Identification of dibucaine derivatives as novel potent enterovirus 2C helicase inhibitors: In vitro, in vivo, and combination therapy study

Non-Polio Enterovirus Inhibitors: Scaffolds, Targets, and Potency─What's New?

Enterovirus (EV) is a genus that includes a large diversity of viruses spread around the world. They are the main cause of numerous diseases with seasonal clusters, like hand-foot-mouth disease (HFMD). A vaccine is marketed in China for the prevention of HFMD caused by EV-A71. Despite the need, no antiviral is marketed to date. Therefore, several compounds have been currently evaluated to inhibit non-polio Enterovirus (NPEV), namely direct antiviral agents and host target inhibitor. We propose to make a review of the latest molecules evaluated as NPEV inhibitors and to summarize structure-activity relationships between these inhibitors and their target. We provide access to all recent information on Enterovirus inhibitors, regardless of the species, to facilitate the design of future broad-spectrum drugs.

Repurposing of dibucaine and niflumic acid as antimicrobial agents in combination with antibiotics against Staphylococcus aureus

The versatile human commensal bacteria and pathogen Staphylococcus aureus cause several community and hospital-acquired illnesses associated with significant morbidity and death. Antibiotic therapy for S. aureus infections has grown increasingly difficult as the organism has developed a wide spectrum of antibiotic resistance mechanisms. This situation emphasizes the significance of developing and advocating new antimicrobials for preventative and therapeutic measures. Our study aimed to identify and evaluate new therapeutic options against S. aureus. We investigated the efficacy of two drugs, dibucaine, and niflumic acid, as potential adjuvant for anti-staphylococcal therapeutics. Dibucaine and niflumic acid found to have bactericidal activity against S. aureus. These drugs acted synergistically with antibiotics reducing the required dose of antibiotics up to 4 times. In combination with antibiotics, they were effectively and synergistically inhibited the formation of biofilms of S. aureus. The best synergistic partner of dibucaine was with kanamycin and tetracycline, whereas niflumic acid was with streptomycin and ampicillin. Both the drugs showed significant efflux inhibition in the bacteria. Moreover, the drugs are found to be safe at synergistic doses. Our findings suggest that dibucaine and niflumic acid could be potential adjuvant with antibiotics for the treatment of S. aureus infections. Their ability to significantly enhance the efficacy of antibiotics highlights their potential clinical significance as adjunct therapies.

Chemoproteomics enables identification of coatomer subunit zeta-1 targeted by a small molecule for enterovirus A71 inhibition

Human enterovirus A71 (EV-A71) is a significant etiological agent responsible for epidemics of hand, foot, and mouth disease (HFMD) in Asia-Pacific regions. There are presently no licensed antivirals against EV-A71, and the druggable target for EV-A71 remains very limited. The phenotypic hit 10,10'-bis(trifluoromethyl) marinopyrrole A derivative, herein termed MPA-CF3, is a novel potent small-molecule inhibitor against EV-A71, but its pharmacological target(s) and antiviral mechanisms are not defined. Here, quantitative chemoproteomics deciphered the antiviral target of MAP-CF3 as host factor coatomer subunit zeta-1 (COPZ1). Mechanistically, MPA-CF3 disrupts the interaction of COPZ1 with the EV-A71 nonstructural protein 2C by destabilizing COPZ1 upon binding. The destruction of this interaction blocks the coatomer-mediated transport of 2C to endoplasmic reticulum, and ultimately inhibits EV-A71 replication. Taken together, our study disclosed that MPA-CF3 can be a structurally novel host-targeting anti-EV-A71 agent, providing a structural basis for developing the COPZ1-targeting broad-spectrum antivirals against enteroviruses. The mechanistic elucidation of MPA-CF3 against EV-A71 may offer an alternative COPZ1-involved therapeutic pathway for enterovirus infection.

