome system is a central mode of signaling in the eukaryotic cell and may be a promising target for therapies that bolster the host's ability to control infection. Deubiquitinase (DUB) enzymes are key regulators of the host inflammatory response, and we previously demonstrated that a selective DUB inhibitor and its derivative promote anti-infective activities in host cells. To find compounds with anti-infective efficacy but improved toxicity profiles, we tested a library of predominantly 2-cyano-3-acrylamide small-molecule DUB inhibitors for anti-infective activity in macrophages against two intracellular pathogens: murine norovirus (MNV) and Listeria monocytogenes We identified compound C6, which inhibited DUB activity in human and murine cells and reduced intracellular replication of both pathogens with minimal toxicity in cell culture. Treatment with C6 did not significantly affect the ability of macrophages to internalize virus, suggesting that the anti-infective activity interferes with postentry stages of the MNV life cycle. Metabolic stability and pharmacokinetic assays showed that C6 has a half-life in mouse liver microsomes of ∼20 min and has a half-life of approximately 4 h in mice when administered intravenously. Our results provide a framework for targeting the host ubiquitin system in the development of host-based therapies for infectious disease. Compound C6 represents a promising tool with which to elucidate the role of DUBs in the macrophage response to infection.

Antiviral targets of human noroviruses

Human noroviruses are major causative agents of sporadic and epidemic gastroenteritis both in children and adults. Currently there are no licensed therapeutic intervention measures either in terms of vaccines or drugs available for these highly contagious human pathogens. Genetic and antigenic diversity of these viruses, rapid emergence of new strains, and their ability to infect a broad population by using polymorphic histo-blood group antigens for cell attachment, pose significant challenges for the development of effective antiviral agents. Despite these impediments, there is progress in the design and development of therapeutic agents. These include capsid-based candidate vaccines, and potential antivirals either in the form of glycomimetics or designer antibodies that block HBGA binding, as well as those that target essential non-structural proteins such as the viral protease and RNA-dependent RNA polymerase. In addition to these classical approaches, recent studies suggest the possibility of interferons and targeting host cell factors as viable approaches to counter norovirus infection. This review provides a brief overview of this progress.

Alphavirus Infection: Host Cell Shut-Off and Inhibition of Antiviral Responses

Alphaviruses cause debilitating disease in humans and animals and are transmitted by blood-feeding arthropods, typically mosquitoes. With a traditional focus on two models, Sindbis virus and Semliki Forest virus, alphavirus research has significantly intensified in the last decade partly due to the re-emergence and dramatic expansion of chikungunya virus in Asia, Europe, and the Americas. As a consequence, alphavirus–host interactions are now understood in much more molecular detail, and important novel mechanisms have been elucidated. It has become clear that alphaviruses not only cause a general host shut-off in infected vertebrate cells, but also specifically suppress different host antiviral pathways using their viral nonstructural proteins, nsP2 and nsP3. Here we review the current state of the art of alphavirus host cell shut-off of viral transcription and translation, and describe recent insights in viral subversion of interferon induction and signaling, the unfolded protein response, and stress granule assembly.

Advances Toward a Norovirus Antiviral: From Classical Inhibitors to Lethal Mutagenesis

Human noroviruses are a leading cause of gastroenteritis worldwide, yet there are no licensed antivirals. There is an urgent need for norovirus therapeutics, particularly for chronic infections in immunocompromised individuals, but also a potential need for prophylactic use in epidemics. Continued research has led to the identification of compounds that inhibit norovirus replication in vitro and, at least in some cases, are also effective in vivo against murine norovirus. Progress has included classical approaches targeting viral proteins and harnessing the antiviral action of interferon, strategies targeting essential host cell factors, and novel strategies exploiting the high mutation rate of noroviruses.

Anti-norovirus therapeutics: a patent review (2010-2015)

INTRODUCTION

Human noroviruses are the primary causative agents of acute gastroenteritis and are a pressing public health burden worldwide. There are currently no vaccines or small molecule therapeutics available for the treatment or prophylaxis of norovirus infections. An improved understanding of norovirus biology, as well as the pathogenic mechanisms underlying the disease, has provided the impetus for a range of intense exploratory drug discovery efforts targeting viral and host factors.

AREAS COVERED

An overview of norovirus inhibitors disclosed in the patent literature (2010-present) and Clinicaltrials.gov is presented. The review is further enriched and supplemented by recent literature reports.

EXPERT OPINION

Seminal discoveries made in recent years, including a better understanding of the pathobiology and life cycle of norovirus, the identification and targeting of multiple viral and host factors, the advent of a replicon system and a small animal model for the preclinical evaluation of lead compounds, and the availability of high resolution X-ray crystal structures that can be utilized in structure-based drug design and lead optimization campaigns, collectively suggest that a small molecule therapeutic and prophylactic for norovirus infection is likely to emerge in the not too distant future.

