Efficacy of Tilorone Dihydrochloride against Ebola Virus Infection

The MHC-E peptide ligands for checkpoint CD94/NKG2A are governed by inflammatory signals, whereas LILRB1/2 receptors are peptide indifferent

The immune checkpoint NKG2A/CD94 is a promising target for cancer immunotherapy, and its ligand major histocompatibility complex E (MHC-E) is frequently upregulated in cancer. NKG2A/CD94-mediated inhibition of lymphocytes depends on the presence of specific leader peptides in MHC-E, but when and where they are presented in situ is unknown. We apply a nanobody specific for the Qdm/Qa-1b complex, the NKG2A/CD94 ligand in mouse, and find that presentation of Qdm peptide depends on every member of the endoplasmic reticulum-resident peptide loading complex. With a turnover rate of 30 min, the Qdm peptide reflects antigen processing capacity in real time. Remarkably, Qdm/Qa-1b complexes require inflammatory signals for surface expression in situ, despite the broad presence of Qa-1b molecules in homeostasis. Furthermore, we identify LILRB1 as a functional inhibition receptor for MHC-E in steady state. These data provide a molecular understanding of NKG2A blockade in immunotherapy and assign MHC-E as a convergent ligand for multiple immune checkpoints.

Learning from COVID-19: How drug hunters can prepare for the next pandemic

Over 3 years, the SARS-CoV-2 pandemic killed nearly 7 million people and infected more than 767 million globally. During this time, our very small company was able to contribute to antiviral drug discovery efforts through global collaborations with other researchers, which enabled the identification and repurposing of multiple molecules with activity against SARS-CoV-2 including pyronaridine tetraphosphate, tilorone, quinacrine, vandetanib, lumefantrine, cetylpyridinium chloride, raloxifene, carvedilol, olmutinib, dacomitinib, crizotinib, and bosutinib. We highlight some of the key findings from this experience of using different computational and experimental strategies, and detail some of the challenges and strategies for how we might better prepare for the next pandemic so that potential antiviral treatments are available for future outbreaks.

Glycyrrhiza glabra L. Extracts and Other Therapeutics against SARS-CoV-2 in Central Eurasia: Available but Overlooked

In Central Eurasia, the availability of drugs that are inhibitors of the SARS-CoV-2 virus and have proven clinical efficacy is still limited. The aim of this study was to evaluate the activity of drugs that were available in Kazakhstan during the acute phase of the epidemic against SARS-CoV-2. Antiviral activity is reported for Favipiravir, Tilorone, and Cridanimod, which are registered drugs used for the treatment of respiratory viral infections in Kazakhstan. A licorice (Glycyrrhiza glabra) extract was also incorporated into this study because it offered an opportunity to develop plant-derived antivirals. The Favipiravir drug, which had been advertised in local markets as an anti-COVID cure, showed no activity against SARS-CoV-2 in cell cultures. On the contrary, Cridanimod showed impressive high activity (median inhibitory concentration 66 μg/mL) against SARS-CoV-2, justifying further studies of Cridanimod in clinical trials. Tilorone, despite being in the same pharmacological group as Cridanimod, stimulated SARS-CoV-2 replication in cultures. The licorice extract inhibited SARS-CoV-2 replication in cultures, with a high median effective concentration of 16.86 mg/mL. Conclusions: The synthetic, low-molecular-weight compound Cridanimod suppresses SARS-CoV-2 replication at notably low concentrations, and this drug is not toxic to cells at therapeutic concentrations. In contrast to its role as an inducer of interferons, Cridanimod is active in cells that have a genetic defect in interferon production, suggesting a different mechanism of action. Cridanimod is an attractive drug for inclusion in clinical trials against SARS-CoV-2 and, presumably, other coronaviruses. The extract from licorice shows low activity against SARS-CoV-2. At the same time, high doses of 2 g/kg of this plant extract show little or no acute toxicity in animal studies; for this reason, licorice products can still be considered for further development as a safe, orally administered adjunctive therapy.

The Susceptibility of BALB/c Mice to a Mouse-Adapted Ebola Virus Intravaginal Infection

Ebola virus (EBOV) causes Ebola virus disease (EVD), which is characterized by hemorrhagic fever with high mortality rates in humans. EBOV sexual transmission has been a concern since the 2014-2016 outbreak in Africa, as persistent infection in the testis and transmission to women was demonstrated. The only study related to establishing an intravaginal small animal infection model was recently documented in IFNAR^-/- mice using wild-type and mouse-adapted EBOV (maEBOV), and resulted in 80% mortality, supporting epidemiological data. However, this route of transmission is still poorly understood in women, and the resulting EVD from it is understudied. Here, we contribute to this field of research by providing data from immunocompetent BALB/c mice. We demonstrate that progesterone priming increased the likelihood of maEBOV vaginal infection and of exhibiting the symptoms of disease and seroconversion. However, our data suggest subclinical infection, regardless of the infective dose. We conclude that maEBOV can infect BALB/c mice through vaginal inoculation, but that this route of infection causes significantly less disease compared to intraperitoneal injection at a similar dose, which is consistent with previous studies using other peripheral routes of inoculation in that animal model. Our data are inconsistent with the disease severity described in female patients, therefore suggesting that BALB/c mice are unsuitable for modeling typical EVD following vaginal challenge with maEBOV. Further studies are required to determine the mechanisms by which EVD is attenuated in BALB/c mice, using maEBOV via the vaginal route, as in our experimental set-up.

