An Orally Available 3-Ethoxybenzisoxazole Capsid Binder with Clinical Activity against Human Rhinovirus

Molecular mechanism of rhinovirus escape from the Pyrazolo[3,4-d]pyrimidine capsid-binding inhibitor OBR-5-340 via mutations distant from the binding pocket: Derivatives that brake resistance

Rhinoviruses (RVs) cause the common cold. Attempts at discovering small molecule inhibitors have mainly concentrated on compounds supplanting the medium chain fatty acids residing in the sixty icosahedral symmetry-related hydrophobic pockets of the viral capsid of the Rhinovirus-A and -B species. High-affinity binding to these pockets stabilizes the capsid against structural changes necessary for the release of the ss(+) RNA genome into the cytosol of the host cell. However, single-point mutations may abolish this binding. RV-B5 is one of several RVs that are naturally resistant against the well-established antiviral agent pleconaril. However, RV-B5 is strongly inhibited by the pyrazolopyrimidine OBR-5-340. Here, we report on isolation and characterization of RV-B5 mutants escaping OBR-5-340 inhibition and show that substitution of amino acid residues not only within the binding pocket but also remote from the binding pocket hamper inhibition. Molecular dynamics network analysis revealed that strong inhibition occurs when an ensemble of several sequence stretches of the capsid proteins enveloping OBR-5-340 move together with OBR-5-340. Mutations abrogating this dynamic, regardless of whether being localized within the binding pocket or distant from it result in escape from inhibition. Pyrazolo [3,4-d]pyrimidine derivatives overcoming OBR-5-340 escape of various RV-B5 mutants were identified. Our work contributes to the understanding of the properties of capsid-binding inhibitors necessary for potent and broad-spectrum inhibition of RVs.

The pyridazine heterocycle in molecular recognition and drug discovery

The pyridazine ring is endowed with unique physicochemical properties, characterized by weak basicity, a high dipole moment that subtends π-π stacking interactions and robust, dual hydrogen-bonding capacity that can be of importance in drug-target interactions. These properties contribute to unique applications in molecular recognition while the inherent polarity, low cytochrome P450 inhibitory effects and potential to reduce interaction of a molecule with the cardiac hERG potassium channel add additional value in drug discovery and development. The recent approvals of the gonadotropin-releasing hormone receptor antagonist relugolix (24) and the allosteric tyrosine kinase 2 inhibitor deucravacitinib (25) represent the first examples of FDA-approved drugs that incorporate a pyridazine ring. In this review, the properties of the pyridazine ring are summarized in comparison to the other azines and its potential in drug discovery is illustrated through vignettes that explore applications that take advantage of the inherent physicochemical properties as an approach to solving challenges associated with candidate optimization.

Graphical Abstract

Targeting the Virus Capsid as a Tool to Fight RNA Viruses

Several strategies have been developed to fight viral infections, not only in humans but also in animals and plants. Some of them are based on the development of efficient vaccines, to target the virus by developed antibodies, others focus on finding antiviral compounds with activities that inhibit selected virus replication steps. Currently, there is an increasing number of antiviral drugs on the market; however, some have unpleasant side effects, are toxic to cells, or the viruses quickly develop resistance to them. As the current situation shows, the combination of multiple antiviral strategies or the combination of the use of various compounds within one strategy is very important. The most desirable are combinations of drugs that inhibit different steps in the virus life cycle. This is an important issue especially for RNA viruses, which replicate their genomes using error-prone RNA polymerases and rapidly develop mutants resistant to applied antiviral compounds. Here, we focus on compounds targeting viral structural capsid proteins, thereby inhibiting virus assembly or disassembly, virus binding to cellular receptors, or acting by inhibiting other virus replication mechanisms. This review is an update of existing papers on a similar topic, by focusing on the most recent advances in the rapidly evolving research of compounds targeting capsid proteins of RNA viruses.

Comparative analysis of the molecular mechanism of resistance to vapendavir across a panel of picornavirus species

Vapendavir is a rhino/enterovirus inhibitor that targets a hydrophobic pocket in the viral capsid preventing the virus from entering the cell. We set out to study and compare the molecular mechanisms of resistance to vapendavir among clinically relevant Picornavirus species. To this end in vitro resistance selection of drug-resistant isolates was applied in rhinovirus 2 and 14, enterovirus-D68 and Poliovirus 1 Sabin. Mutations in the drug-binding pocket in VP1 (C199R/Y in hRV14; I194F in PV1; M252L and A156T in EV-D68), typical for this class of compounds, were identified.

