Construction of an infectious horsepox virus vaccine from chemically synthesized DNA fragments.

Edward Jenner and his contemporaries believed that his variolae vaccinae originated in horses and molecular analyses show that modern vaccinia virus (VACV) strains share common ancestry with horsepox virus (HPXV). Given concerns relating to the toxicity of modern VACV vaccines, we asked whether an HPXV-based vaccine might provide a superior alternative. Since HPXV may be extinct and the only specimen of HPXV that has been identified is unavailable for investigation, we explored whether HPXV could be obtained by large-scale gene synthesis. Ten large (10-30 kb) fragments of DNA were synthesized based on the HPXV sequence along with two 157 nt VACV terminal sequences, and were recombined into a live synthetic chimeric HPXV (scHPXV) in cells infected with Shope fibroma virus (SFV). Sequencing of the 212 kbp scHPXV confirmed it encoded a faithful copy of the input DNA. We believe this is the first complete synthesis of a poxvirus using synthetic biology approaches. This scHPXV produced smaller plaques, produced less extracellular virus and exhibited less virulence in mice than VACV, but still provided vaccine protection against a lethal VACV challenge. Collectively, these findings support further development of scHPXV as a novel replication-proficient smallpox vaccine.

Development of a High-Content Orthopoxvirus Infectivity and Neutralization Assays.

Currently, a number of assays measure Orthopoxvirus neutralization with serum from individuals, vaccinated against smallpox. In addition to the traditional plaque reduction neutralization test (PRNT), newer higher throughput assays are based on neutralization of recombinant vaccinia virus, expressing reporter genes such as ß-galactosidase or green fluorescent protein. These methods could not be used to evaluate neutralization of variola virus, since genetic manipulations of this virus are prohibited by international agreements. Currently, PRNT is the assay of choice to measure neutralization of variola virus. However, PRNT assays are time consuming, labor intensive, and require considerable volume of serum sample for testing. Here, we describe the development of a high-throughput, cell-based imaging assay that can be used to measure neutralization, and characterize replication kinetics of various Orthopoxviruses, including variola, vaccinia, monkeypox, and cowpox.

Molecular investigation and cultivation of camelpox virus in Iran.

Camelpox virus (genus Orthopoxvirus, family Poxviridae) is the etiologic agent of camel pox. The clinical manifestations of this virus range from inapparent infection to mild, moderate and, less commonly, severe systemic infection and death. Following an outbreak of camelpox, samples that were collected from camel flocks suspected to have camelpox in Qom Province in central Iran and Khash city, Sistan and Baluchestan Province and South Khorasan Province in eastern Iran were sent to Razi Vaccine and Serum Research Institute in Mashhad. DNA extraction was performed primarily by the phenol-chloroform method, and PCR was carried out using a Bioneer kit. Using the primer pair 5'-AAT-ACA-AGG-AGG-ATC-T-3' and 5'-CTT-AAC-TTT-TTC-TTT-CTC-3', the gene sequence encoding the A-type inclusion protein (ATIP) was amplified. The size of the PCR product, specific for camelpox virus, was 881 bp. The PCR product was purified, and to confirm its sequence, it was sent to the reference laboratory. The sequence was subjected to a BLAST search and then phylogenetically analyzed using CLC software. The results showed that all samples were nearly 100 % identical to each other and to strains CMS and M-96. These isolates also had 99 % and 95 % similarity to the CP-1 strain and isolate FIN/T2000, respectively. In Vero cell culture, inoculation with this virus caused a cytopathic effect (CPE), which appeared 2-5 days post-inoculation. Characteristic CPE showing foci of rounded cells, ballooning, giant-cell formation and syncytia with degenerative changes appeared.

Activities of several classes of acyclic nucleoside phosphonates against camelpox virus replication in different cell culture models.

Camelpox virus (CMLV) is the closest known virus to variola virus. Here we report on the anti-CMLV activities of several acyclic nucleoside phosphonates (ANPs) related to cidofovir [(S)-1-(3-hydroxy-2-phosphonomethoxypropyl)cytosine (HPMPC; Vistide)] against two CMLV strains, CML1 and CML14. Cytopathic effect (CPE) reduction assays performed with human embryonic lung fibroblast monolayers revealed the selectivities of the first two classes of ANPs (cHPMPA, HPMPDAP, and HPMPO-DAPy) and of the hexadecyloxyethyl ester of 1-{[(5S)-2-hydroxy-2-oxido-1,4,2-dioxaphosphinan-5-yl]methyl}-5-azacytosine (HDE-cHPMP-5-azaC), belonging to the newly synthesized ANPs, which are HPMP derivatives containing a 5-azacytosine moiety. The inhibitory activities of ANPs against both strains were also confirmed with primary human keratinocyte (PHK) monolayers, despite the higher toxicity of those molecules on growing PHKs. Virus yield assays confirmed the anti-CML1 and anti-CML14 efficacies of the compounds selected for the highest potencies in CPE reduction experiments. Ex vivo studies were performed with a 3-dimensional model of human skin, i.e., organotypic epithelial raft cultures of PHKs. It was ascertained by histological evaluation, as well as by virus yield assays, that CMLV replicated in the human skin equivalent. HPMPC and the newly synthesized ANPs proved to be effective at protecting the epithelial cells against CMLV-induced CPE. Moreover, in contrast to the toxicity on PHK monolayers, signs of toxicity in the differentiated epithelium were seen only at high ANP concentrations. Our results demonstrate that compounds belonging to the newly synthesized ANPs, in addition to cidofovir, represent promising candidates for the treatment of poxvirus infections.

