Ribavirin reduces mortality in enterovirus 71-infected mice by decreasing viral replication

6-thioguanine inhibits EV71 replication by reducing BIRC3-mediated autophagy

BACKGROUND

Enterovirus 71 (EV71) is one of the major causative agents of hand, foot, and mouth disease (HFMD), and can cause severe cerebral complications and even fatality in children younger than 5 years old. However, there is no specific medication for EV71 infection in clinical practice. Our previous studies had identified the 6-thioguanine (6-TG), an FDA-approved anticancer drug, as a potential antiviral agent, but its anti-EV71 activity is largely unknown, therefore, we aim to explore the antiviral effect of 6-TG on EV71.

RESULTS

6-TG significantly suppressed EV71 mRNA level, VP1 protein expression, and viral progeny production in HT-29 cells. In EV71-infected HT-29 cells, the 50% cytotoxicity concentration of 6-TG (CC50) was > 2000 µM and the 50% inhibitory concentration of 6-TG against EV71 (IC50) was 0.9302 µM. Interestingly, the selectivity index (SI) value of 6-TG against EV71 was > 2150.1, which was higher than the SI value (> 66.7) of ribavirin. Mechanistically, 6-TG treatment reduced the expression of baculoviral IAP repeat containing 3 (BIRC3), and further inhibited EV71 replication by attenuating BIRC3-mediated the complete autophagy.

CONCLUSIONS

6-TG exerted a significant inhibitory effect on EV71 infection in vitro and prevented EV71-induced the complete autophagy by decreasing BIRC3 expression. Our work provided a basis for the further development of 6-TG as a therapy for EV71-associated HFMD.

Recent Progress in Human Milk Oligosaccharides and Its Antiviral Efficacy

Gastrointestinal (GI)-associated viruses, including rotavirus (RV), norovirus (NV), and enterovirus, usually invade host cells, transmit, and mutate their genetic information, resulting in influenza-like symptoms, acute gastroenteritis, encephalitis, or even death. The unique structures of human milk oligosaccharides (HMOs) enable them to shape the gut microbial diversity and endogenous immune system of human infants. Growing evidence suggests that HMOs can enhance host resistance to GI-associated viruses but without a systematic summary to review the mechanism. The present review examines the lactose- and neutral-core HMOs and their antiviral effects in the host. The potential negative impacts of enterovirus 71 (EV-A71) and other GI viruses on children are extensive and include neurological sequelae, neurodevelopmental retardation, and cognitive decline. However, the differences in the binding affinity of HMOs for GI viruses are vast. Hence, elucidating the mechanisms and positive effects of HMOs against different viruses may facilitate the development of novel HMO derived oligosaccharides.

Miltefosine reduces coxsackievirus B3 lethality of mice with enhanced STAT3 activation

Coxsackievirus B3 (CVB3), one serotype of enteroviruses, can induce fatal myocarditis and hepatitis in neonates, but both treatment and vaccine are unavailable. Few reports tested antivirals to reduce CVB3. Several antivirals were developed against other enterovirus serotypes, but these antivirals failed in clinical trials due to side effects and drug resistance. Repurposing of clinical drugs targeting cellular factors, which enhance viral replication, may be another option. Parasite and cancer studies showed that the cellular protein kinase B (Akt) decreases interferon (IFN), apoptosis, and interleukin (IL)-6-induced STAT3 responses, which suppress CVB3 replication. Furthermore, miltefosine, the Akt inhibitor used in the clinic for parasite infections, enhances IL-6, IFN, and apoptosis responses in treated patients, suggesting that miltefosine could be the potential antiviral for CVB3. This study was therefore designated to test the antiviral effects of miltefosine against CVB3 in vitro and especially, in mice, as few studies test miltefosine in vitro, but not in vivo. In vitro results showed that miltefosine inhibited viral replication with enhanced activation of the cellular transcription factor, STAT3, which is reported to reduce CVB3 both in vitro and in mice. Notably, STAT3 knockdown abolished the anti-CVB3 activity of miltefosine in vitro. Mouse studies demonstrated that miltefosine pretreatment reduced CVB3 lethality of mice with decreased virus loads, organ damage, and apoptosis, but enhanced STAT3 activation. Miltefosine could be prophylaxis for CVB3 by targeting Akt to enhance STAT3 activation in the mechanism, which is independent of IFN responses and hardly reported in pathogen infections.

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.

Recent Advances in Enterovirus A71 Infection and Antiviral Agents

Enterovirus A71 (EV-A71) is one of the major causative agents of hand, foot, and mouth disease (HFMD) that majorly affects children. Most of the time, HFMD is a mild disease but can progress to severe complications, such as meningitis, brain stem encephalitis, acute flaccid paralysis, and even death. HFMD caused by EV-A71 has emerged as an acutely infectious disease of highly pathogenic potential in the Asia-Pacific region. In this review, we introduced the properties and life cycle of EV-A71, and the pathogenesis and the pathophysiology of EV-A71 infection, including tissue tropism and host range of virus infection, the diseases caused by the virus, as well as the genes and host cell immune mechanisms of major diseases caused by enterovirus 71 (EV-A71) infection, such as encephalitis and neurologic pulmonary edema. At the same time, clinicopathologic characteristics of EV-A71 infection were introduced. There is currently no specific medication for EV-A71 infection, highlighting the urgency and significance of developing suitable anti-EV-A71 agents. This overview also summarizes the targets of existing anti-EV-A71 agents, including virus entry, translation, polyprotein processing, replication, assembly and release; interferons; interleukins; the mitogen-activated protein kinase, phosphatidylinositol 3-kinase, and protein kinase B signaling pathways; the oxidative stress pathway; the ubiquitin-proteasome system; and so on. Furthermore, it overviews the effects of natural products, monoclonal antibodies, and RNA interference against EV-A71. It also discusses issues limiting the research of antiviral drugs. This review is a systematic and comprehensive summary of the mechanism and pathological characteristics of EV-A71 infection, the latest progress of existing anti-EV-A71 agents. It would provide better understanding and guidance for the research and application of EV-A71 infection and antiviral inhibitors.

A mouse model and pathogenesis study for CVA19 first isolated from hand, foot, and mouth disease

ABSTRACTCoxsackievirus A19 (CVA19) is a member of Enterovirus (EV) C group in the Picornaviridae family. Recently, we reported a case of CVA19-infected hand, foot, and mouth disease (HFMD) for the first time. However, the current body of knowledge on the CVA19 infection, particularly the pathogenesis of encephalomyelitis and diarrhoea is still very limited, due to the lack of suitable animal models. Here, we successfully established a CVA19 mouse model via oral route based on 7-day-old ICR mice. Our results found the virus strain could directly infect the neurons, astrocytes of brain, and motor neurons of spinal cord causing neurological complications, such as acute flaccid paralysis. Importantly, viruses isolated from the spinal cords of infected mice caused severe illness in suckling mice, fulfilling Koch's postulates to some extent. CVA19 infection led to diarrhoea with typical pathological features of shortened intestinal villi, increased number of secretory cells and apoptotic intestinal cells, and inflammatory cell infiltration. Much higher concentrations of serum cytokines and more peripheral blood inflammatory cells in CVA19-infected mice indicated a systematic inflammatory response induced by CVA19 infection. Finally, we found ribavirin and CVA19 VP1 monoclonal antibody could not prevent the disease progression, but higher concentrations of antisera and interferon alpha 2 (IFN-α2) could provide protective effects against CVA19. In conclusion, this study shows that a natural mouse-adapted CVA19 strain leads to diarrhoea and encephalomyelitis in a mouse model via oral infection, which provides a useful tool for studying CVA19 pathogenesis and evaluating the efficacy of vaccines and antivirals.

Recent Developments of Gramine: Chemistry and Biological Activity

The natural alkaloid gramine has attracted significant attention in both academic and industrial circles because of its potential and diverse biological activities, including antiviral, antibacterial, antifungal, anti-inflammatory and antitumor activities; application in therapy for Alzheimer's disease; serotonin-receptor-related activity; insecticidal activity; and application as an algicide. In this review, we focus on the research advances that have been made for gramine-based molecules since their discovery, providing key information on their extraction and separation, chemical synthesis and diverse biological activities. Data regarding their mechanisms of action are also presented. This comprehensive and critical review will serve as a guide for developing more drug candidates based on gramine skeletons.

