Animal experiments show impact of vaccination on reduction of SARS-CoV-2 virus circulation: A model for vaccine development?

BACKGROUND

In the pre-clinical phase, SARS-CoV-2 vaccines were tested in animal models, including exposure trials, to investigate protection against SARS-CoV-2. These studies paved the way for clinical development. The objective of our review was to provide an overview of published animal exposure results, focussing on the capacity of vaccines to reduce/prevent viral shedding.

METHOD

Using Medline, we retrieved eighteen papers on eight different vaccine platforms in four animal models. Data were extracted on presence/absence of viral RNA in nose, throat, or lungs, and neutralizing antibody levels in the blood.

RESULTS

All vaccines showed a tendency of reduced viral load after exposure. Particularly nasal swab results are likely to give an indication about the impact on virus excretion in the environment. Similarly, the reduction or prevention of viral replication in the bronchoalveolar environment might be related with disease prevention, explaining the high efficacy in clinical trials.

DISCUSSION

Although it remains difficult to compare the results directly, the potential for a strong reduction of transmission was shown, indicating that the animal models predicted what is observed in the field after large scale human vaccination. This merits further attention for standardization of exposure experiments, with the intention to speed up future vaccine development.

Monocyte-driven atypical cytokine storm and aberrant neutrophil activation as key mediators of COVID-19 disease severity

Epidemiological and clinical reports indicate that SARS-CoV-2 virulence hinges upon the triggering of an aberrant host immune response, more so than on direct virus-induced cellular damage. To elucidate the immunopathology underlying COVID-19 severity, we perform cytokine and multiplex immune profiling in COVID-19 patients. We show that hypercytokinemia in COVID-19 differs from the interferon-gamma-driven cytokine storm in macrophage activation syndrome, and is more pronounced in critical versus mild-moderate COVID-19. Systems modelling of cytokine levels paired with deep-immune profiling shows that classical monocytes drive this hyper-inflammatory phenotype and that a reduction in T-lymphocytes correlates with disease severity, with CD8+ cells being disproportionately affected. Antigen presenting machinery expression is also reduced in critical disease. Furthermore, we report that neutrophils contribute to disease severity and local tissue damage by amplification of hypercytokinemia and the formation of neutrophil extracellular traps. Together our findings suggest a myeloid-driven immunopathology, in which hyperactivated neutrophils and an ineffective adaptive immune system act as mediators of COVID-19 disease severity.

Emerging preclinical evidence does not support broad use of hydroxychloroquine in COVID-19 patients

There is an urgent need for drugs, therapies and vaccines to be available to protect the human population against COVID-19. One of the first approaches taken in the COVID-19 global response was to consider repurposing licensed drugs. This commentary highlights an extraordinary international collaborative effort of independent researchers who have recently all come to the same conclusion—that chloroquine or hydroxchloroquine are unlikely to provide clinical benefit against COVID-19.

ZikaPLAN: Zika Preparedness Latin American Network

The ongoing Zika virus (ZIKV) outbreak in Latin America, the Caribbean, and the Pacific Islands has underlined the need for a coordinated research network across the whole region that can respond rapidly to address the current knowledge gaps in Zika and enhance research preparedness beyond Zika. The European Union under its Horizon 2020 Research and Innovation Programme awarded three research consortia to respond to this need. Here we present the ZikaPLAN (Zika Preparedness Latin American Network) consortium. ZikaPLAN combines the strengths of 25 partners in Latin America, North America, Africa, Asia, and various centers in Europe. We will conduct clinical studies to estimate the risk and further define the full spectrum and risk factors of congenital Zika virus syndrome (including neurodevelopmental milestones in the first 3 years of life), delineate neurological complications associated with ZIKV due to direct neuroinvasion and immune-mediated responses in older children and adults, and strengthen surveillance for birth defects and Guillain-Barré Syndrome. Laboratory-based research to unravel neurotropism and investigate the role of sexual transmission, determinants of severe disease, and viral fitness will underpin the clinical studies. Social messaging and engagement with affected communities, as well as development of wearable repellent technologies against Aedes mosquitoes will enhance the impact. Burden of disease studies, data-driven vector control, and vaccine modeling as well as risk assessments on geographic spread of ZIKV will form the foundation for evidence-informed policies. While addressing the research gaps around ZIKV, we will engage in capacity building in laboratory and clinical research, collaborate with existing and new networks to share knowledge, and work with international organizations to tackle regulatory and other bottlenecks and refine research priorities. In this way, we can leverage the ZIKV response toward building a long-term emerging infectious diseases response capacity in the region to address future challenges.

Extra-hepatic replication and infection of hepatitis E virus in neuronal-derived cells

Hepatitis E virus (HEV) is the causative agent of hepatitis E in humans and a member of the genus Orthohepevirus in the family Hepeviridae. Infection usually leads to acute hepatitis that can become fulminant, particularly among pregnant women and in patients with preexisting liver disease, or may evolve to a chronic state, especially in immunosuppressed individuals. HEV has been shown to produce a range of extra-hepatic manifestations including aplastic anaemia, acute thyroiditis, glomerulonephritis as well as neurological disorders such as Guillain-Barré syndrome, neuralgic amyotrophy and encephalitis. The pathogenesis of these neurological injuries remains largely unknown, and it is also uncertain whether or not HEV can directly infect neuronal cells. In this study, we investigated whether HEV is capable of completing the viral life cycle in human neuronal-derived cell lines such as neuroepithelioma (SK-N-MC), desmoplastic cerebellar medulloblastoma (DAOY), glioblastoma multiforme (DBTRG), glioblastoma astrocytoma (U-373 MG) and oligodendrocytic (M03.13) cells. Following transfection of these cells with HEV Gaussia luciferase reporter virus, all tested cell lines supported HEV RNA replication. Furthermore, extra- and intracellular viral capsid was detected by an HEV antigen ELISA as a marker for virus assembly and release. Permissiveness for HEV cell entry could be demonstrated for the oligodendrocytic cell line M03.13. In conclusion, these results indicate that HEV tropism is not restricted to the liver and HEV can potentially complete the full viral life cycle in neuronal-derived tissues explaining neurologic disorders during HEV infection.

