A cell-based luminescence assay is effective for high-throughput screening of potential influenza antivirals

A high-throughput response to the SARS-CoV-2 pandemic

Four years after the beginning of the COVID-19 pandemic, it is important to reflect on the events that have occurred during that time and the knowledge that has been gained. The response to the pandemic was rapid and highly resourced; it was also built upon a foundation of decades of federally funded basic and applied research. Laboratories in government, pharmaceutical, academic, and non-profit institutions all played roles in advancing pre-2020 discoveries to produce clinical treatments. This perspective provides a summary of how the development of high-throughput screening methods in a biosafety level 3 (BSL-3) environment at Southern Research Institute (SR) contributed to pandemic response efforts. The challenges encountered are described, including those of a technical nature as well as those of working under the pressures of an unpredictable virus and pandemic.

High-Throughput cell-based immunofluorescence assays against influenza

A rapid drug discovery response to influenza outbreaks with the potential to reach pandemic status could help minimize the virus's impact by reducing the time to identify anti-influenza drugs. Although several anti-influenza strategies have been considered in the search for new drugs, only a few therapeutic agents are approved for clinical use. The cytopathic effect induced by the influenza virus in Madin Darby canine kidney (MDCK) cells has been widely used for high-throughput anti-influenza drug screening, but the fact that the MDCK cells are not human cells constitutes a disadvantage when searching for new therapeutic agents for human use. We have developed a highly sensitive cell-based imaging assay for the identification of inhibitors of influenza A and B virus that is high-throughput compatible using the A549 human cell line. The assay has also been optimized for the assessment of the neutralizing effect of anti-influenza antibodies in the absence of trypsin, which allows testing of purified antibodies and serum samples. This assay platform can be applied to full high-throughput screening campaigns or later stages requiring quantitative potency determinations for structure-activity relationships.

Factors associated with viral RNA shedding and evaluation of potential viral infectivity at returning to school in influenza outpatients after treatment with baloxavir marboxil and neuraminidase inhibitors during 2013/2014-2019/2020 seasons in Japan: an observational study

BACKGROUND

This study assessed the differences in daily virus reduction and the residual infectivity after the recommended home stay period in Japan in patients infected with influenza and treated with baloxavir (BA), laninamivir (LA), oseltamivir (OS), and zanamivir (ZA).

METHODS

We conducted an observational study on children and adults at 13 outpatient clinics in 11 prefectures in Japan during seven influenza seasons from 2013/2014 to 2019/2020. Virus samples were collected twice from influenza rapid test-positive patients at the first and second visit 4-5 days after the start of treatment. The viral RNA shedding was quantified using quantitative RT-PCR. Neuraminidase (NA) and polymerase acidic (PA) variant viruses that reduce susceptibility to NA inhibitors and BA, respectively, were screened using RT-PCR and genetic sequencing. Daily estimated viral reduction was evaluated using univariate and multivariate analyses for the factors such as age, treatment, vaccination status, or the emergence of PA or NA variants. The potential infectivity of the viral RNA shedding at the second visit samples was determined using the Receiver Operator Curve based on the positivity of virus isolation.

RESULTS

Among 518 patients, 465 (80.0%) and 116 (20.0%) were infected with influenza A (189 with BA, 58 with LA, 181 with OS, 37 with ZA) and influenza B (39 with BA, 10 with LA, 52 with OS, 15 with ZA). The emergence of 21 PA variants in influenza A was detected after BA treatment, but NA variants were not detected after NAIs treatment. Multiple linear regression analysis showed that the daily viral RNA shedding reduction in patients was slower in the two NAIs (OS and LA) than in BA, influenza B infection, aged 0-5 years, or the emergence of PA variants. The residual viral RNA shedding potentially infectious was detected in approximately 10-30% of the patients aged 6-18 years after five days of onset.

CONCLUSIONS

Viral clearance differed by age, type of influenza, choice of treatment, and susceptibility to BA. Additionally, the recommended homestay period in Japan seemed insufficient, but reduced viral spread to some extent since most school-age patients became non-infectious after 5 days of onset.

Transcriptomes of Clusterin- and S100B-transfected neuronal cells elucidate protective mechanisms against hypoxia and oxidative stress in the hooded seal (Cystophora cristata) brain

BACKGROUND

The hooded seal (Cystophora cristata) exhibits impressive diving skills and can tolerate extended durations of asphyxia, hypoxia and oxidative stress, without suffering from irreversible neuronal damage. Thus, when exposed to hypoxia in vitro, neurons of fresh cortical and hippocampal tissue from hooded seals maintained their membrane potential 4-5 times longer than neurons of mice. We aimed to identify the molecular mechanisms underlying the intrinsic neuronal hypoxia tolerance. Previous comparative transcriptomics of the visual cortex have revealed that S100B and clusterin (apolipoprotein J), two stress proteins that are involved in neurological disorders characterized by hypoxic conditions, have a remarkably high expression in hooded seals compared to ferrets. When overexpressed in murine neuronal cells (HN33), S100B and clusterin had neuroprotective effects when cells were exposed to hypoxia. However, their specific roles in hypoxia have remained largely unknown.

METHODS

In order to shed light on potential molecular pathways or interaction partners, we exposed HN33 cells transfected with either S100B, soluble clusterin (sCLU) or nuclear clusterin (nCLU) to normoxia, hypoxia and oxidative stress for 24 h. We then determined cell viability and compared the transcriptomes of transfected cells to control cells. Potential pathways and upstream regulators were identified via Gene Ontology (GO) and Ingenuity Pathway Analysis (IPA).

RESULTS

HN33 cells transfected with sCLU and S100B demonstrated improved glycolytic capacity and reduced aerobic respiration at normoxic conditions. Additionally, sCLU appeared to enhance pathways for cellular homeostasis to counteract stress-induced aggregation of proteins. S100B-transfected cells sustained lowered energy-intensive synaptic signaling. In response to hypoxia, hypoxia-inducible factor (HIF) pathways were considerably elevated in nCLU- and sCLU-transfected cells. In a previous study, S100B and sCLU decreased the amount of reactive oxygen species and lipid peroxidation in HN33 cells in response to oxidative stress, but in the present study, these functional effects were not mirrored in gene expression changes.

CONCLUSIONS

sCLU and S100B overexpression increased neuronal survival by decreasing aerobic metabolism and synaptic signaling in advance to hypoxia and oxidative stress conditions, possibly to reduce energy expenditure and the build-up of deleterious reactive oxygen species (ROS). Thus, a high expression of CLU isoforms and S100B is likely beneficial during hypoxic conditions.

