Antiviral activity of cationic amphiphilic drugs

Integration of genetically regulated gene expression and pharmacological library provides therapeutic drug candidates

Approaches toward new therapeutics using disease genomics, such as genome-wide association study (GWAS), are anticipated. Here, we developed Trans-Phar [integration of transcriptome-wide association study (TWAS) and pharmacological database], achieving in silico screening of compounds from a large-scale pharmacological database (L1000 Connectivity Map), which have inverse expression profiles compared with tissue-specific genetically regulated gene expression. Firstly we confirmed the statistical robustness by the application of the null GWAS data and enrichment in the true-positive drug–disease relationships by the application of UK-Biobank GWAS summary statistics in broad disease categories, then we applied the GWAS summary statistics of large-scale European meta-analysis (17 traits; n_average = 201 849) and the hospitalized COVID-19 (n = 900 687), which has urgent need for drug development. We detected potential therapeutic compounds as well as anisomycin in schizophrenia (false discovery rate (FDR)-q = 0.056) and verapamil in hospitalized COVID-19 (FDR-q = 0.068) as top-associated compounds. This approach could be effective in disease genomics-driven drug development.

Platycodin D, a natural component of Platycodon grandiflorum, prevents both lysosome- and TMPRSS2-driven SARS-CoV-2 infection by hindering membrane fusion

An ongoing pandemic of coronavirus disease 2019 (COVID-19) is now the greatest threat to global public health. Herbal medicines and their derived natural products have drawn much attention in the treatment of COVID-19, but the detailed mechanisms by which natural products inhibit SARS-CoV-2 have not been elucidated. Here, we show that platycodin D (PD), a triterpenoid saponin abundant in Platycodon grandiflorum (PG), a dietary and medicinal herb commonly used in East Asia, effectively blocks the two main SARS-CoV-2 infection routes via lysosome- and transmembrane protease serine 2 (TMPRSS2)-driven entry. Mechanistically, PD prevents host entry of SARS-CoV-2 by redistributing membrane cholesterol to prevent membrane fusion, which can be reinstated by treatment with a PD-encapsulating agent. Furthermore, the inhibitory effects of PD are recapitulated by the pharmacological inhibition or gene silencing of NPC1, which is mutated in patients with Niemann-Pick type C (NPC) displaying disrupted membrane cholesterol distribution. Finally, readily available local foods or herbal medicines containing PG root show similar inhibitory effects against SARS-CoV-2 infection. Our study proposes that PD is a potent natural product for preventing or treating COVID-19 and that briefly disrupting the distribution of membrane cholesterol is a potential novel therapeutic strategy for SARS-CoV-2 infection.

Fludarabine Inhibits Infection of Zika Virus, SFTS Phlebovirus, and Enterovirus A71

Viral infections are one of the leading causes in human mortality and disease. Broad-spectrum antiviral drugs are a powerful weapon against new and re-emerging viruses. However, viral resistance to existing broad-spectrum antivirals remains a challenge, which demands development of new broad-spectrum therapeutics. In this report, we showed that fludarabine, a fluorinated purine analogue, effectively inhibited infection of RNA viruses, including Zika virus, Severe fever with thrombocytopenia syndrome virus, and Enterovirus A71, with all IC₅₀ values below 1 μM in Vero, BHK21, U251 MG, and HMC3 cells. We observed that fludarabine has shown cytotoxicity to these cells only at high doses indicating it could be safe for future clinical use if approved. In conclusion, this study suggests that fludarabine could be developed as a potential broad-spectrum anti-RNA virus therapeutic agent.

Resources and computational strategies to advance small molecule SARS-CoV-2 discovery: Lessons from the pandemic and preparing for future health crises

There is an urgent need to identify new therapies that prevent SARS-CoV-2 infection and improve the outcome of COVID-19 patients. This pandemic has thus spurred intensive research in most scientific areas and in a short period of time, several vaccines have been developed. But, while the race to find vaccines for COVID-19 has dominated the headlines, other types of therapeutic agents are being developed. In this mini-review, we report several databases and online tools that could assist the discovery of anti-SARS-CoV-2 small chemical compounds and peptides. We then give examples of studies that combined in silico and in vitro screening, either for drug repositioning purposes or to search for novel bioactive compounds. Finally, we question the overall lack of discussion and plan observed in academic research in many countries during this crisis and suggest that there is room for improvement.

Targeting Ebola virus replication through pharmaceutical intervention

Introduction. The consistent emergence/reemergence of filoviruses into a world that previously lacked an approved pharmaceutical intervention parallels an experience repeatedly played-out for most other emerging pathogenic zoonotic viruses. Investment to preemptively develop effective and low-cost prophylactic and therapeutic interventions against viruses that have high potential for emergence and societal impact should be a priority.Areas covered. Candidate drugs can be characterized into those that interfere with cellular processes required for Ebola virus (EBOV) replication (host-directed), and those that directly target virally encoded functions (direct-acting). We discuss strategies to identify pharmaceutical interventions for EBOV infections. PubMed/Web of Science databases were searched to establish a detailed catalog of these interventions.Expert opinion. Many drug candidates show promising in vitro inhibitory activity, but experience with EBOV shows the general lack of translation to in vivo efficacy for host-directed repurposed drugs. Better translation is seen for direct-acting antivirals, in particular monoclonal antibodies. The FDA-approved monoclonal antibody treatment, Inmazeb™ is a success story that could be improved in terms of impact on EBOV-associated disease and mortality, possibly by combination with other direct-acting agents targeting distinct aspects of the viral replication cycle. Costs need to be addressed given EBOV emergence primarily in under-resourced countries.

Chemoinformatic Analysis of Psychotropic and Antihistaminic Drugs in the Light of Experimental Anti-SARS-CoV-2 Activities

Introduction

There is an urgent need to identify therapies that prevent SARS-CoV-2 infection and improve the outcome of COVID-19 patients.

Objective

Based upon clinical observations, we proposed that some psychotropic and antihistaminic drugs could protect psychiatric patients from SARS-CoV-2 infection. This observation is investigated in the light of experimental in vitro data on SARS-CoV-2.

Methods

SARS-CoV-2 high-throughput screening results are available at the NCATS COVID-19 portal. We investigated the in vitro anti-viral activity of many psychotropic and antihistaminic drugs using chemoinformatics approaches.

