Sodium Polyoxotungstate Inhibits the Replication of Influenza Virus by Blocking the Nuclear Import of vRNP

Both pandemic and seasonal influenza are major health concerns, causing significant mortality and morbidity. Current influenza drugs primarily target viral neuraminidase and RNA polymerase, which are prone to drug resistance. Polyoxometalates (POMs) are metal cation clusters bridged by oxide anions. They have exhibited potent anti-tumor, antiviral, and antibacterial effects. They have remarkable activity against various DNA and RNA viruses, including human immunodeficiency virus, herpes simplex virus, hepatitis B and C viruses, dengue virus, and influenza virus. In this study, we have identified sodium polyoxotungstate (POM-1) from an ion channel inhibitor library. In vitro, POM-1 has been demonstrated to have potent antiviral activity against H1N1, H3N2, and oseltamivir-resistant H1N1 strains. POM-1 can cause virion aggregation during adsorption, as well as endocytosis. However, the aggregation is reversible; it does not interfere with virus adsorption and endocytosis. Our results suggest that POM-1 exerts its antiviral activity by inhibiting the nuclear import of viral ribonucleoprotein (vRNP). This distinct mechanism of action, combined with its wide range of efficacy, positions POM-1 as a promising therapeutic candidate for influenza treatment and warrants further investigation.

Synthesis and anti-HIV-1 activity evaluation of Keggin-type polyoxometalates with amino acid as organic cations

Polyoxometalates (POMs), as a class of multinuclear metal oxygen clusters, have promising biological activities. And their amino acid derivatives will lead to better pharmacological activity by the diversity in structures and properties. With reference to the anti-HIV-1 activities of PM-19 (K7PTi2W10O40) and its pyridinium derivatives, a series of novel Keggin-type POMs with amino acid as organic cations (A7PTi2W10O40) were synthesized by hydrothermal synthetic method. The final products were characterized by 1H NMR, Elemental analyzes and single crystal X-ray diffraction. All the synthesized compounds were obtained in the yields of 44.3-61.7% and evaluated the cytotoxicity and anti-HIV-1 activity in vitro. Compared with the reference compound PM-19, the target compounds had a lower toxicity to TZM-bl cells and a higher inhibitory activity against HIV-1. Among them, compound A3 showed higher anti-HIV-1 activity with IC50 of 0.11 nM than that of PM-19 with 4.68 nM. This study demonstrated that combination of Keggin-type POMs and amino acids can be a new strategy to enhance the anti-HIV-1 biological activity of POMs. All results will be expected to helpful for developing more potent and effective HIV-1 inhibitors.

Anti-RNA virus activity of polyoxometalates

The anti-RNA virus activity of polyoxometalates (POM) is reviewed, with a special emphasis on the anti-respiratory virus activities. There are many causative agents of acute viral respiratory infections; and it is rather difficult to identify the relevant agent in a given case by rapid clinical means. During acute progress of infection before the definitive diagnosis is obtained physicians need to prescribe certain broad spectrum anti-viral drugs. A titanium containing polyoxotungstate, PM-523 exhibited potent anti-influenza virus (FluV) A and anti-respiratory syncytial virus (RSV) activities in vitro. Therapeutic effect of FluV A infected mice with aerosol inhalation of PM-523 was proven. A vanadium substituted polyoxotungstate, PM-1001 has antiviral activity against FluV A, RSV, parainfluenza virus (PfluV) type 2, Dengue fiver virus, HIV-1 and SARS coronavirus in vitro. Thus, POMs have been proven to be broad spectrum and non-toxic anti-RNA virus agents in both in vitro and in vivo experiments and are promising candidates for first-line therapeutics in acute respiratory diseases.

Synthesis, characterization and antiviral activity against influenza virus of a series of novel manganese-substituted rare earth borotungstates heteropolyoxometalates

A series of novel manganese-substituted mixed-valence rare earth borotungsto-heteropoly blues, Ln2H3[BW9(VI)W2(V)Mn(H2O)O39] x 12H2O (Ln(2), Ln = La, Ce, Pr, Nd, Sm, Eu and Gd), as well as their corresponding heteropoly acids (Ln(0)), have been prepared and characterized by cyclic voltammetry (CV), infrared (IR), ultraviolet (UV), thermal gravimetric (TG) and differential thermal (DTA) analysis, X-ray photoelectron spectroscopy (XPS) and electrochemistry. It's shown that the heteropoly blues anion in Ln(2) still retains the alpha-Keggin structure but with a slight distortion as heteropoly acids do, and Mn and W atoms distribute statistically in the whole molecular. At the same time, the cell toxicity and antiviral activity of these rare earth borotungstateheteropoly blues against influenza virus type A and type B in MDCK cells have been investigated using plaque reduction assay. The results elucidated that these complexes exhibit a significantly inhibitory activity and almost no cytotoxicity comparable with those obtained from virazole, and the anti-virus activity depend on the structure of these complexes.