Interestingly, we also observed mutations located outside the pocket (K167E in EV-D68 and G149C in hRV2) that contribute to the resistant phenotype. Remarkably, the G149C substitution rendered the replication of human rhinovirus 2 dependent on the presence of vapendavir. Our data suggest that the binding of vapendavir to the capsid of the G149C isolate may be required to stabilize the viral particle and to allow efficient dissemination of the virus. We observed the dependency of the G149C isolate on other compounds of this class, suggesting that this phenotype is common for capsid binders. In addition the VP1 region containing the G149C substitution has not been associated with antiviral resistance before. Our results demonstrate that the phenotype and genotype of clinically relevant vapendavir-resistant picornavirus species is more complex than generally believed.

Rhinovirus Inhibitors: Including a New Target, the Viral RNA

Rhinoviruses (RVs) are the main cause of recurrent infections with rather mild symptoms characteristic of the common cold. Nevertheless, RVs give rise to enormous numbers of absences from work and school and may become life-threatening in particular settings. Vaccination is jeopardised by the large number of serotypes eliciting only poorly cross-neutralising antibodies. Conversely, antivirals developed over the years failed FDA approval because of a low efficacy and/or side effects. RV species A, B, and C are now included in the fifteen species of the genus Enteroviruses based upon the high similarity of their genome sequences. As a result of their comparably low pathogenicity, RVs have become a handy model for other, more dangerous members of this genus, e.g., poliovirus and enterovirus 71. We provide a short overview of viral proteins that are considered potential drug targets and their corresponding drug candidates. We briefly mention more recently identified cellular enzymes whose inhibition impacts on RVs and comment novel approaches to interfere with infection via aggregation, virus trapping, or preventing viral access to the cell receptor. Finally, we devote a large part of this article to adding the viral RNA genome to the list of potential drug targets by dwelling on its structure, folding, and the still debated way of its exit from the capsid. Finally, we discuss the recent finding that G-quadruplex stabilising compounds impact on RNA egress possibly via obfuscating the unravelling of stable secondary structural elements.

Novel capsid binder and PI4KIIIbeta inhibitors for EV-A71 replication inhibition

The Hand, Foot and Mouth Disease (HFMD) is a highly contagious viral illness generally manifests as a mild disease in young children and immunocompromised adults. It has however emerged as a significant public health threat in recent years as outbreaks have been occurring regularly, especially in the Asia–Pacific. The disease can result from infections by a wide variety of human enteroviruses, particularly, Enterovirus A71 (EV-A71) has garnered more attention due to its association with severe disease in infected patients. Despite the potential to result severe neurological complications or even fatality, there is currently no effective antiviral for treatment of EV-A71 infections and the only vaccines available are restricted to distribution in China. In this study, we report the in vitro and in vivo evaluation of two candidate antiviral compounds active against EV-A71, a viral capsid inhibitor (G197) and a novel host-targeting phosphatidylinositol 4-kinase III beta inhibitor (N373) which, especially when used in combination, can significantly improve the survival and pathology of infected mice.

Antivirals blocking entry of enteroviruses and therapeutic potential

Viruses from the genus Enterovirus (EV) of the Picornaviridae family are known to cause diseases such as hand foot and mouth disease (HFMD), respiratory diseases, encephalitis and myocarditis. The capsid of EV is an attractive target for the development of direct-acting small molecules that can interfere with viral entry. Some of the capsid binders have been evaluated in clinical trials but the majority have failed due to insufficient efficacy or unacceptable off-target effects. Furthermore, most of the capsid binders exhibited a low barrier to resistance. Alternatively, host-targeting inhibitors such as peptides derived from the capsid of EV that can recognize cellular receptors have been identified. However, the majority of these peptides displayed low anti-EV potency (µM range) as compared to the potency of small molecule compounds (nM range). Nonetheless, the development of anti-EV peptides is warranted as they may complement the small-molecules in a drug combination strategy to treat EVs. Lastly, structure-based approach to design antiviral peptides should be utilized to unearth potent anti-EV peptides.

