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

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

An extract from Taxodium distichum targets hemagglutinin- and neuraminidase-related activities of influenza virus in vitro.

Influenza virus remains an emerging virus and causes pandemics with high levels of fatality. After screening different plant extracts with potential anti-influenza activity, a water extract of Taxodium distichum stems (TDSWex) showed excellent activity against influenza viruses. The EC50 of TDSWex was 0.051 ± 0.024 mg/mL against influenza virus A/WSN/33. TDSWex had excellent antiviral efficacy against various strains of human influenza A and B viruses, particularly oseltamivir-resistant clinical isolates and a swine-origin influenza strain. We observed that the synthesis of viral RNA and protein were inhibited in the presence of TDSWex. The results of the time-of-addition assay suggested that TDSWex inhibited viral entry and budding. In the hemagglutination inhibition assay, TDSWex inhibited the hemagglutination of red blood cells, implying that the extract targeted hemagglutin-related functions such as viral entry. In the attachment and penetration assay, TDSWex showed antiviral activity with EC50s of 0.045 ± 0.026 and 0.012 ± 0.003 mg/mL, respectively. In addition, TDSWex blocked neuraminidase activity. We conclude that TDSWex has bimodal activities against both hemagglutinin and neuraminidase during viral replication.

Screening and evaluation of commonly-used anti-influenza Chinese herbal medicines based on anti-neuraminidase activity.

Anti-influenza Chinese herbal medicines (anti-flu CHMs) have advantages in preventing and treating influenza virus infection. Despite various data on antiviral activities of some anti-flu CHMs have been reported, most of them could not be compared using the standard evaluation methods for antiviral activity. This situation poses an obstacle to a wide application of anti-flu CHMs. Thus, it was necessary to develop an evaluation method to estimate antiviral activities of anti-flu CHMs. In the present study, we searched for anti-flu CHMs, based on clinic usage, to select study objects from commonly-used patented anti-flu Chinese medicines. Then, a neuraminidase-based bioassay, optimized and verified by HPLC method by our research group, was adopted to detect antiviral activities of selected 26 anti-flu CHMs. Finally, eight of these herbs, including Coptidis Rhizoma, Isatidis Folium, Lonicerae Flos, Scutellaria Radix, Cyrtomium Rhizome, Houttuynia Cordata, Gardeniae Fructus, and Chrysanthemi Indici Flos, were shown to have strong antiviral activities with half maximal inhibitory concentration (IC50) values being 2.02 to 6.78 mg·mL-1 (expressed as raw materials). In contrast, the IC50 value of positive control peramivir was 0.38 mg·mL-1. Considering the extract yields of CHMs, the active component in these herbs may have a stronger antiviral activity than peramivir, suggesting that these herbs could be further researched for active compounds. Moreover, the proposed neuraminidase-based bioassay was high-throughput and simple and could be used for evaluation and screening of anti-flu CHMs as well as for their quality control.

Anti-influenza activities of polyphenols from the medicinal mushroom Phellinus baumii.

Five polyphenols were isolated from the ethanolic extract of the fruiting bodies of Phellinus baumii. These compounds were identified by various spectroscopic methods as hispidin, hypholomine B, inoscavin A, davallialactone, and phelligridin D. All compounds inhibited noncompetitively H1N1, H5N1, and H3N2 neuraminidase activity and reduced the amount of virally-induced cytopathic effect (CPE) according to an MDCK cell-based assay.

[Screening bioactive compounds inhibiting influenza virus from isatidis radix by ultrafiltration mass spectrometry].

In vitro neuraminidase inhibition assays and ultrafiltration liquid chromatography with diodearray detector coupled to time of flight mass spectrometer (UPLC-DAD-TOF-MS) were combined to screen bioactive compounds inhibiting neuraminidase from Isatidis Radix. By comparing the compounds from Isatidis Radix before and after ultrafiltration, we found that arginine, goitrin and adenosinea can bind with neuraminidase, and the binding degree of the three compounds were (36.23 +/- 1.12)%, (32.54 +/- 1.02)% and (9.38 +/- 0.47)%, respectively. The IC50 of arginine and goitrin were (1.16 +/- 0.02), (1.20 +/- 0.02) g x L(-1), respectively. While the IC50 of adenosinea was higher than 500 g x L(-1). The results showed that arginine and goitrin might be the main compounds with antiviral activity of Isatidis Radix. This study may provide a useful method for the screening of bioactive compounds and quality control of Isatidis Radix.