Broad spectrum anti-RNA virus activities of titanium and vanadium substituted polyoxotungstates

Seven polyoxotungstates substituted with vanadium or titanium atoms were examined for their activity against Flaviviridae (Dengue fever virus, DFV), Orthomyxoviridae (influenza virus type A, fluV-A), Paramyxoviridae (respiratory syncytial virus, RSV, parainfluenza virus type 2, PfluV-2 and canine distemper virus, CDV) and Lentiviridae (human immunodeficiency virus type 1, HIV-1) families. Among the seven polyoxotungstates examined, PM-43 [K(5)[SiVW(11)O(40)]], PM-47 [K(7)[BVW(11)O(40)]], and PM-1001 [K(10)Na(VO)(3)(SbW(9)O(33))(2)]26H(2)O contained vanadium. PM-1002 had the same core structure of (VO)(3)(SbW(9)O(33))(2) as PM-1001; however, three V atoms of PM-1001 consisted of two V(IV) and one V(V) and those of PM-1002 consisted of three V(IV). On the other hand, PM-518 [[Et(2)NH(2)](7)[PTi(2)W(10)O(40)]], PM-520 [Pri(2)NH(2)](5)[PTiW(11)O(40)] and PM-523 [PriNH(3)](6)H[PTi(2)W(10)O(38)(O(2))(2)]H(2)O all contained titanium. All compounds showed broad spectrum antiviral activity against all viruses examined except for PMs-43, -518 and -523 which did not exhibit inhibitory activity at >/=50 microM against PfluV-2, CDV and DFV, respectively. All compounds were inhibitory against HIV replication at an EC(50) of less than 2.0 microM. Among them, PMs-1001 and -1002 showed the most potent inhibition. The compounds were not toxic for MDCK, HEp-2 and Vero cells at a concentration of 200 microM. For the exponentially growing MT-4 cells, the vanadium containing polyoxometalates (PMs-43, 47, 1001, 1002) showed toxicity at concentrations between 41 and 47 microM. On the other hand, titanium containing polyoxometalates (PMs-518, -520, -523) were not toxic at 100 microM. The mechanism of anti-HIV action of PM-1001 was analyzed: it affected the binding of HIV to the cell membrane and syncytium formation between HIV-infected and uninfected cells.

Antiviral activity of mixed-valence rare earth borotungstate heteropoly blues against influenza virus in mice

The acute and accumulated toxicity of the rare earth borotungstate heteropoly blues, HPB-2, Ce2H3[BW9(VI)W2(V)Mn(H2O)O39].12H2O, which is active against influenza virus in Kunming mice, were investigated in Kunming mice following oral and intraperitoneal administration. The activity of HPB-2 against influenza virus (FM1) in the mice was then investigated. HPB-2, given either orally (p.o.) or intraperitoneally (i.p.), was shown to have activity. HPB-2 was shown to be more effective than the positive control, ribavirin, and it was also found that i.p. administration was more effective than p.o. administration.

In vitro and in vivo assay systems for study of influenza virus inhibitors

Evaluation of potential influenza virus inhibitors may utilize multiple steps. First would be to determine if the viral target (e.g. influenza virus neuraminidase) being focused upon will be inhibited in the appropriate assay. Standard in vitro antiviral assays, used next in antiviral evaluations, may utilize inhibition of viral plaques, viral cytopathic effect (CPE), and viral hemagglutinin or other protein, with inhibition of viral yield used in follow-up evaluations. The CPE can be determined visually and by dye uptake. Animal models used for study of potential influenza virus inhibitors include the ferret, the laboratory mouse, and the chicken, with a variety of parameters used to indicate the severity of the infection and its inhibition by therapy. Multiple parameters are recommended in any in vivo antiviral evaluation. The ferret and the mouse infection models have been useful in studying the development of drug resistance and the relative virulence of drug-resistant viruses. The influenza mouse model has also been of value for the evaluation of immunomodulating effects of test compounds and for the study of the utility of antiviral drugs for use against influenza virus infections in the immunocompromised host. In considering the use of any animal model, species differences in drug pharmacology and metabolism must be taken into account. This review has described the systems which have been used most frequently by antiviral investigators, using, as examples, recent studies with the clinically approved influenza virus neuraminidase inhibitors oseltamivir and zanamivir.

