JMX0207, a Niclosamide Derivative with Improved Pharmacokinetics, Suppresses Zika Virus Infection Both In Vitro and In Vivo

Salicylamide derivatives as potent HBV inhibitors: insights into structure-activity relationships

Current HBV treatment with nucleos(t)ide analogs requires lifelong administration and is associated with the risk of drug resistance, underscoring the urgent need for novel antivirals with alternative targets. Herein, we reported the design, synthesis, and biological evaluation of a series of salicylamide derivatives as potent anti-HBV agents. The nine selected compounds exhibited dose-dependent inhibitory effects on HBV replication, as evidenced by significant reductions in both virion DNA and the secretion levels of HBsAg and HBeAg. Among them, compounds 50 and 56 exhibited the highest anti-HBV activity (IC50 = 0.52 and 0.47 μM, respectively) and selectivity (SI = 20.1 and 17.6, respectively). Mechanistic studies revealed that compounds 27, 31, and 47 impaired HBV core protein (HBc) expression, while compound 50 disrupted capsid formation without significantly affecting HBc expression. These findings highlight the therapeutic potential of salicylamide derivatives as promising anti-HBV agents and provide a foundation for further structural optimization and mechanistic exploration.

Advances in antiviral strategies targeting mosquito-borne viruses: cellular, viral, and immune-related approaches

Mosquito-borne viruses (MBVs) are a major global health threat, causing significant morbidity and mortality. MBVs belong to several distinct viral families, each with unique characteristics. The primary families include Flaviviridae (e.g., Dengue, Zika, West Nile, Yellow Fever, Japanese Encephalitis), transmitted predominantly by Aedes and Culex mosquitoes; Togaviridae, which consists of the genus Alphavirus (e.g., Chikungunya, Eastern and Western Equine Encephalitis viruses), also transmitted by Aedes and Culex; Bunyaviridae (recently reorganized), containing viruses like Rift Valley Fever and Oropouche virus, transmitted by mosquitoes and sometimes sandflies; and Reoviridae, which includes the genus Orbivirus (e.g., West Nile and Bluetongue viruses), primarily affecting animals and transmitted by mosquitoes and sandflies. Despite extensive research, effective antiviral treatments for MBVs remain scarce, and current therapies mainly provide symptomatic relief and supportive care. This review examines the viral components and cellular and immune factors involved in the life cycle of MBVs. It also highlights recent advances in antiviral strategies targeting host factors such as lipid metabolism, ion channels, and proteasomes, as well as viral targets like NS2B-NS3 proteases and nonstructural proteins. Additionally, it explores immunomodulatory therapies to enhance antiviral responses and emphasizes the potential of drug repurposing, bioinformatics, artificial intelligence, and deep learning in identifying novel antiviral candidates. Continued research is crucial in mitigating MBVs' impact and preventing future outbreaks.

A Comprehensive Review of the Development and Therapeutic Use of Antivirals in Flavivirus Infection

Flaviviruses are a diverse group of viruses primarily transmitted through hematophagous insects like mosquitoes and ticks. Significant expansion in the geographic range, prevalence, and vectors of flavivirus over the last 50 years has led to a dramatic increase in infections that can manifest as hemorrhagic fever or encephalitis, leading to prolonged morbidity and mortality. Millions of infections every year pose a serious threat to worldwide public health, encouraging scientists to develop a better understanding of the pathophysiology and immune evasion mechanisms of these viruses for vaccine development and antiviral therapy. Extensive research has been conducted in developing effective antivirals for flavivirus. Various approaches have been extensively utilized in clinical trials for antiviral development, targeting virus entry, replication, polyprotein synthesis and processing, and egress pathways exploiting virus as well as host proteins. However, to date, no licensed antiviral drug exists to treat the diseases caused by these viruses. Understanding the mechanisms of host-pathogen interaction, host immunity, viral immune evasion, and disease pathogenesis is highly warranted to foster the development of antivirals. This review provides an extensively detailed summary of the most recent advances in the development of antiviral drugs to combat diseases.

Trends in surface plasmon resonance biosensing: materials, methods, and machine learning

Surface plasmon resonance (SPR) proves to be one of the most effective methods of label-free detection and has been integral for the study of biomolecular interactions and the development of biosensors. This trend delves into the latest SPR research and progress built upon the Kretschmann configuration, a pivotal platform, and highlights three key developments that have enhanced the capabilities of the technique. We will first cover a range of explorations of novel plasmonic materials that have shaped SPR performance. Innovative signal transduction and collection, which leverages traditional materials and emerging alternatives, will then be discussed. Finally, the evolving landscape of data analysis, including the integration of machine learning algorithms to navigate complex SPR datasets, will be reviewed. We will also discuss the implementation of these improvements that have enabled new biosensing functions. These advancements not only pave the way for enhanced biosensing in general but also open new avenues for the technique to play a more significant role in research concerning human health.