Synthesis and anti-influenza virus activity of 4-oxo- or thioxo-4,5-dihydrofuro[3,4-c]pyridin-3(1H)-ones.

A target-free approach was applied to discover anti-influenza viral compounds, where influenza infected Madin-Darby canine kidney cells were treated 7500 different small organic chemicals individually and reduction of virus-induced cytopathic effect was measured. One of the hit compounds was (Z)-1-((5-fluoro-1H-indol-3-yl)methylene)-6-methyl-4-thioxo-4,5-dihydrofuro[3,4-c]pyridin-3(1H)-one (15a) with half-maximal effective concentrations of 17.4-21.1µM against influenza A/H1N1, A/H3N2 and B viruses without any cellular toxicity at 900µM. To investigate the structure-activity relationships, two dozens of the hit analogs were synthesized. Among them, 15g, 15j, 15q, 15s, 15t and 15x had anti-influenza viral activity comparable or superior to that of the initial hit. The anti-influenza viral compounds efficiently suppressed not only viral protein level of the infected cells but also production of viral progeny in the culture supernatants in a dose-dependent manner. Based on a mode-of-action study, they did not affect virus entry or RNA replication. Instead, they suppressed viral neuraminidase activity. This study is the first to demonstrate that dihydrofuropyridinones could serve as lead compounds for the discovery of alternative influenza virus inhibitors.

Crystallographic fragment screening and structure-based optimization yields a new class of influenza endonuclease inhibitors.

Seasonal and pandemic influenza viruses continue to be a leading global health concern. Emerging resistance to the current drugs and the variable efficacy of vaccines underscore the need for developing new flu drugs that will be broadly effective against wild-type and drug-resistant influenza strains. Here, we report the discovery and development of a class of inhibitors targeting the cap-snatching endonuclease activity of the viral polymerase. A high-resolution crystal form of pandemic 2009 H1N1 influenza polymerase acidic protein N-terminal endonuclease domain (PAN) was engineered and used for fragment screening leading to the identification of new chemical scaffolds binding to the PAN active site cleft. During the course of screening, binding of a third metal ion that is potentially relevant to endonuclease activity was detected in the active site cleft of PAN in the presence of a fragment. Using structure-based optimization, we developed a highly potent hydroxypyridinone series of compounds from a fragment hit that defines a new mode of chelation to the active site metal ions. A compound from the series demonstrating promising enzymatic inhibition in a fluorescence-based enzyme assay with an IC50 value of 11 nM was found to have an antiviral activity (EC50) of 11 µM against PR8 H1N1 influenza A in MDCK cells.

Synthesis and biological evaluation of purine 2'-fluoro-2'-deoxyriboside ProTides as anti-influenza virus agents.

2'-Fluoro-2'-deoxyguanosine has been reported to have potent anti-influenza virus activity in vitro and in vivo. Herein we describe the synthesis and biological evaluation of 6-modified 2'-fluoro-2'-deoxyguanosine analogues and their corresponding phosphoramidate ProTides as potential anti-influenza virus agents. Whereas the parent nucleosides were devoid of antiviral activity in two different cellular assays, the 5'-O-naphthyl(methoxy-L-alaninyl) ProTide derivatives of 6-O-methyl-2'-fluoro-2'-deoxyguanosine, 6-O-ethyl-2'-fluoro-2'-deoxyguanosine, and 2'-deoxy-2'-fluoro-6-chloroguanosine, and the 5'-O-naphthyl(ethoxy-L-alaninyl) ProTide of 6-O-ethyl-2'-fluoro-2'-deoxyguanosine displayed antiviral EC(99) values of ~12 µM. The antiviral results are supported by metabolism studies. Rapid conversion into the L-alaninyl metabolite and then 6-modified 2'-fluoro-2'-deoxyguanosine 5'-monophosphate was observed in enzymatic assays with yeast carboxypeptidase Y or crude cell lysate. Evidence for efficient removal of the 6-substituent on the guanine part was provided by enzymatic studies with adenosine deaminase, and by molecular modeling of the nucleoside 5'-monophosphates in the catalytic site of a model of ADAL1, thus indicating the utility of the double prodrug concept.

