Glycosylated diphyllin as a broad-spectrum antiviral agent against Zika virus

Bioactive atropisomers: Unraveling design strategies and synthetic routes for drug discovery

Atropisomerism, an expression of axial chirality caused by limited bond rotation, is a prominent aspect within the field of medicinal chemistry. It has been shown that atropisomers of a wide range of compounds, including established FDA-approved drugs and experimental molecules, display markedly different biological activities. The time-dependent reversal of chirality in atropisomers poses complexity and obstacles in the process of drug discovery and development. Nonetheless, recent progress in understanding atropisomerism and enhanced characterization methods have greatly assisted medicinal chemists in the effective development of atropisomeric drug molecules. This article provides a comprehensive review of their special design thoughts, synthetic routes, and biological activities, serving as a reference for the synthesis and biological evaluation of bioactive atropisomers in the future.

The Dynamic Landscape of Capsid Proteins and Viral RNA Interactions in Flavivirus Genome Packaging and Virus Assembly

The Flavivirus genus of the Flaviviridae family of enveloped single-stranded RNA viruses encompasses more than 70 members, many of which cause significant disease in humans and livestock. Packaging and assembly of the flavivirus RNA genome is essential for the formation of virions, which requires intricate coordination of genomic RNA, viral structural, and nonstructural proteins in association with virus-induced, modified endoplasmic reticulum (ER) membrane structures. The capsid (C) protein, a small but versatile RNA-binding protein, and the positive single-stranded RNA genome are at the heart of the elusive flavivirus assembly process. The nucleocapsid core, consisting of the genomic RNA encapsidated by C proteins, buds through the ER membrane, which contains viral glycoproteins prM and E organized as trimeric spikes into the lumen, forming an immature virus. During the maturation process, which involves the low pH-mediated structural rearrangement of prM and E and furin cleavage of prM in the secretory pathway, the spiky immature virus with a partially ordered nucleocapsid core becomes a smooth, mature virus with no discernible nucleocapsid. This review focuses on the mechanisms of genome packaging and assembly by examining the structural and functional aspects of C protein and viral RNA. We review the current lexicon of critical C protein features and evaluate interactions between C and genomic RNA in the context of assembly and throughout the life cycle.

Insights into Zika Virus Pathogenesis and Potential Therapeutic Strategies

Zika virus (ZIKV) has emerged as a significant public health threat, reaching pandemic levels in 2016. Human infection with ZIKV can manifest as either asymptomatic or as an acute illness characterized by symptoms such as fever and headache. Moreover, it has been associated with severe neurological complications in adults, including Guillain-Barre syndrome, and devastating fetal abnormalities, like microcephaly. The primary mode of transmission is through Aedes spp. mosquitoes, and with half of the world's population residing in regions where Aedes aegypti, the principal vector, thrives, the reemergence of ZIKV remains a concern. This comprehensive review provides insights into the pathogenesis of ZIKV and highlights the key cellular pathways activated upon ZIKV infection. Additionally, we explore the potential of utilizing microRNAs (miRNAs) and phytocompounds as promising strategies to combat ZIKV infection.

Bioactivities and Mechanisms of Action of Diphyllin and Its Derivatives: A Comprehensive Systematic Review

Natural products are treasure houses for modern drug discovery. Diphyllin is a natural arylnaphthalene lignan lactone isolated from the leaf of Astilboides tabularis. Studies have found that it possesses plenty of bioactivity characteristics. In this paper, we reviewed the structure, bioactivity, and mechanism of action of diphyllin and its derivatives. The references were obtained from PubMed, Web of Science, and Science Direct databases up to August 2023. Papers without a bio-evaluation were excluded. Diphyllin and its derivatives have demonstrated V-ATPase inhibition, anti-tumor, anti-virus, anti-biofilm, anti-inflammatory, and anti-oxidant activities. The most studied activities of diphyllin and its derivatives are V-ATPase inhibition, anti-tumor activities, and anti-virus activities. Furthermore, V-ATPase inhibition activity is the mechanism of many bioactivities, including anti-tumor, anti-virus, and anti-inflammatory activities. We also found that the galactosylated modification of diphyllin is a common phenomenon in plants, and therefore, galactosylated modification is applied by researchers in the laboratory to obtain more excellent diphyllin derivatives. This review will provide useful information for the development of diphyllin-based anti-tumor and anti-virus compounds.