Long-lasting stability of vaccinia virus (orthopoxvirus) in food and environmental samples.

Poxviruses are known to remain infectious in the scabs of patients for months to years. The aim of this study was to investigate viral stability in storm water, food or gauze spiked with vaccinia virus strain Munich 1 (VACV M1). Storm water, storm water supplemented with either fetal calf serum (FCS) or potting soil was stored at two different temperatures (refrigerator, room temperature; 4 degrees C/25 degrees C). In addition, we analysed the viability of VACV M1 on the surface of bread, salad, sausages and gauze bandages stored at 4 degrees C. Samples were titrated in MA 104 cells and the presence of viral DNA was demonstrated by orthopoxvirus-specific PCRs. After 2 weeks, reisolation of VACV M1 from all kinds of food, bandage and water samples except for storm water supplemented with potting soil was possible. Viral DNA was detected in almost all samples by PCR. Prolonged experiments with VACV M1-spiked storm water and storm water supplemented with FCS revealed that samples kept at 4.5 degrees C are infectious for up to 166 days. Our data demonstrate that VACV M1 has a longlasting stability in water and food. The results obtained during this study should be taken into account for risk assessment calculations for poxvirus transmission. Implying that variola virus and vaccinia virus behave in a similar way, our data call for sophisticated countermeasures in cases of a variola release in biological warfare.

Activity of the anti-orthopoxvirus compound ST-246 against vaccinia, cowpox and camelpox viruses in cell monolayers and organotypic raft cultures.

BACKGROUND: The potential use of variola virus as a biological weapon has renewed efforts in the development of antiviral agents against orthopoxviruses. ST-246 [4-trifluoromethyl-N-(3,3a,4,4a,5,5a,6,6a-octahydro-1,3-di oxo-4,6-ethenocycloprop [f]isoindol-2(1 H)-yl)-benzamide] is an anti-orthopoxvirus compound active against several orthopoxviruses including vaccinia virus (VV), cowpox virus (CPV), camelpox virus (CMLV), ectromelia virus (ECTV) and variola virus in cell culture. The compound has been shown to inhibit the release of extracellular virus by targeting the F13L W protein and to protect mice from W, CPV and ECTV orthopoxvirus-induced disease. METHODS: The antiviral activity of ST-246 was assessed against extracellular and intracellular W, CPV and CMLV production in human embryonic lung (HEL) fibroblasts and primary human keratinocyte (PHK) cell monolayers, as well as in three-dimensional raft cultures. RESULTS: ST-246 inhibited preferentially the production of extracellular virus compared with intracellular virus production in HEL and PHK cells (for W) and in PHK cells (for CMLV). In organotypic epithelial raft cultures, ST-246 at 20 microg/ml inhibited extracellular W and CMLV production by 6 logs, whereas intracellular virus yield was reduced by 2 logs. In the case of CPV, both extracellular and intracellular virus production were completely inhibited by ST-246 at 20 microg/ml. Histological sections of the infected rafts, treated with increasing amounts of drug, confirmed the antiviral activity of ST-246: the epithelium was protected and there was no evidence of viral infection. Electron microscopic examination confirmed the absence of intracellular enveloped virus forms in W-, CPV- and CMLV-infected cells treated with 10 microg/ml of ST-246. CONCLUSIONS: These data indicate that ST-246 is a potent anti-orthopoxvirus compound; the mode of inhibition is dependent on the virus and cell type.

Inhibitory efficacy of cyclosal-nucleoside monophosphates of aciclovir and brivudin on DNA synthesis of orthopoxvi ruses.

