Comparison of colorimetric, fluorometric, and visual methods for determining anti-influenza (H1N1 and H3N2) virus activities and toxicities of compounds

Establishment of a screening platform based on human coronavirus OC43 for the identification of microbial natural products with antiviral activity

IMPORTANCE

The COVID-19 pandemic has revealed the lack of effective treatments against betacoronaviruses and the urgent need for new broad-spectrum antivirals. Natural products are a valuable source of bioactive compounds with pharmaceutical potential that may lead to the discovery of new antiviral agents. Specifically, compared to conventional synthetic molecules, microbial natural extracts possess a unique and vast chemical diversity and are amenable to large-scale production. The implementation of a high-throughput screening platform using the betacoronavirus OC43 in a human cell line infection model has provided proof of concept of the approach and has allowed for the rapid and efficient evaluation of 1,280 microbial extracts. The identification of several active compounds validates the potential of the platform for the search for new compounds with antiviral capacity.

Impact of different Agrobacterium rhizogenes strains on secondary metabolites accumulation in Nitraria schoberi L. hairy roots and antiviral activity of their extracts against influenza virus of subtypes A (H5N1) and A (H3N2)

To optimize protocol for obtaining hairy roots of Nitraria schoberi L. with high antiviral activities, factors such as four strain types of Agrobacterium rhizogenes (A4, ATCC15834, R-1601, 8196), two explant types, namely cotyledonous and primary leaves of seedlings, and different cultivation durations (30 and 90 d) were studied. The formation of hairy roots was observed after 2 to 4 wk of incubation, depending on the type of explant and the strain of A. rhizogenes used. The maximum transformation frequency (85.7%) was observed in the cotyledons genetically modified with the strain ATCC15834. The transgenic nature of hairy roots was revealed by PCR with primers to the Agrobacterium oncogenes rolB and rolC. The absence of contamination of the culture by A. rhizogenes was confirmed by primers to the virC and virD1 genes. Phytochemical analysis showed that accumulation of individual metabolites in the line samples exceeded their levels in the native Nitraria roots. Catechin content in the cultures of long-term cultivation (90 d) was found 1.4 to 2.2 times higher than the same samples of short cultivation (30 d) and 4.8 to 10.8 times higher in comparison with the native roots. The most productive in terms of catechin level were hairy roots of long-term cultivation obtained during the transformation of primary leaves of N. schoberi seedlings with ATCC15834 strain. These data were consistent with the highest antiviral activities against influenza viruses of A (H5N1) and A (H3N2) subtypes with neutralization indexes 6.5 to 6.75 log10, and selectivity index values were in the range 15.4 to 16.4.

Design, synthesis, and evaluation of 4'-phosphonomethoxy pyrimidine ribonucleosides as potential anti-influenza agents

Influenza viruses belong to the Orthomyxoviridae family and cause acute respiratory distress in humans. The developed drug resistance toward existing drugs and the emergence of viral mutants that can escape vaccines mandate the search for novel antiviral drugs. Herein, the synthesis of epimeric 4'-methyl-4'-phosphonomethoxy [4'-C-Me-4'-C-(O-CH₂ P═O)] pyrimidine ribonucleosides, their phosphonothioate [4'-C-Me-4'-C-(O-CH₂ P═S)] derivatives, and their evaluation against an RNA viral panel are described. Selective formation of the α- l-lyxo epimer, [4'-C-(α)-Me-4'-C-(β)-(O-CH₂ -P(═O)(OEt)₂ )] over the β- d-ribo epimer [4'-C-(β)-Me-4'-C-(α)-(O-CH₂ -P(═O)(OEt)₂ )] was explained by DFT equilibrium geometry optimizations studies. Pyrimidine nucleosides having the [4'-C-(α)-Me-4'-C-(β)-(O-CH₂ -P(═O)(OEt)₂ )] framework showed specific activity against influenza A virus. Significant anti-influenza virus A (H1N1 California/07/2009 isolate) was observed with the 4'-C-(α)-Me-4'-C-(β)-O-CH₂ -P(═O)(OEt)₂ -uridine derivative 1 (EC₅₀  = 4.56 mM, SI₅₀  > 56), 4-ethoxy-2-oxo-1(2H)-pyrimidin-1-yl derivative 3 (EC₅₀  = 5.44 mM, SI₅₀  > 43) and the cytidine derivative 2 (EC₅₀  = 0.81 mM, SI₅₀  > 13), respectively. The corresponding thiophosphonates 4'-C-(α)-Me-4'-C-(β)-(O-CH₂ -P( S)(OEt)₂ ) and thionopyrimidine nucleosides were devoid of any antiviral activity. This study shows that the 4'-C-(α)-Me-4'-(β)-O-CH₂ -P(═O)(OEt)₂ ribonucleoside can be further optimized to provide potent antiviral agents.

NITD-688, a pan-serotype inhibitor of the dengue virus NS4B protein, shows favorable pharmacokinetics and efficacy in preclinical animal models

Dengue virus (DENV) is a mosquito-borne flavivirus that poses a threat to public health, yet no antiviral drug is available. We performed a high-throughput phenotypic screen using the Novartis compound library and identified candidate chemical inhibitors of DENV. This chemical series was optimized to improve properties such as anti-DENV potency and solubility. The lead compound, NITD-688, showed strong potency against all four serotypes of DENV and demonstrated excellent oral efficacy in infected AG129 mice. There was a 1.44-log reduction in viremia when mice were treated orally at 30 milligrams per kilogram twice daily for 3 days starting at the time of infection. NITD-688 treatment also resulted in a 1.16-log reduction in viremia when mice were treated 48 hours after infection. Selection of resistance mutations and binding studies with recombinant proteins indicated that the nonstructural protein 4B is the target of NITD-688. Pharmacokinetic studies in rats and dogs showed a long elimination half-life and good oral bioavailability. Extensive in vitro safety profiling along with exploratory rat and dog toxicology studies showed that NITD-688 was well tolerated after 7-day repeat dosing, demonstrating that NITD-688 may be a promising preclinical candidate for the treatment of dengue.

Simple rapid in vitro screening method for SARS-CoV-2 anti-virals that identifies potential cytomorbidity-associated false positives

Background

The international SARS-CoV-2 pandemic has resulted in an urgent need to identify new anti-viral drugs for treatment of COVID-19. The initial step to identifying potential candidates usually involves in vitro screening that includes standard cytotoxicity controls. Under-appreciated is that viable, but stressed or otherwise compromised cells, can also have a reduced capacity to replicate virus. A refinement proposed herein for in vitro drug screening thus includes a simple growth assay to identify drug concentrations that cause cellular stress or “cytomorbidity”, as distinct from cytotoxicity or loss of viability.

Methods

A simple rapid bioassay is presented for antiviral drug screening using Vero E6 cells and inhibition of SARS-CoV-2 induced cytopathic effects (CPE) measured using crystal violet staining. We use high cell density for cytotoxicity assays, and low cell density for cytomorbidity assays.