Untargeted-based metabolomics analysis and in vitro/in silico antiviral activity of extracts from Phyllanthus brasiliensis (Aubl.) Poir

INTRODUCTION

This study describes the molecular profile and the potential antiviral activity of extracts from Phyllanthus brasiliensis, a plant widely found in the Brazilian Amazon. The research aims to shed light on the potential use of this species as a natural antiviral agent.

METHODS

The extracts were analysed using liquid chromatography-mass spectrometry (LC-MS) system, a potent analytical technique to discover drug candidates. In the meantime, in vitro antiviral assays were performed against Mayaro, Oropouche, Chikungunya, and Zika viruses. In addition, the antiviral activity of annotated compounds was predicted by in silico methods.

RESULTS

Overall, 44 compounds were annotated in this study. The results revealed that P. brasiliensis has a high content of fatty acids, flavones, flavan-3-ols, and lignans. Furthermore, in vitro assays revealed potent antiviral activity against different arboviruses, especially lignan-rich extracts against Zika virus (ZIKV), as follows: methanolic extract from bark (MEB) [effective concentration for 50% of the cells (EC50 ) = 0.80 μg/mL, selectivity index (SI) = 377.59], methanolic extract from the leaf (MEL) (EC50  = 0.84 μg/mL, SI = 297.62), and hydroalcoholic extract from the leaf (HEL) (EC50  = 1.36 μg/mL, SI = 735.29). These results were supported by interesting in silico prediction, where tuberculatin (a lignan) showed a high antiviral activity score.

CONCLUSIONS

Phyllanthus brasiliensis extracts contain metabolites that could be a new kick-off point for the discovery of candidates for antiviral drug development, with lignans becoming a promising trend for further virology research.

Structural and Synthetic Aspects of Small Ring Oxa- and Aza-Heterocyclic Ring Systems as Antiviral Activities

Antiviral properties of different oxa- and aza-heterocycles are identified and properly correlated with their structural features and discussed in this review article. The primary objective is to explore the activity of such ring systems as antiviral agents, as well as their synthetic routes and biological significance. Eventually, the structure-activity relationship (SAR) of the heterocyclic compounds, along with their salient characteristics are exhibited to build a suitable platform for medicinal chemists and biotechnologists. The synergistic conclusions are extremely important for the introduction of a newer tool for the future drug discovery program.

Specialized metabolites from plants as a source of new multi-target antiviral drugs: a systematic review

Viral infections have always been the main global health challenge, as several potentially lethal viruses, including the hepatitis virus, herpes virus, and influenza virus, have affected human health for decades. Unfortunately, most licensed antiviral drugs are characterized by many adverse reactions and, in the long-term therapy, also develop viral resistance; for these reasons, researchers have focused their attention on investigating potential antiviral molecules from plants. Natural resources indeed offer a variety of specialized therapeutic metabolites that have been demonstrated to inhibit viral entry into the host cells and replication through the regulation of viral absorption, cell receptor binding, and competition for the activation of intracellular signaling pathways. Many active phytochemicals, including flavonoids, lignans, terpenoids, coumarins, saponins, alkaloids, etc., have been identified as potential candidates for preventing and treating viral infections. Using a systematic approach, this review summarises the knowledge obtained to date on the in vivo antiviral activity of specialized metabolites extracted from plant matrices by focusing on their mechanism of action.