Recent Advances in the Discovery of Norovirus Therapeutics

Noroviruses are members of the family Caliciviridae. Norovirus infections are a global health burden that impacts >20 million individuals annually in the U.S. alone. Noroviruses are associated with high morbidity among vulnerable populations, particularly immunocompromised patients. This perspective highlights recent developments related to the discovery and development of norovirus-specific small-molecule therapeutics as well as recent advances in our understanding of norovirus biology and pathogenesis. Most of the work in this area is at the early discovery stage and has been primarily focused on inhibitors of norovirus 3C-like protease and RNA dependent RNA polymerase. However, recent discoveries emanating from basic studies in norovirus research have resulted in the identification of new host-related drug targets that can be exploited. A repurposed compound has been advanced to human clinical studies.

Norovirus vaccines and potential antinorovirus drugs: recent advances and future perspectives

Human noroviruses (HuNoVs) are a leading cause of acute, nonbacterial gastroenteritis worldwide. The lack of a cell culture system and smaller animal model has delayed the development and commercial availability of vaccines and antiviral drugs. Current vaccines rely on recombinant capsid proteins, such as P particles and virus-like particles (VLPs), which have been promising in clinical trials. Anti-HuNoV drug development is another area of extensive research, including currently available antiviral drugs for other viral pathogens. This review will provide an overview of recent advances in vaccine and antiviral development. The implication of recent advances in HuNoV cell culture for improving vaccine and antiviral development is also discussed.

Repurposing of rutin for the inhibition of norovirus replication

Drug repurposing is a strategy employed to circumvent some of the bottlenecks involved in drug development, such as the cost and time needed for developing new molecular entities. Noroviruses cause recurrent epidemics and sporadic outbreaks of gastroenteritis associated with significant mortality and economic costs, but no treatment has been approved to date. Herein, a library of molecules previously used in humans was screened to find compounds with anti-noroviral activity. Antiviral testing for four selected compounds against murine norovirus infection revealed that rutin has anti-murine norovirus activity in cell-based assays.

Inhibiting the deubiquitinating enzymes (DUBs)

The diverse roles of deubiquitinating enzymes, or DUBs, in determining the fate of specific proteins continue to unfold. Concurrent with the revelation of DUBs as potential therapeutic targets are publications of small molecule inhibitors of these enzymes. In this review, we summarize these molecules and their associated data and suggest additional experiments to further validate and characterize these compounds. We believe the field of drug discovery against DUBs is still in its infancy, but advances in assay development, biophysical techniques, and screening libraries hold promise for identifying suitable agents that could advance into the clinic.

Chikungunya virus non-structural protein 2-mediated host shut-off disables the unfolded protein response

The unfolded protein response (UPR) is a cellular defence mechanism against high concentrations of misfolded protein in the endoplasmic reticulum (ER). In the presence of misfolded proteins, ER-transmembrane proteins PERK and IRE1α become activated. PERK phosphorylates eIF2α leading to a general inhibition of cellular translation, whilst the expression of transcription factor ATF4 is upregulated. Active IRE1α splices out an intron from XBP1 mRNA, to produce a potent transcription factor. Activation of the UPR increases the production of several proteins involved in protein folding, degradation and apoptosis. Here, we demonstrated that transient expression of chikungunya virus (CHIKV) (family Togaviridae, genus Alphavirus) envelope glycoproteins induced the UPR and that CHIKV infection resulted in the phosphorylation of eIF2α and partial splicing of XBP1 mRNA. However, infection with CHIKV did not increase the expression of ATF4 and known UPR target genes (GRP78/BiP, GRP94 and CHOP). Moreover, nuclear XBP1 was not observed during CHIKV infection. Even upon stimulation with tunicamycin, the UPR was efficiently inhibited in CHIKV-infected cells. Individual expression of CHIKV non-structural proteins (nsPs) revealed that nsP2 alone was sufficient to inhibit the UPR. Mutations that rendered nsP2 unable to cause host-cell shut-off prevented nsP2-mediated inhibition of the UPR. This indicates that initial UPR induction takes place in the ER but that expression of functional UPR transcription factors and target genes is efficiently inhibited by CHIKV nsP2.

Small molecule deubiquitinase inhibitors promote macrophage anti-infective capacity

The global spread of anti-microbial resistance requires urgent attention, and diverse alternative strategies have been suggested to address this public health concern. Host-directed immunomodulatory therapies represent one approach that could reduce selection for resistant bacterial strains. Recently, the small molecule deubiquitinase inhibitor WP1130 was reported as a potential anti-infective drug against important human food-borne pathogens, notably Listeria monocytogenes and noroviruses. Utilization of WP1130 itself is limited due to poor solubility, but given the potential of this new compound, we initiated an iterative rational design approach to synthesize new derivatives with increased solubility that retained anti-infective activity. Here, we test a small library of novel synthetic molecules based on the structure of the parent compound, WP1130, for anti-infective activity in vitro. Our studies identify a promising candidate, compound 9, which reduced intracellular growth of L. monocytogenes at concentrations that caused minimal cellular toxicity. Compound 9 itself had no bactericidal activity and only modestly slowed Listeria growth rate in liquid broth culture, suggesting that this drug acts as an anti-infective compound by modulating host-cell function. Moreover, this new compound also showed anti-infective activity against murine norovirus (MNV-1) and human norovirus, using the Norwalk virus replicon system. This small molecule inhibitor may provide a chemical platform for further development of therapeutic deubiquitinase inhibitors with broad-spectrum anti-infective activity.