Mechanisms of antiviral action and toxicities of ipecac alkaloids: Emetine and dehydroemetine exhibit anti-coronaviral activities at non-cardiotoxic concentrations

The emergence of highly infectious pathogens with their potential for triggering global pandemics necessitate the development of effective treatment strategies, including broad-spectrum antiviral therapies to safeguard human health. This study investigates the antiviral activity of emetine, dehydroemetine (DHE), and congeneric compounds against SARS-CoV-2 and HCoV-OC43, and evaluates their impact on the host cell. Concurrently, we assess the potential cardiotoxicity of these ipecac alkaloids. Significantly, our data reveal that emetine and the (-)-R,S isomer of 2,3-dehydroemetine (designated in this paper as DHE4) reduce viral growth at nanomolar concentrations (i.e., IC50 ∼ 50-100 nM), paralleling those required for inhibition of protein synthesis, while calcium channel blocking activity occurs at elevated concentrations (i.e., IC50 ∼ 40-60 µM). Our findings suggest that the antiviral mechanisms primarily involve disruption of host cell protein synthesis and is demonstrably stereoisomer specific. The prospect of a therapeutic window in which emetine or DHE4 inhibit viral propagation without cardiotoxicity renders these alkaloids viable candidates in strategies worthy of clinical investigation.

Picornavirus 2C proteins: structure-function relationships and interactions with host factors

Picornaviruses, which are positive-stranded, non-enveloped RNA viruses, are known to infect people and animals with a broad spectrum of diseases. Among the nonstructural proteins in picornaviruses, 2C proteins are highly conserved and exhibit multiple structural domains, including amphipathic α-helices, an ATPase structural domain, and a zinc finger structural domain. This review offers a comprehensive overview of the functional structures of picornaviruses' 2C protein. We summarize the mechanisms by which the 2C protein enhances viral replication. 2C protein interacts with various host factors to form the replication complex, ultimately promoting viral replication. We review the mechanisms through which picornaviruses' 2C proteins interact with the NF-κB, RIG-I, MDA5, NOD2, and IFN pathways, contributing to the evasion of the antiviral innate immune response. Additionally, we provide an overview of broad-spectrum antiviral drugs for treating various enterovirus infections, such as guanidine hydrochloride, fluoxetine, and dibucaine derivatives. These drugs may exert their inhibitory effects on viral infections by targeting interactions with 2C proteins. The review underscores the need for further research to elucidate the precise mechanisms of action of 2C proteins and to identify additional host factors for potential therapeutic intervention. Overall, this review contributes to a deeper understanding of picornaviruses and offers insights into the antiviral strategies against these significant viral pathogens.

Advances in anti-EV-A71 drug development research

BACKGROUND

Enterovirus A71 (EV-A71) is capable of causing hand, foot and mouth disease (HFMD), which may lead to neurological sequelae and even death. As EV-A71 is resistant to environmental changes and mutates easily, there is still a lack of effective treatments or globally available vaccines.

AIM OF REVIEW

For more than 50 years since the HFMD epidemic, related drug research has been conducted. Progress in this area can promote the further application of existing potential drugs and develop more efficient and safe antiviral drugs, and provide useful reference for protecting the younger generation and maintaining public health security.

KEY SCIENTIFIC CONCEPTS OF REVIEW

At present, researchers have identified hundreds of EV-A71 inhibitors based on screening repurposed drugs, targeted structural design, and rational modification of previously effective drugs as the main development strategies. This review systematically introduces the current potential drugs to inhibit EV-A71 infection, including viral inhibitors targeting key sites such as the viral capsid, RNA-dependent RNA polymerase (RdRp), 2C protein, internal ribosome entry site (IRES), 3C proteinase (3Cpro), and 2A proteinase (2Apro), starting from each stage of the viral life cycle. Meanwhile, the progress of host-targeting antiviral drugs and their development are summarized in terms of regulating host immunity, inhibiting autophagy or apoptosis, and regulating the cellular redox environment. In addition, the current clinical methods for the prevention and treatment of HFMD are summarized and discussed with the aim of providing support and recommendations for the treatment of enterovirus infections including EV-A71.