Antiviral effects and mechanisms against EV71 of the novel 2-Benzoxyl-Phenylpyridine Derivatives

A series of 2-Benzoxyl-Phenylpyridine derivatives were evaluated for their potential antiviral activities against EV71. The preliminary assays indicated that some of these compounds exhibited excellent antiviral effects on EV71, they could effectively inhibit virus-induced cytopathic effects (CPEs), reduce progeny viral yields, and present similar or better antiviral activities compared to the positive control drug ribavirin. Among these derivatives, compounds WY7, WY13 and WY14 showed the most potency against EV71. Investigation of the underlying mechanism of action revealed that these compounds target EV71 replication in cells post infection, they could profoundly inhibit viral RNA replication and protein synthesis, and inhibit virus-induced cell apoptosis. Further experiments demonstrated that compound WY7 potently inhibited the activity of the EV71 3C protease (3Cpro), and to some extent, it affected the activity of 3D polymerase (3Dpol), thus blocking viral replication, but not the activity of the 2A proteinase (2Apro). Modeling of the molecular binding of the 3Cpro-WY7 complex revealed that compound WY7 was predicted to insert into the substrate-binding pocket of EV71 3Cpro, blocking substrate recognition and thereby inhibiting EV71 3Cpro activity. These results indicate that these compounds might be feasible therapeutic agents against EV71 infection and that these compounds may provide promising lead scaffolds for the further design and synthesis of potential antiviral agents.

The development and characterization of a stable Coxsackievirus A16 infectious clone with Nanoluc reporter gene

Coxsackievirus A16 (CA16) belongs to the Human Enterovirus A species, which is a common pathogen causing hand, foot, and mouth disease in children. Currently, specific vaccines and drugs against CA16 are unavailable, and there is an unmet need to further understand the virus and invent effective treatment. Constructing a CA16 infectious clone with a reporter gene will greatly facilitate its virological studies. Here, we first reported the construction of a CA16 infectious clone (rCA16) whose progeny is highly replicative and virulent in suckling mice. On the basis of rCA16, we further inserted a NanoLuc (Nluc) reporter gene and made the rCA16-Nluc clone. We found that the Nluc gene in rCA16-Nluc is stable during continuous growing in Vero cells and thus allowed detection of a steady luciferase signal in rCA16-Nluc-infected Vero cells over 10 passages. Its application in antivirals characterization and high-throughput screening is exemplified by measuring IC₅₀, CC₅₀, and selection index of guanidine hydrochloride, ribavirin, chloroquine, and ammonium chloride against CA16. Finally, we showed that rCA16-Nluc based assay greatly simplified the CA16 neutralizing antibody tests. Thus, these two CA16 infectious clones will be robust tools for future enterovirus studies and antivirals development.

Human Dendritic Cells Transmit Enterovirus A71 via Heparan Sulfates to Target Cells Independent of Viral Replication

Enterovirus A71 (EV-A71) is a causative agent of life-threatening neurological diseases in young children. EV-A71 is highly infectious but it remains unclear how the virus disseminates from primary entry sites-the mucosa of the respiratory tract or the intestine-to secondary replication sites-skin or brain. Here, we investigated the role of dendritic cells (DCs) in EV-A71 dissemination. DCs reside in the mucosa of the airway and gut, and migrate to lymphoid tissues upon activation and, therefore, could facilitate EV-A71 dissemination to secondary replication sites. Monocyte-derived DCs were not permissive to different genotypes of EV-A71 but, notably, coculture with EV-A71-susceptiblle RD99 cells led to very efficient infection of RD99 cells. Notably, EV-A71 transmission of DCs to RD99 was independent of viral replication as a replication inhibitor did not affect transmission. Soluble heparin blocked EV-A71 transmission by DCs to RD99 cells, in contrast to antibodies against known attachment receptor DC-SIGN. These results strongly suggest that DCs might be a first target for EV-A71 and involved in viral dissemination via heparan sulfates and heparin derivatives might be an effective treatment to attenuate dissemination. IMPORTANCE EV-A71 is an emerging neurotropic virus that is of emerging concern and can result in polio-like illness. The exact mechanism of how EV-A71 results in neurological symptoms are unknown. In particular, the early dissemination of the virus from primary replication sites (airway and intestine) to secondary sites (central nervous system and skin) needs to be elucidated. There is evidence pointing toward a role for dendritic cells (DC) in EV-A71 transmission. Moreover, heparan sulfate (HS) binding mutations are observed in patients with severe diseases. Therefore, we evaluated the potential role of HS on DC in transmission. We find that HS are critical for transmitting EV-A71 by DC to target cells. Our data are consistent with other clinical and in vitro observations highlighting the importance of HS in EV-A71-induced disease.

Berberine prevents lethal EV71 neurological infection in newborn mice

Enterovirus 71 (EV71) is the major pathogen causing fatal neurological complications of hand, foot, and mouth disease (HFMD) in young children. Currently no effective antiviral therapy is available. In the present study, we found that natural compound Berberine (BBR) displayed potent inhibitory effects on EV71 replication in various neural cells (IC₅₀ of 2.79–4.03 μM). In a newborn mouse model of lethal EV71 infection, Berberine at 2–5 mg/kg markedly reduced mortality and clinical scores. Consistently, the replication of EV71 and pathological changes were attenuated in various infected organs including brain and lung with BBR treatment. Interestingly, EV71 infection in the brain mainly localized in the peripheral zone of brainstem and largely in astrocytes. Primary culture of astrocytes from newborn mouse brain confirmed the efficient EV71 replication that was mostly inhibited by BBR treatment at 5 μM. Further investigations revealed remarkably elevated cellular reactive oxygen species (ROS) levels that coincided with EV71 replication in primary cultured astrocytes and various cell lines. BBR largely abolished the virus-elevated ROS production and greatly diminished EV71 replication by up-regulating NFE2 like bZIP transcription factor 2 (Nrf2) via the kelch like ECH associated protein 1 (Keap)-Nrf2 axis. The nuclear localization of Nrf2 and expression of downstream antioxidant enzymes heme oxygenase 1 (HO-1) and NAD(P)H quinone dehydrogenase 1 (NQO1) were increased significantly by BBR treatment. Collectively, our findings revealed that BBR prevents lethal EV71 neurological infection via inhibiting virus replication through regulating Keap-Nrf2 axis and ROS generation in astrocytes of brainstem, thus providing a potential antiviral treatment for severe EV71 infection associated with neurological complications.

Isolation and Identification of Andrographis paniculata (Chuanxinlian) and Its Biologically Active Constituents Inhibited Enterovirus 71-Induced Cell Apoptosis

Aim:Andrographis paniculata (Burm. f.) Nees (also known as Chuanxinlian in Chinese) of Acanthaceae family is one of the Chinese herbs reputed to be effective in the treatment of inflammation, infection, cold, and fever. Enterovirus 71 (EV71) is one of the most important enteroviruses that cause hand, foot, and mouth disease (HFMD) accompanied with neurological complication.

Methods: To explore an anti-infective Chinese herb medicine, pure compounds isolated or synthesized analogues from A. paniculata (AP) ethyl acetate (EtOAc) extract are used to explore their anti-EV71-induced cytotoxicity. The antiviral activity was determined by cytopathic effect (CPE) reduction, and sub-G1 assays were used for measuring lysis and apoptosis of EV71-infected rhabdomyosarcoma (RD) cells. IFNγ-driven luciferase reporter assay was used to evaluate their potential roles in activation of immune responses.

Results: Our data showed that EV71-induced sub-G1 phase of RD cells was dose dependently increased. Highly apoptotic EV71-infected RD cells were reduced by AP extract treatment. Ergosterol peroxide (4) has the most anti-apoptotic effect among these seven compounds. In addition, 3,19-O-acetyl-14-deoxy-11,12-didehydroandrographolide (8) synthesized from acetylation of compound 7 showed significantly better antiviral activity and the lowest sub-G1 phase of 6%–18%. Further investigation of IFNγ-inducer activity of these compounds showed that compounds 3, 6, 10, 11, and 12 had significantly higher IFNγ luciferase activities, suggesting their potential to promote IFNγ expression and thus activate immune responses for antivirus function.

Conclusion: Our study demonstrated that bioactive compounds of AP and its derivatives either protecting EV71-infected RD cells from sub-G1 arrest or possessing IFNγ-inducer activity might be feasible for the development of anti-EV71 agents.