Inhibitory Effects of Polycations on the Replication of Enveloped Viruses (HIV, HSV, CMV, RSV, Influenza A Virus and Togaviruses) in vitro

Polycationic compounds, i.e. poly-l-lysines and poly-d-lysines, were evaluated for their in vitro effect on the replication of various viruses. Poly-l-lysines of different molecular weight proved inhibitory to the replication of several enveloped viruses, such as human immunodeficiency virus type 1 and type 2 (HIV-1 and HIV-2), respiratory syncytial virus (RSV), influenza A virus, Sindbis virus, Semliki Forest virus, vesicular stomatitis virus (VSV), herpes simplex virus type 1 (HSV-1) and human cytomegalovirus (CMV). The mechanism of action of the polylysines against HIV-1, RSV and CMV could be attributed to an inhibitory effect on virus binding to the host cells, as demonstrated by an indirect immunofluorescence/laser flow cytofluorographic method, virus plaque reduction and measurement of radiolabelled virion association with the cells, respectively.

Anti-HIV and anti-HCMV Activities of New Aurintricarboxylic Acid Analogues

A variety of aurintricarboxylic acid (ATA) polymer analogues were prepared by substituting certain salicylic acid derivatives and carbonyl compounds for salicylic acid and formaldehyde in the ATA polymerization reaction. The new polymers were evaluated for prevention of the cytopathic effects of human immunodeficiency virus (HIV-1 and HIV-2) in MT-4 cell culture, HIV-1 in CEM cell culture, and human cytomegalovirus (HCMV) in HEL cell culture. The abilities of the analogues to inhibit syncytium formation between HIV-1- or HIV-2-infected HUT-78 cells and uninfected MOLT-4 cells were also evaluated. Several of the new analogues were found to be equipotent with ATA and dextran sulfate against HIV-1, HIV-2 and HCMV. The anti-HIV potencies of the new substances paralleled their activities against HCMV. The antiviral activities of the new analogues probably result from inhibition of virion binding to the cell membrane.

Sulphated Polymers are Potent and Selective Inhibitors of Various Enveloped Viruses, Including Herpes Simplex Virus, Cytomegalovirus, Vesicular Stomatitis Virus, Respiratory Syncytial Virus, and Toga-, Arena- and Retroviruses

The sulphated polymers, such as polyvinylalcohol sulphate (PVAS) and its co-polymer with acrylic acid (PAVAS), have proved to be potent inhibitors for herpes simplex virus, human cytomegalovirus, vesicular stomatitis virus, respiratory syncytial virus, Sindbis virus, Semliki Forest virus, Junin virus, Tacaribe virus, murine sarcoma virus and human immunodeficiency virus. They are not inhibitory to non-enveloped viruses, such as poliovirus and reovirus. The broad-spectrum antiviral effects of these compounds depend on their molecular weight and degree of sulphation. Pharmacokinetic studies in rabbits have indicated that after intravenous bolus injection the serum concentrations of these compounds decay biphasically, with an initial half-life of approximately 90–120 min.

In vitro Activity of a Novel Series of Polyoxosilicotungstates against Human Myxo-, Herpes- and Retroviruses

A series of silicon-containing polyoxotungstates belonging to the ‘Keggin-type’ (‘Keggin’, ‘Keggin sandwich’) were evaluated for their antiviral activity against enveloped viruses (myxo-, herpes- and retroviruses). The compounds exhibited antiviral activity against influenza virus type A, respiratory syncytial virus (RSV), herpes simplex virus type-1 (HSV-1), type-2 (HSV-2), thymidine kinase-deficient (TIC) HSV-1, human cytomegalovirus (HCMV), human immunodeficiency virus type-1 (HIV-1) and type-2 (HIV-2) at concentrations that were well below their cytotoxic threshold. The ‘Keggin’ compound JM2815 (K5[Si-(TiCp)W11O39].12H2O) and the ‘Keggin sandwich’ compound JM1590 (K13[Ce(SiW11O39)2].26H2O) resulted in the highest selectivity indices against HIV-1 and HIV-2, and compound JM2820 ([Me3NH]8.[Si2Nb6W18O77]) was the most potent inhibitor of HSV and HCMV replication. These compounds proved active against HCMV and HSV when present during virus adsorption, and against influenza virus A and RSV when present after virus adsorption. Polyoxosilicotungstates inhibited the binding of radiolabeled HCMV particles to the cells at concentrations that were antivirally active, and the compounds were able to displace HCMV particles that were bound to a heparin-Sepharose matrix. Presumably, the polyoxosilicotungstates interact with positively charged domains on the viral envelope site(s) involved in the attachment of the (HCMV) virions to the cell surface receptor heparan sulphate.

HPMPC (cidofovir), PMEA (adefovir) and Related Acyclic Nucleoside Phosphonate Analogues: A Review of their Pharmacology and Clinical Potential in the Treatment of Viral Infections