Results and Discussion

We analyze our clinical observations in the light of SARS-CoV-2 experimental screening results and propose that several cationic amphiphilic psychotropic and antihistaminic drugs could protect people from SARS-CoV-2 infection; some of these molecules have very limited adverse effects and could be used as prophylactic drugs. Other cationic amphiphilic drugs used in other disease areas are also highlighted. Recent analyses of patient electronic health records reported by several research groups indicate that some of these molecules could be of interest at different stages of the disease progression. In addition, recently reported drug combination studies further suggest that it might be valuable to associate several cationic amphiphilic drugs. Taken together, these observations underline the need for clinical trials to fully evaluate the potentials of these molecules, some fitting in the so-called category of broad-spectrum antiviral agents. Repositioning orally available drugs that have moderate side effects and should act on molecular mechanisms less prone to drug resistance would indeed be of utmost importance to deal with COVID-19.

Molecular Dynamic Simulation Search for Possible Amphiphilic Drug Discovery for Covid-19

To determine whether quaternary ammonium (k21) binds to Severe Acute Respiratory Syndrome–Coronavirus 2 (SARS-CoV-2) spike protein via computational molecular docking simulations, the crystal structure of the SARS-CoV-2 spike receptor-binding domain complexed with ACE-2 (PDB ID: 6LZG) was downloaded from RCSB PD and prepared using Schrodinger 2019-4. The entry of SARS-CoV-2 inside humans is through lung tissues with a pH of 7.38–7.42. A two-dimensional structure of k-21 was drawn using the 2D-sketcher of Maestro 12.2 and trimmed of C18 alkyl chains from all four arms with the assumption that the core moiety k-21 was without C18. The immunogenic potential of k21/QA was conducted using the C-ImmSim server for a position-specific scoring matrix analyzing the human host immune system response. Therapeutic probability was shown using prediction models with negative and positive control drugs. Negative scores show that the binding of a quaternary ammonium compound with the spike protein’s binding site is favorable. The drug molecule has a large Root Mean Square Deviation fluctuation due to the less complex geometry of the drug molecule, which is suggestive of a profound impact on the regular geometry of a viral protein. There is high concentration of Immunoglobulin M/Immunoglobulin G, which is concomitant of virus reduction. The proposed drug formulation based on quaternary ammonium to characterize affinity to the SARS-CoV-2 spike protein using simulation and computational immunological methods has shown promising findings.

Antimalarial Quinacrine and Chloroquine Lose Their Activity by Decreasing Cationic Amphiphilic Structure with a Slight Decrease in pH

Quinacrine (QC) and chloroquine (CQ) have antimicrobial and antiviral activities as well as antimalarial activity, although the mechanisms remain unknown. QC increased the antimicrobial activity against yeast exponentially with a pH-dependent increase in the cationic amphiphilic drug (CAD) structure. CAD-QC localized in the yeast membranes and induced glucose starvation by noncompetitively inhibiting glucose uptake as antipsychotic chlorpromazine (CPZ) did. An exponential increase in antimicrobial activity with pH-dependent CAD formation was also observed for CQ, indicating that the CAD structure is crucial for its pharmacological activity. A decrease in CAD structure with a slight decrease in pH from 7.4 greatly reduced their effects; namely, these drugs would inefficiently act on falciparum malaria and COVID-19 pneumonia patients with acidosis, resulting in resistance. The decrease in CAD structure at physiological pH was not observed for quinine, primaquine, or mefloquine. Therefore, restoring the normal blood pH or using pH-insensitive quinoline drugs might be effective for these infectious diseases with acidosis.

Phospholipidosis is a shared mechanism underlying the in vitro antiviral activity of many repurposed drugs against SARS-CoV-2

Repurposing drugs as treatments for COVID-19 has drawn much attention. A common strategy has been to screen for established drugs, typically developed for other indications, that are antiviral in cells or organisms. Intriguingly, most of the drugs that have emerged from these campaigns, though diverse in structure, share a common physical property: cationic amphiphilicity. Provoked by the similarity of these repurposed drugs to those inducing phospholipidosis, a well-known drug side effect, we investigated phospholipidosis as a mechanism for antiviral activity. We tested 23 cationic amphiphilic drugs-including those from phenotypic screens and others that we ourselves had found-for induction of phospholipidosis in cell culture. We found that most of the repurposed drugs, which included hydroxychloroquine, azithromycin, amiodarone, and four others that have already progressed to clinical trials, induced phospholipidosis in the same concentration range as their antiviral activity; indeed, there was a strong monotonic correlation between antiviral efficacy and the magnitude of the phospholipidosis. Conversely, drugs active against the same targets that did not induce phospholipidosis were not antiviral. Phospholipidosis depends on the gross physical properties of drugs, and does not reflect specific target-based activities, rather it may be considered a confound in early drug discovery. Understanding its role in infection, and detecting its effects rapidly, will allow the community to better distinguish between drugs and lead compounds that more directly impact COVID-19 from the large proportion of molecules that manifest this confounding effect, saving much time, effort and cost.

Nuisance compounds in cellular assays

Compounds that exhibit assay interference or undesirable mechanisms of bioactivity ("nuisance compounds") are routinely encountered in cellular assays, including phenotypic and high-content screening assays. Much is known regarding compound-dependent assay interferences in cell-free assays. However, despite the essential role of cellular assays in chemical biology and drug discovery, there is considerably less known about nuisance compounds in more complex cell-based assays. In our view, a major obstacle to realizing the full potential of chemical biology will not just be difficult-to-drug targets or even the sheer number of targets, but rather nuisance compounds, due to their ability to waste significant resources and erode scientific trust. In this review, we summarize our collective academic, government, and industry experiences regarding cellular nuisance compounds. We describe assay design strategies to mitigate the impact of nuisance compounds and suggest best practices to efficiently address these compounds in complex biological settings.

The role of lysosomal ion channels in lysosome dysfunction

Lysosomes offer a unique arrangement of degradative, exocytic, and signaling capabilities that make their continued function critical to cellular homeostasis. Lysosomes owe their function to the activity of lysosomal ion channels and transporters, which maintain concentration gradients of H⁺, K⁺, Ca²⁺, Na⁺, and Cl^- across the lysosomal membrane. This review examines the contributions of lysosomal ion channels to lysosome function, showing how ion channel function is integral to degradation and autophagy, maintaining lysosomal membrane potential, controlling Ca²⁺ signaling, and facilitating exocytosis. Evidence of lysosome dysfunction in a variety of disease pathologies creates a need to understand how lysosomal ion channels contribute to lysosome dysfunction. For example, the loss of function of the TRPML1 Ca²⁺ lysosome channel in multiple lysosome storage diseases leads to lysosome dysfunction and disease pathogenesis while neurodegenerative diseases are marked by lysosome dysfunction caused by changes in ion channel activity through the TRPML1, TPC, and TMEM175 ion channels. Autoimmune disease is marked by dysregulated autophagy, which is dependent on the function of multiple lysosomal ion channels. Understanding the role of lysosomal ion channel activity in lysosome membrane permeability and NLRP3 inflammasome activation could provide valuable mechanistic insight into NLRP3 inflammasome-mediated diseases. Finally, this review seeks to show that understanding the role of lysosomal ion channels in lysosome dysfunction could give mechanistic insight into the efficacy of certain drug classes, specifically those that target the lysosome, such as cationic amphiphilic drugs.