Results

The assay clearly illustrated the anti-viral activity of remdesivir, a drug known to inhibit SARS-CoV-2 replication. In contrast, nitazoxanide, oleuropein, cyclosporine A and ribavirin all showed no ability to inhibit SARS-CoV-2 CPE. Hydroxychloroquine, cyclohexamide, didemnin B, γ-mangostin and linoleic acid were all able to inhibit viral CPE at concentrations that did not induce cytotoxicity. However, these drugs inhibited CPE at concentrations that induced cytomorbidity, indicating non-specific anti-viral activity.

Conclusions

We describe the methodology for a simple in vitro drug screening assay that identifies potential anti-viral drugs via their ability to inhibit SARS-CoV-2-induced CPE. The additional growth assay illustrated how several drugs display anti-viral activity at concentrations that induce cytomorbidity. For instance, hydroxychloroquine showed anti-viral activity at concentrations that slow cell growth, arguing that its purported in vitro anti-viral activity arises from non-specific impairment of cellular activities. The cytomorbidity assay can therefore rapidly exclude potential false positives.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12985-021-01587-z.

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.

2-Hydroxyimino-6-aza-pyrimidine nucleosides: synthesis, DFT calculations, and antiviral evaluations

Synthesis, DFT calculations, and antiviral evaluation of a series of novel 2-hydroxyimino-6-aza-pyrimidine ribonucleosides is reported. The hydrogen bonding between the C²N–OH moiety and N³–H and/or N³ moieties shapes the pyrimidine nucleoside as purine.

Study of Antiviral Efficiency of Oxidized Dextrans In Vitro and In Vivo

Antiviral efficiency of oxidized dextrans (OD) with different molecular weights and oxidation degree (OD40min, OD70min, OD40max, and OD70 max) was studied in vitro and in vivo. Dextrans OD40max and OD70max prevented the development of the cytopathic effect of influenza A(H1N1)pdm09 virus in more than 50% MDCK cells vs. control (no OD). Four intranasal doses of OD40min, OD40max, and OD70min and one intranasal dose of OD70max before infection of BALB/c mice with A(H1N1)pdm09 influenza virus significantly reduced mortality and prolonged life span in comparison with controls receiving saline. These and our previous data attest to clear-cut preventive effect of OD in influenza infection.

Evaluation of cell viability dyes in antiviral assays with RNA viruses that exhibit different cytopathogenic properties

Studies were conducted to determine the performance of four dyes in assessing antiviral activities of compounds against three RNA viruses with differing cytopathogenic properties. Dyes included alamarBlue® measured by absorbance (ALB-A) and fluorescence (ALB-F), neutral red (NR), Viral ToxGlo™ (VTG), and WST-1. Viruses were chikungunya, dengue type 2, and Junin, which generally cause 100, 80-90, and 50% maximal cytopathic effect (CPE), respectively, in Vero or Vero 76 cells Compounds evaluated were 6-azauridine, BCX-4430, 3-deazaguanine, EICAR, favipiravir, infergen, mycophenolic acid (MPA), ribavirin, and tiazofurin. The 50% virus-inhibitory (EC50) values for each inhibitor and virus combination did not vary significantly based on the dye used. However, dyes varied in distinguishing the vitality of virus-infected cultures when not all cells were killed by virus infection. For example, VTG uptake into dengue-infected cells was nearly 50% when visual examination showed only 10-20% cell survival. ALB-A measured infected cell viability differently than ALB-F as follows: 16% versus 32% (dengue-infected), respectively, and 51% versus 72% (Junin-infected), respectively. Cytotoxicity (CC50) assays with dyes in uninfected proliferating cells produced similar CC50 values for EICAR (1.5-8.9μM) and MPA (0.8-2.5μM). 6-Azauridine toxicity was 6.1-17.5μM with NR, VTG, and WST-1, compared to 48-92μM with ALB-A and ALB-F (P<0.001). Curiously, the CC50 values for 3-deazaguanine were 83-93μM with ALB-F versus 2.4-7.0μM with all other dyes including ALB-A (P<0.001). Overall, ALB minimized the toxicities detected with these two inhibitors. Because the choice of dyes affected CC50 values, this impacted on the resulting in vitro selectivity indexes (calculated as CC50/EC50 ratio).

Fibroblast Viability after Storage at 20 °C in Milk, Hank's Balanced Salt Solution and Coconut Water

The objective of this study was to evaluate the effectiveness of various storage media at 20 °C in maintaining the viability of human periodontal ligament fibroblasts (HPLF) over time. HPLF were maintained at 20 °C in skim milk (SM), whole milk (WM), freshly prepared Hank's balanced salt solution (HBSS), Save-A-Tooth(r), natural coconut water (NCW), coconut water industrialized (ICW) and tap water (negative control) for 3, 6, 24, 48, 72, 96 and 120 h. Cells maintained in Minimal Essential Medium (MEM-37) at 37 °C served as a positive control. Cell viability was determined by MTT assay. Statistical analysis was performed by Kruskal-Wallis test and Scheffe test (α = 5%). From 24 h, NCW was significantly better in maintaining cell viability than all other tested storage media (p<0.05). SM and WM were significantly better than HBSS for up to 72 h. Save-A-Tooth(r) and ICW were the worst conservation storage media. In conclusion, the effectiveness of the tested storage media to maintain the viability of the periodontal ligament cells was as follows, in a descending order: NCW > MEM-37> SM and IM> HBSS> ICW > Save-A-Tooth(r)> tap water.

Amantadine resistance among highly pathogenic avian influenza viruses (H5N1) isolated from India

Emergence of antiviral resistance among H5N1 avian influenza viruses is the major challenge in the control of pandemic influenza. Matrix 2 (M2) inhibitors (amantadine and rimantadine) and neuraminidase inhibitors (oseltamivir and zanamivir) are the two classes of antiviral agents that are specifically active against influenza viruses and are used for both treatment and prophylaxis of influenza infections. Amantadine targets the M2 ion channel of influenza A virus and interrupts virus life cycle through blockade of hydrogen ion influx. This prevents uncoating of the virus in infected host cells which impedes the release of ribonucleoprotein required for transcription and replication of virion in the nucleus. The present study was carried out to review the status of amantadine resistance in H5N1 viruses isolated from India and to study their replicative capability. Results of the study revealed resistance to amantadine in antiviral assay among four H5N1 viruses out of which two viruses had Serine 31 Asparagine (AGT-AAT i.e., S31N) mutation and two had Valine 27 Alanine (GTT-GCT i.e., V27A) mutation. The four resistant viruses not only exhibited significant difference in effective concentration 50% (EC50) values of amantadine hydrochloride from that of susceptible viruses (P < 0.0001) but also showed significant difference between two different types (S31N and V27A) of mutant viruses (P < 0.05). Resistance to amantadine could also be demonstrated in a simple HA test after replication of the viruses in MDCK cells in presence of amantadine. The study identifies the correlation between in vitro antiviral assay and presence of established molecular markers of resistance, the retention of replicative capacity in the presence of amantadine hydrochloride by the resistant viruses and the emergence of resistant mutations against amantadine among avian influenza viruses (H5N1) without selective drug pressure.