Sodium Copper Chlorophyllin Is Highly Effective against Enterovirus (EV) A71 Infection by Blocking Its Entry into the Host Cell

Human enteroviruses (HEVs) pose an ongoing threat to global public health. Particularly, enterovirus-A71 (EV-A71), the main pathogen causing hand-foot-and-mouth disease (HFMD), has caused ongoing outbreaks globally in recent years associated with severe neurological manifestations and several deaths. Currently, no effective antivirals are available for the prevention or treatment of EV-A71 infection. In this study, we found that sodium copper chlorophyllin (CHL), a health food additive and an over-the-counter anticancer medicine or treatment to reduce the odor of urine or feces, exhibited potent inhibitory activity against infection by divergent EV-A71 and coxsackievirus-A16 (CV-A16) isolates at a low micromolar concentration with excellent safety. The antiviral activity of each was confirmed by colorimetric viral infection and qRT-PCR assays. A series of mechanistic studies showed that CHL did not target the host cell but blocked the entry of EV-A71 and CV-A16 into the host cell at the postattachment stage. In the mouse model, CHL could significantly reduce the viral titer in the lungs and muscles. Since CHL has been used in clinics for many years with excellent safety, it has the potential to be further developed into a prophylactic or therapeutic to prevent or treat HFMD caused by EV-A71 or CV-A16 infection.

The life cycle of non-polio enteroviruses and how to target it

The genus Enterovirus (EV) of the family Picornaviridae includes poliovirus, coxsackieviruses, echoviruses, numbered enteroviruses and rhinoviruses. These diverse viruses cause a variety of diseases, including non-specific febrile illness, hand-foot-and-mouth disease, neonatal sepsis-like disease, encephalitis, paralysis and respiratory diseases. In recent years, several non-polio enteroviruses (NPEVs) have emerged as serious public health concerns. These include EV-A71, which has caused epidemics of hand-foot-and-mouth disease in Southeast Asia, and EV-D68, which recently caused a large outbreak of severe lower respiratory tract disease in North America. Infections with these viruses are associated with severe neurological complications. For decades, most research has focused on poliovirus, but in recent years, our knowledge of NPEVs has increased considerably. In this Review, we summarize recent insights from enterovirus research with a special emphasis on NPEVs. We discuss virion structures, host-receptor interactions, viral uncoating and the recent discovery of a universal enterovirus host factor that is involved in viral genome release. Moreover, we briefly explain the mechanisms of viral genome replication, virion assembly and virion release, and describe potential targets for antiviral therapy. We reflect on how these recent discoveries may help the development of antiviral therapies and vaccines.

Structure-Based Drug Design of Potent Pyrazole Derivatives against Rhinovirus Replication

Rhinoviruses (RVs) have been linked to exacerbations of many pulmonary diseases, thus increasing morbidity and/or mortality in subjects at risk. Unfortunately, the wide variety of RV genotypes constitutes a major hindrance for the development of Rhinovirus replication inhibitors. In the current investigation, we have developed a novel series of pyrazole derivatives that potently inhibit the Rhinovirus replication. Compounds 10e and 10h behave as early stage inhibitors of Rhinovirus infection with a broad-spectrum activity against RV-A and RV-B species (EC₅₀ < 0.1 μM). We also evaluate the dynamics of the emerging resistance of these promising compounds and their in vitro genotoxicity. Molecular docking experiments shed light on the pharmacophoric elements interacting with residues of the drug-binding pocket.

Development and characterization of DNAzyme candidates demonstrating significant efficiency against human rhinoviruses

BACKGROUND

Infections with human rhinoviruses (RVs) are responsible for millions of common cold episodes and the majority of asthma exacerbations, especially in childhood. No drugs specifically targeting RVs are available.

OBJECTIVE

We sought to identify specific anti-RV molecules based on DNAzyme technology as candidates to a clinical study.