Transporter Inhibition Profile for the Antivirals Tilorone, Quinacrine and Pyronaridine

Pyronaridine, tilorone and quinacrine are cationic molecules that have in vitro activity against Ebola, SARS-CoV-2 and other viruses. All three molecules have also demonstrated in vivo activity against Ebola in mice, while pyronaridine showed in vivo efficacy against SARS-CoV-2 in mice. We have recently tested these molecules and other antivirals against human organic cation transporters (OCTs) and apical multidrug and toxin extruders (MATEs). Quinacrine was found to be an inhibitor of OCT2, while tilorone and pyronaridine were less potent, and these displayed variability depending on the substrate used. To assess whether any of these three molecules have other potential interactions with additional transporters, we have now screened them at 10 μM against various human efflux and uptake transporters including P-gp, OATP1B3, OAT1, OAT3, MRP1, MRP2, MRP3, BCRP, as well as confirmational testing against OCT1, OCT2, MATE1 and MATE2K. Interestingly, in this study tilorone appears to be a more potent inhibitor of OCT1 and OCT2 than pyronaridine or quinacrine. However, both pyronaridine and quinacrine appear to be more potent inhibitors of MATE1 and MATE2K. None of the three compounds inhibited MRP1, MRP2, MRP3, OAT1, OAT3, P-gp or OATP1B3. Similarly, we previously showed that tilorone and pyronaridine do not inhibit OATP1B1 and have confirmed that quinacrine behaves similarly. In total, these observations suggest that the three compounds only appear to interact with OCTs and MATEs to differing extents, suggesting they may be involved in fewer clinically relevant drug-transporter interactions involving pharmaceutical substrates of the other major transporters tested.

Advances in the Development of Small Molecule Antivirals against Equine Encephalitic Viruses

Venezuelan, western, and eastern equine encephalitic alphaviruses (VEEV, WEEV, and EEEV, respectively) are arboviruses that are highly pathogenic to equines and cause significant harm to infected humans. Currently, human alphavirus infection and the resulting diseases caused by them are unmitigated due to the absence of approved vaccines or therapeutics for general use. These circumstances, combined with the unpredictability of outbreaks-as exemplified by a 2019 EEE surge in the United States that claimed 19 patient lives-emphasize the risks posed by these viruses, especially for aerosolized VEEV and EEEV which are potential biothreats. Herein, small molecule inhibitors of VEEV, WEEV, and EEEV are reviewed that have been identified or advanced in the last five years since a comprehensive review was last performed. We organize structures according to host- versus virus-targeted mechanisms, highlight cellular and animal data that are milestones in the development pipeline, and provide a perspective on key considerations for the progression of compounds at early and later stages of advancement.

Pyronaridine Protects against SARS-CoV-2 Infection in Mouse

There are currently relatively few small-molecule antiviral drugs that are either approved or emergency-approved for use against severe acute respiratory coronavirus 2 (SARS-CoV-2). One of these is remdesivir, which was originally repurposed from its use against Ebola. We evaluated three molecules we had previously identified computationally with antiviral activity against Ebola and Marburg and identified pyronaridine, which inhibited the SARS-CoV-2 replication in A549-ACE2 cells. The in vivo efficacy of pyronaridine has now been assessed in a K18-hACE transgenic mouse model of COVID-19. Pyronaridine treatment demonstrated a statistically significant reduction of viral load in the lungs of SARS-CoV-2-infected mice, reducing lung pathology, which was also associated with significant reduction in the levels of pro-inflammatory cytokines/chemokine and cell infiltration. Pyronaridine inhibited the viral PLpro activity in vitro (IC50 of 1.8 μM) without any effect on Mpro, indicating a possible molecular mechanism involved in its ability to inhibit SARS-CoV-2 replication. We have also generated several pyronaridine analogs to assist in understanding the structure activity relationship for PLpro inhibition. Our results indicate that pyronaridine is a potential therapeutic candidate for COVID-19.

Tilorone and Cridanimod Protect Mice and Show Antiviral Activity in Rats despite Absence of the Interferon-Inducing Effect in Rats

The synthetic compounds, Tilorone and Cridanimod, have the antiviral activity which initially had been ascribed to the capacity to induce interferon. Both drugs induce interferon in mice but not in humans. This study investigates whether these compounds have the antiviral activity in mice and rats since rats more closely resemble the human response. Viral-infection models were created in CD-1 mice and Wistar rats. Three strains of Venezuelan equine encephalitis virus were tested for the performance in these models. One virus strain is the molecularly cloned attenuated vaccine. The second strain has major virulence determinants converted to the wild-type state which are present in virulent strains. The third virus has wild-type virulence determinants, and in addition, is engineered to express green fluorescent protein. Experimentally infected animals received Tilorone or Cridanimod, and their treatment was equivalent to the pharmacopoeia-recomended human treatment regimen. Tilorone and Cridanimod show the antiviral activity in mice and rats and protect the mice from death. In rats, both drugs diminish the viremia. These drugs do not induce interferon-alpha or interferon-beta in rats. The presented observations allow postulating the existence of an interferon-independent and species-independent mechanism of action.

Evaluation of Phenol-Substituted Diphyllin Derivatives as Selective Antagonists for Ebola Virus Entry

Ebola virus (EBOV) is an aggressive filoviral pathogen that can induce severe hemorrhagic fever in humans with up to 90% fatality rate. To date, there are no clinically effective small-molecule drugs for postexposure therapies to treat filoviral infections. EBOV cellular entry and infection involve uptake via macropinocytosis, navigation through the endocytic pathway, and pH-dependent escape into the cytoplasm. We report the inhibition of EBOV cell entry via selective inhibition of vacuolar (V)-ATPase by a new series of phenol-substituted derivatives of the natural product scaffold diphyllin. In cells challenged with Ebola virus, the diphyllin derivatives inhibit viral entry dependent upon structural variations to low nanomolar potencies. Mechanistically, the diphyllin derivatives had no effect on uptake and colocalization of viral particles with endocytic marker LAMP1 but directly modulated endosomal pH. The most potent effects were reversible exhibiting higher selectivity than bafilomycin or the parent diphyllin. Unlike general lysosomotrophic agents, the diphyllin derivatives showed no major disruptions of endocytic populations or morphology when examined with Rab5 and LAMP1 markers. The dilated vacuole phenotype induced by apilimod treatment or in constitutively active Rab5 mutant Q79L-expressing cells was both blocked and reversed by the diphyllin derivatives. The results are consistent with the action of the diphyllin scaffold as a selective pH-dependent viral entry block in late endosomes. Overall, the compounds show improved selectivity and minimal cytotoxicity relative to classical endosomal acidification blocking agents.