Characterization of Enterovirus Associated m6A RNA Methylation in Children With Neurological Symptoms: A Prospective Cohort Study

Little is known about the particular changes of N6-methyladenosine (m6A) RNA methylation in enterovirus (EV) infection among children with neurologic symptoms. Here, we determined the characterization of EV associated m6A RNA methylation in this population. A prospective cohort study was conducted from 2018/2 to 2019/12 at the Guangzhou Women and Children’s Medical Center. We included EV infected children with and without neurological symptoms. High-throughput m(6)A-RNA immunoprecipitation sequencing (MeRIP-seq) and RNA-seq analysis were used to evaluate the m6A RNA methylation and transcript expression of cerebrospinal fluid samples. The functional annotation and pathways of differentially methylated m6A genes with synchronously differential expression were analyzed by Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG). Seven patients were enrolled in the control group, and 13 cases were in the neurological symptoms (NS) group. A total of 3472 differentially expressed genes and 957 m6A modified genes were identified. A conjoint analysis of MeRIP-seq and RNA-seq data found 1064 genes with significant changes in both the m6A modifications and mRNA levels. The different m6A RNA methylation was increased in the transcriptome’s CDS regions but decreased in both the 3′UTRs and stop codon among the NS group. Functional annotation like the “oxidative phosphorylation” gene pathway, “Parkinson’s disease” and GO terms like “respiratory electron transport chain,” “cellular metabolic process,” and “oxidation-reduction process” was enriched in symptomatic patients. Our study elucidated the changes of RNA m6A methylation patterns and related cellular functions and signaling pathways in EV patients with neurologic symptoms.

Ribavirin as a curative and prophylactic agent against foot and mouth disease virus infection in C57BL/6 suckling and adult mice model

Despite the availability of control measures for foot-and-mouth disease (FMD), the application of antiviral agents is imperative due to certain limitations in the prevention and control of FMD. This study pertains to systematic in vivo investigation of ribavirin as a prophylactic/curative agent, both in suckling and adult C57BL/6 mice against foot-and-mouth disease virus (FMDV) infection. In the adult mice, antiviral efficacy was assessed based on standard clinical score, body weight, and viral load. Only 13.33 to 33.33% of adult mice exhibited disease-specific symptoms following treatment and infection and vice versa, respectively, indicating the antiviral efficacy of the ribavirin. Further, the distribution of virus in different vital organs following ribavirin treatment and virus infection, and vice versa using SYBR green-based real-time PCR is reported. In the blood sample, the viral RNA was detected as early as two days post-infection and there was a significant reduction in virus titer (1000 to 10,000-folds) in the treatment groups compared to the infection control group. Animals receiving ribavirin had significantly lower organ virus titers at 2, 4, 6, 9, and 14 days post-challenge (dpc) than placebo-treated. In suckling mice, the treatment groups were 100% protected/cured compared to the control group. Thus, our data demonstrate that ribavirin may provide a feasible therapeutic approach to prevent as well as to treat FMDV infection.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13337-021-00746-8.

Discovery of 14S-(2'-chloro-4'-nitrophenoxy)-8R/S,17-epoxy andrographolide as EV-A71 infection inhibitor

Human enterovirus A71 (EV-A71) is a major etiological agent of hand-foot-and-mouth disease (HFMD) and there is presently no internationally approved antiviral against EV-A71. In this study, it is disclosed that 14S-(2'-chloro-4'-nitrophenoxy)-8R/S,17-epoxy andrographolide (2) was discovered to be an effective inhibitor against EV-A71 infection showing significant reduction of viral titre. In addition to EV-A71, compound 2 exerts broad-spectrum antiviral effects against other enteroviruses. It is revealed that compound 2 inhibits the post-entry stages of EV-A71 viral replication cycle and significantly reduces viral protein expression of structural proteins such as VP0 and VP2 via inhibiting EV-A71 RNA replication. Moreover, the inhibitory property of compound 2 is specific to viral RNA replication. Furthermore, compound 2 is more likely to target a host factor in EV-A71 RNA replication. As a result, introduction of epoxide at positions 8 and 17 of andrographolide is effective for anti-EV-A71 infection and is a potential anti-EV-A71 strategy. Further work to discover more potent andrographolide derivatives and elucidate comprehensive SAR is under way.

Effective Use of Student-Created Case Studies as Assessment in an Undergraduate Neuroscience Course

Case studies and student-led learning activities are both effective active learning methods for increasing student engagement, promoting student learning, and improving student performance. Here, we describe combining these instructional methods to use student-created case studies as assessment for an online neurovirology module in a neuroanatomy and physiology course. First, students learned about neurovirology in a flipped classroom format using free, open-access virology resources. Then, students used iterative writing practices to write an interrupted case study incorporating a patient narrative and primary literature data on the neurovirulent virus of their choice, which was graded as a writing assessment. Finally, students exchanged case studies with their peers, and both taught and completed the case studies as low-stakes assessment. Student performance and evaluations support the efficacy of case studies as assessment, where iterative writing improved student performance, and students reported increased knowledge and confidence in the corresponding learning objectives. Overall, we believe that using student-created case studies as assessment is a valuable, student-led extension of effective case study pedagogy, and has wide applicability to a variety of undergraduate courses.

Potential Virus Involvement in Alzheimer's Disease: Results from a Phase IIa Trial Evaluating Apovir, an Antiviral Drug Combination

Background:

Accumulating data suggest infectious agents are involved in Alzheimer’s disease (AD). The two primary aims of this trial were to assess safety and efficacy of an antiviral drug combination on AD progression.

Objective:

The trial evaluated whether Apovir, a combination of two antiviral agents, pleconaril (active on enteroviruses) and ribavirin (active on several viruses), could slow AD progression.

Methods:

Sixty-nine patients 60–85 years were treated with Apovir or placebo for 9 months and followed until 12 months after end of treatment. Cognitive tests, safety, biomarkers, drug plasma, and cerebrospinal fluid concentrations were assessed.

Results:

The tolerability of Apovir was compromised as demonstrated by the large drop-out rate and increased frequency and severity of adverse events. The primary endpoint, demonstrating a difference in change from baseline to 9 months between groups in ADAS-cog total score, was not met (p = 0.1809). However, there were observations indicating potential effects on both ADAS-cog and CDR-SB but these effects need to be verified. Also, there was a decrease in cerebrospinal fluid amyloid-β in Apovir at 9 months (p = 0.0330) but no change in placebo.

Conclusion:

This was the first randomized, placebo controlled clinical trial exploring antiviral treatment on AD progression. The trial is considered inconclusive due to the large drop-out rate. New trials are needed to verify if the indications of effect observed can be confirmed and which component(s) in Apovir contributed to such effects. Pleconaril alone may be studied to improve the tolerability and to verify if enterovirus is involved in the disease process.

An Update on Antiviral Therapy Against SARS-CoV-2: How Far Have We Come?

COVID-19 pandemic has spread worldwide at an exponential rate affecting millions of people instantaneously. Currently, various drugs are under investigation to treat an enormously increasing number of COVID-19 patients. This dreadful situation clearly demands an efficient strategy to quickly identify drugs for the successful treatment of COVID-19. Hence, drug repurposing is an effective approach for the rapid discovery of frontline arsenals to fight against COVID-19. Successful application of this approach has resulted in the repurposing of some clinically approved drugs as potential anti-SARS-CoV-2 candidates. Several of these drugs are either antimalarials, antivirals, antibiotics or corticosteroids and they have been repurposed based on their potential to negate virus or reduce lung inflammation. Large numbers of clinical trials have been registered to evaluate the effectiveness and clinical safety of these drugs. Till date, a few clinical studies are complete and the results are primary. WHO also conducted an international, multi-country, open-label, randomized trials-a solidarity trial for four antiviral drugs. However, solidarity trials have few limitations like no placebos were used, additionally any drug may show effectiveness for a particular population in a region which may get neglected in solidarity trial analysis. The ongoing randomized clinical trials can provide reliable long-term follow-up results that will establish both clinical safety and clinical efficacy of these drugs with respect to different regions, populations and may aid up to worldwide COVID-19 treatment research. This review presents a comprehensive update on majorly repurposed drugs namely chloroquine, hydroxychloroquine, remdesivir, lopinavir-ritonavir, favipiravir, ribavirin, azithromycin, umifenovir, oseltamivir as well as convalescent plasma therapy used against SARS-CoV-2. The review also summarizes the data recorded on the mechanism of anti-SARS-CoV-2 activity of these repurposed drugs along with the preclinical and clinical findings, therapeutic regimens, pharmacokinetics, and drug-drug interactions.