Rational design and optimization of acylthioureas as novel potent influenza virus non-nucleoside polymerase inhibitors

Evidence suggests that rapidly evolving virus subvariants risk rendering current vaccines and anti-influenza drugs ineffective. Hence, exploring novel scaffolds or new targets of anti-influenza drugs is of great urgency. Herein, we report the discovery of a series of acylthiourea derivatives produced via a scaffold-hopping strategy as potent antiviral agents against influenza A and B subtypes. The most effective compound 10m displayed subnanomolar activity against H1N1 proliferation (EC50 = 0.8 nM) and exhibited inhibitory activity toward other influenza strains, including influenza B virus and H1N1 variant (H1N1, H274Y). Additionally, druggability evaluation revealed that 10m exhibited favorable pharmacokinetic properties and was metabolically stable in liver microsome preparations from three different species as well as in human plasma. In vitro and in vivo toxicity studies confirmed that 10m demonstrated a high safety profile. Furthermore, 10m exhibited satisfactory antiviral activity in a lethal influenza virus mouse model. Moreover, mechanistic studies indicated that these acylthiourea derivatives inhibited influenza virus proliferation by targeting influenza virus RNA-dependent RNA polymerase. Thus, 10m is a potential lead compound for the further exploration of treatment options for influenza.

Research progress on pathogenic and therapeutic mechanisms of Enterovirus A71

In recent years, enterovirus A71 (EV-A71) infection has become a major global public health problem, especially for infants and young children. The results of epidemiological research show that EV-A71 infection can cause acute hand, foot, and mouth disease (HFMD) and complications of the nervous system in severe cases, including aseptic pediatric meningoencephalitis, acute flaccid paralysis, and even death. Many studies have demonstrated that EV-A71 infection may trigger a variety of intercellular and intracellular signaling pathways, which are interconnected to form a network that leads to the innate immune response, immune escape, inflammation, and apoptosis in the host. This article aims to provide an overview of the possible mechanisms underlying infection, signaling pathway activation, the immune response, immune evasion, apoptosis, and the inflammatory response caused by EV-A71 infection and an overview of potential therapeutic strategies against EV-A71 infection to better understand the pathogenesis of EV-A71 and to aid in the development of antiviral drugs and vaccines.

Quinoline derivatives volunteering against antimicrobial resistance: rational approaches, design strategies, structure activity relationship and mechanistic insights

Emergence of antimicrobial resistance has become a great threat to human species as there is shortage of development of new antimicrobial agents. So, its mandatary to combat AMR by initiating research and developing new novel antimicrobial agents. Among phytoconstituents, Quinoline (nitrogen containing heterocyclic) have played a wide role in providing new bioactive molecules. So, this review provides rational approaches, design strategies, structure activity relationship and mechanistic insights of newly developed quinoline derivatives as antimicrobial agents.

Identification of a novel acylthiourea-based potent broad-spectrum inhibitor for enterovirus 3D polymerase in vitro and in vivo

Enterovirus infections have become a serious public health threat to young children, leading to hand-foot-and-mouth disease and more severe nervous system diseases. Due to the lack of licensed anti enterovirus drugs, we reported herein that a Tenovin-1 analog, acylthiourea-based 4-(tert-butyl)-N-((4-(4-(tert-butyl)benzamido)phenyl)carbamothioyl) benzamide (AcTU), displayed low nanomolar anti-EV-A71 activity with an EC₅₀ of 1.0 nM in RD cells. Moreover, AcTU exhibited nanomolar to picomolar inhibitory activity against a series of enteroviruses including EV-D68, CV-A21, CV-A16 and CV-B1 (EC₅₀ = 0.75-17.15 nM). Mechanistic studies indicated that AcTU inhibited enterovirus proliferation by targeting 3D polymerase. In addition, AcTU displayed moderate pharmacokinetic properties in rats (F = 7.4%, T_1/2 = 3.26 h), and in vivo protection studies demonstrated that AcTU orally administered at 0.6 mg/kg/d was highly protective against lethal EV-A71 challenge in mice, potentially reducing mortality from 100% to 20% as well as alleviating symptoms. These results suggested that AcTU could be a potent clinical candidate for the treatment of enterovirus infections.

