An E460D Substitution in the NS5 Protein of Tick-Borne Encephalitis Virus Confers Resistance to the Inhibitor Galidesivir (BCX4430) and Also Attenuates the Virus for Mice

Adjusting susceptibilities of C57BL/6 mice to orthoflaviviruses for evaluation of antiviral drugs by altering the levels of interferon alpha/beta receptor function

The purpose of this study was to optimize the infectivity of four different orthoflaviviruses in mice for evaluating antiviral drugs by using wild-type mice with intact interferon responses, type 1 interferon alpha/beta receptor knockout mice, or by injecting wild type C57BL/6 mice with varying doses of anti-type 1 interferon receptor antibody (MAR1-5A3) to optimize the infectivity and lethality. West Nile virus productively infected wild-type C57BL/6 mice to cause lethality, whereas Usutu virus required a complete absence of type 1 interferon receptor function. Deer tick virus (lineage 2 Powassan virus) and Japanese encephalitis viruses required a dampening of type 1 interferon responses by adjusting the doses of MAR1-5A3 antibody injections. Challenge dose-responsive mortality, weight loss, and viral titers of these two viruses were observed if the type 1 interferon responses were dampened with MAR1-5A3. Conversely, without MAR1-5A3 injections, these disease phenotypes were not viral challenge dose-responsive. From these different interferon-responsive models, the appropriate lethality was identified to determine that 7-deaza-2'-C-methyladenosine has high efficacy for West Nile and Usutu viruses, and low efficacy for deer tick and Japanese encephalitis viruses.

Plausible mechanism of drug resistance and side-effects of COVID-19 therapeutics: a bottleneck for its eradication

BACKGROUND

COVID-19 pandemic has turned our world upside down by meddling with our normal lives. While there is no definitive drug against SARS-CoV-2, antiviral drugs that are already in the market, are being repurposed against it, could now complete long-term as well as all age-specific investigations, and they are successful in saving millions of lives. Nevertheless, side-effects are emergingly seen in the patients undergoing treatment, and ineffectiveness is increasingly found due to the emerging notorious variants of the virus. Many of them are also facing serious co-infections including black fungus, Zika, and H1N1 virus to name a few.

OBJECTIVES

Therefore, this review highlights both drug resistance, their side-effects, and the significance for proper and long-term clinical trials of all age groups including children.

METHODS

We have explored and proposed the mechanisms of drug resistance that may arise due to the misuse or overuse of drugs based on available experimental reports.

RESULTS

The review provides solutions to the aforesaid issues of drug-resistance and side-effects by providing combination therapies, ancillary treatments, and other preventive strategies that can be useful in preventing drawbacks thereby curbing COVID-19 or similar future infections to maintain our normal lives.

CONCLUSION

COVID-19 and its long-term effects, if any, can be eradicated with strategic and mindful use of related therapeutics in a controlled manner.

Tick-Borne Encephalitis (TBE): From Tick to Pathology

Tick-borne encephalitis (TBE) is a viral arthropod infection, endemic to large parts of Europe and Asia, and is characterised by neurological involvement, which can range from mild to severe, and in 33-60% of cases, it leads to a post-encephalitis syndrome and long-term morbidity. While TBE virus, now identified as Orthoflavivirus encephalitidis, was originally isolated in 1937, the pathogenesis of TBE is not fully appreciated with the mode of transmission (blood, tick, alimentary), viral strain, host immune response, and age, likely helping to shape the disease phenotype that we explore in this review. Importantly, the incidence of TBE is increasing, and due to global warming, its epidemiology is evolving, with new foci of transmission reported across Europe and in the UK. As such, a better understanding of the symptomatology, diagnostics, treatment, and prevention of TBE is required to inform healthcare professionals going forward, which this review addresses in detail. To this end, the need for robust national surveillance data and randomised control trial data regarding the use of various antivirals (e.g., Galidesivir and 7-deaza-2'-CMA), monoclonal antibodies, and glucocorticoids is required to improve the management and outcomes of TBE.

