Biomedical subjects
Publications and source records attributed to Johan Neyts.
A key compound, 2-amino-6-chlor-9-(2,3-dideoxy-3-fluoro-beta-D-erythro-pentofuranosyl)puine, was prepared from 2-amino-6-chloropurine riboside in 5 steps, then subjected to the nucleophilic displacement with benzenethiols to afford 6-arylthio congeners. These compounds showed a similar anti-HBV effect to that of 2',3' dideoxy-3'-fluoroguanosine.
Ribavirin antagonizes the in vitro anti-hepatitis C virus (HCV) activity of the pyrimidine nucleoside analogue 2'-C-methylcytidine, the active component of the experimental anti-HCV drug valopicitabine. In contrast, the combination of ribavirin with either the purine nucleoside analogue 2'-C-methyladenosine or the HCV protease inhibitor VX-950 resulted in an additive antiviral activity. These findings may have implications when planning clinical studies with valopicitabine.
We report on the highly potent and selective antipestivirus activity of 5-[(4-bromophenyl)methyl]-2-phenyl-5H-imidazo[4,5-c]pyridine (BPIP). The 50% effective concentration (EC50) for inhibition of bovine viral diarrhea virus (BVDV)-induced cytopathic effect formation was 0.04 +/- 0.01 microM. Comparable reduction of viral RNA synthesis (EC50 = 0.12 +/- 0.02 microM) and production of infectious virus (EC50= 0.074 +/- 0.003 microM) were observed. The selectivity index (ratio of 50% cytostatic concentration/EC50) of BPIP was approximately 2,000. BPIP was inactive against the hepatitis C virus subgenomic replicon and yellow fever virus but demonstrated weak activity against GB virus. Drug-resistant mutants were at least 300-fold less susceptible to BPIP than wild-type virus; showed cross-resistance to N-propyl-N-[2-(2H-1,2,4-triazino[5,6-b]indol-3-ylthio)ethyl]-1-propanamine (VP32947), and carried the F224S mutation in the viral RNA-dependent RNA polymerase (RdRp). When the F224S mutation was introduced into an infectious clone, the drug-resistant phenotype was obtained. BPIP did not inhibit the in vitro activity of recombinant BVDV RdRp, but did inhibit the activity of replication complexes (RCs). Computational docking revealed that F224 is located at the top of the finger domain of the polymerase. Docking of BPIP in the crystal structure of the BVDV RdRp revealed aromatic ring stacking, some hydrophobic contacts, and a hydrogen bond. Since two structurally unrelated compounds, i.e., BPIP and VP32947, target the same region of the BVDV RdRp, this position may be expected to be critical in the functioning of the polymerase or assembly of the RC. The potential of BPIP for the treatment of pestivirus and hepacivirus infections is discussed.
There is concern that variola virus, the aetiological agent of smallpox, may be used as a biological weapon. For this reason several countries are now stockpiling (vaccinia virus-based) smallpox vaccine. Although the preventive use of smallpox vaccination has been well documented, little is known about its efficacy when used after exposure to the virus. Here we compare the effectiveness of (1) post-exposure smallpox vaccination and (2) antiviral treatment with either cidofovir (also called HPMPC or Vistide) or with a related acyclic nucleoside phosphonate analogue (HPMPO-DAPy) after lethal intratracheal infection of cynomolgus monkeys (Macaca fascicularis) with monkeypox virus (MPXV). MPXV causes a disease similar to human smallpox and this animal model can be used to measure differences in the protective efficacies of classical and new-generation candidate smallpox vaccines. We show that initiation of antiviral treatment 24 h after lethal intratracheal MPXV infection, using either of the antiviral agents and applying various systemic treatment regimens, resulted in significantly reduced mortality and reduced numbers of cutaneous monkeypox lesions. In contrast, when monkeys were vaccinated 24 h after MPXV infection, using a standard human dose of a currently recommended smallpox vaccine (Elstree-RIVM), no significant reduction in mortality was observed. When antiviral therapy was terminated 13 days after infection, all surviving animals had virus-specific serum antibodies and antiviral T lymphocytes. These data show that adequate preparedness for a biological threat involving smallpox should include the possibility of treating exposed individuals with antiviral compounds such as cidofovir or other selective anti-poxvirus drugs.