The Pandemic Response Box─Accelerating Drug Discovery Efforts after Disease Outbreaks

The current Covid-19 pandemic has underlined the need for a more coordinated and forward-looking investment in the search for new medicines targeting emerging health care threats. Repositioning currently approved drugs is a popular approach to any new emerging disease, but it represents a first wave of response. Behind this would be a second wave of more specifically designed therapies based on activities against specific molecular targets or in phenotypic assays. Following the successful deployment and uptake of previous open access compound collections, we assembled the Pandemic Response Box, a collection of 400 compounds to facilitate drug discovery in emerging infectious disease. These are based on public domain information on chemotypes currently in discovery and early development which have been shown to have useful activities and were prioritized by medicinal chemistry experts. They are freely available to the community as a pharmacological test set with the understanding that data will be shared rapidly in the public domain.

Tilorone-Dihydrochloride Protects against Rift Valley Fever Virus Infection and Disease in the Mouse Model

Rift Valley fever (RVF) is a mosquito-borne zoonotic disease endemic to Africa and the Middle East that can affect humans and ruminant livestock. Currently, there are no approved vaccines or therapeutics for the treatment of severe RVF disease in humans. Tilorone-dihydrochloride (Tilorone) is a broad-spectrum antiviral candidate that has previously shown efficacy against a wide range of DNA and RNA viruses, and which is clinically utilized for the treatment of respiratory infections in Russia and other Eastern European countries. Here, we evaluated the antiviral activity of Tilorone against Rift Valley fever virus (RVFV). In vitro, Tilorone inhibited both vaccine (MP-12) and virulent (ZH501) strains of RVFV at low micromolar concentrations. In the mouse model, treatment with Tilorone significantly improved survival outcomes in BALB/c mice challenged with a lethal dose of RVFV ZH501. Treatment with 30 mg/kg/day resulted in 80% survival when administered immediately after infection. In post-exposure prophylaxis, Tilorone resulted in 30% survival at one day after infection when administered at 45 mg/kg/day. These findings demonstrate that Tilorone has potent antiviral efficacy against RVFV infection in vitro and in vivo and supports further development of Tilorone as a potential antiviral therapeutic for treatment of RVFV infection.

Defending Antiviral Cationic Amphiphilic Drugs That May Cause Drug-Induced Phospholipidosis

A recent publication in Science has proposed that cationic amphiphilic drugs repurposed for COVID-19 typically use phosholipidosis as their antiviral mechanism of action in cells but will have no in vivo efficacy. On the contrary, our viewpoint, supported by additional experimental data for similar cationic amphiphilic drugs, indicates that many of these molecules have both in vitro and in vivo efficacy with no reported phospholipidosis, and therefore, this class of compounds should not be avoided but further explored, as we continue the search for broad spectrum antivirals.

Remdesivir and EIDD-1931 Interact with Human Equilibrative Nucleoside Transporters 1 and 2: Implications for Reaching SARS-CoV-2 Viral Sanctuary Sites

Equilibrative nucleoside transporters (ENTs) are present at the blood-testis barrier (BTB), where they can facilitate antiviral drug disposition to eliminate a sanctuary site for viruses detectable in semen. The purpose of this study was to investigate ENT-drug interactions with three nucleoside analogs, remdesivir, molnupiravir, and molnupiravir's active metabolite, β-d-N⁴-hydroxycytidine (EIDD-1931), and four non-nucleoside molecules repurposed as antivirals for coronavirus disease 2019 (COVID-19). The study used three-dimensional pharmacophores for ENT1 and ENT2 substrates and inhibitors and Bayesian machine learning models to identify potential interactions with these transporters. In vitro transport experiments demonstrated that remdesivir was the most potent inhibitor of ENT-mediated [³H]uridine uptake (ENT1 IC₅₀: 39 μM; ENT2 IC₅₀: 77 μM), followed by EIDD-1931 (ENT1 IC₅₀: 259 μM; ENT2 IC₅₀: 467 μM), whereas molnupiravir was a modest inhibitor (ENT1 IC₅₀: 701 μM; ENT2 IC₅₀: 851 μM). Other proposed antivirals failed to inhibit ENT-mediated [³H]uridine uptake below 1 mM. Remdesivir accumulation decreased in the presence of 6-S-[(4-nitrophenyl)methyl]-6-thioinosine (NBMPR) by 30% in ENT1 cells (P = 0.0248) and 27% in ENT2 cells (P = 0.0054). EIDD-1931 accumulation decreased in the presence of NBMPR by 77% in ENT1 cells (P = 0.0463) and by 64% in ENT2 cells (P = 0.0132), which supported computational predictions that both are ENT substrates that may be important for efficacy against COVID-19. NBMPR failed to decrease molnupiravir uptake, suggesting that ENT interaction is likely inhibitory. Our combined computational and in vitro data can be used to identify additional ENT-drug interactions to improve our understanding of drugs that can circumvent the BTB. SIGNIFICANCE STATEMENT: This study identified remdesivir and EIDD-1931 as substrates of equilibrative nucleoside transporters 1 and 2. This provides a potential mechanism for uptake of these drugs into cells and may be important for antiviral potential in the testes and other tissues expressing these transporters.