The acyclic nucleoside phosphonate (ANP) analogues are broad-spectrum antiviral agents, with potent and selective antiviral activity in vitro and in vivo. The prototype compounds are: ( S)-1-(3-hydroxy-2-phosphonylmethoxypropyl)cytosine (HPMPC, cidofovir), which is active against a wide variety of DNA viruses; 9-(2-phosphonylmethoxyethyl)adenine (PMEA, adefovir), which is active against retro-, herpes- and hepadnaviruses, and ( R)-9-(2-phosphonylmethoxypropyl) adenine (PMPA), which is active against retro- and hepadnaviruses. The antiviral action of the ANP analogues is based on a specific interaction of the active diphosphorylated metabolite with the viral DNA polymerase. The long intracellular half-life of the active metabolite accounts for the optimal efficacy in infrequent dosing schedules. The potential of HPMPC as a broad-spectrum anti-DNA virus agent, as originally observed in vitro and in vivo, has been confirmed in clinical trials. HPMPC has recently been commercially released in the USA for the treatment of cytomegalovirus retinitis in AIDS patients. In addition, topical systemic HPMPC is being (or will be) explored for use against other herpesviruses (i.e. herpes simplex virus, Epstein-Barr virus, or varicella-zoster virus), by adenoviruses, or by human papilloma- or polyomaviruses. Intravenous HPMPC is associated with dose-dependent nephrotoxicity, that should be counteracted by prehydration and concomitant administration of probenecid, and by the application of an infrequent dosing schedule. The oral prodrug of PMEA, bis(pivaloyloxymethyl)-PMEA, is currently being evaluated in patients infected with human immunodeficiency virus (HIV) or hepatitis B virus. Finally, preclinical data on the efficacy of PMPA in animal retrovirus models point to its potential usefulness against HIV infections, when given either prophylactically or therapeutically in the treatment of established HIV infections.

Mechanism of the Antiviral Activity of New Aurintricarboxylic Acid Analogues

Various new aurintricarboxylic acid (ATA) polymer analogues have been evaluated for their antiviral activity against a wide array of DNA and RNA viruses, and their mechanism of action against human cytomegalovirus (HCMV) and human immunodeficiency virus type 1 (HIV-1). Most of the polymers exhibited marked antiviral activity against a variety of enveloped viruses, but not against non-enveloped viruses. The ATA polymers displayed the most pronounced activity against HIV-1, HCMV and human herpesvirus type 6 (HHV-6). Their action against HCMV and HIV could be ascribed to inhibition of the initial attachment of virus particles to the cells. Using radiolabelled virus, we proved that the polymers inhibit the binding of HCMV to HEL fibroblasts. By flow cytometric analysis, we demonstrated that these new polymers interfere with (i) the binding of OKT4A monoclonal antibody (mAb) to the cellular CD4 receptor, (ii) the binding of anti-gp120 mAb to HIV-1 glycoprotein (gp) 120, and (iii) the adsorption of HIV-1 virions and recombinant HIV-1gp120 (rgp120) to MT-4 cells. The presence of a salicylic acid substituent on the central bridging carbon in the parent compound ATA seems to play an important role in the anti-HIV activity of these ATA related polymer analogues.

Prophylactic treatment with the nucleoside analogue 2'-C-methylcytidine completely prevents transmission of norovirus

OBJECTIVES

Norovirus outbreaks of acute gastroenteritis are highly prevalent, extensive and can disturb the functioning of health institutions, leading to the closure of hospital wards and causing life-threatening infections in long-term care facilities. There is no vaccine available; hence there is a pressing need for antivirals for the treatment (in immunodeficient patients) and prophylaxis of norovirus infections. We explored in a mouse model whether an inhibitor of norovirus replication can prevent/reduce transmission of the virus.

METHODS

We reported recently that the viral polymerase inhibitor 2'-C-methylcytidine (2CMC) efficiently protects against murine norovirus (MNV)-induced diarrhoea and mortality in mice. Here, we established an MNV-transmission model, determined the 50% infectious dose and assessed the ability of an antiviral molecule to prevent or reduce transmission of (murine) norovirus when given either to the infected (seeder) mice or to the uninfected (sentinel) mice.

RESULTS

A robust norovirus transmission model was established using genogroup V (murine) norovirus in AG129 mice. The 50% infectious dose was determined to be ∼ 270 CCID50 (50% cell culture infectious dose). Treatment of infected mice with 2CMC reduced viral shedding and markedly reduced transmission to uninfected sentinels. Also, prophylactic treatment of sentinels with 2CMC resulted in protection against infection with MNV.

CONCLUSIONS

These findings constitute an important first step towards developing an efficient prophylaxis for the control of norovirus outbreaks.

Proof of concept for the inhibition of foot-and-mouth disease virus replication by the anti-viral drug 2'-C-methylcytidine in severe combined immunodeficient mice

Recent European contingency plans envisage emergency vaccination as an animal-friendly control strategy for foot-and-mouth disease (FMD). Anti-viral drugs may be used as an alternative or complementary measure. We here demonstrate that the nucleoside analogue 2'-C-methylcytidine (2'CMC) protects severe combined immunodeficient (SCID) mice against lethal FMD virus infection. In brief, SCID mice were inoculated with serotype A FMD virus and treated for five consecutive days with 2'CMC. All 15 treated mice remained healthy until the end of the study at 14 days post-infection (dpi). At that time, viral RNA was no longer detected in 13 of 15 treated mice. All eight untreated mice suffered from an acute generalized disease and were euthanized for ethical reasons on average at 4 dpi. These results illustrate the potential of small molecules to control FMD.

Inhibition of norovirus replication by the nucleoside analogue 2'-C-methylcytidine

We here report on the activity of 2'-C-methylcytidine (2CMC) [a nucleoside polymerase inhibitor of the hepatitis C virus (HCV)] on the in vitro replication of (murine) norovirus (MNV). 2CMC inhibits (i) virus-induced CPE formation, (ii) viral RNA synthesis and (iii) infectious progeny formation with EC(50) values of ∼2μM. 2CMC acts at a time-point that coincides with the onset of viral RNA synthesis. Even following 30 passages of selective pressure no MNV-resistant virus was selected, which is in line with the high barrier to resistance of the nucleoside analogue for HCV. When combined with the broad-spectrum RNA virus inhibitor ribavirin, a marked antagonistic activity was observed indicating that these molecules should not be combined for the treatment of norovirus infections. Our results suggest that 2'-C-methyl nucleoside analogues should be further explored for the treatment and prophylaxis of norovirus infections.