INTRODUCTION: Severe acute respiratory syndrome (SARS) is an emerging infectious disease that first occurred in humans in the People's Republic of China in November 2002 and has subsequently spread worldwide. A novel virus belonging to the Coronaviridae family has been identified as the cause of this pulmonary disease. The severity of the disease combined with its rapid spread requires the development of fast and sensitive diagnostic assays. RESULTS: A real-time quantitative RT-PCR was designed in the nsp11 region of the replicase 1B domain of the SARS-coronavirus (SARS-CoV) genome. To evaluate this quantitative RT-PCR, cRNA standards were constructed by in vitro transcription of SARS-CoV Frankfurt 1 RNA using T7 RNA polymerase, followed by real-time RT-PCR. The assay allowed quantitation over a range of 10(2) to 10(8) RNA copies per reaction. CONCLUSIONS: Extrapolated to clinical samples, this novel assay has a detection range of 10(4) to 10(10) copies of viral genome equivalents per millilitre. In comparison to the current de facto cRNA Artus Biotech standard, the in-house cRNA standard gives a 100-fold higher absolute quantity, suggesting a possible underestimation of the viral load when using the Artus Biotech standard.
Vero E6 cells are commonly used for in vitro studies of the severe acute respiratory syndrome-associated coronavirus (SARS-CoV) and for antiviral evaluation purposes. A better understanding of the SARS-CoV growth kinetics in Vero E6 cells is crucial to help elucidate the mechanism of antiviral activity of selective antiviral agents. In this study, the growth kinetics of SARS-CoV in Vero E6 cells were studied by quantitation of intra- and extracellular viral RNA load as well as extracellular virus yield at different time points post-infection. At 12h post-infection, the intracellular viral RNA load was 3x10(2)-fold higher than at the time of infection, and the extracellular viral RNA load was increased with a factor of 2 x 10(3). Intracellular viral RNA levels started to rise at 6h post-infection. One hour later (at 7h post-infection), the levels of extracellular SARS-CoV RNA also began to rise. This was corroborated by the fact that infectious progeny SARS-CoV also first appeared in the supernatant between 6 and 7h post-infection. At 12h post-infection, SARS-CoV reached titers in the supernatant of 5.2 x 10(3) CCID(50)/ml.
Starting from commercially available (rac)-3-cyclohexene-1-carboxylic acid, a series of purine and pyrimidine cis-substituted cyclohexenyl and cyclohexanyl nucleosides were synthesized through a key Mitsunobu reaction. Antiviral evaluations were performed on HIV, coxsackie B3, and herpes viruses (HSV-1, HSV-2, VZV, HCMV). Three compounds showed moderate activity against HSV-1 and coxsackie viruses. Specific computer modeling studies were performed on HSV-1 thymidine kinase in order to understand the enzyme activation of an analogue showing moderate antiviral activity.
ST-246 is a low-molecular-weight compound (molecular weight = 376), that is potent (concentration that inhibited virus replication by 50% = 0.010 microM), selective (concentration of compound that inhibited cell viability by 50% = >40 microM), and active against multiple orthopoxviruses, including vaccinia, monkeypox, camelpox, cowpox, ectromelia (mousepox), and variola viruses. Cowpox virus variants selected in cell culture for resistance to ST-246 were found to have a single amino acid change in the V061 gene. Reengineering this change back into the wild-type cowpox virus genome conferred resistance to ST-246, suggesting that V061 is the target of ST-246 antiviral activity. The cowpox virus V061 gene is homologous to vaccinia virus F13L, which encodes a major envelope protein (p37) required for production of extracellular virus. In cell culture, ST-246 inhibited plaque formation and virus-induced cytopathic effects. In single-cycle growth assays, ST-246 reduced extracellular virus formation by 10 fold relative to untreated controls, while having little effect on the production of intracellular virus. In vivo oral administration of ST-246 protected BALB/c mice from lethal infection, following intranasal inoculation with 10x 50% lethal dose (LD(50)) of vaccinia virus strain IHD-J. ST-246-treated mice that survived infection acquired protective immunity and were resistant to subsequent challenge with a lethal dose (10x LD(50)) of vaccinia virus. Orally administered ST-246 also protected A/NCr mice from lethal infection, following intranasal inoculation with 40,000x LD(50) of ectromelia virus. Infectious virus titers at day 8 postinfection in liver, spleen, and lung from ST-246-treated animals were below the limits of detection (<10 PFU/ml). In contrast, mean virus titers in liver, spleen, and lung tissues from placebo-treated mice were 6.2 x 10(7), 5.2 x 10(7), and 1.8 x 10(5) PFU/ml, respectively. Finally, oral administration of ST-246 inhibited vaccinia virus-induced tail lesions in Naval Medical Research Institute mice inoculated via the tail vein. Taken together, these results validate F13L as an antiviral target and demonstrate that an inhibitor of extracellular virus formation can protect mice from orthopoxvirus-induced disease.