Identification of desoxyrhapontigenin as a novel antiviral agent against congenital Zika virus infection

Zika virus (ZIKV) infection arises as a global health threat owing to its association with Guillain-Barre syndrome and microcephaly in adults and fetuses since the most recent epidemics. Although extraordinary efforts have been underway globally to identify safe and effective treatments for ZIKV, therapeutic progressions seem to remain stagnant, especially for treating congenital ZIKV infection. Bio-compounds from medicinal plants evolutionarily optimized as drug-like molecules offer eligible sources of pharmaceuticals and lead drugs to fight against viral infections. Here, we identified desoxyrhapontigenin (DES), a naturally occurring bioactive product, as the strongest inhibitory compound against ZIKV infection among six conventional polyphenols in vitro. We also leveraged the trophoblast cell line, human trophoblast stem cells, and complex placental organoid models to provide solid evidence to support the anti-ZIKV bioactivity of DES. Notably, DES treatment effectively reduced the ZIKV burden in serum and target tissues, and correspondingly improved ZIKV-induced pathologic changes including weight loss, tissue inflammation, cell apoptosis, and adverse pregnancy outcomes, while it did not lead to obvious toxicity in both adult and pregnant mice. Furthermore, mechanistic studies revealed that DES could suppress ZIKV entry via dual mechanisms of direct targeting ZIKV E proteins and downregulating putative ZIKV receptors. These findings elucidate a previously unappreciated protective role of desoxyrhapontigenin against ZIKV infection both in vitro and in vivo, which shed light on the development of a novel and potent treatment for congenital ZIKV infection.

Novel Therapeutic Nutrients Molecules That Protect against Zika Virus Infection with a Special Note on Palmitoleate

Zika virus (ZIKV) is a Flavivirus from the Flaviviridae family and a positive-sense single strand RNA virus. ZIKV infection can cause a mild infection to the mother but can be vertically transmitted to the developing fetus, causing congenital anomalies. The prevalence of ZIKV infections was relatively insignificant with sporadic outbreaks in the Asian and African continents until 2006. However, recent epidemic in the Caribbean showed significant increased incidence of Congenital Zika Syndrome. ZIKV infection results in placental pathology which plays a crucial role in disease transmission from mother to fetus. Currently, there is no Food and Drug Administration (FDA) approved vaccine or therapeutic drug against ZIKV. This review article summarizes the recent advances on ZIKV transmission and diagnosis and reviews nutraceuticals which can protect against the ZIKV infection. Further, we have reviewed recent advances related to the novel therapeutic nutrient molecules that have been shown to possess activity against Zika virus infected cells. We also review the mechanism of ZIKV-induced endoplasmic reticulum and apoptosis and the protective role of palmitoleate (nutrient molecule) against ZIKV-induced ER stress and apoptosis in the placental trophoblasts.

Contemporary exploitation of natural products for arthropod-borne pathogen transmission-blocking interventions

An integrated approach to innovatively counter the transmission of various arthropod-borne diseases to humans would benefit from strategies that sustainably limit onward passage of infective life cycle stages of pathogens and parasites to the insect vectors and vice versa. Aiming to accelerate the impetus towards a disease-free world amid the challenges posed by climate change, discovery, mindful exploitation and integration of active natural products in design of pathogen transmission-blocking interventions is of high priority. Herein, we provide a review of natural compounds endowed with blockade potential against transmissible forms of human pathogens reported in the last 2 decades from 2000 to 2021. Finally, we propose various translational strategies that can exploit these pathogen transmission-blocking natural products into design of novel and sustainable disease control interventions. In summary, tapping these compounds will potentially aid in integrated combat mission to reduce disease transmission trends.

Linum lewisii Adventitious and Hairy-Roots Cultures as Lignan Plant Factories

Plants synthesize specific secondary metabolites for survival, reproduction, environmental resilience, and defense. Among them, lignans are a class of polyphenols with several bioactive properties: chemopreventive, anti-inflammatory, antiviral, and antioxidant. These compounds are often extracted from field-grown plants with very low yields. To overcome these constraints, in vitro tissue cultures provide a tool to optimize large-scale production. Moreover, the use of elicitation to increase secondary metabolite production is gaining importance. The aim of this work was to develop adventitious (ARL) and hairy roots (HRL) from Linum lewisi, a species able to synthesize arylnaphthalene lignans such as justicidin B. The ARL and HRL were obtained for the first time and characterized for their phenol content, antioxidant activity, and the production of justicidin B after treatments with several elicitors and precursor feeding. Through NMR spectroscopy, other four lignans were highlighted and identified in the roots extracts. A pilot-scale bioreactor was adopted to assess the suitability of the developed root cultures for future large-scale production. The ARL and HRL cultures showed a justicidin B production higher than other Linum species cultures described up to now (75.8 mg/L and 82.2 g/L), and the production more than doubled after elicitation with MeJA.