Determination of cytotoxicity of traditional Chinese medicine herbs, Rhizoma coptidis, Radix scutellariae, and Cortex phellodendri, by three methods

BACKGROUND

Many herbs are used in traditional Chinese medicine TCM) for treatment of infections but their properties, in particular, their effects on normal cells have received little attention. This study investigated the cytotoxic properties of three TCM herbs with potential use in prevention and treatment of ocular infections, including Acanthamoeba keratitis.

METHOD

The study investigated cytotoxic effects of the herbal extracts of Rhizoma coptidis, Radix scutellariae, and Cortex phellodendri on human corneal epithelial cells using trypan blue staining, MTT production, and flow cytometry. Differences between herbs were determined using repeated measures one-way analysis of variance, followed by paired t-tests where appropriate.

RESULTS

These three herbs appeared to lack cytotoxicity when tested with trypan blue and MTT, but flow cytometry revealed that R. coptidis led to cell membrane damage.

CONCLUSION

Lack of cytotoxicity of R. scutellariae and C. phellodendri extracts suggest that these are potentially suitable for use in ocular preparations. Only flow cytometry was able to accurately predict cytotoxic effects of extracts of TCM herbs on HCEC, demonstrating the importance of using a sensitive method of detection of cytotoxicity.

Inactivation of avian influenza virus, newcastle disease virus and goose parvovirus using solution of nano-sized scallop shell powder

Scallop shell powder produced by calcination process − the average diameter of the powder particles being 20 µm (SSP) − was further ground into nano-sized particles, with average diameter of 500 nm, here designated CaO-Nano. Solution of CaO-Nano could inactivate avian influenza virus within 5 sec, whereas the solution of SSP could not even after 1 hr incubation. CaO-Nano solution could also inactivate Newcastle disease virus and goose parvovirus within 5 sec and 30 sec, respectively. The virus-inactivating capacity (neutralizing index: NI>3) of the solution was not reduced by the presence of 20% fetal bovine serum. CaO-Nano solution seems to be a good candidate of materials for enhancement of biosecurity in farms.

Lassomycin, a ribosomally synthesized cyclic peptide, kills mycobacterium tuberculosis by targeting the ATP-dependent protease ClpC1P1P2

Languishing antibiotic discovery and flourishing antibiotic resistance have prompted the development of alternative untapped sources for antibiotic discovery, including previously uncultured bacteria. Here, we screen extracts from uncultured species against Mycobacterium tuberculosis and identify lassomycin, an antibiotic that exhibits potent bactericidal activity against both growing and dormant mycobacteria, including drug-resistant forms of M. tuberculosis, but little activity against other bacteria or mammalian cells. Lassomycin is a highly basic, ribosomally encoded cyclic peptide with an unusual structural fold that only partially resembles that of other lasso peptides. We show that lassomycin binds to a highly acidic region of the ClpC1 ATPase complex and markedly stimulates its ATPase activity without stimulating ClpP1P2-catalyzed protein breakdown, which is essential for viability of mycobacteria. This mechanism, uncoupling ATPase from proteolytic activity, accounts for the bactericidal activity of lassomycin.

Antivirally active ribavirin analogues--4,5-disubstituted 1,2,3-triazole nucleosides: biological evaluation against certain respiratory viruses and computational modelling

BACKGROUND

Ribavirin is a broad-spectrum antiviral agent that derives some of its activity from inhibition of cellular inosine monophosphate dehydrogenase (IMPDH), resulting in lower guanosine triphosphate (GTP) levels. Here we report the biological activities of three ribavirin analogues.

METHODS

Antiviral activities of test compounds were performed by in vitro cytopathic effect inhibition assays against influenza A (H1N1, H3N2 and H5N1), influenza B, measles, parainfluenza type 3 (PIV-3) and respiratory syncytial viruses. Compounds were modelled into the ribavirin 5'-monophosphate binding site of the crystallographic structure of the human type II IMPDH (hIMPDH2) ternary complex. Effects of compounds on intracellular GTP levels were performed by strong anion exchange HPLC analysis.

RESULTS

Of the three compounds evaluated, the 5-ethynyl nucleoside (ETCAR) exhibited virus-inhibitory activities (at 1.2-20 μM, depending upon the virus) against most of the viruses, except for weak activity against PIV-3 (62 μM). Antiviral activity of ETCAR was similar to ribavirin; however, cytotoxicity of ETCAR was greater than ribavirin. Replacing the 5-ethynyl group with a 5-propynyl or bromo substituent (BrCAR) considerably reduced antiviral activity. Computational studies of ternary complexes of hIMPDH2 enzyme with 5'-monophosphates of the compounds helped rationalize the observed differences in biological activity. All compounds suppressed GTP levels in cells; additionally, BrCAR suppressed adenosine triphosphate and elevated uridine triphosphate levels.

CONCLUSIONS

Three compounds related to ribavirin inhibited IMPDH and had weak to moderate antiviral activity. Cytotoxicity adversely affected the antiviral selectivity of ETCAR. As with ribavirin, reduction in intracellular GTP may play a role in virus inhibition.

Structural basis for a class of nanomolar influenza A neuraminidase inhibitors

The influenza virus neuraminidase (NA) is essential for the virus life cycle. The rise of resistance mutations against current antiviral therapies has increased the need for the development of novel inhibitors. Recent efforts have targeted a cavity adjacent to the catalytic site (the 150-cavity) in addition to the primary catalytic subsite in order to increase specificity and reduce the likelihood of resistance. This study details structural and in vitro analyses of a class of inhibitors that bind uniquely in both subsites. Crystal structures of three inhibitors show occupation of the 150-cavity in two distinct and novel binding modes. We believe these are the first nanomolar inhibitors of NA to be characterized in this way. Furthermore, we show that one inhibitor, binding within the catalytic site, offers reduced susceptibility to known resistance mutations via increased flexibility of a pendant pentyloxy group and the ability to pivot about a strong hydrogen-bonding network.

