In vitro and in vivo activities of anti-influenza virus compound T-705

Sangju Cold Granule exerts anti-viral and anti-inflammatory activities against influenza A virus in vitro and in vivo

ETHNOPHARMACOLOGICAL RELEVANCE

Sangju Cold Granule (SJCG) is a classical traditional Chinese medicine (TCM) prescription described in "Item Differentiation of Warm Febrile Diseases". Historically, SJCG was employed to treat respiratory illnesses. Despite its popular usage, the alleviating effect of SJCG on influenza A virus infection and its mechanisms have not been fully elucidated.

AIM OF THE STUDY

Influenza is a severe respiratory disease that threatens human health. This study aims to assess the therapeutic potential of SJCG and the possible molecular mechanism underlying its activity against influenza A virus in vitro and in vivo.

MATERIALS AND METHODS

Ultrahigh-performance liquid chromatography (UPLC)-Q-Exactive was used to identify the components of SJCG. The 50% cytotoxic concentration of SJCG in MDCK and A549 cells were determined using the CCK-8 assay. The activity of SJCG against influenza A virus H1N1 was evaluated in vitro using plaque reduction and progeny virus titer reduction assays. RT-qPCR was performed to obtain the expression levels of inflammatory mediators and the transcriptional regulation of RIG-I and MDA5 in H1N1-infected A549 cells. Then, the mechanism of SJCG effect on viral replication and inflammation was further explored by measuring the expressions of proteins of the RIG-I/NF-kB/IFN(I/III) signaling pathway by Western blot. The impact of SJCG was explored in vivo in an intranasally H1N1-infected BALB/c mouse pneumonia model treated with varying doses of SJCG. The protective role of SJCG in this model was evaluated by survival, body weight monitoring, lung viral titers, lung index, lung histological changes, lung inflammatory mediators, and peripheral blood leukocyte count.

RESULTS

The main SJCG chemical constituents were flavonoids, carbohydrates and glycosides, amino acids, peptides, and derivatives, organic acids and derivatives, alkaloids, fatty acyls, and terpenes. The CC50 of SJCG were 24.43 mg/mL on MDCK cells and 20.54 mg/mL on A549 cells, respectively. In vitro, SJCG significantly inhibited H1N1 replication and reduced the production of TNF-α, IFN-β, IL-6, IL-8, IL-13, IP-10, RANTES, TRAIL, and SOCS1 in infected A549 cells. Intracellularly, SJCG reduced the expression of RIG-I, MDA5, P-NF-κB P65 (P-P65), P-IκBα, P-STAT1, P-STAT2, and IRF9. In vivo, SJCG enhanced the survival rate and decreased body weight loss in H1N1-infected mice. Mice with H1N1-induced pneumonia treated with SJCG showed a lower lung viral load and lung index than untreated mice. SJCG effectively alleviated lung damage and reduced the levels of TNF-α, IFN-β, IL-6, IP-10, RANTES, and SOCS1 in lung tissue. Moreover, SJCG significantly ameliorated H1N1-induced leukocyte changes in peripheral blood.

CONCLUSIONS

SJCG significantly reduced influenza A virus and virus-mediated inflammation through inhibiting the RIG-I/NF-kB/IFN(I/III) signaling pathway. Thus, SJCG could provide an effective TCM for influenza treatment.

Influenza C virus susceptibility to antivirals with different mechanisms of action

Antiviral susceptibility of influenza viruses was assessed using a high-content imaging-based neutralization test. Cap-dependent endonuclease inhibitors, baloxavir and AV5116, were superior to AV5115 against type A viruses, and AV5116 was most effective against PA mutants tested. However, these three inhibitors displayed comparable activity (EC50 8-22 nM) against type C viruses from six lineages. Banana lectin and a monoclonal antibody, YA3, targeting the hemagglutinin-esterase protein effectively neutralized some, but not all, type C viruses.

Pharmacogenomic Studies of Antiviral Drug Favipiravir

In this work, we conducted a study of the interaction between DNA and favipiravir (FAV). This chemotherapeutic compound is an antiviral drug for the treatment of COVID-19 and other infections caused by RNA viruses. This paper examines the electroanalytical characteristics of FAV. The determined concentrations correspond to therapeutically significant ones in the range of 50-500 µM (R2 = 0.943). We have shown that FAV can be electro-oxidized around the potential of +0.96 V ÷ +0.98 V (vs. Ag/AgCl). A mechanism for electrochemical oxidation of FAV was proposed. The effect of the drug on DNA was recorded as changes in the intensity of electrochemical oxidation of heterocyclic nucleobases (guanine, adenine and thymine) using screen-printed graphite electrodes modified with single-walled carbon nanotubes and titanium oxide nanoparticles. In this work, the binding constants (Kb) of FAV/dsDNA complexes for guanine, adenine and thymine were calculated. The values of the DNA-mediated electrochemical decline coefficient were calculated as the ratio of the intensity of signals for the electrochemical oxidation of guanine, adenine and thymine in the presence of FAV to the intensity of signals for the electro-oxidation of these bases without drug (S, %). Based on the analysis of electrochemical parameters, values of binding constants and spectral data, intercalation was proposed as the principal mechanism of the antiviral drug FAV interaction with DNA. The interaction with calf thymus DNA also confirmed the intercalation mechanism. However, an additional mode of interaction, such as a damage effect together with electrostatic interactions, was revealed in a prolonged exposure of DNA to FAV.

Clinical antiviral efficacy of favipiravir in early COVID-19 (PLATCOV): an open-label, randomised, controlled, adaptive platform trial

In early symptomatic COVID-19 treatment, high dose oral favipiravir did not accelerate viral clearance.

BACKGROUND

Favipiravir, an anti-influenza drug, has in vitro antiviral activity against SARS-CoV-2. Clinical trial evidence to date is inconclusive. Favipiravir has been recommended for the treatment of COVID-19 in some countries.

METHODS

In a multicentre open-label, randomised, controlled, adaptive platform trial, low-risk adult patients with early symptomatic COVID-19 were randomised to one of ten treatment arms including high dose oral favipiravir (3.6g on day 0 followed by 1.6g daily to complete 7 days treatment) or no study drug. The primary outcome was the rate of viral clearance (derived under a linear mixed-effects model from the daily log10 viral densities in standardised duplicate oropharyngeal swab eluates taken daily over 8 days [18 swabs per patient]), assessed in a modified intention-to-treat population (mITT). The safety population included all patients who received at least one dose of the allocated intervention. This ongoing adaptive platform trial was registered at ClinicalTrials.gov (NCT05041907) on 13/09/2021.

RESULTS

In the final analysis, the mITT population contained data from 114 patients randomised to favipiravir and 126 patients randomised concurrently to no study drug. Under the linear mixed-effects model fitted to all oropharyngeal viral density estimates in the first 8 days from randomisation (4,318 swabs), there was no difference in the rate of viral clearance between patients given favipiravir and patients receiving no study drug; a -1% (95% credible interval: -14 to 14%) difference. High dose favipiravir was well-tolerated.

INTERPRETATION

Favipiravir does not accelerate viral clearance in early symptomatic COVID-19. The viral clearance rate estimated from quantitative measurements of oropharyngeal eluate viral densities assesses the antiviral efficacy of drugs in vivo with comparatively few studied patients.

Assessment of toxicological effects of favipiravir (T-705) on the lung tissue of rats: An experimental study

This study aimed to present new data on the side effects of favipiravir on healthy lung tissue and the respiratory system. In the study, two different durations (5 and 10 days) were preferred to determine the effect of favipiravir treatment due to clinical improvement rates of approximately 5 and 10 days during the use of favipiravir in COVID-19 patients. In addition, after 10 days of favipiravir treatment, animals were kept for 5 days without any treatment to determine the regeneration of lung tissues. Favipiravir was administered to rats by oral gavage at a daily dose of 200 mg/kg for 5 and 10 days, as in previous studies. At the end of the experiment, the histopathological and biochemical effects of favipiravir in the lung tissue were investigated. The data obtained from the study showed that favipiravir increased oxidative stress parameters, expression of apoptotic markers, and pro-inflammatory markers in lung tissue. Since malondialdehydes is an oxidant parameter, it increased in favipiravir-administered groups; It was determined that the antioxidant parameters glutathione, superoxide dismutase, glutathione peroxidase, and catalase decreased. Other markers used in the analysis are Bcl-2, Bax, NF-κB, interleukin (IL)-6, Muc1, iNOS, P2X7R, IL-6 and caspase-3. The levels of Bax, caspase-3, NF-κB, IL-6, Muc1, and P2X7R were increased in the Fav-treated groups compared with the control. However, the levels of Bcl-2 decreased in the Fav-treated groups. The present study proves that favipiravir, widely used today, causes side effects in lung tissue.