Quantification of Infectious SARS-CoV-2 by the 50% Tissue Culture Infectious Dose Endpoint Dilution Assay

A number of viral quantification methods are used to measure the concentration of infectious severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). While the traditional plaque-based assay allows for direct enumeration of replication competent lytic virions and remains the gold standard for the quantification of infectious virus, the 50% tissue culture infectious dose (TCID₅₀) endpoint dilution assay allows for a more rapid, large-scale analysis of experimental samples. In this chapter, we describe a well-established TCID₅₀ assay protocol to measure the SARS-CoV-2 infectious titer in viral stocks, in vitro cell or organoid models, and animal tissue. We also present alternative assays for scoring the cytopathic effect of SARS-CoV-2 in cell culture and comparable methods to calculate the 50% endpoint by serial dilution.

Novel β-Cyclodextrin-Based Heptavalent Glycyrrhetinic Acid Conjugates: Synthesis, Characterization, and Anti-Influenza Activity

In our continuing efforts toward the design of novel pentacyclic triterpene derivatives as potential anti-influenza virus entry inhibitors, a series of homogeneous heptavalent glycyrrhetinic acid derivatives based on β-cyclodextrin scaffold were designed and synthesized by click chemistry. The structure was unambiguously characterized by NMR, IR, and MALDI-TOF-MS measurements. Seven conjugates showed sufficient inhibitory activity against influenza virus infection based on the cytopathic effect reduction assay with IC50 values in the micromolar range. The interactions of conjugate 37, the most potent compound (IC50 = 2.86 μM, CC50 > 100 μM), with the influenza virus were investigated using the hemagglutination inhibition assay. Moreover, the surface plasmon resonance assay further confirmed that compound 37 bound to the influenza HA protein specifically with a dissociation constant of 5.15 × 10−7 M. Our results suggest the promising role of β-cyclodextrin as a scaffold for preparing a variety of multivalent compounds as influenza entry inhibitors.

Approaches for discovery of small-molecular antivirals targeting to influenza A virus PB2 subunit

Influenza is an acute respiratory infectious disease caused by influenza virus, leading to huge morbidity and mortality in humans worldwide. Despite the availability of antivirals in the clinic, the emergence of resistant strains calls for antivirals with novel mechanisms of action. The PB2 subunit of the influenza A virus polymerase is a promising target because of its vital role in the 'cap-snatching' mechanism. In this review, we summarize the technologies and medicinal chemistry strategies for hit identification, hit-to-lead and lead-to-candidate optimization, and current challenges in PB2 inhibitor development, as well as offering insights for the fight against drug resistance.

High throughput screening identifies inhibitors for parvovirus B19 infection of human erythroid progenitor cells

Parvovirus B19 (B19V) infection can cause hematological disorders and fetal hydrops during pregnancy. Currently, no antivirals or vaccines are available for the treatment or the prevention of B19V infection. To identify novel small-molecule antivirals against B19V replication, we developed a high throughput screening assay, which is based on an in vitro nicking assay using recombinant N-terminal 1-176 amino acids of the viral large nonstructural protein (NS1N) and a fluorescently labeled DNA probe (OriQ) that spans the nicking site of the viral DNA replication origin. We collectively screened 17,040 compounds and identified 2,178 (12.78%) hits that possess >10% inhibition of the NS1 nicking activity, among which 84 hits were confirmed to inhibit nicking in a dose-dependent manner. Using ex vivo expanded primary human erythroid progenitor cells (EPCs) infected by B19V, we validated 24 compounds demonstrated >50% in vivo inhibition of B19V infection at 10 μM, which can be categorized into 7 structure scaffolds. Based on the therapeutic index [half maximal cytotoxic concentration (CC₅₀)/half maximal effective concentration (EC₅₀)] in EPCs, the top 4 compounds were chosen to examine their inhibitions of B19V infection in EPCs at two times of the 90% maximal effective concentration (EC₉₀). A purine derivative (P7), demonstrated an antiviral effect (EC₅₀=1.46 μM) without prominent cytotoxicity (CC₅₀=71.8 μM) in EPCs, exhibited 92% inhibition of B19V infection in EPCs at 3.32 μM, which can be used as the lead compound in future studies for the treatment of B19V infection caused hematological disorders. Importance B19V encodes a large non-structural protein NS1. Its N-terminal domain (NS1N) consisting of 1-176 amino acids binds to viral DNA and serves as an endonuclease to nick the viral DNA replication origins, which is a pivotal step in rolling hairpin-dependent B19V DNA replication. For high throughput screening (HTS) of anti-B19V antivirals, we miniaturized a fluorescence-based in vitro nicking assay, which employs a fluorophore-labeled probe spanning the trs and the NS1N protein, into a 384-well plate format. The HTS assay showed a high reliability and capability in screening 17,040 compounds. Based on the therapeutic index [half maximal cytotoxic concentration (CC₅₀)/half maximal effective concentration (EC₅₀)] in EPCs, a purine derivative demonstrated an antiviral effect of 92% inhibition of B19V infection in EPCs at 3.32 μM (two times EC₉₀). Our study demonstrated a robust HTS assay for screening antivirals against B19V infection.

Baloxavir-oseltamivir combination therapy inhibits the emergence of resistant substitutions in influenza A virus PA gene in a mouse model

Baloxavir marboxil (BXM) treatment-emergent polymerase acid (PA) I38X amino acid substitution (AAS) in the resistant variants of influenza viruses raise concerns regarding their emergence and spread. This study investigated the impact of 1 or 5 mg/kg BXM and 25 mg/kg oseltamivir phosphate (OS) (single or combination therapy) on the occurrence of resistance-related substitutions during the sequential lung-to-lung passages of AH1N1)pdm09 virus in mice. Deep sequencing analysis revealed that 67% (n = 4/6) of the population treated with BXM single therapy (1 or 5 mg/kg) possessed the treatment-emergent PA-I38X AAS variants (I38T, I38S, and I38V). Notably, BXM-OS combination therapy impeded PA-I38X AAS emergence. Although the doses utilized in the mouse model may not be directly translated into the clinically equivalent doses of each drugs, these findings offer insights toward alternative therapies to mitigate the emergence of influenza antiviral resistance.

