Design of MERS-CoV entry inhibitory short peptides based on helix-stabilizing strategies.

Interaction between Middle East respiratory syndrome coronavirus (MERS-CoV) spike (S) protein heptad repeat-1 domain (HR1) and heptad repeat-2 domain (HR2) is critical for the MERS-CoV fusion process. This interaction is mediated by the α-helical region from HR2 and the hydrophobic groove in a central HR1 trimeric coiled coil. We sought to develop a short peptidomimetic to act as a MERS-CoV fusion inhibitor by reproducing the key recognition features of HR2 helix. This was achieved by the use of helix-stabilizing strategies, including substitution with unnatural helix-favoring amino acids, introduction of ion pair interactions, and conjugation of palmitic acid. The resulting 23-mer lipopeptide, termed AEEA-C16, inhibits MERS-CoV S protein-mediated cell-cell fusion at a low micromolar level comparable to that of the 36-mer HR2 peptide HR2P-M2. Collectively, our studies provide new insights into developing short peptide-based antiviral agents to treat MERS-CoV infection.

Harnessing autophagy to fight SARS-CoV-2: An update in view of recent drug development efforts.

Drug repurposing is an attractive option for identifying new treatment strategies, in particular in extraordinary situations of urgent need such as the current coronavirus disease 2019 (Covid-19) pandemic. Recently, the World Health Organization announced testing of three drugs as potential Covid-19 therapeutics that are known for their dampening effect on the immune system. Thus, the underlying concept of selecting these drugs is to temper the potentially life-threatening overshooting of the immune system reacting to severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection. This viewpoint discusses the possibility that the impact of these and other drugs on autophagy contributes to their therapeutic effect by hampering the SARS-CoV-2 life cycle.

Middle East Respiratory Syndrome Coronavirus.

The past two decades have witnessed the emergence of three zoonotic coronaviruses which have jumped species to cause lethal disease in humans: severe acute respiratory syndrome coronavirus 1 (SARS-CoV-1), Middle East respiratory syndrome coronavirus (MERS-CoV), and SARS-CoV-2. MERS-CoV emerged in Saudi Arabia in 2012 and the origins of MERS-CoV are not fully understood. Genomic analysis indicates it originated in bats and transmitted to camels. Human-to-human transmission occurs in varying frequency, being highest in healthcare environment and to a lesser degree in the community and among family members. Several nosocomial outbreaks of human-to-human transmission have occurred, the largest in Riyadh and Jeddah in 2014 and South Korea in 2015. MERS-CoV remains a high-threat pathogen identified by World Health Organization as a priority pathogen because it causes severe disease that has a high mortality rate, epidemic potential, and no medical countermeasures. MERS-CoV has been identified in dromedaries in several countries in the Middle East, Africa, and South Asia. MERS-CoV-2 causes a wide range of clinical presentations, although the respiratory system is predominantly affected. There are no specific antiviral treatments, although recent trials indicate that combination antivirals may be useful in severely ill patients. Diagnosing MERS-CoV early and implementation infection control measures are critical to preventing hospital-associated outbreaks. Preventing MERS relies on avoiding unpasteurized or uncooked animal products, practicing safe hygiene habits in health care settings and around dromedaries, community education and awareness training for health workers, as well as implementing effective control measures. Effective vaccines for MERS-COV are urgently needed but still under development.

A genome-wide CRISPR screen identifies interactors of the autophagy pathway as conserved coronavirus targets.

Over the past 20 years, 3 highly pathogenic human coronaviruses (HCoVs) have emerged-Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV), Middle East Respiratory Syndrome Coronavirus (MERS-CoV), and, most recently, Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2)-demonstrating that coronaviruses (CoVs) pose a serious threat to human health and highlighting the importance of developing effective therapies against them. Similar to other viruses, CoVs are dependent on host factors for their survival and replication. We hypothesized that evolutionarily distinct CoVs may exploit similar host factors and pathways to support their replication cycles. Herein, we conducted 2 independent genome-wide CRISPR/Cas-9 knockout (KO) screens to identify MERS-CoV and HCoV-229E host dependency factors (HDFs) required for HCoV replication in the human Huh7 cell line. Top scoring genes were further validated and assessed in the context of MERS-CoV and HCoV-229E infection as well as SARS-CoV and SARS-CoV-2 infection. Strikingly, we found that several autophagy-related genes, including TMEM41B, MINAR1, and the immunophilin FKBP8, were common host factors required for pan-CoV replication. Importantly, inhibition of the immunophilin protein family with the compounds cyclosporine A, and the nonimmunosuppressive derivative alisporivir, resulted in dose-dependent inhibition of CoV replication in primary human nasal epithelial cell cultures, which recapitulate the natural site of virus replication. Overall, we identified host factors that are crucial for CoV replication and demonstrated that these factors constitute potential targets for therapeutic intervention by clinically approved drugs.