Previous studies have shown that cycloSaligenyl-monophosphate (cycloSal-MP) derivatives of aciclovir (ACV), penciclovir (PCV) and brivudin (BVDU) can act as inhibitors of vaccinia virus and cowpox virus replication in vitro. The aim of the present study was to evaluate the inhibatory efficacy on DNA synthesis in vaccinia and cowpox viruses of several cycloSal-pro-nucleotides of ACV and BVDU, which have proven activity against pox viruses. Viral DNA was quantified in treated and non-treated virus-infected cells by semi-quantitative PCR on the basis of the haemagglutinin protein gene of orthopoxviruses. As result, an inhibitory efficacy on vaccinia and cowpox virus DNA replication could be demonstrated for 3-methyl-cycloSal-ACVMP, 5-H-cycloSal-ACVMP, 6-chloro-7-ECM-cycloSal-3'-OH-BVDUMP, and 6-chloro-7-methyl-cycloSal-3'-OH-BVDUMP. At concentrations of 32-128 mg/ml, 3-methyl-cyc/oSal-ACVMP and 6-chloro-7-ECM-cycloSal-3'OH-BVDUMP inhibited synthesis of viral DNA to a similar extent as the well-known inhibitors of pox viruses, cidofovir and 5-iodo-dUrd (deoxyuridine). When concentrations of 128 mg/ml were administered, both test substances diminished the amount of viral genome copies by > or =4 log10 corresponding to > or =99.99% reduction. In conclusion, selected cycloSal-pro-nucleotide derivatives of ACV and BVDU can inhibit orthopoxviral DNA synthesis. The high inhibitory efficacy on both replication of viral DNA and infectious viral particles in cell cultures makes these compounds promising candidates for in vivo experiments.

Development in lipid drugs.

Lipopeptide lipid moieties induce dendritic cell (DC) internalization and epitopes are recognized by MHC, the major histocompatibility complex. HIV-1 (human immunodeficiency virus type 1) lipopeptide vaccine candidate elicits immune responses, and sustains HIV control after highly active antiretroviral therapy (HAART). Mp- and Dp-MART (anti-melanoma lipopeptides) induce strong CTL (cytolytic T lymphocyte) response. New BGTC, BGDA, TGKC lipoplexes mediate gene delivery, e.g., into mouse pancreatic tumor nodules. Triterpene glycyrrhizic acid (GL) inhibits SARS-CoV (severe acute respiratory syndrome associated coronavirus) replication. Compared to CDV (cidofovir), CDV ether lipid esters have enhanced activity against vaccinia (VV) and cowpox (CV) viruses in vitro. Oral treatment of VV and CV infected mice with CDV ether lipid esters, as effective as i.p. CDV, may be useful against orthopoxvirus infections in humans.

The 4',4'-difluoro analog of 5'-noraristeromycin: a new structural prototype for possible antiviral drug development toward orthopoxvirus and cytomegalovirus.

As a surrogate for 4'-hydroxy-5'-noraristeromycin and related carbocyclic nucleosides, an efficient, enantiodivergent synthetic route to both enantiomers of 5-(6-amino-9H-purin-9-yl)-3,3-difluorocyclopentane-1,2-diol (6 and ent-6) has been developed from a common starting material ((+)-(1R,4S)-4-hydroxy-2-cyclopenten-1-yl acetate, 10). Both compounds were assayed versus a series of viruses. The only response found was for compound 6 toward vaccinia and cowpox (EC50 of 143 and 94 microM, respectively) and human cytomegalovirus (EC50 of 6.2 microM). Both compounds were non-cytotoxic. While not as active as cidofovir toward the orthopox viruses and ganciclovir toward cytomegalovirus, compound 6 offers a new structural prototype upon which to build for uncovering new agents effective against these viral types.

Cutaneous infections of mice with vaccinia or cowpox viruses and efficacy of cidofovir.

Orthopoxviruses, including smallpox, monkeypox and molluscipox, pose risks to human health through bioterrorist acts or natural transmission. There is no approved therapy for orthopoxvirus infections; however, cidofovir (CDV) has been approved as an investigational new drug for emergency treatment of adverse effects following smallpox vaccination. For evaluation of new therapies directed against orthopoxvirus infections, we have utilized immunocompetent, hairless mice (SKH-1) inoculated by a cutaneous route with cowpox virus (CV) or vaccinia virus (VV). Mice subsequently developed skin lesions and virus was recovered from the site of inoculation and quantified. Skin biopsies were evaluated microscopically, revealing brick-like eosinophilic, intracytoplasmic inclusion bodies characteristic of orthopoxvirus infection. SKH-1 mice fully recovered from either CV or VV infection. Immunodeficient Athymic or Rhino mice inoculated with CV or VV had more lesions and severe disease than SKH-1 mice. CV-infected SKH-1 mice were treated either with systemic or topical CDV. Although some protection was achieved with systemic treatment, 5% topical CDV was most effective at reducing virus titers in skin, lung, kidney, and spleen. These models may provide a means for evaluating efficacy of new therapies directed against orthopoxvirus diseases and further confirm the topical activity of CDV against cutaneous infections.

Evaluation of nucleoside phosphonates and their analogs and prodrugs for inhibition of orthopoxvirus replication.