A combination of two resistance mechanisms is critical for tick-borne encephalitis virus escape from a broadly neutralizing human antibody

Tick-borne encephalitis virus (TBEV) is a flavivirus that causes human neuroinfections and represents a growing health problem. The human monoclonal antibody T025 targets envelope protein domain III (EDIII) of TBEV and related tick-borne flaviviruses, potently neutralizing TBEV in vitro and in preclinical models, representing a promising candidate for clinical development. We demonstrate that TBEV escape in the presence of T025 or T028 (another EDIII-targeting human monoclonal antibody) results in virus variants of reduced pathogenicity, characterized by distinct sets of amino acid changes in EDII and EDIII that are jointly needed to confer resistance. EDIII substitution K311N impairs formation of a salt bridge critical for T025-epitope interaction. EDII substitution E230K is not on the T025 epitope but likely induces quaternary rearrangements of the virus surface because of repulsion of positively charged residues on the adjacent EDI. A combination of T025 and T028 prevents virus escape and improves neutralization.

Galidesivir Triphosphate Promotes Stalling of Dengue-2 Virus Polymerase Immediately Prior to Incorporation

Millions of people are infected by the dengue and Zika viruses each year, resulting in significant morbidity and mortality. Galidesivir is an adenosine nucleoside analog that can attenuate flavivirus replication in cell-based assays and animal models of infection. Galidesivir is converted to the triphosphorylated form by host kinases and subsequently incorporated into viral RNA by viral RNA polymerases. This has been proposed to lead to the delayed termination of RNA synthesis. Here, we report direct in vitro testing of the effects of Galidesivir triphosphate on dengue-2 and Zika virus polymerase activity. Galidesivir triphosphate was chemically synthesized, and inhibition of RNA synthesis followed using a dinucleotide-primed assay with a homopolymeric poly(U) template. Galidesivir triphosphate was equipotent against dengue-2 and Zika polymerases, with IC50 values of 42 ± 12 μM and 47 ± 5 μM, respectively, at an ATP concentration of 20 μM. RNA primer extension assays show that the dengue-2 polymerase stalls while attempting to add a Galidesivir nucleotide to the nascent RNA chain, evidenced by the accumulation of RNA products truncated immediately upstream of Galidesivir incorporation sites. Nevertheless, Galidesivir is incorporated at isolated sites with low efficiency, leading to the subsequent synthesis of full-length RNA with no evidence of delayed chain termination. The incorporation of Galidesivir at consecutive sites is strongly disfavored, highlighting the potential for modulation of inhibitory effects of nucleoside analogs by the template sequence. Our results suggest that attenuation of dengue replication by Galidesivir may not derive from the early termination of RNA synthesis following Galidesivir incorporation.

Rescue and in vitro characterization of a divergent TBEV-Eu strain from the Netherlands

Tick-borne encephalitis virus (TBEV) may cause tick-borne encephalitis (TBE), a potential life-threatening infection of the central nervous system in humans. Phylogenetically, TBEVs can be subdivided into three main subtypes, which differ in endemic region and pathogenic potential. In 2016, TBEV was first detected in the Netherlands. One of two detected strains, referred to as Salland, belonged to the TBEV-Eu subtype, yet diverged ≥ 2% on amino acid level from other members of this subtype. Here, we report the successful rescue of this strain using infectious subgenomic amplicons and its subsequent in vitro characterization by comparison to two well-characterized TBEV-Eu strains; Neudoerfl and Hypr. In the human alveolar epithelial cell line A549, growth kinetics of Salland were comparable to the high pathogenicity TBEV-Eu strain Hypr, and both strains grew considerably faster than the mildly pathogenic strain Neudoerfl. In the human neuroblastoma cell line SK-N-SH, Salland replicated faster and to higher infectious titers than both reference strains. All three TBEV strains infected primary human monocyte-derived dendritic cells to a similar extent and interacted with the type I interferon system in a similar manner. The current study serves as the first in vitro characterization of the novel, divergent TBEV-Eu strain Salland.