The ribavirin analog ICN 17261 demonstrates reduced toxicity and antiviral effects with retention of both immunomodulatory activity and reduction of hepatitis-induced serum alanine aminotransferase levels

The demonstrated utility of the nucleoside analog ribavirin in the treatment of certain viral diseases can be ascribed to its multiple distinct properties. These properties may vary in relative importance in differing viral disease conditions and include the direct inhibition of viral replication, the promotion of T-cell-mediated immune responses via an enhanced type 1 cytokine response, and a reduction of circulating alanine aminotransferase (ALT) levels associated with hepatic injury. Ribavirin also has certain known toxicities, including the induction of anemia upon chronic administration. To determine if all these properties are linked, we compared the D-nucleoside ribavirin to its L-enantiomer (ICN 17261) with regard to these properties. Strong similarities were seen for these two compounds with respect to induction of type 1 cytokine bias in vitro, enhancement of type 1 cytokine responses in vivo, and the reduction of serum ALT levels in a murine hepatitis model. In contrast, ICN 17261 had no in vitro antiviral activity against a panel of RNA and DNA viruses, while ribavirin exhibited its characteristic activity profile. Importantly, the preliminary in vivo toxicology profile of ICN 17261 is significantly more favorable than that of ribavirin. Administration of 180 mg of ICN 17261 per kg of body weight to rats by oral gavage for 4 weeks generated substantial serum levels of drug but no observable clinical pathology, whereas equivalent doses of ribavirin induced a significant anemia and leukopenia. Thus, structural modification of ribavirin can dissociate its immunomodulatory properties from its antiviral and toxicologic properties, resulting in a compound (ICN 17261) with interesting therapeutic potential.

Antiviral properties of a series of 1,6-naphthyridine and 7, 8-dihydroisoquinoline derivatives exhibiting potent activity against human cytomegalovirus

A series of 1,6-naphthyridine (L. Chan, H. Jin, T. Stefanac, J. F. Lavallee, G. Falardeau, W. Wang, J. Bedard, S. May, and L. Yuen, J. Med. Chem. 42:3023-3025, 1999) and isoquinoline (L. Chan, H. Jin, T. Stefanac, W. Wang, J. F. Lavallee, J. Bedard, and S. May, Bioorg. Med. Chem. Lett. 9:2583-2586, 1999) analogues exhibiting a high level of anti-human cytomegalovirus (HCMV) activity were investigated in a series of studies aimed at better understanding the mechanism of action of some representatives of this class of compounds. In vitro antiviral profiling revealed that these compounds were active against a narrow spectrum of viruses, essentially the human herpesviruses and type 2 rhinovirus. In HCMV assays, a 39- to 223-fold lower 50% inhibitory concentration was obtained for compound A1 than for ganciclovir against strains AD 169 and Towne. In addition, ganciclovir, foscarnet, cidofovir, and BDCRB (2-bromo-5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole)-resistant HCMV strains remained susceptible to 1,6-naphthyridines and 7, 8-dihydroisoquinolines tested in this study, supporting the view that a novel mechanism of action could be involved. Drug combination studies showed a small but significant synergistic antiviral effect between compound B2 and ganciclovir. Cytotoxicity profiling of representative compounds under various cell growth conditions indicated a generally similar cytotoxic effect, relative to ganciclovir, in log-phase growing cells. However, in stationary cells, a relatively higher level of toxicity was observed than that for control compound. Effect of time of drug addition showed that the anti-HCMV activity of compound A1, ganciclovir, and cidofovir was lost at approximately the same time (72 h postinfection), indicating that the compound was affecting events at the early and late stage of virus replication. This interpretation is also supported by reduction of de novo synthesis of pp65 tegument protein and lack of any effect of the compound on viral adsorption. A reduction of the HCMV enhancer-promoter-directed luciferase expression was also observed in a stably transfected cell line when compound A1 was present at relatively high concentrations.

