Drug Repurposing Approach Identifies Inhibitors of the Prototypic Viral Transcription Factor IE2 that Block Human Cytomegalovirus Replication

Optimization of potent, broad-spectrum, and specific anti-influenza compounds targeting RNA polymerase PA-PB1 heterodimerization

Influenza viruses (IV) are single-stranded RNA viruses with a negative-sense genome and have the potential to cause pandemics. While vaccines exist for influenza, their protection is only partial. Additionally, there is only a limited number of approved anti-IV drugs, which are associated to emergence of drug resistance. To address these issues, for years we have focused on the development of small-molecules that can interfere with the heterodimerization of PA and PB1 subunits of the IV RNA-dependent RNA polymerase (RdRP). In this study, starting from a cycloheptathiophene-3-carboxamide compound that we recently identified, we performed iterative cycles of medicinal chemistry optimization that led to the identification of compounds 43 and 45 with activity in the nanomolar range against circulating A and B strains of IV. Mechanistic studies demonstrated the ability of 43 and 45 to interfere with viral RdRP activity by disrupting PA-PB1 subunits heterodimerization and to bind to the PA C-terminal domain through biophysical assays. Most important, ADME studies of 45 also showed an improvement in the pharmacokinetic profile with respect to the starting hit.

Synergistic activity of an RNA polymerase PA-PB1 interaction inhibitor with oseltamivir against human and avian influenza viruses in cell culture and in ovo

In search of novel therapeutic options to treat influenza virus (IV) infections, we previously identified a series of inhibitors that act by disrupting the interactions between the PA and PB1 subunits of the viral RNA polymerase. These compounds showed broad-spectrum antiviral activity against human influenza A and B viruses and a high barrier to the induction of drug resistance in vitro. In this short communication, we investigated the effects of combinations of the PA-PB1 interaction inhibitor 54 with oseltamivir carboxylate (OSC), zanamivir (ZA), favipiravir (FPV), and baloxavir marboxil (BXM) on the inhibition of influenza A and B virus replication in vitro. We observed a synergistic effect of the 54/OSC and 54/ZA combinations and an antagonistic effect when 54 was combined with either FPV or BXM. Moreover, we demonstrated the efficacy of 54 against highly pathogenic avian influenza viruses (HPAIVs) both in cell culture and in the embryonated chicken eggs model. Finally, we observed that 54 enhances OSC protective effect against HPAIV replication in the embryonated eggs model. Our findings represent an advance in the development of alternative therapeutic strategies against both human and avian IV infections.

Exploring a New Generation of Pyrimidine and Pyridine Derivatives as Anti-Influenza Agents Targeting the Polymerase PA-PB1 Subunits Interaction

The limited range of available flu treatments due to virus mutations and drug resistance have prompted the search for new therapies. RNA-dependent RNA polymerase (RdRp) is a heterotrimeric complex of three subunits, i.e., polymerase acidic protein (PA) and polymerase basic proteins 1 and 2 (PB1 and PB2). It is widely recognized as one of the most promising anti-flu targets because of its critical role in influenza infection and high amino acid conservation. In particular, the disruption of RdRp complex assembly through protein-protein interaction (PPI) inhibition has emerged as a valuable strategy for discovering a new therapy. Our group previously identified the 3-cyano-4,6-diphenyl-pyridine core as a privileged scaffold for developing PA-PB1 PPI inhibitors. Encouraged by these findings, we synthesized a small library of pyridine and pyrimidine derivatives decorated with a thio-N-(m-tolyl)acetamide side chain (compounds 2a-n) or several amino acid groups (compounds 3a-n) at the C2 position. Interestingly, derivative 2d, characterized by a pyrimidine core and a phenyl and 4-chloro phenyl ring at the C4 and C6 positions, respectively, showed an IC50 value of 90.1 μM in PA-PB1 ELISA, an EC50 value of 2.8 μM in PRA, and a favorable cytotoxic profile, emerging as a significant breakthrough in the pursuit of new PPI inhibitors. A molecular modeling study was also completed as part of this project, allowing us to clarify the biological profile of these compounds.

Design, synthesis, and biological evaluation of first-in-class indomethacin-based PROTACs degrading SARS-CoV-2 main protease and with broad-spectrum antiviral activity

