Identification of small molecules capable of enhancing viral membrane fusion.

Several approaches have been developed to analyze the entry of highly pathogenic viruses. In this study, we report the implementation of a Bimolecular Multicellular Complementation (BiMuC) assay to safely and efficiently monitor SARS-CoV-2 S-mediated membrane fusion without the need for microscopy-based equipment. Using BiMuC, we screened a library of approved drugs and identified compounds that enhance S protein-mediated cell-cell membrane fusion. Among them, ethynylestradiol promotes the growth of SARS-CoV-2 and Influenza A virus in vitro. Our findings demonstrate the potential of BiMuC for identifying small molecules that modulate the life cycle of enveloped viruses, including SARS-CoV-2.

In Silico Binding of 2-Aminocyclobutanones to SARS-CoV-2 Nsp13 Helicase and Demonstration of Antiviral Activity.

The landscape of viral strains and lineages of SARS-CoV-2 keeps changing and is currently dominated by Delta and Omicron variants. Members of the latest Omicron variants, including BA.1, are showing a high level of immune evasion, and Omicron has become a prominent variant circulating globally. In our search for versatile medicinal chemistry scaffolds, we prepared a library of substituted ɑ-aminocyclobutanones from an ɑ-aminocyclobutanone synthon (11). We performed an in silico screen of this actual chemical library as well as other virtual 2-aminocyclobutanone analogs against seven SARS-CoV-2 nonstructural proteins to identify potential drug leads against SARS-CoV-2, and more broadly against coronavirus antiviral targets. Several of these analogs were initially identified as in silico hits against SARS-CoV-2 nonstructural protein 13 (Nsp13) helicase through molecular docking and dynamics simulations. Antiviral activity of the original hits as well as ɑ-aminocyclobutanone analogs that were predicted to bind more tightly to SARS-CoV-2 Nsp13 helicase are reported. We now report cyclobutanone derivatives that exhibit anti-SARS-CoV-2 activity. Furthermore, the Nsp13 helicase enzyme has been the target of relatively few target-based drug discovery efforts, in part due to a very late release of a high-resolution structure accompanied by a limited understanding of its protein biochemistry. In general, antiviral agents initially efficacious against wild-type SARS-CoV-2 strains have lower activities against variants due to heavy viral loads and greater turnover rates, but the inhibitors we are reporting have higher activities against the later variants than the wild-type (10-20X). We speculate this could be due to Nsp13 helicase being a critical bottleneck in faster replication rates of the new variants, so targeting this enzyme affects these variants to an even greater extent. This work calls attention to cyclobutanones as a useful medicinal chemistry scaffold, and the need for additional focus on the discovery of Nsp13 helicase inhibitors to combat the aggressive and immune-evading variants of concern (VOCs).

High throughput screening for drugs that inhibit 3C-like protease in SARS-CoV-2.

The SARS coronavirus 2 (SARS-CoV-2) pandemic remains a major problem in many parts of the world and infection rates remain at extremely high levels. This high prevalence drives the continued emergence of new variants, and possibly ones that are more vaccine-resistant and that can drive infections even in highly vaccinated populations. The high rate of variant evolution makes clear the need for new therapeutics that can be clinically applied to minimize or eliminate the effects of COVID-19. With a hurdle of 10 years, on average, for first in class small molecule therapeutics to achieve FDA approval, the fastest way to identify therapeutics is by drug repurposing. To this end, we developed a high throughput cell-based screen that incorporates the essential viral 3C-like protease and its peptide cleavage site into a luciferase complementation assay to evaluate the efficacy of known drugs encompassing approximately 15,000 clinical-stage or FDA-approved small molecules. Confirmed inhibitors were also tested to determine their cytotoxic properties. Medicinal chemistry efforts to optimize the hits identified Tranilast as a potential lead. Here, we report the rapid screening and identification of potentially relevant drugs that exhibit selective inhibition of the SARS-CoV-2 viral 3C-like protease.