Exploration of binary virus-host interactions using an infectious protein complementation assay

A precise mapping of pathogen-host interactions is essential for comprehensive understanding of the processes of infection and pathogenesis. The most frequently used techniques for interactomics are the yeast two-hybrid binary methodologies, which do not recapitulate the pathogen life cycle, and the tandem affinity purification mass spectrometry co-complex methodologies, which cannot distinguish direct from indirect interactions. New technologies are thus needed to improve the mapping of pathogen-host interactions. In the current study, we detected binary interactions between influenza A virus polymerase and host proteins during the course of an actual viral infection, using a new strategy based on trans-complementation of the Gluc1 and Gluc2 fragments of Gaussia princeps luciferase. Infectious recombinant influenza viruses that encode a Gluc1-tagged polymerase subunit were engineered to infect cultured cells transiently expressing a selected set of Gluc2-tagged cellular proteins involved in nucleocytoplasmic trafficking pathways. A random set and a literature-curated set of Gluc2-tagged cellular proteins were tested in parallel. Our assay allowed the sensitive and accurate recovery of previously described interactions, and it revealed 30% of positive, novel viral-host protein-protein interactions within the exploratory set. In addition to cellular proteins involved in the nuclear import pathway, components of the nuclear pore complex such as NUP62 and mRNA export factors such as NXF1, RMB15B, and DDX19B were identified for the first time as interactors of the viral polymerase. Gene silencing experiments further showed that NUP62 is required for efficient viral replication. Our findings give new insights regarding the subversion of host nucleocytoplasmic trafficking pathways by influenza A viruses. They also demonstrate the potential of our infectious protein complementation assay for high-throughput exploration of influenza virus interactomics in infected cells. With more infectious reverse genetics systems becoming available, this strategy should be widely applicable to numerous pathogens.

In vitro antiviral activity of Brazilian plants (Maytenus ilicifolia and Aniba rosaeodora) against bovine herpesvirus type 5 and avian metapneumovirus

CONTEXT

Medicinal plants are well known for their use in traditional folk medicine as treatments for many diseases including infectious diseases.

OBJECTIVE

Six Brazilian medicinal plant species were subjected to an antiviral screening bioassay to investigate and evaluate their biological activities against five viruses: bovine herpesvirus type 5 (BHV-5), avian metapneumovirus (aMPV), murine hepatitis virus type 3, porcine parvovirus and bovine respiratory syncytial virus.

MATERIALS AND METHODS

The antiviral activity was determined by a titration technique that depends on the ability of plant extract dilutions (25 or 2.5 µg/mL) to inhibit the viral induced cytopathic effect and the extracts' inhibition percentage (IP).

RESULTS

Two medicinal plant species showed potential antiviral activity. The Aniba rosaeodora Ducke (Lauraceae) extract had the best results, with 90% inhibition of viral growth at 2.5 µg/mL when the extract was added during the replication period of the aMPV infection cycle. The Maytenus ilicifolia (Schrad.) Planch. (Celastraceae) extracts at a concentration of 2.5 µg/mL exhibited antiviral activity during the attachment phase of BHV-5 (IP = 100%).

DISCUSSION AND CONCLUSION

The biomonitored fractionation of the active extracts from M. ilicifolia and A. rosaeodora could be a potential tool for identifying their active compounds and determining the exact mechanism of action.

D282, a non-nucleoside inhibitor of influenza virus infection that interferes with de novo pyrimidine biosynthesis

BACKGROUND

The discovery of novel influenza virus inhibitors remains an important priority in light of the emergence of drug-resistant viruses. Toward this end, a library of over 6,000 compounds was tested for antiviral activity.

METHODS

Strains of influenza virus were evaluated by cytopathic effect (CPE) inhibition and virus yield reduction assays. Intracellular nucleoside triphosphate pools were analysed by strong anion exchange HPLC. Dihydroorotate dehydrogenase inhibition assays were conducted. Influenza virus-infected mice were treated for 5 days with D282.

RESULTS

A non-nucleoside, 4-[(4-butylphenyl)amino]-2-methylene-4-oxo-butanoic acid (D282), was discovered that inhibited influenza A and B virus CPE by 50% at 6-31 μM (giving selectivity indices of >13 to >67, based on cytotoxicity of >400 µM in stationary cell cultures). Ribavirin (positive control) was active at 14-44 µM (yielding selectivity indices of >9 to >29, with >400 µM toxicity). D282 and ribavirin inhibited virus yield by 90% at 9.5 ±3.3 and 10.8 ±3.2 µM, respectively. The antiviral activity of D282 in vitro was reversed by addition of uridine, cytidine and orotic acid. D282 exhibited an uncompetitive inhibition of mouse liver dihydroorotate dehydrogenase (inhibitor constant [Ki] of 2.3 ±0.9 µM, Michaelis constant [Km] of 150 ±16 µM). Because cellular pyrimidine biosynthesis was inhibited, D282-treated cells had decreased uridine triphosphate and cytidine triphosphate levels. D282 (≤100 mg/kg/day) failed to prevent death of mice infected with influenza.

CONCLUSIONS

D282 was active against influenza A and B viruses by inhibiting de novo pyrimidine biosynthesis. Although effective in vitro, the compound, like others in its class, was devoid of antiviral activity in infected mice.

Treatment of oseltamivir-resistant influenza A (H1N1) virus infections in mice with antiviral agents

Influenza A/Mississippi/03/2001 (H1N1) and A/Hong Kong/2369/2009 (H1N1) viruses containing the neuraminidase gene mutation H275Y (conferring resistance to oseltamivir) were adapted to mice and evaluated for suitability as models for lethal infection and antiviral treatment. The viral neuraminidases were resistant to peramivir and oseltamivir carboxylate but sensitive to zanamivir. Similar pattern of antiviral activity were seen in MDCK cell assays. Lethal infections were achieved in mice with the two viruses. Oral oseltamivir at 100 and 300mg/kg/day bid for 5day starting at -2h gave 30% and 60% protection from death, respectively, due to the A/Mississippi/03/2001 infection. Intraperitoneal treatments with zanamivir at 30 and 100mg/kg/day starting at -2h gave 60% and 90% protection, respectively. Neither compound at <300mg/kg/day protected mice when treatments began at +24h. Amantadine was effective at 10, 30, and 100mg/kg/day, rimantadine was protective at 10 and 30mg/kg/day (highest dose tested), and ribavirin was active at 30 and 75mg/kg/day, with survival ranging from 60-100% for oral treatments initiated at -2h. For treatments begun at +24h, amantadine was protective at 30 and 100mg/kg/day, rimantadine showed efficacy at 10 and 30mg/kg/day, and ribavirin was active at 75mg/kg/day, with 60-100% survival per group. In the A/Hong Kong/2369/2009 infection, oral oseltamivir at 100 and 300mg/kg/day starting at -2h gave 50% and 70% protection from death, respectively. These infection models will be useful to study newly discovered anti-influenza virus agents and to evaluate compounds in combination.

Xanthones from Polygala karensium inhibit neuraminidases from influenza A viruses

The emergence of the H1N1 swine flu pandemic has the possibility to develop the occurrence of disaster- or drug-resistant viruses by additional reassortments in novel influenza A virus. In the course of an anti-influenza screening program for natural products, 10 xanthone derivatives (1-10) were isolated by bioassay-guided fractionation from the EtOAc-soluble extract of Polygala karensium. Compounds 1, 3, 5, 7, and 9 with a hydroxy group at C-1 showed strong inhibitory effects on neuraminidases from various influenza viral strains, H1N1, H9N2, novel H1N1 (WT), and oseltamivir-resistant novel H1N1 (H274Y) expressed in 293T cells. In addition, these compounds reduced the cytopathic effect of H1N1 swine influenza virus in MDCK cells. Our results suggest that xanthones from P. karensium may be useful in the prevention and treatment of disease by influenza viruses.

