Synthesis and biological evaluation of a library of hybrid derivatives as inhibitors of influenza virus PA-PB1 interaction

Novel benzamide derivatives with indole moiety as dual-target antiviral agents: Rational design, efficient synthesis, and potent anti-influenza activity through concurrent binding to PAC terminal domain and viral nucleoprotein

In this study, a series of benzamide derivatives with an indole moiety as dual-target inhibitors were designed, synthesized and evaluated against the RNA-dependent RNA polymerase (RdRp) complex of influenza viruses. The target compounds can simultaneously disrupt two key molecular interactions: the PAC terminal domain and the nucleoprotein (NP) oligomerization. Through efficient synthesis and structure-activity relationship (SAR) analysis, compounds 8e and 8f as highly potent inhibitors were identified. Both compounds (8e and 8f) exhibited submicromolar EC50 values (1.64 ± 0.05 μM and 1.41 ± 0.27 μM) against influenza A virus (H1N1, A/WSN/33) and broad-spectrum activity against other influenza strains, including influenza B virus and multiple subtypes of influenza A. Notably, their cytotoxicity was significantly reduced compared to previous benzofurazan derivatives, with CC50 values exceeding 100 μM. Surface plasmon resonance (SPR) experiments confirmed that 8e and 8f bound strongly to the PA C-terminal domain (KD = 8.90 μM and 4.82 μM) and NP (KD = 52.5 μM and 3.13 μM). Computational modeling approaches, including molecular docking, molecular dynamics (MD) simulations, and dynamical cross-correlation matrix (DCCM) analysis, principal component analysis (PCA) analysis and density functional theory (DFT) calculations, were employed to elucidate the putative binding modes and delineate critical interaction sites between the ligands and target proteins. These insights not only modulated subsequent structure-based lead optimization but also strengthened our understanding of the molecular determinants governing antiviral activity. This research provides a promising scaffold for developing dual-target antiviral agents with enhanced potency and safety, offering new strategies to combat influenza viruses.

Novel Pyrrolidine-bearing quinoxaline inhibitors of DNA Gyrase, RNA polymerase and spike glycoprotein

Anti-infective agents are a class of drugs used to prevent, treat, or control infections caused by microorganisms such as bacteria, viruses, fungi, and parasites. They play a crucial role in modern medicine, helping to reduce the severity of infections and, in many cases, save lives. This study aims at the design and synthesis of hybrid compounds containing quinoxaline, pyrrolidine, and an azo bridge to combat antimicrobial resistance, and evaluating their antimicrobial, antifungal, and antiviral activities against various pathogenic strains. Eight most potent bactericidal derivatives 2, 4, 5, 7, 9, 11, 12, and 13 were further assessed for their antibiofilm activity. Additionally, these compounds were tested for their inhibitory effects on DNA gyrase using a DNA supercoiling assay with IC50 ranging from 26.57 to 84.84 μM when compared to ciprofloxacin as standard drug. The antiviral activities were performed against HSV-1, H1N1 and SARS-CoV-2 viruses, which showed that compound 9 has the highest antiviral activity with IC50 = 0.32 µM, IC50 = 1.76 µM and 1.06 µM, respectively, as well as the best safety profile with CC50 = 30000 µM. Compound 9 displayed the highest SI value against HSV-1, H1N1 and SARS-CoV-2 with values of 93685, 17,034 and 28368, respectively. Compound 9 inhibited RdRp and spike glycoprotein (IC50 = 2.437 ± 0.102 and 1425.1 ± 55.3 nM; respectively). The physicochemical and pharmacokinetic properties of the most active compounds were screened to identify those with optimal drug-like characteristics. Molecular docking studies were conducted on the most effective compounds to elucidate their binding interactions and mechanisms of action.