Ginsenoside Rb1 is an immune-stimulatory agent with antiviral activity against enterovirus 71

ETHNOPHARMACOLOGICAL RELEVANCE

According to the theory of traditional Chinese medicine, the main pathogenesis of severe hand, foot and mouth disease (HFMD) is that the heat and wet poisons are deeply trapped in the viscera, which causes the deficiency of Qi and Yin in the patient's body. Ginsenoside Rb1 (Rb1) is the most abundant triterpenoid saponin in Panax quinquefolius L., which has the function of Qi-invigorating and Yin-nourishing. Enterovirus 71 (EV71) is one of the causative pathogens of HFMD, especially the form associated with some lethal complications. Therefore, the therapeutic effect of Rb1 on this disease caused by EV71 infection is worth exploring.

AIM OF THE STUDY

We explored the effective antiviral activities of Rb1 against EV71 in vitro and in vivo and investigated its preliminary antiviral mechanisms.

MATERIAL AND METHODS

EV71-infected two-day-old suckling mice model was employed to detect the antiviral effects of Rb1 in vivo. To detect the antiviral effects of Rb1 in vitro, cytopathic effect (CPE) reduction assay was performed in EV71-infected Rhabdomyosarcoma (RD) cells. Interferon (IFN)-β interference experiment was employed to detect the antiviral mechanism of Rb1.

RESULTS

In this paper, we first found that Rb1 exhibited strong antiviral activities in EV71-infected suckling mice when compared to those of ribavirin. Administration of Rb1 reduced the CPE of EV71-infected RD cells in a dose-dependent manner. Moreover, EV71-induced viral protein-1 (VP-1) expression was significantly reduced by Rb1 administration in vitro and in vivo. Furthermore, Rb1 treatment could induce high cellular and humoral immune responses in vivo. Meanwhile, Rb1 contributed to the enhanced Type I IFN responses and IFN-β knockdown reversed the antiviral activity of Rb1 in vitro.

CONCLUSION

In summary, our findings suggest that Rb1 is an immune-stimulatory agent and provide an insight into therapeutic potentials of Rb1 for the treatment of EV71 infection.

Ribavirin inhibits Chandipura virus replication in Vero cells

Chandipura virus (CHPV) is an emerging tropical pathogen in India. The virus has been reported to be associated with an acute encephalitis syndrome in young children with a case fatality rate of 55% to 75%. Clinical management with symptomatic treatment is the only option available to treat infected patients. No vaccines are available for prophylaxis. In light of the prophylactic limitations, antiviral therapy would play an important role in control of CHPV infection. In the present study, ribavirin (RBV), an antiviral drug widely accepted for human use and having an antiviral effect on many RNA and DNA viruses, was tested against the CHPV. A screening assay that scores for the virus-mediated plaque formation in the cultured Vero cells was used. RBV exhibited 50% inhibitory concentration (IC50 ) at 89.84 ± 1.8 µM. The drug was very effective when the cells were treated either within an hour postinfection or 4 to 6 hours before infection. The plaque morphology was different in RBV treated cells; the plaques were smaller in size as compared with the plaques in the virus infected cells. The study reports the antiviral activity of RBV against CHPV, and hence, suggests the possible utility of RBV in CHPV infected patients to mitigate the disease. A further clinical trial is needed before introducing the drug for human use against CHPV infection.

Structure activity relationship of novel antiviral nucleosides against Enterovirus A71

Various (North)-methanocarba adenosine derivatives, containing rigid bicyclo[3.1.0]hexane ribose substitution, were screened for activity against representative viruses, and inhibition was observed after treatment of Enterovirus A71 with a 2-chloro-N6-1-cyclopropyl-2-methylpropan-1-yl derivative (17). µM activity was also seen when testing 17 against other enteroviruses in the Picornaviridae family. Based on this hit, structural congeners of 17, containing other N6-alkyl groups and 5' modifications, were synthesized and tested. The structure activity relationship is relatively narrow, with most modifications of the adenine or the methanocarba ring reducing or abolishing the inhibitory potency. 4'-Truncated 31 (MRS5474), 4'-fluoromethyl 48 (MRS7704) and 4'-chloromethyl 49 nucleosides displayed EC50 ~3-4 µM, and 31 and 48 achieved SI ≥10. However, methanocarba analogues of ribavirin and N6-benzyladenosine, shown previously to have anti-EV-A71 activity, were inactive. Thus, we identified methanocarba nucleosides as a new scaffold for enterovirus inhibition with a narrow structure activity relationship and no similarity to previously published anti-enteroviral nucleosides.

Human Antibodies to VP4 Inhibit Replication of Enteroviruses Across Subgenotypes and Serotypes, and Enhance Host Innate Immunity

Hand, foot, and mouth disease (HFMD) is a highly contagious disease that usually affects infants and young children (<5 years). HFMD outbreaks occur frequently in the Asia-Pacific region, and these outbreaks are associated with enormous healthcare and socioeconomic burden. There is currently no specific antiviral agent to treat HFMD and/or the severe complications that are frequently associated with the enterovirus of serotype EV71. Therefore, the development of a broadly effective and safe anti-enterovirus agent is an existential necessity. In this study, human single-chain antibodies (HuscFvs) specific to the EV71-internal capsid protein (VP4) were generated using phage display technology. VP4 specific-HuscFvs were linked to cell penetrating peptides to make them cell penetrable HuscFvs (transbodies), and readily accessible to the intracellular target. The transbodies, as well as the original HuscFvs that were tested, entered the enterovirus-infected cells, bound to intracellular VP4, and inhibited replication of EV71 across subgenotypes A, B, and C, and coxsackieviruses CVA16 and CVA6. The antibodies also enhanced the antiviral response of the virus-infected cells. Computerized simulation, indirect and competitive ELISAs, and experiments on cells infected with EV71 particles to which the VP4 and VP1-N-terminus were surface-exposed (i.e., A-particles that don’t require receptor binding for infection) indicated that the VP4 specific-antibodies inhibit virus replication by interfering with the VP4-N-terminus, which is important for membrane pore formation and virus genome release leading to less production of virus proteins, less infectious virions, and restoration of host innate immunity. The antibodies may inhibit polyprotein/intermediate protein processing and cause sterically strained configurations of the capsid pentamers, which impairs virus morphogenesis. These antibodies should be further investigated for application as a safe and broadly effective HFMD therapy.

Prunin suppresses viral IRES activity and is a potential candidate for treating enterovirus A71 infection

Human enterovirus A71 (HEVA71) causes hand, foot, and mouth disease (HFMD) in young children and is considered a major neurotropic pathogen but lacks effective antivirals. To identify potential therapeutic agents against HFMD, we screened a 502-compound flavonoid library for compounds targeting the HEVA71 internal ribosome entry site (IRES) that facilitates translation of the HEVA71 genome and is vital for the production of HEVA71 viral particles. We validated hits using cell viability and viral plaque assays and found that prunin was the most potent inhibitor of HEVA71. Downstream assays affirmed that prunin disrupted viral protein and RNA synthesis and acted as a narrow-spectrum antiviral against enteroviruses A and B, but not enterovirus C, rhinovirus A, herpes simplex 1, or chikungunya virus. Continuous HEVA71 passaging with prunin yielded HEVA71-resistant mutants with five mutations that mapped to the viral IRES. Knockdown studies showed that the mutations allowed HEVA71 to overcome treatment-induced suppression by differentially regulating recruitment of the IRES trans-acting factors Sam68 and hnRNPK without affecting the hnRNPA1-IRES interaction required for IRES translation. Furthermore, prunin effectively reduced HEVA71-associated clinical symptoms and mortality in HEVA71-infected BALB/c mice and suppressed hepatitis C virus at higher concentrations, suggesting a similar mechanism of prunin-mediated IRES inhibition for both viruses. These studies establish prunin as a candidate for further development as a HEVA71 therapeutic agent.

Immunization with a fusion protein vaccine candidate generated from truncated peptides of human enterovirus 71 protects mice from lethal enterovirus 71 infections

Background

Prophylactic vaccines are critical in preventing hand, foot, and mouth disease (HFMD) primarily caused by human enterovirus 71 (EV71) infection. Children aged less than 5 years are especially susceptible to EV71 infections. In addition to the development of vaccines containing the inactivated virus, those containing virus-like particles (VLPs) with repeated antigens also constitute an effective preventive strategy for EV71 infections, with safety and productivity advantages. We previously developed a fusion protein composed with truncated peptides of the EV71 capsid protein, which assembled into spherical particles. This study aimed to assess the immunoprotective effects of this fusion protein as a vaccine candidate in a mouse model of EV71 infection.