Drug repurposing against SARS-CoV-1, SARS-CoV-2 and MERS-CoV.

Since the beginning of the COVID-19 pandemic, large in silico screening studies and numerous in vitro studies have assessed the antiviral activity of various drugs on SARS-CoV-2. In the context of health emergency, drug repurposing represents the most relevant strategy because of the reduced time for approval by international medicines agencies, the low cost of development and the well-known toxicity profile of such drugs. Herein, we aim to review drugs with in vitro antiviral activity against SARS-CoV-2, combined with molecular docking data and results from preliminary clinical studies. Finally, when considering all these previous findings, as well as the possibility of oral administration, 11 molecules consisting of nelfinavir, favipiravir, azithromycin, clofoctol, clofazimine, ivermectin, nitazoxanide, amodiaquine, heparin, chloroquine and hydroxychloroquine, show an interesting antiviral activity that could be exploited as possible drug candidates for COVID-19 treatment.

Promising Antiviral Activities of Natural Flavonoids against SARS-CoV-2 Targets: Systematic Review.

The ongoing COVID-19 pandemic, caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) became a globally leading public health concern over the past two years. Despite the development and administration of multiple vaccines, the mutation of newer strains and challenges to universal immunity has shifted the focus to the lack of efficacious drugs for therapeutic intervention for the disease. As with SARS-CoV, MERS-CoV, and other non-respiratory viruses, flavonoids present themselves as a promising therapeutic intervention given their success in silico, in vitro, in vivo, and more recently, in clinical studies. This review focuses on data from in vitro studies analyzing the effects of flavonoids on various key SARS-CoV-2 targets and presents an analysis of the structure-activity relationships for the same. From 27 primary papers, over 69 flavonoids were investigated for their activities against various SARS-CoV-2 targets, ranging from the promising 3C-like protease (3CLpro) to the less explored nucleocapsid (N) protein; the most promising were quercetin and myricetin derivatives, baicalein, baicalin, EGCG, and tannic acid. We further review promising in silico studies featuring activities of flavonoids against SARS-CoV-2 and list ongoing clinical studies involving the therapeutic potential of flavonoid-rich extracts in combination with synthetic drugs or other polyphenols and suggest prospects for the future of flavonoids against SARS-CoV-2.

A novel class of TMPRSS2 inhibitors potently block SARS-CoV-2 and MERS-CoV viral entry and protect human epithelial lung cells.

The host cell serine protease TMPRSS2 is an attractive therapeutic target for COVID-19 drug discovery. This protease activates the Spike protein of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and of other coronaviruses and is essential for viral spread in the lung. Utilizing rational structure-based drug design (SBDD) coupled to substrate specificity screening of TMPRSS2, we have discovered covalent small-molecule ketobenzothiazole (kbt) TMPRSS2 inhibitors which are structurally distinct from and have significantly improved activity over the existing known inhibitors Camostat and Nafamostat. Lead compound MM3122 (4) has an IC50 (half-maximal inhibitory concentration) of 340 pM against recombinant full-length TMPRSS2 protein, an EC50 (half-maximal effective concentration) of 430 pM in blocking host cell entry into Calu-3 human lung epithelial cells of a newly developed VSV-SARS-CoV-2 chimeric virus, and an EC50 of 74 nM in inhibiting cytopathic effects induced by SARS-CoV-2 virus in Calu-3 cells. Further, MM3122 blocks Middle East respiratory syndrome coronavirus (MERS-CoV) cell entry with an EC50 of 870 pM. MM3122 has excellent metabolic stability, safety, and pharmacokinetics in mice, with a half-life of 8.6 h in plasma and 7.5 h in lung tissue, making it suitable for in vivo efficacy evaluation and a promising drug candidate for COVID-19 treatment.

Viral Inactivation with Emphasis on SARS-CoV-2 Using Physical and Chemical Disinfectants.