[Screening based on response surface methodology of multi-fractions traditional Chinese medicine with anti-influenza virus neuraminidase activity: take shuanghuanglian injection as an example].

This study aimed to establish a novel method to screen out the combined components of multi-fractions traditional Chinese medicine (TCM), so that the internal relationship between multi-ingredients could be objectively assessed and the proportioning ratio could be optimized. Taking antiviral effect on neuraminidase activity of influenza virus as the evaluating indicator and using Box-Behnken response surface methodology, the main effective ingredients of Shuanghuanglian injection (SHL) were screened. Meanwhile, the relationship between active ingredients was discussed. Taking SHL as a comparison, the optimum proportioning ratio was predicted. The results indicated that chlorogenic acid, cryptochlorogenic acid, caffeic acid and baicalin have comparatively strong antiviral activity against influenza virus. Moreover, antagonistic action existed between chlorogenic acid and cryptochlorogenic acid, whereas synergistic action between caffeic acid and other components. The optimum proportioning ratio resulted from fitted model is: chlorogenic acid, cryptochlorogenic acid, caffeic acid and baicalin (107 microg x mL(-1) : 279 microg x mL(-1) : 7.99 microg x mL(-1) : 92 microg x mL(-1)). The antiviral activity of the recombined components is stronger than that of SHL, which was consistent with the experiment results (P < 0.05). Box-Behnken response surface methodology has the advantages of general-screening, high-performance and accurate-prediction etc, which is appropriate for screening the combined components of multi-fractions TCM and the optimization of the proportioning ratio. The proposed method can serve as a technological support for the development of modern multi-fractions TCM.

Characterization of compounds and potential neuraminidase inhibitors from the n-butanol extract of Compound Indigowoad Root Granule using ultrafiltration and liquid chromatography-tandem mass spectrometry.

The liquid chromatography-tandem mass spectrometry (LC-MS/MS) methods were used to identify the pharmacologically active n-butanol extract from Compound Indigowoad Root Granule. As a result, eighteen compounds belonging to various structural classes such as nucleosides, purines, flavonoids and amino acid were unambiguously identified. Then an in vitro neuraminidase (NA) inhibition assay was carried out to examine the inhibitory activity of the standard samples and extracts on NA. After which, ultrafiltration liquid chromatography with photodiode array detection coupled to electrospray ionization tandem mass spectrometry (ultrafiltration LC-MS/MS) was used to study NA inhibitory activity of standard flavones and n-butanol extract of Compound Indigowoad Root Granule. This method is highly selective and sensitive, and it could be used for characterization of bioactive compounds and botanical extracts. The result provides some enlightenment for the explanation of the antiviral activity of Compound Indigowoad Root Granule and some guidance for natural anti-influenza medicine development.

Characteristic of alkylated chalcones from Angelica keiskei on influenza virus neuraminidase inhibition.

As part of our ongoing effort to develop influenza virus neuraminidase (NA) inhibitors from various medicinal plants, we utilized bioassay-guided fractionation to isolated six alkylated chalcones (1-6) from Angelica keiskei. Xanthokeistal A (1) emerged as new compound containing the rare alkyl substitution, 6,6-dimethoxy-3-methylhex-2-enyl. When we tested the ability of these individual alkyl substituted chalcones to inhibit influenza virus NA hydrolysis, we found that 2-hydroxy-3-methyl-3-butenyl alkyl (HMB) substituted chalcone (3, IC(50)=12.3 µM) showed most potent inhibitory activity. The order of potency of substituted alkyl groups on for NA inhibition was HMB>6-hydroxyl-3,7-dimethyl-octa-2,7-dienyl>dimethylallyl>geranyl. All NA inhibitors screened were found to be reversible noncompetitive inhibitors.