In vitro antiviral activity of favipiravir and its 6- and 3-O-substituted derivatives against coronavirus: Acetylation leads to improvement of antiviral activity

Favipiravir is currently approved for the treatment of the influenza virus and has shown encouraging results in terms of antiviral capacity in clinical studies against severe acute respiratory syndrome coronavirus 2. Favipiravir is a prodrug, where its favipiravir-ribofuranosyl-5B-triphosphate metabolite is capable of blocking RNA replication of the virus. However, the antiviral efficiency of favipiravir is limited by two factors: (i) low accumulation in plasma and rapid excretion/elimination post-administration and (ii) low conversion rate into the active metabolite. To tackle these problems, herein, we have designed new favipiravir analogues focusing on the replacement of the fluorine atom at the 6-position by halogen or hydrogen atoms and 3-O-functionalization with labile groups. The first type of functionalization seeks to increase the antiviral activity because of the better ability of the keto-tautomer as a function of the halogen, and it is hypothesized that the keto-tautomer tends to promote the formation of the ribofuranosyl-5B-triphosphate (RTP) metabolite. Meanwhile, the second type of functionalization seeks to promote lipophilicity and increase accumulation in cells. From the in vitro antiviral activity against two coronavirus models (bovine and human 229E), it was identified that the replacement did not improve the antiviral activity against both the models, which seems to be attributable to the low water solubility of these new 6-functionalized analogues. Meanwhile, with 3-O-functionalization, acetylation provided the most active compounds with higher half-maximal inhibitory concentration and selectivity than favipiravir, whereas benzylation/methanosulfonation yielded the least active compounds. In summary, acetylation is found to be a convenient functionalization to enhance the antiviral profile of favipiravir.

Tautomerism and Rotamerism of Favipiravir and Halogenated Analogues in Solution and in the Solid State

Favipiravir is an important selective antiviral against RNA-based viruses, and currently, it is being repurposed as a potential drug for the treatment of COVID-19. This type of chemical system presents different carboxamide-rotameric and hydroxyl-tautomeric states, which could be essential for interpreting its selective antiviral activity. Herein, the tautomeric 3-hydroxypyrazine/3-pyrazinone pair of favipiravir and its 6-substituted analogues, 6-Cl, 6-Br, 6-I, and 6-H, were fully investigated in solution and in the solid state through ultraviolet-visible, 1H nuclear magnetic resonance, infrared spectroscopy, and X-ray diffraction techniques. Also, a study of the gas phase was performed using density functional theory calculations. In general, the keto-enol balance in these 3-hydroxy-2-pyrazinecarboxamides is finely modulated by external and internal electrical variations via changes in solvent polarity or by replacement of substituents at position 6. The enol tautomer was prevalent in an apolar environment, whereas an increase in the level of the keto tautomer was favored by an increase in solvent polarity and, even moreso, with a strong hydrogen-donor solvent. Keto tautomerization was favored either in solution or in the solid state with a decrease in 6-substituent electronegativity as follows: H ≫ I ≈ Br > Cl ≥ F. Specific rotameric states based on carboxamide, "cisoide" and "transoide", were identified for the enol and keto tautomer, respectively; their rotamerism is dependent on the tautomerism and not the aggregation state.

Fitness-Dependent, Mild Mutagenic Activity of Sofosbuvir for Hepatitis C Virus

The concept of a mild mutagen was coined to describe a minor mutagenic activity exhibited by some nucleoside analogues that potentiated their efficacy as antiretroviral agents. In the present study, we report the mild mutagen activity of sofosbuvir (SOF) for hepatitis C virus (HCV). Serial passages of HCV in human hepatoma cells, in the presence of SOF at a concentration well below its cytotoxic concentration 50 (CC50) led to pre-extinction populations whose mutant spectra exhibited a significant increase of C→U transitions, relative to populations passaged in the absence of SOF. This was reflected in an increase in several diversity indices that were used to characterize viral quasispecies. The mild mutagenic activity of SOF was largely absent when it was tested with isogenic HCV populations that displayed high replicative fitness. Thus, SOF can act as a mild mutagen for HCV, depending on HCV fitness. Possible mechanisms by which the SOF mutagenic activity may contribute to its antiviral efficacy are discussed.

Aprotinin-Drug against Respiratory Diseases

Aprotinin (APR) was discovered in 1930. APR is an effective pan-protease inhibitor, a typical "magic shotgun". Until 2007, APR was widely used as an antithrombotic and anti-inflammatory drug in cardiac and noncardiac surgeries for reduction of bleeding and thus limiting the need for blood transfusion. The ability of APR to inhibit proteolytic activation of some viruses leads to its use as an antiviral drug for the prevention and treatment of acute respiratory virus infections. However, due to incompetent interpretation of several clinical trials followed by incredible controversy in the literature, the usage of APR was nearly stopped for a decade worldwide. In 2015-2020, after re-analysis of these clinical trials' data the restrictions in APR usage were lifted worldwide. This review discusses antiviral mechanisms of APR action and summarizes current knowledge and prospective regarding the use of APR treatment for diseases caused by RNA-containing viruses, including influenza and SARS-CoV-2 viruses, or as a part of combination antiviral treatment.

The combined effect of oseltamivir and favipiravir on influenza a virus evolution in patients hospitalized with severe influenza

Our previous study shows favipiravir and oseltamivir combination therapy may accelerate clinical recovery compared to oseltamivir monotherapy in severe influenza, but its effect on virological evolution and resistance mutation against oseltamivir is still unknown. In this study, we collected longitudinal respiratory samples from influenza patients who underwent combination therapy and applied them to next generation sequencing of the whole genome of the influenza A virus (IAV). We also included a cohort untreated with any antivirals to serve as the control. In total, 62 samples from 19 patients treated with combination therapy and 20 samples from 20 patients untreated were successfully sequenced. The nucleotide diversity in the whole genome of IAV in the combination group showed no difference compared to that in the control group (P > 0.05). Moreover, we observed 174 kinds of nonsynonymous nucleotide substitutions in patients with combination therapy, mostly in NA (n = 44) and HA (n = 43). Of them, the G→A transition was the dominant variant type (27%) and 46/174 (26%) was reported to have biological effects, such as increased pathogenicity and polymerase activity. Among the 29 mutations conferring reduction in oseltamivir sensitivity we investigated, H275Y was the only mutation detected in the 4 samples from 1 of 19 patients and demonstrated increasing frequency during the treatment. Mutations conferring favipiravir resistance were not observed. Our studies showed combination therapy of favipiravir and oseltamivir has little effect on virus nucleotide diversity, nor prevents the increase of oseltamivir-resistant variants.

Repurposing clinically available drugs and therapies for pathogenic targets to combat SARS-CoV-2

The coronavirus disease 2019 (COVID-19) pandemic has affected a large portion of the global population, both physically and mentally. Current evidence suggests that the rapidly evolving coronavirus subvariants risk rendering vaccines and antibodies ineffective due to their potential to evade existing immunity, with enhanced transmission activity and higher reinfection rates that could lead to new outbreaks across the globe. The goal of viral management is to disrupt the viral life cycle as well as to relieve severe symptoms such as lung damage, cytokine storm, and organ failure. In the fight against viruses, the combination of viral genome sequencing, elucidation of the structure of viral proteins, and identifying proteins that are highly conserved across multiple coronaviruses has revealed many potential molecular targets. In addition, the time- and cost-effective repurposing of preexisting antiviral drugs or approved/clinical drugs for these targets offers considerable clinical advantages for COVID-19 patients. This review provides a comprehensive overview of various identified pathogenic targets and pathways as well as corresponding repurposed approved/clinical drugs and their potential against COVID-19. These findings provide new insight into the discovery of novel therapeutic strategies that could be applied to the control of disease symptoms emanating from evolving SARS-CoV-2 variants.