Methods

To evaluate the protective effect of fusion protein vaccine candidate, neonatal mice born by immunized female mice, as well as normal neonatal mice immunized twice were infected with EV71 virus. Whereafter, the survival rates, clinical scores and viral loads were measured.

Results

The high dosage and booster immunization helped induce specific serum antibodies with high neutralization titers, which were transferred to neonatal mice, thereby facilitating effective resistance towards EV71 infection. An active immune response was also observed in neonatal mice which generated following immunization.

Conclusions

The present results suggest that this fusion protein is a suitable vaccine candidate in treating EV71 infections.

The Pyrimidine Analog FNC Potently Inhibits the Replication of Multiple Enteroviruses

Human enteroviruses (EVs), including coxsackieviruses, the numbered enteroviruses, and echoviruses, cause a wide range of diseases, such as hand, foot, and mouth disease (HFMD), encephalitis, myocarditis, acute flaccid myelitis (AFM), pneumonia, and bronchiolitis. Therefore, broad-spectrum anti-EV drugs are urgently needed to treat EV infection. Here, we demonstrate that FNC (2'-deoxy-2'-β-fluoro-4'-azidocytidine), a small nucleoside analog inhibitor that has been demonstrated to be a potent inhibitor of HIV and entered into a clinical phase II trial in China, potently inhibits the viral replication of a multitude of EVs, including enterovirus 71 (EV71), coxsackievirus A16 (CA16), CA6, EVD68, and coxsackievirus B3 (CVB3), at the nanomolar level. The antiviral mechanism of FNC involves mainly positive- and negative-strand RNA synthesis inhibition by targeting and competitively inhibiting the activity of EV71 viral RNA-dependent RNA polymerase (3D^pol), as demonstrated through quantitative real-time reverse transcription-PCR (RT-qPCR), in vitro 3D^pol activity, and isothermal titration calorimetry (ITC) experiments. We further demonstrated that FNC treatment every 2 days with 1 mg/kg of body weight in EV71 and CA16 infection neonatal mouse models successfully protected mice from lethal challenge with EV71 and CA16 viruses and reduced the viral load in various tissues. These findings provide important information for the clinical development of FNC as a broad-spectrum inhibitor of human EV pathogens.IMPORTANCE Human enterovirus (EV) pathogens cause various contagious diseases such as hand, foot, and mouth disease, encephalitis, myocarditis, acute flaccid myelitis, pneumonia, and bronchiolitis, which have become serious health threats. However, except for the EV71 vaccine on the market, there are no effective strategies to prevent and treat other EV pathogen infections. Therefore, broad-spectrum anti-EV drugs are urgently needed. In this study, we demonstrated that FNC, a small nucleoside analog inhibitor that has been demonstrated to be a potent inhibitor of HIV and entered into a clinical phase II trial in China, potently inhibits the viral replication of a multitude of EVs at the nanomolar level. Further investigation revealed that FNC inhibits positive- and negative-strand RNA synthesis of EVs by interacting and interfering with the activity of EV71 viral RNA-dependent RNA polymerase (3D^pol). Our findings demonstrate for the first time that FNC is an effective broad-spectrum inhibitor for human EV pathogens.

Construction of eGFP-Tagged Senecavirus A for Facilitating Virus Neutralization Test and Antiviral Assay

Senecavirus A (SVA), also known as Seneca Valley virus, is an emerging virus that causes vesicular disease in pigs. This virus belongs to the genus Senecavirus in the family Picornaviridae. The SVA CH-LX-01-2016 was isolated from Guangdong Province of China in 2016. In this study, a recombinant SVA CH-LX-01-2016 was constructed using reverse genetics, and proven to be able to express efficiently an enhanced green fluorescent protein (eGFP) in vitro. This eGFP-tagged recombinant SVA (rSVA-eGFP) exhibited a high capacity for viral replication. Its fluorescence-tracked characteristics greatly facilitated both virus neutralization test (VNT) and antiviral assay. The rSVA-eGFP-based VNT was used to detect eight porcine serum samples, out of which four were determined to be neutralization titer-positive. Subsequently, two antiviral drugs, ribavirin and apigenin, were assayed for evaluating both effects against the rSVA-eGFP in vitro. The result showed that only the ribavirin exhibited an anti-SVA activity.

A neonatal murine model of coxsackievirus A4 infection for evaluation of vaccines and antiviral drugs

Coxsackievirus A4 (CVA4) infection can cause hand, foot and mouth disease (HFMD), an epidemic illness affecting neonatal and paediatric cohorts, which can develop to severe neurological disease with high mortality. In this study, we established the first ICR mouse model of CVA4 infection for the evaluation of inactivated vaccines and antiviral drug screening. The CVA4 YT226R strain was selected to infect the neonatal mice and three infectious factors were optimized to establish the infection model. The 3-day-old neonatal mice exhibited clinical symptoms such as hind limb paralysis and death. The severe inflammatory reactions were closely related to the abnormal expression of the acute phase response proinflammatory cytokine IL-6 and an imbalance in the IFN-γ/IL-4 ratio. Importantly, the inactivated CVA4 whole-virus vaccine induced humoral immune responses in adult females and the maternal antibodies afforded mice complete protection against lethal dose challenges of homologous or heterologous CVA4 strains. Both IFN-α2a and antiserum inhibited the replication of CVA4 and increased the survival rates of neonatal mice during the early stages of infection. This neonatal murine model of CVA4 infection will be useful for the development of prophylactic and therapeutic vaccines and for screening of antiviral drugs targeting CVA4 to decrease morbidity and mortality.

Enterovirus-Associated Hand-Foot and Mouth Disease and Neurological Complications in Japan and the Rest of the World

Enteroviruses (EVs) are responsible for extremely large-scale, periodic epidemics in pediatric cohorts, particularly in East and Southeast Asia. Clinical presentation includes a diverse disease spectrum, including hand-foot and mouth disease (HFMD), aseptic meningitis, encephalitis, acute flaccid paralysis, and acute flaccid myelitis. HFMD is predominantly attributable to EV-A types, including the major pathogen EV-A71, and coxsackieviruses, particularly CV-A6, CV-A16, and CV-A10. There have been multiple EV-A71 outbreaks associated with a profound burden of neurological disease and fatal outcomes in Asia since the early 1980s. Efficacious vaccines against EV-A71 have been developed in China but widespread pediatric vaccination programs have not been introduced in other countries. Encephalitis, as a consequence of complications arising from HFMD infection, leads to damage to the thalamus and medulla oblongata. Studies in Vietnam suggest that myoclonus is a significant indicator of central nervous system (CNS) complications in EV-A71-associated HFMD cases. Rapid response in HFMD cases in children is imperative to prevent the progression to a CNS infection; however, prophylactic and therapeutic agents have not been well established internationally, therefore surveillance and functional studies including development of antivirals and multivalent vaccines is critically important to reduce disease burden in pediatric populations.

High Amplification of the Antiviral Activity of Curcumin through Transformation into Carbon Quantum Dots

It is demonstrated that carbon quantum dots derived from curcumin (Cur-CQDs) through one-step dry heating are effective antiviral agents against enterovirus 71 (EV71). The surface properties of Cur-CQDs, as well as their antiviral activity, are highly dependent on the heating temperature during synthesis. The one-step heating of curcumin at 180 °C preserves many of the moieties of polymeric curcumin on the surfaces of the as-synthesized Cur-CQDs, resulting in superior antiviral characteristics. It is proposed that curcumin undergoes a series of structural changes through dehydration, polymerization, and carbonization to form core-shell CQDs whose surfaces remain a pyrolytic curcumin-like polymer, boosting the antiviral activity. The results reveal that curcumin possesses insignificant inhibitory activity against EV71 infection in RD cells [half-maximal effective concentration (EC₅₀ ) >200 µg mL^-1 ] but exhibits high cytotoxicity toward RD cells (half-maximal cytotoxic concentration (CC₅₀ ) <13 µg mL^-1 ). The EC₅₀ (0.2 µg mL^-1 ) and CC₅₀ (452.2 µg mL^-1 ) of Cur-CQDs are >1000-fold lower and >34-fold higher, respectively, than those of curcumin, demonstrating their far superior antiviral capabilities and high biocompatibility. In vivo, intraperitoneal administration of Cur-CQDs significantly decreases mortality and provides protection against virus-induced hind-limb paralysis in new-born mice challenged with a lethal dose of EV71.