It is not yet clear to what extent depletion of intracellular GTP pools contributes to the antiviral activity of ribavirin. Therefore, the antiviral activities of (i) ribavirin, (ii) its 5-ethynyl analogue, 5-ethynyl-1-beta-D-ribofuranosylimidazole-4-carboxamide (EICAR), and (iii) mycophenolic acid (MPA) (a compound that inhibits only cellular IMP dehydrogenase activity) were studied on the replication of flaviviruses and paramyxoviruses. In addition, the effects of these three compounds on intracellular GTP pools were assessed. A linear correlation was observed over a broad concentration range between the antiviral activities of ribavirin, EICAR, and MPA and the effects of these compounds on GTP pool depletion. When the 50% effective concentrations (EC50s) for the antiviral activities of ribavirin, EICAR, and MPA were plotted against the respective EC50 values for GTP pool depletion, a linear correlation was calculated. These data provide compelling evidence that the predominant mechanism of action of ribavirin in vitro against flavi- and paramyxoviruses is based on inhibition of cellular IMP dehydrogenase activity.
We report on chloroquine, a 4-amino-quinoline, as an effective inhibitor of the replication of the severe acute respiratory syndrome coronavirus (SARS-CoV) in vitro. Chloroquine is a clinically approved drug effective against malaria. We tested chloroquine phosphate for its antiviral potential against SARS-CoV-induced cytopathicity in Vero E6 cell culture. Results indicate that the IC50 of chloroquine for antiviral activity (8.8 +/- 1.2 microM) was significantly lower than its cytostatic activity; CC50 (261.3 +/- 14.5 microM), yielding a selectivity index of 30. The IC50 of chloroquine for inhibition of SARS-CoV in vitro approximates the plasma concentrations of chloroquine reached during treatment of acute malaria. Addition of chloroquine to infected cultures could be delayed for up to 5h postinfection, without an important drop in antiviral activity. Chloroquine, an old antimalarial drug, may be considered for immediate use in the prevention and treatment of SARS-CoV infections.
Myocarditis is a common cause of dilated cardiomyopathy, one of the most important single causes of heart transplantation. Coxsackie B viruses (CBV) are considered to be the principal etiological agents of viral myocarditis and direct virus-induced damage to the heart tissue has been suggested to be the main mechanism underlying myocarditis in the murine model [Horwitz et al. 2000 Nat Med 6:693-697]. We demonstrate that 2-(3,4-dichloro-phenoxy)-5-nitrobenzonitrile (DNB), a compound that was earlier shown to exhibit broad-spectrum anti-picornavirus activity is also markedly active against CBV replication in primary human myocard fibroblast. To challenge the hypothesis of [Horwitz et al. 2000 Nat Med 6:693-697] we assessed whether DNB is able to prevent the development of CBV-induced myocarditis in a murine model. Subcutaneous (s.c.) administration of DNB at 250 mg/kg/day, at multiple injection sites (m.i.s.), for a period of seven consecutive days (starting at 1 day before infection) to 4-week old C3H-mice resulted in a (i) 62% reduction in the number of myocarditis foci as compared to the untreated control animals (p = 1.7 x 10(-10)) and (ii) a concomitant reduction in viral titers in the heart. These findings indicate that selective inhibition of the replication of CBV may have a beneficial effect on the development of viral myocarditis and confirms that direct viral induced damage is the main mechanism underlying CBV-induced myocarditis. Early diagnosis of virus-induced myocarditis will likely be mandatory for an antiviral drug treatment regimen to achieve its greatest clinical benefit.