Approaches and strategies for the treatment of influenza virus infections

Influenza A and B viruses belong to the Orthomyxoviridae family of viruses. These viruses are responsible for severe morbidity and significant excess mortality each year. Infection with influenza viruses usually leads to respiratory involvement and can result in pneumonia and secondary bacterial infections. Vaccine approaches to the prophylaxis of influenza virus infections have been problematic owing to the ability of these viruses to undergo antigenic shift by exchanging genomic segments or by undergoing antigenic drift, consisting of point mutations in the haemagglutinin (HA) and neuraminidase (NA) genes as a result of an error-prone viral polymerase. Historically, antiviral approaches for the therapy of both influenza A and B viruses have been largely unsuccessful until the elucidation of the X-ray crystallographic structure of the viral NA, which has permitted structure-based drug design of inhibitors of this enzyme. In addition, recent advances in the elucidation of the structure and complex function of influenza HA have resulted in the discovery of a number of diverse compounds that target this viral protein. This review article will focus largely on newer antiviral agents including those that inhibit the influenza virus NA and HA. Other novel approaches that have entered clinical trials or been considered for their clinical utility will be mentioned.

Comparative study of the anti-human cytomegalovirus activities and toxicities of a tetrahydrofuran phosphonate analogue of guanosine and cidofovir

Cidofovir is the first nucleoside monophosphate analogue currently being used for the treatment of human cytomegalovirus (HCMV) retinitis in individuals with AIDS. Unfortunately, the period of therapy with the use of this compound may be limited due to the possible emergence of serious irreversible nephrotoxic effects. New drugs with improved toxicity profiles are needed. The goal of this study was to investigate the anticytomegaloviral properties and drug-induced toxicity of a novel phosphonate analogue, namely, (-)-2-(R)-dihydroxyphosphinoyl-5-(S)-(guanin-9'-yl-methyl) tetrahydrofuran (compound 1), in comparison with those of cidofovir. The inhibitory activities of both compounds on HCMV propagation in vitro were similar against the AD 169 and Towne strains, with 50% inhibitory concentrations ranging from 0.02 to 0.17 microgram/ml for cidofovir and < 0.05 to 0.09 microgram/ml for compound 1. A clinical HCMV isolate that was resistant to ganciclovir and that had a known mutation within the UL54 DNA polymerase gene and a cidofovir-resistant laboratory strain derived from strain AD 169 remained sensitive to compound 1, whereas their susceptibilities to ganciclovir and cidofovir were reduced by 33- and 10-fold, respectively. Both compound 1 and cidofovir exhibited equal potencies in an experimentally induced murine cytomegalovirus (MCMV) infection in mice, with a prevention or prolongation of mean day to death at dosages of 1.0, 3.2, and 10.0 mg/kg of body weight/day. In cytotoxicity experiments, compound 1 was found to be generally more toxic than cidofovir in cell lines Hs68, HFF, and 3T3-L1 (which are permissive for HCMV or MCMV replication) but less toxic than cidofovir in MRC-5 cells (which are permissive for HCMV replication). Drug-induced toxic side effects were noticed for both compounds in rats and guinea pigs in a 5-day repeated-dose study. In guinea pigs, a greater weight loss was noticed with cidofovir than with compound 1 at dosages of 3.0 and 10.0 mg/kg/day. An opposite effect was detected in rats, which were treated with the compounds at relatively high dosages (up to 100 mg/kg/day). Compound 1 and cidofovir were nephrotoxic in both rats and guinea pigs, with the epithelium lining the proximal convoluted tubules in the renal cortex being the primary target site. The incidence and the severity of the lesions were found to be dose dependent. The lesions observed were characterized by cytoplasm degeneration and nuclear modifications such as karyomegaly, the presence of pseudoinclusions, apoptosis, and degenerative changes. In the guinea pig model, a greater incidence and severity of lesions were observed for cidofovir than for compound 1 (P < 0.001) with a drug regimen of 10 mg/kg/day.

Oral administration of a prodrug of the influenza virus neuraminidase inhibitor GS 4071 protects mice and ferrets against influenza infection

We have recently described GS 4071, a carbocyclic transition-state analog inhibitor of the influenza virus neuraminidase, which has potent inhibitory activity comparable to that of 4-guanidino-Neu5Ac2en (GG167; zanamivir) when tested against influenza A virus replication and neuraminidase activity in vitro. We now report that GS 4071 is active against several strains of influenza A and B viruses in vitro and that oral GS 4104, an ethyl ester prodrug which is converted to GS 4071 in vivo, is active in the mouse and ferret models of influenza virus infection. Oral administration of 10 mg of GS 4104 per kg of body weight per day caused a 100-fold reduction in lung homogenate viral titers and enhanced survival in mice infected with influenza A or B viruses. In ferrets, a 25-mg/kg dose of GS 4104 given twice daily reduced peak viral titers in nasal washings and eliminated constitutional responses to influenza virus infection including fever, increased nasal signs (sneezing, nasal discharge, mouth breathing), and decreased activity. Consistent with our demonstration that the parent compound is highly specific for influenza virus neuraminidases, no significant drug-related toxicity was observed after the administration of oral dosages of GS 4104 of up to 800 mg/kg/day for 14 days in nonclinical toxicology studies with rats. These results indicate that GS 4104 is a novel, orally active antiviral agent with the potential to be used for the prophylaxis and treatment of influenza A and B virus infections.