BACKGROUND: Recently, an outbreak of a novel human coronavirus SARS-CoV-2 has become a world health concern leading to severe respiratory tract infections in humans. Virus transmission occurs through person-to-person contact, respiratory droplets, and contaminated hands or surfaces. Accordingly, we aim at reviewing the literature on all information available about the persistence of coronaviruses, including human and animal coronaviruses, on inanimate surfaces and inactivation strategies with biocides employed for chemical and physical disinfection. METHOD: A comprehensive search was systematically conducted in main databases from 1998 to 2020 to identify various viral disinfectants associated with HCoV and methods for control and prevention of this newly emerged virus. RESULTS: The analysis of 62 studies shows that human coronaviruses such as severe acute respiratory syndrome (SARS) coronavirus, Middle East respiratory syndrome (MERS) coronavirus or endemic human coronaviruses (HCoV), canine coronavirus (CCV), transmissible gastroenteritis virus (TGEV), and mouse hepatitis virus (MHV) can be efficiently inactivated by physical and chemical disinfectants at different concentrations (70, 80, 85, and 95%) of 2-propanol (70 and 80%) in less than or equal to 60 s and 0.5% hydrogen peroxide or 0.1% sodium hypochlorite within 1 minute. Additionally, glutaraldehyde (0.5-2%), formaldehyde (0.7-1%), and povidone-iodine (0.1-0.75%) could readily inactivate coronaviruses. Moreover, dry heat at 56°C, ultraviolet light dose of 0.2 to 140 J/cm2, and gamma irradiation could effectively inactivate coronavirus. The WHO recommends the use of 0.1% sodium hypochlorite solution or an ethanol-based disinfectant with an ethanol concentration between 62% and 71%. CONCLUSION: The results of the present study can help researchers, policymakers, health decision makers, and people perceive and take the correct measures to control and prevent further transmission of COVID-19. Prevention and decontamination will be the main ways to stop the ongoing outbreak of COVID-19.

Identification of ZDHHC17 as a Potential Drug Target for Swine Acute Diarrhea Syndrome Coronavirus Infection.

The recent emergence and spread of zoonotic viruses highlights that animal-sourced viruses are the biggest threat to global public health. Swine acute diarrhea syndrome coronavirus (SADS-CoV) is an HKU2-related bat coronavirus that was spilled over from Rhinolophus bats to swine, causing large-scale outbreaks of severe diarrhea disease in piglets in China. Unlike other porcine coronaviruses, SADS-CoV possesses broad species tissue tropism, including primary human cells, implying a significant risk of cross-species spillover. To explore host dependency factors for SADS-CoV as therapeutic targets, we employed genome-wide CRISPR knockout library screening in HeLa cells. Consistent with two independent screens, we identified the zinc finger DHHC-type palmitoyltransferase 17 (ZDHHC17 or ZD17) as an important host factor for SADS-CoV infection. Through truncation mutagenesis, we demonstrated that the DHHC domain of ZD17 that is involved in palmitoylation is important for SADS-CoV infection. Mechanistic studies revealed that ZD17 is required for SADS-CoV genomic RNA replication. Treatment of infected cells with the palmitoylation inhibitor 2-bromopalmitate (2-BP) significantly suppressed SADS-CoV infection. Our findings provide insight on SADS-CoV-host interactions and a potential therapeutic application. IMPORTANCE The recent emergence of deadly zoonotic viral diseases, including Ebola virus and SARS-CoV-2, emphasizes the importance of pandemic preparedness for the animal-sourced viruses with potential risk of animal-to-human spillover. Over the last 2 decades, three significant coronaviruses of bat origin, SARS-CoV, MERS-CoV, and SARS-CoV-2, have caused millions of deaths with significant economy and public health impacts. Lack of effective therapeutics against these coronaviruses was one of the contributing factors to such losses. Although SADS-CoV, another coronavirus of bat origin, was only known to cause fatal diarrhea disease in piglets, the ability to infect cells derived from multiple species, including human, highlights the potential risk of animal-to-human spillover. As part of our effort in pandemic preparedness, we explore SADS-CoV host dependency factors as targets for host-directed therapeutic development and found zinc finger DHHC-type palmitoyltransferase 17 is a promising drug target against SADS-CoV replication. We also demonstrated that a palmitoylation inhibitor, 2-bromopalmitate (2-BP), can be used as an inhibitor for SADS-CoV treatment.

Leveraging publicly available coronavirus data to identify new therapeutic targets for COVID-19.