Brilacidin Demonstrates Inhibition of SARS-CoV-2 in Cell Culture

Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), the newly emergent causative agent of coronavirus disease-19 (COVID-19), has resulted in more than two million deaths worldwide since it was first detected in 2019. There is a critical global need for therapeutic intervention strategies that can be deployed to safely treat COVID-19 disease and reduce associated morbidity and mortality. Increasing evidence shows that both natural and synthetic antimicrobial peptides (AMPs), also referred to as Host Defense Proteins/Peptides (HDPs), can inhibit SARS-CoV-2, paving the way for the potential clinical use of these molecules as therapeutic options. In this manuscript, we describe the potent antiviral activity exerted by brilacidin-a de novo designed synthetic small molecule that captures the biological properties of HDPs-on SARS-CoV-2 in a human lung cell line (Calu-3) and a monkey cell line (Vero). These data suggest that SARS-CoV-2 inhibition in these cell culture models is likely to be a result of the impact of brilacidin on viral entry and its disruption of viral integrity. Brilacidin demonstrated synergistic antiviral activity when combined with remdesivir. Collectively, our data demonstrate that brilacidin exerts potent inhibition of SARS-CoV-2 against different strains of the virus in cell culture.

Cytokine storm syndrome in coronavirus disease 2019: A narrative review

Cytokine storm syndrome (CSS) is a critical clinical condition induced by a cascade of cytokine activation, characterized by overwhelming systemic inflammation, hyperferritinaemia, haemodynamic instability and multiple organ failure (MOF). At the end of 2019, the disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) emerged in Wuhan, China, and rapidly developed into a global pandemic. More and more evidence shows that there is a dramatic increase of inflammatory cytokines in patients with COVID-19, suggesting the existence of cytokine storm in some critical illness patients. Here, we summarize the pathogenesis, clinical manifestation of CSS, and highlight the current understanding about the recognition and potential therapeutic options of CSS in COVID-19.

Tutankhamun's Antimalarial Drug for Covid-19

Drug repositioning is a strategy that identifies new uses of approved drugs to treat conditions different from their original purpose. Current efforts to treat Covid-19 are based on this strategy. The first drugs used in patients infected with SARS-CoV-2 were antimalarial drugs. It is their mechanism of action, i. e., rise in endosomal pH, which recommends them against the new coronavirus. Disregarding their side effects, the study of their antiviral activity provides valuable hints for the choice and design of drugs against SARS-CoV-2. One prominent drug candidate is thymoquinone, an antimalarial substance contained in Nigella sativa - most likely one of the first antimalarial drugs in human history. Since the outbreak of the pandemic, the number of articles relating thymoquinone to Covid-19 continuously increases. Here, we use it as an exemplary model drug, compare its antiviral mechanism with that of conventional antimalarial drugs and establish an irreducible parametric scheme for the identification of drugs with a potential in Covid-19.Translation into the laboratory is simple. Starting with the discovery of Nigella sativa seeds in the tomb of Pharaoh Tutankhamun, we establish a physicochemical model for the interaction of thymoquinone with both coronavirus and cells. Exploiting the predictive capability of the model, we provide a generalizable scheme for the systematic choice and design of drugs for Covid-19. An unexpected offshoot of our research is that Tutankhamun could not have died of malaria, a finding contrary to the mainstream theory.

Search, Identification, and Design of Effective Antiviral Drugs Against Pandemic Human Coronaviruses

Recent coronavirus outbreaks of SARS-CoV-1 (2002-2003), MERS-CoV (since 2012), and SARS-CoV-2 (since the end of 2019) are examples of how viruses can damage health care and generate havoc all over the world. Coronavirus can spread quickly from person to person causing high morbidity and mortality. Unfortunately, the antiviral armamentarium is insufficient to fight these infections. In this chapter, we provide a detailed summary of the current situation in the development of drugs directed against pandemic human coronaviruses. Apart from the recently licensed remdesivir, other antiviral agents discussed in this review include molecules targeting viral components (e.g., RNA polymerase inhibitors, entry inhibitors, or protease inhibitors), compounds interfering with virus-host interactions, and drugs identified in large screening assays, effective against coronavirus replication, but with an uncertain mechanism of action.

Repurposing therapeutic agents against SARS-CoV-2 infection: most promising and neoteric progress

INTRODUCTION

The pathogenic and highly transmissible etiological agent, SARS-CoV-2, has caused a serious threat COVID-19 pandemic. WHO has declared the epidemic a public health emergency of international concern owing to its high contagiosity, mortality rate, and morbidity. Till now, there is no approved vaccine or drug to combat the COVID-19 and avert this global crisis.

AREAS COVERED

In this narrative review, we summarized the updated results (January to August 2020) of the most promising repurposing therapeutic candidates to treat the SARS-CoV-2 viral infection. The repurposed drugs classified under four headlines like antivirals, anti-parasitic, immune-modulating, and miscellaneous drugs were discussed with their in vitro efficacy to recent clinical advancements against COVID-19.

EXPERT OPINION

Currently, palliative care, ranging from outpatient management to intensive care, including oxygen administration, ventilator support, intravenous fluids therapy, with some repurposed drugs, are the primary weapons to fight against COVID-19. Until a safe and effective vaccine is developed, an evidence-based drug repurposing strategy might be the wisest option to save people from this catastrophe. Several existing drugs are now under clinical trials, and some of them are approved in different places of the world for emergency use or as adjuvant therapy in COVID-19 with standard of care.

Identifying SARS-CoV-2 Entry Inhibitors through Drug Repurposing Screens of SARS-S and MERS-S Pseudotyped Particles

While vaccine development will hopefully quell the global pandemic of COVID-19 caused by SARS-CoV-2, small molecule drugs that can effectively control SARS-CoV-2 infection are urgently needed. Here, inhibitors of spike (S) mediated cell entry were identified in a high throughput screen of an approved drugs library with SARS-S and MERS-S pseudotyped particle entry assays. We discovered six compounds (cepharanthine, abemaciclib, osimertinib, trimipramine, colforsin, and ingenol) to be broad spectrum inhibitors for spike-mediated entry. This work could contribute to the development of effective treatments against the initial stage of viral infection and provide mechanistic information that might aid the design of new drug combinations for clinical trials for COVID-19 patients.