Antiviral strategies against influenza virus: an update on approved and innovative therapeutic approaches

Influenza viruses still represent a great concern for Public Health by causing yearly seasonal epidemics and occasionally worldwide pandemics. Moreover, spillover events at the animal-human interface are becoming more frequent nowadays, also involving animal species not previously found as reservoirs. To restrict the effects of influenza virus epidemics, especially in at-risk population, and to prepare a drug arsenal for possible future pandemics, researchers worldwide have been working on the development of antiviral strategies since the 80's of the last century. One of the main obstacles is the considerable genomic variability of influenza viruses, which constantly poses the issues of drug-resistance emergence and immune evasion. This review summarizes the approved therapeutics for clinical management of influenza, promising new anti-flu compounds and monoclonal antibodies currently undergoing clinical evaluation, and molecules with efficacy against influenza virus in preclinical studies. Moreover, we discuss some innovative anti-influenza therapeutic approaches such as combination therapies and targeted protein degradation. Given the limited number of drugs approved for influenza treatment, there is a still strong need for novel potent anti-influenza drugs endowed with a high barrier to drug resistance and broad-spectrum activity against influenza viruses of animal origin that may be responsible of future large outbreaks and pandemics.

Elaborate Structural Modifications Yielding Novel Boron-Containing N-Substituted Oseltamivir Derivatives as Potent Neuraminidase Inhibitors with Significantly Improved Broad-Spectrum Antiresistance Profiles

Inspired by our previous finding that targeting the 150-cavity with a multisite-binding strategy emerged as an effective approach to obtain more potent and selective neuraminidase (NA) inhibitors against influenza virus, we present here the design, synthesis, and optimization of novel boron-containing N-substituted oseltamivir (OSC) derivatives. Exploratory structure-activity relationship (SAR) studies led to the identification of compounds 27c and 33c as the most potent NA inhibitors, surpassing OSC in potency against both wild-type group-1 NAs and oseltamivir-resistant NAs. These compounds demonstrated significant antiviral activity against several wild-type strains and H1N1pdm09 strains (EC50 = 0.03 ± 0.005 and 0.03 ± 0.0008 μM, respectively). Additionally, these compounds did not exhibit significant toxicity (CC50 > 200 μM in CEF cells; CC50 > 250 μM in MDCK cells). These findings highlight 27c and 33c as promising next-generation anti-influenza agents.

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

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

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

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

Switching the three-component Biginelli-like reaction conditions for the regioselective synthesis of new 2-amino[1,2,4]triazolo[1,5-a]pyrimidines

Among the eight different triazolopyrimidine isomers existing in nature, 1,2,4-triazolo[1,5-a]pyrimidine (TZP) is one of the most studied and used isomers in medicinal chemistry. For some years, our group has been involved in developing regioselective one-pot procedures for the synthesis of 2-amino-7-aryl-5-methyl- and 2-amino-5-aryl-7-methyl-TZPs of interest in the preparation of antiviral agents. In this work, taking advantage of a Biginelli-like multicomponent reaction (MCR), we report the identification of finely tunable conditions to regioselectively synthesize C-6 ester-substituted amino-TZP analogues, both in dihydro and oxidized forms. Indeed, the use of mild acidic conditions is strongly directed toward the regioselective synthesis of 5-aryl-7-methyl C-6-substituted TZP analogues, while the use of neutral ionic liquids shifted the regioselectivity towards 7-aryl-5-methyl derivatives. In addition, the novel synthesized scaffolds were functionalized at the C-2 position and evaluated for their antiviral activity against RNA viruses (influenza virus, flaviviruses, and SARS-CoV-2). Compounds 25 and 26 emerged as promising anti-flavivirus agents, showing activity in the low micromolar range.

A novel N-heterocycles substituted oseltamivir derivatives as potent inhibitors of influenza virus neuraminidase: discovery, synthesis and biological evaluation

Our previous studies have shown that the introduction of structurally diverse benzyl side chains at the C5-NH2 position of oseltamivir to occupy 150-cavity contributes to the binding affinity with neuraminidase and anti-influenza activity. To obtain broad-spectrum neuraminidase inhibitors, we designed and synthesised a series of novel oseltamivir derivatives bearing different N-heterocycles substituents that have been proved to induce opening of the 150-loop of group-2 neuraminidases. Among them, compound 6k bearing 4-((r)-2-methylpyrrolidin-1-yl) benzyl group exhibited antiviral activities similar to or weaker than those of oseltamivir carboxylate against H1N1, H3N2, H5N1, H5N6 and H5N1-H274Y mutant neuraminidases. More encouragingly, 6k displayed nearly 3-fold activity enhancement against H3N2 virus over oseltamivir carboxylate and 2-fold activity enhancement over zanamivir. Molecular docking studies provided insights into the explanation of its broad-spectrum potency against wild-type neuraminidases. Overall, as a promising lead compound, 6k deserves further optimisation by fully considering the ligand induced flexibility of the 150-loop.