Many important questions remain regarding severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), the viral pathogen responsible for COVID-19. These questions include the mechanisms explaining the high percentage of asymptomatic but highly infectious individuals, the wide variability in disease susceptibility, and the mechanisms of long-lasting debilitating effects. Bioinformatic analysis of four coronavirus datasets representing previous outbreaks (SARS-CoV-1 and MERS-CoV), as well as SARS-CoV-2, revealed evidence of diverse host factors that appear to be coopted to facilitate virus-induced suppression of interferon-induced innate immunity, promotion of viral replication and subversion and/or evasion of antiviral immune surveillance. These host factors merit further study given their postulated roles in COVID-19-induced loss of smell and brain, heart, vascular, lung, liver, and gut dysfunction.

Multi-level inhibition of coronavirus replication by chemical ER stress.

Coronaviruses (CoVs) are important human pathogens for which no specific treatment is available. Here, we provide evidence that pharmacological reprogramming of ER stress pathways can be exploited to suppress CoV replication. The ER stress inducer thapsigargin efficiently inhibits coronavirus (HCoV-229E, MERS-CoV, SARS-CoV-2) replication in different cell types including primary differentiated human bronchial epithelial cells, (partially) reverses the virus-induced translational shut-down, improves viability of infected cells and counteracts the CoV-mediated downregulation of IRE1α and the ER chaperone BiP. Proteome-wide analyses revealed specific pathways, protein networks and components that likely mediate the thapsigargin-induced antiviral state, including essential (HERPUD1) or novel (UBA6 and ZNF622) factors of ER quality control, and ER-associated protein degradation complexes. Additionally, thapsigargin blocks the CoV-induced selective autophagic flux involving p62/SQSTM1. The data show that thapsigargin hits several central mechanisms required for CoV replication, suggesting that this compound (or derivatives thereof) may be developed into broad-spectrum anti-CoV drugs.

The TMPRSS2 Inhibitor Nafamostat Reduces SARS-CoV-2 Pulmonary Infection in Mouse Models of COVID-19.

The coronavirus disease 2019 (COVID-19) pandemic has caused significant morbidity and mortality on a global scale. The etiologic agent, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), initiates host cell entry when its spike protein (S) binds to its receptor, angiotensin-converting enzyme 2 (ACE2). In airway epithelia, the spike protein is cleaved by the cell surface protease TMPRSS2, facilitating membrane fusion and entry at the cell surface. This dependence on TMPRSS2 and related proteases suggests that protease inhibitors might limit SARS-CoV-2 infection in the respiratory tract. Here, we tested two serine protease inhibitors, camostat mesylate and nafamostat mesylate, for their ability to inhibit entry of SARS-CoV-2 and that of a second pathogenic coronavirus, Middle East respiratory syndrome coronavirus (MERS-CoV). Both camostat and nafamostat reduced infection in primary human airway epithelia and in the Calu-3 2B4 cell line, with nafamostat exhibiting greater potency. We then assessed whether nafamostat was protective against SARS-CoV-2 in vivo using two mouse models. In mice sensitized to SARS-CoV-2 infection by transduction with human ACE2, intranasal nafamostat treatment prior to or shortly after SARS-CoV-2 infection significantly reduced weight loss and lung tissue titers. Similarly, prophylactic intranasal treatment with nafamostat reduced weight loss, viral burden, and mortality in K18-hACE2 transgenic mice. These findings establish nafamostat as a candidate for the prevention or treatment of SARS-CoV-2 infection and disease pathogenesis. IMPORTANCE The causative agent of COVID-19, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), requires host cell surface proteases for membrane fusion and entry into airway epithelia. We tested the hypothesis that inhibitors of these proteases, the serine protease inhibitors camostat and nafamostat, block infection by SARS-CoV-2. We found that both camostat and nafamostat reduce infection in human airway epithelia, with nafamostat showing greater potency. We then asked whether nafamostat protects mice against SARS-CoV-2 infection and subsequent COVID-19 lung disease. We performed infections in mice made susceptible to SARS-CoV-2 infection by introducing the human version of ACE2, the SARS-CoV-2 receptor, into their airway epithelia. We observed that pretreating these mice with nafamostat prior to SARS-CoV-2 infection resulted in better outcomes, in the form of less virus-induced weight loss, viral replication, and mortality than that observed in the untreated control mice. These results provide preclinical evidence for the efficacy of nafamostat in treating and/or preventing COVID-19.