In‐silico Computational Investigations of AntiViral Lignan Derivatives as Potent Inhibitors of SARS CoV‐2

Due to alarming outbreak of pandemic COVID‐19 in recent times, there is a strong need to discover and identify new antiviral agents acting against SARS CoV‐2. Among natural products, lignan derivatives have been found effective against several viral strains including SARS CoV‐2. Total of twenty‐seven reported antiviral lignan derivatives of plant origin have been selected for computational studies to identify the potent inhibitors of SARS CoV‐2. Molecular docking study has been carried out in order to predict and describe molecular interaction between active site of enzyme and lignan derivatives. Out of identified hits, clemastatin B and erythro‐strebluslignanol G demonstrated stronger binding and high affinity with all selected proteins. Molecular dynamics simulation studies of clemastin B and savinin against promising targets of SARS CoV‐2 have revealed their inhibitory potential against SARS CoV‐2. In fine, in‐silico computational studies have provided initial breakthrough in design and discovery of potential SARS CoV‐2 inhibitors.

Evaluation of Phenol-Substituted Diphyllin Derivatives as Selective Antagonists for Ebola Virus Entry

Ebola virus (EBOV) is an aggressive filoviral pathogen that can induce severe hemorrhagic fever in humans with up to 90% fatality rate. To date, there are no clinically effective small-molecule drugs for postexposure therapies to treat filoviral infections. EBOV cellular entry and infection involve uptake via macropinocytosis, navigation through the endocytic pathway, and pH-dependent escape into the cytoplasm. We report the inhibition of EBOV cell entry via selective inhibition of vacuolar (V)-ATPase by a new series of phenol-substituted derivatives of the natural product scaffold diphyllin. In cells challenged with Ebola virus, the diphyllin derivatives inhibit viral entry dependent upon structural variations to low nanomolar potencies. Mechanistically, the diphyllin derivatives had no effect on uptake and colocalization of viral particles with endocytic marker LAMP1 but directly modulated endosomal pH. The most potent effects were reversible exhibiting higher selectivity than bafilomycin or the parent diphyllin. Unlike general lysosomotrophic agents, the diphyllin derivatives showed no major disruptions of endocytic populations or morphology when examined with Rab5 and LAMP1 markers. The dilated vacuole phenotype induced by apilimod treatment or in constitutively active Rab5 mutant Q79L-expressing cells was both blocked and reversed by the diphyllin derivatives. The results are consistent with the action of the diphyllin scaffold as a selective pH-dependent viral entry block in late endosomes. Overall, the compounds show improved selectivity and minimal cytotoxicity relative to classical endosomal acidification blocking agents.

Flavivirus Entry Inhibitors

Flaviviruses, including Dengue virus, Zika virus, Yellow fever virus, Japanese encephalitis virus, West Nile virus, cause thousands of deaths and millions of illnesses each year. The large outbreak of ZIKV in 2016 reminds us that flaviviruses can pose a serious threat to human safety and public health as emerging and re-emerging viruses. However, there are no specific drugs approved for the treatment of flavivirus infections. Due to no need to enter the cells, viral entry inhibitors have the unique advantage in suppressing viral infections. Flaviviruses bind to receptors and attach to the cell surface, then enter the endosome in a clathrin-dependent manner and finalizes the viral entry process after fusion with the cell membrane in a low pH environment. Small molecules, antibodies or peptides can inhibit flavivirus entry by targeting the above processes. Here, we focus on flavivirus entry inhibitors with well-defined target and antiviral activity. We hope that our review will provide a theoretical basis for flavivirus treatment and drug research and help to accelerate the clinical application of flavivirus entry inhibitors.