METHODS

A total of 226 candidate DNAzymes were designed against 2 regions of RV RNA genome identified to be sufficiently highly conserved between virus strains (ie, the 5'-untranslated region and cis-acting replication element) by using 3 test strains: RVA1, RVA16, and RVA29. All DNAzymes were screened for their cleavage efficiency against in vitro-expressed viral RNA. Those showing any catalytic activity were subjected to bioinformatic analysis of their reverse complementarity to 322 published RV genomic sequences. Further molecular optimization was conducted for the most promising candidates. Cytotoxic and off-target effects were excluded in HEK293 cell-based systems. Antiviral efficiency was analyzed in infected human bronchial BEAS-2B cells and ex vivo-cultured human sinonasal tissue.

RESULTS

Screening phase-generated DNAzymes characterized by either good catalytic activity or by high RV strain coverage but no single molecule represented a satisfactory combination of those 2 features. Modifications in length of the binding domains of 2 lead candidates, Dua-01(-L12R9) and Dua-02(-L10R11), improved their cleavage efficiency to an excellent level, with no loss in eminent strain coverage (about 98%). Both DNAzymes showed highly favorable cytotoxic/off-target profiles. Subsequent testing of Dua-01-L12R9 in BEAS-2B cells and sinonasal tissue demonstrated its significant antiviral efficiency.

CONCLUSIONS

Effective and specific management of RV infections with Dua-01-L12R9 might be useful in preventing asthma exacerbations, which should be verified by clinical trials.

3-Aryl-1,2,4-oxadiazole Derivatives Active Against Human Rhinovirus

The human rhinovirus (hRV) is the causative agent of the common cold that often aggravates respiratory complications in patients with asthma or chronic obstructive pulmonary disease. The high rate of mutations and variety of serotypes are limiting the development of anti-hRV drugs, which emphasizes the need for the discovery of novel lead compounds. Previously, we identified antiviral compound 1 that we used here as the starting material for developing a novel compound series with high efficacy against hRV-A and -B. Improved metabolic stability was achieved by substituting an ester moiety with a 1,2,4-oxadiazole group. Specifically, compound 3k exhibited a high efficacy against hRV-B14, hRV-A21, and hRV-A71, with EC₅₀ values of 66.0, 22.0, and 3.7 nM, respectively, and a relevant hepatic stability (59.6 and 40.7% compound remaining after 30 min in rat and human liver microsomes, respectively). An in vivo study demonstrated that 3k possessed a desirable pharmacokinetic profile with low systemic clearance (0.158 L·h^-1·kg^-1) and modest oral bioavailability (27.8%). Hence, 3k appears to be an interesting candidate for the development of antiviral lead compounds.

Antiviral therapeutic approaches for human rhinovirus infections

Human rhinoviruses are the primary etiological agent of the common cold. This infection can be mild and self-limiting in immunocompetent hosts, but can be associated with bronchiolitis in infants, pneumonia in the immunosuppressed and exacerbations of pre-existing pulmonary conditions such as asthma or chronic obstructive pulmonary disease. Many of these conditions can place significant economic costs upon healthcare infrastructure. There is currently no licensed vaccine for rhinovirus, as the large variety of rhinovirus serotypes has posed significant challenges for research. In this review, we discuss current knowledge around antiviral drugs and small molecule inhibitors of rhinovirus infection, as well as antiviral host defense peptides as exciting prospects to approach the development of novel therapeutics which target human rhinovirus.

Heterocyclic pharmacochemistry of new rhinovirus antiviral agents: A combined computational and experimental study

Rhinovirus (RV), member of the Enterovirus genus, is known to be involved in more than half of the common colds. Through advances in molecular biology, rhinoviruses have also been associated with exacerbations of chronic pulmonary diseases (e.g. asthma, chronic obstructive pulmonary disease (COPD) and cystic fibrosis). In the current investigation, we develop a novel series of 4,5-dimethoxybenzyl derivatives that potently inhibits rhinovirus replication. Compound (S)-7f blocks RV-B14 replication with an EC₅₀ value of 0.25 μM and shows a low toxicity in HeLa cells (CC₅₀ > 271 μM). Enantioseparation followed by an absolute configuration determination by a Mosher's method revealed the interest of enantiopure compounds. Molecular docking studies permitted the identification of key biological interactions within the drug-binding pocket and an in silico drug-like study revealed a good potential for the development of these derivatives.