The SARS-CoV-2 Cytopathic Effect Is Blocked by Lysosome Alkalizing Small Molecules

Understanding the SARS-CoV-2 virus’ pathways of infection, virus–host–protein interactions, and mechanisms of virus-induced cytopathic effects will greatly aid in the discovery and design of new therapeutics to treat COVID-19. Chloroquine and hydroxychloroquine, extensively explored as clinical agents for COVID-19, have multiple cellular effects including alkalizing lysosomes and blocking autophagy as well as exhibiting dose-limiting toxicities in patients. Therefore, we evaluated additional lysosomotropic compounds to identify an alternative lysosome-based drug repurposing opportunity. We found that six of these compounds blocked the cytopathic effect of SARS-CoV-2 in Vero E6 cells with half-maximal effective concentration (EC₅₀) values ranging from 2.0 to 13 μM and selectivity indices (SIs; SI = CC₅₀/EC₅₀) ranging from 1.5- to >10-fold. The compounds (1) blocked lysosome functioning and autophagy, (2) prevented pseudotyped particle entry, (3) increased lysosomal pH, and (4) reduced (ROC-325) viral titers in the EpiAirway 3D tissue model. Consistent with these findings, the siRNA knockdown of ATP6V0D1 blocked the HCoV-NL63 cytopathic effect in LLC-MK2 cells. Moreover, an analysis of SARS-CoV-2 infected Vero E6 cell lysate revealed significant dysregulation of autophagy and lysosomal function, suggesting a contribution of the lysosome to the life cycle of SARS-CoV-2. Our findings suggest the lysosome as a potential host cell target to combat SARS-CoV-2 infections and inhibitors of lysosomal function could become an important component of drug combination therapies aimed at improving treatment and outcomes for COVID-19.

Cell Culture Experiments Reveal that High S100B and Clusterin Levels may Convey Hypoxia-tolerance to the Hooded Seal (Cystophora cristata) Brain

While the brain of most mammals suffers from irreversible damage after only short periods of low oxygen levels (hypoxia), marine mammals are excellent breath-hold divers that have adapted to hypoxia. In addition to physiological adaptations, such as large oxygen storing capacity and strict oxygen economy during diving, the neurons of the deep-diving hooded seal (Cystophora cristata) have an intrinsic tolerance to hypoxia. We aim to understand the molecular basis of this neuronal hypoxia tolerance. Previously, transcriptomics of the cortex of the hooded seal have revealed remarkably high expression levels of S100B and clusterin (apolipoprotein J) when compared to the ferret, a non-diving carnivore. Both genes have much-debated roles in hypoxia and oxidative stress. Here, we evaluated the effects of S100B and of two isoforms of clusterin (soluble and nucleus clusterin) on the survival, metabolic activity and the amount of reactive oxygen species (ROS) in HN33 neuronal mouse cells exposed to hypoxia and oxidative stress. S100B and soluble clusterin had neuroprotective effects, with reduced ROS-levels and retention of normoxic energy status of cells during both stress conditions. The protective effects of nucleus clusterin were restricted to hypoxia. S100B and clusterin showed purifying selection in marine and terrestrial mammals, indicating a functional conservation across species. Immunofluorescence revealed identical cellular distributions of S100B and clusterin in mice, ferrets and hooded seals, further supporting the functional conservation. Taken together, our data suggest that the neuroprotective effects of all three proteins are exclusively facilitated by their increased expression in the brain of the hooded seal.

Potent antiviral effect of silver nanoparticles on SARS-CoV-2

The pandemic of COVID-19 is spreading unchecked due to the lack of effective antiviral measures. Silver nanoparticles (AgNP) have been studied to possess antiviral properties and are presumed to inhibit SARS-CoV-2. Due to the need for an effective agent against SARS-CoV-2, we evaluated the antiviral effect of AgNPs. We evaluated a plethora of AgNPs of different sizes and concentration and observed that particles of diameter around 10 nm were effective in inhibiting extracellular SARS-CoV-2 at concentrations ranging between 1 and 10 ppm while cytotoxic effect was observed at concentrations of 20 ppm and above. Luciferase-based pseudovirus entry assay revealed that AgNPs potently inhibited viral entry step via disrupting viral integrity. These results indicate that AgNPs are highly potent microbicides against SARS-CoV-2 but should be used with caution due to their cytotoxic effects and their potential to derange environmental ecosystems when improperly disposed.

Rhodamine B-based fluorescent probes for molecular mechanism study of the anti-influenza activity of pentacyclic triterpenes

The antiviral activity of pentacyclic triterpenes has attracted increasing attention. However, the detailed antiviral mechanism remains fully unclear. In the present study, four C28 or C30 modified pentacyclic triterpene probes via conjugating with rhodamine B were designed and synthesized, and their anti-influenza virus activity was evaluated. The results indicated that two compounds 14 and 23 showed significant antiviral activity to influenza A/WSN/33 (H1N1) virus in Madin-Darby canine kidney (MDCK) cells with IC₅₀ values of 8.36 and 8.24 μM, respectively. The mechanism of action studies of representative probe 23 indicated that it could inhibit the membrane fusion by binding with influenza virus hemagglutinin (HA), and the apparent dissociation constant (K_D) value for probe 23-HA interaction was successfully evaluated (1.78 × 10^-5 M) using surface plasmon resonance spectroscopy. In addition, the subcellular localization of probe 23 in MDCK cells was determined by confocal microscopy and flow cytometry, and the results suggested that fluorescent probe 23 was rapidly taken up in MDCK cells and accumulated in cytoplasm, but no antiviral activity was observed after its entry into cells. The present study further confirmed our previous finding that pentacyclic triterpenes could tightly bind to the viral envelope HA protein, thus blocking the virus entry into host cells.

The SARS-CoV-2 cytopathic effect is blocked with autophagy modulators

SARS-CoV-02 is a new type of coronavirus capable of rapid transmission and causing severe clinical symptoms; much of which has unknown biological etiology. It has prompted researchers to rapidly mobilize their efforts towards identifying and developing anti-viral therapeutics and vaccines. Discovering and understanding the virus' pathways of infection, host-protein interactions, and cytopathic effects will greatly aid in the design of new therapeutics to treat COVID-19. While it is known that chloroquine and hydroxychloroquine, extensively explored as clinical agents for COVID-19, have multiple cellular effects including inhibiting autophagy, there are also dose-limiting toxicities in patients that make clearly establishing their potential mechanisms-of-action problematic. Therefore, we evaluated a range of other autophagy modulators to identify an alternative autophagy-based drug repurposing opportunity. In this work, we found that 6 of these compounds blocked the cytopathic effect of SARS-CoV-2 in Vero-E6 cells with EC50 values ranging from 2.0 to 13 μM and selectivity indices ranging from 1.5 to >10-fold. Immunofluorescence staining for LC3B and LysoTracker dye staining assays in several cell lines indicated their potency and efficacy for inhibiting autophagy correlated with the measurements in the SARS-CoV-2 cytopathic effect assay. Our data suggest that autophagy pathways could be targeted to combat SARS-CoV-2 infections and become an important component of drug combination therapies to improve the treatment outcomes for COVID-19.