Discovery of N-substituted oseltamivir derivatives as novel neuraminidase inhibitors with improved drug resistance profiles and favorable drug-like properties

To yield potent neuraminidase inhibitors with improved drug resistance and favorable drug-like properties, two series of novel oseltamivir derivatives targeting the 150-cavity of neuraminidase were designed, synthesized, and biologically evaluated. Among the synthesized compounds, the most potent compound 43b bearing 3-floro-4-cyclopentenylphenzyl moiety exhibited weaker or slightly improved inhibitory activity against wild-type neuraminidases (NAs) of H1N1, H5N1, and H5N8 compared to oseltamivir carboxylate (OSC). Encouragingly, 43b displayed 62.70- and 5.03-fold more potent activity than OSC against mutant NAs of H5N1-H274Y and H1N1-H274Y, respectively. In cellular antiviral assays, 43b exerted equivalent or more potent activities against H1N1, H5N1, and H5N8 compared to OSC with no significant cytotoxicity up to 200 μM. Notably, 43b displayed potent antiviral efficacy in the embryonated egg model, in which achieved a protective effect against H5N1 and H5N8 similar to OSC. Molecular docking studies were implemented to reveal the binding mode of 43b in the binding pocket. Moreover, 43b possessed improved physicochemical properties and ADMET properties compared to OSC by in silico prediction. Taken together, 43b appeared to be a promising lead compound for further investigation.

Discovery of Novel Boron-Containing N-Substituted Oseltamivir Derivatives as Anti-Influenza A Virus Agents for Overcoming N1-H274Y Oseltamivir-Resistant

To address drug resistance to influenza virus neuraminidase inhibitors (NAIs), a series of novel boron-containing N-substituted oseltamivir derivatives were designed and synthesized to target the 150-cavity of neuraminidase (NA). In NA inhibitory assays, it was found that most of the new compounds exhibited moderate inhibitory potency against the wild-type NAs. Among them, compound 2c bearing 4-(3-boronic acid benzyloxy)benzyl group displayed weaker or slightly improved activities against group-1 NAs (H1N1, H5N1, H5N8 and H5N1-H274Y) compared to that of oseltamivir carboxylate (OSC). Encouragingly, 2c showed 4.6 times greater activity than OSC toward H5N1-H274Y NA. Moreover, 2c exerted equivalent or more potent antiviral activities than OSC against H1N1, H5N1 and H5N8. Additionally, 2c demonstrated low cytotoxicity in vitro and no acute toxicity at the dose of 1000 mg/kg in mice. Molecular docking of 2c was employed to provide a possible explanation for the improved anti-H274Y NA activity, which may be due to the formation of key additional hydrogen bonds with surrounding amino acid residues, such as Arg152, Gln136 and Val149. Taken together, 2c appeared to be a promising lead compound for further optimization.

Antiviral Peptides as Anti-Influenza Agents

Influenza viruses represent a leading cause of high morbidity and mortality worldwide. Approaches for fighting flu are seasonal vaccines and some antiviral drugs. The development of the seasonal flu vaccine requires a great deal of effort, as careful studies are needed to select the strains to be included in each year's vaccine. Antiviral drugs available against Influenza virus infections have certain limitations due to the increased resistance rate and negative side effects. The highly mutative nature of these viruses leads to the emergence of new antigenic variants, against which the urgent development of new approaches for antiviral therapy is needed. Among these approaches, one of the emerging new fields of "peptide-based therapies" against Influenza viruses is being explored and looks promising. This review describes the recent findings on the antiviral activity, mechanism of action and therapeutic capability of antiviral peptides that bind HA, NA, PB1, and M2 as a means of countering Influenza virus infection.