Revisiting Niclosamide Formulation Approaches - a Pathway Toward Drug Repositioning

Niclosamide (NIC), an anthelmintic drug, has garnered recent attention for its potential as an antiviral, antibacterial, and chemotherapeutic agent, among other applications. Repurposing NIC presents a current trend, offering significant time and cost savings compared to developing entirely new therapeutic chemical entities. However, its drawback lies in poor solubility, resulting in notably low oral bioavailability. This review consolidates efforts to overcome this limitation by summarizing twelve categories of formulations, spanning derivatives, amorphous solid dispersions, co-crystals, nanocrystals, micelles, nanohybrids, lipid nanoparticles and emulsions, cyclodextrins, polymeric nanoparticles, dry powders for inhalation, 3D printlets, and nanofibers. These formulations cover oral, injectable, inhalable and potentially (trans)dermal routes of administration. Additionally, we present a comprehensive overview of NIC characteristics, including physico-chemical properties, metabolism, safety, and pharmacokinetics. Moreover, we identify gaps in formulation and administration pathways that warrant further investigation to address NIC poor bioavailability.

Orthoflaviviral Inhibitors in Clinical Trials, Preclinical In Vivo Efficacy Targeting NS2B-NS3 and Cellular Antiviral Activity via Competitive Protease Inhibition

Orthoflaviviruses, including zika (ZIKV), West Nile (WNV), and dengue (DENV) virus, induce severely debilitating infections and contribute significantly to the global disease burden, yet no clinically approved antiviral treatments exist. This review offers a comprehensive analysis of small-molecule drug development targeting orthoflaviviral infections, with a focus on NS2B-NS3 inhibition. We systematically examined clinical trials, preclinical efficacy studies, and modes of action for various viral replication inhibitors, emphasizing allosteric and orthosteric drugs inhibiting NS2B-NS3 protease with in vivo efficacy and in vitro-tested competitive NS2B-NS3 inhibitors with cellular efficacy. Our findings revealed that several compounds with in vivo preclinical efficacy failed to show clinical antiviral efficacy. NS3-NS4B inhibitors, such as JNJ-64281802 and EYU688, show promise, recently entering clinical trials, underscoring the importance of developing novel viral replication inhibitors targeting viral machinery. To date, the only NS2B-NS3 inhibitor that has undergone clinical trials is doxycycline, however, its mechanism of action and clinical efficacy as viral growth inhibitor require additional investigation. SYC-1307, an allosteric inhibitor, exhibits high in vivo efficacy, while temoporfin and methylene blue represent promising orthosteric non-competitive inhibitors. Compound 71, a competitive NS2B-NS3 inhibitor, emerges as a leading preclinical candidate due to its high cellular antiviral efficacy, minimal cytotoxicity, and favorable in vitro pharmacokinetic parameters. Challenges remain in developing competitive NS2B-NS3 inhibitors, including appropriate biochemical inhibition assays as well as the selectivity and conformational flexibility of the protease, complicating effective antiviral treatment design.

A universal fluorescence polarization high throughput screening assay to target the SAM-binding sites of SARS-CoV-2 and other viral methyltransferases

SARS-CoV-2 has caused a global pandemic with significant humanity and economic loss since 2020. Currently, only limited options are available to treat SARS-CoV-2 infections for vulnerable populations. In this study, we report a universal fluorescence polarization (FP)-based high throughput screening (HTS) assay for SAM-dependent viral methyltransferases (MTases), using a fluorescent SAM-analogue, FL-NAH. We performed the assay against a reference MTase, NSP14, an essential enzyme for SARS-CoV-2 to methylate the N7 position of viral 5'-RNA guanine cap. The assay is universal and suitable for any SAM-dependent viral MTases such as the SARS-CoV-2 NSP16/NSP10 MTase complex and the NS5 MTase of Zika virus (ZIKV). Pilot screening demonstrated that the HTS assay was very robust and identified two candidate inhibitors, NSC 111552 and 288387. The two compounds inhibited the FL-NAH binding to the NSP14 MTase with low micromolar IC50. We used three functional MTase assays to unambiguously verified the inhibitory potency of these molecules for the NSP14 N7-MTase function. Binding studies indicated that these molecules are bound directly to the NSP14 MTase with similar low micromolar affinity. Moreover, we further demonstrated that these molecules significantly inhibited the SARS-CoV-2 replication in cell-based assays at concentrations not causing cytotoxicity. Furthermore, NSC111552 significantly synergized with known SARS-CoV-2 drugs including nirmatrelvir and remdesivir. Finally, docking suggested that these molecules bind specifically to the SAM-binding site on the NSP14 MTase. Overall, these molecules represent novel and promising candidates to further develop broad-spectrum inhibitors for the management of viral infections.

Vector-Transmitted Flaviviruses: An Antiviral Molecules Overview

Flaviviruses cause numerous pathologies in humans across a broad clinical spectrum with potentially severe clinical manifestations, including hemorrhagic and neurological disorders. Among human flaviviruses, some viral proteins show high conservation and are good candidates as targets for drug design. From an epidemiological point of view, flaviviruses cause more than 400 million cases of infection worldwide each year. In particular, the Yellow Fever, dengue, West Nile, and Zika viruses have high morbidity and mortality-about an estimated 20,000 deaths per year. As they depend on human vectors, they have expanded their geographical range in recent years due to altered climatic and social conditions. Despite these epidemiological and clinical premises, there are limited antiviral treatments for these infections. In this review, we describe the major compounds that are currently under evaluation for the treatment of flavivirus infections and the challenges faced during clinical trials, outlining their mechanisms of action in order to present an overview of ongoing studies. According to our review, the absence of approved antivirals for flaviviruses led to in vitro and in vivo experiments aimed at identifying compounds that can interfere with one or more viral cycle steps. Still, the currently unavailability of approved antivirals poses a significant public health issue.