A Novel Series of Highly Potent Small Molecule Inhibitors of Rhinovirus Replication

Human rhinoviruses (hRVs) are the main causative pathogen for common colds and are associated with the exacerbation of asthma. The wide variety in hRV serotypes has complicated the development of rhinovirus replication inhibitors. In the current investigation, we developed a novel series of benzothiophene derivatives and their analogues (6-8) that potently inhibit the replication of both hRV-A and hRV-B strains. Compound 6g inhibited the replication of hRV-B14, A21, and A71, with respective EC₅₀ values of 0.083, 0.078, and 0.015 μM. The results of a time-of-addition study against hRV-B14 and hRV-A16 and resistant mutation analysis on hRV-B14 implied that 6g acts at the early stage of the viral replication process, interacting with viral capsid protein. A molecular docking study suggested that 6g has a capsid-binding mode similar to that of pleconaril. Finally, derivatives of 6 also displayed significant inhibition against poliovirus 3 (PV3) replication, implying their potential inhibitory activities against other enterovirus species.

VP1 crystal structure-guided exploration and optimization of 4,5-dimethoxybenzene-based inhibitors of rhinovirus 14 infection

Human rhinoviruses (HRV) are the predominant cause of common colds and flu-like illnesses, but are also responsible for virus-induced exacerbations of asthma and chronic obstructive pulmonary disease. However, to date, no drug has been approved yet for clinical use. In this study, we present the results of the structure-based lead optimization of a class of new small-molecule inhibitors that we previously reported to bind into the pocket beneath the canyon of the VP1 protein. A small series of analogues that we designed based on the available structure and interaction data were synthesized and evaluated for their potency to inhibit the replication of HRV serotype 14. 2-(4,5-Dimethoxy-2-nitrophenyl)-1-(4-(pyridin-4-yl)phenyl)ethanol (3v) was found to be a potent inhibitor exhibiting micromolar activity (EC50 = 3.4 ± 1.0 μM) with a toxicity for HeLa cells that was significantly lower than that of our previous hit (LPCRW_0005, CC50 = 104.0 ± 22.2 μM; 3v, CC50 > 263 μM).

Virus-inhibiting activity of dihydroquercetin, a flavonoid from Larix sibirica, against coxsackievirus B4 in a model of viral pancreatitis

Members of the family Picornaviridae, in particular, enteroviruses, represent a serious threat to human health. They are responsible for numerous pathologies ranging from mild disease to fatal outcome. Due to the limited number of safe and effective antivirals against enteroviruses, there is a need for search and development of novel drugs with various mechanisms of activity against enteroviruses-induced pathologies. We studied the effect of dihydroquercetin (DHQ), a flavonoid from larch wood, on the course of pancreatitis of white mice caused by coxsackievirus B4 (CVB4). DHQ was applied intraperitoneally at doses of 75 or 150 mg/kg/day once a day for 5 days postinfection (p.i.) starting on day 1 p.i., and its effect was compared to that of the reference compound ribavirin. The application of DHQ resulted in a dose-dependent decrease in the virus titer in pancreatic tissue, reaching, at the highest dose, 2.4 logs on day 5 p.i. Also, the application of DHQ led to restoration of antioxidant activity of pancreatic tissue that was impaired in the course of pancreatitis. Morphologically, pancreatic tissue of DHQ-treated animals demonstrated less infiltration with inflammatory cells and no signs of tissue destruction compared to placebo-treated mice. Both ribavirin- and DHQ-treated animals developed fewer foci of pancreatic inflammation per mouse, and these foci contained fewer infiltrating cells than those in placebo-treated mice. The effect of DHQ was comparable to or exceeded that of ribavirin. Taken together, our results suggest high antiviral activity of DHQ and its promising potential in complex treatment of viral pancreatitis.