Potential treatments of COVID-19: Drug repurposing and therapeutic interventions

The coronavirus disease 2019 (COVID-19) is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The infection is caused when Spike-protein (S-protein) present on the surface of SARS-CoV-2 interacts with human cell surface receptor, Angiotensin-converting enzyme 2 (ACE2). This binding facilitates SARS-CoV-2 genome entry into the human cells, which in turn causes infection. Since the beginning of the pandemic, many different therapies have been developed to combat COVID-19, including treatment and prevention. This review is focused on the currently adapted and certain other potential therapies for COVID-19 treatment, which include drug repurposing, vaccines and drug-free therapies. The efficacy of various treatment options is constantly being tested through clinical trials and in vivo studies before they are made medically available to the public.

Synthesis and Behavior of DNA Oligomers Containing the Ambiguous Z-Nucleobase 5-Aminoimidazole-4-carboxamide

5-Amino-1-β-D-ribofuranosylimidazole-4-carboxamide 5'-monophosphate (ZMP) is a central intermediate in de novo purine nucleotide biosynthesis. Its nucleobase moiety, 5-aminoimidazole-4-carboxamide (Z-base), is considered an ambiguous base that can pair with any canonical base owing to the rotatable nature of its 5-carboxamide group. This idea of ambiguous base pairing due to free rotation of the carboxamide has been applied to designing mutagenic antiviral nucleosides, such as ribavirin and T-705. However, the ambiguous base-pairing ability of Z-base has not been elucidated, because the synthesis of Z-base-containing oligomers is problematic. Herein, we propose a practical method for the synthesis of Z-base-containing DNA oligomers based on the ring-opening reaction of an N¹-dinitrophenylhypoxanthine (Hxa^DNP) base. Thermal denaturation studies of the resulting oligomers revealed that the Z-base behaves physiologically as an A-like nucleobase, preferentially forming pairs with T. We tested the behavior of Z-base-containing DNA oligomers in enzyme-catalyzed reactions: in single nucleotide insertion, Klenow fragment DNA polymerase recognized Z-base as an A-like analog and incorporated dTTP as a complementary nucleotide to Z-base in the DNA template; in PCR amplification, Taq DNA polymerase similarly incorporated dTTP as a complementary nucleotide to Z-base. Our findings will contribute to the development of new mutagenic antiviral nucleoside analogs.

FACTORS AFFECTING PROGNOSIS AND MORTALITY IN SEVERE COVID-19 PNEUMONIA PATIENTS

Fatality rate in coronavirus disease 2019 (COVID-19) cases has been reported to be 3.4% worldwide. The aim of this study was to evaluate the factors that determine prognosis and mortality in severe COVID-19 pneumonia patients. Eighty adult patients with severe COVID-19 pneumonia hospitalized and monitored at Izzet Baysal State Hospital (Bolu, Turkey) between August and November 2020 were included in this retrospective single-center study. Demographic and laboratory data, severity of radiological involvement, comorbidities, agents used in treatment, and clinical results were recorded, and data were grouped as survivors and non-survivors. The mean patient age was 67.8±12.6 years. There were 59 (73.8%) male patients. Comorbid diseases were present in 53 (66.3%) patients. There was no significant relationship between patient age, gender, smoking status or presence of comorbidity and mortality (p>0.05). The variables such as pulmonary involvement above 50%, intubation, or ferritin (>434.8 µg/L), troponin I (>14.05 ng/L) and procalcitonin (>0.125 ng/mL) as the sole variables of laboratory data were found to have significant relationship with increased mortality (p<0.05). Mortality was significantly higher in patients using steroid pulse therapy + tocilizumab, steroid pulse therapy + hydroxychloroquine, or solely steroid pulse therapy, while it was significantly lower in patients receiving azithromycin therapy and those in the plasma + steroid pulse therapy group. The severity of pulmonary involvement, intubation, and increase in inflammation markers such as ferritin, troponin and procalcitonin were found to be significantly associated with mortality (p<0.05). Treatment approaches with azithromycin and plasma + steroid pulse therapy were found to reduce mortality.

Cheminformatics-Based Study Identifies Potential Ebola VP40 Inhibitors

The Ebola virus (EBOV) is still highly infectious and causes severe hemorrhagic fevers in primates. However, there are no regulatorily approved drugs against the Ebola virus disease (EVD). The highly virulent and lethal nature of EVD highlights the need to develop therapeutic agents. Viral protein 40 kDa (VP40), the most abundantly expressed protein during infection, coordinates the assembly, budding, and release of viral particles into the host cell. It also regulates viral transcription and RNA replication. This study sought to identify small molecules that could potentially inhibit the VP40 protein by targeting the N-terminal domain using an in silico approach. The statistical quality of AutoDock Vina’s capacity to discriminate between inhibitors and decoys was determined, and an area under the curve of the receiver operating characteristic (AUC-ROC) curve of 0.791 was obtained. A total of 29,519 natural-product-derived compounds from Chinese and African sources as well as 2738 approved drugs were successfully screened against VP40. Using a threshold of −8 kcal/mol, a total of 7, 11, 163, and 30 compounds from the AfroDb, Northern African Natural Products Database (NANPDB), traditional Chinese medicine (TCM), and approved drugs libraries, respectively, were obtained after molecular docking. A biological activity prediction of the lead compounds suggested their potential antiviral properties. In addition, random-forest- and support-vector-machine-based algorithms predicted the compounds to be anti-Ebola with IC50 values in the micromolar range (less than 25 μM). A total of 42 natural-product-derived compounds were identified as potential EBOV inhibitors with desirable ADMET profiles, comprising 1, 2, and 39 compounds from NANPDB (2-hydroxyseneganolide), AfroDb (ZINC000034518176 and ZINC000095485942), and TCM, respectively. A total of 23 approved drugs, including doramectin, glecaprevir, velpatasvir, ledipasvir, avermectin B1, nafarelin acetate, danoprevir, eltrombopag, lanatoside C, and glycyrrhizin, among others, were also predicted to have potential anti-EBOV activity and can be further explored so that they may be repurposed for EVD treatment. Molecular dynamics simulations coupled with molecular mechanics Poisson–Boltzmann surface area calculations corroborated the stability and good binding affinities of the complexes (−46.97 to −118.9 kJ/mol). The potential lead compounds may have the potential to be developed as anti-EBOV drugs after experimental testing.

Evaluation of a novel severe combined immunodeficiency mouse model for antiviral drug evaluation against Chandipura virus infection

Chandipura virus (CHPV) is a negative-sense single-stranded RNA virus known to cause fatal encephalitis outbreaks in the Indian subcontinent. The virus displays tropism towards the pediatric population and holds significant public health concerns. Currently, there is no specific, effective therapy for CHPV encephalitis. In this study, we evaluated a novel C.B-17 severe combined immunodeficiency (SCID) mouse model which can be used for pre-clinical antiviral evaluation. Inoculation of CHPV developed a lethal infection in our model. Plaque assay and immunohistochemistry detected increased viral loads and antigens in various organs, including the brain, spinal cord, adrenal glands, and whole blood. We further conducted a proof-of-concept evaluation of favipiravir in the SCID mouse model. Favipiravir treatment improved survival with pre-symptomatic (days 5-14) and post-symptomatic (days 9-18) treatment. Reduced viral loads were observed in whole blood, kidney/adrenal gland, and brain tissue with favipiravir treatment. The findings in this study demonstrate the utility of SCID mouse for in vivo drug efficacy evaluation and the potential efficacy of favipiravir against CHPV infection.

Direct observation of backtracking by influenza A and B polymerases upon consecutive incorporation of the nucleoside analog T1106

The antiviral pseudo-base T705 and its de-fluoro analog T1106 mimic adenine or guanine and can be competitively incorporated into nascent RNA by viral RNA-dependent RNA polymerases. Although dispersed, single pseudo-base incorporation is mutagenic, consecutive incorporation causes polymerase stalling and chain termination. Using a template encoding single and then consecutive T1106 incorporation four nucleotides later, we obtained a cryogenic electron microscopy structure of stalled influenza A/H7N9 polymerase. This shows that the entire product-template duplex backtracks by 5 nt, bringing the singly incorporated T1106 to the +1 position, where it forms an unexpected T1106:U wobble base pair. Similar structures show that influenza B polymerase also backtracks after consecutive T1106 incorporation, regardless of whether prior single incorporation has occurred. These results give insight into the unusual mechanism of chain termination by pyrazinecarboxamide base analogs. Consecutive incorporation destabilizes the proximal end of the product-template duplex, promoting irreversible backtracking to a more energetically favorable overall configuration.