Preparation of PLGA microspheres loaded with niclosamide via microfluidic technology and their inhibition of Caco-2 cell activity in vitro

Niclosamide (NIC) is a multifunctional drug that regulates various signaling pathways and biological processes. It is widely used for the treatment of cancer, viral infections, and metabolic disorders. However, its low water solubility limits its efficacy. In this study, poly(lactic-co-glycolic acid) (PLGA) and hyaluronic acid (HA), which exhibit good biocompatibility, biodegradability, and non-immunogenicity, were conjugated with niclosamide to prepare PLGA-HA-niclosamide polymeric nanoparticles (NIC@PLGA-HA) using microfluidic technology. The obtained microspheres had a uniform size distribution, with an average mean size of 442.0 ± 18.8 nm and zeta potential of -25.4 ± 0.41 mV, indicating their stable dispersion in water. The drug-loading efficiency was 8.70%. The drug-loaded microspheres showed sustained release behavior at pH 7.4 and 5.0, but not at pH 2.0, and the drug release kinetics were described by a quasi-first-order kinetic equation. The effect of the drug-loaded microspheres on the proliferation of Caco-2 cells was detected using the MTT assay. Hydrophilic HA-modified NIC@PLGA-HA microspheres prepared via microfluidic technology increased the cellular uptake by Caco-2 cells. Compared to the same concentration of NIC, the NIC@PLGA-HA microspheres demonstrated a stronger inhibitory effect on Caco-2 cells owing to the combined effect of PLGA, HA, and NIC. Therefore, the pH-responsive NIC@PLGA-HA microspheres synthesized using microfluid technology increased the solubility of NIC and improved its biological activity, thus contributing to the demand for intestinal drug carriers.

Broad-Spectrum Small-Molecule Inhibitors Targeting the SAM-Binding Site of Flavivirus NS5 Methyltransferase

Flavivirus infections, such as those caused by dengue virus (DENV), West Nile virus (WNV), yellow fever virus (YFV), and Zika virus (ZIKV), pose a rising threat to global health. There are no FDA-approved drugs for flaviviruses, although a small number of flaviviruses have vaccines. For flaviviruses or unknown viruses that may appear in the future, it is particularly desirable to identify broad-spectrum inhibitors. The NS5 protein is regarded as one of the most promising flavivirus drug targets because it is conserved across flaviviruses. In this study, we used FL-NAH, a fluorescent analog of the methyl donor S-adenosyl methionine (SAM), to develop a fluorescence polarization (FP)-based high throughput screening (HTS) assay to specifically target methyltransferase (MTase), a vital enzyme for flaviviruses that methylates the N7 and 2'-O positions of the viral 5'-RNA cap. Pilot screening identified two candidate MTase inhibitors, NSC 111552 and 288387. The two compounds inhibited the FL-NAH binding to the DENV3 MTase with low micromolar IC50. Functional assays verified the inhibitory potency of these molecules for the flavivirus MTase activity. Binding studies indicated that these molecules are bound directly to the DENV3 MTase with similar low micromolar affinity. Furthermore, we showed that these compounds greatly reduced ZIKV replication in cell-based experiments at dosages that did not cause cytotoxicity. Finally, docking studies revealed that these molecules bind to the SAM-binding region on the DENV3 MTase, and further mutagenesis studies verified residues important for the binding of these compounds. Overall, these compounds are innovative and attractive candidates for the development of broad-spectrum inhibitors for the treatment of flavivirus infections.

Therapeutic potential of salicylamide derivatives for combating viral infections

Since time immemorial human beings have constantly been fighting against viral infections. The ongoing and devastating coronavirus disease 2019 pandemic represents one of the most severe and most significant public health emergencies in human history, highlighting an urgent need to develop broad-spectrum antiviral agents. Salicylamide (2-hydroxybenzamide) derivatives, represented by niclosamide and nitazoxanide, inhibit the replication of a broad range of RNA and DNA viruses such as flavivirus, influenza A virus, and coronavirus. Moreover, nitazoxanide was effective in clinical trials against different viral infections including diarrhea caused by rotavirus and norovirus, uncomplicated influenza A and B, hepatitis B, and hepatitis C. In this review, we summarize the broad antiviral activities of salicylamide derivatives, the clinical progress, and the potential targets or mechanisms against different viral infections and highlight their therapeutic potential in combating the circulating and emerging viral infections in the future.

