Treatment of lethal vaccinia virus respiratory infections in mice with cidofovir

Treatment Efficacy of Cidofovir and Brincidofovir against Clade II Monkeypox Virus isolates

While historically confined to endemic areas, Monkeypox virus (MPXV) infection has increasingly garnered international attention due to sporadic outbreaks in non-endemic countries in the last two decades and its potential for human-to-human transmission. In 2022, a multi-country outbreak of mpox disease was declared by the World Health Organization (WHO) and nearly 100,000 mpox cases have been reported since the beginning of this pandemic. The clade II variant of the virus appears to be responsible for the vast majority of these infections. While there are no antiviral drugs currently approved to treat mpox specifically, the use of tecovirimat (TPOXX®) and brincidofovir (Tembexa®) is recommended by the Centers for Disease Control and Prevention (CDC) for compassionate use in severe mpox cases, since both are FDA-approved for the treatment of the closely related smallpox disease. Given the emergence of multiple tecovirimat-resistant infections, we aimed to evaluate the treatment efficacy of brincidofovir and its active compound, cidofovir, against MPXV clade II strains. Following intranasal infection, we show that cidofovir and brincidofovir can strongly reduce the viral replication of MPXV clade IIa and IIb viruses in the respiratory tract of susceptible mice when administered systemically and orally, respectively. The high antiviral activity of both compounds against historical and currently circulating MPXV strains supports their therapeutic potential for clinical application.

Poxvirus A51R proteins regulate microtubule stability and antagonize a cell-intrinsic antiviral response

Numerous viruses alter host microtubule (MT) networks during infection, but how and why they induce these changes is unclear in many cases. We show that the vaccinia virus (VV)-encoded A51R protein is a MT-associated protein (MAP) that directly binds MTs and stabilizes them by both promoting their growth and preventing their depolymerization. Furthermore, we demonstrate that A51R-MT interactions are conserved across A51R proteins from multiple poxvirus genera, and highly conserved, positively charged residues in A51R proteins mediate these interactions. Strikingly, we find that viruses encoding MT interaction-deficient A51R proteins fail to suppress a reactive oxygen species (ROS)-dependent antiviral response in macrophages that leads to a block in virion morphogenesis. Moreover, A51R-MT interactions are required for VV virulence in mice. Collectively, our data show that poxviral MAP-MT interactions overcome a cell-intrinsic antiviral ROS response in macrophages that would otherwise block virus morphogenesis and replication in animals.

Biology of Variola Virus

Variola virus is an anthroponotic agent that belongs to the orthopoxvirus family. It is an etiological agent of smallpox, an ancient disease that caused massive mortality of human populations. Twentieth century has witnessed the death of about 300 million people due to the unavailability of an effective vaccine. Early detection is the primary strategy to prevent an outbreak of smallpox. Variola virus forms the characteristic pus-filled pustules and centrifugal rash distribution in the infected patients while transmission occurs mainly through respiratory droplets during the early stage of infection. No antiviral drugs are approved for variola virus till date. Generation of first-generation vaccines helped in the eradication of smallpox which was declared by the World Health Organization.

mRNA vaccines encoding fusion proteins of monkeypox virus antigens protect mice from vaccinia virus challenge

The recent outbreaks of mpox have raised concerns over the need for effective vaccines. However, the current approved vaccines have either been associated with safety concerns or are in limited supply. mRNA vaccines, which have shown high efficacy and safety against SARS-CoV-2 infection, are a promising alternative. In this study, three mRNA vaccines are developed that encode monkeypox virus (MPXV) proteins A35R and M1R, including A35R extracellular domain -M1R fusions (VGPox 1 and VGPox 2) and a mixture of encapsulated full-length mRNAs for A35R and M1R (VGPox 3). All three vaccines induce early anti-A35R antibodies in female Balb/c mice, but only VGPox 1 and 2 generate detectable levels of anti-M1R antibodies at day 7 after vaccination. However, all three mRNA vaccine groups completely protect mice from a lethal dose of vaccinia virus (VACV) challenge. A single dose of VGPox 1, 2, and 3 provide protection against the lethal viral challenge within 7 days post-vaccination. Long-term immunity and protection were also observed in all three candidates. Additionally, VGPox 2 provided better passive protection. These results suggest that the VGPox series vaccines enhance immunogenicity and can be a viable alternative to current whole-virus vaccines to defend against mpox.