In the event of a bioterrorism attack using smallpox virus, there currently is no approved drug for the treatment of infections with this virus. We have reported previously that (S)-1-[3-hydroxy-2-(phosphonomethoxy)propyl]cytosine (HPMPC) (also known as cidofovir [CDV]) has good activity against poxvirus infections; however, a major limitation is the requirement for intravenous administration. Two related acyclic nucleoside phosphonates (ANPs), adefovir (PMEA) and tenofovir (PMPA), are active against human immunodeficiency virus or hepatitis B virus but do not have activity against the orthopoxviruses. Therefore, we have evaluated a number of analogs and potential oral prodrugs of these three compounds for their ability to inhibit the replication of vaccinia virus or cowpox virus in tissue culture cells. The most-active compounds within the CDV series were (S)-HPMPA and (butyl L-alaninyl) cyclic HPMPC, with 50% effective concentrations (EC(50)s) from 4 to 8 microM, compared with 33 to 43 microM for CDV. Although PMEA itself was not active, adefovir dipivoxil [bis[(pivaloyl)oxymethyl] PMEA] and bis(butyl L-alaninyl) PMEA were active against both viruses, and bis(butyl L-alaninyl) PME-N6-(cyclopropyl)DAP and (isopropyl L-alaninyl)phenyl PME-N6-(cyclopropyl)DAP were the most active compounds tested, with EC(50)s of 0.1 to 2.6 microM. In the PMPA series, none of the analogs tested had significantly better activity than PMPA itself. These data indicate that a number of these ANP derivatives have activity against vaccinia virus and cowpox virus in vitro and should be evaluated for their efficacies in animal models.

Potential antiviral therapeutics for smallpox, monkeypox and other orthopoxvirus infections.

We assessed the activities of 24 different antiviral compounds against smallpox (two strains of variola major and one of variola minor), monkeypox, vaccinia and cowpox viruses by a neutral red uptake assay. To establish assay parameters, we examined viral replication and its inhibition at various times postinfection and at several multiplicities of infection. Drugs were selected to target a range of functions involved in viral replication. Eight compounds (cidofovir, cyclic HPMPC (cHPMPC), HPMPA, ribavirin, tiazofurin, carbocyclic 3-deazaadenosine, 3-deazaneplanocin A and DFBA (1-(2,4-difluorobenzyloxy)adenosine perchlorate)-a derivative of adenosine N1-oxide) inhibited the replication of all three variola strains and the other orthopoxviruses at drug concentrations within a pharmacologically achievable range. Two others (methisazone and bis-POM-PMEA) showed a lesser degree of antiviral effect, while the remainder were inactive. To examine possible naturally occurring drug resistance among a large number of variola isolates obtained from different geographical regions and at different times, we examined the sensitivity of 35 different strains of variola as well as other orthopoxviruses to a subset of three of the most active compounds: cidofovir, cHPMPC, and ribavirin. Preliminary data indicate that nearly all isolates appear to have similar drug sensitivities. These findings are currently being verified and expanded.

[Molecular factors of orthopoxvirus virulence]. / Molekuliarnye faktory virulentnosti ortopoksvirusov.

Orthopoxviruses encode numerous virulence factors. Viral inhibitors of apoptosis of infected cells have been revealed in recent years. Viral inhibitors of the host's non-specific inflammatory reactions are shown to play an important role in effectively propagating the virus. A number of inhibitors of antiviral interferon action cause a high interferon resistance of orthopoxviruses. Some modulators of immune response of the infected body encoded by orthopoxviruses have been discovered in the past years. Viral growth factor, some proteins of the envelope of extracellular virions, etc. are shown to be important for viral dissemination in the host. A general scheme of synthesis of molecular factors of orthopoxviral virulence is discussed.

Multigenic evasion of inflammation by poxviruses.

Analyses of different cowpox virus (Brighton Red strain [CPV-BR]) mutants indicate that there is a minimum of three genes encoded by CPV-BR that are nonessential for virus replication in tissue culture but are involved in inhibiting the generation of an inflammatory response in the chicken embryo chorioallantoic membrane (CAM) model. The CPV-BR-encoded anti-inflammatory genes include the gene encoding the 38-kDa protein (also called 38K, crmA, SPI-2, or VV-WR-ORF-B13R), a tumor necrosis factor receptor homolog, and an unidentified gene that maps to the right end of the CPV genome. The kinetics of triggering of an inflammatory response at the site of virus infection as well as the magnitude of the response is dependent on the virus-encoded inhibitor that is deleted. Virus yields recovered from pocks decreased in proportion to the magnitude of the inflammatory response. The deletion of these identified inhibitors of inflammation was associated with attenuation of the mutant viruses in mice. These data confirm the existence of multiple poxvirus-encoded host defense modifiers whose function is to block the generation of an inflammatory response at the site of virus infection, which allows enhanced virus replication and potentially facilitates virus transmission.