STAT-1 Knockout Mice as a Model for Wild-Type Sudan Virus (SUDV)

Currently there is no FDA-licensed vaccine or therapeutic against Sudan ebolavirus (SUDV) infections. The largest ever reported 2014–2016 West Africa outbreak, as well as the 2021 outbreak in the Democratic Republic of Congo, highlight the critical need for countermeasures against filovirus infections. A well-characterized small animal model that is susceptible to wild-type filoviruses would greatly add to the screening of antivirals and vaccines. Here, we infected signal transducer and activator of transcription-1 knock out (STAT-1 KO) mice with five different wildtype filoviruses to determine susceptibility. SUDV and Marburg virus (MARV) were the most virulent, and caused 100% or 80% lethality, respectively. Zaire ebolavirus (EBOV), Bundibugyo ebolavirus (BDBV), and Taï Forest ebolavirus (TAFV) caused 40%, 20%, and no mortality, respectively. Further characterization of SUDV in STAT-1 KO mice demonstrated lethality down to 3.1 × 10¹ pfu. Viral genomic material was detectable in serum as early as 1 to 2 days post-challenge. The onset of viremia was closely followed by significant changes in total white blood cells and proportion of neutrophils and lymphocytes, as well as by an influx of neutrophils in the liver and spleen. Concomitant significant fluctuations in blood glucose, albumin, globulin, and alanine aminotransferase were also noted, altogether consistent with other models of filovirus infection. Finally, favipiravir treatment fully protected STAT-1 KO mice from lethal SUDV challenge, suggesting that this may be an appropriate small animal model to screen anti-SUDV countermeasures.

Quantum Machine Learning Algorithms for Drug Discovery Applications

The growing quantity of public and private data sets focused on small molecules screened against biological targets or whole organisms provides a wealth of drug discovery relevant data. This is matched by the availability of machine learning algorithms such as Support Vector Machines (SVM) and Deep Neural Networks (DNN) that are computationally expensive to perform on very large data sets with thousands of molecular descriptors. Quantum computer (QC) algorithms have been proposed to offer an approach to accelerate quantum machine learning over classical computer (CC) algorithms, however with significant limitations. In the case of cheminformatics, which is widely used in drug discovery, one of the challenges to overcome is the need for compression of large numbers of molecular descriptors for use on a QC. Here, we show how to achieve compression with data sets using hundreds of molecules (SARS-CoV-2) to hundreds of thousands of molecules (whole cell screening data sets for plague and M. tuberculosis) with SVM and the data reuploading classifier (a DNN equivalent algorithm) on a QC benchmarked against CC and hybrid approaches. This study illustrates the steps needed in order to be "quantum computer ready" in order to apply quantum computing to drug discovery and to provide the foundation on which to build this field.

Repurposing the Ebola and Marburg Virus Inhibitors Tilorone, Quinacrine, and Pyronaridine: In Vitro Activity against SARS-CoV-2 and Potential Mechanisms

Severe acute respiratory coronavirus 2 (SARS-CoV-2) is a newly identified virus that has resulted in over 2.5 million deaths globally and over 116 million cases globally in March, 2021. Small-molecule inhibitors that reverse disease severity have proven difficult to discover. One of the key approaches that has been widely applied in an effort to speed up the translation of drugs is drug repurposing. A few drugs have shown in vitro activity against Ebola viruses and demonstrated activity against SARS-CoV-2 in vivo. Most notably, the RNA polymerase targeting remdesivir demonstrated activity in vitro and efficacy in the early stage of the disease in humans. Testing other small-molecule drugs that are active against Ebola viruses (EBOVs) would appear a reasonable strategy to evaluate their potential for SARS-CoV-2. We have previously repurposed pyronaridine, tilorone, and quinacrine (from malaria, influenza, and antiprotozoal uses, respectively) as inhibitors of Ebola and Marburg viruses in vitro in HeLa cells and mouse-adapted EBOV in mice in vivo. We have now tested these three drugs in various cell lines (VeroE6, Vero76, Caco-2, Calu-3, A549-ACE2, HUH-7, and monocytes) infected with SARS-CoV-2 as well as other viruses (including MHV and HCoV 229E). The compilation of these results indicated considerable variability in antiviral activity observed across cell lines. We found that tilorone and pyronaridine inhibited the virus replication in A549-ACE2 cells with IC50 values of 180 nM and IC50 198 nM, respectively. We used microscale thermophoresis to test the binding of these molecules to the spike protein, and tilorone and pyronaridine bind to the spike receptor binding domain protein with K d values of 339 and 647 nM, respectively. Human Cmax for pyronaridine and quinacrine is greater than the IC50 observed in A549-ACE2 cells. We also provide novel insights into the mechanism of these compounds which is likely lysosomotropic.

Old Drug, New Trick: Tilorone, a Broad-Spectrum Antiviral Drug as a Potential Anti-Fibrotic Therapeutic for the Diseased Heart

Cardiac fibrosis is associated with most forms of cardiovascular disease. No reliable therapies targeting cardiac fibrosis are available, thus identifying novel drugs that can resolve or prevent fibrosis is needed. Tilorone, an antiviral agent, can prevent fibrosis in a mouse model of lung disease. We investigated the anti-fibrotic effects of tilorone in human cardiac fibroblasts in vitro by performing a radioisotopic assay for [³H]-proline incorporation as a proxy for collagen synthesis. Exploratory studies in human cardiac fibroblasts treated with tilorone (10 µM) showed a significant reduction in transforming growth factor-β induced collagen synthesis compared to untreated fibroblasts. To determine if this finding could be recapitulated in vivo, mice with established pathological remodelling due to four weeks of transverse aortic constriction (TAC) were administered tilorone (50 mg/kg, i.p) or saline every third day for eight weeks. Treatment with tilorone was associated with attenuation of fibrosis (assessed by Masson's trichrome stain), a favourable cardiac gene expression profile and no further deterioration of cardiac systolic function determined by echocardiography compared to saline treated TAC mice. These data demonstrate that tilorone has anti-fibrotic actions in human cardiac fibroblasts and the adult mouse heart, and represents a potential novel therapy to treat fibrosis associated with heart failure.