Antiviral activity of the HSP90 inhibitor VER-50589 against enterovirus 71

Enterovirus 71 (EV71) is the major pathogen responsible for hand, foot, and mouth disease (HFMD) outbreaks; to date, there is no specific anti-EV71 agent. HSP90 is a crucial host factor for the viral life cycle and an ideal therapeutic target for limiting viral proliferation. However, the specific role of HSP90 in EV71-related signaling pathways and anti-EV71 agents targeting HSP90 remains unclear. This study aimed to verify the role of HSP90 in signaling pathways involved in EV71 replication and investigate the antiviral effects of a small molecule of VER-50589, a potent HSP90 inhibitor, against EV71 both in vitro and in vivo. Viral plaque assay, western blotting, and qPCR results showed that VER-50589 diminished the plaque formation induced by EV71 and inhibited EV71 mRNA and protein synthesis. A single daily dose of VER-50589 treatment significantly improved the survival rate of EV71-infected mice (p < 0.005). Interestingly, VER-50589 also exhibits activities against a series of human enteroviruses, including Coxsackievirus B3 (CVB3), Coxsackievirus B4-5 (CVB4-5), Coxsackievirus B4-7 (CVB4-7), and Echovirus 11 (Echo11). EV71 infection activated the AKT and ERK signaling pathways, and phosphorylation of AKT and RAF/MEK/ERK was weakened by VER-50589 administration. Thus, VER-50589 exhibits robust antiviral activity by inhibiting HSP90 and mediating the AKT and RAF/MEK/ERK signaling pathways. Considering that there are no effective antivirals or vaccines for the prevention and cure of HFMD in a clinical setting, the development of an anti-EV71 agent would be a straightforward and feasible therapeutic approach.

Hand, Foot, and Mouth Disease Challenges and Its Antiviral Therapeutics

Hand, Foot, and Mouth Disease (HFMD) is an infectious disease caused by enteroviruses (EVs) and is extremely contagious and prevalent among infants and children under 5 years old [...]

Predicting for anti-(mutant) SARS-CoV-2 and anti-inflammation compounds of Lianhua Qingwen Capsules in treating COVID-19

BACKGROUND

Lianhua Qingwen Capsules (LHQW) is a traditional Chinese medicine prescription commonly used to treat viral influenza in China. There has been sufficient evidence that LHQW could effectively treat COVID-19. Nevertheless, the potential anti-(mutant) SARS-CoV-2 and anti-inflammation compounds in LHQW are still vague.

METHODS

The compounds of LHQW and targets were collected from TCMSP, TCMID, Shanghai Institute of Organic Chemistry of CAS database, and relevant literature. Autodock Vina was used to carry out molecular docking. The pkCSM platform to predict the relevant parameters of compound absorption in vivo. The protein-protein interaction (PPI) network was constructed by the STRING database. The Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis was carried out by Database for Annotation, Visualization, and Integrated Discovery (DAVID). The anti-(mutant) SARS-CoV-2 and anti-inflammation networks were constructed on the Cytoscape platform.

RESULTS

280 compounds, 16 targets related to SARS-CoV-2, and 54 targets related to cytokine storm were obtained by screening. The key pathways Toll-like receptor signaling, NOD-like receptor signal pathway, and Jak-STAT signaling pathway, and the core targets IL6 were obtained by PPI network and KEGG pathway enrichment analysis. The network analysis predicted and discussed the 16 main anti-SARS-CoV-2 active compounds and 12 main anti-inflammation active compounds. Ochnaflavone and Hypericin are potential anti-mutant virus compounds in LHQW.