A real-time quantitative PCR was developed to assess antiviral activity of molecules against human herpesvirus 8 (HHV-8) and the Epstein-Barr virus (EBV). The antiviral activity of the reference molecules acyclovir, ganciclovir, cidofovir, adefovir and brivudin, as assessed by this methodology, proved very similar to the activity as determined by a DNA-DNA hybridisation method.
Flaviviruses cause a variety of diseases including (meningo)encephalitis and hemorrhagic fevers. There is no specific antiviral therapy available for the treatment of infections with flaviviruses and such therapy should be urgently developed. Small animal models that are reminiscent of the disease in man will be instrumental to identify therapeutic strategies against flavivirus infections. Here we review models in mice and hamsters that may be used to assess the efficacy of novel antiviral strategies against flavivirus infections.
In vivo imaging of structural changes in the brain of patients with encephalitis has become an important aid in diagnostic and therapeutic procedures. Diffusion-weighted magnetic resonance imaging (DWI) was employed to quantitate regional and whole-brain diffusion-weighted MRI changes in a hamster model for acute flavivirus encephalitis. The regional apparent diffusion coefficient (ADC) was determined in hyperintense regions seen on T2-weighted images (i.e., the thalamic area and the temporal lobe), but anatomical variation and structural heterogeneity of encephalitic lesions severely impeded the placement of regions of interest (ROI). Therefore, quantitative whole-brain diffusion-weighted imaging was carried out and revealed a significantly reduced ADC (P = .02) in the brain of hamsters with acute encephalitis (n = 7) as compared to that of healthy, uninfected controls (n = 3). Furthermore, the ADC histogram demonstrated a reduced peak height and center of gravity during the acute encephalitis. Our findings could further support the use of diffusion-weighted imaging for in vivo monitoring of acute flavivirus encephalitis and for the study of therapeutic approaches.
Viral replication, as well as an immunopathological component, is assumed to be involved in coxsackie B virus-induced myocarditis. We evaluated the efficacy of the interferon inducer Ampligen on coxsackie B3 virus-induced myocarditis in C3H/HeNHsd mice. The efficacy of Ampligen was compared with that of the interferon inducer poly(inosinic acid)-poly(cytidylic acid) [poly(IC)], alpha interferon 2b (INTRON A), and pegylated alpha interferon 2b (PEG-INTRON-alpha-2b). Ampligen at 20 mg/kg of body weight/day was able to reduce the severity of virus-induced myocarditis, as assessed by morphometric analysis, by 98% (P = 3.0 x 10(-8)). When poly(IC) was administered at 15 mg/kg/day, it reduced the severity of virus-induced myocarditis by 93% (P = 5.6 x 10(-5)). Alpha interferon 2b (1 x 10(5) U/day) and pegylated alpha interferon 2b (5 x 10(5) U/day) were less effective and reduced the severity of virus-induced myocarditis by 66% (P = 0.0009) and 78% (P = 0.0002), respectively. The observed efficacies of Ampligen and poly(IC) were corroborated by the observation that the drugs also markedly reduced the virus titers in the heart, as detected by (i) quantitative real-time reverse transcription-PCR and (ii) titration for infectious virus content. Whereas the electrocardiograms for untreated mice with myocarditis were severely disturbed, the electrocardiographic parameters were normalized in Ampligen- and poly(IC)-treated mice. Even when start of treatment with Ampligen was delayed until day 2 postinfection, a time at which lesions had already appeared in untreated control animals, a marked protective effect on the development of viral myocarditis (as assessed at day 6 postinfection) was still noted.