Studies of Antiviral Activity and Cytotoxicity of Wrightia tinctoria and Morinda citrifolia

Different extracts of leaf parts of Wrightia tinctoria and fruit powder of Morinda citrifolia have been studied against replication of HIV-1(IIIB) in MT-4 cells and HCV in Huh 5.2 cells. Chloroform extract of Wrightia tinctoria exhibited a maximum protection of 48% against the cytopathic effect of HIV-1(IIIB) in MT-4 cells. Fruit juice of Morinda citrifolia exhibited a displayed marked cytotoxic activity in lymphocyte (MT-4) cells (CC50: 0.19 mg/ml). The 50% effective concentration for inhibition of HCV subgenomic replicon replication in Huh 5-2 cells by Morinda citrifolia was 0.98 mug/ml and by chloroform extract of Wrightia tinctoria was 10 mug/ml. The concentration that reduced the growth of exponentially proliferating Huh 5-2 cells by 50% was greater than 50 mug/ml.

Adefovir serum levels do not differ between responders and nonresponders

Primary or secondary failure of adefovir dipivoxil (ADV) therapy of chronic hepatitis B is not infrequent. The reasons for suboptimal responses are not well defined. In HIV and hepatitis C virus infection, failure of antiviral drug therapy has been linked with low blood drug levels. We have studied 20 well-defined patients with chronic hepatitis B who were treated with ADV for drug and virus kinetics. Importantly, neither Cmax levels (mean 26 ng/mL, range 14-59 ng/mL) nor the time to maximal drug levels (mean 4 h, range 2-8 h) differed between patients showing a complete virological response to adefovir (n = 10), patients with secondary treatment failure (n = 7) and patients with suboptimal primary response (hepatitis B virus-DNA >10,000 IU/mL after 6 months of treatment; n = 3). Thus, adefovir treatment failure is unlikely to be due to an inability to mount sufficient drug levels in the blood.

The reduction of CSFV transmission to untreated pigs by the pestivirus inhibitor BPIP: a proof of concept

5-[(4-Bromophenyl)methyl]-2-phenyl-5H-imidazo[4,5-c]pyridine (BPIP) is a representative molecule of a novel class of highly active in vitro inhibitors of the replication of Classical swine fever virus (CSFV). We recently demonstrated in a proof of concept study that the molecule has a marked effect on viral replication in CSFV-infected pigs. Here, the effect of antiviral treatment on virus transmission to untreated sentinel pigs was studied. Therefore, BPIP-treated pigs (n=4), intra-muscularly infected with CSFV, were placed into contact with untreated sentinel pigs (n=4). Efficient transmission of CSFV from four untreated seeder pigs to four untreated sentinels was observed. In contrast, only two out of four sentinel animals in contact with BPIP-treated seeder animals developed a short transient infection, of which one was likely the result of sentinel to sentinel transmission. A significant lower viral genome load was measured in tonsils of sentinels in contact with BPIP-treated seeder animals compared to the positive control group (p=0.015). Although no significant difference (p=0.126) in the time of onset of viraemia could be detected between the groups of contact animals, a tendency towards the reduction of virus transmission was observed. Since sentinel animals were left untreated in this exploratory trial, the study can be regarded as a worst case scenario and gives therefore an underestimation of the potential efficacy of the activity of BPIP on virus transmission.

Antiviral agents acting as DNA or RNA chain terminators

Nucleoside or nucleotide analogue inhibitors of viral replication almost act as chain terminators during DNA (DNA- and retroviruses) or RNA (RNA viruses) synthesis. Following intracellular phosphorylation, by viral and/or cellular kinases, the 5'-triphosphate metabolites (or 2'-diphosphate metabolites in the case of acyclic nucleoside phosphonate analogues) compete with the natural substrate in the DNA or RNA polymerization reaction. Obligatory chain terminators (e.g., acyclovir) do not offer the 3'-hydroxyl function at the riboside moiety of the molecule. Nucleoside analogues that possess a hydroxyl function at a position equivalent of the 3'-hydroxyl position may act as chain terminators if this hydroxyl group is conformationally constrained (e.g., ganciclovir) or sterically hindered to enter into a phosphodiester linkage with the incoming nucleotide. In case that the 3'-hydroxylgroup is correctly positioned, chain elongation may be hampered through steric hindrance from neighboring substituents (e.g., 2'-C-methyl or 4'-azido nucleoside inhibitors of HCV replication). Here, we review the molecular mechanism of action and the clinical applications of the nucleosides and nucleotides acting as chain terminators. A further discussion of clinical applications in combination therapy can be found in Chap. 12.

In Vitro Antiviral Activity of some Novel Isatin Derivatives against HCV and SARS-CoV Viruses

4-[(1,2-dihydro-2-oxo-3H-indol-3-ylidene)amino]-N(4,6-dimethyl-2-pyrimidiny)benzene sulphonamide and its derivatives were evaluated for antiviral activity against Pathogenic viruses such as Hepatitis C Virus and SARS-CoV in Vero and Huh 5-2 cells, respectively. The 5-fluoro derivative inhibited the HCV RNA synthesis at 6 mug/ml, without toxicity at a concentration up to 42 mug/ml in Huh 5-2 cells. Among the compounds tested SPIII-5F exhibits the 45% maximum protection against replication of SARS-CoV in Vero cells.

The VIZIER project: preparedness against pathogenic RNA viruses

Life-threatening RNA viruses emerge regularly, and often in an unpredictable manner. Yet, the very few drugs available against known RNA viruses have sometimes required decades of research for development. Can we generate preparedness for outbreaks of the, as yet, unknown viruses? The VIZIER (VIral enZymes InvolvEd in Replication) (http://www.vizier-europe.org/) project has been set-up to develop the scientific foundations for countering this challenge to society. VIZIER studies the most conserved viral enzymes (that of the replication machinery, or replicases) that constitute attractive targets for drug-design. The aim of VIZIER is to determine as many replicase crystal structures as possible from a carefully selected list of viruses in order to comprehensively cover the diversity of the RNA virus universe, and generate critical knowledge that could be efficiently utilized to jump-start research on any emerging RNA virus. VIZIER is a multidisciplinary project involving (i) bioinformatics to define functional domains, (ii) viral genomics to increase the number of characterized viral genomes and prepare defined targets, (iii) proteomics to express, purify, and characterize targets, (iv) structural biology to solve their crystal structures, and (v) pre-lead discovery to propose active scaffolds of antiviral molecules.