Design, Synthesis, Molecular Docking Analysis and Biological Evaluations of 4-[(Quinolin-4-yl)amino]benzamide Derivatives as Novel Anti-Influenza Virus Agents

In this study, a series of 4-[(quinolin-4-yl)amino]benzamide derivatives as the novel anti-influenza agents were designed and synthesized. Cytotoxicity assay, cytopathic effect assay and plaque inhibition assay were performed to evaluate the anti-influenza virus A/WSN/33 (H1N1) activity of the target compounds. The target compound G07 demonstrated significant anti-influenza virus A/WSN/33 (H1N1) activity both in cytopathic effect assay (EC₅₀ = 11.38 ± 1.89 µM) and plaque inhibition assay (IC₅₀ = 0.23 ± 0.15 µM). G07 also exhibited significant anti-influenza virus activities against other three different influenza virus strains A/PR/8 (H1N1), A/HK/68 (H3N2) and influenza B virus. According to the result of ribonucleoprotein reconstitution assay, G07 could interact well with ribonucleoprotein with an inhibition rate of 80.65% at 100 µM. Furthermore, G07 exhibited significant activity target PA−PB1 subunit of RNA polymerase according to the PA−PB1 inhibitory activity prediction by the best pharmacophore Hypo1. In addition, G07 was well drug-likeness based on the results of Lipinski’s rule and ADMET prediction. All the results proved that 4-[(quinolin-4-yl)amino]benzamide derivatives could generate potential candidates in discovery of anti-influenza virus agents.

Contemporary medicinal chemistry strategies for the discovery and optimization of influenza inhibitors targeting vRNP constituent proteins

Influenza is an acute respiratory infectious disease caused by the influenza virus, affecting people globally and causing significant social and economic losses. Due to the inevitable limitations of vaccines and approved drugs, there is an urgent need to discover new anti-influenza drugs with different mechanisms. The viral ribonucleoprotein complex (vRNP) plays an essential role in the life cycle of influenza viruses, representing an attractive target for drug design. In recent years, the functional area of constituent proteins in vRNP are widely used as targets for drug discovery, especially the PA endonuclease active site, the RNA-binding site of PB1, the cap-binding site of PB2 and the nuclear export signal of NP protein. Encouragingly, the PA inhibitor baloxavir has been marketed in Japan and the United States, and several drug candidates have also entered clinical trials, such as favipiravir. This article reviews the compositions and functions of the influenza virus vRNP and the research progress on vRNP inhibitors, and discusses the representative drug discovery and optimization strategies pursued.

Design, synthesis, and biological activity of a novel series of 2-ureidonicotinamide derivatives against influenza A virus

BACKGROUND

Viral resistance to existing inhibitors and the time-dependent effectiveness of neuraminidase inhibitors have limited the number of antivirals that can be used for prophylaxis and therapeutic treatment of severe influenza infection. Thus, there is an urgent need to develop new drugs to prevent and treat influenza infection.

OBJECTIVE

The aim of this study was to design and synthesize a novel series of 2-ureidonicotinamide derivatives, and evaluate their anti-IAV activities. Furthermore, we predicted the abilities of these compounds inhibiting PA-PB1 subunit and forecasted the docking poses of these compounds with RNA polymerase protein (PDB ID 3CM8).

METHOD

The novel designed compounds were synthesized using classical methods of organic chemistry and tested in vitro for their abilities inhibiting RNP and against influenza A virus. In addition, the 23 synthesized molecules were subjected to the generated pharmacophore Hypo1 to forecast the activity target PA-PB1 subunit of RNA polymerase. The ADMET pharmacokinetic parameters were calculated by the ADMET modules in Discovery Studio 2016. The docking results helped us to demonstrate the possible interactions between these compounds with 3CM8.

RESULTS

The synthesized 2-ureidonicotinamide derivatives were characterized as potent anti-influenza inhibitors. The target compounds 7b and 7c demonstrated significant antiviral activities, and could be considered as novel lead compounds of antiviral inhibitors. In addition, compound 7b revealed suitable ADME properties expressed, and might be a significant RNA polymerase inhibitor targeting PA-PB1 subunit based on the predictable results and the docking results.