CONCLUSIONS

In summary, this study explored the potential anti-(mutant) SARS-CoV-2 and anti-inflammation compounds of LHQW against COVID-19, which can provide new ideas and valuable references for discovering active compounds in the treatment of COVID-19.

Guignardones Y-Z, antiviral meroterpenes from Penicillium sp. NBUF154 associated with a Crella sponge from the marine mesophotic zone

Guignardones Y-Z (1-2), two new meroterpenoids, and six known metabolites involving guignardone A-H (3-4), gyorgy-isoflavone (5), daidzein (6), blumenol A (7) and guignardianone A (8) were isolated from the fungus Penicillium sp. NBUF154, which was obtained from a 60 m deep Crella sponge. Their structures including absolute configurations were unambiguously elucidated by exhaustive spectroscopic analysis and ECD calculations. A putative biosynthetic pathway toward guignardones (1-4) is here proposed. Biological evaluation of compounds 1-8 showed that 1 and 7 exert potent inhibitory effects towards human enterovirus 71 (EV71).

Structure Prediction and Potential Inhibitors Docking of Enterovirus 2C Proteins

Human enterovirus infections are mostly asymptomatic and occasionally could be severe and life-threatening. The conserved non-structural 2C from enteroviruses protein is a promising target in antiviral therapies against human enteroviruses. Understanding of 2C-drug interactions is crucial for developing the potential antiviral agents. While functions of enterovirus 2C proteins have been widely studied, three-dimensional structure information of 2C is limited. In this study, the structures of 2C proteins from 20 enteroviruses were simulated and reconstructed using I-TASSER programs. Subsequent docking studies of the known 22 antiviral inhibitors for 2C proteins were performed to uncover the inhibitor-binding characteristics of 2C. Among the potential inhibitors, the compound hydantoin exhibited the highest broad-spectrum antiviral activities with binding to 2C protein. The anti-enteroviral activity of GuaHCL, compound 19b, R523062, compound 12a, compound 12b, quinoline analogs 12a, compound 19d, N⁶-benzyladenosine, dibucaine derivatives 6i, TBZE-029, fluoxetine analogs 2b, dibucaine, 2-(α-hydroxybenzyl)-benzimidazole (HBB), metrifudil, pirlindole, MRL-1237, quinoline analogs 10a, zuclopenthixol, fluoxetine, fluoxetine HCl, and quinoline analogs 12c showed a trend of gradual decrease. In addition, the free energy with 22 compounds binding to EV 2C ranged from −0.35 to −88.18 kcal/mol. Our in silico studies will provide important information for the development of pan-enterovirus antiviral agents based on 2C.

Enterovirus A71 antivirals: Past, present, and future

Enterovirus A71 (EV-A71) is a significant human pathogen, especially in children. EV-A71 infection is one of the leading causes of hand, foot, and mouth diseases (HFMD), and can lead to neurological complications such as acute flaccid myelitis (AFM) in severe cases. Although three EV-A71 vaccines are available in China, they are not broadly protective and have reduced efficacy against emerging strains. There is currently no approved antiviral for EV-A71. Significant progress has been made in developing antivirals against EV-A71 by targeting both viral proteins and host factors. However, viral capsid inhibitors and protease inhibitors failed in clinical trials of human rhinovirus infection due to limited efficacy or side effects. This review discusses major discoveries in EV-A71 antiviral development, analyzes the advantages and limitations of each drug target, and highlights the knowledge gaps that need to be addressed to advance the field forward.