Imidazo[4,5-c]pyridines inhibit the in vitro replication of the classical swine fever virus and target the viral polymerase

Selective inhibitors of the replication of the classical swine fever virus (CSFV) may have the potential to control the spread of the infection in an epidemic situation. We here report that 5-[(4-bromophenyl)methyl]-2-phenyl-5H-imidazo[4,5-c]pyridine (BPIP) is a highly potent inhibitor of the in vitro replication of CSFV. The compound resulted in a dose-dependent antiviral effect in PK(15) cells with a 50% effective concentration (EC(50)) for the inhibition of CSFV Alfort(187) (subgroup 1.1) of 1.6+/-0.4 microM and for CSFV Wingene (subgroup 2.3) 0.8+/-0.2 microM. Drug-resistant virus was selected by serial passage of the virus in increasing drug-concentration. The BPIP-resistant virus (EC(50): 24+/-4.0 microM) proved cross-resistant with VP32947 [3-[((2-dipropylamino)ethyl)thio]-5H-1,2,4-triazino[5,6-b]indole], an unrelated earlier reported selective inhibitor of pestivirus replication. BPIP-resistant CSFV carried a T259S mutation in NS5B, encoding the RNA-dependent RNA-polymerase (RdRp). This mutation is located near F224, a residue known to play a crucial role in the antiviral activity of BPIP against bovine viral diarrhoea virus (BVDV). The T259S mutation was introduced in a computational model of the BVDV RdRp. Molecular docking of BPIP in the BVDV polymerase suggests that T259S may have a negative impact on the stacking interaction between the imidazo[4,5-c]pyridine ring system of BPIP and F224.

In vitro susceptibility of six isolates of equine herpesvirus 1 to acyclovir, ganciclovir, cidofovir, adefovir, PMEDAP and foscarnet

Equine herpesvirus 1 (EHV-1) is an important equine pathogen that causes respiratory disease, abortion, neonatal death and paralysis. Although vaccines are available, they are not fully protective and outbreaks of disease may occur in vaccinated herds. Therefore, there is an urgent need for effective antiviral treatment. For three abortigenic (94P247, 97P70 and 99P96) and three neuropathogenic isolates (97P82, 99P136 and 03P37), the effect of acyclovir, ganciclovir, cidofovir, adefovir, 9-(2-phosphonylmethoxyethyl)-2,6-diaminopurine (PMEDAP) and foscarnet on plaque number was studied. Additionally, for isolate 97P70, the effect on plaque size was investigated. Ganciclovir was most potent in reducing plaque number, followed by PMEDAP and acyclovir. Adefovir and cidofovir were less effective and foscarnet was the least effective compound. There were no differences detected for acyclovir, ganciclovir, adefovir and PMEDAP between the abortigenic and neuropathogenic isolates. One abortigenic isolate (99P96) was more susceptible to cidofovir and two neuropathogenic isolates (99P136 and 03P37) were less susceptible to foscarnet. For isolate 97P70, all compounds resulted in a significant reduction of plaque size. The most remarkable effect was observed for cidofovir. It was 40-fold more effective in reducing plaque size than in reducing plaque number. In conclusion, ganciclovir was the most potent compound and therefore, may be a valuable candidate for the treatment of EHV-1 infections in horses. The antiviral effect of foscarnet on plaque number was highly dependent on the viral isolate tested. Therefore, it is no valuable antiviral for the treatment of herpesvirus-infections. Cidofovir, although less effective in reducing plaque number, had a strong effect on plaque size.

In vitro activity of 2,4-diamino-6-[2-(phosphonomethoxy)ethoxy]-pyrimidine against multidrug-resistant hepatitis B virus mutants

The susceptibilities of drug-resistant hepatitis B virus (HBV) mutants to lamivudine, adefovir, tenofovir, entecavir, and 2,4-diamino-6-[2-(phosphonomethoxy)ethoxy]-pyrimidine (PMEO-DAPym), a novel acyclic pyrimidine analogue, were assessed in vitro. Most drug-resistant mutants, including multidrug-resistant strains, remained sensitive to tenofovir and PMEO-DAPym. Therefore, the latter molecule deserves further evaluation for the treatment of HBV infection.

239 EMBRYOTOXICITY ASSAY FOR ANTIVIRAL COMPOUND BPIP (5-[(4-BROMOPHENYL)METHYL]-2-PHENYL-5H-IMIDAZO[4,5-c]PYRIDINE) IN BOVINE IN VITRO-PRODUCED EMBRYOS