To date, Proteolysis Targeting Chimera (PROTAC) technology has been successfully applied to mediate proteasomal-induced degradation of several pharmaceutical targets mainly related to oncology, immune disorders, and neurodegenerative diseases. On the other hand, its exploitation in the field of antiviral drug discovery is still in its infancy. Recently, we described two indomethacin (INM)-based PROTACs displaying broad-spectrum antiviral activity against coronaviruses. Here, we report the design, synthesis, and characterization of a novel series of INM-based PROTACs that recruit either Von-Hippel Lindau (VHL) or cereblon (CRBN) E3 ligases. The panel of INM-based PROTACs was also enlarged by varying the linker moiety. The antiviral activity resulted very susceptible to this modification, particularly for PROTACs hijacking VHL as E3 ligase, with one piperazine-based compound (PROTAC 6) showing potent anti-SARS-CoV-2 activity in infected human lung cells. Interestingly, degradation assays in both uninfected and virus-infected cells with the most promising PROTACs emerged so far (PROTACs 5 and 6) demonstrated that INM-PROTACs do not degrade human PGES-2 protein, as initially hypothesized, but induce the concentration-dependent degradation of SARS-CoV-2 main protease (Mpro) both in Mpro-transfected and in SARS-CoV-2-infected cells. Importantly, thanks to the target degradation, INM-PROTACs exhibited a considerable enhancement in antiviral activity with respect to indomethacin, with EC50 values in the low-micromolar/nanomolar range. Finally, kinetic solubility as well as metabolic and chemical stability were measured for PROTACs 5 and 6. Altogether, the identification of INM-based PROTACs as the first class of SARS-CoV-2 Mpro degraders demonstrating activity also in SARS-CoV-2-infected cells represents a significant advance in the development of effective, broad-spectrum anti-coronavirus strategies.

Human neural progenitor cell models to study the antiviral effects and neuroprotective potential of approved and investigational human cytomegalovirus inhibitors

Human cytomegalovirus (HCMV) is the viral leading cause of congenital defects in newborns worldwide. Many aspects of congenital CMV (cCMV) infection, which currently lacks a specific treatment, as well as the main determinants of neuropathogenesis in the developing brain during HCMV infection are unclear. In this study, we modeled HCMV infection at different stages of neural development. Moreover, we evaluated the effects of both approved and investigational anti-HCMV drugs on viral replication and gene expression in two different neural progenitor cell lines, i.e., human embryonic stem cells-derived neural stem cells (NSCs) and fetus-derived neuroepithelial stem (NES) cells. Ganciclovir, letermovir, nitazoxanide, and the ozonide OZ418 reduced viral DNA synthesis and the production of infectious virus in both lines of neural progenitors. HCMV infection dysregulated the expression of genes that either are markers of neural progenitors, such as SOX2, NESTIN, PAX-6, or play a role in neurogenesis, such as Doublecortin. Treatment with antiviral drugs had different effects on HCMV-induced dysregulation of the genes under investigation. This study contributes to the understanding of the molecular mechanisms of cCMV neuropathogenesis and paves the way for further consideration of anti-HCMV drugs as candidate therapeutic agents for the amelioration of cCMV-associated neurological manifestations.

Antiviral alternatives against important members of the subfamily Parvovirinae: a review

Parvoviruses are responsible for multiple diseases, and there is a critical need for effective antiviral therapies. Specific antiviral treatments for parvovirus infections are currently lacking, and the available options are mostly supportive and symptomatic. In recent years, significant research efforts have been directed toward understanding the molecular mechanisms of parvovirus replication and identifying potential targets for antiviral interventions. This review highlights the structure, pathogenesis, and treatment options for major viruses of the subfamily Parvovirinae, such as parvovirus B19 (B19V), canine parvovirus type 2 (CPV-2), and porcine parvovirus (PPV) and also describes different approaches in the development of antiviral alternatives against parvovirus, including drug repurposing, serendipity, and computational tools (molecular docking and artificial intelligence) in drug discovery. These advances greatly increase the likelihood of discoveries that will lead to potent antiviral strategies against different parvovirus infections.

Transcriptional Differential Analysis of Nitazoxanide-Mediated Anticanine Parvovirus Effect in F81 Cells

Canine parvovirus (CPV) is a single-stranded DNA virus that can cause typical hemorrhagic enteritis, and it is one of the common canine lethal viruses. In previous studies, we screened the Food and Drug Administration (FDA)'s drug library and identified nitazoxanide (NTZ), which has anti-CPV capabilities. To investigate the potential antiviral mechanisms, we first reconfirmed the inhibitory effect of NTZ on the CPV by inoculating with different doses and treating for different lengths of time. Then, the differences in the transcription levels between the 0.1%-DMSO-treated virus group and the NTZ-treated virus group were detected using RNA-seq, and a total of 758 differential expression genes (DEGs) were finally identified. Further Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses of the DEGs revealed that these genes are involved in a variety of biological processes and/or signaling pathways, such as cell cycle, mitosis and cell proliferation and differentiation. A protein-protein interaction (PPI) analysis further identified hub genes associated with cell cycle and division among the DEGs. In addition, the expression levels of some of the enriched genes were detected, which were consistent with the high-throughput sequencing results. Moreover, when the cell cycle was regulated with cell cycle checkpoint kinase 1 (Chk1) inhibitor MK-8776 or Prexasertib HCl, both inhibitors inhibited the CPV. In summary, the transcriptome differential analysis results presented in this paper lay the foundation for further research on the molecular mechanism and potential targets of NTZ anti-CPV.