New directions in the experimental therapy of tick-borne encephalitis

Tick-borne encephalitis (TBE) is a potentially fatal disease common in much of Europe and Asia. There is no specific therapy for the treatment of TBE patients. However, several efforts are being made to develop small molecules that specifically interfere with the life cycle of TBE virus. In particular, recently various nucleoside analogues that can inhibit the viral replicase, such as the RNA-dependent RNA polymerase or viral methyltransferases, have been explored. In addition, human or chimeric (i.e., structural chimeras that combine mouse variable domains with human constant domains) monoclonal antibodies with promising potential for post-exposure prophylaxis or early therapy have been developed. This review summarizes the latest directions and experimental approaches that may be used to combat TBE in humans.

Guanine quadruplexes in the RNA genome of the tick-borne encephalitis virus: their role as a new antiviral target and in virus biology

We have identified seven putative guanine quadruplexes (G4) in the RNA genome of tick-borne encephalitis virus (TBEV), a flavivirus causing thousands of human infections and numerous deaths every year. The formation of G4s was confirmed by biophysical methods on synthetic oligonucleotides derived from the predicted TBEV sequences. TBEV-5, located at the NS4b/NS5 boundary and conserved among all known flaviviruses, was tested along with its mutated variants for interactions with a panel of known G4 ligands, for the ability to affect RNA synthesis by the flaviviral RNA-dependent RNA polymerase (RdRp) and for effects on TBEV replication fitness in cells. G4-stabilizing TBEV-5 mutations strongly inhibited RdRp RNA synthesis and exhibited substantially reduced replication fitness, different plaque morphology and increased sensitivity to G4-binding ligands in cell-based systems. In contrast, strongly destabilizing TBEV-5 G4 mutations caused rapid reversion to the wild-type genotype. Our results suggest that there is a threshold of stability for G4 sequences in the TBEV genome, with any deviation resulting in either dramatic changes in viral phenotype or a rapid return to this optimal level of G4 stability. The data indicate that G4s are critical elements for efficient TBEV replication and are suitable targets to tackle TBEV infection.

Evaluation of two artificial infection methods of live ticks as tools for studying interactions between tick-borne viruses and their tick vectors

Up to 170 tick-borne viruses (TBVs) have been identified to date. However, there is a paucity of information regarding TBVs and their interaction with respective vectors, limiting the development of new effective and urgently needed control methods. To overcome this gap of knowledge, it is essential to reproduce transmission cycles under controlled laboratory conditions. In this study we assessed an artificial feeding system (AFS) and an immersion technique (IT) to infect Ixodes ricinus ticks with tick-borne encephalitis (TBE) and Kemerovo (KEM) virus, both known to be transmitted predominantly by ixodid ticks. Both methods permitted TBEV acquisition by ticks and we further confirmed virus trans-stadial transmission and onward transmission to a vertebrate host. However, only artificial feeding system allowed to demonstrate both acquisition by ticks and trans-stadial transmission for KEMV. Yet we did not observe transmission of KEMV to mice (IFNAR^-/- or BALB/c). Artificial infection methods of ticks are important tools to study tick-virus interactions. When optimally used under laboratory settings, they provide important insights into tick-borne virus transmission cycles.

Human genetic risk of treatment with antiviral nucleoside analog drugs that induce lethal mutagenesis: The special case of molnupiravir

This review considers antiviral nucleoside analog drugs, including ribavirin, favipiravir, and molnupiravir, which induce genome error catastrophe in SARS-CoV or SARS-CoV-2 via lethal mutagenesis as a mode of action. In vitro data indicate that molnupiravir may be 100 times more potent as an antiviral agent than ribavirin or favipiravir. Molnupiravir has recently demonstrated efficacy in a phase 3 clinical trial. Because of its anticipated global use, its relative potency, and the reported in vitro "host" cell mutagenicity of its active principle, β-d-N4-hydroxycytidine, we have reviewed the development of molnupiravir and its genotoxicity safety evaluation, as well as the genotoxicity profiles of three congeners, that is, ribavirin, favipiravir, and 5-(2-chloroethyl)-2'-deoxyuridine. We consider the potential genetic risks of molnupiravir on the basis of all available information and focus on the need for additional human genotoxicity data and follow-up in patients treated with molnupiravir and similar drugs. Such human data are especially relevant for antiviral NAs that have the potential of permanently modifying the genomes of treated patients and/or causing human teratogenicity or embryotoxicity. We conclude that the results of preclinical genotoxicity studies and phase 1 human clinical safety, tolerability, and pharmacokinetics are critical components of drug safety assessments and sentinels of unanticipated adverse health effects. We provide our rationale for performing more thorough genotoxicity testing prior to and within phase 1 clinical trials, including human PIG-A and error corrected next generation sequencing (duplex sequencing) studies in DNA and mitochondrial DNA of patients treated with antiviral NAs that induce genome error catastrophe via lethal mutagenesis.