Bovine viral diarrhea virus (BVDV) causes serious economic losses in the cattle industry. Evidence exists that only zona pellucida (ZP)-free bovine embryos are susceptible to BVDV infection (Vanroose et al. 1998 Biol. Reprod. 58, 857–866); however, BVDV can adhere to and therefore ‘infect’ both in vivo-(Waldrop et al. 2004 Theriogenology 62, 387–397) and in vitro-produced ZP intact embryos (Stringfellow et al. 2000 Theriogenology 53, 827–839). To eliminate these sanitary risks, pre-treatment of embryos with antiviral compounds may be a promising approach (Givens et al. 2006 Theriogenology 65, 344–355). BPIP (5-[(4-bromophenyl)methyl]-2-phenyl-5H-imidazo[4,5-c]pyridine) has been reported to display antiviral activity against BVDV, with a 50% effective inhibition of BVDV-induced cytopathic effect formation at a concentration of 0.04 µM (Paeshuyse et al. 2006 J. Virol. 80, 149–160). However, since the short- and long-term effects of BPIP have not been described, the aim of the current study was to assess whether addition of BPIP for 2 days at a concentration of 5 µM is toxic for ZP-free cattle embryos. Oocytes were aspirated from 3–6-mm follicles of cattle ovaries, matured for 24 h, and subsequently co-incubated with 1 × 106 sperm cells mL−1 in IVF-TALP with 20 µg/mL−1 heparin for 24 h at 39°C and 5% CO2 in air. After fertilization, presumptive zygotes were put in groups of 25 into 50-µL droplets of SOF under oil in 5% CO2, 5% O2, and 90% N2 for 6 days. Afterwards, morulae and blastocysts were collected, rendered ZP-free by means of pronase treatment, and divided into 4 groups: (i) ZP-free control group, (ii) ZP-free control group treated with a volume of DMSO equal to condition (iv), (iii) ZP-free group treated with 5 µM BPIP in DMSO, and (iv) ZP-free group treated with 10 µM BPIP in DMSO. Because BPIP is a fat-soluble molecule, embryos were cultured in 0.5 mL SOF without oil for 2 days. At Day 8, all embryos were fixed, TUNEL-stained, and analyzed for total cell number and percentage of apoptotic cells. Three independent replicates were performed. Results are shown in Table 1 and were analyzed by means of ANOVA. Only group iv showed a significant decrease in total cell number, indicating that at 10 µM BPIP may negatively influence embryo development. At both 5 and 10 µM, BPIP treatment resulted in an increase in percentage of apoptotic cells compared to the control group. However, a similar increase was observed using DMSO alone (group ii), indicating that the apoptotic effect may be due solely to the DMSO. In conclusion, BPIP does not appear to cause embryo toxicity at 5 µM, but an alternative, less toxic, dissolving agent may be considered. Table 1.Embryotoxicity assay of BPIP

Poly(I)-poly(C12U) but not ribavirin prevents death in a hamster model of Nipah virus infection

Clinical nonrandomized trials demonstrate some efficacy for ribavirin in the treatment of patients with severe Nipah virus-induced encephalitis. We report here that EICAR, the 5-ethynyl analogue of ribavirin, and the OMP-decarboxylase inhibitors 6-aza-uridine and pyrazofurin have strong antiviral activity against Nipah virus replication in vitro. Ribavirin and 6-aza-uridine were tested further in hamsters infected with a lethal dose of Nipah virus. The activity of these small-molecule inhibitors was compared with that of the interferon inducer poly(I)-poly(C(12)U). Both ribavirin and 6-aza-uridine were able to delay but not prevent Nipah virus-induced mortality. Poly(I)-poly(C(12)U), at 3 mg/kg of body weight daily from the day of infection to 10 days postinfection, prevented mortality in 5 of 6 infected animals.

Antiviral potential of a new generation of acyclic nucleoside phosphonates, the 6-[2-(phosphonomethoxy)alkoxy]-2,4-diaminopyrimidines

Three acyclic nucleoside phosphonates (ANPs) have been formally approved for clinical use in the treatment of 1) cytomegalovirus retinitis in AIDS patients (cidofovir, by the intravenous route), 2) chronic hepatitis B virus (HBV) infections (adefovir dipivoxil, by the oral route), and 3) human immunodeficiency virus (HIV) infections (tenofovir disoproxil fumarate, by the oral route). The activity spectrum of cidofovir {(S)- 1-[3-hydroxy-2-(phosphonomethoxy)propyl]cytosine [(S)-HPMPC)]}, like that of (S)-HPMPA [(S)-9-[3-hydroxy-2-(phosphonomethoxy)propyl]adenine) and (S)-HPMPDAP [(S)-9-[3-hydroxy-2-(phosphonomethoxy)propyl]-2, 6-diaminopurine), encompasses a broad spectrum of DNA viruses, including polyoma-, papilloma-, adeno-, herpes-, and poxviruses. Adefovir {9-[2-(phosphonomethoxy)ethyl]adenine (PMEA)} and tenofovir [(R)-9-[2-(phosphonomethoxy) propyl]adenine [(R)-PMPA)]} are particularly active against retroviruses (ie., HIV) and hepadnaviruses (ie., HBV); additionally, PMEA also shows activity against herpes- and poxviruses. We have recently identified a new class of ANPs, namely 6-[2-(phosphonomethoxy)alkoxy]-2,4-diaminopyrimidines, named, in analogy with their alkylpurine counterparts, HPMPO-DAPy, PMEO-DAPy, and (R)-PMPO-DAPy. These compounds exhibit an antiviral activity spectrum and potency that is similar to that of (S)-HPMPDAP, PMEA, and (R)-PMPA, respectively. Thus, PMEO-DAPy and (R)-PMPO-DAPy, akin to PMEA and (R)-PMPA, proved particularly active against HIV- 1, HIV-2, and the murine retrovirus Moloney sarcoma virus (MSV). PMEO-DAPy and (R)-PMPO-DAPy also showed potent activity against both wild-type and lamivudine-resistant strains of HBV. HPMPO-DAPy was found to inhibit different poxviruses (ie., vaccinia, cowpox, and orf) at a similar potency as cidofovir. HPMPO-DAPy also proved active against adenoviruses. In vivo, HPMPO-DAPy proved equipotent to cidofovir in suppressing vaccinia virus infection (tail lesion formation) in immunocompetent mice and promoting healing of disseminated vaccinia lesions in athymic-nude mice. The 6-[2-(phosphonomethoxy)alkoxy]-2,4-diaminopyrimidines offer substantial potential for the treatment of a broad range of retro-, hepadna-, herpes-, adeno-, and poxvirus infections.

Novel acyclic nucleoside phosphonate analogues with potent anti-hepatitis B virus activities

Novel acyclic nucleoside phosphonates with a pyrimidine base preferentially containing an amino group at C-2 and C-4 and a 2-(phosphonomethoxy)ethoxy or (R)-2-(phosphonomethoxy)propoxy group at C-6 selectively inhibit the replication of wild-type and lamivudine-resistant hepatitis B viruses. The activity of the most potent compounds was comparable to that of adefovir.

Synthesis and antiviral evaluation of ribavirin congeners containing a hexitol moiety

Several ribavirin congeners containing a hexitol moiety were prepared via ring opening of two different epoxides with the methylcarboxylate ester of triazole and further elaboration. Unfortunately, none of the newly synthesized compounds displayed appreciable antiviral activity.