Protective effects of new aryl sulfone derivatives against radiation-induced hematopoietic injury

The hematopoietic system is sensitive to radiation. In this research, new aryl sulfone derivatives (XH-201 and XH-202) containing a nitrogen heterocycle were designed and synthesized and their radio-protective efficacies with regard to the hematopoietic system were evaluated. XH-201 administration significantly increased the survival rate of mice after 8.0 Gy total body irradiation (TBI). The results showed that XH-201 treatment not only increased the white blood cells, platelets counts and the percentage of hematopoietic progenitor cells and hematopoietic stem cells in mice exposed to 4.0 Gy TBI but also decreased DNA damage, as determined by flow cytometric analysis of histone H2AX phosphorylation. In addition, our data demonstrated that XH-201 decreased the mitochondrial reactive oxygen species (ROS) levels in hematopoietic cells. Overall, these data suggest that XH-201 is beneficial for the protection of the hemoatopoietic system against radiation-induced injuries.

Identification and Characterization of Novel Compounds with Broad-Spectrum Antiviral Activity against Influenza A and B Viruses

Influenza A (IAV) and influenza B (IBV) viruses are highly contagious pathogens that cause fatal respiratory disease every year, with high economic impact. In addition, IAV can cause pandemic infections with great consequences when new viruses are introduced into humans. In this study, we evaluated 10 previously described compounds with antiviral activity against mammarenaviruses for their ability to inhibit IAV infection using our recently described bireporter influenza A/Puerto Rico/8/34 (PR8) H1N1 (BIRFLU). Among the 10 tested compounds, eight (antimycin A [AmA], brequinar [BRQ], 6-azauridine, azaribine, pyrazofurin [PF], AVN-944, mycophenolate mofetil [MMF], and mycophenolic acid [MPA]), but not obatoclax or Osu-03012, showed potent anti-influenza virus activity under posttreatment conditions [median 50% effective concentration (EC₅₀) = 3.80 nM to 1.73 μM; selective index SI for 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay, >28.90 to 13,157.89]. AmA, 6-azauridine, azaribine, and PF also showed potent inhibitory effect in pretreatment (EC₅₀ = 0.14 μM to 0.55 μM; SI-MTT = 70.12 to >357.14) or cotreatment (EC₅₀ = 34.69 nM to 7.52 μM; SI-MTT = 5.24 to > 1,441.33) settings. All of the compounds tested inhibited viral genome replication and gene transcription, and none of them affected host cellular RNA polymerase II activities. The antiviral activity of the eight identified compounds against BIRFLU was further confirmed with seasonal IAVs (A/California/04/2009 H1N1 and A/Wyoming/3/2003 H3N2) and an IBV (B/Brisbane/60/2008, Victoria lineage), demonstrating their broad-spectrum prophylactic and therapeutic activity against currently circulating influenza viruses in humans. Together, our results identified a new set of antiviral compounds for the potential treatment of influenza viral infections.IMPORTANCE Influenza viruses are highly contagious pathogens and are a major threat to human health. Vaccination remains the most effective tool to protect humans against influenza infection. However, vaccination does not always guarantee complete protection against drifted or, more noticeably, shifted influenza viruses. Although U.S. Food and Drug Administration (FDA) drugs are approved for the treatment of influenza infections, influenza viruses resistant to current FDA antivirals have been reported and continue to emerge. Therefore, there is an urgent need to find novel antivirals for the treatment of influenza viral infections in humans, a search that could be expedited by repurposing currently approved drugs. In this study, we assessed the influenza antiviral activity of 10 compounds previously shown to inhibit mammarenavirus infection. Among them, eight drugs showed antiviral activities, providing a new battery of drugs that could be used for the treatment of influenza infections.

Structure, function, and evolution of Gga-AvBD11, the archetype of the structural avian-double-β-defensin family

Out of the 14 avian β-defensins identified in the Gallus gallus genome, only 3 are present in the chicken egg, including the egg-specific avian β-defensin 11 (Gga-AvBD11). Given its specific localization and its established antibacterial activity, Gga-AvBD11 appears to play a protective role in embryonic development. Gga-AvBD11 is an atypical double-sized defensin, predicted to possess 2 motifs related to β-defensins and 6 disulfide bridges. The 3-dimensional NMR structure of the purified Gga-AvBD11 is a compact fold composed of 2 packed β-defensin domains. This fold is the archetype of a structural family, dubbed herein as avian-double-β-defensins (Av-DBD). We speculate that AvBD11 emanated from a monodomain gene ancestor and that similar events might have occurred in arthropods, leading to another structural family of less compact DBDs. We show that Gga-AvBD11 displays antimicrobial activities against gram-positive and gram-negative bacterial pathogens, the avian protozoan Eimeria tenella, and avian influenza virus. Gga-AvBD11 also shows cytotoxic and antiinvasive activities, suggesting that it may not only be involved in innate protection of the chicken embryo, but also in the (re)modeling of embryonic tissues. Finally, the contribution of either of the 2 Gga-AvBD11 domains to these biological activities was assessed, using chemically synthesized peptides. Our results point to a critical importance of the cationic N-terminal domain in mediating antibacterial, antiparasitic, and antiinvasive activities, with the C-terminal domain potentiating the 2 latter activities. Strikingly, antiviral activity in infected chicken cells, accompanied by marked cytotoxicity, requires the full-length protein.