Therapeutic potential of salicylamide derivatives for combating viral infections

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

Toward inhibition of human cytomegalovirus replication with compounds targeting cellular proteins

Antiviral therapy for human cytomegalovirus (HCMV) currently relies upon direct-acting antiviral drugs. However, it is now well known that these drugs have shortcomings, which limit their use. Here I review the identification and investigation of compounds targeting cellular proteins that have anti-HCMV activity and could supersede those anti-HCMV drugs currently in use. This includes discussion of drug repurposing, for example the use of artemisinin compounds, and discussion of new directions to identify compounds that target cellular factors in HCMV-infected cells, for example screening of kinase inhibitors. In addition, I highlight developing areas such as the use of machine learning and emphasize how interaction with fields outside virology will be critical for development of anti-HCMV compounds.

Discovery of novel SARS-CoV-2 inhibitors targeting the main protease Mpro by virtual screenings and hit optimization

Two years after its emergence, SARS-CoV-2 still represents a serious and global threat to human health. Antiviral drug development usually takes a long time and, to increase the chances of success, chemical variability of hit compounds represents a valuable source for the discovery of new antivirals. In this work, we applied a platform of variably oriented virtual screening campaigns to seek for novel chemical scaffolds for SARS-CoV-2 main protease (M^pro) inhibitors. The study on the resulting 30 best hits led to the identification of a series of structurally unrelated M^pro inhibitors. Some of them exhibited antiviral activity in the low micromolar range against SARS-CoV-2 and other human coronaviruses (HCoVs) in different cell lines. Time-of-addition experiments demonstrated an antiviral effect during the viral replication cycle at a time frame consistent with the inhibition of SARS-CoV-2 M^pro activity. As a proof-of-concept, to validate the pharmaceutical potential of the selected hits against SARS-CoV-2, we rationally optimized one of the hit compounds and obtained two potent SARS-CoV-2 inhibitors with increased activity against M^pro both in vitro and in a cellular context, as well as against SARS-CoV-2 replication in infected cells. This study significantly contributes to the expansion of the chemical variability of SARS-CoV-2 M^pro inhibitors and provides new scaffolds to be exploited for pan-coronavirus antiviral drug development.

Identification and characterization of bisbenzimide compounds that inhibit human cytomegalovirus replication

The shortcomings of current anti-human cytomegalovirus (HCMV) drugs has stimulated a search for anti-HCMV compounds with novel targets. We screened collections of bioactive compounds and identified a range of compounds with the potential to inhibit HCMV replication. Of these compounds, we selected bisbenzimide compound RO-90-7501 for further study. We generated analogues of RO-90-7501 and found that one compound, MRT00210423, had increased anti-HCMV activity compared to RO-90-7501. Using a combination of compound analogues, microscopy and biochemical assays we found RO-90-7501 and MRT00210423 interacted with DNA. In single molecule microscopy experiments we found RO-90-7501, but not MRT00210423, was able to compact DNA, suggesting that compaction of DNA was non-obligatory for anti-HCMV effects. Using bioinformatics analysis, we found that there were many putative bisbenzimide binding sites in the HCMV DNA genome. However, using western blotting, quantitative PCR and electron microscopy, we found that at a concentration able to inhibit HCMV replication our compounds had little or no effect on production of certain HCMV proteins or DNA synthesis, but did have a notable inhibitory effect on HCMV capsid production. We reasoned that these effects may have involved binding of our compounds to the HCMV genome and/or host cell chromatin. Therefore, our data expand our understanding of compounds with anti-HCMV activity and suggest targeting of DNA with bisbenzimide compounds may be a useful anti-HCMV strategy.

Characterization of a thiourea derivative that targets viral transactivators of cytomegalovirus and herpes simplex virus type 1

Although currently available antivirals against certain herpesviruses are effective, the development of resistance during long-term use has necessitated the search for seed compounds that work against novel target molecules. In this report, we identified a thiourea derivative compound, 147B3, that inhibits the infection of human cytomegalovirus (HCMV) in fibroblasts and herpes simplex virus type 1 (HSV-1) in Vero cells at a 50% effective concentration of 0.5 μM and 1.9 μM, respectively. Characterization of the compound provided the following clues regarding its mode of action. 1) Time-of-addition and block-release assays showed that 147B3 behaved similarly to ganciclovir. 2) 147B3 reduced the expression of early and late but not immediate-early gene products and the accumulation of viral genomic DNA in both HCMV-infected and HSV-1-infected cells. 3) 147B3 inhibited the HCMV IE2-dependent activation of viral early gene promoters. 4) Four HSV-1 clones resistant to 147B3 were isolated and next-generation sequencing analysis of their genome DNA revealed that all of them had a mutation(s) in the infected cell protein 4 (ICP4) gene, which encodes a viral transcriptional factor. 5) Although 147B3 did not reduce the amount of ICP4 in an immunoblotting analysis, it changed the localization of the ICP4 from the speckles in the nuclei to diffused dots in the cytoplasm. 6) 147B3 did not affect the localization of promyelocytic leukemia (PML) bodies. Our findings suggest that 147B3 targets viral transactivators, potentially through their interaction with factors required for the viral gene expression system.