Structural Modifications Introduced by NS2B Cofactor Binding to the NS3 Protease of the Kyasanur Forest Disease Virus

Kyasanur Forest Disease virus (KFDV), a neglected human pathogenic virus, is a Flavivirus that causes severe hemorrhagic fever in humans. KFDV is transmitted to humans by the bite of the hard tick (Haemaphysalis spinigera), which acts as a reservoir of KFDV. The recent expansion of the endemic area of KFDV is of concern and requires the development of new preventive measures against KFDV. Currently, there is no antiviral therapy against KFDV, and the existing vaccine has limited efficacy. To develop a new antiviral therapy against KFDV, we focused on the nonstructural proteins NS2B and NS3 of KFDV, which are responsible for serine protease activity. Viral proteases have shown to be suitable therapeutic targets in the development of antiviral drugs against many diseases. However, success has been limited in flaviviruses, mainly because of the important features of the active site, which is flat and highly charged. In this context, the present study focuses on the dynamics of NS2B and NS3 to identify potential allosteric sites in the NS2B/NS3 protease of KDFV. To our knowledge, there are no reports on the dynamics of NS2B and NS3 in KFDV, and the crystal structure of the NS2B/NS3 protease of KFDV has not yet been solved. Overall, we created the structure of the NS2B/NS3 protease of KFDV using AlphaFold and performed molecular dynamics simulations with and without NS2B cofactor to investigate structural rearrangements due to cofactor binding and to identify alternative allosteric sites. The identified allosteric site is promising due to its geometric and physicochemical properties and druggability and can be used for new drug development. The applicability of the proposed allosteric binding sites was verified for the best-hit molecules from the virtual screening and MD simulations.

Repurposing of Doramectin as a New Anti-Zika Virus Agent

Zika virus (ZIKV), belonging to the Flavivirus family and mainly transmitted by mosquitoes, causes a variety of adverse outcomes, including Guillain-Barré syndrome, microcephaly, and meningoencephalitis. However, there are no approved vaccines or drugs available for ZIKV. The discovery and research on drugs for ZIKV are still essential. In this study, we identified doramectin, an approved veterinary antiparasitic drug, as a novel anti-ZIKV agent (EC₅₀ value from 0.85 μM to 3.00 μM) with low cytotoxicity (CC₅₀ > 50 μM) in multiple cellular models. The expression of ZIKV proteins also decreased significantly under the treatment of doramectin. Further study showed that doramectin directly interacted with the key enzyme for ZIKV genome replication, RNA-dependent RNA polymerase (RdRp), with a stronger affinity (K_d = 16.9 μM), which may be related to the effect on ZIKV replication. These results suggested that doramectin might serve as a promising drug candidate for anti-ZIKV.

Synthesis, cytotoxicity, and pharmacokinetic evaluations of niclosamide analogs for anti-SARS-CoV-2

Niclosamide, an oral anthelmintic drug, could inhibit SARS-CoV-2 virus replication through autophagy induction, but high cytotoxicity and poor oral bioavailability limited its application. Twenty-three niclosamide analogs were designed and synthesized, of which compound 21 was found to exhibit the best anti-SARS-CoV-2 efficacy (EC₅₀ = 1.00 μM for 24h), lower cytotoxicity (CC₅₀ = 4.73 μM for 48h), better pharmacokinetic, and it was also well tolerated in the sub-acute toxicity study in mice. To further improve the pharmacokinetics of 21, three prodrugs have been synthesized. The pharmacokinetics of 24 indicates its potential for further research (AUC_last was 3-fold of compound 21). Western blot assay indicated that compound 21 could down-regulate SKP2 expression and increase BECN1 levels in Vero-E6 cells, indicating the antiviral mechanism of 21 was related to modulating the autophagy processes in host cells.

iPSC-derived three-dimensional brain organoid models and neurotropic viral infections

Progress in stem cell research has revolutionized the medical field for more than two decades. More recently, the discovery of induced pluripotent stem cells (iPSCs) has allowed for the development of advanced disease modeling and tissue engineering platforms. iPSCs are generated from adult somatic cells by reprogramming them into an embryonic-like state via the expression of transcription factors required for establishing pluripotency. In the context of the central nervous system (CNS), iPSCs have the potential to differentiate into a wide variety of brain cell types including neurons, astrocytes, microglial cells, endothelial cells, and oligodendrocytes. iPSCs can be used to generate brain organoids by using a constructive approach in three-dimensional (3D) culture in vitro. Recent advances in 3D brain organoid modeling have provided access to a better understanding of cell-to-cell interactions in disease progression, particularly with neurotropic viral infections. Neurotropic viral infections have been difficult to study in two-dimensional culture systems in vitro due to the lack of a multicellular composition of CNS cell networks. In recent years, 3D brain organoids have been preferred for modeling neurotropic viral diseases and have provided invaluable information for better understanding the molecular regulation of viral infection and cellular responses. Here we provide a comprehensive review of the literature on recent advances in iPSC-derived 3D brain organoid culturing and their utilization in modeling major neurotropic viral infections including HIV-1, HSV-1, JCV, ZIKV, CMV, and SARS-CoV2.