History of Arbovirus Research in the Czech Republic

The aim of this review is to follow the history of studies on endemiv arboviruses and the diseases they cause which were detected in the Czech lands (Bohemia, Moravia and Silesia (i.e., the Czech Republic)). The viruses involve tick-borne encephalitis, West Nile and Usutu flaviviruses; the Sindbis alphavirus; Ťahyňa, Batai, Lednice and Sedlec bunyaviruses; the Uukuniemi phlebovirus; and the Tribeč orbivirus. Arboviruses temporarily imported from abroad to the Czech Republic have been omitted. This brief historical review includes a bibliography of all relevant papers.

An update on the progress of galidesivir (BCX4430), a broad-spectrum antiviral

Galidesivir (BCX4430) is an adenosine nucleoside analog that is broadly active in cell culture against several RNA viruses of various families. This activity has also been shown in animal models of viral disease associated with Ebola, Marburg, yellow fever, Zika, and Rift Valley fever viruses. In many cases, the compound is more efficacious in animal models than cell culture activity would predict. Based on favorable data from in vivo animal studies, galidesivir has recently undergone evaluation in several phase I clinical trials, including against severe acute respiratory syndrome coronavirus 2, and as a medical countermeasure for the treatment of Marburg virus disease.

Recovery of a Far-Eastern Strain of Tick-Borne Encephalitis Virus with a Full-Length Infectious cDNA Clone

Tick-borne encephalitis virus (TBEV) is a pathogenic virus known to cause central nervous system (CNS) diseases in humans, and has become an increasing public health threat nowadays. The rates of TBEV infection in the endemic countries are increasing. However, there is no effective antiviral against the disease. This underscores the urgent need for tools to study the emergence and pathogenesis of TBEV and to accelerate the development of vaccines and antivirals. In this study, we reported an infectious cDNA clone of TBEV that was isolated in China (the WH2012 strain). A beta-globin intron was inserted in the coding region of nonstructural protein 1 (NS1) gene to improve the stability of viral genome in bacteria. In mammalian cells, the inserted intron was excised and spliced precisely, which did not lead to the generation of inserted mutants. High titers of infectious progeny viruses were generated after the transfection of the infectious clone. The cDNA-derived TBEV replicated efficiently, and caused typical cytopathic effect (CPE) and plaques in BHK-21 cells. In addition, the CPE and growth curve of cDNA-derived virus were similar to that of its parental isolate in cells. Together, we have constructed the first infectious TBEV cDNA clone in China, and the clone can be used to investigate the genetic determinants of TBEV virulence and disease pathogenesis, and to develop countermeasures against the virus.

Strategy, Progress, and Challenges of Drug Repurposing for Efficient Antiviral Discovery

Emerging or re-emerging viruses are still major threats to public health. Prophylactic vaccines represent the most effective way to prevent virus infection; however, antivirals are more promising for those viruses against which vaccines are not effective enough or contemporarily unavailable. Because of the slow pace of novel antiviral discovery, the high disuse rates, and the substantial cost, repurposing of the well-characterized therapeutics, either approved or under investigation, is becoming an attractive strategy to identify the new directions to treat virus infections. In this review, we described recent progress in identifying broad-spectrum antivirals through drug repurposing. We defined the two major categories of the repurposed antivirals, direct-acting repurposed antivirals (DARA) and host-targeting repurposed antivirals (HTRA). Under each category, we summarized repurposed antivirals with potential broad-spectrum activity against a variety of viruses and discussed the possible mechanisms of action. Finally, we proposed the potential investigative directions of drug repurposing.