High-Throughput Bioassays using "Dip-and-Go" Multiplexed Electrospray Mass Spectrometry

A multiplexed system based on inductive nanoelectrospray mass spectrometry (nESI-MS) has been developed for high-throughput screening (HTS) bioassays. This system combines inductive nESI and field amplification micro-electrophoresis to achieve a "dip-and-go" sample loading and purification strategy that enables nESI-MS based HTS assays in 96-well microtiter plates. The combination of inductive nESI and micro-electrophoresis makes it possible to perform efficient in situ separations and clean-up of biological samples. The sensitivity of the system is such that quantitative analysis of peptides from 1-10 000 nm can be performed in a biological matrix. A prototype of the automation system has been developed to handle 12 samples (one row of a microtiter plate) at a time. The sample loading and electrophoretic clean-up of biosamples can be done in parallel within 20 s followed by MS analysis at a rate of 1.3 to 3.5 s per sample. The system was used successfully for the quantitative analysis of BACE1-catalyzed peptide hydrolysis, a prototypical HTS assay of relevance to drug discovery. IC₅₀ values for this system were in agreement with LC-MS but recorded in times more than an order of magnitude shorter.

Design, synthesis of oleanolic acid-saccharide conjugates using click chemistry methodology and study of their anti-influenza activity

The development of entry inhibitors is an emerging approach to the inhibition of influenza virus. In our previous research, oleanolic acid (OA) was discovered as a mild influenza hemagglutinin (HA) inhibitor. Herein, as a further study, we report the preparation of a series of OA-saccharide conjugates via the CuAAC reaction, and the anti-influenza activity of these compounds was evaluated in vitro. Among them, compound 11b, an OA-glucose conjugate, showed a significantly increased anti-influenza activity with an IC₅₀ of 5.47 μM, and no obvious cytotoxic effect on MDCK cells was observed at 100 μM. Hemagglutination inhibition assay and docking experiment indicated that 11b might interfere with influenza virus infection by acting on HA protein. Broad-spectrum anti-influenza experiments showed 11b to be robustly potent against 5 different strains, including influenza A and B viruses, with IC₅₀ values at the low-micromole level. Overall, this finding further extends the utility of OA-saccharide conjugates in anti-influenza virus drug design.

Automated cell-based luminescence assay for profiling antiviral compound activity against enteroviruses

We describe the development, optimisation, and validation of an automated, cell-based and high-throughput screening assay using existing luminescence-based ATPlite reagents for identifying antiviral compounds that inhibit enterovirus replication. Antiviral efficacy was determined by measuring the ATP levels in cells that were protected from the viral cytopathic effect (CPE) by the antiviral compounds pleconaril and rupintrivir. CPE-based assay conditions were optimised at a cell density of 5000 cells/well and a viral infection dose of 100 CCID₅₀ in 384-well plates. The assay exhibited excellent robustness, with Z'-factor values between 0.75 and 0.82, coefficients of variation between 0.33% and 1.45%, and signal-to-background ratios ranging from 6.92 to 22.6 when testing three enterovirus A71 isolates circulating in China. The assay was also suitable for screening other picornaviruses, such as poliovirus, coxsackievirus, echovirus, and parechovirus.

Screening and evaluation of antiviral compounds against Equid alpha-herpesviruses using an impedance-based cellular assay

Equid alpha-herpesviruses (EHV) are responsible for different diseases in equine population. EHV-1 causes respiratory diseases, abortions and nervous disorders, EHV-4 causes respiratory diseases and sporadic abortion, while EHV-3 is responsible of equine coital exanthema. In view of the lack of efficacy of vaccines against EHV-1 and EHV-4 and in the absence of vaccines against EHV-3, the use of antiviral treatment is of great interest. In this study, we documented the interest of the Real-Time Cell Analysis (RTCA) technology to monitor the cytopathic effects induced by these viruses on equine dermal cells, and established the efficacy of this method to evaluate the antiviral effect of aciclovir (ACV) and ganciclovir (GCV). In addition, the RTCA technology has also been found appropriate for the high-throughput screening of small molecules against EHV, allowing the identification of spironolactone as a novel antiviral against EHV.

Investigating Different Mechanisms of Action in Combination Therapy for Influenza

Combination therapy for influenza can have several benefits, from reducing the emergence of drug resistant virus strains to decreasing the cost of antivirals. However, there are currently only two classes of antivirals approved for use against influenza, limiting the possible combinations that can be considered for treatment. However, new antivirals are being developed that target different parts of the viral replication cycle, and their potential for use in combination therapy should be considered. The role of antiviral mechanism of action in the effectiveness of combination therapy has not yet been systematically investigated to determine whether certain antiviral mechanisms of action pair well in combination. Here, we use a mathematical model of influenza to model combination treatment with antivirals having different mechanisms of action to measure peak viral load, infection duration, and synergy of different drug combinations. We find that antivirals that lower the infection rate and antivirals that increase the duration of the eclipse phase perform poorly in combination with other antivirals.

Design, synthesis and biological evaluation of water-soluble per-O-methylated cyclodextrin-C60 conjugates as anti-influenza virus agents

The most common fullerene member C₆₀ displays many biological applications, such as, anticancer, human immunodeficiency virus and hepatitis C virus inhibitors, O₂ uptake inhibitor and vectors for drug and DNA. Nevertheless, the innate hydrophobicity of C₆₀ constrains its further development. We introduced cyclodextrins to enhance the water-solubility of C₆₀. Nine cyclodextrin-C₆₀ conjugates, including seven α-cyclodextrin-C₆₀ conjugates and two γ-cyclodextrin-C₆₀ conjugates, were designed and synthesized. All of these conjugates did not show obvious cytotoxicity. The anti-influenza virus activity of nine conjugates was assessed. Two γ-cyclodextrin-C₆₀ conjugates, which were relatively more water-soluble, exerted higher inhibition with IC₅₀ values of 87.73 μM and 75.06 μM, respectively, than seven α-cyclodextrin-C₆₀ conjugates.

Identification of Inhibitory Compounds Against Singapore Grouper Iridovirus Infection by Cell Viability-Based Screening Assay and Droplet Digital PCR

Singapore grouper iridovirus (SGIV) is one of the major causative agents of fish diseases and has caused significant economic losses in the aquaculture industry. There is currently no commercial vaccine or effective antiviral treatment against SGIV infection. Annually, an increasing number of small molecule compounds from various sources have been produced, and many are proved to be potential inhibitors against viruses. Here, a high-throughput in vitro cell viability-based screening assay was developed to identify antiviral compounds against SGIV using the luminescent-based CellTiter-Glo reagent in cultured grouper spleen cells by quantificational measurement of the cytopathic effects induced by SGIV infection. This assay was utilized to screen for potential SGIV inhibitors from five customized compounds which had been reported to be capable of inhibiting other viruses and 30 compounds isolated from various marine organisms, and three of them [ribavirin, harringtonine, and 2-hydroxytetradecanoic acid (2-HOM)] were identified to be effective on inhibiting SGIV infection, which was further confirmed with droplet digital PCR (ddPCR). In addition, the ddPCR results revealed that ribavirin and 2-HOM inhibited SGIV replication and entry in a dose-dependent manner, and harringtonine could reduce SGIV replication rather than entry at the working concentration without significant toxicity. These findings provided an easy and reliable cell viability-based screening assay to identify compounds with anti-SGIV effect and a way of studying the anti-SGIV mechanism of compounds.