Unraveling the mystery of efficacy in Chinese medicine formula: New approaches and technologies for research on pharmacodynamic substances.

Traditional Chinese medicine (TCM) is the key to unlock treasures of Chinese civilization. TCM and its compound play a beneficial role in medical activities to cure diseases, especially in major public health events such as novel coronavirus epidemics across the globe. The chemical composition in Chinese medicine formula is complex and diverse, but their effective substances resemble "mystery boxes". Revealing their active ingredients and their mechanisms of action has become focal point and difficulty of research for herbalists. Although the existing research methods are numerous and constantly updated iteratively, there is remain a lack of prospective reviews. Hence, this paper provides a comprehensive account of existing new approaches and technologies based on previous studies with an in vitro to in vivo perspective. In addition, the bottlenecks of studies on Chinese medicine formula effective substances are also revealed. Especially, we look ahead to new perspectives, technologies and applications for its future development. This work reviews based on new perspectives to open horizons for the future research. Consequently, herbal compounding pharmaceutical substances study should carry on the essence of TCM while pursuing innovations in the field.

A DNA-based non-infectious replicon system to study SARS-CoV-2 RNA synthesis.

The coronavirus disease-2019 (COVID-19) pandemic caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has seriously affected public health around the world. In-depth studies on the pathogenic mechanisms of SARS-CoV-2 is urgently necessary for pandemic prevention. However, most laboratory studies on SARS-CoV-2 have to be carried out in bio-safety level 3 (BSL-3) laboratories, greatly restricting the progress of relevant experiments. In this study, we used a bacterial artificial chromosome (BAC) method to assemble a SARS-CoV-2 replication and transcription system in Vero E6 cells without virion envelope formation, thus avoiding the risk of coronavirus exposure. Furthermore, an improved real-time quantitative reverse transcription PCR (RT-qPCR) approach was used to distinguish the replication of full-length replicon RNAs and transcription of subgenomic RNAs (sgRNAs). Using the SARS-CoV-2 replicon, we demonstrated that the nucleocapsid (N) protein of SARS-CoV-2 facilitates the transcription of sgRNAs in the discontinuous synthesis process. Moreover, two high-frequency mutants of N protein, R203K and S194L, can obviously enhance the transcription level of the replicon, hinting that these mutations likely allow SARS-CoV-2 to spread and reproduce more quickly. In addition, remdesivir and chloroquine, two well-known drugs demonstrated to be effective against coronavirus in previous studies, also inhibited the transcription of our replicon, indicating the potential applications of this system in antiviral drug discovery. Overall, we developed a bio-safe and valuable replicon system of SARS-CoV-2 that is useful to study the mechanisms of viral RNA synthesis and has potential in novel antiviral drug screening.

Identifying Small-Molecule Inhibitors of SARS-CoV-2 RNA-Dependent RNA Polymerase by Establishing a Fluorometric Assay.

SARS-CoV-2 (severe acute respiratory syndrome coronavirus-2), a member of the coronavirus family, appeared in 2019 and has caused the largest global public health and economic emergency in recent history, affecting almost all sectors of society. SARS-CoV-2 is a single-stranded positive-sense RNA virus that relies on RNA-dependent RNA polymerase (RdRp) activity in viral transcription and replication. Due to its high sequence and structural conservation in coronavirus and new SARS-CoV-2 variants, RdRp has been recognized as the key therapeutic target to design novel antiviral strategies. Nucleotide analogs (NAs), such as remdesivir, is the most promising class of RdRp inhibitors to be used in the treatment of COVID-19. However, the presence of exonucleases in SARS-CoV-2 caused a great challenge to NAs; the excision of incorporated NAs will lead to viral resistance to this group of inhibitors. Here, we expressed active RdRp protein in both a eukaryotic expression system of baculovirus-infected insect cells and a prokaryotic expression system of Escherichia coli cells. Nsp7 and nsp8 of the functional RdRp holoenzyme were generated in E. coli. An in vitro RdRp activity assay has been established with a reconstituted nsp12/nsp7/nsp8 complex and biotin-labeled self-priming RNAs, and the activity of the RdRp complex was determined by detecting binding and extension of RNAs. Moreover, to meet the needs of high-throughput drug screening, we developed a fluorometric approach based on dsRNA quantification to assess the catalytic activity of the RdRp complex, which is also suitable for testing in 96-well plates. We demonstrated that the active triphosphate form of remdesivir (RTP) and several reported non-nucleotide analog viral polymerase inhibitors blocked the RdRp in the in vitro RdRp activity assay and high-throughput screening model. This high-throughput screening model has been applied to a custom synthetic chemical and natural product library of thousands of compounds for screening SARS-CoV-2 RdRp inhibitors. Our efficient RdRp inhibitor discovery system provides a powerful platform for the screening, validation, and evaluation of novel antiviral molecules targeting SARS-CoV-2 RdRp, particularly for non-nucleotide antivirals drugs (NNAs).