Toward antiviral therapy/prophylaxis for rhinovirus-induced exacerbations of chronic obstructive pulmonary disease: challenges, opportunities, and strategies

Chronic obstructive pulmonary disease (COPD) is a life-threatening lung illness characterized by persistent and progressive airflow limitation. Exacerbations of COPD contribute to the severity of this pathology and accelerate disease progression. To date, pharmacological treatment of both stable COPD patients and patients experiencing exacerbations is mainly symptomatic with bronchodilators and steroids as the mainstay of therapy. Bacteria trigger such exacerbations in a number of cases; hence, antibiotics might be included in the treatment as well. Several respiratory viruses are frequently detected in sputum from patients during COPD exacerbations. These include influenza viruses, respiratory syncytial virus, and, most often, rhinoviruses. In this review, we discuss the potential use of an anti-rhinovirus drug for the treatment and prophylaxis of rhinovirus-induced COPD exacerbations and the path forward toward the development and use of such a drug. Copyright © 2015 John Wiley & Sons, Ltd.

Potent antiviral agents fail to elicit genetically-stable resistance mutations in either enterovirus 71 or Coxsackievirus A16

Enterovirus 71 (EV71) and Coxsackievirus A16 (CVA16) are the two major causative agents of hand, foot and mouth disease (HFMD), for which there are currently no licenced treatments. Here, the acquisition of resistance towards two novel capsid-binding compounds, NLD and ALD, was studied and compared to the analogous compound GPP3. During serial passage, EV71 rapidly became resistant to each compound and mutations at residues I113 and V123 in VP1 were identified. A mutation at residue 113 was also identified in CVA16 after passage with GPP3. The mutations were associated with reduced thermostability and were rapidly lost in the absence of inhibitors. In silico modelling suggested that the mutations prevented the compounds from binding the VP1 pocket in the capsid. Although both viruses developed resistance to these potent pocket-binding compounds, the acquired mutations were associated with large fitness costs and reverted to WT phenotype and sequence rapidly in the absence of inhibitors. The most effective inhibitor, NLD, had a very large selectivity index, showing interesting pharmacological properties as a novel anti-EV71 agent.

Molecular mechanism of a specific capsid binder resistance caused by mutations outside the binding pocket

Enteroviruses cause various acute and chronic diseases. The most promising therapeutics for these infections are capsid-binding molecules. These can act against a broad spectrum of enteroviruses, but emerging resistant virus variants threaten their efficacy. All known enterovirus variants with high-level resistance toward capsid-binding molecules have mutations of residues directly involved in the formation of the hydrophobic binding site. This is a first report of substitutions outside the binding pocket causing this type of drug resistance: I1207K and I1207R of the viral capsid protein 1 of coxsackievirus B3. Both substitutions completely abolish the antiviral activity of pleconaril (a capsid-binding molecule) but do not affect viral replication rates in vitro. Molecular dynamics simulations indicate that the resistance mechanism is mediated by a conformational rearrangement of R1095, which is a neighboring residue of 1207 located at the heel of the binding pocket. These insights provide a basis for the design of resistance-breaking inhibitors.

Resveratrol inhibits rhinovirus replication and expression of inflammatory mediators in nasal epithelia

Human rhinoviruses (HRV), the cause of common colds, are the most frequent precipitants of acute exacerbation of asthma and chronic obstructive pulmonary disease, as well as causes of other serious respiratory diseases. No vaccine or antiviral agents are available for the prevention or treatment of HRV infection. Resveratrol exerts antiviral effect against different DNA and RNA viruses. The antiviral effect of a new resveratrol formulation containing carboxymethylated glucan was analyzed in H1HeLa cell monolayers and ex vivo nasal epithelia infected with HRV-16. Virus yield was evaluated by plaque assay and expression of viral capsid proteins by Western blot. IL-10, IFN-β, IL-6, IL-8 and RANTES levels were evaluated by ELISA assay. ICAM-1 was assessed by Western blot and immunofluorescence. Resveratrol exerted a high, dose-dependent, antiviral activity against HRV-16 replication and reduced virus-induced secretion of IL-6, IL-8 and RANTES to levels similar to that of uninfected nasal epithelia. Basal levels of IL-6 and RANTES were also significantly reduced in uninfected epithelia confirming an anti-inflammatory effect of the compound. HRV-induced expression of ICAM-1 was reversed by resveratrol. Resveratrol may be useful for a therapeutic approach to reduce HRV replication and virus-induced cytokine/chemokine production.