Antiviral Susceptibilities of Distinct Lineages of Influenza C and D Viruses

The emergence and spread of antiviral-resistant influenza viruses are of great concern. To minimize the public health risk, it is important to monitor antiviral susceptibilities of influenza viruses. Analyses of the antiviral susceptibilities of influenza A and B viruses have been conducted globally; however, those of influenza C and D viruses are limited. Here, we determined the susceptibilities of influenza C viruses representing all six lineages (C/Taylor, C/Yamagata, C/Sao Paulo, C/Aichi, C/Kanagawa, and C/Mississippi) and influenza D viruses representing four lineages (D/OK, D/660, D/Yama2016, and D/Yama2019) to RNA polymerase inhibitors (baloxavir and favipiravir) by using a focus reduction assay. All viruses tested were susceptible to both drugs. We then performed a genetic analysis to check for amino acid substitutions associated with baloxavir and favipiravir resistance and found that none of the viruses tested possessed these substitutions. Use of the focus reduction assay with the genotypic assay has proven valuable for monitoring the antiviral susceptibilities of influenza C and D viruses as well as influenza A and B viruses. Antiviral susceptibility monitoring of all influenza virus types should continue in order to assess the public health risks posed by these viruses.

2(1H)-Pyrazinones from acyclic building blocks: methods of synthesis and further derivatizations

Pyrazinones (2(1H)-pyrazinones) are found as components of a range of natural substances and are involved in the preparation of a great number of bioactive molecules. Synthesis of such compounds, and analogues, requires knowledge of the heterocyclic properties of pyrazinones and, in particular, methods for their ring construction. This review deals with the strategies that have been developed for the synthesis of pyrazinones from acyclic precursors, especially α-amino acid-derived units, from the first examples in 1905 up to the most recent in 2021.

CURRENT ASPECTS OF ETIOTROPIC COVID-19 THERAPY

Since the beginning of the pandemic, repeated attempts have been made to develop etiotropic therapy for a novel coronavirus infection. Hydroxychloroquine, lopinavir/ritonavir, etc. derivatives were used as antiviral agents, however, they demonstrated a low efficiency and an insufficient safety. In this connection, other groups of drugs with a more effective and safe pharmacological profile are currently being actively used.

The aim of the study was to analyze the literature references on the efficacy and safety of antiviral drugs for the COVID-19 treatment.

Materials and methods. When searching for the materials for the review article writing, such abstract databases as PubMed, Google Scholar, e-Library were used. The search was carried out on publications for the period from January 2020 to september 2022. The key queries were: COVID-19, etiotropic therapy; immunological drugs; antiviral drugs; interferons.

Results. Currently, there are various degrees of effective etiotropic drugs for the treatment of COVID-19 patients. The review has considered a few groups of drugs that are of interest from the point of view of etiotropic therapy: immunological drugs (anticovid plasma, the drugs based on antiviral antibodies, the drugs of recombinant interferons-α2 and -β1, as well as interferon inducers, i.e., the drugs based on double-stranded RNA sodium salt, and others); drugs that block the penetration of the virus into the cell (umifenovir); the drugs that disrupt the process of the viral replication (favipiravir, remdesivir, molnupiravir, nirmatrelvir/ritonavir).

Conclusion. Synthetic antivirals, in particular favipiravir, molnupiravir, remdesivir, and nirmatrelvir/ritonavir, have the largest evidence base for their efficacy and safety. The search for new effective and safe etiotropic drugs for the treatment of COVID-19, as well as the collection and analysis of post-registration data on the drugs already used in clinical practice, continues.

Predicting In Vitro and In Vivo Anti-SARS-CoV-2 Activities of Antivirals by Intracellular Bioavailability and Biochemical Activity

Cellular drug response (concentration required for obtaining 50% of a maximum cellular effect, EC₅₀) can be predicted by the intracellular bioavailability (F _ic) and biochemical activity (half-maximal inhibitory concentration, IC₅₀) of drugs. In an ideal model, the cellular negative log of EC₅₀ (pEC₅₀) equals the sum of log F _ic and the negative log of IC₅₀ (pIC₅₀). Here, we measured F _ic's of remdesivir, favipiravir, and hydroxychloroquine in various cells and calculated their anti-SARS-CoV-2 EC₅₀'s. The predicted EC₅₀'s are close to the observed EC₅₀'s in vitro. When the lung concentrations of antiviral drugs are higher than the predicted EC₅₀'s in alveolar type 2 cells, the antiviral drugs inhibit virus replication in vivo, and vice versa. Overall, our results indicate that both in vitro and in vivo antiviral activities of drugs can be predicted by their intracellular bioavailability and biochemical activity without using virus. This virus-free strategy can help medicinal chemists and pharmacologists to screen antivirals during early drug discovery, especially for researchers who are not able to work in the high-level biosafety lab.

Favipiravir induces oxidative stress and genotoxicity in cardiac and skin cells

Favipiravir (T-705), used against influenza viruses, is approved for emergency use in many countries for the treatment of COVID-19. The frequent adverse effects of favipiravir are related with the gastrointestinal system, however, studies suggest a positive association of favipiravir on QTc prolongation, which can cause cardiotoxicity. Also, there are reports of skin reactions such as angioedema due to favipiravir. Despite the several adverse effects, studies examining the drug's effects at the molecular level are insufficient, e.g., the genotoxic and oxidative stress-inducing effects of favipiravir, which are among the primary mechanisms of drug-induced toxicity. The cytotoxicity of favipiravir was analyzed with the measurement of the ATP content in H9c2 cardiomyoblasts and CCD-1079Sk skin fibroblasts. The ATP level decreased starting from 200 µM. The inhibitory effect on the mitochondrial electron transport chain enzymes complex I and complex V was also evaluated where favipiravir showed significant enzyme inhibitory effects in the highest concentration studied. A molecular docking study evaluating the interaction between favipiravir-RTP and mitochondrial DNA polymerase (POLG1) was done. The relationship of favipiravir with oxidative stress was examined by measuring glutathione (GSH) and protein carbonyl levels which were observed higher after drug treatment compared to the control group. The genotoxicity study was done using the Comet assay and increase in DNA tail has been detected. Furthermore, 8-OHdG levels were measured higher in favipiravir treated cells indicating oxidative DNA damage. Favipiravir induced oxidative stress leading to DNA damage in cardiomyoblast cells and fibroblastic skin cells. Oxidative stress and DNA damage might eventually lead to organ-specific damage such as cardiotoxicity and dermal toxicity. Considering the increased use of favipiravir in recent years, and that oxidative stress and genotoxicity are two important indicators of drug-induced toxicity, the obtained results are worth attention.

Repurposing of Chemotherapeutics to Combat COVID-19

Severe acute respiratory syndrome corona virus 2 (SARS-CoV-2) is a novel strain of SARS coronavirus. The COVID-19 disease caused by this virus was declared a pandemic by the World Health Organization (WHO). SARS-CoV-2 mainly spreads through droplets sprayed by coughs or sneezes of the infected to a healthy person within the vicinity of 6 feet. It also spreads through asymptomatic carriers and has negative impact on the global economy, security and lives of people since 2019. Numerous lives have been lost to this viral infection; hence there is an emergency to build up a potent measure to combat SARS-CoV-2. In view of the non-availability of any drugs or vaccines at the time of its eruption, the existing antivirals, antibacterials, antimalarials, mucolytic agents and antipyretic paracetamol were used to treat the COVID-19 patients. Still there are no specific small molecule chemotherapeutics available to combat COVID-19 except for a few vaccines approved for emergency use only. Thus, the repurposing of chemotherapeutics with the potential to treat COVID-19 infected people is being used. The antiviral activity for COVID-19 and biochemical mechanisms of the repurposed drugs are being explored by the biological assay screening and structure-based in silico docking simulations. The present study describes the various US-FDA approved chemotherapeutics repositioned to combat COVID-19 along with their screening for biological activity, pharmacokinetic and pharmacodynamic evaluation.