Identification of potent small molecule inhibitors of SARS-CoV-2 entry.

The severe acute respiratory syndrome coronavirus 2 responsible for COVID-19 remains a persistent threat to mankind, especially for the immunocompromised and elderly for which the vaccine may have limited effectiveness. Entry of SARS-CoV-2 requires a high affinity interaction of the viral spike protein with the cellular receptor angiotensin-converting enzyme 2. Novel mutations on the spike protein correlate with the high transmissibility of new variants of SARS-CoV-2, highlighting the need for small molecule inhibitors of virus entry into target cells. We report the identification of such inhibitors through a robust high-throughput screen testing 15,000 small molecules from unique libraries. Several leads were validated in a suite of mechanistic assays, including whole cell SARS-CoV-2 infectivity assays. The main lead compound, calpeptin, was further characterized using SARS-CoV-1 and the novel SARS-CoV-2 variant entry assays, SARS-CoV-2 protease assays and molecular docking. This study reveals calpeptin as a potent and specific inhibitor of SARS-CoV-2 and some variants.

A short survey of dengue protease inhibitor development in the past 6 years (2015-2020) with an emphasis on similarities between DENV and SARS-CoV-2 proteases.

Dengue remains a disease of significant concern, responsible for nearly half of all arthropod-borne disease cases across the globe. Due to the lack of potent and targeted therapeutics, palliative treatment and the adoption of preventive measures remain the only available options. Compounding the problem further, the failure of the only dengue vaccine, Dengvaxia®, also delivered a significant blow to any hopes for the treatment of dengue fever. However, the success of Human Immuno-deficiency Virus (HIV) and Hepatitis C Virus (HCV) protease inhibitors in the past have continued to encourage researchers to investigate other viral protease targets. Dengue virus (DENV) NS2B-NS3 protease is an attractive target partly due to its role in polyprotein processing and also for being the most conserved domain in the viral genome. During the early days of the COVID-19 pandemic, a few cases of Dengue-COVID 19 co-infection were reported. In this review, we compared the substrate-peptide residue preferences and the residues lining the sub-pockets of the proteases of these two viruses and analyzed the significance of this similarity. Also, we attempted to abridge the developments in anti-dengue drug discovery in the last six years (2015-2020), focusing on critical discoveries that influenced the research.

Discovery of SARS-CoV-2-E channel inhibitors as antiviral candidates.

Lack of efficiency has been a major problem shared by all currently developed anti-SARS-CoV-2 therapies. Our previous study shows that SARS-CoV-2 structural envelope (2-E) protein forms a type of cation channel, and heterogeneously expression of 2-E channels causes host cell death. In this study we developed a cell-based high throughput screening (HTS) assay and used it to discover inhibitors against 2-E channels. Among 4376 compounds tested, 34 hits with cell protection activity were found. Followed by an anti-viral analysis, 15 compounds which could inhibit SARS-CoV-2 replication were identified. In electrophysiological experiments, three representatives showing inhibitory effect on 2-E channels were chosen for further characterization. Among them, proanthocyanidins directly bound to 2-E channel with binding affinity (KD) of 22.14 µM in surface plasmon resonance assay. Molecular modeling and docking analysis revealed that proanthocyanidins inserted into the pore of 2-E N-terminal vestibule acting as a channel blocker. Consistently, mutations of Glu 8 and Asn 15, two residues lining the proposed binding pocket, abolished the inhibitory effects of proanthocyanidins. The natural product proanthocyanidins are widely used as cosmetic, suggesting a potential of proanthocyanidins as disinfectant for external use. This study further demonstrates that 2-E channel is an effective antiviral drug target and provides a potential antiviral candidate against SARS-CoV-2.