Identification of a novel binding inhibitor that blocks the interaction between hSCARB2 and VP1 of enterovirus 71

Enterovirus 71 (EV-A71) infection causes severe hand-foot-and-mouth disease that leads to cardiopulmonary complications and death in young children under 5 years of age. Although there are available vaccines for EV-A71 C4, however, there are no efficient drugs for severe cases. Thus, there is an urgent need to find new direct-antiviral agents (DAAs) to control EV-A71 infection. In this study, we report our discovery of the EV-A71 capsid inhibitor PTC-209HBr, a small-molecule Bmi-1 inhibitor and an anticancer agent, and its derivatives that inhibit multiple enteroviruses with an EC50 at a submicromolar efficacy. The mechanism of action of PTC-209HBr was confirmed by time-of-addition, resistance selection and reverse genetics experiments, microscale thermophoresis (MST), viral binding and entry assays, coimmunoprecipitation (Co-IP) and immunofluorescence experiments (IF). Mechanistic studies indicated that PTC-209HBr inhibited EV-A71 infection by impeding the binding between VP1 and the receptor hSCARB2 during the early stage of EV-A71 infection through hindering viral entry into host cells. Collectively, these findings indicated that PCT-209HBr is a novel inhibitor of enteroviruses with a confirmed mechanism of action that can be further developed into EV-A71 DAAs.

Anti-viral triterpenes: a review

Triterpenes are naturally occurring derivatives biosynthesized following the isoprene rule of Ruzicka. The triterpenes have been reported to possess a wide range of therapeutic applications including anti-viral properties. In this review, the recent studies (2010-2020) concerning the anti-viral activities of triterpenes have been summarized. The structure activity relationship studies have been described as well as brief biosynthesis of these triterpenes is discussed.

Recovery Infectious Enterovirus 71 by Bac-to-Bac Expression System in vitro and in vivo

Enterovirus 71 (EV71) is one of the most important etiological agents for hand-foot-mouth disease. Compared with coxsackievirus A16 infection, EV71 infection is often associated with severe central nervous system complications, such as encephalitis, encephalomyelitis, and acute flaccid paralysis in infants and young children. In this study, we constructed a recombinant baculovirus with T7 ribonucleic acid polymerase under the control of a cytomegalovirus promoter and simultaneously engineered the T7 promoter upstream of a full-length EV71 complementary deoxyribonucleic acid. After transduction into mammalian cells, typical cytopathic effects (CPEs) and VP1 signals were detected in cells transfected with recombinant baculovirus. Additionally, viral particles located in the cytoplasm of human rhabdomyosarcoma cells (Rd) and Vero cells were observed by electron microscope, indicating that EV71 was recovered using a Bac-to-Bac expression system in vitro. After four passages, the rescued virus had a growth curve and plaque morphology similar to those of the parental virus. Furthermore, the Vp1 gene and the protein from the mouse brain were detected by reverse transcription polymerase chain reaction and immunohistochemistry after intracerebral injection of purified recombinant baculovirus. Typical CPEs were observed after inoculation of the supernatant from mouse brain to Rd cells, revealing a reconstruction of EV71 in vivo. Thus, we established a new approach to rescue EV71 based on a baculovirus expression system in vitro and in vivo, which may provide a safe and convenient platform for fundamental research and a strategy to rescue viruses that currently lack suitable cell culture and animal models.

Fluoxetine targets an allosteric site in the enterovirus 2C AAA+ ATPase and stabilizes a ring-shaped hexameric complex

Enteroviruses are globally prevalent human pathogens responsible for many diseases. The nonstructural protein 2C is a AAA+ helicase and plays a key role in enterovirus replication. Drug repurposing screens identified 2C-targeting compounds such as fluoxetine and dibucaine, but how they inhibit 2C is unknown. Here, we present a crystal structure of the soluble and monomeric fragment of coxsackievirus B3 2C protein in complex with (S)-fluoxetine (SFX), revealing an allosteric binding site. To study the functional consequences of SFX binding, we engineered an adenosine triphosphatase (ATPase)–competent, hexameric 2C protein. Using this system, we show that SFX, dibucaine, HBB [2-(α-hydroxybenzyl)-benzimidazole], and guanidine hydrochloride inhibit 2C ATPase activity. Moreover, cryo–electron microscopy analysis demonstrated that SFX and dibucaine lock 2C in a defined hexameric state, rationalizing their mode of inhibition. Collectively, these results provide important insights into 2C inhibition and a robust engineering strategy for structural, functional, and drug-screening analysis of 2C proteins.