A favipiravir-induced angioedema and urticaria in a COVID-19 patient

Although favipiravir is a promising drug for coronavirus disease 2019, some adverse effects, including skin lesions, have been reported. A 56-year-old female who was prescribed favipiravir by a filiation team following a positive severe acute respiratory syndrome coronavirus 2 polymerase chain reaction test presented to our hospital. After examination, favipiravir and paracetamol were prescribed. She represented to the hospital with facial swelling and itchy rashes on her forearm. Angioedema and urticaria were diagnosed. Favipiravir was discontinued. Steroid and antihistaminic therapy were administered for angioedema. To our knowledge, this is the first reported case of favipiravir-induced angioedema and urticaria in Turkey.

Favipiravir Treatment of Uncomplicated Influenza in Adults: Results of Two Phase 3, Randomized, Double-Blind, Placebo-Controlled Trials

BACKGROUND

We conducted double-blind, placebo-controlled trials assessing the efficacy and tolerability of favipiravir in acute influenza.

METHODS

Otherwise healthy adults with influenza-like symptoms and fever of ≤48 hours were randomized to favipiravir (1800 mg twice daily [BID] on day 1, 800 mg BID on days 2-5) or placebo tablets (1:1 in US316; 3:1 in US317). The primary efficacy endpoint was the time to illness alleviation when 6 influenza symptoms were self-rated as absent or mild and fever was absent in the intention-to-treat, influenza-infected participants.

RESULTS

In US316 (301 favipiravir, 322 placebo), favipiravir was associated with a 14.4-hour reduction (median, 84.2 vs 98.6 hours; P = .004) in time to illness alleviation vs placebo. In US317 (526 favipiravir, 169 placebo), favipiravir did not significantly reduce time to alleviation (median, 77.8 vs 83.9 hours). In both trials favipiravir was associated with reduced viral titers, RNA load area under the curve over days 1-5, and median times to cessation of virus detection (P < .001). Aside from asymptomatic hyperuricemia, no important differences in adverse events were found.

CONCLUSIONS

This favipiravir dosing regimen demonstrated significant antiviral efficacy but inconsistent illness alleviation in uncomplicated influenza. Studies of higher doses and antiviral combinations for treating serious influenza and other RNA viral infections are warranted. Clinical Trials Registration. NCT02026349; NCT02008344.

The Assessment of the Efficacy and Safety of Favipiravir for Patients with SARS-CoV-2 Infection: A Multicenter Non-randomized, Uncontrolled Single-arm Prospective Study

Objective Among treatment options for coronavirus infectious disease 2019 (COVID-19), well-studied oral medications are limited. We conducted a multicenter non-randomized, uncontrolled single-arm prospective study to assess the efficacy and safety of favipiravir for patients with COVID-19. Methods One hundred participants were sequentially recruited to 2 cohorts: cohort 1 (Day 1: 1,600 mg/day, Day 2 to 14: 600 mg/day, n=50) and cohort 2 (Day 1: 1,800 mg/day, Day 2 to 14: 800 mg/day, n=50). The efficacy endpoint was the negative conversion rate of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), and the odds ratio (OR) of cohort 2 to cohort 1 for negative conversion on Day 10 was calculated. Characteristics of all participants and profiles of adverse events (AEs) were collected and analyzed. Results The mean age of participants was 62.8±17.6 years old. Thirty-four patients (34.0%) experienced worsening pneumonia, 7 (7.0%) were intubated, and 4 (4.0%) died during the observation period. Cohort 2 showed a higher negative conversion rate than cohort 1 [adjusted OR 3.32 (95% confidence interval (CI), 1.17 to 9.38), p=0.024], and this association was maintained after adjusting for the age, sex, body mass index, and baseline C-reactive protein level. Regarding adverse events, hyperuricemia was most frequently observed followed by an elevation of the liver enzyme levels (all-grade: 49.0%, Grade ≥3: 12.0%), and cohort 2 tended to have a higher incidence than cohort 1. However, no remarkable association of adverse events was observed between patients <65 and ≥65 years old. Conclusion The antiviral efficacy of favipiravir was difficult to interpret due to the limitation of the study design. However, no remarkable issues with safety or tolerability associated with favipiravir were observed, even in elderly patients with COVID-19.

Antiviral Treatment Options for Severe Fever with Thrombocytopenia Syndrome Infections

Severe fever with thrombocytopenia syndrome virus (SFTSV) is a tick-borne virus that produces severe fever with thrombocytopenia syndrome (SFTS). It is widespread in Japan, South Korea, and Central and Eastern China. The epidemic has developed rapidly through China in recent years. SFTS cases have been reported in 25 provinces in China, mainly distributed in rural areas in mountainous and hilly areas. The infection has a high case fatality rate and no specific treatments or vaccinations. Therefore, early diagnosis and treatment of SFTS infection is important to survival and disease control. In this article, we provide an overview on different aspects of SFTS with an emphasis on management, to explore the current treatment and prophylactic measures further.

Effects of Vitamin C on the Oral-Nasal Mucosal Damage Caused by Favipiravir in Old and Young Rats

Background

Favipiravir was widely used to treat coronavirus disease 2019 (COVID-19) early in the pandemic. Later, many reports began to be published about the side effects of favipiravir on different tissues. However, the side effects of favipiravir on the oral and nasal mucosa remain unknown. This experimental study aimed to evaluate the pathological effects of favipiravir on the oral-nasal mucosa and investigate whether vitamin C (Vit C) reduces these lesions in old and young rats.

Methodology

A total of 100 rats were used for this study. The rats were administered favipiravir (20 mg/kg and 100 mg/kg) and Vit C (150 mg/kg/day) for 14 days. At the end of the study, rats were euthanatized, and oral-nasal mucosal histopathological changes were evaluated. Nuclear factor kappa-ligand (RANKL) and caspase-3 expressions were immunohistochemically examined.

Results

Favipiravir caused severe lesions in old rats compared to young, and the severity of the lesions increased with the dosage. Severe hyperemia and erosive-ulcerative lesions were observed in the oral-nasal mucosa. In addition, increased RANKL and caspase-3 expressions were observed in a dose-dependent manner. In both young and old groups, Vit C treatment showed decreased caspase-3 and RANKL expression; a more prominent decrease was seen in young rats.

Conclusions

This study showed that favipiravir could cause histopathological lesions in the oral and nasal mucosa. However, the administration of Vit C with favipiravir can provide a protective effect against this damage. The curative effect of Vit C was more pronounced in young rats and at low doses.

Analysis of the responsible site for favipiravir resistance in RNA-dependent RNA polymerase of influenza virus A/PR/8/34 (H1N1) using site-directed mutagenesis

Favipiravir (T-705, 6-fluoro-3-hydroxy-2-pyrazinecarboxamide) selectively and strongly inhibits the replication of influenza virus in vitro and in vivo. Favipiravir is converted to favipiravir-4-ribofuranosyl-5-triphosphate (favipiravir RTP) by intracellular enzymes and functions as a nucleotide analog to selectively inhibit RNA-dependent RNA polymerase (RdRP) of influenza virus. Our previous experiments failed in an attempt to obtain a favipiravir-resistant influenza virus in vitro using influenza virus A/PR/8/34(H1N1). Conversely, Goldhill et al. reported a favipiravir-resistant influenza virus generated by in vitro passage of influenza virus A/England/195/2009 (H1N1), an early isolate from the 2009 H1N1 pandemic (pdm09), in the presence of favipiravir with K229R mutation in PB1. This study focused on K229R mutation near the NTP cross-linked region in PB1 based on the above conflicting findings to confirm whether K229R mutation brings favipiravir resistance to influenza virus A/PR/8/34. Thirty PB1 mutants generated by site-directed mutagenesis of the NTP cross-linked region were evaluated using an influenza virus A/PR/8/34 replicon system. Among the 30 mutants, 10 possessed but 20 lost replicon activity. When susceptibility to favipiravir in 10 mutants was further assessed, the PB1 E491D mutant was five times more sensitive than the wild-type (WT), while only the PB1 K229R mutant was resistant to favipiravir. Results suggested that the evaluated region was essential for polymerase activity, and K229 mutation was responsible for polymerase inhibition of favipiravir in the influenza virus A/PR/8/34. Interestingly, the tested K229X series mutants entirely lost replicon activity, except for K229R. This suggested that the amino acid at position 229 in PB1 of influenza virus may play a pivotal role in polymerase activity. Moreover, this lysine residue is highly conserved among positive- and negative-sense single-stranded RNA viruses, in which favipiravir showed potent activity, suggesting that this mutation may determine the characterization of the in vitro broad-spectrum activity of favipiravir. Additionally, this mutation acquisition greatly influences the viral replication and the susceptibility to favipiravir.