Natural Products and Their Derivatives against Human Herpesvirus Infection

Herpesviruses establish long-term latent infection for the life of the host and are known to cause numerous diseases. The prevalence of viral infection is significantly increased and causes a worldwide challenge in terms of health issues due to drug resistance. Prolonged treatment with conventional antiviral drugs is more likely to develop drug-resistant strains due to mutations of thymidine nucleoside kinase or DNA polymerase. Hence, the development of alternative treatments is clearly required. Natural products and their derivatives have played a significant role in treating herpesvirus infection rather than nucleoside analogs in drug-resistant strains with minimal undesirable effects and different mechanisms of action. Numerous plants, animals, fungi, and bacteria-derived compounds have been proved to be efficient and safe for treating human herpesvirus infection. This review covers the natural antiherpetic agents with the chemical structural class of alkaloids, flavonoids, terpenoids, polyphenols, anthraquinones, anthracyclines, and miscellaneous compounds, and their antiviral mechanisms have been summarized. This review would be helpful to get a better grasp of anti-herpesvirus activity of natural products and their derivatives, and to evaluate the feasibility of natural compounds as an alternative therapy against herpesvirus infections in humans.

Main protease inhibitors and drug surface hotspots for the treatment of COVID-19: A drug repurposing and molecular docking approach

Here, drug repurposing and molecular docking were employed to screen approved MPP inhibitors and their derivatives to suggest a specific therapeutic agent for the treatment of COVID-19. The approved MPP inhibitors against HIV and HCV were prioritized, while RNA dependent RNA Polymerase (RdRp) inhibitor remdesivir including Favipiravir, alpha-ketoamide were studied as control groups. The target drug surface hotspot was also investigated through the molecular docking technique. Molecular dynamics was performed to determine the binding stability of docked complexes. Absorption, distribution, metabolism, and excretion analysis was conducted to understand the pharmacokinetics and drug-likeness of the screened MPP inhibitors. The results of the study revealed that Paritaprevir (-10.9 kcal/mol) and its analog (CID 131982844) (-16.3 kcal/mol) showed better binding affinity than the approved MPP inhibitors compared in this study, including remdesivir, Favipiravir, and alpha-ketoamide. A comparative study among the screened putative MPP inhibitors revealed that the amino acids T25, T26, H41, M49, L141, N142, G143, C145, H164, M165, E166, D187, R188, and Q189 are at potentially critical positions for being surface hotspots in the MPP of SARS-CoV-2. The top 5 predicted drugs (Paritaprevir, Glecaprevir, Nelfinavir, and Lopinavir) and the topmost analog showed conformational stability in the active site of the SARS-CoV-2 MP protein. The study also suggested that Paritaprevir and its analog (CID 131982844) might be effective against SARS-CoV-2. The current findings are limited to in silico analysis and lack in vivo efficacy testing; thus, we strongly recommend a quick assessment of Paritaprevir and its analog (CID 131982844) in a clinical trial.

Valspodar limits human cytomegalovirus infection and dissemination

Human cytomegalovirus (HCMV) is a ubiquitous pathogen that establishes a life-long infection affecting up to 80% of the US population. HCMV periodically reactivates leading to enhanced morbidity and mortality in immunosuppressed patients causing a range of complications including organ transplant failure and cognitive disorders in neonates. Therapeutic options for HCMV are limited to a handful of antivirals that target late stages of the virus life cycle and efficacy is often challenged by the emergence of mutations that confer resistance. In addition, these antiviral therapies may have adverse reactions including neutropenia in newborns and an increase in adverse cardiac events in HSCT patients. These findings highlight the need to develop novel therapeutics that target different steps of the viral life cycle. To this end, we screened a small molecule library against ion transporters to identify new antivirals against the early steps of virus infection. We identified valspodar, a 2nd-generation ABC transporter inhibitor, that limits HCMV infection as demonstrated by the decrease in IE2 expression of virus infected cells. Cells treated with increasing concentrations of valspodar over a 9-day period show minimal cytotoxicity. Importantly, valspodar limits HCMV plaque numbers in comparison to DMSO controls demonstrating its ability to inhibit viral dissemination. Collectively, valspodar represents a potential new anti-HCMV therapeutic that limits virus infection by likely targeting a host factor. Further, the data suggest that specific ABC transporters may participate in the HCMV life-cycle.