Rhinovirus Inhibitors: Including a New Target, the Viral RNA

Rhinoviruses (RVs) are the main cause of recurrent infections with rather mild symptoms characteristic of the common cold. Nevertheless, RVs give rise to enormous numbers of absences from work and school and may become life-threatening in particular settings. Vaccination is jeopardised by the large number of serotypes eliciting only poorly cross-neutralising antibodies. Conversely, antivirals developed over the years failed FDA approval because of a low efficacy and/or side effects. RV species A, B, and C are now included in the fifteen species of the genus Enteroviruses based upon the high similarity of their genome sequences. As a result of their comparably low pathogenicity, RVs have become a handy model for other, more dangerous members of this genus, e.g., poliovirus and enterovirus 71. We provide a short overview of viral proteins that are considered potential drug targets and their corresponding drug candidates. We briefly mention more recently identified cellular enzymes whose inhibition impacts on RVs and comment novel approaches to interfere with infection via aggregation, virus trapping, or preventing viral access to the cell receptor. Finally, we devote a large part of this article to adding the viral RNA genome to the list of potential drug targets by dwelling on its structure, folding, and the still debated way of its exit from the capsid. Finally, we discuss the recent finding that G-quadruplex stabilising compounds impact on RNA egress possibly via obfuscating the unravelling of stable secondary structural elements.

Picornaviral 2C proteins: A unique ATPase family critical in virus replication

The 2C proteins of Picornaviridae are unique members of AAA+ protein family. Although picornavirus 2C shares many conserved motifs with Super Family 3 DNA helicases, duplex unwinding activity of many 2C proteins remains undetected, and high-resolution structures of 2C hexamers are unavailable. All characterized 2C proteins exhibit ATPase activity, but the purpose of ATP hydrolysis is not fully understood. 2C is highly conserved among picornaviruses and plays crucial roles in nearly all steps of the virus lifecycle. It is therefore considered as an effective target for broad-spectrum antiviral drug development. Crystallographic investigation of enterovirus 2C proteins provide structural details important for the elucidation of 2C function and development of antiviral drugs. This chapter summarizes not only the findings of enzymatic activities, biochemical and structural characterizations of the 2C proteins, but also their role in virus replication, immune evasion and morphogenesis. The linkage between structure and function of the 2C proteins is discussed in detail. Inhibitors targeting the 2C proteins are also summarized to provide an overview of drug development. Finally, we raise several key questions to be addressed in this field and provide future research perspective on this unique class of ATPases.

Antiviral activity of Mulberroside C against enterovirus A71 in vitro and in vivo

Enterovirus A71 (EV-A71) is one of the main causative agents of hand, foot and mouth disease which seriously threatens young children's health and lives. However, there is no effective therapy currently available for treating these infections. Therefore, effective drugs to prevent and treat EV-A71 infections are urgently needed. Here, we identified Mulberroside C potently against the proliferation of EV-A71. The in-vitro anti-EV-A71 activity of Mulberroside C was assessed by cytopathic effect inhibition and viral plaque reduction assays, and the results showed that Mulberroside C significantly inhibited EV-A71 infection. The downstream assays affirmed that Mulberroside C inhibited viral protein and RNA synthesis. Furthermore, Mulberroside C effectively reduced clinical symptoms in EV-A71 infected mice and reduced mortality at higher concentrations. The mechanism study indicated that Mulberroside C bound to the hydrophobic pocket of viral capsid protein VP1, thereby preventing viral uncoating and genome release. Taken together, our study indicated that Mulberroside C could be a promising EV-A71 inhibitor and worth extensive preclinical investigation as a lead compound.