Novel, real-time cell analysis for measuring viral cytopathogenesis and the efficacy of neutralizing antibodies to the 2009 influenza A (H1N1) virus

A novel electronic cell sensor array technology, the real-time cell analysis (RTCA) system, was developed to monitor cell events. Unlike the conventional methods labeling the target cells with fluorescence, luminescence, or light absorption, the RTCA system allows for label-free detection of cell processes directly without the incorporation of labels. Here, we used this new format to measure the cytopathic effect (CPE) of the 2009 influenza A (H1N1) virus and the efficacy of neutralizing antibodies in human sera to this virus. The real-time dynamic monitoring of CPE was performed on MDCK cell cultures infected with the H1N1 virus, ranging from 5.50×10² to 5.50×10⁷ copies/mL. The resulting CPE kinetic curves were automatically recorded and were both time and viral load dependent. The CPE kinetics were also distinguishable between different H1N1 stains, as the onset of CPE induced by the A/Shanghai/37T/2009 H1N1 virus was earlier than that of the A/Shanghai/143T/2009 H1N1 virus. Furthermore, inhibition of H1N1 virus-induced CPE in the presence of human specific anti-sera was detected and quantified using the RTCA system. Antibody titers determined using this new neutralization test correlated well with those obtained independently via the standard hemagglutination inhibition test. Taken together, this new CPE assay format provided label-free and high-throughput measurement of viral growth and the effect of neutralizing antibodies, illustrating its potential in influenza vaccine studies.

Development of a high-throughput human rhinovirus infectivity cell-based assay for identifying antiviral compounds

Asthma and chronic obstructive pulmonary disease exacerbations are associated with human rhinovirus (HRV) lung infections for which there are no current effective antiviral therapies. To date, HRV infectivity of cells in vitro has been measured by a variety of biochemical and immunological methods. This paper describes the development of a high-throughput HRV infectivity assay using HeLa OHIO cells and a chemiluminescent-based ATP cell viability system, CellTiter-Glo from Promega, to measure HRV-induced cytopathic effect (CPE). This CellTiter-Glo assay was validated with standard antiviral agents and employed to screen AstraZeneca compounds for potential antiviral activity. Compound potency values in this assay correlated well with the quantitative RT-PCR assay measuring HRV infectivity and replication in human primary airway epithelial cells. In order to improve pan-HRV screening capability, compound potency was also measured in the CellTiter-Glo assay with a combination of 3 different HRV serotypes. This HRV serotype combination assay could be used to identify quickly compounds with desirable broad spectrum antiviral activity.

Identification of phenanthroindolizines and phenanthroquinolizidines as novel potent anti-coronaviral agents for porcine enteropathogenic coronavirus transmissible gastroenteritis virus and human severe acute respiratory syndrome coronavirus

The discovery and development of new, highly potent anti-coronavirus agents and effective approaches for controlling the potential emergence of epidemic coronaviruses still remains an important mission. Here, we identified tylophorine compounds, including naturally occurring and synthetic phenanthroindolizidines and phenanthroquinolizidines, as potent in vitro inhibitors of enteropathogenic coronavirus transmissible gastroenteritis virus (TGEV). The potent compounds showed 50% maximal effective concentration (EC₅₀) values ranging from 8 to 1468 nM as determined by immunofluorescent assay of the expression of TGEV N and S proteins and by real time-quantitative PCR analysis of viral yields. Furthermore, the potent tylophorine compounds exerted profound anti-TGEV replication activity and thereby blocked the TGEV-induced apoptosis and subsequent cytopathic effect in ST cells. Analysis of the structure-activity relations indicated that the most active tylophorine analogues were compounds with a hydroxyl group at the C14 position of the indolizidine moiety or at the C3 position of the phenanthrene moiety and that the quinolizidine counterparts were more potent than indolizidines. In addition, tylophorine compounds strongly reduced cytopathic effect in Vero 76 cells induced by human severe acute respiratory syndrome coronavirus (SARS CoV), with EC₅₀ values ranging from less than 5 to 340 nM. Moreover, a pharmacokinetic study demonstrated high and comparable oral bioavailabilities of 7-methoxycryptopleurine (52.7%) and the naturally occurring tylophorine (65.7%) in rats. Thus, our results suggest that tylophorine compounds are novel and potent anti-coronavirus agents that may be developed into therapeutic agents for treating TGEV or SARS CoV infection.

Gene expression signature-based screening identifies new broadly effective influenza a antivirals

Classical antiviral therapies target viral proteins and are consequently subject to resistance. To counteract this limitation, alternative strategies have been developed that target cellular factors. We hypothesized that such an approach could also be useful to identify broad-spectrum antivirals. The influenza A virus was used as a model for its viral diversity and because of the need to develop therapies against unpredictable viruses as recently underlined by the H1N1 pandemic. We proposed to identify a gene-expression signature associated with infection by different influenza A virus subtypes which would allow the identification of potential antiviral drugs with a broad anti-influenza spectrum of activity. We analyzed the cellular gene expression response to infection with five different human and avian influenza A virus strains and identified 300 genes as differentially expressed between infected and non-infected samples. The most 20 dysregulated genes were used to screen the connectivity map, a database of drug-associated gene expression profiles. Candidate antivirals were then identified by their inverse correlation to the query signature. We hypothesized that such molecules would induce an unfavorable cellular environment for influenza virus replication. Eight potential antivirals including ribavirin were identified and their effects were tested in vitro on five influenza A strains. Six of the molecules inhibited influenza viral growth. The new pandemic H1N1 virus, which was not used to define the gene expression signature of infection, was inhibited by five out of the eight identified molecules, demonstrating that this strategy could contribute to identifying new broad anti-influenza agents acting on cellular gene expression. The identified infection signature genes, the expression of which are modified upon infection, could encode cellular proteins involved in the viral life cycle. This is the first study showing that gene expression-based screening can be used to identify antivirals. Such an approach could accelerate drug discovery and be extended to other pathogens.