SARS-COV-2 spike binding to ACE2 in living cells monitored by TR-FRET.

Targeting the interaction between the SARS-CoV-2 spike protein and human ACE2, its primary cell membrane receptor, is a promising therapeutic strategy to prevent viral entry. Recent in vitro studies revealed that the receptor binding domain (RBD) of the spike protein plays a prominent role in ACE2 binding, yet a simple and quantitative assay for monitoring this interaction in a cellular environment is lacking. Here, we developed an RBD-ACE2 binding assay that is based on time-resolved FRET, which reliably monitors the interaction in a physiologically relevant and cellular context. Because it is modular, the assay can monitor the impact of different cellular components, such as heparan sulfate, lipids, and membrane proteins on the RBD-ACE2 interaction and it can be extended to the full-length spike protein. The assay is HTS compatible and can detect small-molecule competitive and allosteric modulators of the RBD-ACE2 interaction with high relevance for SARS-CoV-2 therapeutics.

High-throughput Sequencing in Vaccine Research.

The world of vaccines has changed tremendously since the time of Louis Pasteur. In the present day, it is regarded as vaccinology, a discipline which includes not only the knowledge of vaccine production, strategies for its delivery and influence on the clinical course of disease and the response of the host immune system but also regulatory, ethical, economic and ecological aspects of their use. A hundred years after Pasteur created the first vaccine, there was another scientific breakthrough of great importance in this field, i. e. Sanger sequencing. Progress in genome sequencing and other molecular techniques over the intervening 40 years has been enormous. High-throughput sequencing (HTS) platforms and bioinformatics tools are becoming widely available, falling in cost, and results are achieved very quickly. They enable the construction of modern vaccines, as well as the assessment of their safety, effectiveness and impact on the host organism and the environment. These techniques can also provide a tool for quality control of vaccines. Unprecedented possibilities are opened up by the HTS technique, but limiting factors on its implementation have to be contended with such as lack of reference materials and problems with method optimisation or validation. In the face of the current COVID-19 pandemic, a significant role is allotted to this sequencing technique while an effective vaccine against the disease caused by SARS-CoV-2 is sough.

A new high-content screening assay of the entire hepatitis B virus life cycle identifies novel antivirals.