Antiviral Peptides Targeting the Helicase Activity of Enterovirus Nonstructural Protein 2C

Enteroviruses belong to the genus Enterovirus of the family Picornaviridae and include four human enterovirus groups (EV-A to -D): the epidemic of enteroviruses such as human enterovirus A71 (EV-A71) and coxsackievirus A16 (CVA16) is a threat to global public health. Enteroviral protein 2C is the most conserved nonstructural protein among all enteroviruses and possesses RNA helicase activity that plays pivotal roles during enteroviral life cycles, which makes 2C an attractive target for developing antienterovirus drugs. In this study, we designed a peptide, named 2CL, based on the structure of EV-A71 2C. This peptide effectively impaired the oligomerization of EV-A71 2C protein and inhibited the RNA helicase activities of 2C proteins encoded by EV-A71 and CVA16, both of which belong to EV-A, and showed potent antiviral efficacy against EV-A71 and CVA16 in cells. Moreover, the 2CL treatment elicited a strong in vivo protective efficacy against lethal EV-A71 challenge. In addition, the antiviral strategy of targeting the 2C helicase activity can be applied to inhibit the replication of EV-B. Either 2CL or B-2CL, the peptide redesigned based on the 2CL-corresponding sequence of EV-Bs, could exert effective antiviral activity against two important EV-Bs, coxsackievirus B3 and echovirus 11. Together, our findings demonstrated that targeting the helicase activity of 2C with a rationally designed peptide is an efficient antiviral strategy against enteroviruses, and 2CL and B-2CL show promising clinical potential to be further developed as broad-spectrum antienterovirus drugs.IMPORTANCE Enteroviruses are a large group of positive-sense single-stranded RNA viruses and include numerous human pathogens, such as enterovirus A71 (EV-A71), coxsackieviruses, and echoviruses. However, no approved EV antiviral drugs are available. Enteroviral 2C is the most conserved nonstructural protein among all enteroviruses and contains the RNA helicase activity critical for the viral life cycle. Herein, according to the structure of EV-A71 2C, we designed a peptide that effectively inhibited the RNA helicase activities of EV-A71- and coxsackievirus A16 (CVA16)-encoded 2C proteins. Moreover, this peptide exerted potent antiviral effects against EV-A71 and CVA16 in cells and elicited therapeutic efficacy against lethal EV-A71 challenge in vivo Furthermore, we demonstrate that the strategy of targeting the 2C helicase activity can be used for other relevant enteroviruses, including coxsackievirus B3 and echovirus 11. In summary, our findings provide compelling evidence that the designed peptides targeting the helicase activity of 2C could be broad-spectrum antivirals for enteroviruses.

The Structure, Function, and Mechanisms of Action of Enterovirus Non-structural Protein 2C

Enteroviruses are a group of RNA viruses belonging to the family Picornaviridae. They include human enterovirus groups A, B, C, and D as well as non-human enteroviruses. Enterovirus infections can lead to hand, foot, and mouth disease and herpangina, whose clinical manifestations are often mild, although some strains can result in severe neurological complications such as encephalitis, myocarditis, meningitis, and poliomyelitis. To date, research on enterovirus non-structural proteins has mainly focused on the 2A and 3C proteases and 3D polymerase. However, another non-structural protein, 2C, is the most highly conserved protein, and plays a vital role in the enterovirus life cycle. There are relatively few studies on this protein. Previous studies have demonstrated that enterovirus 2C is involved in virus uncoating, host cell membrane rearrangements, RNA replication, encapsidation, morphogenesis, ATPase, helicase, and chaperoning activities. Despite ongoing research, little is known about the pathogenesis of enterovirus 2C proteins in viral replication or in the host innate immune system. In this review, we discuss and summarize the current understanding of the structure, function, and mechanism of the enterovirus 2C proteins, focusing on the key mutations and motifs involved in viral infection, replication, and immune regulation. We also focus on recent progress in research into the role of 2C proteins in regulating the pattern recognition receptors and type I interferon signaling pathway to facilitate viral replication. Given these functions and mechanisms, the potential application of the 2C proteins as a target for anti-viral drug development is also discussed. Future studies will focus on the determination of more crystal structures of enterovirus 2C proteins, which might provide more potential targets for anti-viral drug development against enterovirus infections.