The Antiviral Drug Tilorone Is a Potent and Selective Inhibitor of Acetylcholinesterase

Acetylcholinesterase (AChE) is an important drug target in neurological disorders like Alzheimer's disease, Lewy body dementia, and Parkinson's disease dementia as well as for other conditions like myasthenia gravis and anticholinergic poisoning. In this study, we have used a combination of high-throughput screening, machine learning, and docking to identify new inhibitors of this enzyme. Bayesian machine learning models were generated with literature data from ChEMBL for eel and human AChE inhibitors as well as butyrylcholinesterase inhibitors (BuChE) and compared with other machine learning methods. High-throughput screens for the eel AChE inhibitor model identified several molecules including tilorone, an antiviral drug that is well-established outside of the United States, as a newly identified nanomolar AChE inhibitor. We have described how tilorone inhibits both eel and human AChE with IC₅₀'s of 14.4 nM and 64.4 nM, respectively, but does not inhibit the closely related BuChE IC₅₀ > 50 μM. We have docked tilorone into the human AChE crystal structure and shown that this selectivity is likely due to the reliance on a specific interaction with a hydrophobic residue in the peripheral anionic site of AChE that is absent in BuChE. We also conducted a pharmacological safety profile (SafetyScreen44) and kinase selectivity screen (SelectScreen) that showed tilorone (1 μM) only inhibited AChE out of 44 toxicology target proteins evaluated and did not appreciably inhibit any of the 485 kinases tested. This study suggests there may be a potential role for repurposing tilorone or its derivatives in conditions that benefit from AChE inhibition.

Design, synthesis, and biological evaluation of N-arylpiperazine derivatives as interferon inducers

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We designed and synthesized a series of arylpiperazine derivatives as interferon inducers.

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We tested different linker system and carbonyl moiety resulted in increase of potency.

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5i exhibited the activity of interferon inducer with EC₅₀ of 13.1 μM and no cytotoxicity.

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5i initiated immune responses by mediating type I IFN signaling.

Type I Interferon (IFN) signaling plays an important role in the immune defense system against virus infection and in the innate immune response, thus IFNs are widely used as anti-viral agents and treatment for immune disorder or cancer. However, there is a growing demand for novel small-molecule IFN inducer due to tolerance, toxicity, or short duration of action following direct administration of IFNs. In this study, we assessed arylpiperazine (ARP) as a new core skeleton of IFN inducer. To investigate structure–activity relationship, we designed and synthesized a series of ARP analogues and evaluated the ability to stimulate IFN response in THP-1 human monocyte cells. Compound 5i was identified as a potent type I IFN inducer as it significantly increased cytokine secretion and increased expression of various IFN-stimulating genes which are representative biomarkers of type I IFN pathway. Our results suggested a beneficial therapeutic potential of 5i as an anti-viral agent.

Repurposing the Ebola and Marburg Virus Inhibitors Tilorone, Quinacrine and Pyronaridine: In vitro Activity Against SARS-CoV-2 and Potential Mechanisms

SARS-CoV-2 is a newly identified virus that has resulted in over 1.3 M deaths globally and over 59 M cases globally to date. Small molecule inhibitors that reverse disease severity have proven difficult to discover. One of the key approaches that has been widely applied in an effort to speed up the translation of drugs is drug repurposing. A few drugs have shown in vitro activity against Ebola virus and demonstrated activity against SARS-CoV-2 in vivo . Most notably the RNA polymerase targeting remdesivir demonstrated activity in vitro and efficacy in the early stage of the disease in humans. Testing other small molecule drugs that are active against Ebola virus would seem a reasonable strategy to evaluate their potential for SARS-CoV-2. We have previously repurposed pyronaridine, tilorone and quinacrine (from malaria, influenza, and antiprotozoal uses, respectively) as inhibitors of Ebola and Marburg virus in vitro in HeLa cells and of mouse adapted Ebola virus in mouse in vivo . We have now tested these three drugs in various cell lines (VeroE6, Vero76, Caco-2, Calu-3, A549-ACE2, HUH-7 and monocytes) infected with SARS-CoV-2 as well as other viruses (including MHV and HCoV 229E). The compilation of these results indicated considerable variability in antiviral activity observed across cell lines. We found that tilorone and pyronaridine inhibited the virus replication in A549-ACE2 cells with IC 50 values of 180 nM and IC 50 198 nM, respectively. We have also tested them in a pseudovirus assay and used microscale thermophoresis to test the binding of these molecules to the spike protein. They bind to spike RBD protein with K d values of 339 nM and 647 nM, respectively. Human C max for pyronaridine and quinacrine is greater than the IC 50 hence justifying in vivo evaluation. We also provide novel insights into their mechanism which is likely lysosomotropic.

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.

Pyronaridine tetraphosphate efficacy against Ebola virus infection in guinea pig

The recent outbreaks of the Ebola virus (EBOV) in Africa have brought global visibility to the shortage of available therapeutic options to treat patients infected with this or closely related viruses. We have recently computationally identified three molecules which have all demonstrated statistically significant efficacy in the mouse model of infection with mouse adapted Ebola virus (ma-EBOV). One of these molecules is the antimalarial pyronaridine tetraphosphate (IC50 range of 0.82-1.30 μM against three strains of EBOV and IC50 range of 1.01-2.72 μM against two strains of Marburg virus (MARV)) which is an approved drug in the European Union and used in combination with artesunate. To date, no small molecule drugs have shown statistically significant efficacy in the guinea pig model of EBOV infection. Pharmacokinetics and range-finding studies in guinea pigs directed us to a single 300 mg/kg or 600 mg/kg oral dose of pyronaridine 1hr after infection. Pyronaridine resulted in statistically significant survival of 40% at 300 mg/kg and protected from a lethal challenge with EBOV. In comparison, oral favipiravir (300 mg/kg dosed once a day) had 43.5% survival. All animals in the vehicle treatment group succumbed to disease by study day 12 (100% mortality). The in vitro metabolism and metabolite identification of pyronaridine and another of our EBOV active molecules, tilorone, suggested significant species differences which may account for the efficacy or lack thereof, respectively in guinea pig. In summary, our studies with pyronaridine demonstrates its utility for repurposing as an antiviral against EBOV and MARV.