Single Immunization of a Vaccine Vectored by a Novel Recombinant Vaccinia Virus Affords Effective Protection Against Respiratory Syncytial Virus Infection in Cotton Rats

Respiratory syncytial virus (RSV) is a leading cause of respiratory infections worldwide and disease management measures are hampered by the lack of a safe and effective vaccine against the infection. We constructed a novel recombinant RSV vaccine candidate based on a deletion mutant vaccinia virus platform, in that the host range genes E3L and K3L were deleted (designated as VACVΔE3LΔK3L) and a poxvirus K3L ortholog gene was used as a marker for the rapid and efficient selection of recombinant viruses. The safety of the modified vaccinia virus was investigated by intranasal administration of BALB/c mice with the modified vaccinia vector using a dose known to be lethal in the wild-type Western Reserve. Only a minor loss of body weight by less than 5% and mild pulmonary inflammation were observed, both of which were transient in nature following nasal administration of the high-dose modified vaccinia virus. In addition, the viruses were cleared from the lung in 2 days with no viral invasions of the brain and other vital organs. These results suggest that the virulence of the virus has been essentially abolished. We then investigated the efficiency of the vector for the delivery of vaccines against RSV through comparison with another RSV vaccine delivered by the widely used Modified Vaccinia virus Ankara (MVA) backbone. In the cotton rats, we found a single intramuscular administration of VACVΔE3LΔK3L-vectored vaccine elicited immune responses and protection at a level comparable to the MVA-vectored vaccine against RSV infection. The distinct features of this novel VACV vector, such as an E3L deletion for attenuation and a K3L ortholog for positive selection and high efficiency for vaccine delivery, could provide unique advantages to the application of VACV as a platform for vaccine development.

The Virulence of Different Vaccinia Virus Strains Is Directly Proportional to Their Ability To Downmodulate Specific Cell-Mediated Immune Compartments In Vivo

Vaccinia virus (VACV) is a notorious virus for a number of scientific reasons; however, most of its notoriety comes from the fact that it was used as a vaccine against smallpox, being ultimately responsible for the eradication of that disease. Nonetheless, many different vaccinia virus strains have been obtained over the years; some are suitable to be used as vaccines, whereas others are virulent and unsuitable for this purpose. Interestingly, different vaccinia virus strains elicit different immune responses in vivo, and this is a direct result of the genomic differences among strains. In order to evaluate the net result of virus-encoded immune evasion strategies of vaccinia viruses, we compared antiviral immune responses in mice intranasally infected by the highly attenuated and nonreplicative MVA strain, the attenuated and replicative Lister strain, or the virulent WR strain. Overall, cell responses elicited upon WR infections are downmodulated compared to those elicited by MVA and Lister infections, especially in determined cell compartments such as macrophages/monocytes and CD4⁺ T cells. CD4⁺ T cells are not only diminished in WR-infected mice but also less activated, as evaluated by the expression of costimulatory molecules such as CD25, CD212, and CD28 and by the production of cytokines, including tumor necrosis factor alpha (TNF-α), gamma interferon (IFN-γ), interleukin-4 (IL-4), and IL-10. On the other hand, MVA infections are able to induce strong T-cell responses in mice, whereas Lister infections consistently induced responses that were intermediary between those induced by WR and MVA. Together, our results support a model in which the virulence of a VACV strain is proportional to its potential to downmodulate the host's immune responses.IMPORTANCE Vaccinia virus was used as vaccine against smallpox and was instrumental in the successful eradication of that disease. Although smallpox vaccination is no longer in place in the overall population, the use of vaccinia virus in the development of viral vector-based vaccines has become popular. Nonetheless, different vaccinia virus strains are known and induce different immune responses. To look into this, we compared immune responses triggered by mouse infections with the nonreplicative MVA strain, the attenuated Lister strain, or the virulent WR strain. We observed that the WR strain was capable of downmodulating mouse cell responses, whereas the highly attenuated MVA strain induced high levels of cell-mediated immunity. Infections by the intermediately attenuated Lister strain induced cell responses that were intermediary between those induced by WR and MVA. We propose that the virulence of a vaccinia virus strain is directly proportional to its ability to downmodulate specific compartments of antiviral cell responses.