The acyclic nucleoside phosphonate analogues, adefovir, tenofovir and PMEDAP, efficiently eliminate banana streak virus from banana (Musa spp.)

We report that the anti-retroviral and anti-hepadnavirus molecules, adefovir, tenofovir and 9-(2-phosphonomethoxyethyl)-2,6-diaminopurine (PMEDAP), efficiently eradicate the episomal form of Banana streak virus (BSV) from banana plants. Up to 90% of plants regenerated from BSV-infected highly proliferating meristems were virus free following a 6-month treatment period with 10 microg/ml (a non-phytotoxic concentration) of either compounds.

Genome sequence analysis of Tamana bat virus and its relationship with the genus Flavivirus

Tamana bat virus (TABV, isolated from the bat Pteronotus parnellii) is currently classified as a tentative species in the genus FLAVIVIRUS: We report here the determination and analysis of its complete coding sequence. Low but significant similarity scores between TABV and member-viruses of the genus Flavivirus were identified in the amino acid sequences of the structural, NS3 and NS5 genes. A series of cysteines located in the envelope protein and the most important enzymatic domains of the virus helicase/NTPase, methyltransferase and RNA-dependent RNA polymerase were found to be highly conserved. In the serine-protease domain, the catalytic sites were conserved, but variations in sequence were found in the putative substrate-binding sites, implying possible differences in the protease specificity. In accordance with this finding, the putative cleavage sites of the TABV polyprotein by the virus protease are substantially different from those of flaviviruses. The phylogenetic position of TABV could not be determined precisely, probably due to the extremely significant genetic divergence from other member-viruses of the family FLAVIVIRIDAE: However, analysis based on both genetic distances and maximum-likelihood confirmed that TABV is more closely related to the flaviviruses than to the other genera. These findings have implications for the evolutionary history and taxonomic classification of the family as a whole: (i) the possibility that flaviviruses were derived from viruses infecting mammals rather than from mosquito viruses cannot be excluded; (ii) using the current criteria for the definition of genera in the family Flaviviridae, TABV should be assigned to a new genus.

Antiviral and immunomodulatory activity of the metal chelator ethylenediaminedisuccinic acid against cytomegalovirus in vitro and in vivo

Antiviral activity of the metal chelator ethylenediaminedisuccinic acid (EDDS) was examined in vitro against human cytomegalovirus (HCMV) wild type strains and strains that are resistant against ganciclovir (GCV) and cidofovir (HPMPC). EDDS inhibited the replication of wild-type as well as GCV- and HPMPC-resistant strains with a 50% effective concentration of 7.4-12 microg/ml. At concentrations of 100 microg/ml EDDS, unlike GCV or HPMPC, suppressed HCMV-induced up-regulation of intercellular adhesion molecule-1 (ICAM-1) and reduced T-cell adhesion to HCMV-infected cells in a monolayer adhesion model. In vitro EDDS inhibited murine cytomegalovirus (MCMV) replication (EC50 8.6 microg/ml) and caused in mice some protection against MCMV induced mortality at a non-toxic dose. Since immunopathological factors may play a significant role in HCMV disease it will be of interest to further study whether EDDS is effective in terms of modulation of inflammatory responses to HCMV infections.

Sulphated and sulphonated polymers inhibit the initial interaction of hepatitis B virus with hepatocytes

The initial step during hepatitis B virus (HBV) infection is the specific attachment of the virus to the hepatocyte. Here we studied whether the binding of HBV to hepatocytes can, as is the case with most other enveloped viruses, be blocked by polyanionic compounds. Viral particles produced by HepAD38 cells were used as inoculum and HBV-negative HepG2 cells, as well as primary human hepatocytes, as target cells. Three sulphated polymers, that is, PAVAS (a co-polymer of acrylic acid with vinyl alcohol sulphate), heparin and dextran sulphate (DS) (MW 5000), and the sulphonated polymer PAMPS [poly(2-acryl-amido-2-methyl-1-propanesulfonic acid] (MW approximately 7000-12000), proved strong inhibitors of the binding of HBV to HepG2 cells and primary hepatocytes. The 50% effective concentration (EC50) for inhibition of HBV binding to HepG2 cells by PAVAS, heparin, DS and PAMPS was 1.3 microg/ml, 1.6 microg/ml, 1.8 microg/ml and 3.3 microg/ml, respectively, and to primary hepatocytes 1.6 microg/ml (PAVAS), 1.6 microg/ml (heparin), 2.6 microg/ml (DS) and 4.1 microg/ml (PAMPS). These values are in the same range as the concentrations required for these compounds to prevent such viruses as herpesviruses and HIV from binding to cells. These findings may be helpful in elucidating the mechanism of the initial interaction of HBV with hepatocytes.

Amino-terminal truncation of CXCR3 agonists impairs receptor signaling and lymphocyte chemotaxis, while preserving antiangiogenic properties

The interferon (IFN)-inducible chemokines, specifically, IFN-gamma-inducible protein-10 (IP-10), monokine induced by IFN-gamma (Mig), and IFN-inducible T-cell alpha-chemoattractant (I-TAC), share a unique CXC chemokine receptor (CXCR3). Recently, the highly specific membrane-bound protease and lymphocyte surface marker CD26/dipeptidyl peptidase IV (DPP IV) was found to be responsible for posttranslational processing of chemokines. Removal of NH(2)-terminal dipeptides by CD26/DPP IV alters chemokine receptor binding and signaling, and hence inflammatory and anti-human immunodeficiency virus (HIV) activities. CD26/DPP IV and CXCR3 are both markers for Th1 lymphocytes and, moreover, CD26/DPP IV is present in a soluble, active form in human plasma. This study reports that at physiologic enzyme concentrations CD26/DPP IV cleaved 50% of I-TAC within 2 minutes, whereas for IP-10 and Mig the kinetics were 3- and 10-fold slower, respectively. Processing of IP-10 and I-TAC by CD26/DPP IV resulted in reduced CXCR3-binding properties, loss of calcium-signaling capacity through CXCR3, and more than 10-fold reduced chemotactic potency. Moreover, IP-10 and I-TAC cleaved by CD26/DPP IV acted as chemotaxis antagonists and CD26/DPP IV-truncated IP-10 and Mig retained their ability to inhibit the angiogenic activity of interleukin-8 in the rabbit cornea micropocket model. These data demonstrate a negative feedback regulation by CD26/DPP IV in CXCR3-mediated chemotaxis without affecting the angiostatic potential of the CXCR3 ligands IP-10 and Mig.

