5'-Homoaristeromycin. Synthesis and antiviral activity against orthopox viruses

An efficient synthesis of 5'-homoaristeromycin has been developed. This permitted an extensive antiviral analysis, which found potent activity toward vaccinia, cowpox, and monkeypox viruses. For comparative purposes, 5'-homoadenosine was made available by a newly designed route and found to be inactive.     

Properties of the recombinant TNF-binding proteins from variola, monkeypox, and cowpox viruses are different

Tumor necrosis factor (TNF), a potent proinflammatory and antiviral cytokine, is a critical extracellular immune regulator targeted by poxviruses through the activity of virus-encoded family of TNF-binding proteins (CrmB, CrmC, CrmD, and CrmE). The only TNF-binding protein from variola virus (VARV), the causative agent of smallpox, infecting exclusively humans, is CrmB. Here we have aligned the amino acid sequences of CrmB proteins from 10 VARV, 14 cowpox virus (CPXV), and 22 monkeypox virus (MPXV) strains. Sequence analyses demonstrated a high homology of these proteins. The regions homologous to cd00185 domain of the TNF receptor family, determining the specificity of ligand-receptor binding, were found in the sequences of CrmB proteins. In addition, a comparative analysis of the C-terminal SECRET domain sequences of CrmB proteins was performed. The differences in the amino acid sequences of these domains characteristic of each particular orthopoxvirus species were detected. It was assumed that the species-specific distinctions between the CrmB proteins might underlie the differences in these physicochemical and biological properties. The individual recombinant proteins VARV-CrmB, MPXV-CrmB, and CPXV-CrmB were synthesized in a baculovirus expression system in insect cells and isolated. Purified VARV-CrmB was detectable as a dimer with a molecular weight of 90 kDa, while MPXV- and CPXV-CrmBs, as monomers when fractioned by non-reducing SDS-PAGE. The CrmB proteins of VARV, MPXV, and CPXV differed in the efficiencies of inhibition of the cytotoxic effects of human, mouse, or rabbit TNFs in L929 mouse fibroblast cell line. Testing of CrmBs in the experimental model of LPS-induced shock using SPF BALB/c mice detected a pronounced protective effect of VARV-CrmB. Thus, our data demonstrated the difference in anti-TNF activities of VARV-, MPXV-, and CPXV-CrmBs and efficiency of VARV-CrmB rather than CPXV- or MPXV-CrmBs against LPS-induced mortality in mice.     

Smallpox vaccine-induced antibodies are necessary and sufficient for protection against monkeypox virus

Vaccination with live vaccinia virus affords long-lasting protection against variola virus, the agent of smallpox. Its mode of protection in humans, however, has not been clearly defined. Here we report that vaccinia-specific B-cell responses are essential for protection of macaques from monkeypox virus, a variola virus ortholog. Antibody-mediated depletion of B cells, but not CD4+ or CD8+ T cells, abrogated vaccine-induced protection from a lethal intravenous challenge with monkeypox virus. In addition, passive transfer of human vaccinia-neutralizing antibodies protected nonimmunized macaques from severe disease. Thus, vaccines able to induce long-lasting protective antibody responses may constitute realistic alternatives to the currently available smallpox vaccine (Dryvax).     

Antiviral activity of magnesium and magnesium/poly r(A-U) combinations against two RNA viruses.

Magnesium (Mg2+) potentiated the anti-vesicular stomatitis virus (VSV) activity of poly r(A-U) or poly r(G-C) and the anti-HIV-1 activity of poly r(A-U). Mg2+ did not affect the anti-VSV activity of poly (rI).poly (rC), poly (dA-dT).poly (dA-dT) or poly (dG-dC).poly (dG-dC). Modulation of one or more nuclear (nucleolar) processes of the host cell may be responsible for the synergistic antiviral activity.     

Antiviral activity of the long chain pentraxin PTX3 against influenza viruses

Proteins of the innate immune system can act as natural inhibitors of influenza virus, limiting growth and spread of the virus in the early stages of infection before the induction of adaptive immune responses. In this study, we identify the long pentraxin PTX3 as a potent innate inhibitor of influenza viruses both in vitro and in vivo. Human and murine PTX3 bound to influenza virus and mediated a range of antiviral activities, including inhibition of hemagglutination, neutralization of virus infectivity and inhibition of viral neuraminidase. Antiviral activity was associated with binding of the viral hemagglutinin glycoprotein to sialylated ligands present on PTX3. Using a mouse model we found PTX3 to be rapidly induced following influenza infection and that PTX3-/- mice were more susceptible than wild-type mice to infection by PTX3-sensitive virus strains. Therapeutic treatment of mice with human PTX3 promoted survival and reduced viral load in the lungs following infection with PTX3-sensitive, but not PTX3-resistant, influenza viruses. Together, these studies describe a novel antiviral role for PTX3 in early host defense against influenza infections both in vitro and in vivo and describe the therapeutic potential of PTX3 in ameliorating disease during influenza infection.     