Comparison of trace element (selenium, iron), electrolyte (calcium, sodium), and physical activity levels in COVID-19 patients before and after the treatment

OBJECTIVE

Severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2), a worldwide health problem, is the cause of 2019 coronavirus disease. This study aimed to compare the trace element (selenium and iron), electrolyte (calcium and sodium), and physical activity levels of COVID-19 patients before and after COVID-19 treatment.

METHOD

This prospective study was conducted in patients diagnosed with COVID-19 (n = 15). Trace element (selenium and iron), electrolyte (calcium and sodium), and physical activity levels of the patients were compared before and after the treatment.

RESULT

Most of patients had selenium deficiency (86.7 %), iron deficiency (73.3 %), calcium deficiency (66.7 %) and sodium deficiency (46.7 %) before COVID-19 treatment. The most important improvements were seen in iron deficiency (from 73.3 % to 26.7 %) and sodium deficiency (from 46.7 % to 13.3 %) after the treatment. Selenium, iron, calcium, and sodium levels of the patients were significantly higher after the treatment (p < 0.05). The patients had low physical activity before and after COVID-19 treatment. In addition, no statistically significant difference was found in the comparison of physical activity levels (p > 0.05).

CONCLUSION

This study indicated that selenium, iron, calcium, and sodium levels and deficiencies might improve after treating patients with COVID-19. However, the results of this study showed that the physical activity levels of COVID-19 patients might remain stable and low throughout the treatment process.

The Efficacy of Aprotinin Combinations with Selected Antiviral Drugs in Mouse Models of Influenza Pneumonia and Coronavirus Infection Caused by SARS-CoV-2

The efficacy of aprotinin combinations with selected antiviral-drugs treatment of influenza virus and coronavirus (SARS-CoV-2) infection was studied in mice models of influenza pneumonia and COVID-19. The high efficacy of the combinations in reducing virus titer in lungs and body weight loss and in increasing the survival rate were demonstrated. This preclinical study can be considered a confirmatory step before introducing the combinations into clinical assessment.

Keeping up with the COVID's-Could siRNA-based antivirals be a part of the answer?

Coronavirus disease 2019 (COVID-19) is a highly contagious viral disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). This deadly infection has resulted in more than 5.2 million deaths worldwide. The global rollout of COVID-19 vaccines has without doubt saved countless lives by reducing the severity of symptoms for patients. However, as the virus continues to evolve, there is a risk that the vaccines and antiviral designed to target the infection will no longer be therapeutically viable. Furthermore, there remain fears over both the short and long-term side effects of repeat exposure to currently available vaccines. In this review, we discuss the pros and cons of the vaccine rollout and promote the idea of a COVID medicinal toolbox made up of different antiviral treatment modalities, and present some of the latest therapeutic strategies that are being explored in this respect to try to combat the COVID-19 virus and other COVID viruses that are predicted to follow. Lastly, we review current literature on the use of siRNA therapeutics as a way to remain adaptable and in tune with the ever-evolving mutation rate of the COVID-19 virus.

Antiviral therapy for COVID-19: Derivation of optimal strategy based on past antiviral and favipiravir experiences

Favipiravir, a broad-spectrum RNA-dependent RNA polymerase inhibitor, inhibits the replication of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) at significantly lower concentrations than the plasma trough levels achieved by the dosage adopted for influenza treatment and exhibits efficacy against coronavirus disease 2019 (COVID-19) pneumonia. Although high doses of favipiravir are required due to the molecule being a purine analog, its conversion into the active form in infected cells with active viral RNA synthesis enhances the antiviral specificity and selectivity as a chain terminator with lethal mutagenesis. Another characteristic feature is the lack of generation of favipiravir-resistant virus. COVID-19 pneumonia is caused by strong cell-mediated immunity against virus-infected cells, and the inflammatory response induced by adaptive immunity continues to peak for 3 to 5 days despite antiviral treatment. This has also been observed in herpes zoster (HZ) and cytomegalovirus (CMV) pneumonia. Inflammation due to an immune response may mask the effectiveness of favipiravir against COVID-19 pneumonia. Favipiravir significantly shortened the recovery time in patients with mild COVID-19 pneumonia by 3 days with the start of treatment by the 5th day of symptom onset. Since both CMV and COVID-19 pneumonia are caused by adaptive immunity and prevention of cytomegalovirus pneumonia is the standard treatment due to difficulties in treating refractory CMV pneumonia, COVID-19 pneumonia should be prevented with early treatment as well. In the present study, we have comprehensively reviewed the optimal antiviral therapy for COVID-19 based on clinical trials of favipiravir for the treatment of COVID-19 pneumonia and the concurrently established therapies for other viral infections, particularly HZ and CMV pneumonia. Optimally, antivirals should be administered immediately after COVID-19 diagnosis, similar to that after influenza diagnosis, to prevent COVID-19 pneumonia and complications resulting from microangiopathy.

Inhibition of influenza virus replication by Apiaceae plants, with special reference to Peucedanum japonicum (Sacna) constituents

ETHNOPHARMACOLOGICAL RELEVANCE

Apiaceae plants possess various pharmacological properties, such as antimicrobial, antioxidant, hypoglycemic, hypolipidemic, anxiolytic, analgesic, anti-inflammatory, anti-convulsant, and anti-cancer activities; however, data on their antiviral activity are limited. Peucedanum japonicum, also known as Sacna, is a plant used as food and as a traditional folk medicine for treating coughs. However, the active components in the leaves of this plant are yet unexplored.

AIM OF THE STUDY

To assess Apiaceae plants, especially Peucedanum japonicum, with anti-viral activity, and the function and antiviral potential of Sacna constituents, considering the emergence of influenza virus strains resistant to the currently available drugs.

MATERIALS AND METHODS

We prepared grinds of the freeze-dried leaves and roots of the Apiaceae family and the hot water extracts. The antiviral activities of the extracts were determined by focus formation reduction assay. In the time-of-addition assay, the test medium containing Sacna extract at 2 mg/mL was added at -1 to 0 h (adsorption) or from 0 to 4, 4 to 8, or 0 to 8 h (replication). The Sacna extract was separated by reversed-phase flash column chromatography using an Isolera Spektra system. The antiviral activity of each fraction was then determined using the focus formation reduction assay. The active fraction was analyzed using an LC20ADXR high performance liquid chromatography system equipped with a microTOF-QII quadrupole time-of-flight tandem mass spectrometer.

RESULTS

All examined extracts of Apiaceae plants showed anti-influenza activity. Sacna extract most strongly inhibited the replication of influenza viruses. Individual components of Sacna possess antiviral activities against the influenza A/PR/8/34 virus. Sacna was found to inhibit the multiplication of A (H1N1 and H3N2) types and B types of influenza viruses, including amantadine-resistant and oseltamivir-resistant viruses. Sacna also inhibited influenza infection during viral replication. However, Sacna did not inhibit influenza infection during cell adsorption and did not suppress hemagglutination inhibition or cell fusion. Further, our findings suggest that the antiviral compounds in Sacna include flavonoids (quercetin and luteolin) and other polyphenols (caffeic acid, hymecromone, and umbelliferone). Although several effective compounds in Sacna inhibit multiple steps of viral replication, caffeic acid, which was increased by heat treatment at the time of extraction, significantly inhibited only the late period of viral growth, similar to the Sacna extract, indicating that it is the major component responsible for the antiviral activity of Sacna.

CONCLUSIONS

Apiaceae plants possess antiviral activity. Caffeic acid is the major component responsible for the antiviral activity of Sacna. To our knowledge, this is the first report regarding the anti-influenza virus activity of Sacna. Overall, these results indicate that Sacna has potential as a novel treatment against influenza A and B viruses.