CONCLUSION

This study revealed a novel series of compounds that might be useful in the search for an effective drug against influenza virus.

Inhibition of Influenza Virus Polymerase by Interfering with Its Protein-Protein Interactions

Influenza (flu) virus is a serious threat to global health with the potential to generate devastating pandemics. The availability of broad spectrum antiviral drugs is an unequaled weapon during pandemic events, especially when a vaccine is still not available. One of the most promising targets for the development of new antiflu therapeutics is the viral RNA-dependent RNA polymerase (RdRP). The assembly of the flu RdRP heterotrimeric complex from the individual polymerase acidic protein (PA), polymerase basic protein 1 (PB1), and polymerase basic protein 2 (PB2) subunits is a prerequisite for RdRP functions, such as mRNA synthesis and genome replication. In this Review, we report the known protein-protein interactions (PPIs) occurring by RdRP that could be disrupted by small molecules and analyze their benefits and drawbacks as drug targets. An overview of small molecules able to interfere with flu RdRP functions exploiting the PPI inhibition approach is described. In particular, an update on the most recent inhibitors targeting the well-consolidated RdRP PA-PB1 subunit heterodimerization is mainly reported, together with pioneer inhibitors targeting other virus-virus or virus-host interactions involving RdRP subunits. As demonstrated by the PA-PB1 interaction inhibitors discussed herein, the inhibition of flu RdRP functions by PPI disrupters clearly represents a valid means to identify compounds endowed with a broad spectrum of action and a reduced propensity to develop drug resistance, which are the main issues of antiviral drugs.

Insights into RNA-dependent RNA Polymerase Inhibitors as Antiinfluenza Virus Agents

BACKGROUND

Influenza is a seasonal disease that affects millions of people every year and has a significant economic impact. Vaccines are the best strategy to fight this viral pathology, but they are not always available or administrable, prompting the search for antiviral drugs. RNA-dependent RNA polymerase (RdRp) recently emerged as a promising target because of its key role in viral replication and its high conservation among viral strains.

DISCUSSION

This review presents an overview of the most interesting RdRp inhibitors that have been discussed in the literature since 2000. Compounds already approved or in clinical trials and a selection of inhibitors endowed with different scaffolds are described, along with the main features responsible for their activity.

RESULTS

RdRp inhibitors are emerging as a new strategy to fight viral infections and the importance of this class of drugs has been confirmed by the FDA approval of baloxavir marboxil in 2018. Despite the complexity of the RdRp machine makes the identification of new compounds a challenging research topic, it is likely that in the coming years, this field will attract the interest of a number of academic and industrial scientists because of the potential strength of this therapeutic approach.

Design, synthesis and cytotoxic evaluation of a library of oxadiazole-containing hybrids

The development of hybrid compounds led to the discovery of new pharmacologically active agents for some of the most critical diseases, including cancer. Herein, we describe a new series of oxadiazole-containing structures designed by a molecular hybridization approach. Penicillin derivatives and amino acids were linked to amino acid and aromatic moieties through the formation of a 1,2,4-oxadiazole ring. Alternatively, condensation between amino acid-derived hydrazides and an activated penicillanic acid led to a series of 1,3,4-oxadiazole penicillin-containing hybrids and non-cyclized diacylhydrazides. From the cytotoxicity assays it is highlighted that two 1,2,4-oxadiazoles and one 1,3,4-oxadiazole connecting a penicillin and aliphatic amino acids displayed a high degree of cytotoxic selectivity, ranging between being three and four times more potent against tumor cells than normal cells. The results give a very interesting perspective suggesting that these hybrid compounds can offer a novel antitumor scaffold with promising cytotoxicity profiles.

Synthesized hybrids of 1,2,4-oxadiazole and 1,3,4-oxadiazole connecting a penicillin and aliphatic amino acids displayed a high degree of cytotoxic selectivity.