Synthesis and antiviral activity of 7-deazaneplanocin A against orthopoxviruses (vaccinia and cowpox virus)

An efficient method for the synthesis of 7-deazaneplanocin A (2) has been accomplished by the condensation of cyclopentenol 3 with 6-chloro-7-deazapurine followed by subsequent functional group manipulations. The synthesized 7-deazaneplanocin A (2) exhibited potent antiviral activity against cowpox and vaccinia viruses without cytotoxicity in HFF cells.     

Antiviral activity of lactoferrin towards naked viruses

It is well known that lactoferrin (Lf) is a potent inhibitor towards several enveloped and naked viruses, such as rotavirus, enterovirus and adenovirus. Lf is resistant to tryptic digestion and breast-fed infants excrete high levels of faecal Lf, so that its effect on viruses replicating in the gastrointestinal tract is of great interest. In this report, we analysed the mechanism of the antiviral action of this protein in three viral models which, despite representing different genoma and replication strategies, share the ability to infect the gut. Concerning the mechanism of action against rotavirus, Lf from bovine milk (BLf) possesses a dual role, preventing virus attachment to intestinal cells by binding to viral particles, and inhibiting a post adsorption step. The BLf effect towards poliovirus is due to the interference with an early infection step but, when the BLf molecule is saturated with Zn+2 ions, it is also capable of inhibiting viral replication after the viral adsorption phase. The anti-adenovirus action of BLf takes place on virus attachment to cell membranes through competition for common glycosaminoglycan receptors and a specific interaction with viral structural polypeptides. Taken together, these findings provide further evidence that Lf is an excellent candidate in the search of natural agents against viral enteric diseases, as it mainly acts by hindering adsorption and internalisation into cells through specific binding to cell receptors and/or viral particles.     

Antiviral activity of tenofovir (PMPA) against nucleoside-resistant clinical HIV samples

The presence of the lamivudine-associated M184V RT mutation increases tenofovir susceptibility in multiple HIV genotypes. Tenofovir is uniquely active against multinucleoside-resistant HIV expressing the Q151M mutation, but shows reduced susceptibility to the T69S insertion mutations. HIV with common forms of zidovudine and lamivudine resistance are susceptible to tenofovir, corroborating phase II clinical results demonstrating the activity of tenofovir DF in treatment-experienced patients.     

Antiviral efficacy of Limonium densiflorum against HSV-1 and influenza viruses

Viral infections remain a major threat to humans and animals and there is a crucial need for new antiviral agents especially with the development of resistant viruses. Several Limonium genus members (Plumbaginacea) have been widely used in traditional medicine for the treatment of infections. In this study, we investigated the antiviral activities of different fractions after successive extraction (hexane, dichloromethane, ethanol and methanol) of the halophyte Limonium densiflorum against H1N1 influenza and HSV-1 herpes viruses. In addition, TLC phytochemicals of the shoot extracts were analyzed. All extracts were tested for their cytotoxicity using a fluorometric resazurin assay. The antiviral activity of extracts was tested using four modes of action: virucidal test, pretreatment of cells with samples before infection, attachment assay and plaque reduction test. A good antiviral activity was found with ethanol and methanol extracts. They were most potent in HSV-1 inhibition than H1N1 influenza virus. The most potent inhibition was observed with ethanol extract, and it exhibited high levels of virucidal activity against HSV-1 (IC₅₀ = 6 μg/mL). It inhibits the replication of the virus by 75% when added after penetration of the virus, and by 100% when added during the viral attachment. It protects MDCK cells against influenza virus by abolishing virus to entry into the host cell (IC₅₀ = 55 μg/mL). After attachment of influenza virus, the ethanol extract displayed an appreciable inhibition of virus replication (IC₅₀ = 193 μg/mL). Methanol extract showed a moderate antiviral capacity against both viruses. While dichloromethane has excellent antiherpes potential, results were inappropriate because it was toxic to Vero cells, hexane extract has no effect. TLC analysis of these extracts showed that flavonoids and saponins were the major classes of natural products found in the shoot extracts that may be responsible for these antiviral activities.     

Independent evolution of monkeypox and variola viruses.