BACKGROUND & AIMS: Chronic hepatitis B is an incurable disease. Addressing the unmet medical need for therapies has been hampered by a lack of suitable cell culture models to investigate the HBV life cycle in a single experimental setup. We sought to develop a platform suitable to investigate all aspects of the entire HBV life cycle. METHODS: HepG2-NTCPsec+ cells were inoculated with HBV. Supernatants of infected cells were transferred to naïve cells. Inhibition of infection was determined in primary and secondary infected cells by high-content imaging of viral and cellular factors. Novel antivirals were triaged in cells infected with cell culture- or patient-derived HBV and in stably virus replicating cells. HBV internalisation and target-based receptor binding assays were conducted. RESULTS: We developed an HBV platform, screened 2,102 drugs and bioactives, and identified 3 early and 38 late novel HBV life cycle inhibitors using infectious HBV genotype D. Two early inhibitors, pranlukast (EC50 4.3 µM; 50% cytotoxic concentration [CC50] >50 µM) and cytochalasin D (EC50 0.07 µM; CC50 >50 µM), and 2 late inhibitors, fludarabine (EC50 0.1 µM; CC50 13.4 µM) and dexmedetomidine (EC50 6.2 µM; CC50 >50 µM), were further investigated. Pranlukast inhibited HBV preS1 binding, whereas cytochalasin D prevented the internalisation of HBV. Fludarabine inhibited the secretion of HBV progeny DNA, whereas dexmedetomidine interfered with the infectivity of HBV progeny. Patient-derived HBV genotype C was efficiently inhibited by fludarabine (EC50 0.08 µM) and dexmedetomidine (EC50 8.7 µM). CONCLUSIONS: The newly developed high-content assay is suitable to screen large-scale drug libraries, enables monitoring of the entire HBV life cycle, and discriminates between inhibition of early and late viral life cycle events. LAY SUMMARY: HBV infection is an incurable, chronic disease with few available treatments. Addressing this unmet medical need has been hampered by a lack of suitable cell culture models to study the entire viral life cycle in a single experimental setup. We developed an image-based approach suitable to screen large numbers of drugs, using a cell line that can be infected by HBV and produces large amounts of virus particles. By transferring viral supernatants from these infected cells to uninfected target cells, we could monitor the entire viral life cycle. We used this system to screen drug libraries and identified novel anti-HBV inhibitors that potently inhibit HBV in various phases of its life cycle. This assay will be an important new tool to study the HBV life cycle and accelerate the development of novel therapeutic strategies.

High-Throughput Affinity Selection Mass Spectrometry Using SAMDI-MS to Identify Small-Molecule Binders of the Human Rhinovirus 3C Protease.

Affinity selection mass spectrometry (ASMS) has emerged as a powerful high-throughput screening tool used in drug discovery to identify novel ligands against therapeutic targets. This report describes the first high-throughput screen using a novel self-assembled monolayer desorption ionization (SAMDI)-ASMS methodology to reveal ligands for the human rhinovirus 3C (HRV3C) protease. The approach combines self-assembled monolayers of alkanethiolates on gold with matrix-assisted laser desorption ionization time-of-flight (MALDI TOF) mass spectrometry (MS), a technique termed SAMDI-ASMS. The primary screen of more than 100,000 compounds in pools of 8 compounds per well was completed in less than 8 h, and informs on the binding potential and selectivity of each compound. Initial hits were confirmed in follow-up SAMDI-ASMS experiments in single-concentration and dose-response curves. The ligands identified by SAMDI-ASMS were further validated using differential scanning fluorimetry (DSF) and in functional protease assays against HRV3C and the related SARS-CoV-2 3CLpro enzyme. SAMDI-ASMS offers key benefits for drug discovery over traditional ASMS approaches, including the high-throughput workflow and readout, minimizing compound misbehavior by using smaller compound pools, and up to a 50-fold reduction in reagent consumption. The flexibility of this novel technology opens avenues for high-throughput ASMS assays of any target, thereby accelerating drug discovery for diverse diseases.

Drug repurposing screens reveal cell-type-specific entry pathways and FDA-approved drugs active against SARS-Cov-2.

There is an urgent need for antivirals to treat the newly emerged severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). To identify new candidates, we screen a repurposing library of ∼3,000 drugs. Screening in Vero cells finds few antivirals, while screening in human Huh7.5 cells validates 23 diverse antiviral drugs. Extending our studies to lung epithelial cells, we find that there are major differences in drug sensitivity and entry pathways used by SARS-CoV-2 in these cells. Entry in lung epithelial Calu-3 cells is pH independent and requires TMPRSS2, while entry in Vero and Huh7.5 cells requires low pH and triggering by acid-dependent endosomal proteases. Moreover, we find nine drugs are antiviral in respiratory cells, seven of which have been used in humans, and three are US Food and Drug Administration (FDA) approved, including cyclosporine. We find that the antiviral activity of cyclosporine is targeting Cyclophilin rather than calcineurin, revealing essential host targets that have the potential for rapid clinical implementation.

Drug Repurposing Screen for Compounds Inhibiting the Cytopathic Effect of SARS-CoV-2.