In vivo and in vitro antiviral effects of berberine on influenza virus.

OBJECTIVE: To explore the potential effects of berberine on influenza virus infection both in vitro and in vivo. METHODS: In vitro anti-influenza virus assays were performed by cytopathogenic effect and neuraminidase assays in Madin Darby canine kidney cells. In vivo anti-influenza virus assays were performed on the viral pneumonia model of mice. The numbers of mice that died within day 2 to day 14 postinfection were recorded to calculate the mortality. On days 2, 4, and 6, the viral titers in the lungs were determined by hemagglutination assay; hematoxylin/eosin staining was used to assess the pathogenic changes of lung tissues; the concentrations of tumor necrosis factor-alpha (TNF-α) and monocyte specific chemoattractant molecule (MCP-1) were measured by radio immunoassay or enzyme-linked immunosorbent assay; the concentrations of nitric oxide (NO) and inducible nitric oxide synthetase (iNOS) were detected by colorimetric method; reverse transcription polymerase chain reaction was used to detect the mRNA level of TNF-α and MCP-1. RESULTS: Berberine showed inhibitory effects on cytopathogenic effects and neuraminidase activity of virus, with the therapeutic index 9.69. In vivo, berberine decreased mice mortality from 90% to 55%, reduced virus titers in the lungs on day 2 postinfection (P<0.05). The lung histology scores were 1.50 ± 0.67, 4.50 ± 1.00, and 5.50 ± 1.00 in the berberine group on days 2, 4, and 6, respectively, which were significantly reduced compared to 2.17 ± 0.22, 6.83 ± 0.44, and 8.50 ± 0.33 in the infected group (P<0.05). The productions of NO and iNOS were repressed by berberine compared with those in the infected group (P<0.01). The transcription and expression of TNF-α were inhibited by berberine on day 4 (P<0.01) and day 6 (P<0.05), and those of MCP-1 were inhibited on day 6 (P<0.01) compared with the infected group. CONCLUSIONS: Berberine exhibited antiviral effects on the influenza virus both in vitro and in vivo. The possible therapeutic mechanism of berberine on influenza-induced viral pneumonia might be inhibiting the virus infection, as well as improving the pathogenic changes by repressing inflammatory substances release.

Evaluation of the antiviral drug susceptibility of influenza viruses in Italy from 2004/05 to 2009/10 epidemics and from the recent 2009 pandemic.

Antiviral monitoring of influenza viruses circulating in Italy has been carried out since 2007 by the National Influenza Centre (NIC), using both phenotypic and sequence-based assays. Here, we report results of the susceptibility evaluation to neuraminidase (NA) inhibitors (NAIs, zanamivir and oseltamivir) and adamantanes of nearly 300 influenza type A and B seasonal viruses isolated in Italy during six recent seasons, together with over 30 pandemic (H1N1) 2009 virus strains. The present work is the first such study conducted in Italy, aimed to develop national data on antiviral drug profile and to establish a nationwide surveillance programme on antiviral susceptibility. Sequencing of the NA gene was undertaken either to confirm the phenotypic findings or to identify any NA change, in potentially resistant viruses (outliers), which might be associated with reduced susceptibility to NAIs. The 50% inhibitory concentration values (IC(50)s) showed slightly different sensitivities of the seasonal Italian isolates to the two NAI drugs, depending on the specific NA subtype. We found mean zanamivir IC(50)s of 0.74, 1.33 and 7 nM, and oseltamivir IC(50)s of 0.67, 2.34 and 30.1 nM for the N2, N1 and B NAs, respectively. The pandemic (H1N1) 2009 viruses showed IC(50)values overall comparable to the seasonal N1 viruses from previous years, showing mean zanamivir IC(50)s of 1.02 nM and mean oseltamivir IC(50)s of 2.82 nM. Oseltamivir resistance was found in a total of 19 seasonal N1viruses of 2007/2008 and 2008/2009, and in three pandemic (H1N1) 2009 strains. A gradual increase of resistance to adamantanes was observed among the N2 viruses isolated in recent seasons; no resistant viruses were found among the seasonal N1 strains, whereas all the pandemic (H1N1) 2009 isolates analysed were resistant to the M2 blockers.