Pyrazolopyrimidines: Potent Inhibitors Targeting the Capsid of Rhino- and Enteroviruses

There are currently no drugs available for the treatment of enterovirus (EV)-induced acute and chronic diseases such as the common cold, meningitis, encephalitis, pneumonia, and myocarditis with or without consecutive dilated cardiomyopathy. Here, we report the discovery and characterization of pyrazolopyrimidines, a well-tolerated and potent class of novel EV inhibitors. The compounds inhibit the replication of a broad spectrum of EV in vitro with IC₅₀ values between 0.04 and 0.64 μm for viruses resistant to pleconaril, a known capsid-binding inhibitor, without affecting cytochrome P450 enzyme activity. Using virological and genetics methods, the viral capsid was identified as the target of the most promising, orally bioavailable compound 3-(4-trifluoromethylphenyl)amino-6-phenylpyrazolo[3,4-d]pyrimidine-4-amine (OBR-5-340). Its prophylactic as well as therapeutic application was proved for coxsackievirus B3-induced chronic myocarditis in mice. The favorable pharmacokinetic, toxicological, and pharmacodynamics profile in mice renders OBR-5-340 a highly promising drug candidate, and the regulatory nonclinical program is ongoing.

In vitro characterisation of a pleconaril/pirodavir-like compound with potent activity against rhinoviruses

BACKGROUND

Rhinovirus infections do not only cause common colds, but may also trigger severe exacerbations of asthma and chronic obstructive pulmonary disease (COPD). Even though rhinoviruses have been the focus of extensive drug development efforts in the past, an anti-rhinoviral drug still has to make it to the market. In the past, the viral capsid protein VP1 has been shown to be an important target for the development of antiviral molecules. Furthermore, many different chemical scaffolds appear to possess the properties that are required to inhibit virus replication by this mechanism of action. I-6602, an analogue of the rhinovirus inhibitor pirodavir, was previously identified as a potent inhibitor of rhinovirus infection. Here, we describe the antiviral activity of its analogue ca603, a molecule with a modified linker structure, and corroborate its mechanism of action as a capsid binder.

FINDINGS

The molecule ca603 shows antiviral activity against a panel of rhino-and enteroviruses. Cross-resistance is observed against viruses with mutations that render them resistant to the inhibitory effect of the capsid binder pleconaril and thermostability assays demonstrate that the compound binds and stabilizes the viral capsid. Binding of the molecule to the VP1 protein is corroborated by in silico modeling.

CONCLUSIONS

It is confirmed that ca603 inhibits rhinovirus replication by interaction with the VP1 protein and, by this, allows to further expand the chemical diversity of capsid-binding molecules.

More-powerful virus inhibitors from structure-based analysis of HEV71 capsid-binding molecules

Enterovirus 71 (HEV71) epidemics in children and infants result mainly in mild symptoms; however, especially in the Asia-Pacific region, infection can be fatal. At present, no therapies are available. We have used structural analysis of the complete virus to guide the design of HEV71 inhibitors. Analysis of complexes with four 3-(4-pyridyl)-2-imidazolidinone derivatives with varying anti-HEV71 activities pinpointed key structure-activity correlates. We then identified additional potentially beneficial substitutions, developed methods to reliably triage compounds by quantum mechanics-enhanced ligand docking and synthesized two candidates. Structural analysis and in vitro assays confirmed the predicted binding modes and their ability to block viral infection. One ligand (with IC50 of 25 pM) is an order of magnitude more potent than the best previously reported inhibitor and is also more soluble. Our approach may be useful in the design of effective drugs for enterovirus infections.

The Influence of Bioisosteres in Drug Design: Tactical Applications to Address Developability Problems

The application of bioisosteres in drug discovery is a well-established design concept that has demonstrated utility as an approach to solving a range of problems that affect candidate optimization, progression, and durability. In this chapter, the application of isosteric substitution is explored in a fashion that focuses on the development of practical solutions to problems that are encountered in typical optimization campaigns. The role of bioisosteres to affect intrinsic potency and selectivity, influence conformation, solve problems associated with drug developability, including P-glycoprotein recognition, modulating basicity, solubility, and lipophilicity, and to address issues associated with metabolism and toxicity is used as the underlying theme to capture a spectrum of creative applications of structural emulation in the design of drug candidates.