Drug repurposing is a rapid approach to identify therapeutics for the treatment of emerging infectious diseases such as COVID-19. To address the urgent need for treatment options, we carried out a quantitative high-throughput screen using a SARS-CoV-2 cytopathic assay with a compound collection of 8,810 approved and investigational drugs, mechanism-based bioactive compounds, and natural products. Three hundred and nineteen compounds with anti-SARS-CoV-2 activities were identified and confirmed, including 91 approved drugs and 49 investigational drugs. The anti-SARS-CoV-2 activities of 230 of these confirmed compounds, of which 38 are approved drugs, have not been previously reported. Chlorprothixene, methotrimeprazine, and piperacetazine were the three most potent FDA-approved drugs with anti-SARS-CoV-2 activities. These three compounds have not been previously reported to have anti-SARS-CoV-2 activities, although their antiviral activities against SARS-CoV and Ebola virus have been reported. These results demonstrate that this comprehensive data set is a useful resource for drug repurposing efforts, including design of new drug combinations for clinical trials for SARS-CoV-2.

High-Throughput Screening for Drugs That Inhibit Papain-Like Protease in SARS-CoV-2.

The emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in late 2019 has triggered an ongoing global pandemic whereby infection may result in a lethal severe pneumonia-like disease designated as coronavirus disease 2019 (COVID-19). To date, millions of confirmed cases and hundreds of thousands of deaths have been reported worldwide, and there are currently no medical countermeasures available to prevent or treat the disease. The purported development of a vaccine could require at least 1-4 years, while the typical timeline from hit finding to drug registration of an antiviral is >10 years. Thus, repositioning of known drugs can significantly accelerate the development and deployment of therapies for COVID-19. To identify therapeutics that can be repurposed as SARS-CoV-2 antivirals, we developed and initiated a high-throughput cell-based screen that incorporates the essential viral papain-like protease (PLpro) and its peptide cleavage site into a luciferase complementation assay to evaluate the efficacy of known drugs encompassing approximately 15,000 clinical-stage or US Food and Drug Administration (FDA)-approved small molecules. Confirmed inhibitors were also tested to determine their cytotoxic properties. Here, we report the identification of four clinically relevant drugs that exhibit selective inhibition of the SARS-CoV-2 viral PLpro.

High-throughput viral microneutralization method for feline coronavirus using image cytometry.

Feline coronaviruses (FCoV) are members of the alphacoronavirus genus that are further characterized by serotype (types I and II) based on the antigenicity of the spike (S) protein and by pathotype based on the associated clinical conditions. Feline enteric coronaviruses (FECV) are associated with the vast majority of infections and are typically asymptomatic. Within individual animals, FECV can mutate and cause a severe and usually fatal disease called feline infectious peritonitis (FIP), the leading infectious cause of death in domestic cat populations. There are no approved antiviral drugs or recommended vaccines to treat or prevent FCoV infection. The plaque reduction neutralization test (PRNT) traditionally employed to assess immune responses and to screen therapeutic and vaccine candidates is time-consuming, low-throughput, and typically requires 2-3 days for the formation and manual counting of cytolytic plaques. Host cells are capable of carrying heavy viral burden in the absence of visible cytolytic effects, thereby reducing the sensitivity of the assay. In addition, operator-to-operator variation can generate uncertainty in the results and digital records are not automatically created. To address these challenges we developed a novel high-throughput viral microneutralization assay, with quantification of virus-infected cells performed in a plate-based image cytometer. Host cell seeding density, microplate surface coating, virus concentration and incubation time, wash buffer and fluorescent labeling were optimized. Subsequently, this FCoV viral neutralization assay was used to explore immune correlates of protection using plasma from naturally FECV-infected cats. We demonstrate that the high-throughput viral neutralization assay using the Celigo Image Cytometer provides a robust and efficient method for the rapid screening of therapeutic antibodies, antiviral compounds, and vaccines. This method can be applied to various viral infectious diseases to accelerate vaccine and antiviral drug discovery and development.