Influenza antivirals and animal models

Influenza A and B viruses are among the most prominent human respiratory pathogens. About 3-5 million severe cases of influenza are associated with 300 000-650 000 deaths per year globally. Antivirals effective at reducing morbidity and mortality are part of the first line of defense against influenza. FDA-approved antiviral drugs currently include adamantanes (rimantadine and amantadine), neuraminidase inhibitors (NAI; peramivir, zanamivir, and oseltamivir), and the PA endonuclease inhibitor (baloxavir). Mutations associated with antiviral resistance are common and highlight the need for further improvement and development of novel anti-influenza drugs. A summary is provided for the current knowledge of the approved influenza antivirals and antivirals strategies under evaluation in clinical trials. Preclinical evaluations of novel compounds effective against influenza in different animal models are also discussed.

The Prognostic Significance of C-Reactive Protein to Albumin Ratio in Patients With Severe Fever With Thrombocytopenia Syndrome

Background

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease with the high case-fatality rate, lacking effective therapies and vaccines. Inflammation-based indexes have been widely used to predict the prognosis of patients with cancers and some inflammatory diseases. In our study, we aim to explore the predictive value of the inflammation-based indexes in SFTS patients.

Methods

We retrospectively analyzed 82 patients diagnosed with SFTS. The inflammation-based indexes, including neutrophil-to-lymphocyte ratio (NLR), monocyte-to-lymphocyte ratio (MLR), platelet-to-lymphocyte ratio (PLR), systemic immune-inflammation index (SII), systemic inflammation response index (SIRI), aggregate index of systemic inflammation (AISI) and C-reactive protein to albumin ratio (CAR), were compared between the survival and death patients. Receiver operating characteristic (ROC) curves were used to compare the predictive ability of MLR, AISI, and CAR. The survival analysis was based on the Kaplan–Meier (KM) method. Multivariate logistic regression analysis was used to analyze the independent risk factors of poor prognosis in patients with SFTS.

Results

The CAR is higher in the death group while MLR and AISI were higher in the survival group. The ROC curve analysis indicated CAR exhibited more predictive value than the other indexes and the optimal cut-off value of CAR was equal to or greater than 0.14. KM survival curve showed that higher CAR was significantly correlated to the lower overall survival in SFTS patients. Multivariate logistic regression analysis indicated that CAR was an independent risk factor for poor prognosis in patients with SFTS.

Conclusion

The CAR is an independent risk factor for death in patients with SFTS and could predict the poor prognosis of SFTS patients. It could be used as a biomarker to help physicians to monitor and treat patients more aggressively to improve clinical prognosis.

Evaluation of favipiravir in the treatment of COVID-19 based on the real-world

BACKGROUND

The role of favipiravir (FVP) as a COVID-19 treatment is recognized but not fully elucidated. We aimed to evaluate whether FVP has definite clinical efficacy and safety in the treatment of COVID-19.

METHODS

International and Chinese databases were searched for randomized controlled clinical trials evaluating FVP for the treatment of COVID-19. A meta-analysis was performed and published literature was synthesized to evaluate the corresponding therapeutic effects.

RESULTS

We included 13 studies (1430 patients in total). Meta-analysis showed that patients with mild-to-moderate disease treated with FVP had a significantly higher viral clearance rate than those in the control group 10 and 14 days after initiation of treatment [RR: 1.13 (95% CI: 1.00, 1.28), P = 0.04; I² = 39% for day 10 and RR: 1.16 (95% CI: 1.04, 1.30), P = 0.008; I² = 38% for day 14] and a significantly shorter hospital stay [MD: -1.52 (95% CI: -2.82, -0.23), P = 0.02; I² = 0%].

CONCLUSIONS

FVP significantly promotes viral clearance and reduces the hospitalization duration in mild-to-moderate COVID-19 patients, which can reduce the risk of severe disease outcomes in patients. However, more importantly, the results showed no benefit of FVP in severe patients, and caution should be taken regarding the treatment options of FVP in severe patients.

Favipiravir and Its Structural Analogs: Antiviral Activity and Synthesis Methods

1,4-Pyrazine-3-carboxamide-based antiviral compounds have been under intensive study for the last 20 years. One of these compounds, favipiravir (6-fluoro-3-hydroxypyrazine-2-carboxamide, T-705), is approved for use against the influenza infection in a number of countries. Now, favipiravir is being actively used against COVID-19. This review describes the in vivo metabolism of favipiravir, the mechanism of its antiviral activity, clinical findings, toxic properties, and the chemical synthesis routes for its production. We provide data on the synthesis and antiviral activity of structural analogs of favipiravir, including nucleosides and nucleotides based on them.

Effective Drugs Against Severe Fever With Thrombocytopenia Syndrome Virus in an in vitro Model

Background

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging tick-borne infectious disease caused by the SFTS virus (SFTSV). This syndrome is endemic in China, South Korea, and Japan, with a fatality rate of approximately 20–30%. Although the World Health Organization has listed SFTS as a disease that requires urgent steps for the development of its treatment, no treatments are available.

Methods

We analyzed the antiviral activity of 41 drugs against the SFTSV to explore potential therapeutic candidates using real-time reverse transcription-polymerase chain reaction and plaque assay in vitro.

Results

Peramivir, nitazoxanide, and favipiravir were found to have inhibitory effects on the SFTSV at concentrations below the maximum plasma concentration (Cmax). The concentrations that inhibited the SFTSV by 50% were as follows: peramivir, half maximal effective concentration (EC₅₀) 12.9 μg/mL; nitazoxanide, EC₅₀ 0.57 μg/mL; and favipiravir, EC₅₀ 4.14 μg/mL.

Conclusion

The effects of peramivir and nitazoxanide on the SFTSV were identified for the first time in this study. Future studies need to include animal models of SFTSV infection, clinical trials including dose-ranging trials, and evaluation of combination therapy with other potential antivirals.

Severe fever with thrombocytopenia syndrome, a viral hemorrhagic fever, endemic to Japan: achievements and directions to the future in the scientific and medical research

A novel infectious disease, severe fever with thrombocytopenia syndrome (SFTS) caused by a novel bunyavirus, with high case fatality rate (CFR) was reported by Chinese scientists in 2011. The causative virus, Dabie bandavirus [former SFTS virus (SFTSV)] belonged to the Bandavirus genus (former Phlebovirus genus) of Phenuiviridae family (former Bunyaviridae family). SFTS was also reported to be endemic to South Korea and Japan in 2013. Humans are infected with SFTSV through bites by ticks such as Haemophysalis longicornis and Amblyomma testidinarium. However, it was reported that domesticated animals such as cats and dogs were also infected with SFTSV probably through tick bites in living environment and show the SFTS-like symptoms with high CFR. Furthermore, there have been the cases of SFTS patients, who were infected with SFTSV through close contacts with sick cats or dogs. The high CFR in patients with SFTS is approximately 30% in Japan. SFTSV is circulating in nature between some species of ticks and animals. There are always the risks of SFTSV infection for human populations living in the endemic areas. Therefore, development of specific therapies and vaccines is an urgent need to reduce the number of fatal SFTS patients.

Pleiotropic Effects of Influenza H1, H3, and B Baloxavir-Resistant Substitutions on Replication, Sensitivity to Baloxavir, and Interferon Expression

Baloxavir is an anti-influenza endonuclease inhibitor that targets the polymerase acidic (PA) protein of influenza A and B viruses. Our knowledge regarding the pleiotropic effects of baloxavir resistance-associated substitutions is limited. We generated recombinant A/California/04/09 (H1N1)-, A/Hong Kong/218849/2006 (H3N2)-, and B/Victoria/504/2000-like viruses that contained PA substitutions identified in baloxavir clinical trials and surveillance that could potentially be associated with baloxavir resistance. We characterized their susceptibility to baloxavir, impact on polymerase activity, viral growth, and ability to induce interferon (IFN) and IFN-stimulated genes expression in vitro. Four PA substitutions, H1N1 I38L/T, E199D, and B G199R, significantly reduced the sensitivity of the recombinant viruses to baloxavir (14.1-fold). We confirmed our findings by using the luciferase-based ribonucleoprotein minigenome assay and by using virus yield reduction assay in Calu-3 and normal human bronchial epithelial (NHBE) cells. We observed that I38L and E199D resulted in decreased viral replication of the H1N1 wild-type virus (1.4-fold) but the H1N1 I38T and B G199R substitutions did not significantly alter replication capacity in Calu-3 cells. In addition, H1N1 variants with PA I38L/T and E199D induced significantly higher levels of IFNB1 gene expression compared to the wild-type virus (4.2-fold). In contrast, the B variant, G199R, triggered the lowest levels of IFN genes in Calu-3 cells (1.6-fold). Because baloxavir is a novel anti-influenza therapeutic agent, identifying and characterizing substitutions associated with reduced sensitivity to baloxavir, as well as the impact of these substitutions on viral fitness, is paramount to the strategic implementation of this novel countermeasure.