The antifungal drug isavuconazole inhibits the replication of human cytomegalovirus (HCMV) and acts synergistically with anti-HCMV drugs

We recently reported that some clinically approved antifungal drugs are potent inhibitors of human cytomegalovirus (HCMV). Here, we report the broad-spectrum activity against HCMV of isavuconazole (ICZ), a new extended-spectrum triazolic antifungal drug. ICZ inhibited the replication of clinical isolates of HCMV as well as strains resistant to the currently available DNA polymerase inhibitors. The antiviral activity of ICZ against HCMV could be linked to the inhibition of human cytochrome P450 51 (hCYP51), an enzyme whose activity we previously demonstrated to be required for productive HCMV infection. Moreover, time-of-addition studies indicated that ICZ might have additional inhibitory effects during the first phase of HCMV replication. Importantly, ICZ showed synergistic antiviral activity in vitro when administered in combination with different approved anti-HCMV drugs at clinically relevant doses. Together, these results pave the way to possible future clinical studies aimed at evaluating the repurposing potential of ICZ in the treatment of HCMV-associated diseases.

Effective deploying of a novel DHODH inhibitor against herpes simplex type 1 and type 2 replication

Emergence of drug resistance and adverse effects often affect the efficacy of nucleoside analogues in the therapy of Herpes simplex type 1 (HSV-1) and type 2 (HSV-2) infections. Host-targeting antivirals could therefore be considered as an alternative or complementary strategy in the management of HSV infections. To contribute to this advancement, here we report on the ability of a new generation inhibitor of a key cellular enzyme of de novo pyrimidine biosynthesis, the dihydroorotate dehydrogenase (DHODH), to inhibit HSV-1 and HSV-2 in vitro replication, with a potency comparable to that of the reference drug acyclovir. Analysis of the HSV replication cycle in MEDS433-treated cells revealed that it prevented the accumulation of viral genomes and reduced late gene expression, thus suggesting an impairment at a stage prior to viral DNA replication consistent with the ability of MEDS433 to inhibit DHODH activity. In fact, the anti-HSV activity of MEDS433 was abrogated by the addition of exogenous uridine or of the product of DHODH, the orotate, thus confirming DHODH as the MEDS433 specific target in HSV-infected cells. A combination of MEDS433 with dipyridamole (DPY), an inhibitor of the pyrimidine salvage pathway, was then observed to be effective in inhibiting HSV replication even in the presence of exogenous uridine, thus mimicking in vivo conditions. Finally, when combined with acyclovir and DPY in checkerboard experiments, MEDS433 exhibited highly synergistic antiviral activity. Taken together, these findings suggest that MEDS433 is a promising candidate as either single agent or in combination regimens with existing direct-acting anti-HSV drugs to develop new strategies for treatment of HSV infections.

The Clinically Approved Antifungal Drug Posaconazole Inhibits Human Cytomegalovirus Replication

Posaconazole (PCZ) is a clinically approved drug used predominantly for prophylaxis and salvage therapy of fungal infections. Here, we report its previously undescribed anti-human cytomegalovirus (HCMV) activity. By using antiviral assays, we demonstrated that PCZ, along with other azolic antifungals, has a broad anti-HCMV activity, being active against different strains, including low-passage-number clinical isolates and strains resistant to viral DNA polymerase inhibitors. Using a pharmacological approach, we identified the inhibition of human cytochrome P450 51 (hCYP51), or lanosterol 14α demethylase, a cellular target of posaconazole in infected cells, as a mechanism of anti-HCMV activity of the drug. Indeed, hCYP51 expression was stimulated upon HCMV infection, and the inhibition of its enzymatic activity by either the lanosterol analog VFV {(R)-N-(1-(3,4'-difluoro-[1,1'-biphenyl]-4-yl)-2-(1H-imidazol-1-yl)ethyl)-4-(5-phenyl-1,3,4-oxadiazol-2-yl)benzamide} or PCZ decreased HCMV yield and infectivity of released virus particles. Importantly, we observed that the activity of the first-line anti-HCMV drug ganciclovir was boosted tenfold by PCZ and that ganciclovir (GCV) and PCZ act synergistically in inhibiting HCMV replication. Taken together, these findings suggest that this clinically approved drug deserves further investigation in the development of host-directed antiviral strategies as a candidate anti-HCMV drug with a dual antimicrobial effect.

Human Neural Stem Cell Systems to Explore Pathogen-Related Neurodevelopmental and Neurodegenerative Disorders

Building and functioning of the human brain requires the precise orchestration and execution of myriad molecular and cellular processes, across a multitude of cell types and over an extended period of time. Dysregulation of these processes affects structure and function of the brain and can lead to neurodevelopmental, neurological, or psychiatric disorders. Multiple environmental stimuli affect neural stem cells (NSCs) at several levels, thus impairing the normal human neurodevelopmental program. In this review article, we will delineate the main mechanisms of infection adopted by several neurotropic pathogens, and the selective NSC vulnerability. In particular, TORCH agents, i.e., Toxoplasma gondii, others (including Zika virus and Coxsackie virus), Rubella virus, Cytomegalovirus, and Herpes simplex virus, will be considered for their devastating effects on NSC self-renewal with the consequent neural progenitor depletion, the cellular substrate of microcephaly. Moreover, new evidence suggests that some of these agents may also affect the NSC progeny, producing long-term effects in the neuronal lineage. This is evident in the paradigmatic example of the neurodegeneration occurring in Alzheimer's disease.