Identification of multipotent drugs for COVID-19 therapeutics with the evaluation of their SARS-CoV2 inhibitory activity

The SARS-CoV2 is a highly contagious pathogen that causes COVID-19 disease. It has affected millions of people globally with an average lethality of ~3%. There is an urgent need of drugs for the treatment of COVID-19. In the current studies, we have used bioinformatics techniques to screen the FDA approved drugs against nine SARS-CoV2 proteins to identify drugs for repurposing. Additionally, we analyzed if the identified molecules can also affect the human proteins whose expression in lung changed during SARS-CoV2 infection. Targeting such genes may also be a beneficial strategy to curb disease manifestation. We have identified 74 molecules that can bind to various SARS-CoV2 and human host proteins. We experimentally validated our in-silico predictions using vero E6 cells infected with SARS-CoV2 virus. Interestingly, many of our predicted molecules viz. capreomycin, celecoxib, mefloquine, montelukast, and nebivolol showed good activity (IC50) against SARS-CoV2. We hope that these studies may help in the development of new therapeutic options for the treatment of COVID-19.

Zika virus pathogenesis and current therapeutic advances

Zika virus (ZIKV) is an emerging arthropod-borne flavivirus that, upon infection, results in teratogenic effects and neurological disorders. ZIKV infections pose serious global public health concerns, prompting scientists to increase research on antivirals and vaccines against the virus. These efforts are still ongoing as the pathogenesis and immune evasion mechanisms of ZIKV have not yet been fully elaborated. Currently, no specific vaccines or drugs have been approved for ZIKV; however, some are undergoing clinical trials. Notably, several strategies have been used to develop antivirals, including drugs that target viral and host proteins. Additionally, drug repurposing is preferred since it is less costly and takes less time than other strategies because the drugs used have already been approved for human use. Likewise, different platforms have been evaluated for the design of vaccines, including DNA, mRNA, peptide, protein, viral vectors, virus-like particles (VLPSs), inactivated-virus, and live-attenuated virus vaccines. These vaccines have been shown to induce specific humoral and cellular immune responses and reduce viremia and viral RNA both in vitro and in vivo. Importantly, most of these vaccines have entered clinical trials. Understanding the viral disease mechanism will provide better strategies for developing therapeutic agents against ZIKV. This review provides a comprehensive summary of the viral pathogenesis of ZIKV and current advancements in the development of vaccines and drugs against this virus.

Targeting viral genome synthesis as broad-spectrum approach against RNA virus infections

Zoonotic spillover, i.e. pathogen transmission from animal to human, has repeatedly introduced RNA viruses into the human population. In some cases, where these viruses were then efficiently transmitted between humans, they caused large disease outbreaks such as the 1918 flu pandemic or, more recently, outbreaks of Ebola and Coronavirus disease. These examples demonstrate that RNA viruses pose an immense burden on individual and public health with outbreaks threatening the economy and social cohesion within and across borders. And while emerging RNA viruses are introduced more frequently as human activities increasingly disrupt wild-life eco-systems, therapeutic or preventative medicines satisfying the “one drug-multiple bugs”-aim are unavailable. As one central aspect of preparedness efforts, this review digs into the development of broadly acting antivirals via targeting viral genome synthesis with host- or virus-directed drugs centering around nucleotides, the genomes’ universal building blocks. Following the first strategy, selected examples of host de novo nucleotide synthesis inhibitors are presented that ultimately interfere with viral nucleic acid synthesis, with ribavirin being the most prominent and widely used example. For directly targeting the viral polymerase, nucleoside and nucleotide analogues (NNAs) have long been at the core of antiviral drug development and this review illustrates different molecular strategies by which NNAs inhibit viral infection. Highlighting well-known as well as recent, clinically promising compounds, structural features and mechanistic details that may confer broad-spectrum activity are discussed. The final part addresses limitations of NNAs for clinical development such as low efficacy or mitochondrial toxicity and illustrates strategies to overcome these.