Inhibition of influenza virus infection by multivalent pentacyclic triterpene-functionalized per-O-methylated cyclodextrin conjugates

Multivalent ligands that exhibit high binding affinity to influenza hemagglutinin (HA) trimer can block the interaction of HA with its sialic acid receptor. In this study, a series of multivalent pentacyclic triterpene-functionalized per-O-methylated cyclodextrin (CD) derivatives were designed and synthesized using 1, 3-dipolar cycloaddition click reaction. A cell-based assay showed that three compounds (25, 28 and 31) exhibited strong inhibitory activity against influenza A/WSN/33 (H1N1) virus. Compound 28 showed the most potent anti-influenza activity with IC₅₀ of 4.7 μM. The time-of-addition assay indicated that compound 28 inhibited the entry of influenza virus into host cell. Further hemagglutination inhibition (HI) and surface plasmon resonance (SPR) assays indicated that compound 28 tightly bound to influenza HA protein with a dissociation constant (K_D) of 4.0 μM. Our results demonstrated a strategy of using per-O-methylated β-CD as a scaffold for designing multivalent compounds to disrupt influenza HA protein-host receptor protein interaction and thus block influenza virus entry into host cells.

3,3'-diindolylmethane mitigates total body irradiation-induced hematopoietic injury in mice

We have reported that hematopoietic system injury induced by total body irradiation (TBI) leads to generation of intracellular reactive oxygen species (ROS) and DNA damage, which are ameliorated by antioxidant agents. In the present study, we reported that administration of DIM, a potent antioxidant agent, not only protected mice against TBI-induced lethality, also ameliorated TBI-induced hematopoietic injury. The latter effect was probably attributable to DIM's inhibition of TBI-induced increases in ROS production in hematopoietic stem cells (HSCs) and the phosphorylation of histone H2AX (γ-H2AX). In particular, DIM led to significant improvements in bone marrow (BM) HSC frequency, hematopoietic progenitor cell (HPC) clonogenic function, and multilineage engraftment after transplantation. A downregulation of NADPH oxidase 4 (NOX4) and an upregulation of nuclear factor erythroid 2-related factor 2 (Nrf2) and heme oxygenase-1 (HO-1) expression were observed following DIM treatment. Notably, the anti-apoptotic potential of DIM was correlated with increased expression of the anti-apoptotic protein Bcl-2 and decreased expression of the pro-apoptotic protein Bax. These findings suggest that DIM attenuates TBI-induced hematopoietic injury through the inhibition of both oxidative stress in HSCs and hematopoietic cell apoptosis. Furthermore, we demonstrated that DIM protected BM hematopoietic cells against ionizing radiation and led to increased clonogenicity in vitro. Therefore, DIM has the potential to be used as an effective radioprotectant to ameliorate TBI-induced hematopoietic injury.

Olig2-Dependent Reciprocal Shift in PDGF and EGF Receptor Signaling Regulates Tumor Phenotype and Mitotic Growth in Malignant Glioma

Malignant gliomas exhibit extensive heterogeneity and poor prognosis. Here we identify mitotic Olig2-expressing cells as tumor-propagating cells in proneural gliomas, elimination of which blocks tumor initiation and progression. Intriguingly, deletion of Olig2 resulted in tumors that grow, albeit at a decelerated rate. Genome occupancy and expression profiling analyses reveal that Olig2 directly activates cell-proliferation machinery to promote tumorigenesis. Olig2 deletion causes a tumor phenotypic shift from an oligodendrocyte precursor-correlated proneural toward an astroglia-associated gene expression pattern, manifest in downregulation of platelet-derived growth factor receptor-α and reciprocal upregulation of epidermal growth factor receptor (EGFR). Olig2 deletion further sensitizes glioma cells to EGFR inhibitors and extends the lifespan of animals. Thus, Olig2-orchestrated receptor signaling drives mitotic growth and regulates glioma phenotypic plasticity. Targeting Olig2 may circumvent resistance to EGFR-targeted drugs.

Pentacyclic triterpenes grafted on CD cores to interfere with influenza virus entry: A dramatic multivalent effect

Multivalent effect plays an important role in biological processes, particularly in the specific recognition of virus with its host cell during the first step of infection. Here we report the synthesis of multivalent pentacyclic triterpene grafted on cyclodextrin core and potency of against influenza entry activity. Nine star-shaped compounds containing six, seven and eight pentacyclic triterpene pharmacophore on cyclodextrin scaffold were prepared by way of copper-catalyzed azide-alkyl cycloaddition reaction under microwave activation. Some of the multimers exhibited much potent antiviral activity against H1N1 virus (A/WSN/33), even equivalent or superior to oseltamivir. The most active compound 31, a heptavalent oleanolic acid-β-cyclodextrin conjugate, shows an up to 125-fold potency enhancement by its IC50 value over the corresponding monovalent conjugate and oleanolic acid, disclosing a clear multivalent effect. Further studies show that three compounds 31-33 exhibited broad spectrum inhibitory activity against other two human influenza A/JX/312 (H3N2) and A/HN/1222 (H3N2) viruses with the IC50 values at 2.47-14.90 μM. Most importantly, we found that compound 31, one of the best representative conjugate, binds tightly to the viral envelope hemagglutinin with a dissociation constant of KD = 2.08 μM, disrupting the interaction of hemagglutinin with the sialic acid receptor and thus the attachment of viruses to host cells. Our study might establish a strategy for the design of new pharmaceutical agents based on multivalency so as to block influenza virus entry into host cells.

