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

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

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

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

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

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

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

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.

A small molecule targeting the interaction between human papillomavirus E7 oncoprotein and cellular phosphatase PTPN14 exerts antitumoral activity in cervical cancer cells

Human papillomavirus (HPV)-induced cancers still represent a major health issue for worldwide population and lack specific therapeutic regimens. Despite substantial advancements in anti-HPV vaccination, the incidence of HPV-related cancers remains high, thus there is an urgent need for specific anti-HPV drugs. The HPV E7 oncoprotein is a major driver of carcinogenesis that acts by inducing the degradation of several host factors. A target is represented by the cellular phosphatase PTPN14 and its E7-mediated degradation was shown to be crucial in HPV oncogenesis. Here, by exploiting the crystal structure of E7 bound to PTPN14, we performed an in silico screening of small-molecule compounds targeting the C-terminal CR3 domain of E7 involved in the interaction with PTPN14. We discovered a compound able to inhibit the E7/PTPN14 interaction in vitro and to rescue PTPN14 levels in cells, leading to a reduction in viability, proliferation, migration, and cancer-stem cell potential of HPV-positive cervical cancer cells. Mechanistically, as a consequence of PTPN14 rescue, treatment of cancer cells with this compound altered the Yes-associated protein (YAP) nuclear-cytoplasmic shuttling and downstream signaling. Notably, this compound was active against cervical cancer cells transformed by different high-risk (HR)-HPV genotypes indicating a potential broad-spectrum activity. Overall, our study reports the first-in-class inhibitor of E7/PTPN14 interaction and provides the proof-of-principle that pharmacological inhibition of this interaction by small-molecule compounds could be a feasible therapeutic strategy for the development of novel antitumoral drugs specific for HPV-associated cancers.

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.

Small-Molecule Inhibitor of Flaviviral NS3-NS5 Interaction with Broad-Spectrum Activity and Efficacy In Vivo

Every year, dengue virus (DENV) causes one hundred million infections worldwide that can result in dengue disease and severe dengue. Two other mosquito-borne flaviviruses, i.e., Zika virus (ZIKV) and West Nile virus (WNV), are responsible of prolonged outbreaks and are associated with severe neurological diseases, congenital defects, and eventually death. These three viruses, despite their importance for global public health, still lack specific drug treatments. Here, we describe the structure-guided discovery of small molecules with pan-flavivirus antiviral potential by a virtual screening of ~1 million structures targeting the NS3-NS5 interaction surface of different flaviviruses. Two molecules inhibited the interaction between DENV NS3 and NS5 in vitro and the replication of all DENV serotypes as well as ZIKV and WNV and exhibited low propensity to select resistant viruses. Remarkably, one molecule demonstrated efficacy in a mouse model of dengue by reducing peak viremia, viral load in target organs, and associated tissue pathology. This study provides the proof of concept that targeting the flaviviral NS3-NS5 interaction is an effective therapeutic strategy able to reduce virus replication in vivo and discloses new chemical scaffolds that could be further developed, thus providing a significant milestone in the development of much awaited broad-spectrum antiflaviviral drugs. IMPORTANCE More than one-third of the human population is at risk of infection by different mosquito-borne flaviviruses. Despite this, no specific antiviral drug is currently available. In this work, using a computational approach based on molecular dynamics simulation and virtual screening of ~1 million small-molecule structures, we identified a compound that targets the interaction between the two sole flaviviral enzymes, i.e., NS3 and NS5. This compound demonstrated pan-serotype anti-DENV activity and pan-flavivirus potential in infected cells, low propensity to select viral resistant mutant viruses, and efficacy in a mouse model of dengue. Broad-spectrum antivirals are much awaited, and this work represents a significant advance toward the development of therapeutic molecules with extended antiflavivirus potential that act by an innovative mechanism and could be used alone or in combination with other antivirals.

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.