A Novel Frameshifting Inhibitor Having Antiviral Activity against Zoonotic Coronaviruses.

Recent outbreaks of zoonotic coronaviruses, such as Middle East respiratory syndrome coronavirus (MERS-CoV) and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), have caused tremendous casualties and great economic shock. Although some repurposed drugs have shown potential therapeutic efficacy in clinical trials, specific therapeutic agents targeting coronaviruses have not yet been developed. During coronavirus replication, a replicase gene cluster, including RNA-dependent RNA polymerase (RdRp), is alternatively translated via a process called -1 programmed ribosomal frameshift (-1 PRF) by an RNA pseudoknot structure encoded in viral RNAs. The coronavirus frameshifting has been identified previously as a target for antiviral therapy. In this study, the frameshifting efficiencies of MERS-CoV, SARS-CoV and SARS-CoV-2 were determined using an in vitro -1 PRF assay system. Our group has searched approximately 9689 small molecules to identify potential -1 PRF inhibitors. Herein, we found that a novel compound, 2-(5-acetylthiophen-2yl)furo[2,3-b]quinoline (KCB261770), inhibits the frameshifting of MERS-CoV and effectively suppresses viral propagation in MERS-CoV-infected cells. The inhibitory effects of 87 derivatives of furo[2,3-b]quinolines were also examined showing less prominent inhibitory effect when compared to compound KCB261770. We demonstrated that KCB261770 inhibits the frameshifting without suppressing cap-dependent translation. Furthermore, this compound was able to inhibit the frameshifting, to some extent, of SARS-CoV and SARS-CoV-2. Therefore, the novel compound 2-(5-acetylthiophen-2yl)furo[2,3-b]quinoline may serve as a promising drug candidate to interfere with pan-coronavirus frameshifting.

Pharmacophore-Based Virtual Screening, Quantum Mechanics Calculations, and Molecular Dynamics Simulation Approaches Identified Potential Natural Antiviral Drug Candidates against MERS-CoV S1-NTD.

Middle East respiratory syndrome coronavirus (MERS-CoV) is a highly infectious zoonotic virus first reported into the human population in September 2012 on the Arabian Peninsula. The virus causes severe and often lethal respiratory illness in humans with an unusually high fatality rate. The N-terminal domain (NTD) of receptor-binding S1 subunit of coronavirus spike (S) proteins can recognize a variety of host protein and mediates entry into human host cells. Blocking the entry by targeting the S1-NTD of the virus can facilitate the development of effective antiviral drug candidates against the pathogen. Therefore, the study has been designed to identify effective antiviral drug candidates against the MERS-CoV by targeting S1-NTD. Initially, a structure-based pharmacophore model (SBPM) to the active site (AS) cavity of the S1-NTD has been generated, followed by pharmacophore-based virtual screening of 11,295 natural compounds. Hits generated through the pharmacophore-based virtual screening have re-ranked by molecular docking and further evaluated through the ADMET properties. The compounds with the best ADME and toxicity properties have been retrieved, and a quantum mechanical (QM) based density-functional theory (DFT) has been performed to optimize the geometry of the selected compounds. Three optimized natural compounds, namely Taiwanhomoflavone B (Amb23604132), 2,3-Dihydrohinokiflavone (Amb23604659), and Sophoricoside (Amb1153724), have exhibited substantial docking energy >-9.00 kcal/mol, where analysis of frontier molecular orbital (FMO) theory found the low chemical reactivity correspondence to the bioactivity of the compounds. Molecular dynamics (MD) simulation confirmed the stability of the selected natural compound to the binding site of the protein. Additionally, molecular mechanics generalized born surface area (MM/GBSA) predicted the good value of binding free energies (ΔG bind) of the compounds to the desired protein. Convincingly, all the results support the potentiality of the selected compounds as natural antiviral candidates against the MERS-CoV S1-NTD.

Statistical optimization of bile salt deployed nanovesicles as a potential platform for oral delivery of piperine: accentuated antiviral and anti-inflammatory activity in MERS-CoV challenged mice.