Emerging strategies on in silico drug development against COVID-19: challenges and opportunities

The importance of coronaviruses as human pathogen has been highlighted by the recent outbreak of SARS-CoV-2 leading to the search of suitable drugs to overcome respiratory infections caused by the virus. Due to the lack of specific drugs against coronavirus, the existing antiviral and antimalarial drugs are currently being administered to the patients infected with SARS-CoV-2. The scientists are also considering repurposing of some of the existing drugs as a suitable option in search of effective drugs against coronavirus till the establishment of a potent drug and/or vaccine. Computer-aided drug discovery provides a promising attempt to enable scientists to develop new and target specific drugs to combat any disease. The discovery of novel targets for COVID-19 using computer-aided drug discovery tools requires knowledge of the structure of coronavirus and various target proteins present in the virus. Targeting viral proteins will make the drug specific against the virus, thereby, increasing the chances of viral mortality. Hence, this review provides the structure of SARS-CoV-2 virus along with the important viral components involved in causing infection. It also focuses on the role of various target proteins in disease, the mechanism by which currently administered drugs act against the virus and the repurposing of few drugs. The gap arising from the absence of specific drugs is addressed by proposing potential antiviral drug targets which might provide insights into structure-based drug development against SARS-CoV-2.

Emerging Molecular Prospective of SARS-CoV-2: Feasible Nanotechnology Based Detection and Inhibition

The rapid dissemination of SARS-CoV-2 demonstrates how vulnerable it can make communities and is why it has attained the status of global pandemic. According to the estimation from Worldometer, the SARS-CoV-2 affected cases and deaths are exponentially increasing worldwide, marking the mortality rate as ∼3.8% with no probability of its cessation till now. Despite massive attempts and races among scientific communities in search of proper therapeutic options, the termination of this breakneck outbreak of COVID-19 has still not been made possible. Therefore, this review highlights the diverse molecular events induced by a viral infection, such as autophagy, unfolded protein response (UPR), and inflammasome, illustrating the intracellular cascades regulating viral replication inside the host cell. The SARS-CoV-2-mediated endoplasmic reticulum stress and apoptosis are also emphasized in the review. Additionally, host's immune response associated with SARS-CoV-2 infection, as well as the genetic and epigenetic changes, have been demonstrated, which altogether impart a better understanding of its epidemiology. Considering the drawbacks of available diagnostics and medications, herein we have presented the most sensitive nano-based biosensors for the rapid detection of viral components. Moreover, conceptualizing the viral-induced molecular changes inside its target cells, nano-based antiviral systems have also been proposed in this review.

SARS-CoV-2: Pathogenesis, and Advancements in Diagnostics and Treatment

The emergence and rapid spread of SARS-CoV-2 in December 2019 has brought the world to a standstill. While less pathogenic than the 2002-2003 SARS-CoV, this novel betacoronavirus presents a global threat due to its high transmission rate, ability to invade multiple tissues, and ability to trigger immunological hyperactivation. The identification of the animal reservoir and intermediate host were important steps toward slowing the spread of disease, and its genetic similarity to SARS-CoV has helped to determine pathogenesis and direct treatment strategies. The exponential increase in cases has necessitated fast and reliable testing procedures. Although RT-PCR remains the gold standard, it is a time-consuming procedure, paving the way for newer techniques such as serologic tests and enzyme immunoassays. Various clinical trials using broad antiviral agents in addition to novel medications have produced controversial results; however, the advancement of immunotherapy, particularly monoclonal antibodies and immune modulators is showing great promise in clinical trials. Non-orthodox medications such as anti-malarials have been tested in multiple institutions but definitive conclusions are yet to be made. Adjuvant therapies have also proven to be effective in decreasing mortality in the disease course. While no formal guidelines have been established, the multitude of ongoing clinical trials as a result of unprecedented access to research data brings us closer to halting the SARS-CoV-2 pandemic.