Antivirals and vaccines for Enterovirus A71

Enterovirus A71 (EV-A71) is an important emerging virus posing a threat to children under five years old. EV-A71 infection in infants or young children can cause hand-foot-and-mouth disease, herpangina, or severe neurological complications. However, there are still no effective antivirals for treatment of these infections. In this review, we summarize the antiviral compounds developed to date based on various targets of the EV-A71 life cycle. Moreover, development of a vaccine would be the most effective approach to prevent EV-A71 infection. Therefore, we also summarize the development and clinical progress of various candidate EV-A71 vaccines, including inactivated whole virus, recombinant VP1 protein, synthetic peptides, viral-like particles, and live attenuated vaccines.

Recent advances on the role of host factors during non-poliovirus enteroviral infections

Non-polio enteroviruses are emerging viruses known to cause outbreaks of polio-like infections in different parts of the world with several cases already reported in Asia Pacific, Europe and in United States of America. These outbreaks normally result in overstretching of health facilities as well as death in children under the age of five. Most of these infections are usually self-limiting except for the neurological complications associated with human enterovirus A 71 (EV-A71). The infection dynamics of these viruses have not been fully understood, with most inferences made from previous studies conducted with poliovirus.Non-poliovirus enteroviral infections are responsible for major outbreaks of hand, foot and mouth disease (HFMD) often associated with neurological complications and severe respiratory diseases. The myriad of disease presentations observed so far in children calls for an urgent need to fully elucidate the replication processes of these viruses. There are concerted efforts from different research groups to fully map out the role of human host factors in the replication cycle of these viral infections. Understanding the interaction between viral proteins and human host factors will unravel important insights on the lifecycle of this groups of viruses.This review provides the latest update on the interplay between human host factors/processes and non-polio enteroviruses (NPEV). We focus on the interactions involved in viral attachment, entry, internalization, uncoating, replication, virion assembly and eventual egress of the NPEV from the infected cells. We emphasize on the virus- human host interplay and highlight existing knowledge gaps that needs further studies. Understanding the NPEV-human host factors interactions will be key in the design and development of vaccines as well as antivirals against enteroviral infections. Dissecting the role of human host factors during NPEV infection cycle will provide a clear picture of how NPEVs usurp the human cellular processes to establish an efficient infection. This will be a boost to the drug and vaccine development against enteroviruses which will be key in control and eventual elimination of the viral infections.

Antiviral activity of sophoridine against enterovirus 71 in vitro

ETHNOPHARMACOLOGICAL RELEVANCE

Enterovirus 71 (EV71) has a propensity to cause hand-foot-and-mouth disease (HFMD) epidemics associated with neurological sequelae. Unfortunately, no drugs are currently available for the clinical treatment of EV71 infections. Sophoridine (SRI) is one of the most abundant alkaloids in Sophora flavescens Aiton (Leguminosae), which has been used to treat fever, throat inflammation, cancer, and other diseases.

MATERIALS AND METHODS

In this study, we found that SRI inhibits EV71 infection in Vero cells. To study the antiviral activity of SRI, Vero cells were divided into 3 treatment groups based on the timing of SRI dosing: prior to viral adsorption (Group A), during viral adsorption (Group B), and after viral adsorption (Group C). We further revealed the antiviral activity of SRI with the attachment assay and the penetration assay. For Group A, 50% viability of Vero cells was observed at a SRI concentration of 61.39 μg/mL, whereas for Groups B, 50% viability was observed at SRI concentrations of 196.86 μg/mL. Furthermore, 29.7% cell viability was observed even at a SRI concentration of 1000 μg/mL in Groups C. The results show that SRI was highly effective against EV71 when Vero cells were pretreated with SRI for 2 h (Group A). Further researches indicate SRI was highly effective at inhibiting EV71 attachment when the SRI concentrations over 250 μg/mL (P < 0.001).

CONCLUSIONS

We have shown that Vero cell viability increases when SRI is administered prior to viral adsorption. This suggests that SRI has the considerable potential as an antiviral for EV71 disease prevention.

Monoclonal antibody against EV71 3Dpol inhibits the polymerase activity of RdRp and virus replication

BACKGROUND

Enterovirus A 71 (EV71) is a neurotropic virus that may lead to acute flaccid paralysis, encephalitis, cardiopulmonary failure or even death. No vaccine and defensive drug controlling EV71 is currently available, novel and efficient antiviral drug or vaccine is therefore urgently needed. 3D^pol (RNA-dependent RNA polymerase (RdRp)) has been an important target for anti-EV71 drug development.

METHODS

A panel of monoclonal IgG antibodies (mAbs) against EV71 3D^pol were generated by traditional cell fusion methods. And the antibody affinity and specificity to EV71 3D^pol were evaluated by Enzyme-linked Immunosorbent Assay (ELISA), Indirect Fluorescent Assay (IFA) and Western blotting. Antiviral activities of these antibodies were also determined in vitro and in vivo.

RESULTS

Two mAbs towards EV71 3D^pol were able to effectively suppress EV71 replication in Vero-1008 cell when intracellarly delivered. And they also dampened the RNA polymerase activity of 3D^pol in vitro. More importantly, these mAbs provided partial protection in EV71-challenged neonatal murine challenge model.

CONCLUSIONS

These results showed that two of mAbs against EV71 3D^pol inhibited EV71 replication and could be utilized as promising therapeutic drug candidate.

Spiramycin and azithromycin, safe for administration to children, exert antiviral activity against enterovirus A71 in vitro and in vivo

Hand-foot-mouth disease (HFMD) is a common viral disease in young children, mainly caused by enterovirus A71 (EV-A71) and coxsackievirus A16 (CV-A16). Specific antiviral agents are not commercially available yet. Here we report that the macrolide antibiotics spiramycin (SPM) and azithromycin (AZM) possess antiviral activities against EV-A71 and CV-A16. SPM significantly reduced EV-A71 RNA and protein levels, most likely through interfering with viral RNA replication. The SPM-resistant EV-A71 variants showed similar resistance to AZM, indicating a similar anti-EV-A71 mechanism by which these two drugs exert their functions. The mutations of these variants were reproducibly mapped to VP1 and 2A, which were confirmed to confer resistance to SPM. Animal experiments showed that AZM possesses stronger anti-infection efficacy than SPM, greatly alleviated the disease symptoms and increased the survival rate in a mouse model severely infected with EV-A71. In all, our work suggests that AZM is a potential treatment option for EV-A71-induced HFMD, whose proved safety for infants and children makes it even more promising.

Immunocompetent and Immunodeficient Mouse Models for Enterovirus 71 Pathogenesis and Therapy

Enterovirus 71 (EV71) is a global health threat. Children infected with EV71 could develop hand-foot-and-mouth disease (HFMD), encephalitis, paralysis, pulmonary edema, and death. At present, no effective treatment for EV71 is available. We reviewed here various mouse models for EV71 pathogenesis and therapy. Earlier studies relied on the use of mouse-adapted EV71 strains. To avoid artificial mutations arising de novo during the serial passages, recent studies used EV71 clinical isolates without adaptation. Several human receptors for EV71 were shown to facilitate viral entry in cell culture. However, in vivo infection with human SCARB2 receptor transgenic mice appeared to be more limited to certain strains and genotypes of EV71. Efficacy of oral infection in these transgenic models is extremely low. Intriguingly, despite the lack of human receptors, immunodeficient neonatal mouse models can still be infected with EV71 clinical isolates via oral or intraperitoneal routes. Crossbreeding between SCARB2 transgenic and stat1 knockout mice generated a more sensitive and user-friendly hybrid mouse model. Infected hybrid mice developed a higher incidence and earlier onset of CNS disease and death. Different pathogenesis profiles were observed in models deficient in various arms of innate or humoral immunity. These models are being actively used for antiviral research.