Hydroxychloroquine prophylaxis and treatment is ineffective in macaque and hamster SARS-CoV-2 disease models

We remain largely without effective prophylactic/therapeutic interventions for COVID-19. Although many human COVID-19 clinical trials are ongoing, there remains a deficiency of supportive preclinical drug efficacy studies to help guide decisions. Here we assessed the prophylactic/therapeutic efficacy of hydroxychloroquine (HCQ), a drug of interest for COVID-19 management, in 2 animal disease models. The standard human malaria HCQ prophylaxis (6.5 mg/kg given weekly) and treatment (6.5 mg/kg given daily) did not significantly benefit clinical outcome, nor did it reduce SARS-CoV-2 replication/shedding in the upper and lower respiratory tract in the rhesus macaque disease model. Similarly, when used for prophylaxis or treatment, neither the standard human malaria dose (6.5 mg/kg) nor a high dose (50 mg/kg) of HCQ had any beneficial effect on clinical disease or SARS-CoV-2 kinetics (replication/shedding) in the Syrian hamster disease model. Results from these 2 preclinical animal models may prove helpful in guiding clinical use of HCQ for prophylaxis/treatment of COVID-19.

Ionophore antibiotic X-206 is a potent inhibitor of SARS-CoV-2 infection in vitro

Pandemic spread of emerging human pathogenic viruses, such as the current SARS-CoV-2, poses both an immediate and future challenge to human health and society. Currently, effective treatment of infection with SARS-CoV-2 is limited and broad spectrum antiviral therapies to meet other emerging pandemics are absent leaving the World population largely unprotected. Here, we have identified distinct members of the family of polyether ionophore antibiotics with potent ability to inhibit SARS-CoV-2 replication and cytopathogenicity in cells. Several compounds from this class displayed more than 100-fold selectivity between viral-induced cytopathogenicity and inhibition of cell viability, however the compound X-206 displayed >500-fold selectivity and was furthermore able to inhibit viral replication even at sub-nM levels. The antiviral mechanism of the polyether ionophores is currently not understood in detail. We demonstrate, e.g. through unbiased bioactivity profiling, that their effects on the host cells differ from those of cationic amphiphiles such as hydroxychloroquine. Collectively, our data suggest that polyether ionophore antibiotics should be subject to further investigations as potential broad-spectrum antiviral agents.

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The polyether ionophore antibiotic X-206 is revealed as a potent inhibitor of the replication of SARS-CoV-2 in vitro.

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Other members of the same compound family also display strong antiviral potency although selectivity differs widely.

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Morphological profiling allows mechanistic comparison between X-206 and cationic amphiphiles, such as hydroxychloroquine.

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Further pre-clinical development of X-206, and other polyether ionophores, as antiviral agents is warranted.

In silico molecular docking analysis for repurposing therapeutics against multiple proteins from SARS-CoV-2

SARS-CoV-2 has devastated the world with its rapid spread and fatality. The researchers across the globe are struggling hard to search a drug to treat this infection. Understanding the time constraint, the best approach is to study clinically approved drugs for control of this deadly pandemic of COVID 19. The repurposing of such drugs can be supported with the study of molecular interactions to enhance the possibility of application. The present work is a molecular docking study of proteins responsible for viral propagation namely 3Clpro, Nsp10/16, Spike protein, SARS protein receptor binding domain, Nsp 9 viral single strand binding protein and viral helicase. The protein through virus enters the host cell-human angiotensin-converting enzyme 2 (ACE2) receptor, is also used as a target for molecular docking. The docking was done with most discussed drugs for SARS-CoV-2 like Ritonavir, Lopinavir, Remdesivir, Chloroquine, Hydroxychloroquine (HCQ), routine antiviral drugs like Oseltamivir and Ribavirin. In addition, small molecules with anti-inflammatory actions like Mycophenolic acid (MPA), Pemirolast, Isoniazid and Eriodictyol were also tested. The generated data confirms the potential of Ritonavir, Lopinavir and Remdesivir as a therapeutic candidate against SARS-CoV-2. It is observed that Eriodictyol binds to almost all selected target proteins with good binding energy, suggesting its importance in treatment of COVID 19. Molecular interactions of Ritonavir, Lopinavir and Remdesivir against SARS-CoV-2 proteins enhanced their potential as a candidate drug for treatment of COVID-19. Eriodictyol had emerged as a new repurposing drug that can be used in COVID-19.

Lysosomotropic Features and Autophagy Modulators among Medical Drugs: Evaluation of Their Role in Pathologies

The concept of lysosomotropic agents significantly changed numerous aspects of cellular biochemistry, biochemical pharmacology, and clinical medicine. In the present review, we focused on numerous low-molecular and high-molecular lipophilic basic compounds and on the role of lipophagy and autophagy in experimental and clinical medicine. Attention was primarily focused on the most promising agents acting as autophagy inducers, which offer a new window for treatment and/or prophylaxis of various diseases, including type 2 diabetes mellitus, Parkinson's disease, and atherosclerosis. The present review summarizes current knowledge on the lysosomotropic features of medical drugs, as well as autophagy inducers, and their role in pathological processes.

Evidence-Based Management of the Critically Ill Adult With SARS-CoV-2 Infection

Human infection by the novel viral pathogen SARS-CoV-2 results in a clinical syndrome termed Coronavirus Disease 2019 (COVID-19). Although the majority of COVID-19 cases are self-limiting, a substantial minority of patients develop disease severe enough to require intensive care. Features of critical illness associated with COVID-19 include hypoxemic respiratory failure, acute respiratory distress syndrome (ARDS), shock, and multiple organ dysfunction syndrome (MODS). In most (but not all) respects critically ill patients with COVID-19 resemble critically ill patients with ARDS due to other causes and are optimally managed with standard, evidence-based critical care protocols. However, there is naturally an intense interest in developing specific therapies for severe COVID-19. Here we synthesize the rapidly expanding literature around the pathophysiology, clinical presentation, and management of COVID-19 with a focus on those points most relevant for intensivists tasked with caring for these patients. We specifically highlight evidence-based approaches that we believe should guide the identification, triage, respiratory support, and general ICU care of critically ill patients infected with SARS-CoV-2. In addition, in light of the pressing need and growing enthusiasm for targeted COVID-19 therapies, we review the biological basis, plausibility, and clinical evidence underlying these novel treatment approaches.