Drug repurposing of nitazoxanide: can it be an effective therapy for COVID-19?

Background

The current outbreak of pandemic coronavirus disease 2019 (COVID-19) aggravates serious need for effective therapeutics. Over recent years, drug repurposing has been accomplished as an important opportunity in drug development as it shortens the time consumed for development, besides sparing the cost and the efforts exerted in the research and development process.

Main body of the abstract

The FDA-approved antiparasitic drug, nitazoxanide (NTZ), has been found to have antiviral activity against different viral infections such as coronaviruses, influenza, hepatitis C virus (HCV), hepatitis B virus (HBV), and other viruses signifying its potential as a broad spectrum antiviral drug. Moreover, it has been recently reported that NTZ exhibited in vitro inhibition of SARS-CoV-2 at a small micromolar concentration. Additionally, NTZ suppresses the production of cytokines emphasizing its potential to manage COVID-19-induced cytokine storm. Furthermore, the reported efficacy of NTZ to bronchodilate the extremely contracted airways can be beneficial in alleviating COVID-19-associated symptoms.

Short conclusion

All these findings, along with the high safety record of the drug, have gained our interest to urge conductance of clinical trials to assess the potential benefits of using it in COVID-19 patients. Thus, in this summarized article, we review the antiviral activities of NTZ and highlight its promising therapeutic actions that make the drug worth clinical trials.

Validation and Characterization of Five Distinct Novel Inhibitors of Human Cytomegalovirus

The critical consequences of human cytomegalovirus (HCMV) infection in the transplant population and in congenitally infected infants, the limited treatment options for HCMV, and the rise of resistant mutants toward existing therapies has fueled the search for new anti-HCMV agents. A pp28-luciferase recombinant HCMV was used as a reporter system for high-throughput screening of HCMV inhibitors. Approximately 400 000 compounds from existing libraries were screened. Subsequent validation assays using resynthesized compounds, several virus strains, and detailed virology assays resulted in the identification of five structurally unique and selective HCMV inhibitors, active at sub to low micromolar concentrations. Further characterization revealed that each compound inhibited a specific stage of HCMV replication. One compound was also active against herpes simplex virus (HSV1 and HSV2), and another compound was active against Epstein-Barr virus (EBV). Drug combination studies revealed that all five compounds were additive with ganciclovir or letermovir. Future studies will focus on optimization of these new anti-HCMV compounds along with mechanistic studies.

Bright and Early: Inhibiting Human Cytomegalovirus by Targeting Major Immediate-Early Gene Expression or Protein Function

The human cytomegalovirus (HCMV), one of eight human herpesviruses, establishes lifelong latent infections in most people worldwide. Primary or reactivated HCMV infections cause severe disease in immunosuppressed patients and congenital defects in children. There is no vaccine for HCMV, and the currently approved antivirals come with major limitations. Most approved HCMV antivirals target late molecular processes in the viral replication cycle including DNA replication and packaging. “Bright and early” events in HCMV infection have not been exploited for systemic prevention or treatment of disease. Initiation of HCMV replication depends on transcription from the viral major immediate-early (IE) gene. Alternative transcripts produced from this gene give rise to the IE1 and IE2 families of viral proteins, which localize to the host cell nucleus. The IE1 and IE2 proteins are believed to control all subsequent early and late events in HCMV replication, including reactivation from latency, in part by antagonizing intrinsic and innate immune responses. Here we provide an update on the regulation of major IE gene expression and the functions of IE1 and IE2 proteins. We will relate this insight to experimental approaches that target IE gene expression or protein function via molecular gene silencing and editing or small chemical inhibitors.

Inhibitory Effects of Antiviral Drug Candidates on Canine Parvovirus in F81 cells