Toward the Target: Tilorone, Quinacrine, and Pyronaridine Bind to Ebola Virus Glycoprotein

Pyronaridine, tilorone, and quinacrine were recently identified by a machine learning model and demonstrated in vitro and in vivo activity against Ebola virus (EBOV) and represent viable candidates for drug repurposing. The target for these molecules was previously unknown. These drugs have now been docked into the crystal structure of the ebola glycoprotein and then experimentally validated in vitro using microscale thermophoresis to generate K _d values for tilorone (0.73 μM), pyronaridine (7.34 μM), and quinacrine (7.55 μM). These molecules were shown to bind with a higher affinity than the previously reported toremifene (16 μM). These three structures provide more insight into the structural diversity of ebola glycoprotein inhibitors which can be utilized in the discovery and design of additional inhibitors.

Déjà vu: Stimulating open drug discovery for SARS-CoV-2

In the past decade we have seen two major Ebola virus outbreaks in Africa, the Zika virus in Brazil and the Americas and the current pandemic of coronavirus disease (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). There is a strong sense of déjà vu because there are still no effective treatments. In the COVID-19 pandemic, despite being a new virus, there are already drugs suggested as active in in vitro assays that are being repurposed in clinical trials. Promising SARS-CoV-2 viral targets and computational approaches are described and discussed. Here, we propose, based on open antiviral drug discovery approaches for previous outbreaks, that there could still be gaps in our approach to drug discovery.

Tilorone, a Broad-Spectrum Antiviral for Emerging Viruses

Tilorone is a 50-year-old synthetic small-molecule compound with antiviral activity that is proposed to induce interferon after oral administration. This drug is used as a broad-spectrum antiviral in several countries of the Russian Federation. We have recently described activity in vitro and in vivo against the Ebola virus. After a broad screening of additional viruses, we now describe in vitro activity against Chikungunya virus (CHIK) and Middle Eastern respiratory syndrome coronavirus (MERS-CoV).

Tilorone is a 50-year-old synthetic small-molecule compound with antiviral activity that is proposed to induce interferon after oral administration. This drug is used as a broad-spectrum antiviral in several countries of the Russian Federation. We have recently described activity in vitro and in vivo against the Ebola virus. After a broad screening of additional viruses, we now describe in vitro activity against Chikungunya virus (CHIK) and Middle Eastern respiratory syndrome coronavirus (MERS-CoV).

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.

Repurposing the antimalarial pyronaridine tetraphosphate to protect against Ebola virus infection

Recent outbreaks of the Ebola virus (EBOV) have focused attention on the dire need for antivirals to treat these patients. We identified pyronaridine tetraphosphate as a potential candidate as it is an approved drug in the European Union which is currently used in combination with artesunate as a treatment for malaria (EC₅₀ between 420 nM—1.14 μM against EBOV in HeLa cells). Range-finding studies in mice directed us to a single 75 mg/kg i.p. dose 1 hr after infection which resulted in 100% survival and statistically significantly reduced viremia at study day 3 from a lethal challenge with mouse-adapted EBOV (maEBOV). Further, an EBOV window study suggested we could dose pyronaridine 2 or 24 hrs post-exposure to result in similar efficacy. Analysis of cytokine and chemokine panels suggests that pyronaridine may act as an immunomodulator during an EBOV infection. Our studies with pyronaridine clearly demonstrate potential utility for its repurposing as an antiviral against EBOV and merits further study in larger animal models with the added benefit of already being used as a treatment against malaria.

To date there is no approved drug for Ebola Virus infection. Our approach has been to assess drugs that are already approved for other uses in various countries. Using computational models, we have previously identified three such drugs and demonstrated their activity against the Ebola virus in vitro. We now report on the in vitro absorption, metabolism, distribution, excretion and pharmacokinetic properties of one of these molecules, namely the antimalarial pyronaridine. We justify efficacy testing in the mouse model of ebola infection. We also demonstrate that a single dose of this drug is 100% effective against the virus. This study provides important preclinical evaluation of this already approved drug and justifies its selection for larger animal efficacy studies.

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.

Repurposing Quinacrine against Ebola Virus Infection In Vivo

Quinacrine hydrochloride is a small-molecule, orally bioavailable drug that has been used clinically as an antimalarial and for many other applications. A machine learning model trained on Ebola virus (EBOV) screening data identified quinacrine as a potent (nanomolar) in vitro inhibitor. In the current study, quinacrine 25 mg/kg was shown to protect 70% of mice (statistically significant) from a lethal challenge with mouse-adapted EBOV with once-daily intraperitoneal dosing for 8 days.

Antimicrobial and Immunomodulatory Properties and Applications of Marine-Derived Proteins and Peptides

Marine organisms provide an abundant source of potential medicines. Many of the marine-derived biomaterials have been shown to act as different mechanisms in immune responses, and in each case they can significantly control the immune system to produce effective reactions. Marine-derived proteins, peptides, and protein hydrolysates exhibit various physiologic functions, such as antimicrobial, anticancer, antioxidant, antihypertensive, and anti-inflammatory activities. Recently, the immunomodulatory properties of several antimicrobial peptides have been demonstrated. Some of these peptides directly kill bacteria and exhibit a variety of immunomodulatory activities that improve the host innate immune response and effectively eliminate infection. The properties of immunomodulatory proteins and peptides correlate with their amino acid composition, sequence, and length. Proteins and peptides with immunomodulatory properties have been tested in vitro and in vivo, and some of them have undergone different clinical and preclinical trials. This review provides a comprehensive overview of marine immunomodulatory proteins, peptides, and protein hydrolysates as well as their production, mechanisms of action, and applications in human therapy.