Anti-Influenza Drug Discovery and Development: Targeting the Virus and Its Host by All Possible Means

Infections by influenza virus constitute a major and recurrent threat for human health. Together with vaccines, antiviral drugs play a key role in the prevention and treatment of influenza virus infection and disease. Today, the number of antiviral molecules approved for the treatment of influenza is relatively limited, and their use is threatened by the emergence of viral strains with resistance mutations. There is therefore a real need to expand the prophylactic and therapeutic arsenal. This chapter summarizes the state of the art in drug discovery and development for the treatment of influenza virus infections, with a focus on both virus-targeting and host cell-targeting strategies. Novel antiviral strategies targeting other viral proteins or targeting the host cell, some of which are based on drug repurposing, may be used in combination to strengthen our therapeutic arsenal against this major pathogen.

structural characterization of the interaction between the C-terminal domain of the influenza polymerase PA subunit and an optimized small peptide inhibitor

Influenza viruses can cause severe respiratory infections in humans, leading to nearly half a million deaths worldwide each year. Improved antiviral drugs are needed to address the threat of development of novel pandemic strains. Current therapeutic interventions target three key proteins in the viral life cycle: neuraminidase, the M2 channel and RNA-dependent-RNA polymerase. Protein-protein interactions between influenza polymerase subunits are potential new targets for drug development. Using a newly developed assay based on AlphaScreen technology, we screened a peptide panel for protein-protein interaction inhibitors to identify a minimal PB1 subunit-derived peptide that retains high inhibition potential and can be further modified. Here, we present an X-ray structure of the resulting decapeptide bound to the C-terminal domain of PA polymerase subunit from pandemic isolate A/California/07/2009 H1N1 at 1.6 Å resolution and discuss its implications for the design of specific, potent influenza polymerase inhibitors.

Searching for effective antiviral small molecules against influenza A virus: A patent review

Introduction: Despite the current interest caused by SARS-Cov-2, influenza continues to be one of the most serious health concerns, with an estimated 1 billion cases across the globe, including 3-5 million severe cases and 290,000-650,000 deaths worldwide. Areas covered: This manuscript reviews the efforts made in the development of small molecules for the treatment of influenza virus, primarily focused on patent applications in the last 5 years. Attention is paid to compounds targeting key functional viral proteins, such as the M2 channel, neuraminidase, and hemagglutinin, highlighting the evolution toward new ligands and scaffolds motivated by the emergence of resistant strains. Finally, the discovery of compounds against novel viral targets, such as the RNA-dependent RNA polymerase, is discussed. Expert opinion: The therapeutic potential of antiviral agents is limited by the increasing presence of resistant strains. This should encourage research on novel strategies for therapeutic intervention. In this context, the discovery of arbidol and JNJ7918 against hemagglutinin, and current efforts on RNA-dependent RNA polymerase have disclosed novel opportunities for therapeutic treatment. Studies should attempt to expand the therapeutic arsenal of anti-flu agents, often in combined therapies, to prevent future health challenges caused by influenza virus. Abbreviations: AlphaLISA: amplified luminescent proximity homogeneous assay; HA: hemagglutinin; NA: neuraminidase; RBD: receptor binding domain; RdRp: RNA-dependent RNA polymerase; SA: sialic Acid; TBHQ: tert-butyl hydroquinone; TEVC: two-electrode voltage clamp.

Synthesis and characterization of 1,2,4-triazolo[1,5-a]pyrimidine-2-carboxamide-based compounds targeting the PA-PB1 interface of influenza A virus polymerase