In vitro activity of polyhydroxycarboxylates against herpesviruses and HIV

The antiviral activity of 17 polyhydroxycarboxylates derived from phenolic compounds was evaluated against herpesviruses and HIV. When present during virus adsorption several of the polymers exhibited potent activity against herpes simplex virus type 1 (HSV-1), HSV-2, thymidine kinase deficient HSV-1, human cytomegalovirus (HCMV) and HIV-1 and HIV-2 at concentrations that were not toxic to the host cells. A close correlation was found between the 50% inhibitory concentrations of the polyhydroxycarboxylates against HCMV-induced cytopathicity, their inhibitory effect on the expression of HCMV-specific immediate early antigens and their inhibitory effects on HCMV adsorption to the cells. The antiviral activity of the phenolic polymers was dependent on the presence of a sufficient number of carboxylic groups. The mechanism of antiviral action of the polyhydroxycarboxylates can thus be ascribed to inhibition of virus adsorption. This type of compound may have potential in a vaginal gel to prevent sexual transmission of HSV and HIV.

Antiviral agents active against human herpesviruses HHV-6, HHV-7 and HHV-8

A series of antiviral compounds were examined for their activity against human herpesvirus type 6 (HHV-6), type 7 (HHV-7) and type 8 (HHV-8). They were selected either because they are already approved for clinical use in the treatment of herpesvirus infections (acyclovir, valaciclovir, penciclovir, famciclovir, ganciclovir, brivudin, foscarnet and cidofovir) or have demonstrated marked activity against herpesviruses (lobucavir, H2G, A-5021, D/L-cyclohexenyl G and S2242). In view of their host cell specificity, different cells and assays had to be used for determining antiviral activity against these three viruses. The most potent compounds with the highest antiviral selectivity index were: (i) for HHV-6; foscarnet, S2242, A-5021 and cidofovir; (ii) for HHV-7; S2242, cidofovir and foscarnet; and (iii) for HHV-8; S2242, cidofovir and ganciclovir. As mycophenolic acid has been shown to enhance significantly the activity of acyclic guanosine analogues (such as acyclovir, penciclovir and ganciclovir) in vitro against HSV-1, HSV-2, VZV and HCMV, it would seem worth evaluating whether mycophenolic acid also potentiates the activity of these acyclic guanosine analogues against HHV-6, -7 and -8.

Carrier-mediated delivery improves the efficacy of 9-(2-phosphonylmethoxyethyl)adenine against hepatitis B virus

We recently synthesized a lipophilic prodrug of 9-(2-phosphonyl-methoxyethyl)adenine (PMEA), designated PMEA-LO, and incorporated it into reconstituted lactosylated high-density lipoprotein (LacNeoHDL). In a rat model, LacNeoHDL-associated PMEA-LO was internalized by the asialoglycoprotein receptor on parenchymal liver cells and converted into its active diphosphorylated metabolite. To further evaluate the therapeutic potential of the carrier-associated prodrug, we examined in this study the processing of (125)I-labeled PMEA-LO--loaded LacNeoHDL by HepG2 cells. Upon incubation with HepG2 cells, PMEA-LO--loaded LacNeoHDL became rapidly cell-associated. The association was saturable and of high-affinity (k(d) = 3.8 +/- 0.4 nM). Asialofetuin, an established ligand for the asialoglycoprotein receptor, inhibited the association by >75%, which confirms the role of the asialoglycoprotein receptor. Association of the prodrug-loaded particles to HepG2 cells was coupled to degradation. Radiolabeled degradation products appeared in the culture medium with a lag phase of 2 h. Asialofetuin and chloroquine inhibited secretion of degradation products by 75 to 80%, indicating that PMEA-LO--loaded LacNeoHDL is internalized via the asialoglycoprotein receptor and lysosomally processed. The therapeutic potential of LacNeoHDL-associated PMEA-LO was studied by measuring its effects on hepatitis B virus (HBV) replication in Hep AD38 cells (HBV-transfected HepG2 cells). LacNeoHDL-associated PMEA-LO effectively inhibited HBV DNA synthesis. The EC(50) value of carrier-associated PMEA-LO was 35 times lower than that of free PMEA (3.4 +/- 0.4 and 120 +/- 18 ng of PMEA/ml, respectively). We conclude that the present results, combined with our earlier in vivo disposition data, underscore the therapeutic potential and utility of PMEA-LO--loaded LacNeoHDL for treatment of chronic hepatitis B.

Novel 3-(2-adamantyl)pyrrolidines with potent activity against influenza A virus-identification of aminoadamantane derivatives bearing two pharmacophoric amine groups

The 3-(2-adamantyl)pyrrolidines 8a-g, 14 were synthesized and evaluated for activity against influenza A virus. The parent N-H compound 14 was several times more active than amantadine against H(2)N(2) and H(3)N(2) influenza A virus. The combined use of NMR spectroscopy and computational chemistry showed that the conformation around the pyrrolidine-adamantyl carbon-carbon bond is trans and the pyrrolidine heterocycle has an envelope conformation with C-2 out of the plane of the other ring atoms. N-Dialkylaminoethyl substitution of compound 14 resulted in the potent diamine analogues 8e,f,g. Interestingly, their lactam amine precursors were also active. Compounds 8e,f,g are the first adamantane derivatives, bearing two amine groups, reported to be active against influenza A virus.