Iterative Optimization and Structure-Activity Relationship Studies of Oseltamivir Amino Derivatives as Potent and Selective Neuraminidase Inhibitors via Targeting 150-Cavity

With our continuous endeavors in seeking neuraminidase (NA) inhibitors, we reported herein three series of novel oseltamivir amino derivatives with the goal of exploring the druggable chemical space inside the 150-cavity of influenza virus NAs. Among them, around half of the compounds in series C were demonstrated to be better inhibitors against both wild-type and oseltamivir-resistant group-1 NAs than oseltamivir carboxylate (OSC). Notably, compounds 12d, 12e, 15e, and 15i showed more potent or equipotent antiviral activity against H1N1, H5N1, and H5N8 viruses compared to OSC in cellular assays. Furthermore, compounds 12e and 15e exhibited high metabolic stability in human liver microsomes (HLMs) and low inhibitory effect on main cytochrome P450 (CYP) enzymes, as well as low acute/subacute toxicity and certain antiviral efficacy in vivo. Also, pharmacokinetic (PK) and molecular docking studies were performed. Overall, 12e and 15e possess great potential to serve as anti-influenza candidates and are worthy of further investigation.

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

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

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.

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.

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.

Integrating molecular modelling methods to advance influenza A virus drug discovery

Since the discovery of the anti-influenza drugs oseltamivir and zanamivir using computer-aided drug design methods, there have been significant applications of molecular modelling methodologies applied to influenza A virus drug discovery, such as molecular dynamics (MD) simulation, molecular docking, and virtual screening (VS). In this review, we provide a brief general introduction to molecular modelling in the context of drug discovery and then focus on the advances and impact of integrating these methods with specific reference to potential influenza A antiviral drug targets.

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.

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.

Antivirals in medical biodefense

The viruses historically implicated or currently considered as candidates for misuse in bioterrorist events are poxviruses, filoviruses, bunyaviruses, orthomyxoviruses, paramyxoviruses and a number of arboviruses causing encephalitis, including alpha- and flaviviruses. All these viruses are of concern for public health services when they occur in natural outbreaks or emerge in unvaccinated populations. Recent events and intelligence reports point to a growing risk of dangerous biological agents being used for nefarious purposes. Public health responses effective in natural outbreaks of infectious disease may not be sufficient to deal with the severe consequences of a deliberate release of such agents. One important aspect of countermeasures against viral biothreat agents are the antiviral treatment options available for use in post-exposure prophylaxis. These issues were adressed by the organizers of the 16th Medical Biodefense Conference, held in Munich in 2018, in a special session on the development of drugs to treat infections with viruses currently perceived as a threat to societies or associated with a potential for misuse as biothreat agents. This review will outline the state-of-the-art methods in antivirals research discussed and provide an overview of antiviral compounds in the pipeline that are already approved for use or still under development.

Antiviral activity of iridoid glycosides extracted from Fructus Gardeniae against influenza A virus by PACT-dependent suppression of viral RNA replication

Epidemic and pandemic influenza A virus (IAV) poses a significant threat to human populations worldwide. Iridoid glycosides are principal bioactive components from the Gardenia jasminoides J. Ellis fruit that exhibit antiviral activity against several strains of IAV. In the present study, we evaluated the protective effect of Fructus Gardeniae iridoid glycoside extracts (IGEs) against IAV by cytopathogenic effect(CPE), MTT and a plaque formation assay in vitro and examined the reduction in the pulmonary index (PI), restoration of body weight, reduction in mortality and increases in survival time in vivo. As a host factor, PACT provides protection against the pathogenic influenza A virus by interacting with IAV polymerase and activating the IFN-I response. To verify the whether IGEs suppress IAV replication in a PACT-dependent manner, IAV RNA replication, expression of PACT and the phosphorylation of eIF2α in A549 cells were detected; the levels of IFNβ, PACT and PKR in mouse lung tissues were determined; and the activity of IAV polymerase was evaluated in PACT-compromised cells. The results indicated that IGEs sufficiently alleviated cell damage and suppressed IAV replication in vitro, protecting mice from IAV-induced injury and lethal IAV infection. These anti-IAV effects might be related to disrupted interplay between IVA polymerase and PACT and/or prevention of a PACT-dependent overactivated IFN-I antiviral response. Taken together, our findings reveal a new facet of the mechanisms by which IGEs fight the influenza A virus in a PACT-dependent manner.

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.