Approaches to antiviral chemotherapy for acute respiratory infections

The causative agents of acute respiratory infections (ARI) in infants and children are mostly thought to be viruses. Some ARI in adult patients may be caused by bacteria but most often the causes are virus infections. When ARI affect immunocompromised patients or the elderly the mortality rates are significantly higher than in immunocompetent individuals. Many types of viruses cause ARI. Among them, influenza viruses A and B and respiratory syncytial virus (RSV) are thought to be the most important because of the severity of illness after infection and their high communicability in the human population. Recently, several novel antiviral drugs against ARI have been developed and some are proceeding in clinical trials. This review covers current investigations into antiviral compounds targeted at several points in the virus life-cycle. This includes PM-523, which broadly inhibits ortho- and paramyxo-viruses, two neuraminidase inhibitors for influenza virus, neutralizing antibody to RSV and chimeric soluble ICAM-1-IgA molecules targeted against rhinoviruses.

Inhibition of influenza virus infections in mice by GS4104, an orally effective influenza virus neuraminidase inhibitor

The carbocyclic transition state sialic acid analog GS4071 ([3R,4R,5S]-4-acetamido-5-amino-3-[1-ethylpropoxy]-1-cyclohexane-1 -carboxylic acid), a potent influenza virus neuraminidase inhibitor, was highly inhibitory to influenza A/NWS/33 (H1N1), A/Victoria/3/75 (H3N2), A/Shangdong/09/93 (H3N2) and B/Hong Kong/5/72 viruses in Madin Darby canine kidney (MDCK) cells. The 50% effective concentrations in these experiments ranged from 1.8 to 59.5 microM, with no cytotoxicity evident at 1000 microM, using inhibition of viral cytopathic effect determined visually and by neutral red dye uptake. The ethyl ester prodrug of GS4071, GS4104, administered by oral gavage (p.o.), had significant inhibitory effects on infections in mice induced by these viruses. Antiviral effects were seen as prevention of death, increase in mean day to death, inhibition of decline of arterial oxygen saturation, lessened lung consolidation and inhibition of infectious virus recovered from the lungs. No toxicity was seen in dosages up to 100 mg/kg/day (highest evaluated). Comparison experiments run versus the influenza A (H1N1) virus-induced infection using GS4104, GS4071 and the neuraminidase inhibitor zanamivir (GG167, 4-guanidino-Neu5Ac2en), all administered p.o., indicated a 10-fold or greater potency for inhibiting the infection by GS4104. The minimum effective dosage for GS4104 was 0.1 mg/kg/day, with the compound administered twice daily for 5 days beginning 4 h pre-virus exposure. Oral therapy with GS4104 could be delayed from 48 to at least 60 h after exposure of mice to influenza A (H1N1) virus and still render a significant antiviral effect, the time of delay being dependent on the viral challenge dose. Intranasal instillation of GS4071 and GG167 to mice infected with influenza virus was highly inhibitory to the infection, the minimum effective dosages to significantly prevent death being 0.01 mg/kg/day for GS4071 and 0.1 mg/kg/day for GG167. Caging of infected mice treated with 10 mg/kg/day of GS4104 with infected saline-treated animals did not transfer any influenza-inhibitory effect to the latter animals. These data provide strong evidence of the potential of orally administered GS4104 for treatment of influenza A and B virus infections in humans.

Influenza virus resistance to neuraminidase inhibitors

The recent reports from Hong Kong of an avian influenza virus which caused the death of six people has served to remind us of the constant threat of pandemics posed by influenza. Recently, structure-based drug design has resulted in the discovery of a new class of antiviral agents which specifically target the influenza virus neuraminidase. Two neuraminidase inhibitors are currently undergoing clinical evaluation for the prevention and treatment of influenza virus infection in man. Here we review the results of in vitro and in vivo studies relating to the potential development of resistance to this new class of compounds.