Repurposing Pyramax®, quinacrine and tilorone as treatments for Ebola virus disease

We have recently identified three molecules (tilorone, quinacrine and pyronaridine tetraphosphate) which all demonstrated efficacy in the mouse model of infection with mouse-adapted Ebola virus (EBOV) model of disease and had similar in vitro inhibition of an Ebola pseudovirus (VSV-EBOV-GP), suggesting they interfere with viral entry. Using a machine learning model to predict lysosomotropism these compounds were evaluated for their ability to possess a lysosomotropic mechanism in vitro. We now demonstrate in vitro that pyronaridine tetraphosphate is an inhibitor of Lysotracker accumulation in lysosomes (IC50 = 0.56 μM). Further, we evaluated antiviral synergy between pyronaridine and artesunate (Pyramax®), which are used in combination to treat malaria. Artesunate was not found to have lysosomotropic activity in vitro and the combination effect on EBOV inhibition was shown to be additive. Pyramax® may represent a unique example of the repurposing of a combination product for another disease.

Identifying SARS-CoV-2 entry inhibitors through drug repurposing screens of SARS-S and MERS-S pseudotyped particles

While vaccine development will hopefully quell the global pandemic of COVID-19 caused by SARS-CoV-2, small molecule drugs that can effectively control SARS-CoV-2 infection are urgently needed. Here, inhibitors of spike (S) mediated cell entry were identified in a high throughput screen of an approved drugs library with SARS-S and MERS-S pseudotyped particle entry assays. We discovered six compounds (cepharanthine, abemaciclib, osimertinib, trimipramine, colforsin, and ingenol) to be broad spectrum inhibitors for spike-mediated entry. This work should contribute to the development of effective treatments against the initial stage of viral infection, thus reducing viral burden in COVID-19 patients.

Abstract Figure

Existing highly accumulating lysosomotropic drugs with potential for repurposing to target COVID-19

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Lysosomotropic drugs show moderate antiviral effects even on coronaviruses.

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The antiviral activity is likely due to interference with endosomal pathway.

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530 existing drugs were analysed for lysosomotropism, pharmacokinetics and toxicity.

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36 drugs were identified that may possibly be suitable for repurposing for COVID-19.

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Further research is needed to confirm their antiviral effects and safety limits.

Given the speed of viral infection spread, repurposing of existing drugs has been given the highest priority in combating the ongoing COVID-19 pandemic. Only drugs that are already registered or close to registration, and therefore have passed lengthy safety assessments, have a chance to be tested in clinical trials and reach patients quickly enough to help in the current disease outbreak.

Here, we have reviewed available evidence and possible ways forward to identify already existing pharmaceuticals displaying modest broad-spectrum antiviral activity which is likely linked to their high accumulation in cells. Several well studied examples indicate that these drugs accumulate in lysosomes, endosomes and biological membranes in general, and thereby interfere with endosomal pathway and intracellular membrane trafficking crucial for viral infection. With the aim to identify other lysosomotropic drugs with possible inherent antiviral activity, we have applied a set of clear physicochemical, pharmacokinetic and molecular criteria on 530 existing drugs. In addition to publicly available data, we have also used our in silico model for the prediction of accumulation in lysosomes and endosomes. By this approach we have identified 36 compounds with possible antiviral effects, also against coronaviruses. For 14 of them evidence of broad-spectrum antiviral activity has already been reported, adding support to the value of this approach.

Presented pros and cons, knowledge gaps and methods to identify lysosomotropic antivirals, can help in the evaluation of many drugs currently in clinical trials considered for repurposing to target COVID-19, as well as open doors to finding more potent and safer alternatives.

Identification of Estrogen Receptor Modulators as Inhibitors of Flavivirus Infection

Flaviviruses such as Zika virus (ZIKV), dengue virus (DENV), and West Nile virus (WNV) are major global pathogens for which safe and effective antiviral therapies are not currently available. To identify antiviral small molecules with well-characterized safety and bioavailability profiles, we screened a library of 2,907 approved drugs and pharmacologically active compounds for inhibitors of ZIKV infection using a high-throughput cell-based immunofluorescence assay. Interestingly, estrogen receptor modulators raloxifene hydrochloride and quinestrol were among 15 compounds that significantly inhibited ZIKV infection in repeat screens. Subsequent validation studies revealed that these drugs effectively inhibit ZIKV, DENV, and WNV (Kunjin strain) infection at low micromolar concentrations with minimal cytotoxicity in Huh-7.5 hepatoma cells and HTR-8 placental trophoblast cells. Since these cells lack detectable expression of estrogen receptors-α and -β (ER-α and ER-β) and similar antiviral effects were observed in the context of subgenomic DENV and ZIKV replicons, these compounds appear to inhibit viral RNA replication in a manner that is independent of their known effects on estrogen receptor signaling. Taken together, quinestrol, raloxifene hydrochloride, and structurally related analogues warrant further investigation as potential therapeutics for treatment of flavivirus infections.

Model informed dosing of hydroxycholoroquine in COVID-19 patients: Learnings from the recent experience, remaining uncertainties and gaps

AIMS

In the absence of a commonly agreed dosing protocol based on pharmacokinetic (PK) considerations, the dose and treatment duration for hydroxychloroquine (HCQ) in COVID-19 disease currently vary across national guidelines and clinical study protocols. We have used a model-based approach to explore the relative impact of alternative dosing regimens proposed in different dosing protocols for hydroxychloroquine in COVID-19.

METHODS

We compared different PK exposures using Monte Carlo simulations based on a previously published population pharmacokinetic model in patients with rheumatoid arthritis, externally validated using both independent data in lupus erythematous patients and recent data in French COVID-19 patients. Clinical efficacy and safety information from COVID-19 patients treated with HCQ were used to contextualize and assess the actual clinical value of the model predictions.

RESULTS

Literature and observed clinical data confirm the variability in clinical responses in COVID-19 when treated with the same fixed doses. Confounding factors were identified that should be taken into account for dose recommendation. For 80% of patients, doses higher than 800 mg day on day 1 followed by 600 mg daily on following days might not be needed for being cured. Limited adverse drug reactions have been reported so far for this dosing regimen, most often confounded by co-medications, comorbidities or underlying COVID-19 disease effects.

CONCLUSION

Our results were clear, indicating the unmet need for characterization of target PK exposures to inform HCQ dosing optimization in COVID-19. Dosing optimization for HCQ in COVID-19 is still an unmet need. Efforts in this sense are a prerequisite for best benefit/risk balance.