Small-Molecule Inhibitor of Flaviviral NS3-NS5 Interaction with Broad-Spectrum Activity and Efficacy In Vivo

Every year, dengue virus (DENV) causes one hundred million infections worldwide that can result in dengue disease and severe dengue. Two other mosquito-borne flaviviruses, i.e., Zika virus (ZIKV) and West Nile virus (WNV), are responsible of prolonged outbreaks and are associated with severe neurological diseases, congenital defects, and eventually death. These three viruses, despite their importance for global public health, still lack specific drug treatments. Here, we describe the structure-guided discovery of small molecules with pan-flavivirus antiviral potential by a virtual screening of ~1 million structures targeting the NS3-NS5 interaction surface of different flaviviruses. Two molecules inhibited the interaction between DENV NS3 and NS5 in vitro and the replication of all DENV serotypes as well as ZIKV and WNV and exhibited low propensity to select resistant viruses. Remarkably, one molecule demonstrated efficacy in a mouse model of dengue by reducing peak viremia, viral load in target organs, and associated tissue pathology. This study provides the proof of concept that targeting the flaviviral NS3-NS5 interaction is an effective therapeutic strategy able to reduce virus replication in vivo and discloses new chemical scaffolds that could be further developed, thus providing a significant milestone in the development of much awaited broad-spectrum antiflaviviral drugs. IMPORTANCE More than one-third of the human population is at risk of infection by different mosquito-borne flaviviruses. Despite this, no specific antiviral drug is currently available. In this work, using a computational approach based on molecular dynamics simulation and virtual screening of ~1 million small-molecule structures, we identified a compound that targets the interaction between the two sole flaviviral enzymes, i.e., NS3 and NS5. This compound demonstrated pan-serotype anti-DENV activity and pan-flavivirus potential in infected cells, low propensity to select viral resistant mutant viruses, and efficacy in a mouse model of dengue. Broad-spectrum antivirals are much awaited, and this work represents a significant advance toward the development of therapeutic molecules with extended antiflavivirus potential that act by an innovative mechanism and could be used alone or in combination with other antivirals.

Niclosamide as a Promising Therapeutic Player in Human Cancer and Other Diseases

Niclosamide is an FDA-approved anthelmintic drug for the treatment of parasitic infections. However, over the past few years, increasing evidence has shown that niclosamide could treat diseases beyond parasitic diseases, which include metabolic diseases, immune system diseases, bacterial and viral infections, asthma, arterial constriction, myopia, and cancer. Therefore, we systematically reviewed the pharmacological activities and therapeutic prospects of niclosamide in human disease and cancer and summarized the related molecular mechanisms and signaling pathways, indicating that niclosamide is a promising therapeutic player in various human diseases, including cancer.

The magic bullet: Niclosamide

The term 'magic bullet' is a scientific concept proposed by the German Nobel laureate Paul Ehrlich in 1907, describing a medicine that could specifically and efficiently target a disease without harming the body. Oncologists have been looking for a magic bullet for cancer therapy ever since. However, the current therapies for cancers-including chemotherapy, radiation therapy, hormone therapy, and targeted therapy-pose either pan-cytotoxicity or only single-target efficacy, precluding their ability to function as a magic bullet. Intriguingly, niclosamide, an FDA-approved drug for treating tapeworm infections with an excellent safety profile, displays broad anti-cancer activity in a variety of contexts. In particular, niclosamide inhibits multiple oncogenic pathways such as Wnt/β-catenin, Ras, Stat3, Notch, E2F-Myc, NF-κB, and mTOR and activates tumor suppressor signaling pathways such as p53, PP2A, and AMPK. Moreover, niclosamide potentially improves immunotherapy by modulating pathways such as PD-1/PDL-1. We recently discovered that niclosamide ethanolamine (NEN) reprograms cellular metabolism through its uncoupler function, consequently remodeling the cellular epigenetic landscape to promote differentiation. Inspired by the promising results from the pre-clinical studies, several clinical trials are ongoing to assess the therapeutic effect of niclosamide in cancer patients. This current review summarizes the functions, mechanism of action, and potential applications of niclosamide in cancer therapy as a magic bullet.

Allosteric inhibitors of the main protease of SARS-CoV-2

SARS-CoV-2 has raised the alarm to search for effective therapy for this virus. To date several vaccines have been approved but few available drugs reported recently still need approval from FDA. Remdesivir was approved for emergency use only. In this report, the SARS-CoV-2 3CLpro was expressed and purified. By using a FRET-based enzymatic assay, we have screened a library consisting of more than 300 different niclosamide derivatives and identified three molecules JMX0286, JMX0301, and JMX0941 as potent allosteric inhibitors against SARS-CoV-2 3CLpro, with IC50 values similar to that of known covalent inhibitor boceprevir. In a cell-based antiviral assay, these inhibitors can inhibit the virus growth with EC50 in the range of 2-3 μM. The mechanism of action of JMX0286, JMX0301, and JMX0941 were characterized by enzyme kinetics, affinity binding and protein-based substrate digestion. Molecular docking, molecular dynamics (MD) simulations and hydration studies suggested that JMX0286, JMX0301, JMX0941 bind specifically to an allosteric pocket of the SARS-CoV-2 3CL protease. This study provides three potent compounds for further studies.

Using 2D and 3D pluripotent stem cell models to study neurotropic viruses

Understanding the impact of viral pathogens on the human central nervous system (CNS) has been challenging due to the lack of viable human CNS models for controlled experiments to determine the causal factors underlying pathogenesis. Human embryonic stem cells (ESCs) and, more recently, cellular reprogramming of adult somatic cells to generate human induced pluripotent stem cells (iPSCs) provide opportunities for directed differentiation to neural cells that can be used to evaluate the impact of known and emerging viruses on neural cell types. Pluripotent stem cells (PSCs) can be induced to neural lineages in either two- (2D) or three-dimensional (3D) cultures, each bearing distinct advantages and limitations for modeling viral pathogenesis and evaluating effective therapeutics. Here we review the current state of technology in stem cell-based modeling of the CNS and how these models can be used to determine viral tropism and identify cellular phenotypes to investigate virus-host interactions and facilitate drug screening. We focus on several viruses (e.g., human immunodeficiency virus (HIV), herpes simplex virus (HSV), Zika virus (ZIKV), human cytomegalovirus (HCMV), SARS-CoV-2, West Nile virus (WNV)) to illustrate key advantages, as well as challenges, of PSC-based models. We also discuss how human PSC-based models can be used to evaluate the safety and efficacy of therapeutic drugs by generating data that are complementary to existing preclinical models. Ultimately, these efforts could facilitate the movement towards personalized medicine and provide patients and physicians with an additional source of information to consider when evaluating available treatment strategies.