Diphyllin Shows a Broad-Spectrum Antiviral Activity against Multiple Medically Important Enveloped RNA and DNA Viruses

Diphyllin is a natural arylnaphtalide lignan extracted from tropical plants of particular importance in traditional Chinese medicine. This compound has been described as a potent inhibitor of vacuolar (H⁺)ATPases and hence of the endosomal acidification process that is required by numerous enveloped viruses to trigger their respective viral infection cascades after entering host cells by receptor-mediated endocytosis. Accordingly, we report here a revised, updated, and improved synthesis of diphyllin, and demonstrate its antiviral activities against a panel of enveloped viruses from Flaviviridae, Phenuiviridae, Rhabdoviridae, and Herpesviridae families. Diphyllin is not cytotoxic for Vero and BHK-21 cells up to 100 µM and exerts a sub-micromolar or low-micromolar antiviral activity against tick-borne encephalitis virus, West Nile virus, Zika virus, Rift Valley fever virus, rabies virus, and herpes-simplex virus type 1. Our study shows that diphyllin is a broad-spectrum host cell-targeting antiviral agent that blocks the replication of multiple phylogenetically unrelated enveloped RNA and DNA viruses. In support of this, we also demonstrate that diphyllin is more than just a vacuolar (H⁺)ATPase inhibitor but may employ other antiviral mechanisms of action to inhibit the replication cycles of those viruses that do not enter host cells by endocytosis followed by low pH-dependent membrane fusion.

Antiviral, Anticancer and Hypotensive Potential of Diphyllin Glycosides and their Mechanisms of Action

Diphyllin glycosides (DG) are the type of arylnaphthalene lignans isolated from different plants and their synthetic derivatives have shown effective antiviral, cytotoxic, hypotensive and diuretic effects at very low concentrations similar to standard drugs that are under clinical use. The biological activities of the DG interfere with signaling pathways of viral infection and cancer induction. The sugar moieties of DG enhance bioavailability and pharmacological activities. The promising results of DG at nanomolar concentrations under in vitro and in vivo conditions should be explored further with clinical trials to determine its toxic effects, pharmacokinetics and pharmacodynamics. This may identify suitable antiviral and anticancer drugs in the near future. Considering all these activities, the present review is focused on the chemical aspects of DG with a detailed account on the mechanisms of action of DG. An attempt is also made to comment on the status of clinical trials of DG along with the possible limitations in studies based on available literature through September 2020.

Plant-derived lignans as potential antiviral agents: a systematic review

Medicinal plants are one of the most important sources of antiviral agents and lead compounds. Lignans are a large class of natural compounds comprising two phenyl propane units. Many of them have demonstrated biological activities, and some of them have even been developed as therapeutic drugs. In this review, 630 lignans, including those obtained from medicinal plants and their chemical derivatives, were systematically reviewed for their antiviral activity and mechanism of action. The compounds discussed herein were published in articles between 1998 and 2020. The articles were identified using both database searches (e.g., Web of Science, Pub Med and Scifinder) using key words such as: antiviral activity, antiviral effects, lignans, HBV, HCV, HIV, HPV, HSV, JEV, SARS-CoV, RSV and influenza A virus, and directed searches of scholarly publisher's websites including ACS, Elsevier, Springer, Thieme, and Wiley. The compounds were classified on their structural characteristics as 1) arylnaphthalene lignans, 2) aryltetralin lignans, 3) dibenzylbutyrolactone lignans, 4) dibenzylbutane lignans, 5) tetrahydrofuranoid and tetrahydrofurofuranoid lignans, 6) benzofuran lignans, 7) neolignans, 8) dibenzocyclooctadiene lignans and homolignans, and 9) norlignans and other lignoids. Details on isolation and antiviral activities of the most active compounds within each class of lignan are discussed in detail, as are studies of synthetic lignans that provide structure-activity relationship information.