NS5-V372A and NS5-H386Y variations are responsible for differences in interferon α/β induction and co-contribute to the replication advantage of Japanese encephalitis virus genotype I over genotype III in ducklings

Japanese encephalitis virus (JEV) genotype I (GI) replicates more efficiently than genotype III (GIII) in birds, and this difference is considered to be one of the reasons for the JEV genotype shift. In this study, we utilized duck embryo fibroblasts and domestic ducklings as in vitro and in vivo models of a JEV amplifying avian host to identify the viral determinants of the differing replication efficiency between the GI and GIII strains in birds. GI strains induced significantly lower levels of interferon (IFN)-α and β production than GIII strains, an effect orrelated with the enhanced replication efficiency of GI strains over GIII strains. By using a series of chimeric viruses with exchange of viral structural and non-structural (NS) proteins, we identified NS5 as the viral determinant of the differences in IFN-α and β induction and replication efficiency between the GI and III strains. NS5 inhibited IFN-α and β production induced by poly(I:C) stimulation and harbored 11 amino acid variations, of which the NS5-V372A and NS5-H386Y variations were identified to co-contribute to the differences in IFN-α and β induction and replication efficiency between the strains. The NS5-V372A and NS5-H386Y variations resulted in alterations in the number of hydrogen bonds formed with neighboring residues, which were associated with the different ability of the GI and GIII strains to inhibit IFN-α and β production. Our findings indicated that the NS5-V372A and NS5-H386Y variations enabled GI strains to inhibit IFN-α and β production more efficiently than GIII strains for antagonism of the IFN-I mediated antiviral response, thereby leading to the replication and host adaption advantages of GI strains over GIII strains in birds. These findings provide new insight into the molecular basis of the JEV genotype shift.

The Japanese encephalitis virus (JEV) transmission cycle is maintained by mosquitoes and amplification hosts (pigs and birds). In areas without large pig populations, birds play a major role in the maintenance of the JEV transmission cycle. The shift in the dominant JEV genotype from genotype III (GIII) to genotype I (GI) is occurring in most countries in Asia. GI strains replicates more efficiently than GIII strains in birds, and this difference has been considered one of the reasons for the JEV genotype shift. By using a series of chimeric viruses with exchange of viral structural and non-structural (NS) proteins, we demonstrated that NS5 is the viral determinant of the differences in replication efficiencies between the GI and III strains in birds. Furthermore, the NS5-V372A and NS5-H386Y variations were identified to co-contribute to the differences in type I interferon (IFN-I) induction and replication efficiency between the strains. Our findings suggested that the NS5-V372A and NS5-H386Y variations enable GI strains to inhibit IFN-I production more efficiently than GIII strains, thus resulting in antagonism of the IFN-I mediated antiviral response and consequently conferring a replication and host adaption advantage to GI strains over GIII strains in birds. These findings provide new insight into the molecular basis of the JEV genotype shift.

Repurposing Drugs, Ongoing Vaccine, and New Therapeutic Development Initiatives Against COVID-19

As the COVID-19 is still growing throughout the globe, a thorough investigation into the specific immunopathology of SARS-CoV-2, its interaction with the host immune system and pathogen evasion mechanism may provide a clear picture of how the pathogen can breach the host immune defenses in elderly patients and patients with comorbid conditions. Such studies will also reveal the underlying mechanism of how children and young patients can withstand the disease better. The study of the immune defense mechanisms and the prolonged immune memory from patients population with convalescent plasma may help in designing a suitable vaccine candidate not only for the current outbreak but also for similar outbreaks in the future. The vital drug candidates, which are being tested as potential vaccines or therapeutics against COVID-19, include live attenuated vaccine, inactivated or killed vaccine, subunit vaccine, antibodies, interferon treatment, repurposing existing drugs, and nucleic acid-based vaccines. Several organizations around the world have fast-tracked the development of a COVID-19 vaccine, and some drugs already went to phase III of clinical trials. Hence, here, we have tried to take a quick glimpse of the development stages of vaccines or therapeutic approaches to treat this deadly disease.