A small molecule screen in yeast identifies inhibitors targeting protein-protein interactions within the vaccinia virus replication complex

Genetic and biochemical data have identified at least four viral proteins essential for vaccinia virus (VACV) DNA synthesis: the DNA polymerase E9, its processivity factor (the heterodimer A20/D4) and the primase/helicase D5. These proteins are part of the VACV replication complex in which A20 is a central subunit interacting with E9, D4 and D5. We hypothesised that molecules able to modulate protein-protein interactions within the replication complex may represent a new class of compounds with anti-orthopoxvirus activities. In this study, we adapted a forward duplex yeast two-hybrid assay to screen more than 27,000 molecules in order to identify inhibitors of A20/D4 and/or A20/D5 interactions. We identified two molecules that specifically inhibited both interactions in yeast. Interestingly, we observed that these compounds displayed a similar antiviral activity to cidofovir (CDV) against VACV in cell culture. We further showed that these molecules were able to inhibit the replication of another orthopoxvirus (i.e. cowpox virus), but not the herpes simplex virus type 1 (HSV-1), an unrelated DNA virus. We also demonstrated that the antiviral activity of both compounds correlated with an inhibition of VACV DNA synthesis. Hence, these molecules may represent a starting point for the development of new anti-orthopoxvirus drugs.

In vitro characterization of a nineteenth-century therapy for smallpox

In the nineteenth century, smallpox ravaged through the United States and Canada. At this time, a botanical preparation, derived from the carnivorous plant Sarracenia purpurea, was proclaimed as being a successful therapy for smallpox infections. The work described characterizes the antipoxvirus activity associated with this botanical extract against vaccinia virus, monkeypox virus and variola virus, the causative agent of smallpox. Our work demonstrates the in vitro characterization of Sarracenia purpurea as the first effective inhibitor of poxvirus replication at the level of early viral transcription. With the renewed threat of poxvirus-related infections, our results indicate Sarracenia purpurea may act as another defensive measure against Orthopoxvirus infections.

Evaluation of imiquimod for topical treatment of vaccinia virus cutaneous infections in immunosuppressed hairless mice

Imiquimod is an immune response modifier prescribed as a topical medication for a number of viral and neoplastic conditions. We evaluated the antiviral activity of imiquimod against vaccinia virus (WR strain) cutaneous infections in immunosuppressed (with cyclophosphamide) hairless mice when administered after virus exposure. Primary lesions progressed in severity, satellite lesions developed, and infection eventually killed the mice. Once daily topical treatment with 1% imiquimod cream for 3, 4, or 5 days were compared to twice daily topical treatment with 1% cidofovir cream for 7 days. Survival time of mice in all treated groups was significantly prolonged compared to placebo controls. The mean day of death for the placebo group, 3-day imiquimod, 4-day imiquimod, 5-day imiquimod, and cidofovir groups were 15.5, 20.0, 20.5, 19.5, and 20.5 days post-infection, respectively. All treatment groups showed significant reductions in primary lesion size and in the number of satellite lesions. The cidofovir and 4-day imiquimod treatments delayed the appearance of lung virus titers by 3 and 6 days, respectively, although cutaneous lesion and snout virus titers were not as affected by treatment. Benefits in survival and lesion reduction were observed when imiquimod treatment was delayed from 24, 48, and 72 h post-infection. However, increasing the treatment dose of imiquimod from 1% to 5% led to a significant decrease in antiviral efficacy. These results demonstrate the protective effects of topically administered imiquimod against a disseminated vaccinia virus infection in this mouse model.