Structure-based virtual screening of bioactive compounds from Indonesian medical plants against severe acute respiratory syndrome coronavirus-2

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) is a virus that causes the infectious disease coronavirus disease-2019. Currently, there is no effective drug for the prevention and treatment of this virus. This study aimed to identify secondary metabolites that potentially inhibit the key proteins of SARS-CoV-2. This was an in silico molecular docking study of several secondary metabolites of Indonesian herbal plant compounds and other metabolites with antiviral testing history. Virtual screening using AutoDock Vina of 216 Lipinski rule-compliant plant metabolites was performed on 3C-like protease (3CL^pro), RNA-dependent RNA polymerase (RdRp), and spike glycoprotein. Ligand preparation was performed using JChem and Schrödinger's software, and virtual protein elucidation was performed using AutoDockTools version 1.5.6. Virtual screening identified several RdRp, spike, and 3CL^pro inhibitors. Justicidin D had binding affinities of −8.7, −8.1, and −7.6 kcal mol⁻¹ on RdRp, 3CL^pro, and spike, respectively. 10-methoxycamptothecin had binding affinities of −8.5 and −8.2 kcal mol⁻¹ on RdRp and spike, respectively. Inoxanthone had binding affinities of −8.3 and −8.1 kcal mol⁻¹ on RdRp and spike, respectively, while binding affinities of caribine were −9.0 and −7.5 mol⁻¹ on 3CL^pro and spike, respectively. Secondary metabolites of compounds from several plants were identified as potential agents for SARS-CoV-2 therapy.

Stable Axially Chiral Isomers of Arylnaphthalene Lignan Glycosides with Antiviral Potential Discovered from Justicia procumbens

Arylnaphthalene lignans (ANLs) were known to have axial chirality due to the biphenyl skeleton with hindered rotation at the single bond. However, the stable ANL atropisomers have not been isolated from nature until the present study. Phytochemical separation of the methanol extract of the stems and barks of Justicia procumbens led to the isolation of 11 ANL glycosides including four pairs of new atropisomers with stable confirmations at room temperature. Their structures were deduced from elucidation of the extensive spectral data, and their absolute configurations were determined by the circular dichroism, electronic circular dichroism, and X-ray methods as well as the total synthesis of one pair of the atropisomers. The ANL compounds were evaluated for their antiviral potential, and it was found that they displayed great antiviral activity discrepancy between a pair of atropisomers due to the geometric orientation. The 1'P-oriented atropisomers showed much more significant antiviral potency than their corresponding 1'M-oriented counterparts. The biological activity discrepancy caused by the axial chirality will not only inspire synthetic design of novel ANL atropisomers to enrich the structural diversity, but also provide important hints to direct the synthetic approaches toward the antiviral drug development of ANL compounds.

Medicinal Plants, Phytochemicals, and Herbs to Combat Viral Pathogens Including SARS-CoV-2

The coronavirus disease 2019 (COVID-19) pandemic, caused by severe acute respiratory syndrome corona virus-2 (SARS-CoV-2), is the most important health issue, internationally. With no specific and effective antiviral therapy for COVID-19, new or repurposed antiviral are urgently needed. Phytochemicals pose a ray of hope for human health during this pandemic, and a great deal of research is concentrated on it. Phytochemicals have been used as antiviral agents against several viruses since they could inhibit several viruses via different mechanisms of direct inhibition either at the viral entry point or the replication stages and via immunomodulation potentials. Recent evidence also suggests that some plants and its components have shown promising antiviral properties against SARS-CoV-2. This review summarizes certain phytochemical agents along with their mode of actions and potential antiviral activities against important viral pathogens. A special focus has been given on medicinal plants and their extracts as well as herbs which have shown promising results to combat SARS-CoV-2 infection and can be useful in treating patients with COVID-19 as alternatives for treatment under phytotherapy approaches during this devastating pandemic situation.