Smallpox was eradicated more than 10 years ago, but infection with another Orthopoxvirus, monkeypox virus, can result in a clinical picture resembling smallpox. Human infection with monkeypox virus is extremely rare, not easily transmitted, and confined to the rain forest belt of Africa (Z. Jezek and F. Fenner, p. 81-102, in Human Monkeypox, 1988). Evidence that variola virus, the causative agent of smallpox, might be readily derived from monkeypox virus was presented [S. S. Marennikova and E. M. Shelukhina, Nature (London) 276:291-292, 1978; S. S. Marennikova, E. M. Shelukhina, N. N. Maltseva, and G. R. Matsevich Intervirology 11:333-340, 1979], but this was not confirmed [K. R. Dumbell and L. C. Archard, Nature (London) 286:29-32, 1980] and was subsequently discounted (J. J. Esposito, J. H. Nakano, and J. F. Obijeski, Bull. W.H.O. 63:695-703, 1985). Although enough difference between the genomes of monkeypox and variola viruses to rule out a simple interconversion has been demonstrated [K. R. Dumbell and L. C. Archard, Nature (London) 286:29-32, 1980; J. J. Esposito and J. C. Knight, Virology 143:230-251, 1985; J. J. Esposito, J. H. Nakano, and J. F. Obijeski, Bull. W.H.O. 63:695-703, 1985; M. Mackett and L. C. Archard, J. Gen. Virol. 45:683-701, 1979], the possibility that monkeypox virus was a more remote ancestor of variola virus remained. We have now identified a sequence in monkeypox virus DNA which is a homolog of a 1,065-bp open reading frame in the conserved region of the variola virus genome but which has multiple deletions. This is strong evidence that monkeypox virus is not ancestral to variola virus and strengthens confidence in the long-term success of smallpox eradication.     

Antiviral profile of Nyctanthes arbortristis L. against encephalitis causing viruses

The ethanolic extracts, various fractions and two pure compounds isolated from the plant N. arbortris were tested against Encephalomyocarditis Virus (EMCV) and Semliki Forest Virus (SFV). Pronounced in vitro virus inhibitory activity was observed with the ethanolic and n-butanol fractions as well as with the pure compounds arbortristoside A and arbortristoside C. In addition, ethanolic extracts and n-butanol fraction protected EMCV infected mice to the extent of 40 and 60% respectively against SFV at a daily dose of 125 mg/kg body weight.     

Antiviral activity of a bile pigment, biliverdin, against human herpesvirus 6 (HHV-6) in vitro.

Biliverdin (BV), a bile pigment, was examined for its antiviral activity against human herpesvirus-6 (HHV-6) in vitro. BV (10 micrograms/ml) markedly inhibited HHV-6 replication in MT-4 cells when the cells were treated during a virus adsorption period. Its antiviral effect was weakened when cells were treated after adsorption. Treatment of cells with BV (40 micrograms/ml) 3 hr after virus infection had no inhibitory effect on virus replication. Virus replication was also significantly inhibited by treatment of MT-4 cells with BV (10 micrograms/ml) before infection, while the virions were not inactivated by BV (20 micrograms/ml). Bilirubin and urobilin, metabolic derivatives of BV, showed slight inhibitory effects on virus replication in the cells. On the other hand, BV had no potent inhibitory activity in the replication of herpes simplex virus-1 or human cytomegalovirus. These observations suggest that BV could interact with MT-4 cells to inhibit an early stage of HHV-6 infection in a virus-specific manner.     

Antiviral activity of fattiviracin FV-8 against human immunodeficiency virus type 1 (HIV-1)

A novel antiviral agent, fattiviracin FV-8, purified from the culture broth of Streptomyces microflavus strain No. 2445, showed potent antiviral activities against human immunodeficiency virus type 1 (HIV-1), herpes simplex virus type 1 (HSV-1), varicella-zoster virus (VZV), and influenza A and B viruses. The action mechanism of fattiviracin FV-8 against HIV-1 was examined. As a result, the agent was thought to act on HIV-1 particles directly without lysis of the particles, and it affords the inhibition of viral entry into the host cells.     

Antiviral activity of (+)-sattabacin against varicella zoster

The first report of the antiviral activity of (+)-sattabacin against varicella-zoster virus (VZV) is described. Our results show that (+)-sattabacin potently inhibits the growth of VZV at concentrations in the range of other drugs commonly prescribed for VZV infection. Experiments detailing the synthesis of (+)-sattabacin, quantification of cytotoxicity and gene expression data in human fibroblast cells are also presented. Gene expression data was obtained through microarray analysis from human fibroblast cells exposed to sattabacin in order to identify a possible mechanism by which (+)-sattabacin inhibits VZV replication.