An animal model that mimics progressive disseminated vaccinia was elaborated. To this end nude (athymic) mice were inoculated intracutaneously with vaccinia virus in the lumbosacral area. Viral replication (DNA) in the skin was detected as early as day 2 postinfection (p.i.). Mice developed typical vaccinia lesions at the site of inoculation by day 4 to 6 p.i. By about 2 weeks p.i., the infection had spread all over the body, a situation reminiscent of disseminated vaccinia in humans. The infection resulted in viremia and spread of the virus to visceral organs, as well as to the brain. Topical treatment with cidofovir, initiated at the day of infection or at day 1 p.i., completely protected against virus-induced cutaneous lesions and against associated mortality. When treatment was initiated at a later time (day 2 to 5 p.i.), a partial but marked protective effect was noted, which can be explained by the fact that by that time, the virus had spread from the skin to the visceral organs. Next, infected animals were left untreated until the time ( approximately 2 weeks p.i.) at which disseminated vaccinia had developed. When systemic treatment with cidofovir was initiated at that time, it caused lesions to heal and regress. In most of these animals, lesions had completely (or almost completely) disappeared by day 10 to 15 after the start of therapy. The observation that cidofovir is able to cause healing of disseminated vaccinia lesions in animals should have implications for the therapy of complications of vaccination against smallpox.
A chimeric flavivirus infectious cDNA was constructed by exchanging the premembrane (prM) and envelope (E) genes of the yellow fever virus vaccine strain 17D (YF17D) with the corresponding genes of Modoc virus (MOD). This latter virus belongs to the cluster of the "not-known vector" flaviviruses and is, unlike YF17D, neuroinvasive in SCID mice. Replication of in vitro-transcribed RNA from this chimeric flavivirus was shown by [(3)H]uridine labeling and RNA analysis. Expression of the MOD prM and E proteins was monitored by radioimmunoprecipitation and revealed that the MOD proteins were correctly and efficiently produced from the chimeric precursor protein. The MOD E protein was shown to be N-linked glycosylated, whereas prM, as predicted from the genome sequence, did not contain N-linked carbohydrates. In Vero cells, the chimeric virus replicated with a similar efficiency as the parental viruses, although it formed smaller plaques than YF17D and MOD. In SCID mice that had been infected intraperitoneally with the chimeric virus, the viral load increased steadily until death. The MOD/YF virus, like MOD from which it had acquired the prM and E structural proteins, but unlike YF, proved neuroinvasive in SCID mice. Animals developed neurological symptoms about 15 days after inoculation and died shortly thereafter. The distribution of MOD/YF RNA in the brain of infected mice was similar to that observed in MOD-infected mice. The observations provide compelling evidence that the determinants of neuroinvasiveness of flaviviruses are entirely located in the envelope proteins prM and E.
BACKGROUND: Viral replication as well as an immunopathological component are assumed to be involved in the development of coxsackie B virus (CBV)-induced myocarditis. We observed that mycophenolic acid (MPA), the active metabolite of the immunosuppressive agent mycophenolate mofetil (MMF), inhibits coxsackie B3 virus (CBV3) replication in primary Human myocardial fibroblasts. We therefore studied whether MMF, which is thus endowed with a direct antiviral as well as immunosuppressive effect, may prevent CBV-induced myocarditis in a murine model. RESULTS: Four week old C3H-mice were infected with CBV3 and received twice daily, for 7 consecutive days (from one day before to 5 days post-virus inoculation) treatment with MMF via oral gavage. Treatment with MMF resulted in a significant reduction in the development of CBV-induced myocarditis as assessed by morphometric analysis, i.e. 78% reduction when MMF was administered at 300 mg/kg/day (p < 0.001), 65% reduction at 200 mg/kg/day (p < 0.001), and 52% reduction at 100 mg/kg/day (p = 0.001). The beneficial effect could not be ascribed to inhibition of viral replication since titers of infectious virus and viral RNA in heart tissue were increased in MMF-treated animals as compared to untreated animals. CONCLUSION: The immunosuppressive agent MMF results in an important reduction of CBV3-induced myocarditis in a murine model.