Nanotechnology advances in pathogen- and host-targeted antiviral delivery: multipronged therapeutic intervention for pandemic control

The COVID-19 pandemic's high mortality rate and severe socioeconomic impact serve as a reminder of the urgent need for effective countermeasures against viral pandemic threats. In particular, effective antiviral therapeutics capable of stopping infections in its tracks is critical to reducing infection fatality rate and healthcare burden. With the field of drug delivery witnessing tremendous advancement in the last two decades owing to a panoply of nanotechnology advances, the present review summarizes and expounds on the research and development of therapeutic nanoformulations against various infectious viral pathogens, including HIV, influenza, and coronaviruses. Specifically, nanotechnology advances towards improving pathogen- and host-targeted antiviral drug delivery are reviewed, and the prospect of achieving effective viral eradication, broad-spectrum antiviral effect, and resisting viral mutations are discussed. As several COVID-19 antiviral clinical trials are met with lackluster treatment efficacy, nanocarrier strategies aimed at improving drug pharmacokinetics, biodistributions, and synergism are expected to not only contribute to the current disease treatment efforts but also expand the antiviral arsenal against other emerging viral diseases.

Antiviral Activity of Vacuolar ATPase Blocker Diphyllin against SARS-CoV-2

Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) is a causative agent of the pandemic coronavirus disease 2019 (COVID-19), which has resulted in over two million deaths worldwide to date. Diphyllin and diphyllinosides are known as natural blockers of cellular vacuolar ATPases, and so can act as inhibitors of the pH-dependent fusion of viral envelopes with host cell endosomal membranes. Such pH-dependent fusion is a critical early step during the SARS-CoV-2 replication cycle. Accordingly, the anti-SARS-CoV-2 profiles and cytotoxicities of diphyllin, diphyllinoside cleistanthin B, and two structurally related compounds, helioxanthin 8-1 and helioxanthin 5-4-2, are evaluated here using in vitro cell-based assay systems. Neither helioxanthin exhibits any obvious anti-SARS-CoV-2 effects in vitro. By contrast diphyllin and cleistanthin B do exhibit anti-SARS-CoV-2 effects in Vero cells, with respective 50% effective concentrations (EC₅₀) values of 1.92 and 6.51 µM. Diphyllin displays anti-SARS-CoV-2 effect also in colorectal adenocarcinoma (CaCo-2) cells. Moreover, when diphyllin is added at various times post infection, a significant decrease in viral titer is observed in SARS-CoV-2-infected Vero cells, even at high viral multiplicities of infection. Importantly, neither diphyllin nor cleistanthin B are found cytotoxic to Vero cells in concentrations up to 100 µM. However, the cytotoxic effect of diphyllin is more pronounced in Vero E6 and CaCo-2 cells. Overall, our data demonstrate that diphyllin and diphyllin analogues might be perfected as anti-SARS-CoV-2 agents in future preclinical studies, most especially if nanomedicine approaches may be invoked to optimize functional drug delivery to virus infected cells.

Antiviral Compounds for Blocking Arboviral Transmission in Mosquitoes

Mosquito-borne arthropod-borne viruses (arboviruses) such as the dengue virus (DENV), Zika virus (ZIKV), and chikungunya virus (CHIKV) are important human pathogens that are responsible for significant global morbidity and mortality. The recent emergence and re-emergence of mosquito-borne viral diseases (MBVDs) highlight the urgent need for safe and effective vaccines, therapeutics, and vector-control approaches to prevent MBVD outbreaks. In nature, arboviruses circulate between vertebrate hosts and arthropod vectors; therefore, disrupting the virus lifecycle in mosquitoes is a major approach for combating MBVDs. Several strategies were proposed to render mosquitoes that are refractory to arboviral infection, for example, those involving the generation of genetically modified mosquitoes or infection with the symbiotic bacterium Wolbachia. Due to the recent development of high-throughput screening methods, an increasing number of drugs with inhibitory effects on mosquito-borne arboviruses in mammalian cells were identified. These antivirals are useful resources that can impede the circulation of arboviruses between arthropods and humans by either rendering viruses more vulnerable in humans or suppressing viral infection by reducing the expression of host factors in mosquitoes. In this review, we summarize recent advances in small-molecule antiarboviral drugs in mammalian and mosquito cells, and discuss how to use these antivirals to block the transmission of MBVDs.