The objective of this paper is to confine piperine, a poor oral bioavailable herbal drug into bile salt based nano vesicles for improving its aqueous solubility, hence, its therapeutic activity. Piperine-loaded bilosomes were fabricated adopting thin film hydration technique according to 32.21 full factorial design to investigate the impact of different formulation variables on the characters of bilosomes: entrapment efficiency (EE%), particle size, and % of drug released post 8 h (Q8hr). The selected optimum formula was F2 (enclosing 1% bile salt, brij72 as a surfactant, and ratio of surfactant:cholesterol was 9:1) with desirability value 0.801, exhibiting high EE% (97.2 ± 0.8%) nanosized spherical vesicles (220.2 ± 20.5 nm) and Q8hr (88.2%±5.6). The superiority of the optimized formula (F2) over the drug suspension was revealed via ex vivo permeation study, also pharmacokinetic study denoted to the boosted oral bioavailability of piperine-loaded bilosome compared to piperine suspension. Moreover, antiviral activity and safety margin of F2 was significantly higher than that of the drug suspension. The ability of piperine to interact with the key amino acids in the receptor binding domain 4L3N as indicated by its docking configuration, rationalized its observed activity. Furthermore, F2 significantly reduce oxidant markers, inflammatory cytokines in MERS-CoV-infected mice. Hence, bilosomes can be considered as a carrier of choice for piperine with potential antiviral and anti-inflammatory activities.

Middle East Respiratory Syndrome (MERS) Virus-Pathophysiological Axis and the Current Treatment Strategies.

Middle East respiratory syndrome (MERS) is a lethal respiratory disease with its first case reported back in 2012 (Jeddah, Saudi Arabia). It is a novel, single-stranded, positive-sense RNA beta coronavirus (MERS-CoV) that was isolated from a patient who died from a severe respiratory illness. Later, it was found that this patient was infected with MERS. MERS is endemic to countries in the Middle East regions, such as Saudi Arabia, Jordan, Qatar, Oman, Kuwait and the United Arab Emirates. It has been reported that the MERS virus originated from bats and dromedary camels, the natural hosts of MERS-CoV. The transmission of the virus to humans has been thought to be either direct or indirect. Few camel-to-human transmissions were reported earlier. However, the mode of transmission of how the virus affects humans remains unanswered. Moreover, outbreaks in either family-based or hospital-based settings were observed with high mortality rates, especially in individuals who did not receive proper management or those with underlying comorbidities, such as diabetes and renal failure. Since then, there have been numerous reports hypothesising complications in fatal cases of MERS. Over the years, various diagnostic methods, treatment strategies and preventive measures have been strategised in containing the MERS infection. Evidence from multiple sources implicated that no treatment options and vaccines have been developed in specific, for the direct management of MERS-CoV infection. Nevertheless, there are supportive measures outlined in response to symptom-related management. Health authorities should stress more on infection and prevention control measures, to ensure that MERS remains as a low-level threat to public health.

Pathomechanisms, therapeutic targets and potent inhibitors of some beta-coronaviruses from bench-to-bedside.

Since the emergence of their primitive strains, the complexity surrounding their pathogenesis, constant genetic mutation and translation are contributing factors to the scarcity of a successful vaccine for coronaviruses till moment. Although, the recent announcement of vaccine breakthrough for COVID-19 renews the hope, however, there remains a major challenge of accessibility to urgently match the rapid global therapeutic demand for curtailing the pandemic, thereby creating an impetus for further search. The reassessment of results from a stream of experiments is of enormous importance in identifying bona fide lead-like candidates to fulfil this quest. This review comprehensively highlights the common pathomechanisms and pharmacological targets of HCoV-OC43, SARS-CoV-1, MERS-CoV and SARS-CoV-2, and potent therapeutic potentials from basic and clinical experimental investigations. The implicated targets for the prevention and treatment include the viral proteases (Mpro, PLpro, 3CLpro), viral structural proteins (S- and N-proteins), non-structural proteins (nsp 3, 8, 10, 14, 16), accessory protein (ns12.9), viroporins (3a, E, 8a), enzymes (RdRp, TMPRSS2, ADP-ribosyltransferase, MTase, 2'-O-MTase, TATase, furin, cathepsin, deamidated human triosephosphate isomerase), kinases (MAPK, ERK, PI3K, mTOR, AKT, Abl2), interleukin-6 receptor (IL-6R) and the human host receptor, ACE2. Notably among the 109 overviewed inhibitors include quercetin, eriodictyol, baicalin, luteolin, melatonin, resveratrol and berberine from natural products, GC373, NP164 and HR2P-M2 from peptides, 5F9, m336 and MERS-GD27 from specific human antibodies, imatinib, remdesivir, ivermectin, chloroquine, hydroxychloroquine, nafamostat, interferon-ß and HCQ from repurposing libraries, some iron chelators and traditional medicines. This review represents a model for further translational studies for effective anti-CoV therapeutic designs.