Identification of a series of compounds with potent antiviral activity for the treatment of enterovirus infections

Rhinovirus (genus enterovirus) infections are responsible for many of the severe exacerbations of asthma and chronic obstructive pulmonary disease. Other members of the genus can cause life-threatening acute neurological infections. There is currently no antiviral drug approved for the treatment of such infections. We have identified a series of potent, broad-spectrum antiviral compounds that inhibit the replication of the human rhinovirus, Coxsackie virus, poliovirus, and enterovirus-71. The mechanism of action of the compounds has been established as inhibition of a lipid kinase, PI4KIIIβ. Inhibition of hepatitis C replication in a replicon assay correlated with enterovirus inhibition.

From sneeze to wheeze: what we know about rhinovirus Cs

While the discovery of HRV-Cs is recent, there are no indications that they are new viruses, or that they are emerging in real-time. Genetically, HRV-Cs are most closely related to the members of HRV-A and HRV-B but even a small genetic difference can impart encompass significant changes to their clinical impact, complicated by a diverse human background of prior virus exposure and underlying host immune and disease variability. It is well known that HRVs are a major trigger of asthma exacerbations and HRV-Cs are now under investigation for their potential involvement in asthma inception. The newly described HRV-Cs account for a large proportion of HRV-related illness, including common colds and wheezing exacerbations. HRV-Cs are genetically diverse and appear to circulate with seasonal variation, exchanging dominance with HRV-A. Whether HRV-Cs are consistently more pathogenic or "asthmagenic" is unproven. Antigenic diversity complicates passive and active prophylactic interventions (i.e. antibodies or vaccines), so further identification and characterisation of individual types (and their neutralising antigens) is likely to inform future preventive strategies. In the meantime, new antivirals should benefit groups at risk of the most severe disease.

Design, synthesis and biological evaluation of novel aminothiazoles as antiviral compounds acting against human rhinovirus

We describe here the design, synthesis and biological evaluation of antiviral compounds acting against human rhinovirus (HRV). A series of aminothiazoles demonstrated pan-activity against the HRV genotypes screened and productive structure-activity relationships. A comprehensive investigational library was designed and performed allowing the identification of potent compounds with lower molecular weight and improved ADME profile. 31d-1, 31d-2, 31f showed good exposures in CD-1 mice. The mechanism of action was discovered to be a host target: the lipid kinase phosphatidylinositol 4-kinase III beta (PI4KIIIß). The identification of the pan-HRV active compound 31f combined with a structurally distinct literature compound T-00127-HEV1 allowed the assessment of target related tolerability of inhibiting this kinase for a short period of time in order to prevent HRV replication.

Phosphatidylinositol 4-kinase III beta is essential for replication of human rhinovirus and its inhibition causes a lethal phenotype in vivo

Human rhinovirus (HRV) is the predominant cause of the common cold, but more importantly, infection may have serious repercussions in asthmatics and chronic obstructive pulmonary disorder (COPD) patients. A cell-based antiviral screen against HRV was performed with a subset of our proprietary compound collection, and an aminothiazole series with pan-HRV species and enteroviral activity was identified. The series was found to act at the level of replication in the HRV infectious cycle. In vitro selection and sequencing of aminothiazole series-resistant HRV variants revealed a single-nucleotide mutation leading to the amino acid change I42V in the essential HRV 3A protein. This same mutation has been previously implicated in resistance to enviroxime, a former clinical-stage antipicornavirus agent. Enviroxime-like compounds have recently been shown to target the lipid kinase phosphatidylinositol 4-kinase III beta (PI4KIIIβ). A good correlation between PI4KIIIβ activity and HRV antiviral potency was found when analyzing the data over 80 compounds of the aminothiazole series, covering a 750-fold potency range. The mechanism of action through PI4KIIIβ inhibition was further demonstrated by small interfering RNA (siRNA) knockdown of PI4KB, which reduced HRV replication and also increased the potency of the PI4KIIIβ inhibitors. Inhibitors from two different structural classes with promising pharmacokinetic profiles and with very good selectivity for PI4KIIIβ were used to dissociate compound-related toxicity from target-related toxicity. Mortality was seen in all dosing groups of mice treated with either compound, therefore suggesting that short-term inhibition of PI4KIIIβ is deleterious.