Pharmacological and non-pharmacological efforts at prevention, mitigation, and treatment for COVID-19

A global outbreak of the SARS-CoV-2 virus has infected millions of people over a short period of time. The communicability and increased mortality from the SARS-CoV-2 infection mandated the WHO to declare COVID-19 a worldwide pandemic. The virus outbreak has spread when there are no approved vaccines, treatments, or prophylactic therapies available. Researchers from all over the world have prioritised development of vaccines and antivirals. Several vaccine projects have seen successes in preclinical, phase I, and phase II clinical trials using recombinant DNA, mRNA, live attenuated virus, S-protein subunits, virus like particles, and viral vectors. Initial findings from antivirals such as remdesivir, favipiravir, danoprevir or lopinavir with ritonavir are presented. Immunomodulatory molecules such as sarilumab, tocilizumab, janus kinase inhibitors, and hyperimmune convalescent plasma have mixed outcomes from initial clinical findings; however, pending randomised controlled trials will assist national health institutions to make treatment recommendations for COVID-19. Where compassionate use of remdesivir has shown some benefits, therapies such as hydroxychloroquine have proven harmful due to their toxicities. This review discusses pharmacological interventions at play and evidence-based successes and limitations of non-pharmacological therapies such as social distancing, personal protective equipment, and ventilator support associated with the prevention and treatment of COVID-19.

Potential COVID-19 therapeutics from a rare disease: weaponizing lipid dysregulation to combat viral infectivity

The coronavirus disease 2019 (COVID-19) pandemic caused by severe acute respiratory syndrome coronavirus (SARS-CoV)-2 has resulted in the death of more than 328,000 persons worldwide in the first 5 months of 2020. Herculean efforts to rapidly design and produce vaccines and other antiviral interventions are ongoing. However, newly evolving viral mutations, the prospect of only temporary immunity, and a long path to regulatory approval pose significant challenges and call for a common, readily available, and inexpensive treatment. Strategic drug repurposing combined with rapid testing of established molecular targets could provide a pause in disease progression. SARS-CoV-2 shares extensive structural and functional conservation with SARS-CoV-1, including engagement of the same host cell receptor (angiotensin-converting enzyme 2) localized in cholesterol-rich microdomains. These lipid-enveloped viruses encounter the endosomal/lysosomal host compartment in a critical step of infection and maturation. Niemann-Pick type C (NP-C) disease is a rare monogenic neurodegenerative disease caused by deficient efflux of lipids from the late endosome/lysosome (LE/L). The NP-C disease-causing gene (NPC1) has been strongly associated with viral infection, both as a filovirus receptor (e.g., Ebola) and through LE/L lipid trafficking. This suggests that NPC1 inhibitors or NP-C disease mimetics could serve as anti-SARS-CoV-2 agents. Fortunately, there are such clinically approved molecules that elicit antiviral activity in preclinical studies, without causing NP-C disease. Inhibition of NPC1 may impair viral SARS-CoV-2 infectivity via several lipid-dependent mechanisms, which disturb the microenvironment optimum for viral infectivity. We suggest that known mechanistic information on NPC1 could be utilized to identify existing and future drugs to treat COVID-19.

Hydroxychloroquine Proves Ineffective in Hamsters and Macaques Infected with SARS-CoV-2

We remain largely without effective prophylactic/therapeutic interventions for COVID-19. Although many human clinical trials are ongoing, there remains a deficiency of supportive preclinical drug efficacy studies. Here we assessed the prophylactic/therapeutic efficacy of hydroxychloroquine (HCQ), a drug of interest for COVID-19 management, in two animal models. When used for prophylaxis or treatment neither the standard human malaria dose (6.5 mg/kg) nor a high dose (50 mg/kg) of HCQ had any beneficial effect on clinical disease or SARS-CoV-2 kinetics (replication/shedding) in the Syrian hamster disease model. Similarly, HCQ prophylaxis/treatment (6.5 mg/kg) did not significantly benefit clinical outcome nor reduce SARS-CoV-2 replication/shedding in the upper and lower respiratory tract in the rhesus macaque disease model. In conclusion, our preclinical animal studies do not support the use of HCQ in prophylaxis/treatment of COVID-19.

Coalition: Advocacy for prospective clinical trials to test the post-exposure potential of hydroxychloroquine against COVID-19

Our coalition of public health experts, doctors, and scientists worldwide want to draw attention to the need for high-quality evaluation protocols of the potential beneficial effect of hydroxychloroquine (HCQ) as a post-exposure drug for exposed people. In the absence of an approved, recognized effective pre or post-exposure prophylactic drug or vaccine for COVID-19, nor of any approved and validated therapeutic drug, coupled with social and political pressure raised by publicity both regarding the potential beneficial effect of hydroxychloroquine (HCQ) as well as potential risks from HCQ, we urge the immediate proper clinical trials. Specifically, we mean using HCQ for post-exposure of people with close contact with patients with positive COVID19 rtPCR, including home and medical caregivers. We have reviewed the mechanisms of antiviral effect of HCQ, the risk-benefit ratio taking into consideration the PK/PD of HCQ and the thresholds of efficacy. We have studied its use as an antimalarial, an antiviral, and an immunomodulating drug and concluded that the use of HCQ at doses matching that of the standard treatment of Systemic Lupus erythematous, which has proven safety and efficacy in terms of HCQ blood and tissue concentration adapted to bodyweight (2,3), at 6 mg/kg/day 1 (loading dose) followed by 5 mg/kg/ day, with a maximum limit of 600 mg/day in all cases should swiftly be clinically evaluated as a post-exposure drug for exposed people.

Safety and Efficacy of Amiodarone in a Patient With COVID-19

There is an urgent need for effective treatments for coronavirus disease-2019 (COVID-19). Amiodarone, like hydroxychloroquine, exerts antiviral actions by interfering with endocytosis and viral replication. Here, to our knowledge, we report the first case of a patient affected by respiratory failure related to COVID-19 who recovered after only supportive measures and a short amiodarone course. (Level of Difficulty: Beginner.).

[Chloroquine phosphate: therapeutic drug for COVID-19]

Since the outbreak of coronavirus disease 2019 (COVID-19) in the late 2019, a variety of antiviral drugs have been used in the first-line clinical trial. The Diagnostic and Treatment Protocol for COVID-19 (Trial Version 6) in China recommends chloroquine phosphate for the first time as an anti-coronavirus trial drug. As a classic drug for treatment of malaria and rheumatism, chloroquine phosphate has been used clinically for more than 80 years, and has also shown good results in the treatment of various viral infections. As the plasma drug concentration varies greatly among different races and individuals and due to its narrow treatment window, chloroquine in likely to accumulate in the body to cause toxicity. Among the treatment regimens recommended for COVID-19, reports concerning the safety of a short-term high-dose chloroquine regimen remain scarce. In this review, the authors summarize the current research findings of chloroquine phosphate in the treatment of COVID-19, and examine the pharmacokinetic characteristics, antiviral therapy, the therapeutic mechanism and safety of chloroquine.