Riboflavin, a Potent Neuroprotective Vitamin: Focus on Flavivirus and Alphavirus Proteases

Several neurotropic viruses are members of the flavivirus and alphavirus families. Infections caused by these viruses may cause long-term neurological sequelae in humans. The continuous emergence of infections caused by viruses around the world, such as the chikungunya virus (CHIKV) (Alphavirus genus), the zika virus (ZIKV) and the yellow fever virus (YFV) (both of the Flavivirus genus), warrants the development of new strategies to combat them. Our study demonstrates the inhibitory potential of the water-soluble vitamin riboflavin against NS2B/NS3pro of ZIKV and YFV and nsP2pro of CHIKV. Riboflavin presents a competitive inhibition mode with IC50 values in the medium µM range of 79.4 ± 5.0 µM for ZIKV NS2B/NS3pro and 45.7 ± 2.9 μM for YFV NS2B/NS3pro. Against CHIKV nsP2pro, the vitamin showed a very strong effect (93 ± 5.7 nM). The determined dissociation constants (KD) are significantly below the threshold value of 30 µM. The ligand binding increases the thermal stability between 4 °C and 8 °C. Unexpectedly, riboflavin showed inhibiting activity against another viral protein; the molecule was also able to inhibit the viral entry of CHIKV. Molecular dynamics simulations indicated great stability of riboflavin in the protease active site, which validates the repurposing of riboflavin as a promising molecule in drug development against the viruses presented here.

In vitro and in vivo characterization of erythrosin B and derivatives against Zika virus

Zika virus (ZIKV) causes significant human diseases without specific therapy. Previously we found erythrosin B, an FDA-approved food additive, inhibited viral NS2B−NS3 interactions, leading to inhibition of ZIKV infection in cell culture. In this study, we performed pharmacokinetic and in vivo studies to demonstrate the efficacy of erythrosin B against ZIKV in 3D mini-brain organoid and mouse models. Our results showed that erythrosin B is very effective in abolishing ZIKV replication in the 3D organoid model. Although pharmacokinetics studies indicated that erythrosin B had a low absorption profile, mice challenged by a lethal dose of ZIKV showed a significantly improved survival rate upon oral administration of erythrosin B, compared to vehicle control. Limited structure−activity relationship studies indicated that most analogs of erythrosin B with modifications on the xanthene ring led to loss or reduction of inhibitory activities towards viral NS2B−NS3 interactions, protease activity and antiviral efficacy. In contrast, introducing chlorine substitutions on the isobenzofuran ring led to slightly increased activities, suggesting that the isobenzofuran ring is well tolerated for modifications. Cytotoxicity studies indicated that all derivatives are nontoxic to human cells. Overall, our studies demonstrated erythrosin B is an effective antiviral against ZIKV both in vitro and in vivo.

Human Brain Organoids as Models for Central Nervous System Viral Infection

Pathogenesis of viral infections of the central nervous system (CNS) is poorly understood, and this is partly due to the limitations of currently used preclinical models. Brain organoid models can overcome some of these limitations, as they are generated from human derived stem cells, differentiated in three dimensions (3D), and can mimic human neurodevelopmental characteristics. Therefore, brain organoids have been increasingly used as brain models in research on various viruses, such as Zika virus, severe acute respiratory syndrome coronavirus 2, human cytomegalovirus, and herpes simplex virus. Brain organoids allow for the study of viral tropism, the effect of infection on organoid function, size, and cytoarchitecture, as well as innate immune response; therefore, they provide valuable insight into the pathogenesis of neurotropic viral infections and testing of antivirals in a physiological model. In this review, we summarize the results of studies on viral CNS infection in brain organoids, and we demonstrate the broad application and benefits of using a human 3D model in virology research. At the same time, we describe the limitations of the studies in brain organoids, such as the heterogeneity in organoid generation protocols and age at infection, which result in differences in results between studies, as well as the lack of microglia and a blood brain barrier.

Antiviral Agents against Flavivirus Protease: Prospect and Future Direction

Flaviviruses cause a significant amount of mortality and morbidity, especially in regions where they are endemic. A recent example is the outbreak of Zika virus throughout the world. Development of antiviral drugs against different viral targets is as important as the development of vaccines. During viral replication, a single polyprotein precursor (PP) is produced and further cleaved into individual proteins by a viral NS2B-NS3 protease complex together with host proteases. Flavivirus protease is one of the most attractive targets for development of therapeutic antivirals because it is essential for viral PP processing, leading to active viral proteins. In this review, we have summarized recent development in drug discovery targeting the NS2B-NS3 protease of flaviviruses, especially Zika, dengue, and West Nile viruses.