The Natural Product Eugenol Is an Inhibitor of the Ebola Virus In Vitro

PURPOSE

Since the 2014 Ebola virus (EBOV) outbreak in West Africa there has been considerable effort towards developing drugs to treat Ebola virus disease and yet to date there is no FDA approved treatment. This is important as at the time of writing this manuscript there is an ongoing outbreak in the Democratic Republic of the Congo which has killed over 1000.

METHODS

We have evaluated a small number of natural products, some of which had shown antiviral activity against other pathogens. This is exemplified with eugenol, which is found in high concentrations in multiple essential oils, and has shown antiviral activity against feline calicivirus, tomato yellow leaf curl virus, Influenza A virus, Herpes Simplex virus type 1 and 2, and four airborne phages.

RESULTS

Four compounds possessed EC₅₀ values less than or equal to 11 μM. Of these, eugenol, had an EC₅₀ of 1.3 μM against EBOV and is present in several plants including clove, cinnamon, basil and bay. Eugenol is much smaller and structurally unlike any compound that has been previously identified as an inhibitor of EBOV, therefore it may provide new mechanistic insights.

CONCLUSION

This compound is readily accessible in bulk quantities, is inexpensive, and has a long history of human consumption, which endorses the idea for further assessment as an antiviral therapeutic. This work also suggests that a more exhaustive assessment of natural product libraries against EBOV and other viruses is warranted to improve our ability to identify compounds that are so distinct from FDA approved drugs.

Filovirus Virulence in Interferon α/β and γ Double Knockout Mice, and Treatment with Favipiravir

The 2014 Ebolavirus outbreak in West Africa highlighted the need for vaccines and therapeutics to prevent and treat filovirus infections. A well-characterized small animal model that is susceptible to wild-type filoviruses would facilitate the screening of anti-filovirus agents. To that end, we characterized knockout mice lacking α/β and γ interferon receptors (IFNAGR KO) as a model for wild-type filovirus infection. Intraperitoneal challenge of IFNAGR KO mice with several known human pathogenic species from the genus Ebolavirus and Marburgvirus, except Bundibugyo ebolavirus and Taï Forest ebolavirus, caused variable mortality rate. Further characterization of the prototype Ebola virus Kikwit isolate infection in this KO mouse model showed 100% lethality down to a dilution equivalent to 1.0 × 10⁻¹ pfu with all deaths occurring between 7 and 9 days post-challenge. Viral RNA was detectable in serum after challenge with 1.0 × 10² pfu as early as one day after infection. Changes in hematology and serum chemistry became pronounced as the disease progressed and mirrored the histological changes in the spleen and liver that were also consistent with those described for patients with Ebola virus disease. In a proof-of-principle study, treatment of Ebola virus infected IFNAGR KO mice with favipiravir resulted in 83% protection. Taken together, the data suggest that IFNAGR KO mice may be a useful model for early screening of anti-filovirus medical countermeasures.

Ebola Virus Bayesian Machine Learning Models Enable New in Vitro Leads

We have previously described the first Bayesian machine learning models from FDA-approved drug screens, for identifying compounds active against the Ebola virus (EBOV). These models led to the identification of three active molecules in vitro: tilorone, pyronaridine, and quinacrine. A follow-up study demonstrated that one of these compounds, tilorone, has 100% in vivo efficacy in mice infected with mouse-adapted EBOV at 30 mg/kg/day intraperitoneal. This suggested that we can learn from the published data on EBOV inhibition and use it to select new compounds for testing that are active in vivo. We used these previously built Bayesian machine learning EBOV models alongside our chemical insights for the selection of 12 molecules, absent from the training set, to test for in vitro EBOV inhibition. Nine molecules were directly selected using the model, and eight of these molecules possessed a promising in vitro activity (EC50 < 15 μM). Three further compounds were selected for an in vitro evaluation because they were antimalarials, and compounds of this class like pyronaridine and quinacrine have previously been shown to inhibit EBOV. We identified the antimalarial drug arterolane (IC50 = 4.53 μM) and the anticancer clinical candidate lucanthone (IC50 = 3.27 μM) as novel compounds that have EBOV inhibitory activity in HeLa cells and generally lack cytotoxicity. This work provides further validation for using machine learning and medicinal chemistry expertize to prioritize compounds for testing in vitro prior to more costly in vivo tests. These studies provide further corroboration of this strategy and suggest that it can likely be applied to other pathogens in the future.

Hypoxia Mimetic Agents for Ischemic Stroke

Every year stroke claims more than 6 million lives worldwide. The majority of them are ischemic stroke. Small molecule-based therapeutics for ischemic stroke has attracted a lot of attention, but none has been shown to be clinically useful so far. Hypoxia-inducible factor-1 (HIF-1) plays a crucial role in the transcriptional adaptation of cells to hypoxia. Small molecule-based hypoxia-mimetic agents either stabilize HIF-1α via HIF-prolyl hydroxylases (PHDs) inhibition or through other mechanisms. In both the cases, these agents have been shown to confer ischemic neuroprotection in vitro and in vivo. The agents which act via PHD inhibition are mainly classified into iron chelators, iron competitors, and 2 oxoglutarate (2OG) analogs. This review discusses HIF structure and key players in the HIF-1 degradation pathway as well as the genes, proteins and chemical molecules that are connected to HIF-1 and how they affect cell survival following ischemic injury. Furthermore, this review gives a summary of studies that used PHD inhibitors and other HIF-1α stabilizers as hypoxia-mimetic agents for the treatment of ischemic injury.