A novel small molecule inhibitor of hepatitis C virus entry

Small molecule inhibitors of hepatitis C virus (HCV) are being developed to complement or replace treatments with pegylated interferons and ribavirin, which have poor response rates and significant side effects. Resistance to these inhibitors emerges rapidly in the clinic, suggesting that successful therapy will involve combination therapy with multiple inhibitors of different targets. The entry process of HCV into hepatocytes represents another series of potential targets for therapeutic intervention, involving viral structural proteins that have not been extensively explored due to experimental limitations. To discover HCV entry inhibitors, we utilized HCV pseudoparticles (HCVpp) incorporating E1-E2 envelope proteins from a genotype 1b clinical isolate. Screening of a small molecule library identified a potent HCV-specific triazine inhibitor, EI-1. A series of HCVpp with E1-E2 sequences from various HCV isolates was used to show activity against all genotype 1a and 1b HCVpp tested, with median EC50 values of 0.134 and 0.027 µM, respectively. Time-of-addition experiments demonstrated a block in HCVpp entry, downstream of initial attachment to the cell surface, and prior to or concomitant with bafilomycin inhibition of endosomal acidification. EI-1 was equally active against cell-culture adapted HCV (HCVcc), blocking both cell-free entry and cell-to-cell transmission of virus. HCVcc with high-level resistance to EI-1 was selected by sequential passage in the presence of inhibitor, and resistance was shown to be conferred by changes to residue 719 in the carboxy-terminal transmembrane anchor region of E2, implicating this envelope protein in EI-1 susceptibility. Combinations of EI-1 with interferon, or inhibitors of NS3 or NS5A, resulted in additive to synergistic activity. These results suggest that inhibitors of HCV entry could be added to replication inhibitors and interferons already in development.

INIBIÇÃO DOS LENTIVÍRUS DE PEQUENOS RUMINANTES POR DROGAS ANTIVIRAIS

RESUMO Inibidores da enzima transcriptase reversa e da protease foram avaliados quanto ao seu efeito inibitório na replicação do Vírus da Artrite Encefalite Caprina (CAEV) cepa CAEV Cork e do vírus Maedi-Visna (MVV) cepa K1514 cultivados em células fibroblásticas de caprinos. Os fármacos utilizados foram: lamivudina, didanosina, estavudina, zidovudina, efavirenz, atazanavir e lopinavir/ritonavir. A maior concentração utilizada para lamivudina, estavudina, zidovudina e efavirenz foi 500 ?M, para atazanavir foi 50 ?M e 5,0 ?M para lopinavir/r e didanosina. A atividade antiviral in vitro foi pesquisada por meio da avaliação da viabilidade celular através da redução do MTT e pela pesquisa de inibição dos efeitos citopáticos (CPE) dos vírus. A replicação dos vírus só não foi completamente bloqueada pelos inibidores de protease (IP) atazanavir e lopinavir/r enquanto os demais apresentaram eficácia antiviral significativa em diferentes concentrações. Os IP juntamente com o efavirenz, não mostraram atividade antiviral quando foram avaliados pela técnica de redução do MTT. Esses dados indicam que os fármacos inibidores da transcriptase reversa lamivudina, didanosina, estavudina e zidovudina são eficazes na inibição in vitro dos lentivírus de pequenos ruminantes.

Lack of efficacy of aurintricarboxylic acid and ethacrynic acid against vaccinia virus respiratory infections in mice

BACKGROUND

Aurintricarboxylic acid (ATA) and ethacrynic acid (ECA) have been reported to exhibit antiviral activity against vaccinia virus infections in cell culture by inhibiting early and late gene transcription, respectively. The purpose of this work was to determine if these inhibitors would effectively treat vaccinia virus infections in mice, which has not previously been studied.

METHODS

ECA was investigated by cell culture plaque reduction assay for the inhibition of cowpox and vaccinia virus infections to clarify issues regarding its potency and selectivity. Mice infected intranasally with vaccinia virus were treated by intraperitoneal route twice daily for 5 days with ATA (10 and 30 mg/kg/day) and ECA (15 and 30 mg/kg/day) or once daily for 2 days with cidofovir (100 mg/kg/day).

RESULTS

ECA caused 50% inhibition of virus plaque formation at 20-79 muM in four cultured cell lines, with 50% cytotoxicity at 84-173 muM, giving low (1.3-4.2) selectivity index values. Preliminary toxicity tests in uninfected mice indicated that ATA and ECA were both overtly toxic at 100 mg/kg/day. No protection from mortality was afforded by treatment of vaccinia virus infections with ATA or ECA, but 100% survival was achieved in the cidofovir group. ATA- and ECA-treated mice died significantly sooner than placebo-treated animals, indicating that these compounds exacerbated the infection.

CONCLUSIONS

Both ATA and ECA lack antiviral potency and selectivity in cell culture. The compounds were ineffective in treating mice at intraperitoneal doses of <or=30 mg/kg/day. These compounds do not appear to have potential for the treatment of poxvirus infections in vivo.

In vitro cell-toxicity screening as an alternative animal model for coral toxicology: effects of heat stress, sulfide, rotenone, cyanide, and cuprous oxide on cell viability and mitochondrial function

The logistics involved in obtaining and maintaining large numbers of corals hampers research on the toxicological effects of environmental contaminants for this ecologically and economically important taxon. A method for creating and culturing single-cell suspensions of viable coral cells was developed. Cell segregation/separation was based on specific cell densities and resulting cell cultures were viable for at least 2 mos. Low-density cells lacking symbiotic zooxanthallae and rich in mitochondria were isolated and cultured for toxicity studies. Cells were exposed to differing degrees or concentrations of heat stress, rotenone, cyanide, sulfide, and cuprous oxide. Cells were assayed for mitochondrial membrane potential using the fluorescent probe, JC-9, and for overall viability using the MTT/formazan spectrophotometric viability assay. Significant differences were observed between controls and treatments and the efficacy of this method was validated; only 2 cm(2) of tissue was required for a seven-point concentration-exposure series.

Influenza virus assays based on virus-inducible reporter cell lines

BACKGROUND

Virus-inducible reporter genes have been used as the basis of virus detection and quantitation assays for a number of viruses. A strategy for influenza A virus-induction of a reporter gene was recently described. In this report, we describe the extension of this strategy to influenza B virus, the generation of stable cell lines with influenza A and B virus-inducible reporter genes, and the use of these cells in various clinically relevant viral assays. Each of the cell lines described herein constitutively express an RNA transcript that contains a reporter gene coding region flanked by viral 5￠- and 3￠-untranslated regions (UTR) and therefore mimics an influenza virus genomic segment. Upon infection of the cells with influenza virus the virus-inducible reporter gene segment (VIRGS) is replicated and transcribed by the viral polymerase complex resulting in reporter gene expression.

FINDINGS

Reporter gene induction occurs after infection with a number of laboratory strains and clinical isolates of influenza virus including several H5N1 strains. The induction is dose-dependent and highly specific for influenza A or influenza B viruses.

CONCLUSIONS

These cell lines provide the basis of simple, rapid, and objective assays that involve virus quantitation such as determination of viral titer, assessment of antiviral susceptibility, and determination of antibody neutralization titer. These cell lines could be very useful for influenza virus researchers and vaccine manufacturers.