Influenza viruses (Flu) are responsible for seasonal epidemics causing high rates of morbidity, which can dramatically increase during severe pandemic outbreaks. Antiviral drugs are an indispensable weapon to treat infected people and reduce the impact on human health, nevertheless anti-Flu armamentarium still remains inadequate. In search for new anti-Flu drugs, our group has focused on viral RNA-dependent RNA polymerase (RdRP) developing disruptors of PA-PB1 subunits interface with the best compounds characterized by cycloheptathiophene-3-carboxamide and 1,2,4-triazolo[1,5-a]pyrimidine-2-carboxamide scaffolds. By merging these moieties, two very interesting hybrid compounds were recently identified, starting from which, in this paper, a series of analogues were designed and synthesized. In particular, a thorough exploration of the cycloheptathiophene-3-carboxamide moiety led to acquire important SAR insight and identify new active compounds showing both the ability to inhibit PA-PB1 interaction and viral replication in the micromolar range and at non-toxic concentrations. For few compounds, the ability to efficiently inhibit PA-PB1 subunits interaction did not translate into anti-Flu activity. Chemical/physical properties were investigated for a couple of compounds suggesting that the low solubility of compound 14, due to a strong crystal lattice, may have impaired its antiviral activity. Finally, computational studies performed on compound 23, in which the phenyl ring suitably replaced the cycloheptathiophene, suggested that, in addition to hydrophobic interactions, H-bonds enhanced its binding within the PA_C cavity.

Discovery of Influenza Polymerase PA-PB1 Interaction Inhibitors Using an In Vitro Split-Luciferase Complementation-Based Assay

The limited therapeutic options and increasing drug-resistance call for next-generation influenza antivirals. Due to the essential function in viral replication and high sequence conservation among influenza viruses, influenza polymerase PA-PB1 protein-protein interaction becomes an attractive drug target. Here, we developed an in vitro split luciferase complementation-based assay to speed up screening of PA-PB1 interaction inhibitors. By screening 10,000 compounds, we identified two PA-PB1 interaction inhibitors, R160792 and R151785, with potent and broad-spectrum antiviral activity against a panel of influenza A and B viruses, including amantadine-, oseltamivir-, or dual resistant strains. Further mechanistic study reveals that R151785 inhibits PA nuclear localization, reduces the levels of viral RNAs and proteins, and inhibits viral replication at the intermediate stage, all of which are in line with its antiviral mechanism of action. Overall, we developed a robust high throughput-screening assay for screening broad-spectrum influenza antivirals targeting PA-PB1 interaction and identified R151785 as a promising antiviral drug candidate.

Investigational antiviral therapies for the treatment of influenza

INTRODUCTION

Influenza viral ribonucleoprotein complexes (vRNPs) play a key role in viral transcription and replication; hence, the recent development of novel anti-influenza drugs targeting vRNPs has garnered widespread interest.

AREAS COVERED

We discuss the function of the constituents of vRNPs and summarize those vRNPs-targeted synthetic drugs that are in preclinical and early clinical development.

EXPERT OPINION

vRNPs contain high-value drug targets; such targets include the subunits PA, PB1, PB2, and NP. Developing a new generation of antiviral therapies with strategies that utilize existing drugs, natural compounds originated from new resources and novel drug combinations may open up new therapeutic approaches to influenza.

Potent and broad-spectrum cycloheptathiophene-3-carboxamide compounds that target the PA-PB1 interaction of influenza virus RNA polymerase and possess a high barrier to drug resistance

Influenza viruses are major respiratory pathogens responsible for both seasonal epidemics and occasional pandemics worldwide. The current available treatment options have limited efficacy and thus the development of new antivirals is highly needed. We previously reported the identification of a series of cycloheptathiophene-3-carboxamide compounds as influenza A virus inhibitors that act by targeting the protein-protein interactions between the PA-PB1 subunits of the viral polymerase. In this study, we characterized the antiviral properties of the most promising compounds as well as investigated their propensity to induce drug resistance. Our results show that some of the selected compounds possess potent, broad-spectrum anti-influenza activity as they efficiently inhibited the replication of several strains of influenza A and B viruses, including an oseltamivir-resistant clinical isolate, with nanomolar or low-micromolar potency. The most promising compounds specifically inhibited the PA-PB1 binding in vitro and interfered with the influenza A virus polymerase activity in a cellular context, without showing cytotoxicity. The most active PA-PB1 inhibitors showed to possess a drug resistance barrier higher than that of oseltamivir. Indeed, no viral variants with reduced susceptibility to the selected compounds emerged after serial passages of influenza A virus under drug selective pressure. Overall, our studies identified potent PA-PB1 inhibitors as promising candidates for the development of new anti-influenza drugs.