Simplistic perylene-related compounds as inhibitors of tick-borne encephalitis virus reproduction

Rigid amphipathic fusion inhibitors are potent broad-spectrum antivirals based on the perylene scaffold, usually decorated with a hydrophilic group linked via ethynyl or triazole. We have sequentially simplified these structures by removing sugar moiety, then converting uridine to aniline, then moving to perylenylthiophenecarboxylic acids and to perylenylcarboxylic acid. All these polyaromatic compounds, as well as antibiotic heliomycin, still showed pronounced activity against tick-borne encephalitis virus (TBEV) with limited toxicity in porcine embryo kidney (PEK) cell line. 5-(Perylen-3-yl)-2-thiophenecarboxylic acid (5a) showed the highest antiviral activity with 50% effective concentration of approx. 1.6 nM.

Flavivirus RNA-Dependent RNA Polymerase Interacts with Genome UTRs and Viral Proteins to Facilitate Flavivirus RNA Replication

Flaviviruses, most of which are emerging and re-emerging human pathogens and significant public health concerns worldwide, are positive-sense RNA viruses. Flavivirus replication occurs on the ER and is regulated by many mechanisms and factors. NS5, which consists of a C-terminal RdRp domain and an N-terminal methyltransferase domain, plays a pivotal role in genome replication and capping. The C-terminal RdRp domain acts as the polymerase for RNA synthesis and cooperates with diverse viral proteins to facilitate productive RNA proliferation within the replication complex. Here, we provide an overview of the current knowledge of the functions and characteristics of the RdRp, including the subcellular localization of NS5, as well as the network of interactions formed between the RdRp and genome UTRs, NS3, and the methyltransferase domain. We posit that a detailed understanding of RdRp functions may provide a target for antiviral drug discovery and therapeutics.

An E460D Substitution in the NS5 Protein of Tick-Borne Encephalitis Virus Confers Resistance to the Inhibitor Galidesivir (BCX4430) and Also Attenuates the Virus for Mice

The adenosine analogue galidesivir (BCX4430), a broad-spectrum RNA virus inhibitor, has entered a phase 1 clinical safety and pharmacokinetics study in healthy subjects and is under clinical development for treatment of Ebola and yellow fever virus infections. Moreover, galidesivir also inhibits the reproduction of tick-borne encephalitis virus (TBEV) and numerous other medically important flaviviruses. Until now, studies of this antiviral agent have not yielded resistant viruses. Here, we demonstrate that an E460D substitution in the active site of TBEV RNA-dependent RNA polymerase (RdRp) confers resistance to galidesivir in cell culture. Galidesivir-resistant TBEV exhibited no cross-resistance to structurally different antiviral nucleoside analogues, such as 7-deaza-2'-C-methyladenosine, 2'-C-methyladenosine, and 4'-azido-aracytidine. Although the E460D substitution led to only a subtle decrease in viral fitness in cell culture, galidesivir-resistant TBEV was highly attenuated in vivo, with a 100% survival rate and no clinical signs observed in infected mice. Furthermore, no virus was detected in the sera, spleen, or brain of mice inoculated with the galidesivir-resistant TBEV. Our results contribute to understanding the molecular basis of galidesivir antiviral activity, flavivirus resistance to nucleoside inhibitors, and the potential contribution of viral RdRp to flavivirus neurovirulence.IMPORTANCE Tick-borne encephalitis virus (TBEV) is a pathogen that causes severe human neuroinfections in Europe and Asia and for which there is currently no specific therapy. We have previously found that galidesivir (BCX4430), a broad-spectrum RNA virus inhibitor, which is under clinical development for treatment of Ebola and yellow fever virus infections, has a strong antiviral effect against TBEV. For any antiviral drug, it is important to generate drug-resistant mutants to understand how the drug works. Here, we produced TBEV mutants resistant to galidesivir and found that the resistance is caused by a single amino acid substitution in an active site of the viral RNA-dependent RNA polymerase, an enzyme which is crucial for replication of the viral RNA genome. Although this substitution led only to a subtle decrease in viral fitness in cell culture, galidesivir-resistant TBEV was highly attenuated in a mouse model. Our results contribute to understanding the molecular basis of galidesivir antiviral activity.