A recombinant, infectious human parainfluenza virus type 3 expressing the enhanced green fluorescent protein for use in high-throughput antiviral assays

The ability to rescue an infectious, recombinant, negative-stranded, RNA virus from a complementary DNA (cDNA) clone, has led to new opportunities for measuring viral replication from a viral expressed reporter gene. In this study, the enhanced green fluorescent protein (EGFP) gene was inserted into the human parainfluenza virus type 3 (HPIV-3) antigenome and a recombinant, infectious virus was rescued. Maximum EGFP expression levels, measured by fluorescence, were seen at day 3. Comparison of a 3-day, viral expressed EGFP fluorescence assay to a 7-day, neutral red assay, based on complete cell destruction in virus infected MA-104 cells, yielded Z'-factor values of 0.83 and 0.70, respectively. A 3-day, endpoint EGFP-based antiviral assay and a 7-day, endpoint neutral red based antiviral assay were run in parallel to establish antiviral sensitivity profiles of 23 compounds based on selective index (SI) values. Using an SI threshold of 10, the EGFP-based antiviral assay had a sensitivity of 100% and a specificity of 54%. Thus, the use of an EGFP-based antiviral assay for testing potential antiviral compounds against HPIV-3 in a high-throughput format may be justified.

In vitro anti-influenza screening of several Euphorbiaceae species: structure of a bioactive Cyanoglucoside from Codiaeum variegatum

A bio-guided screening against influenza A virus (FLUAV) was carried out with seven Euphorbiaceae species. The results showed that chromatographic fractions from Phyllantus niruri, Euphorbia pulcherrima and Codiaeum variegatum had relevant anti-FLUAV activity, although only chromatographical subfractions from C. variegatum kept the activity. From this plant, the active compound against FLUAV was isolated. Its structure was assigned as 2-(3,4,5)-trihydroxy-6-hydroxymethyltetrahydropyran-2-yloxymethyl)acrylonitrile (1) on the basis of NMR, mass spectrometry and X-ray diffraction analysis. The compound displayed virucidal activity without impairment of haemagglutination properties of the used virus strain. This is the first report indicating antiviral activity of a cyanoglucoside.

Potent immunogenicity and efficacy of a universal influenza vaccine candidate comprising a recombinant fusion protein linking influenza M2e to the TLR5 ligand flagellin

The recognition of specific pathogen associated molecular patterns (PAMPs) by members of the Toll-like receptor (TLR) family is critical for the activation of the adaptive immune response. Thus, incorporation of PAMPs into vaccines should result in more potent, protective antigen-specific responses in the absence of adjuvants or complex formulations. Here we describe an influenza A vaccine that is refractory to the genetic instability of hemagglutinin and neuraminidase and includes a trigger of the innate immune response to enhance immunogenicity and efficacy. A recombinant protein comprising the TLR5 ligand flagellin fused to four tandem copies of the ectodomain of the conserved influenza matrix protein M2 (M2e) was expressed in Escherichia coli and purified to homogeneity. This protein, STF2.4xM2e, retained TLR5 activity and displayed the protective epitope of M2e defined by a monoclonal antibody, 14C2. Mice immunized with STF2.4xM2e in aqueous buffer, without adjuvants or other formulation additives, developed potent M2e-specific antibody responses that were quantitatively and qualitatively superior to those observed with M2e peptide delivered in alum. The antibody response was dependent on the physical linkage of the antigen to flagellin and recognized the epitope defined by monoclonal antibody 14C2, which has been shown to protect mice from challenge with influenza A virus. Moreover, immunization with STF2.4xM2e at a dose of 0.3 microg per mouse protected mice from a lethal challenge with influenza A virus, and significantly reduced weight loss and clinical symptoms. These data demonstrate that the linkage of specific TLR ligand with influenza M2e yields a vaccine candidate that offers significant promise for widespread protection against multiple influenza A virus strains.

NIAID resources for developing new therapies for severe viral infections

Severe viral infections, including hemorrhagic fever and encephalitis, occur throughout the world, but are most prevalent in developing areas that are most vulnerable to infectious diseases. Some of these can also infect related species as illustrated by the threatened extinction of gorillas by Ebola infection in west and central Africa. There are no safe and effective treatments available for these serious infections. In addition to the logistical difficulties inherent in developing a drug for infections that are sporadic and occur mainly in the third world, there is the overwhelming barrier of no hope for return on investment to encourage the pharmaceutical industry to address these unmet medical needs. Therefore, the National Institute of Allergy and infectious Disease (NIAID) has developed and supported a variety of programs and resources to provide assistance and lower the barrier for those who undertake these difficult challenges. The primary programs relevant to the development of therapies for severe viral infections are described and three case studies illustrate how they have been used. In addition, contact information for accessing these resources is supplied.

Synthesis, antiviral and antitumor activity of 2-substituted-5-amidino-benzimidazoles

We have prepared a set of heterocyclic benzimidazole derivatives bearing amidino substituents at C-5 of benzimidazole ring, by introducing various heterocyclic nuclei (pyridine, N-methyl-pyrrole or imidazole) at C-2, and evaluated their antitumor and antiviral activities. The most pronounced antiproliferative activity was shown with compounds 6 and 9, having imidazolinylamidino-substituent. Interestingly, all compounds show noticeable selectivity toward breast cancer cell line MCF-7. The most distinct and selective antiviral activity toward coxsackieviruses and echoviruses was observed with compounds having pyridine ring at C-2. Especially interesting was fairly strong activity of 4 and 8 toward adenoviruses, which could be considered as leads against adenoviral replication.

Anti-influenza virus activities of 4-[(1,2-dihydro-2-oxo-3H-indol-3-ylidene)amino]-N-(4,6-dimethyl-2-pyrimidin-2-yl)benzenesulphonamide and its derivatives

4-[(1,2-Dihydro-2-oxo-3H-indol-3-ylidene)amino]-N-(4,6-dimethyl-2-pyrimidinyl)-benzenesulphonamide (SPIII-5H) and related compounds were tested for antiviral activity against influenza A (H1N1, H3N2, and H5N1) and B viruses in Madin Darby canine kidney (MDCK) cell culture. Among the compounds tested, SPIII-5H and four derivatives (5-chloro [SPill-5Cl], 5-bromo [SPIII-5Br], 5-methyl [SPIII-5Me] and N-acetyl [SPIII-NA]) showed similar antiviral potencies, with only the 5-fluoro (SPIII-5F) derivative being ineffective. Fifty percent effective concentration (EC50) values were determined in cytopathic effect (CPE) inhibition assays quantified by neutral red dye uptake. By this method, the active compounds were inhibitory to the H1N1 strain of influenza A at 2.7-5.2 microg/ml, to the H3N2 strain of influenza A at 13.8-26.0 microg/ml, to the H5N1 strain of influenza A at 3.1-6.3 microg/ml and to influenza B at 7.7-11.5 microg/ml. Confirmatory virus yield reduction studies against influenza A (H1N1) virus demonstrated antiviral activity (90% inhibition) at concentrations of 2-10 microg/ml. No cytotoxic effects were evident in actively growing uninfected cells or stationary monolayers at 100 microg/ml. Potencies of the compounds were similar to those of ribavirin, but much less than those of oseltamivir carboxylate against the various viruses. Time-of-addition studies indicated the compounds inhibited an early step in the virus replication cycle, probably virus adsorption/penetration, and no virucidal activity was evident. The basic molecule is amenable to diverse chemical modifications, which may improve water solubility and antiviral potency.