N1L is an ectromelia virus virulence factor and essential for in vivo spread upon respiratory infection

The emergence of zoonotic orthopoxvirus infections and the threat of possible intentional release of pathogenic orthopoxviruses have stimulated renewed interest in understanding orthopoxvirus infections and the resulting diseases. Ectromelia virus (ECTV), the causative agent of mousepox, offers an excellent model system to study an orthopoxvirus infection in its natural host. Here, we investigated the role of the vaccinia virus ortholog N1L in ECTV infection. Respiratory infection of mice with an N1L deletion mutant virus (ECTVΔN1L) demonstrated profound attenuation of the mutant virus, confirming N1 as an orthopoxvirus virulence factor. Upon analysis of virus dissemination in vivo, we observed a striking deficiency of ECTVΔN1L spreading from the lungs to the livers or spleens of infected mice. Investigating the immunological mechanism controlling ECTVΔN1L infection, we found the attenuated phenotype to be unaltered in mice deficient in Toll-like receptor (TLR) or RIG-I-like RNA helicase (RLH) signaling as well as in those missing the type I interferon receptor or lacking B cells. However, in RAG-1(-/-) mice lacking mature B and T cells, ECTVΔN1L regained virulence, as shown by increasing morbidity and virus spread to the liver and spleen. Moreover, T cell depletion experiments revealed that ECTVΔN1L attenuation was reversed only by removing both CD4(+) and CD8(+) T cells, so the presence of either cell subset was still sufficient to control the infection. Thus, the orthopoxvirus virulence factor N1 may allow efficient ECTV infection in mice by interfering with host T cell function.

Long term recall of memory CD8 T cells in mice to first and third generation smallpox vaccines

Since long-term immunity is a critical component of any effective vaccine, we compared over a 15-month period, the strength, durability and specificity of immunity of an attenuated smallpox vaccine Modified Vaccinia Ankara (MVA) to the New York City Board of Health (NYCBH) vaccine. The frequencies of CD8(+) T cells to an immunodominant CD8 T cell epitope B8R(20-27) remained remarkably stable in mice given either MVA or NYCBH. Both groups were also protected from a lethal intranasal challenge with Western Reserve strain of vaccinia virus (VACV-WR). Cytokine responses to virus-specific peptides were detectable with significant boosting upon challenge. Expression of most phenotypic markers that define antigen-specific memory CD8 T cells was similar while CD27 was differentially expressed on lung-specific T cells compared to the spleen. Our data indicate robust vaccinia-specific CD8(+) T cell recall responses to lethal secondary challenge in protected mice with no apparent effect of age on T cell pools established much earlier in life.

Age-dependent susceptibility to a viral disease due to decreased natural killer cell numbers and trafficking

Although it is well known that aged hosts are generally more susceptible to viral diseases than the young, specific dysfunctions of the immune system directly responsible for this increased susceptibility have yet to be identified. We show that mice genetically resistant to mousepox (the mouse parallel of human smallpox) lose resistance at mid-age. Surprisingly, this loss of resistance is not a result of intrinsically defective T cell responses. Instead, the primary reason for the loss of resistance results from a decreased number of total and mature natural killer (NK) cells in the blood and an intrinsic impairment in their ability to migrate to the lymph node draining the site of infection, which is essential to curb systemic virus spread. Hence, our work links the age-dependent increase in susceptibility to a viral disease to a specific defect of NK cells, opening the possibility of exploring treatments to improve NK cell function in the aged with the goal of enhancing their resistance to viral diseases.