A potent candidate against Zika virus infection: Synthesis, bioactivity, radiolabeling and biodistribution studies

Compound VI exhibits potent activity against Zika virus infection combined with favorable cellular uptake and biodistribution without apparent cytotoxicity in a mouse model.

Methodologies for Generating Brain Organoids to Model Viral Pathogenesis in the CNS

(1) Background: The human brain is of interest in viral research because it is often the target of viruses. Neurological infections can result in consequences in the CNS, which can result in death or lifelong sequelae. Organoids modeling the CNS are notable because they are derived from stem cells that differentiate into specific brain cells such as neural progenitors, neurons, astrocytes, and glial cells. Numerous protocols have been developed for the generation of CNS organoids, and our goal was to describe the various CNS organoid models available for viral pathogenesis research to serve as a guide to determine which protocol might be appropriate based on research goal, timeframe, and budget. (2) Methods: Articles for this review were found in Pubmed, Scopus and EMBASE. The search terms used were "brain + organoid" and "CNS + organoid" (3) Results: There are two main methods for organoid generation, and the length of time for organoid generation varied from 28 days to over 2 months. The costs for generating a population of organoids ranged from USD 1000 to 5000. (4) Conclusions: There are numerous methods for generating organoids representing multiple regions of the brain, with several types of modifications for fine-tuning the model to a researcher's specifications. Organoid models of the CNS can serve as a platform for characterization and mechanistic studies that can reduce or eliminate the use of animals, especially for viruses that only cause disease in the human CNS.

NS2B-NS3 protease inhibitors as promising compounds in the development of antivirals against Zika virus: A systematic review

Zika virus (ZIKV) infections are associated with severe neurological complications and are a global public health concern. There are no approved vaccines or antiviral drugs to inhibit ZIKV replication. NS2B-NS3 protease (NS2B-NS3 pro), which is essential for viral replication, is a promising molecular target for anti-ZIKV drugs. We conducted a systematic review to identify compounds with promising effects against ZIKV; we discussed their pharmacodynamic and pharmacophoric characteristics. The online search, performed using the PubMed/MEDLINE and SCOPUS databases, yielded 56 articles; seven relevant studies that reported nine promising compounds with inhibitory activity against ZIKV NS2B-NS3 pro were selected. Of these, five (niclosamide, nitazoxanide, bromocriptine, temoporfin, and novobiocin) are currently available on the market and have been tested for off-label use against ZIKV. The 50% inhibitory concentration values of these compounds for the inhibition of NS2B-NS3 pro ranged at 0.38-21.6 µM; most compounds exhibited noncompetitive inhibition (66%). All compounds that could inhibit the NS2B-NS3 pro complex showed potent in vitro anti-ZIKV activity with a 50% effective concentration ranging 0.024-50 µM. The 50% cytotoxic concentration of the compounds assayed using A549, Vero, and WRL-69 cell lines ranged at 0.6-1388.02 µM and the selectivity index was 3.07-1698. This review summarizes the most promising antiviral agents against ZIKV that have inhibitory activity against viral proteases.

An update on preclinical pregnancy models of Zika virus infection for drug and vaccine discovery

INTRODUCTION

Congenital Zika syndrome is caused by Zika virus (ZIKV) infection during pregnancy and can culminate in structural and neurological defects in the fetus, including a spectrum of symptoms such as brain calcifications, hydrocephalus, holoprosencephaly, lissencephaly, ventriculomegaly, and microcephaly. Using animal models to study ZIKV infection during pregnancy represents a critical tool for understanding ZIKV pathophysiology, drug testing, vaccine development, and prevention of vertical transmission.

AREAS COVERED

In this review, the authors cover state-of-the-art preclinical pregnancy models of ZIKV infection for drug discovery and vaccine development to prevent vertical transmission.

EXPERT OPINION

The discovery of drugs against ZIKV infection represents an urgent necessity, and until now, no effective drug that can prevent the effects of vertical transmission has been tested in humans. Even after six years of the ZIKV outbreak in Brazil, no drugs or vaccines have been approved for use in humans. In part, this failure could be related to the lack of translatability from available preclinical models to humans.

Structure and Dynamics of Zika Virus Protease and Its Insights into Inhibitor Design

Zika virus (ZIKV)—a member of the Flaviviridae family—is an important human pathogen. Its genome encodes a polyprotein that can be further processed into structural and non-structural proteins. ZIKV protease is an important target for antiviral development due to its role in cleaving the polyprotein to release functional viral proteins. The viral protease is a two-component protein complex formed by NS2B and NS3. Structural studies using different approaches demonstrate that conformational changes exist in the protease. The structures and dynamics of this protease in the absence and presence of inhibitors were explored to provide insights into the inhibitor design. The dynamic nature of residues binding to the enzyme cleavage site might be important for the function of the protease. Due to the charges at the protease cleavage site, it is challenging to develop small-molecule compounds acting as substrate competitors. Developing small-molecule compounds to inhibit protease activity through an allosteric mechanism is a feasible strategy because conformational changes are observed in the protease. Herein, structures and dynamics of ZIKV protease are summarized. The conformational changes of ZIKV protease and other proteases in the same family are discussed. The progress in developing allosteric inhibitors is also described. Understanding the structures and dynamics of the proteases are important for designing potent inhibitors.