Adapting high-throughput screening methods and assays for biocontainment laboratories

High-throughput screening (HTS) has been integrated into the drug discovery process, and multiple assay formats have been widely used in many different disease areas but with limited focus on infectious agents. In recent years, there has been an increase in the number of HTS campaigns using infectious wild-type pathogens rather than surrogates or biochemical pathogen-derived targets. Concurrently, enhanced emerging pathogen surveillance and increased human mobility have resulted in an increase in the emergence and dissemination of infectious human pathogens with serious public health, economic, and social implications at global levels. Adapting the HTS drug discovery process to biocontainment laboratories to develop new drugs for these previously uncharacterized and highly pathogenic agents is now feasible, but HTS at higher biosafety levels (BSL) presents a number of unique challenges. HTS has been conducted with multiple bacterial and viral pathogens at both BSL-2 and BSL-3, and pilot screens have recently been extended to BSL-4 environments for both Nipah and Ebola viruses. These recent successful efforts demonstrate that HTS can be safely conducted at the highest levels of biological containment. This review outlines the specific issues that must be considered in the execution of an HTS drug discovery program for high-containment pathogens. We present an overview of the requirements for HTS in high-level biocontainment laboratories.

Benzimidazole analogs inhibit respiratory syncytial virus G protein function

Human respiratory syncytial virus (hRSV) is a highly contagious Paramyxovirus that infects most children by age two, generating an estimated 75,000-125,000 hospitalizations in the U.S. annually. hRSV is the most common cause of bronchiolitis and pneumonia among infants and children under 1year of age, with significant mortality among high-risk groups. A regulatory agency-approved vaccine is not available, and existing prophylaxis and therapies are limited to use in high-risk pediatric patients; thus additional therapies are sorely needed. Here, we identify a series of benzimidazole analogs that inhibit hRSV infection in vitro with high potency, using a previously-reported high-throughput screening assay. The lead compound, SRI 29365 (1-[6-(2-furyl)[1,2,4]triazolo[3,4-b][1,3,4]thiadiazol-3-yl]methyl-1H-benzimidazole), has an EC50 of 66μM and a selectivity >50. We identified additional compounds with varying potencies by testing commercially-available chemical analogs. Time-of-addition experiments indicated that SRI 29365 effectively inhibits viral replication only if present during the early stages of viral infection. We isolated a virus with resistance to SRI 29365 and identified mutations in the transmembrane domain of the viral G protein genomic sequence that suggested that the compound inhibits G-protein mediated attachment of hRSV to cells. Additional experiments with multiple cell types indicated that SRI 29365 antiviral activity correlates with the binding of cell surface heparin by full-length G protein. Lastly, SRI 29365 did not reduce hRSV titers or morbidity/mortality in efficacy studies using a cotton rat model. Although SRI 29365 and analogs inhibit hRSV replication in vitro, this work suggests that the G-protein may not be a valid drug target in vivo.

Novel Ranking System for Identifying Efficacious Anti-Influenza Virus PB2 Inhibitors

Through antigenic drift and shifts, influenza virus infections continue to be an annual cause of morbidity in healthy populations and of death among elderly and at-risk patients. The emergence of highly pathogenic avian influenza viruses such as H5N1 and H7N9 and the rapid spread of the swine-origin H1N1 influenza virus in 2009 demonstrate the continued need for effective therapeutic agents for influenza. While several neuraminidase inhibitors have been developed for the treatment of influenza virus infections, these have shown a limited window for treatment initiation, and resistant variants have been noted in the population. In addition, an older class of antiviral drugs for influenza, the adamantanes, are no longer recommended for treatment due to widespread resistance. There remains a need for new influenza therapeutic agents with improved efficacy as well as an expanded window for the initiation of treatment. Azaindole compounds targeting the influenza A virus PB2 protein and demonstrating excellent in vitro and in vivo properties have been identified. To evaluate the in vivo efficacy of these PB2 inhibitors, we utilized a mouse influenza A virus infection model. In addition to traditional endpoints, i.e., death, morbidity, and body weight loss, we measured lung function using whole-body plethysmography, and we used these data to develop a composite efficacy score that takes compound exposure into account. This model allowed the rapid identification and ranking of molecules relative to each other and to oseltamivir. The ability to identify compounds with enhanced preclinical properties provides an opportunity to develop more-effective treatments for influenza in patients.

Isosteric replacements of the carboxylic acid of drug candidate VX-787: Effect of charge on antiviral potency and kinase activity of azaindole-based influenza PB2 inhibitors

VX-787 is a first in class, orally bioavailable compound that offers unparalleled potential for the treatment of pandemic and seasonal influenza. As a part of our routine SAR exploration, carboxylic acid isosteres of VX-787 were prepared and tested against influenza A. It was found that the negative charge is important for maintaining potency and selectivity relative to kinase targets. Neutral carboxylic acid replacements generally resulted in compounds that were significantly less potent and less selective relative to the charged species.

Neoechinulin B and its analogues as potential entry inhibitors of influenza viruses, targeting viral hemagglutinin

A class of prenylated indole diketopiperazine alkaloids including 15 new compounds namely rubrumlines A-O obtained from marine-derived fungus Eurotium rubrum, were tested against influenza A/WSN/33 virus. Neoechinulin B (18) exerted potent inhibition against H1N1 virus infected in MDCK cells, and is able to inhibit a panel of influenza virus strains including amantadine- and oseltamivir-resistant clinical isolates. Mechanism of action studies indicated that neoechinulin B binds to influenza envelope hemagglutinin, disrupting its interaction with the sialic acid receptor and the attachment of viruses to host cells. In addition, neoechinulin B was still efficient in inhibiting influenza A/WSN/33 virus propagation even after a fifth passage. The high potency and broad-spectrum activities against influenza viruses with less drug resistance make neoechinulin B as a new lead for the development of potential inhibitor of influenza viruses.

Preclinical activity of VX-787, a first-in-class, orally bioavailable inhibitor of the influenza virus polymerase PB2 subunit

VX-787 is a novel inhibitor of influenza virus replication that blocks the PB2 cap-snatching activity of the influenza viral polymerase complex. Viral genetics and X-ray crystallography studies provide support for the idea that VX-787 occupies the 7-methyl GTP (m(7)GTP) cap-binding site of PB2. VX-787 binds the cap-binding domain of the PB2 subunit with a KD (dissociation constant) of 24 nM as determined by isothermal titration calorimetry (ITC). The cell-based EC50 (the concentration of compound that ensures 50% cell viability of an uninfected control) for VX-787 is 1.6 nM in a cytopathic effect (CPE) assay, with a similar EC50 in a viral RNA replication assay. VX-787 is active against a diverse panel of influenza A virus strains, including H1N1pdm09 and H5N1 strains, as well as strains with reduced susceptibility to neuraminidase inhibitors (NAIs). VX-787 was highly efficacious in both prophylaxis and treatment models of mouse influenza and was superior to the neuraminidase inhibitor, oseltamivir, including in delayed-start-to-treat experiments, with 100% survival at up to 96 h postinfection and partial survival in groups where the initiation of therapy was delayed up to 120 h postinfection. At different doses, VX-787 showed a 1-log to >5-log reduction in viral load (relative to vehicle controls) in mouse lungs. Overall, these favorable findings validate the PB2 subunit of the viral polymerase as a drug target for influenza therapy and support the continued development of VX-787 as a novel antiviral agent for the treatment of influenza infection.