Canine parvovirus (CPV) is a common etiological agent of acute enteritis, which occurs globally in domestic and wild carnivores. Despite the widespread use of inactivated or live attenuated vaccines, the emergence of antigenic variants and the influence of maternal antibodies have raised some concerns regarding the efficacy of commercial vaccines. While no specific antiviral therapy for CPV infection exists, the only treatment option for the infection is supportive therapy based on symptoms. Thus, there is an urgent medical need to develop antiviral therapeutic options to reduce the burden of CPV-related disease. In this study, a cytopathic effect (CPE)-based high-throughput screening assay was used to screen CPV inhibitors from a Food and Drug Administration (FDA)-approved drug library. After two rounds of screening, seven out of 1430 screened drugs were found to have >50% CPE inhibition. Three drugs—Nitazoxanide, Closantel Sodium, and Closantel—with higher anti-CPV effects were further evaluated in F81 cells by absolute PCR quantification and indirect immunofluorescence assay (IFA). The inhibitory effects of all three drugs were dose-dependent. Time of addition assay indicated that the drugs inhibited the early processes of the CPV replication cycle, and the inhibition effects were relatively high within 2 h postinfection. Western blot assay also showed that the three drugs had broad-spectrum antiviral activity against different subspecies of three CPV variants. In addition, antiapoptotic effects were observed within 12 h in Nitazoxanide-treated F81 cells regardless of CPV infection, while Closantel Sodium- or Closantel-treated cells had no pro- or antiapoptotic effects. In conclusion, Nitazoxanide, Closantel Sodium, and Closantel can effectively inhibit different subspecies of CPV. Since the safety profiles of FDA-approved drugs have already been extensively studied, these three drugs can potentially become specific and effective anti-CPV drugs.

The isoquinoline alkaloid berberine inhibits human cytomegalovirus replication by interfering with the viral Immediate Early-2 (IE2) protein transactivating activity

The identification and validation of new small molecules able to inhibit the replication of human cytomegalovirus (HCMV) remains a priority to develop alternatives to the currently used DNA polymerase inhibitors, which are often burdened by long-term toxicity and emergence of cross-resistance. To contribute to this advancement, here we report on the characterization of the mechanism of action of a bioactive plant-derived alkaloid, berberine (BBR), selected in a previous drug repurposing screen expressly devised to identify early inhibitors of HCMV replication. Low micromolar concentrations of BBR were confirmed to suppress the replication of different HCMV strains, including clinical isolates and strains resistant to approved DNA polymerase inhibitors. Analysis of the HCMV replication cycle in infected cells treated with BBR then revealed that the bioactive compound compromised the progression of virus cycle at a stage prior to viral DNA replication and Early (E) genes expression, but after Immediate-Early (IE) proteins expression. Mechanistic studies in fact highlighted that BBR interferes with the transactivating functions of the viral IE2 protein, thus impairing efficient E gene expression and the progression of HCMV replication cycle. Finally, the mechanism of the antiviral activity of BBR appears to be conserved among different CMVs, since BBR suppressed murine CMV (MCMV) replication and inhibited the transactivation of the prototypic MCMV E1 gene by the IE3 protein, the murine homolog of IE2. Together, these observations warrant for further experimentation to obtain proof of concept that BBR could represent an attractive candidate for alternative anti-HCMV therapeutic strategies.

Drug Repurposing for Viral Infectious Diseases: How Far Are We?

Despite the recent advances in controlling some viral pathogens, most viral infections still lack specific treatment. Indeed, the need for effective therapeutic strategies to combat 'old', emergent, and re-emergent viruses is not paralleled by the approval of new antivirals. In the past years, drug repurposing combined with innovative approaches for drug validation, and with appropriate animal models, significantly contributed to the identification of new antiviral molecules and targets for therapeutic intervention. In this review, we describe the main strategies of drug repurposing in antiviral discovery, discuss the most promising candidates that could be repurposed to treat viral infections, and analyze the possible caveats of this trendy strategy of drug discovery.

Inhibition of vaccinia virus replication by nitazoxanide

Nitazoxanide (NTZ) is an FDA-approved anti-protozoal drug that inhibits several bacteria and viruses as well. However, its effect on poxviruses is unknown. Therefore, we investigated the impact of NTZ on vaccinia virus (VACV). We found that NTZ inhibits VACV production with an EC₅₀ of ~2 μM, a potency comparable to that reported for several other viruses. The inhibitory block occurs early during the viral life cycle, prior to viral DNA replication. The mechanism of viral inhibition is likely not due to activation of intracellular innate immune pathways, such as protein kinase R (PKR) or interferon signaling, contrary to what has been suggested to mediate the effects of NTZ against some other viruses. Rather, our finding that addition of exogenous palmitate partially rescues VACV production from the inhibitory effect of NTZ suggests that NTZ impedes adaptations in cellular metabolism that are needed for efficient completion of the VACV replication cycle.