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

The spread of highly pathogenic avian influenza across geographical and species barriers underscores the increasing need for novel antivirals to compliment vaccination and existing antiviral therapies. Identification of new antiviral lead compounds depends on robust primary assays for high-throughput screening (HTS) of large compound libraries. We have developed a cell-based screen for potential influenza antivirals that measures the cytopathic effect (CPE) induced by influenza virus (A/Udorn/72, H3N2) infection in Madin Darby canine kidney (MDCK) cells using the luminescent-based CellTiter Glo system. This 72 h assay is validated for HTS in 384-well plates and performs more consistently and reliably than methods using neutral red, with Z values>0.8, signal-to-background>30 and signal-to-noise>10. In a blinded pilot screen (n=10,781) at 10 microM concentration, four compounds (with previously demonstrated efficacy against influenza) inhibited viral-induced CPE by >50%, with EC50/CC50 values comparable to those determined by other cell-based assays, thereby validating this assay accuracy and ability to simultaneously evaluate compound cellular availability and/or toxicity. This assay is translatable for screening against other influenza strains, such as avian flu, and may facilitate identification of antivirals for other viruses that induce CPE, such as West Nile or Dengue.

Evaluation of antiviral activity of phenolic compounds and derivatives against rabies virus

Human rabies is a viral disease with a great impact on public health, mainly on account of its fatal course in the majority of cases. Despite the well-established prophylaxis by immunization, rabies is believed to be responsible for 40,000-70,000 human deaths per year, mostly in endemic areas. Palliative support and experimental protocols to avoid death have been employed with no expressive results, with the exception of a recent human case of recovery from rabies. No antiviral drugs are currently available to fight against this infection. In combination with the prophylaxis, an antiviral drug would be useful for human rabies treatment, providing enhanced protection against the encephalitis caused by the virus. Phenolic compounds are derived from the secondary plant metabolism, although they can also be obtained by synthetic processes. Many studies have shown a great range of pharmacological effects for these substances, including vasodilatation, antiallergenic, antiinflammatory and antiviral properties, among others. In this study, the potential in-vitro anti-rabies activity of 24 synthetic phenolic compounds was evaluated using McCoy cells and PV rabies strain. The cytotoxicity (CC50) was assayed by the MTT method and the antiviral activity (IC50) was estimated by the inhibition of viral cytopathic effects. Isoprinosine and ketamine were used as positive controls. The tested compounds showed selectivity indices (SI=CC50/IC50) ranging from 1.0 to 3.9. Six phenolic compounds failed to inhibit the cytopathic effect to any degree, and four showed SI > or = 3.0. According to these results, some probable structure-activity relationships are suggested. It was observed that the presence of free hydroxyl and ether groups influenced the anti-rabies activity. However, additional studies are required to establish these relationships.

SIRC-CVS CYTOTOXICITY TEST: AN ALTERNATIVE FOR PREDICTING RODENT ACUTE SYSTEMIC TOXICITY

An in vitro crystal violet staining method using the rabbit cornea-derived cell line (SIRC-CVS) has been developed as an alternative to predict acute systemic toxicity in rodents. Seventy-nine chemicals, the in vitro cytotoxicity of which was already reported by the Multicenter Evaluation of In vitro Toxicity (MEIC) and ICCVAM/ECVAM, were selected as test compounds. The cells were incubated with the chemicals for 72 hrs and the IC(50) and IC(35) values (microg/mL) were obtained. The results were compared to the in vivo (rat or mouse) "most toxic" oral, intraperitoneal, subcutaneous and intravenous LD(50) values (mg/kg) taken from the RTECS database for each of the chemicals by using Pearson's correlation statistics. The following parameters were calculated: accuracy, sensitivity, specificity, prevalence, positive predictability, and negative predictability. Good linear correlations (Pearson's coefficient; r>0.6) were observed between either the IC(50) or the IC(35) values and all the LD(50) values. Among them, a statistically significant high correlation (r=0.8102, p<0.001) required for acute systemic toxicity prediction was obtained between the IC(50) values and the oral LD(50) values. By using the cut-off concentrations of 2,000 mg/kg (LD(50)) and 4,225 microg/mL (IC(50)), no false negatives were observed, and the accuracy was 84.8%. From this, it is concluded that this method could be used to predict the acute systemic toxicity potential of chemicals in rodents.

Use of electric cell-substrate impedance sensing as a tool for quantifying cytopathic effect in influenza A virus infected MDCK cells in real-time

Resulting from its subjective nature, cytopathic effect (CPE) due to virus infection in cell culture has long been difficult to quantify. This report illustrates the use of electric cell-substrate impedance sensing (ECIS) for monitoring the progression of CPE due to influenza A virus infection. ECIS monitors the impedance of a non-invasive ac current flowing through cell culture medium by gold film electrodes placed on the surface of the culture dish. As cultured cells attach and spread onto the electrodes, the current is impeded proportional to the number of attached cells, the number of tight junctions between cells and the shortness in distance between the cells and the substratum. In the case at hand, a healthy monolayer of cells was insulted with influenza A virus infection and exhibited a characteristic rounded cell morphology and cell detachment. These effects resulted in reduced impedance, which was monitored with ECIS. Since data obtained through ECIS are both quantitative and in real-time, it was possible to monitor continuously cell behavior during infection. This, in turn, allowed for a more detailed and comprehensive data set to analyze. More importantly, through ammonium chloride treatment of cells, it was also shown that ECIS may be exploited to examine a treatment's effect on the reduction of resistance because of its antiviral activity. Thus, ECIS may be a powerful approach for screening antiviral compounds quantitatively in a real-time fashion.

Virus-inducible reporter genes as a tool for detecting and quantifying influenza A virus replication

The use of influenza A virus-inducible reporter gene segments in detecting influenza A virus replication was investigated. The RNA polymerase I promoter/terminator cassette was used to express RNA transcripts encoding green fluorescence protein or firefly luciferase flanked by the untranslated regions of the influenza A/WSN/33 nucleoprotein (NP) segment. Reporter gene activity was detected after reconstitution of the influenza A virus polymerase complex from cDNA or after virus infection, and was influenza A virus-specific. Reporter gene activity could be detected as early as 6 h post-infection and was virus dose-dependent. Inhibitory effects of antibodies or amantadine could be detected and quantified rapidly, providing a means of not only identifying influenza A virus-specific replication, but also of determining the antigenic subtype as well as antiviral drug susceptibility. Induction of virus-specific reporter genes provides a rapid, sensitive method for detecting virus replication, quantifying virus titers and assessing antiviral sensitivity as well as antigenic subtype.