Druggability assessment of precursor membrane protein as a target for inhibiting the Zika virus

The Zika virus (ZIKV), a significant zoonotic flavivirus, was neglected as a human pathogen until the recent epidemic. The rapid geographic spread of the virus and association with neurological disorders has created a global public health concern pressing the need for anti-ZIKV drugs. Previous ZIKV drug discovery research has focused on three primary targets, RNA-dependent RNA polymerase, envelope protein, and viral proteases, and none has yet resulted in a commercially viable inhibitor. In the quest for finding effective inhibitors, it is important to expand the number of targets available for drug discovery research. To this end, the ZIKV precursor membrane protein (prM) comes to the forefront as a potential target due to its critical role in virus infectivity and pathogenicity. prM acts as a chaperone for envelope protein folding and prevents premature fusion of virions to the host membrane and has not been attempted as a drug target before. One critical requirement for a protein to be an effective target is the ability of the protein to be druggable, i.e. having active sites that can bind to specific ligands. In this work, the druggability of prM was assessed via molecular docking combined molecular dynamics simulations followed binding affinity kinetics studies. Compounds that had a high affinity to the prM protein were screened in silico and ligand-binding free energies were computed using molecular mechanics with generalized Born and surface area continuum solvation (MM-GBSA) method. In vitro binding kinetics via biolayer interferometry (BLI) and interaction analysis confirmed that prM could be targeted for drug discovery to combat ZIKV infection.Communicated by Ramaswamy H. Sarma.

Challenges at the Time of COVID-19: Opportunities and Innovations in Antivirals from Nature

As viral infections are an increasing threat to human societies, the need for new therapeutic strategies is becoming even more obvious. As no vaccine is available for COVID-19, the development of directly acting antiviral agents and preventive strategies have to be considered. Nature provides a huge reservoir of anti-infectious compounds, from which we can deduce innovative ideas, therapies, and products. Anti-adhesive natural products interact with the receptor-mediated recognition and early interaction of viruses with the host cells, leading to a reduced internalisation of the virus and reduced infections (e.g., procyanidin-B-2-di-O-gallate against influenza and herpes virus). Lignans like podophyllotoxin and bicyclol show strong antiviral activities against different viruses, and essential oils can directly interact with viral membranes and reduce the host's inflammatory responses (e.g., 1,8-cineol). Echinacea extracts stimulate the immune system, and bioavailable alkamides are key players by interacting with immunomodulating cannabinoid receptors. COVID-19 and SARS-CoV-2 infections have, in part, successfully been treated in China by preparations from traditional Chinese medicine and, while it is too early to draw conclusions, some promising data are available. There is huge potential, but intensified research is needed to develop evidence-based medicines with a clearly defined chemical profile. Intensified research and development, and therefore funding, are needed for exploiting nature's reservoir against viral infections. Combined action for basic research, chemistry, pharmacognosy, virology, and clinical studies, but also supply chain, sustainable sourcing, and economic aspects have to be considered. This review calls for intensified innovative science on natural products for the patients and for a healthier world!

Lignans and Their Derivatives from Plants as Antivirals

Lignans are widely produced by various plant species; they are a class of natural products that share structural similarity. They usually contain a core scaffold that is formed by two or more phenylpropanoid units. Lignans possess diverse pharmacological properties, including their antiviral activities that have been reported in recent years. This review discusses the distribution of lignans in nature according to their structural classification, and it provides a comprehensive summary of their antiviral activities. Among them, two types of antiviral lignans—podophyllotoxin and bicyclol, which are used to treat venereal warts and chronic hepatitis B (CHB) in clinical, serve as examples of using lignans for antivirals—are discussed in some detail. Prospects of lignans in antiviral drug discovery are also discussed.