Screening of FDA-Approved Drugs for Inhibitors of Japanese Encephalitis Virus Infection

Japanese encephalitis virus (JEV), an arthropod-borne flavivirus, is a major cause of acute viral encephalitis in humans. No approved drug is available for the specific treatment of JEV infections, and the available vaccines are not effective against all clinical JEV isolates. In the study described here, a high-throughput screening of an FDA-approved drug library for inhibitors of JEV was performed. Five hit drugs that inhibited JEV infection with a selective index of >10 were identified. The antiviral activities of these five hit drugs against other flavivirus, including Zika virus, were also validated. As three of the five hit drugs were calcium inhibitors, additional types of calcium inhibitors that confirmed that calcium is essential for JEV infection, most likely during viral replication, were utilized. Adaptive mutant analysis uncovered that replacement of Q130, located in transmembrane domain 3 of the nonstructural NS4B protein, which is relatively conserved in flaviviruses, with R or K conferred JEV resistance to manidipine, a voltage-gated Ca²⁺ channel (VGCC) inhibitor, without an apparent loss of the viral growth profile. Furthermore, manidipine was indicated to protect mice against JEV-induced lethality by decreasing the viral load in the brain, while it abrogated the histopathological changes associated with JEV infection. This study provides five antiflavivirus candidates and identifies cytoplasmic calcium to be a novel antiviral target for the treatment of JEV infection. The findings reported here provide therapeutic possibilities for combating infections caused by flaviviruses.

IMPORTANCE No approved therapy for the treatment of Japanese encephalitis virus infection is currently available. Repurposing of approved drugs would accelerate the development of a therapeutic stratagem. In this study, we screened a library of FDA-approved drugs and identified five hit drugs, especially calcium inhibitors, exerting antiflavivirus activity that blocked viral replication. The in vivo efficacy and toxicity of manidipine were investigated with a mouse model of JEV infection, and the viral target was identified by generating an adaptive mutant.

Kinome Profiling Identifies Druggable Targets for Novel Human Cytomegalovirus (HCMV) Antivirals

Human cytomegalovirus (HCMV) is a significant cause of disease in immune-compromised adults and immune naïve newborns. No vaccine exists to prevent HCMV infection, and current antiviral therapies have toxic side effects that limit the duration and intensity of their use. There is thus an urgent need for new strategies to treat HCMV infection. Repurposing existing drugs as antivirals is an attractive approach to limit the time and cost of new antiviral drug development. Virus-induced changes in infected cells are often driven by changes in cellular kinase activity, which led us to hypothesize that defining the complement of kinases (the kinome), whose abundance or expression is altered during infection would identify existing kinase inhibitors that could be repurposed as new antivirals. To this end, we applied a kinase capture technique, multiplexed kinase inhibitor bead-mass spectrometry (MIB-MS) kinome, to quantitatively measure perturbations in >240 cellular kinases simultaneously in cells infected with a laboratory-adapted (AD169) or clinical (TB40E) HCMV strain. MIB-MS profiling identified time-dependent increases and decreases in MIB binding of multiple kinases including cell cycle kinases, receptor tyrosine kinases, and mitotic kinases. Based on the kinome data, we tested the antiviral effects of kinase inhibitors and other compounds, several of which are in clinical use or development. Using a novel flow cytometry-based assay and a fluorescent reporter virus we identified three compounds that inhibited HCMV replication with IC50 values of <1 μm, and at doses that were not toxic to uninfected cells. The most potent inhibitor of HCMV replication was OTSSP167 (IC50 <1.2 nm), a MELK inhibitor, blocked HCMV early gene expression and viral DNA accumulation, resulting in a >3 log decrease in virus replication. These results show the utility of MIB-MS kinome profiling for identifying existing kinase inhibitors that can potentially be repurposed as novel antiviral drugs.

Is drug repurposing the answer for cytomegalovirus treatment or prevention?

Medical progress has placed cytomegalovirus (CMV) as one of the most important viral pathogens for which treatment is limited and a vaccine is not yet available. The limited treatment options for CMV triggered efforts to discover new antivirals. Drug screening raised hope but also uncertainties as to whether drug repurposing may be a practical approach for infectious diseases in general and CMV in particular. I summarize here several of such agents as well as an approach to advance repurposing for CMV therapy.

Identification of compounds with anti-human cytomegalovirus activity that inhibit production of IE2 proteins

Using a high throughput screening methodology we surveyed a collection of largely uncharacterized validated or suspected kinase inhibitors for anti-human cytomegalovirus (HCMV) activity. From this screen we identified three structurally related 5-aminopyrazine compounds (XMD7-1, -2 and -27) that inhibited HCMV replication in virus yield reduction assays at low micromolar concentrations. Kinase selectivity assays indicated that each compound was a kinase inhibitor capable of inhibiting a range of cellular protein kinases. Western blotting and RNA sequencing demonstrated that treatment of infected cells with XMD7 compounds resulted in a defect in the production of the major HCMV transcriptional transactivator IE2 proteins (IE2-86, IE2-60 and IE2-40) and an overall reduction in transcription from the viral genome. However, production of certain viral proteins was not compromised by treatment with XMD7 compounds.

Thus, these novel anti-HCMV compounds likely inhibited transcription from the viral genome and suppressed production of a subset of viral proteins by inhibiting IE2 protein production.

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High throughput screening identified novel kinase inhibitors that inhibit HCMV protein production.

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5-aminopyrazine compounds (XMD7-1, -2 and -27) have anti-HCMV activity.

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XMD7 compounds inhibited production of HCMV IE2 proteins.