Flt3 ligand treatment reduces enterovirus A71 lethality in mice with enhanced B cell responses

Enterovirus A71 (EV-A71) infection can induce encephalitis, which causes death or long-term neurological sequelae, especially in young children. Using a murine infection model, we searched for anti-EV-A71 agents, because effective therapies are not available to control fatal infection. In EV-A71-infected mice, treatment with the hematopoietic growth factor, Fms-like tyrosine-kinase 3 ligand (Flt3 ligand) before infection reduced the lethality and tissue viral loads. Flt3 ligand failed to enhance the production of type I interferons. Instead, Flt3 ligand boosted the numbers of dendritic cells and, particularly lymphocytes in infected organs with an expansion of spleen B cells, and resulted in an increased titer of virus-specific antibody with neutralizing activity in the serum. The protective effect of Flt3 ligand was abolished in B cell-deficient mice. Our findings revealed that Flt3 ligand administration promotes resistance to EV-A71 infection with enhanced B cell response in a mechanism rarely reported before.

Inhibition of enterovirus 71 replication and viral 3C protease by quercetin

BACKGROUND

Enterovirus 71 (EV71) is one of the major causative agents of hand, foot, and mouth disease (HFMD), which is sometimes associated with severe central nervous system disease in children. There is currently no specific medication for EV71 infection. Quercetin, one of the most widely distributed flavonoids in plants, has been demonstrated to inhibit various viral infections. However, investigation of the anti-EV71 mechanism has not been reported to date.

METHODS

The anti-EV71 activity of quercetin was evaluated by phenotype screening, determining the cytopathic effect (CPE) and EV71-induced cells apoptosis. The effects on EV71 replication were evaluated further by determining virus yield, viral RNA synthesis and protein expression, respectively. The mechanism of action against EV71 was determined from the effective stage and time-of-addition assays. The possible inhibitory functions of quercetin via viral 2Apro, 3Cpro or 3Dpol were tested. The interaction between EV71 3Cpro and quercetin was predicted and calculated by molecular docking.

RESULTS

Quercetin inhibited EV71-mediated cytopathogenic effects, reduced EV71 progeny yields, and prevented EV71-induced apoptosis with low cytotoxicity. Investigation of the underlying mechanism of action revealed that quercetin exhibited a preventive effect against EV71 infection and inhibited viral adsorption. Moreover, quercetin mediated its powerful therapeutic effects primarily by blocking the early post-attachment stage of viral infection. Further experiments demonstrated that quercetin potently inhibited the activity of the EV71 protease, 3Cpro, blocking viral replication, but not the activity of the protease, 2Apro, or the RNA polymerase, 3Dpol. Modeling of the molecular binding of the 3Cpro-quercetin complex revealed that quercetin was predicted to insert into the substrate-binding pocket of EV71 3Cpro, blocking substrate recognition and thereby inhibiting EV71 3Cpro activity.

CONCLUSIONS

Quercetin can effectively prevent EV71-induced cell injury with low toxicity to host cells. Quercetin may act in more than one way to deter viral infection, exhibiting some preventive and a powerful therapeutic effect against EV71. Further, quercetin potently inhibits EV71 3Cpro activity, thereby blocking EV71 replication.

Acute Flaccid Paralysis and Enteroviral Infections

PURPOSE OF REVIEW

The focus of this review is on enterovirus (EV)-associated acute flaccid paralysis (AFP) due to spinal cord anterior horn cell disease. Emphasis is placed on the epidemiology, pathogenesis, diagnosis, treatment, and outcome of AFP caused by polioviruses, vaccine-derived polioviruses, EV-D68, and EV-A71.

RECENT FINDINGS

Since the launch of The Global Polio Eradication Initiative in 1988, the worldwide incidence of polio has been reduced by 99.9%, with small numbers of poliomyelitis cases being reported only in Afghanistan, Pakistan, and Nigeria. With the planned phaseout of oral polio vaccine, vaccine-associated poliomyelitis is also expected to be eliminated. In their place, other EVs, chiefly EV-D68 and EV-A71, have emerged as the principal causes of AFP. There is evidence that the emergence of EV-D68 as a cause of severe respiratory disease and AFP was due to recent genetic virus evolution. Antiviral medications targeting EV-D68, EV-A71, and other EVs will likely be available in the near future. An effective EV-A71 vaccine has been developed, and preliminary investigations suggest an EV-D68 vaccine could be on the horizon. The eradication of poliomyelitis and vaccine-associated poliomyelitis is near, after which other EVs, presently EV-D68 and EV-A71, will be the principle viral causes of AFP. Moving forward, it is essential that EV outbreaks, in particular those associated with neurologic complications, be investigated carefully and the causal strains identified, so that treatment and prevention efforts can be rapidly developed and implemented.

Suppression of interleukin-6 increases enterovirus A71 lethality in mice

Background

Enterovirus A71 (EV-A71) infection can induce fatal encephalitis in young children. Clinical reports show that interleukin-6 (IL-6) levels in the serum and cerebrospinal fluid of infected patients with brainstem encephalitis are significantly elevated. We used a murine model to address the significance of endogenous IL-6 in EV-A71 infection.

Results

EV-A71 infection transiently increased serum and brain IL-6 protein levels in mice. Most importantly, absence of IL-6 due to gene knockout or depletion of IL-6 using neutralizing monoclonal antibody enhanced the mortality and tissue viral load of infected mice. Absence of IL-6 increased the damage in the central nervous system and decreased the lymphocyte and virus-specific antibody responses of infected mice.

Conclusions

Endogenous IL-6 functions to clear virus and protect the host from EV-A71 infection. Our study raises caution over the use of anti-IL-6 antibody or pentoxifylline to reduce IL-6 for patient treatment.

Electronic supplementary material

The online version of this article (10.1186/s12929-017-0401-5) contains supplementary material, which is available to authorized users.

Immunopathogenesis and Virus-Host Interactions of Enterovirus 71 in Patients with Hand, Foot and Mouth Disease

Enterovirus 71 (EV71) is a global infectious disease that affects millions of people. The virus is the main etiological agent for hand, foot, and mouth disease with outbreaks and epidemics being reported globally. Infection can cause severe neurological, cardiac, and respiratory problems in children under the age of 5. Despite on-going efforts, little is known about the pathogenesis of EV71, how the host immune system responds to the virus and the molecular mechanisms behind these responses. Moreover, current animal models remain limited, because they do not recapitulate similar disease patterns and symptoms observed in humans. In this review the role of the host-viral interactions of EV71 are discussed together with the various models available to examine: how EV71 utilizes its proteins to cleave host factors and proteins, aiding virus replication; how EV71 uses its own viral proteins to disrupt host immune responses and aid in its immune evasion. These discoveries along with others, such as the EV71 crystal structure, have provided possible targets for treatment and drug interventions.

Isochlorogenic acid C prevents enterovirus 71 infection via modulating redox homeostasis of glutathione

Enterovirus 71 (EV71) is a key pathogen of hand, foot and mouth disease (HFMD) in children under 6 years of age. The antiviral potency of antioxidant isochlorogenic acid C (ICAC) extracted from foods was evaluated in cellular and animal models. First, the cytotoxicity of ICAC on Vero cells was investigated. The viral plaques, cytopathic effects and yield induced by EV71 infection were obviously reduced by ICAC, which was consistent with the investigation of VP1 transcripts and protein expression. Moreover, the mortality, weight loss and limb paralysis of mice caused by EV71 challenge were remarkably relieved by ICAC injection, which was achieved through decreases in the viral load and cytokine secretion in the mouse brain. Further biochemical assays showed that ICAC modulated several antioxidant enzymes involved in reduced and oxidized glutathione (GSH and GSSG) homeostasis, including glutathione reductase (GR), glutathione peroxidase (GPX), and glucose-6-phosphate dehydrogenase (G6PD), resulting in restoration of the GSH/GSSG ratio and reactive oxygen species (ROS) level. Finally, the antiviral effects of ICAC were dose-dependently disrupted by BSO, a biosynthesis inhibitor of GSH. This study indicated that ICAC acted as an antioxidant and prevented EV71 infection by modulating the redox homeostasis of glutathione.