Tilorone: a Broad-Spectrum Antiviral Invented in the USA and Commercialized in Russia and beyond

For the last 50 years we have known of a broad-spectrum agent tilorone dihydrochloride (Tilorone). This is a small-molecule orally bioavailable drug that was originally discovered in the USA and is currently used clinically as an antiviral in Russia and the Ukraine. Over the years there have been numerous clinical and non-clinical reports of its broad spectrum of antiviral activity. More recently we have identified additional promising antiviral activities against Middle East Respiratory Syndrome, Chikungunya, Ebola and Marburg which highlights that this old drug may have other uses against new viruses. This may in turn inform the types of drugs that we need for virus outbreaks such as for the new coronavirus severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Tilorone has been long neglected by the west in many respects but it deserves further reassessment in light of current and future needs for broad-spectrum antivirals.

Emetine, Ipecac, Ipecac Alkaloids and Analogues as Potential Antiviral Agents for Coronaviruses

The COVID-19 coronavirus is currently spreading around the globe with limited treatment options available. This article presents the rationale for potentially using old drugs (emetine, other ipecac alkaloids or analogues) that have been used to treat amoebiasis in the treatment of COVID-19. Emetine had amongst the lowest reported half-maximal effective concentration (EC50) from over 290 agents screened for the Middle East respiratory syndrome (MERS) and severe acute respiratory syndrome (SARS) coronaviruses. While EC50 concentrations of emetine are achievable in the blood, studies show that concentrations of emetine can be almost 300 times higher in the lungs. Furthermore, based on the relative EC50s of emetine towards the coronaviruses compared with Entamoeba histolytica, emetine could be much more effective as an anti-coronavirus agent than it is against amoebiasis. This paper also discusses the known side effects of emetine and related compounds, how those side effects can be managed, and the optimal method of administration for the potential treatment of COVID-19. Given the serious and immediate threat that the COVID-19 coronavirus poses, our long history with emetine and the likely ability of emetine to reach therapeutic concentrations within the lungs, ipecac, emetine, and other analogues should be considered as potential treatment options, especially if in vitro studies confirm viral sensitivity.

In Vivo Activity of Amodiaquine against Ebola Virus Infection

During the Ebola virus disease (EVD) epidemic in Western Africa (2013‒2016), antimalarial treatment was administered to EVD patients due to the high coexisting malaria burden in accordance with World Health Organization guidelines. In an Ebola treatment center in Liberia, EVD patients receiving the combination antimalarial artesunate-amodiaquine had a lower risk of death compared to those treated with artemether-lumefantrine. As artemether and artesunate are derivatives of artemisinin, the beneficial anti-Ebola virus (EBOV) effect observed could possibly be attributed to the change from lumefantrine to amodiaquine. Amodiaquine is a widely used antimalarial in the countries that experience outbreaks of EVD and, therefore, holds promise as an approved drug that could be repurposed for treating EBOV infections. We investigated the potential anti-EBOV effect of amodiaquine in a well-characterized nonhuman primate model of EVD. Using a similar 3-day antimalarial dosing strategy as for human patients, plasma concentrations of amodiaquine in healthy animals were similar to those found in humans. However, the treatment regimen did not result in a survival benefit or decrease of disease signs in EBOV-infected animals. While amodiaquine on its own failed to demonstrate efficacy, we cannot exclude potential therapeutic value of amodiaquine when used in combination with artesunate or another antiviral.

Omeprazole Increases the Efficacy of Acyclovir Against Herpes Simplex Virus Type 1 and 2

Omeprazole was shown to improve the anti-cancer effects of the nucleoside analogue 5-fluorouracil. Here, we combined omeprazole with the antiviral nucleoside analogues ribavirin and acyclovir. Omeprazole did not affect the antiviral effects of ribavirin in non-toxic concentrations up to 80 μg/mL but increased the acyclovir-mediated effects on herpes simplex virus 1 and 2 (HSV-1 and -2) replication in a dose-dependent manner. Omeprazole alone reduced HSV-1 and -2 titers [but not HSV-induced formation of cytopathogenic effects (CPE)] at concentrations ≥40 μg/mL. However, it exerted substantially stronger effects on acyclovir activity and also increased acyclovir activity at lower concentrations that did not directly interfere with HSV replication. Omeprazole 80 μg/mL caused a 10.8-fold (Vero cells) and 47.7-fold (HaCaT cells) decrease of the acyclovir concentrations that reduced HSV-1-induced CPE formation by 50% (IC₅₀). In HSV-2-infected cells, omeprazole 80 μg/mL reduced the acyclovir IC₅₀ by 7.3- (Vero cells) and 12.9-fold (HaCaT cells). In HaCaT cells, omeprazole 80 μg/mL reduced the HSV-1 titer in the presence of acyclovir 1 μg/mL by 1.6 × 10⁵-fold and the HSV-2 titer in the presence of acyclovir 2 μg/mL by 9.2 × 10³-fold. The proton pump inhibitors pantoprazole, rabeprazole, lansoprazole, and dexlansoprazole increased the antiviral effects of acyclovir in a similar fashion as omeprazole, indicating this to be a drug class effect. In conclusion, proton pump inhibitors increase the anti-HSV activity of acyclovir and are candidates for antiviral therapies in combination with acyclovir, in particular for topical preparations for the treatment of immunocompromised individuals who are more likely to suffer from severe complications.

Perspectives towards antiviral drug discovery against Ebola virus

Ebola virus disease (EVD), caused by Ebola viruses, resulted in more than 11 500 deaths according to a recent 2018 WHO report. With mortality rates up to 90%, it is nowadays one of the most deadly infectious diseases. However, no Food and Drug Administration‐approved Ebola drugs or vaccines are available yet with the mainstay of therapy being supportive care. The high fatality rate and absence of effective treatment or vaccination make Ebola virus a category‐A biothreat pathogen. Fortunately, a series of investigational countermeasures have been developed to control and prevent this global threat. This review summarizes the recent therapeutic advances and ongoing research progress from research and development to clinical trials in the development of small‐molecule antiviral drugs, small‐interference RNA molecules, phosphorodiamidate morpholino oligomers, full‐length monoclonal antibodies, and vaccines. Moreover, difficulties are highlighted in the search for effective countermeasures against EVD with additional focus on the interplay between available in silico prediction methods and their evidenced potential in antiviral drug discovery.