[Agglutinated activity bioassay method for the determination of antivirus potency of Banlangen granula].

To establish a bioassay method and quality standard of Banlangen granula, agglutinated activity assay was used in the analysis of the traditional Chinese medicine, Banlangen granula. It showed that masculined effect could be picked up effectively and the products quality of different pharmaceutical factories and different batch numbers from the same factory could be revealed conveniently, accurately, quickly and directly with this method (valence value was between 2 and 11). The established bioassay method had a good reproducibility with RSD = 2%. The dependablity of the activity of red cell agglutination and restrainting influenza virus NA was conspicuous (r2 = 0.878 3). In conclusion, this bioassay method is suitable to control and evaluate the quality of Banlangen granula. Thus the method may provide a simple and effective technique in supervising and examining the quality of other traditional Chinese medicine.

Pharmacophore modeling, quantitative structure-activity relationship analysis, and shape-complemented in silico screening allow access to novel influenza neuraminidase inhibitors.

Neuraminidase (NA) enzyme is one of the valid targets against influenza viruses. With this in mind, the pharmacophoric space of influenza NA was explored using three sets of diverse inhibitors. Subsequently, genetic algorithm and multiple linear regression analysis were employed to select optimal combinations of pharmacophoric models and 2D descriptors capable of yielding self-consistent and predictive quantitative structure-activity relationships (QSARs) against 181 training compounds. The optimal QSAR equations were validated against 43 external test compounds with r(2)(PRESS) values ranging from 0.488 to 0.591. Interestingly, five orthogonal pharmacophores emerged in the optimal QSAR equations suggesting the existence of several distinct ligand/NA binding modes within the NA binding pocket. The resulting pharmacophores were complemented with tight shape constraints and employed as three-dimensional (3D) search queries against the National Cancer Institute (NCI) list of compounds. Several hits exhibited potent inhibitory activities against NA. The highest ranking hit demonstrated an in vitro IC(50) value of 1.8 muM. Docking studies supported the binding modes suggested by our pharmacophore/QSAR analysis.

In vitro evaluation of neuraminidase inhibitors using the neuraminidase-dependent release assay of hemagglutinin-pseudotyped viruses.

For the treatment of influenza virus infections, neuraminidase inhibitors (NAIs) that prevent the release of virus particles have been effective against most influenza strains. Several neuraminidase (NA) assays are available for the evaluation of NAIs. To understand the NAI functions under physiological conditions, assays mimicking viral particle release should be useful. We have constructed retrovirus-based reporter viruses that are pseudotyped with hemagglutinin (HA) glycoprotein by transfection of producer cells using plasmids expressing retroviral gag-pol, influenza HA, NA, and firefly luciferase genes. Similarly to the life cycle of influenza viruses, the release of pseudotype viruses also requires neuraminidase functions. This requirement was used to develop an assay to evaluate NAI activities by measuring inhibition of pseudotype virus production at different NAI concentrations. The pseudotype virus release assay was used to determine the IC(50) values of Oseltamivir carboxylate, Zanamivir, and the novel phosphonate congeners of Oseltamivir against N1 group neuraminidases and their H274Y Oseltamivir carboxylate-resistant mutants. The deduced IC(50) values obtained using the release assay correlated with those determined using the fluorogenic substrate 2'-(4-methylumbelliferyl)-alpha-d-N-acetylneuraminic acid (MUNANA) and also correlated with the infectivity results.

Un nuevo y potente inhibidor de la neuraminidasa para el tratamiento de las infecciones gripales / Peramivir. A new and potent neuraminidase inhibitor for the treatment of influenza

No disponible

[On the constituents and biological activities of some Nepalese medicinal plants].

The chemical constituents of medicinal plants which have been used in Ayurvedic and Tibetan system of medicines in Nepal were examined. From 21 species consisting of 13 genera of the plants, 121 new compounds, whose structures are shown in Charts (1 to 13), were isolated mainly in our laboratory. Some of the compounds and their related ones showed several biological activities.