Antiviral effects of Retro-2cycl and Retro-2.1 against Enterovirus 71 in vitro and in vivo

Enterovirus 71 (EV71) is one of the causative pathogens of hand, foot and mouth disease (HFMD), especially the form associated with fatal neurological disorders. Sustained outbreaks of EV71 infections remain a serious health threat worldwide. However, no antiviral agent against EV71 for clinical therapy has been approved. Retro-2^cycl and Retro-2.1 are inhibitors of several pathogens specifically targeting the intracellular vesicle transport, which also participates in the EV71 lifecycle processes including progeny virus release. Here, we reported that Retro-2^cycl and Retro-2.1, respectively, could inhibit EV71 infection with 50% effective concentrations of 12.56 μM and 0.05 μM in a cytopathic effect inhibition assay and showed relatively low cytotoxicity with 50% cytotoxicity concentrations of more than 500 μM and 267.80 μM. Preliminary mechanism studies revealed that Retro-2^cycl and Retro-2.1 did not inhibit EV71 protein synthesis or RNA replication but could block progeny EV71 release specifically. Furthermore, administration of Retro-2^cycl at the dose of 10 mg/kg significantly protected 90% of newborn mice from lethal EV71 challenge. Consequently, our results for the first time identified Retro-2^cycl and Retro-2.1 as effective inhibitors of EV71 as well as lead compounds, which would contribute to anti-EV71 drug development. We also identified progeny virus release and the intracellular vesicle transport as antiviral targets for EV71.

Management of Viral Central Nervous System Infections: A Primer for Clinicians

Viruses are a common cause of central nervous system (CNS) infections with many host, agent, and environmental factors influencing the expression of viral diseases. Viruses can be responsible for CNS disease through a variety of mechanisms including direct infection and replication within the CNS resulting in encephalitis, infection limited to the meninges, or immune-related processes such as acute disseminated encephalomyelitis. Common pathogens including herpes simplex virus, varicella zoster, and enterovirus are responsible for the greatest number of cases in immunocompetent hosts. Other herpes viruses (eg, cytomegalovirus, John Cunningham virus) are more common in immunocompromised hosts. Arboviruses such as Japanese encephalitis virus and Zika virus are important pathogens globally, but the prevalence varies significantly by geographic region and often season. Early diagnosis from radiographic evidence and molecular (eg, rapid) diagnostics is important for targeted therapy. Antivirals may be used effectively against some pathogens, although several viruses have no effective treatment. This article provides a review of epidemiology, diagnostics, and management of common viral pathogens in CNS disease.

Changes of circulating Th22 cells in children with hand, foot, and mouth disease caused by enterovirus 71 infection

Interleukin (IL)-22+CD4+T (Th22) cells play crucial roles in the pathogenesis of autoimmune diseases and infectious diseases, although the role of Th22 cells remains largely unclear in children with hand, foot, and mouth disease (HFMD) caused by enterovirus 71 (EV71). This study aims to explore the role of circulating IL-22+IL-17A-CD4+T (cTh22) cells in children with EV71-associated HFMD. We found that during the acute stage of illness, the frequencies of cTh22 and circulating IL-22+IL-17A+CD4+T (IL-22+cTh17) cells in CD4+T cells infrom affected patients, and especially in severely affected patients, were significantly higher than in healthy controls (HC). The major source of IL-22 production was cTh22 cells, partially from cTh17 cells. Moreover, the protein and mRNA levels of IL-22, IL-17A, IL-23, IL-6, and TNF-α were significantly different among the mild patients, severe patients and HC, as well as AHR and RORγt mRNA levels. A positive correlation was found between plasma IL-22 levels and cTh22 cell frequencies, and cTh17 cell and IL-22+ cTh17 cell frequencies. Furthermore, the frequencies of cTh22 were significantly decreased in the convalescent patients. Our findings indicated that cTh22 cells could play critical roles in the pathogenesis of EV71 infection, and are potential therapeutic targets for patients with EV71-associated HFMD.

Identifying novel antiviral targets against enterovirus 71: where are we?

Human enterovirus 71 (HEV71) has been considered as an essential human pathogen, which causes hand, foot and mouth disease in young children. Several HEV71 outbreaks have been observed in many Asia-Pacific countries for the past two decades with significant fatalities. However, there are no competent vaccines or antivirals against HEV71 infection to date. Thus, it is of critical priority to delve into the search for anti-HEV71 agents. Prior to this, there is a need to gain knowledge about the distinct targets of HEV71 that are available and that have been exploited for antiviral therapy. This review aims to provide a better understanding of HEV71 virology and feature potential antivirals for progressive clinical development with respect to their elucidated mechanistic actions.

Ribavirin suppresses bacterial virulence by targeting LysR-type transcriptional regulators

Targeting bacterial virulence mechanisms without compromising bacterial growth is a promising strategy to prevent drug resistance. LysR-type transcriptional regulators (LTTRs) possess structural conservation across bacterial species and regulate virulence in numerous pathogens, making them attractive targets for antimicrobial agents. We targeted AphB, a Vibrio cholerae LTTR, which regulates the expression of genes encoding cholera toxin and toxin-co-regulated pilus for inhibitor designing. Since AphB ligand is unknown, we followed a molecular fragment-based approach for ligand designing using FDA-approved drugs and subsequent screen to identify molecules that exhibited high-affinity binding to AphB ligand-binding pocket. Among the identified compounds, ribavirin, an anti-viral drug, antagonized AphB functions. Ribavirin perturbed Vibrio cholerae pathogenesis in animal models. The inhibitory effects of the drug was limited to the bacteria expressing wild type AphB, but not its constitutively active mutant (AphB_N100E), which represents the ligand-bound state, suggesting that ribavirin binds to the active site of AphB to exert its inhibitory role and there exists no AphB-independent mechanism of its action. Similarly, ribavirin suppressed the functions of Salmonella Typhi LTTR Hrg, indicating its broad spectrum efficacy. Moreover, ribavirin did not affect the bacterial viability in culture. This study cites an example of drug repurposing for anti-infective therapy.

Antiviral effects of Reduning injection against Enterovirus 71 and possible mechanisms of action

The present study was designed to evaluate the protective effects of Reduning injection against Enterovirus 71 (EV71) in Vero cells and in mice. The Vero cells were infected with 100 and 50 TCID50 (50% tissue culture infective dose) of EV71, respectively. The inhibition of Reduning injection on cytopathic effect (CPE) was detected. Meanwhile, a mouse model produced by intraperitoneal EV71-infection (10(6) TCID50), was used to investigate the protective effects of Reduning injection. The total survival rate, living time, daily survival rate, weight ratio, and score for symptoms were examined. The viral loads in Vero cells and muscle tissues were detected using real-time PCR. Finally, the content of cytokines was analyzed by ELISA. In the Vero cells, 2.5 mg crude drug·mL(-1) of Reduning injection inhibited CPE induced by EV71 infection. In the mice, 1.3 g crude drug·kg(-1) of Reduning injection rescued death triggered by infection, in comparison with model group. Moreover, the survival rate, weight ratio, and clinical scores were also improved. The viral RNA copies in the Vero cells and the mice muscle tissues were reduced. Besides, the steep EV71-induced accumulations of TNF-α and MCP-1 were decreased by Reduning injection. In conclusion, Reduning injection showed promising protective effects against EV71 in Vero cells and in mice.

Antiviral activity of Paulownia tomentosa against enterovirus 71 of hand, foot, and mouth disease

The bark, leaves, and flowers of Paulownia trees have been used in traditional Chinese medicine to treat infectious and inflammatory diseases. We investigated the antiviral effects of Paulownia tomentosa flowers, an herbal medicine used in some provinces of P. R. China for the treatment of skin rashes and blisters. Dried flowers of P. tomentosa were extracted with methanol and tested for antiviral activity against enterovirus 71 (EV71) and coxsackievirus A16 (CAV16), the predominant etiologic agents of hand, foot, and mouth disease in P. R. China. The extract inhibited EV71 infection, although no effect was detected against CAV16 infection. Bioactivity-guided fractionation was performed to identify apigenin as an active component of the flowers. The EC50 value for apigenin to block EV71 infection was 11.0 µM, with a selectivity index of approximately 9.3. Although it is a common dietary flavonoid, only apigenin, and not similar compounds like naringenin and quercetin, were active against EV71 infection. As an RNA virus, the genome of EV71 has an internal ribosome entry site that interacts with heterogeneous nuclear ribonucleoproteins (hnRNPs) and regulates viral translation. Cross-linking followed by immunoprecipitation and reverse transcription-polymerase chain reaction (RT-PCR) analysis showed that EV71 RNA was associated with hnRNPs A1 and A2. Apigenin treatment disrupted this association, indicating that apigenin suppressed EV71 replication through a novel mechanism by targeting the trans-acting factors. This study therefore validates the effects of Paulownia against EV71 infection. It also yielded mechanistic insights on apigenin as an active compound for the antiviral activity of P. tomentosa against EV71 infection.