Ebola Virus Entry: From Molecular Characterization to Drug Discovery

Ebola Virus Disease (EVD) is one of the most lethal transmissible infections, characterized by a high fatality rate, and caused by a member of the Filoviridae family. The recent large outbreak of EVD in Western Africa (2013–2016) highlighted the worldwide threat represented by the disease and its impact on global public health and the economy. The development of highly needed anti-Ebola virus antivirals has been so far hampered by the shortage of tools to study their life cycle in vitro, allowing to screen for potential active compounds outside a biosafety level-4 (BSL-4) containment. Importantly, the development of surrogate models to study Ebola virus entry in a BSL-2 setting, such as viral pseudotypes and Ebola virus-like particles, tremendously boosted both our knowledge of the viral life cycle and the identification of promising antiviral compounds interfering with viral entry. In this context, the combination of such surrogate systems with large-scale small molecule compounds and haploid genetic screenings, as well as rational drug design and drug repurposing approaches will prove priceless in our quest for the development of a treatment for EVD.

Diagnostic tests for Crimean-Congo haemorrhagic fever: a widespread tickborne disease

Crimean-Congo haemorrhagic fever (CCHF) is a widespread tickborne disease that circulates in wild and domestic animal hosts, and causes severe and often fatal haemorrhagic fever in infected humans. Due to the lack of treatment options or vaccines, and a high fatality rate, CCHF virus (CCHFV) is considered a high-priority pathogen according to the WHO R&D Blueprint. Several commercial reverse transcriptase PCR (RT-PCR) and serological diagnostic assays for CCHFV are already available, including febrile agent panels to distinguish CCHFV from other viral haemorrhagic fever agents; however, the majority of international laboratories use inhouse assays. As CCHFV has numerous amplifying animal hosts, a cross-sectoral 'One Health' approach to outbreak prevention is recommended to enhance notifications and enable early warning for genetic and epidemiological shifts in the human, animal and tick populations. However, a lack of guidance for surveillance in animals, harmonisation of case identification and validated serodiagnostic kits for animal testing hinders efforts to strengthen surveillance systems. Additionally, as RT-PCR tests tend to be lineage-specific for regional circulating strains, there is a need for pan-lineage sensitive diagnostics. Adaptation of existing tests to point-of-care molecular diagnostic platforms that can be implemented in clinic or field-based settings would be of value given the potential for CCHFV outbreaks in remote or low-resource areas. Finally, improved access to clinical specimens for validation of diagnostics would help to accelerate development of new tests. These gaps should be addressed by updated target product profiles for CCHFV diagnostics.

Second generation of diazachrysenes: Protection of Ebola virus infected mice and mechanism of action

Ebola virus (EBOV) causes a deadly hemorrhagic fever in humans and non-human primates. There is currently no FDA-approved vaccine or medication to counter this disease. Here, we report on the design, synthesis and anti-viral activities of two classes of compounds which show high potency against EBOV in both in vitro cell culture assays and in vivo mouse models Ebola viral disease. These compounds incorporate the structural features of cationic amphiphilic drugs (CAD), i.e they possess both a hydrophobic domain and a hydrophilic domain consisting of an ionizable amine functional group. These structural features enable easily diffusion into cells but once inside an acidic compartment their amine groups became protonated, ionized and remain trapped inside the acidic compartments such as late endosomes and lysosomes. These compounds, by virtue of their lysomotrophic functions, blocked EBOV entry. However, unlike other drugs containing a CAD moiety including chloroquine and amodiaquine, compounds reported in this study display faster kinetics of accumulation in the lysosomes, robust expansion of late endosome/lysosomes, relatively more potent suppression of lysosome fusion with other vesicular compartments and inhibition of cathepsins activities, all of which play a vital role in anti-EBOV activity. Furthermore, the diazachrysene 2 (ZSML08) that showed most potent activity against EBOV in in vitro cell culture assays also showed significant survival benefit with 100% protection in mouse models of Ebola virus disease, at a low dose of 10 mg/kg/day. Lastly, toxicity studies in vivo using zebrafish models suggest no developmental defects or toxicity associated with these compounds. Overall, these studies describe two new pharmacophores that by virtue of being potent lysosomotrophs, display potent anti-EBOV activities both in vitro and in vivo animal models of EBOV disease.

Antiviral Agents Against Ebola Virus Infection: Repositioning Old Drugs and Finding Novel Small Molecules

Ebola virus (EBOV) causes a deadly hemorrhagic syndrome in humans with mortality rate up to 90%. First reported in Zaire in 1976, EBOV outbreaks showed a fluctuating trend during time and fora long period it was considered a tragic disease confined to the isolated regions of the African continent where the EBOV fear was perpetuated among the poor communities. The extreme severity of the recent 2014-16 EBOV outbreak in terms of fatality rate and rapid spread out of Africa led to the understanding that EBOV is a global health risk and highlights the necessity to find countermeasures against it. In the recent years, several small molecules have been shown to display in vitro and in vivo efficacy against EBOV and some of them have advanced into clinical trials. In addition, also existing drugs have been tested for their anti-EBOV activity and were shown to be promising candidates. However, despite the constant effort addressed to identify anti-EBOV therapeutics, no approved drugs are available against EBOV yet. In this chapter, we describe the main EBOV life cycle steps, providing a detailed picture of the druggable viral and host targets that have been explored so far by different technologies. We then summarize the small molecules, nucleic acid oligomers, and antibody-based therapies reported to have an effect either in in silico, or in biochemical and cell-based assays or in animal models and clinical trials, listing them according to their demonstrated or putative mechanism of action.

Characterization of Novel Piperidine-Based Inhibitor of Cathepsin B-Dependent Bacterial Toxins and Viruses

Exploiting the host endocytic trafficking pathway is a common mechanism by which bacterial exotoxins gain entry to exert virulent effects upon the host cells. A previous study identified a small-molecule, 1-(2,6-dimethyl-1-piperidinyl)-3-[(2-isopropyl-5-methylcyclohexyl)oxy]-2-propanol, that blocks the process of anthrax lethal toxin (LT) cytotoxicity. Here, we report the characterization of the bioactivity of this compound, which we named RC1. We found that RC1 protected host cells independently of LT concentration and also blocked intoxication by other bacterial exotoxins, suggesting that the target of the compound is a host factor. Using the anthrax LT intoxication pathway as a reference, we show that while anthrax toxin is able to bind to cells and establish an endosomal pore in the presence of the drug, the toxin is unable to translocate into the cytosol. We demonstrate that RC1 does not inhibit the toxin directly but rather reduces the enzymatic activity of host cathepsin B that mediates the escape of toxins into the cytoplasm from late endosomes. We demonstrate that the pathogenicity of Human cytomegalovirus and Herpes simplex virus 1, which relies on cathepsin B protease activity, is reduced by RC1. This study reveals the potential of RC1 as a broad-spectrum host-oriented therapy against several aggressive and deadly pathogens.