High Throughput and Computational Repurposing for Neglected Diseases

Purpose

Neglected tropical diseases (NTDs) represent are a heterogeneous group of communicable diseases that are found within the poorest populations of the world. There are 23 NTDs that have been prioritized by the World Health Organization, which are endemic in 149 countries and affect more than 1.4 billion people, costing these developing economies billions of dollars annually. The NTDs result from four different causative pathogens: protozoa, bacteria, helminth and virus. The majority of the diseases lack effective treatments. Therefore, new therapeutics for NTDs are desperately needed.

Methods

We describe various high throughput screening and computational approaches that have been performed in recent years. We have collated the molecules identified in these studies and calculated molecular properties.

Results

Numerous global repurposing efforts have yielded some promising compounds for various neglected tropical diseases. These compounds when analyzed as one would expect appear drug-like. Several large datasets are also now in the public domain and this enables machine learning models to be constructed that then facilitate the discovery of new molecules for these pathogens.

Conclusions

In the space of a few years many groups have either performed experimental or computational repurposing high throughput screens against neglected diseases. These have identified compounds which in many cases are already approved drugs. Such approaches perhaps offer a more efficient way to develop treatments which are generally not a focus for global pharmaceutical companies because of the economics or the lack of a viable market. Other diseases could perhaps benefit from these repurposing approaches.

Electronic supplementary material

The online version of this article (10.1007/s11095-018-2558-3) contains supplementary material, which is available to authorized users.

Thermodynamics and kinetics of joint action of antiviral agent tilorone and DMSO on model lipid membranes

Individual and joint action of two water-soluble drugs, DMSO and tilorone, on model l-α-dipalmitoylphosphatidylcholine (DPPC) membranes were studied in equilibrium and kinetic regimes by differential scanning calorimetry (DSC). For equilibrium experiments, the drugs were introduced during preparation of the model membrane. In kinetic studies, one of the drugs was added to the DPPC membrane already containing the other drug, and the effects of drug-membrane interactions were monitored in real-time regime. It was found that tilorone and DMSO had opposite effects on the membrane melting temperature, which were non-additive under joint introduction of these drugs. Analysis of kinetics of DSC profiles under drugs introduction allowed us to discriminate two processes in drug-membrane interactions with different characteristic times, i.e., drug sorption onto the membrane (minutes) and drug diffusion through stacks of lipid bilayers (hours). It was established that 0.1 mol% DMSO effectively enhanced membrane penetration for tilorone with the rate of tilorone diffusion being dependent upon the scheme of drugs administration. A model was proposed describing how sorption of a dopant onto lipid membrane could affect the membrane permeability for other dopants. Conditions were determined for enhancement of membrane permeability, as it was observed for DPPC/DMSO/tilorone system.

Advances in Designing and Developing Vaccines, Drugs, and Therapies to Counter Ebola Virus

Ebola virus (EBOV), a member of the family Filoviridae, is responsible for causing Ebola virus disease (EVD) (formerly named Ebola hemorrhagic fever). This is a severe, often fatal illness with mortality rates varying from 50 to 90% in humans. Although the virus and associated disease has been recognized since 1976, it was only when the recent outbreak of EBOV in 2014-2016 highlighted the danger and global impact of this virus, necessitating the need for coming up with the effective vaccines and drugs to counter its pandemic threat. Albeit no commercial vaccine is available so far against EBOV, a few vaccine candidates are under evaluation and clinical trials to assess their prophylactic efficacy. These include recombinant viral vector (recombinant vesicular stomatitis virus vector, chimpanzee adenovirus type 3-vector, and modified vaccinia Ankara virus), Ebola virus-like particles, virus-like replicon particles, DNA, and plant-based vaccines. Due to improvement in the field of genomics and proteomics, epitope-targeted vaccines have gained top priority. Correspondingly, several therapies have also been developed, including immunoglobulins against specific viral structures small cell-penetrating antibody fragments that target intracellular EBOV proteins. Small interfering RNAs and oligomer-mediated inhibition have also been verified for EVD treatment. Other treatment options include viral entry inhibitors, transfusion of convalescent blood/serum, neutralizing antibodies, and gene expression inhibitors. Repurposed drugs, which have proven safety profiles, can be adapted after high-throughput screening for efficacy and potency for EVD treatment. Herbal and other natural products are also being explored for EVD treatment. Further studies to better understand the pathogenesis and antigenic structures of the virus can help in developing an effective vaccine and identifying appropriate antiviral targets. This review presents the recent advances in designing and developing vaccines, drugs, and therapies to counter the EBOV threat.

Computer-Aided Discovery and Characterization of Novel Ebola Virus Inhibitors

The Ebola virus (EBOV) causes severe human infection that lacks effective treatment. A recent screen identified a series of compounds that block EBOV-like particle entry into human cells. Using data from this screen, quantitative structure-activity relationship models were built and employed for virtual screening of a ∼17 million compound library. Experimental testing of 102 hits yielded 14 compounds with IC₅₀ values under 10 μM, including several sub-micromolar inhibitors, and more than 10-fold selectivity against host cytotoxicity. These confirmed hits include FDA-approved drugs and clinical candidates with non-antiviral indications, as well as compounds with novel scaffolds and no previously known bioactivity. Five selected hits inhibited BSL-4 live-EBOV infection in a dose-dependent manner, including vindesine (0.34 μM). Additional studies of these novel anti-EBOV compounds revealed their mechanisms of action, including the inhibition of NPC1 protein, cathepsin B/L, and lysosomal function. Compounds identified in this study are among the most potent and well-characterized anti-EBOV inhibitors reported to date.