A BSL-4 high-throughput screen identifies sulfonamide inhibitors of Nipah virus

Nipah virus is a biosafety level 4 (BSL-4) pathogen that causes severe respiratory illness and encephalitis in humans. To identify novel small molecules that target Nipah virus replication as potential therapeutics, Southern Research Institute and Galveston National Laboratory jointly developed an automated high-throughput screening platform that is capable of testing 10,000 compounds per day within BSL-4 biocontainment. Using this platform, we screened a 10,080-compound library using a cell-based, high-throughput screen for compounds that inhibited the virus-induced cytopathic effect. From this pilot effort, 23 compounds were identified with EC50 values ranging from 3.9 to 20.0 μM and selectivities >10. Three sulfonamide compounds with EC50 values <12 μM were further characterized for their point of intervention in the viral replication cycle and for broad antiviral efficacy. Development of HTS capability under BSL-4 containment changes the paradigm for drug discovery for highly pathogenic agents because this platform can be readily modified to identify prophylactic and postexposure therapeutic candidates against other BSL-4 pathogens, particularly Ebola, Marburg, and Lassa viruses.

A cell-based high-throughput approach to identify inhibitors of influenza A virus

Influenza is one of the most common infections threatening public health worldwide and is caused by the influenza virus. Rapid emergence of drug resistance has led to an urgent need to develop new anti-influenza inhibitors. In this study we established a 293T cell line that constitutively synthesizes a virus-based negative strand RNA, which expresses Gaussia luciferase upon influenza A virus infection. Using this cell line, an assay was developed and optimized to search for inhibitors of influenza virus replication. Biochemical studies and statistical analyses presented herein demonstrate the sensitivity and reproducibility of the assay in a high-throughput format (Z' factor value>0.8). A pilot screening provides further evidence for validation of the assay. Taken together, this work provides a simple, convenient, and reliable HTS assay to identify compounds with anti-influenza activity.

Lifting the mask: identification of new small molecule inhibitors of uropathogenic Escherichia coli group 2 capsule biogenesis

Uropathogenic Escherichia coli (UPEC) is the leading cause of community-acquired urinary tract infections (UTIs), with over 100 million UTIs occurring annually throughout the world. Increasing antimicrobial resistance among UPEC limits ambulatory care options, delays effective treatment, and may increase overall morbidity and mortality from complications such as urosepsis. The polysaccharide capsules of UPEC are an attractive target a therapeutic, based on their importance in defense against the host immune responses; however, the large number of antigenic types has limited their incorporation into vaccine development. The objective of this study was to identify small-molecule inhibitors of UPEC capsule biogenesis. A large-scale screening effort entailing 338,740 compounds was conducted in a cell-based, phenotypic screen for inhibition of capsule biogenesis in UPEC. The primary and concentration-response assays yielded 29 putative inhibitors of capsule biogenesis, of which 6 were selected for further studies. Secondary confirmatory assays identified two highly active agents, named DU003 and DU011, with 50% inhibitory concentrations of 1.0 µM and 0.69 µM, respectively. Confirmatory assays for capsular antigen and biochemical measurement of capsular sugars verified the inhibitory action of both compounds and demonstrated minimal toxicity and off-target effects. Serum sensitivity assays demonstrated that both compounds produced significant bacterial death upon exposure to active human serum. DU011 administration in mice provided near complete protection against a lethal systemic infection with the prototypic UPEC K1 isolate UTI89. This work has provided a conceptually new class of molecules to combat UPEC infection, and future studies will establish the molecular basis for their action along with efficacy in UTI and other UPEC infections.

Administration of the resveratrol analogues isorhapontigenin and heyneanol-A protects mice hematopoietic cells against irradiation injuries

Ionizing radiation (IR) is known not only to cause acute bone marrow (BM) suppression but also to lead to long-term residual hematopoietic injury. These effects have been attributed to IR inducing the generation of reactive oxygen species (ROS) in hematopoietic cells. In this study, we examined if isorhapontigenin and heyneanol-A, two analogues of resveratrol, could mitigate IR-induced BM suppression. The results of cell viability assays, clonogenic assays, and competitive repopulation assays revealed that treatment with these compounds could protect mice BM mononuclear cells (BMMNC), hematopoietic progenitor cells, and hematopoietic stem cells from IR-induced BM suppression. Moreover, the expression of genes related to the endogenous cellular antioxidant system in hematopoietic cells was analyzed. The expression and activity of SOD2 and GPX1 were found to be decreased in irradiated BMMNC, and the application of the resveratrol analogues could ameliorate this damage. Our results suggest that in comparison with resveratrol and isorhapontigenin, treatment with heyneanol-A can protect hematopoietic cells from IR-induced damage to a greater degree; the protective effects of these compounds are probably the result of their antioxidant properties.

Global Human-Kinase Screening Identifies Therapeutic Host Targets against Influenza

During viral infection of human cells, host kinases mediate signaling activities that are used by all viruses for replication; therefore, targeting of host kinases is of broad therapeutic interest. Here, host kinases were globally screened during human influenza virus (H1N1) infection to determine the time-dependent effects of virus infection and replication on kinase function. Desthiobiotin-labeled analogs of adenosine triphosphate and adenosine diphosphate were used to probe and covalently label host kinases in infected cell lysates, and probe affinity was determined. Using infected human A549 cells, we screened for time-dependent signal changes and identified host kinases whose probe affinities differed significantly when compared to uninfected cells. Our screen identified 10 novel host kinases that have not been previously shown to be involved with influenza virus replication, and we validated the functional importance of these novel kinases during infection using targeted small interfering RNAs (siRNAs). The effects of kinase-targeted siRNA knockdowns on replicating virus levels were measured by quantitative reverse-transcription PCR and cytoprotection assays. We identified several novel host kinases that, when knocked down, enhanced or reduced the viral load in cell culture. This preliminary work represents the first screen of the changing host kinome in influenza virus-infected human cells.