In Vitro Inhibitory Analysis of Rationally Designed siRNAs against MERS-CoV Replication in Huh7 Cells.

MERS-CoV was identified for the first time in Jeddah, Saudi Arabia in 2012 in a hospitalized patient. This virus subsequently spread to 27 countries with a total of 939 deaths and 2586 confirmed cases and now has become a serious concern globally. Camels are well known for the transmission of the virus to the human population. In this report, we have discussed the prediction, designing, and evaluation of potential siRNA targeting the ORF1ab gene for the inhibition of MERS-CoV replication. The online software, siDirect 2.0 was used to predict and design the siRNAs, their secondary structure and their target accessibility. ORF1ab gene folding was performed by RNAxs and RNAfold software. A total of twenty-one siRNAs were selected from 462 siRNAs according to their scoring and specificity. siRNAs were evaluated in vitro for their cytotoxicity and antiviral efficacy in Huh7 cell line. No significant cytotoxicity was observed for all siRNAs in Huh7 cells. The in vitro study showed the inhibition of viral replication by three siRNAs. The data generated in this study provide preliminary and encouraging information to evaluate the siRNAs separately as well as in combination against MERS-CoV replication in other cell lines. The prediction of siRNAs using online software resulted in the filtration and selection of potential siRNAs with high accuracy and strength. This computational approach resulted in three effective siRNAs that can be taken further to in vivo animal studies and can be used to develop safe and effective antiviral therapies for other prevalent disease-causing viruses.

Type I and III IFNs produced by the nasal epithelia and dimmed inflammation are features of alpacas resolving MERS-CoV infection.

While MERS-CoV (Middle East respiratory syndrome Coronavirus) provokes a lethal disease in humans, camelids, the main virus reservoir, are asymptomatic carriers, suggesting a crucial role for innate immune responses in controlling the infection. Experimentally infected camelids clear infectious virus within one week and mount an effective adaptive immune response. Here, transcription of immune response genes was monitored in the respiratory tract of MERS-CoV infected alpacas. Concomitant to the peak of infection, occurring at 2 days post inoculation (dpi), type I and III interferons (IFNs) were maximally transcribed only in the nasal mucosa of alpacas, while interferon stimulated genes (ISGs) were induced along the whole respiratory tract. Simultaneous to mild focal infiltration of leukocytes in nasal mucosa and submucosa, upregulation of the anti-inflammatory cytokine IL10 and dampened transcription of pro-inflammatory genes under NF-κB control were observed. In the lung, early (1 dpi) transcription of chemokines (CCL2 and CCL3) correlated with a transient accumulation of mainly mononuclear leukocytes. A tight regulation of IFNs in lungs with expression of ISGs and controlled inflammatory responses, might contribute to virus clearance without causing tissue damage. Thus, the nasal mucosa, the main target of MERS-CoV in camelids, seems central in driving an efficient innate immune response based on triggering ISGs as well as the dual anti-inflammatory effects of type III IFNs and IL10.

Screening of FDA-Approved Drugs Using a MERS-CoV Clinical Isolate from South Korea Identifies Potential Therapeutic Options for COVID-19.

Therapeutic options for coronaviruses remain limited. To address this unmet medical need, we screened 5406 compounds, including United States Food and Drug Administration (FDA)-approved drugs and bioactives, for activity against a South Korean Middle East respiratory syndrome coronavirus (MERS-CoV) clinical isolate. Among 221 identified hits, 54 had therapeutic indexes (TI) greater than 6, representing effective drugs. The time-of-addition studies with selected drugs demonstrated eight and four FDA-approved drugs which acted on the early and late stages of the viral life cycle, respectively. Confirmed hits included several cardiotonic agents (TI > 100), atovaquone, an anti-malarial (TI > 34), and ciclesonide, an inhalable corticosteroid (TI > 6). Furthermore, utilizing the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), we tested combinations of remdesivir with selected drugs in Vero-E6 and Calu-3 cells, in lung organoids, and identified ciclesonide, nelfinavir, and camostat to be at least additive in vitro. Our results identify potential therapeutic options for MERS-CoV infections, and provide a basis to treat coronavirus disease 2019 (COVID-19) and other coronavirus-related illnesses.