Brain organoid: a 3D technology for investigating cellular composition and interactions in human neurological development and disease models in vitro

Abstract

The study of human brain physiology, including cellular interactions in normal and disease conditions, has been a challenge due to its complexity and unavailability. Induced pluripotent stem cell (iPSC) study is indispensable in the study of the pathophysiology of neurological disorders. Nevertheless, monolayer systems lack the cytoarchitecture necessary for cellular interactions and neurological disease modeling. Brain organoids generated from human pluripotent stem cells supply an ideal environment to model both cellular interactions and pathophysiology of the human brain. This review article discusses the composition and interactions among neural lineage and non-central nervous system cell types in brain organoids, current studies, and future perspectives in brain organoid research. Ultimately, the promise of brain organoids is to unveil previously inaccessible features of neurobiology that emerge from complex cellular interactions and to improve our mechanistic understanding of neural development and diseases.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02369-8.

Substituted N-(4-amino-2-chlorophenyl)-5-chloro-2-hydroxybenzamide analogues potently inhibit respiratory syncytial virus (RSV) replication and RSV infection-associated inflammatory responses

Respiratory syncytial virus (RSV) is a leading cause of lower respiratory tract infection in young children, and specific treatment for RSV infections remains unavailable. We herein reported a series of substituted N-(4-amino-2-chlorophenyl)-5-chloro-2-hydroxybenzamide analogues as potent RSV inhibitors. Among them, six low cytotoxic compounds (11, 12, 15, 22, 26, and 28) have been identified and selected to study associated inhibitory mechanisms. All these compounds suppressed not only the viral replication but also RSV-induced IRF3 and NF-κB activation and associated production of cytokines/chemokines. The two most potent compounds (15 and 22) were selected for further molecular mechanism studies associated with their suppression effect on RSV-activated IRF3 and NF-κB. These two compounds decreased RSV-induced IRF3 phosphorylation at serine 396 and p65 phosphorylation at serine 536 at both early and late infection phases. In addition, compound 22 also inhibited RSV-induced p65 phosphorylation at serine 276 at the late phase of RSV infection.

Drug repurposing approach to combating coronavirus: Potential drugs and drug targets

In the past two decades, three highly pathogenic human coronaviruses severe acute respiratory syndrome coronavirus (SARS-CoV), Middle East respiratory syndrome coronavirus, and, recently, SARS-CoV-2, have caused pandemics of severe acute respiratory diseases with alarming morbidity and mortality. Due to the lack of specific anti-CoV therapies, the ongoing pandemic of coronavirus disease 2019 (COVID-19) poses a great challenge to clinical management and highlights an urgent need for effective interventions. Drug repurposing is a rapid and feasible strategy to identify effective drugs for combating this deadly infection. In this review, we summarize the therapeutic CoV targets, focus on the existing small molecule drugs that have the potential to be repurposed for existing and emerging CoV infections of the future, and discuss the clinical progress of developing small molecule drugs for COVID-19.

Discovery of a Small Molecule Inhibitor of Human Adenovirus Capable of Preventing Escape from the Endosome

Human adenoviruses (HAdVs) display a wide range of tissue tropism and can cause an array of symptoms from mild respiratory illnesses to disseminated and life-threatening infections in immunocompromised individuals. However, no antiviral drug has been approved specifically for the treatment of HAdV infections. Herein, we report our continued efforts to optimize salicylamide derivatives and discover compound 16 (JMX0493) as a potent inhibitor of HAdV infection. Compound 16 displays submicromolar IC₅₀ values, a higher selectivity index (SI > 100) and 2.5-fold virus yield reduction compared to our hit compound niclosamide. Moreover, unlike niclosamide, our mechanistic studies suggest that the antiviral activity of compound 16 against HAdV is achieved through the inhibition of viral particle escape from the endosome, which bars subsequent uncoating and the presentation of lytic protein VI.

Discovery of Novel Substituted N-(4-Amino-2-chlorophenyl)-5-chloro-2-hydroxybenzamide Analogues as Potent Human Adenovirus Inhibitors

An effective therapy for human adenovirus (HAdV) infections in immunocompromised patients and healthy individuals with community-acquired pneumonia remains an unmet medical need. We herein reported a series of novel substituted N-(4-amino-2-chlorophenyl)-5-chloro-2-hydroxybenzamide analogues as potent HAdV inhibitors. Compounds 6, 15, 29, 40, 43, 46, 47, and 54 exhibited increased selectivity indexes (SI > 100) compared to the lead compound niclosamide, while maintaining sub-micromolar to low micromolar potency against HAdV. The preliminary mechanistic studies indicated that compounds 6 and 43 possibly target the HAdV DNA replication process, while compounds 46 and 47 suppress later steps of HAdV life cycle. Notably, among these derivatives, compound 15 showed improved anti-HAdV activity (IC₅₀ = 0.27 μM), significantly decreased cytotoxicity (CC₅₀ = 156.8 μM), and low in vivo toxicity (maximum tolerated dose = 150 mg/kg in hamster) as compared with niclosamide, supporting its further in vivo efficacy studies for the treatment of HAdV infections.