Approaches for discovery of small-molecular antivirals targeting to influenza A virus PB2 subunit

Influenza is an acute respiratory infectious disease caused by influenza virus, leading to huge morbidity and mortality in humans worldwide. Despite the availability of antivirals in the clinic, the emergence of resistant strains calls for antivirals with novel mechanisms of action. The PB2 subunit of the influenza A virus polymerase is a promising target because of its vital role in the 'cap-snatching' mechanism. In this review, we summarize the technologies and medicinal chemistry strategies for hit identification, hit-to-lead and lead-to-candidate optimization, and current challenges in PB2 inhibitor development, as well as offering insights for the fight against drug resistance.

Favipiravir in the Battle with Respiratory Viruses

Abstract:

Among antiviral drugs, the vast majority targets only one or two related viruses. The conventional model, one virus - one drug, significantly limits therapeutic options. Therefore, in the strategy of controlling viral infections, there is a necessity to develop compounds with pleiotropic effects. Favipiravir (FPV) emerged as a strong candidate to become such a drug. The aim of the study is to present up-to-date information on the role of favipiravir in the treatment of viral respiratory infections. The anti-influenza activity of favipiravir has been confirmed in cell culture experiments, animal models and clinical trials. Thoroughly different - from the previously registered drugs - mechanism of action suggests that FVP can be used as a countermeasure for the novel or re-emerging influenza virus infections. In recent months, favipiravir has been broadly investigated due to its potential efficacy in the treatment of Covid-19. Based on preclinical and clinical studies and a recently published meta-analysis it seems that favipiravir may be a promising antiviral drug in the treatment of patients with Covid-19. FPV is also effective against other RNA respiratory viruses and may be a candidate for the treatment of serious infections caused by human rhinovirus, respiratory syncytial virus, metapneumovirus, parainfluenza viruses and hantavirus pulmonary syndrome.

Detailed Analyses of Molecular Interactions between Favipiravir and RNA Viruses In Silico

There are currently no antiviral agents for human metapneumovirus (HMPV), respiratory syncytial virus (RSV), mumps virus (MuV), or measles virus (MeV). Favipiravir has been developed as an anti-influenza agent, and this agent may be effective against these viruses in vitro. However, the molecular mechanisms through which the agent affects virus replication remain to be fully elucidated. Thus, to clarify the detailed molecular interactions between favipiravir and the RNA-dependent RNA polymerase (RdRp) of HMPV, RSV, MuV, MeV, and influenza virus, we performed in silico studies using authentic bioinformatics technologies. As a result, we found that the active form of favipiravir (favipiravir ribofuranosyl-5′-triphosphate [F-RTP]) can bind to the RdRp active sites of HMPV, RSV, MuV, and MeV. The aspartic acid residue of RdRp active sites was involved in the interaction. Moreover, F-RTP was incorporated into the growing viral RNA chain in the presence of nucleotide triphosphate and magnesium ions. The results suggested that favipiravir shows two distinct mechanisms in various viruses: RdRp active site inhibition and/or genome replication inhibition.

Unveiling of Pyrimidindinones as Potential Anti-Norovirus Agents-A Pharmacoinformatic-Based Approach

The RNA-dependent RNA polymerase (RdRp) receptor is an attractive target for treating human norovirus (HNV). A computer-aided approach like e-pharmacophore, molecular docking, and single point energy calculations were performed on the compounds retrieved from the Development Therapeutics Program (DTP) AIDS Antiviral Screen Database to identify the antiviral agent that could target the HNV RdRp receptor. Induced-fit docking (IFD) results showed that compounds ZINC1617939, ZINC1642549, ZINC6425208, ZINC5887658 and ZINC32068149 bind with the residues in the active site-B of HNV RdRp receptor via hydrogen bonds, salt bridge, and electrostatic interactions. During the molecular dynamic simulations, compounds ZINC6425208, ZINC5887658 and ZINC32068149 displayed an unbalanced backbone conformation with HNV RdRp protein, while ZINC1617939 and ZINC1642549 maintained stability with the protein backbone when interacting with the residues. Hence, the two new concluding compounds discovered by the computational approach can be used as a chemotype to design promising antiviral agents aimed at HNV RdRp.

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.

Identification and Development of Therapeutics for COVID-19

After emerging in China in late 2019, the novel coronavirus severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spread worldwide, and as of mid-2021, it remains a significant threat globally. Only a few coronaviruses are known to infect humans, and only two cause infections similar in severity to SARS-CoV-2: Severe acute respiratory syndrome-related coronavirus, a species closely related to SARS-CoV-2 that emerged in 2002, and Middle East respiratory syndrome-related coronavirus, which emerged in 2012. Unlike the current pandemic, previous epidemics were controlled rapidly through public health measures, but the body of research investigating severe acute respiratory syndrome and Middle East respiratory syndrome has proven valuable for identifying approaches to treating and preventing novel coronavirus disease 2019 (COVID-19). Building on this research, the medical and scientific communities have responded rapidly to the COVID-19 crisis and identified many candidate therapeutics. The approaches used to identify candidates fall into four main categories: adaptation of clinical approaches to diseases with related pathologies, adaptation based on virological properties, adaptation based on host response, and data-driven identification (ID) of candidates based on physical properties or on pharmacological compendia. To date, a small number of therapeutics have already been authorized by regulatory agencies such as the Food and Drug Administration (FDA), while most remain under investigation. The scale of the COVID-19 crisis offers a rare opportunity to collect data on the effects of candidate therapeutics. This information provides insight not only into the management of coronavirus diseases but also into the relative success of different approaches to identifying candidate therapeutics against an emerging disease. IMPORTANCE The COVID-19 pandemic is a rapidly evolving crisis. With the worldwide scientific community shifting focus onto the SARS-CoV-2 virus and COVID-19, a large number of possible pharmaceutical approaches for treatment and prevention have been proposed. What was known about each of these potential interventions evolved rapidly throughout 2020 and 2021. This fast-paced area of research provides important insight into how the ongoing pandemic can be managed and also demonstrates the power of interdisciplinary collaboration to rapidly understand a virus and match its characteristics with existing or novel pharmaceuticals. As illustrated by the continued threat of viral epidemics during the current millennium, a rapid and strategic response to emerging viral threats can save lives. In this review, we explore how different modes of identifying candidate therapeutics have borne out during COVID-19.

DFT and MD simulation investigation of favipiravir as an emerging antiviral option against viral protease (3CLpro) of SARS-CoV-2

As per date, around 20 million COVID-19 cases reported from across the globe due to a tiny 125 nm sized virus: SARS-CoV-2 which has created a pandemic and left an unforgettable impact on our world. Besides vaccine, medical community is in a race to identify an effective drug, which can fight against this disease effectively. Favipiravir (F) has recently attracted too much attention as an effective repurposed drug against COVID-19. In the present study, the pertinency of F has been tested as an antiviral option against viral protease (3CL^pro) of SARS-CoV-2 with the help of density functional theory (DFT) and MD Simulation. Different electronic properties of F such as atomic charges, molecular electrostatic properties (MEP), chemical reactivity and absorption analysis have been studied by DFT. In order to understand the interaction and stability of inhibitor F against viral protease, molecular docking and MD simulation have been performed. Various output like interaction energies, number of intermolecular hydrogen bonding, binding energy etc. have established the elucidate role of F for the management of CoV-2 virus for which there is no approved therapies till now. Our findings highlighted the need to further evaluate F as a potential antiviral against SARS-CoV-2.