Animal models of orthopoxvirus infection

Smallpox was one of the most devastating diseases known to humanity. Although smallpox was eradicated through a historically successful vaccination campaign, there is concern in the global community that either Variola virus (VARV), the causative agent of smallpox, or another species of Orthopoxvirus could be used as agents of bioterrorism. Therefore, development of countermeasures to Orthopoxvirus infection is a crucial focus in biodefense research, and these efforts rely on the use of various animal models. Smallpox typically presented as a generalized pustular rash with 30 to 40% mortality, and although smallpox-like syndromes can be induced in cynomolgus macaques with VARV, research with this virus is highly restricted; therefore, animal models with other orthopoxviruses have been investigated. Monkeypox virus causes a generalized vesiculopustular rash in rhesus and cynomolgus macaques and induces fatal systemic disease in several rodent species. Ectromelia virus has been extensively studied in mice as a model of orthopoxviral infection in its natural host. Intranasal inoculation of mice with some strains of vaccinia virus produces fatal bronchopneumonia, as does aerosol or intranasal inoculation of mice with cowpox virus. Rabbitpox virus causes pneumonia and fatal systemic infections in rabbits and can be naturally transmitted between rabbits by an aerosol route similar to that of VARV in humans. No single animal model recapitulates all known aspects of human Orthopoxvirus infections, and each model has its advantages and disadvantages. This article provides a brief review of the Orthopoxvirus diseases of humans and the key pathologic features of animal models of Orthopoxvirus infections.

Historical perspectives in the development of antiviral agents against poxviruses

The poxvirus vaccinia virus (VV) served as the model virus for which the first antivirals, the thiosemicarbazones, were identified. This dates back to 1950; and, although there is at present no single antiviral drug specifically licensed for the chemotherapy or -prophylaxis of poxvirus infections, numerous candidate compounds have been described over the past 50 years. These compounds include interferon and inducers thereof (i.e., polyacrylic acid), 5-substituted 2’-deoxyuridines (i.e., idoxuridine), IMP dehydrogenase inhibitors, S-adenosylhomocysteine hydrolase inhibitors, acyclic nucleoside phosphonates (such as cidofovir) and alkoxyalkyl prodrugs thereof (such as CMX001), viral egress inhibitors (such as tecovirimat), and cellular kinase inhibitors (such as imatinib).

Activities of certain 5-substituted 4'-thiopyrimidine nucleosides against orthopoxvirus infections

As part of a program to identify new compounds that have activity against orthopoxviruses, a number of 4'-thionucleosides were synthesized and evaluated for their efficacies against vaccinia and cowpox viruses. Seven compounds that were active at about 1 microM against both viruses in human cells but that did not have significant toxicity were identified. The 5-iodo analog, 1-(2-deoxy-4-thio-beta-d-ribofuranosyl)-5-iodouracil (4'-thioIDU), was selected as a representative molecule; and this compound also inhibited viral DNA synthesis at less than 1 microM but only partially inhibited the replication of a recombinant vaccinia virus that lacked a thymidine kinase. This compound retained complete activity against cidofovir- and ST-246-resistant mutants. To determine if this analog had activity in an animal model, mice were infected intranasally with vaccinia or cowpox virus and treatment with 4'-thioIDU was given intraperitoneally or orally twice daily at 50, 15, 5, or 1.5 mg/kg of body weight beginning at 24 to 120 h postinfection and was continued for 5 days. Almost complete protection (87%) was observed when treatment with 1.5 mg/kg was begun at 72 h postinfection, and significant protection (73%) was still obtained when treatment with 5 mg/kg was initiated at 96 h. Virus titers in the liver, spleen, and kidney were reduced by about 4 log(10) units and about 2 log(10) units in mice infected with vaccinia virus and cowpox virus, respectively. These results indicate that 4'-thioIDU is a potent, nontoxic inhibitor of orthopoxvirus replication in cell culture and experimental animal infections and suggest that it may have potential for use in the treatment of orthopoxvirus infections in animals and humans.

Robust intrapulmonary CD8 T cell responses and protection with an attenuated N1L deleted vaccinia virus

Background

Vaccinia viruses have been used as a model for viral disease and as a protective live vaccine.

Methodology and Principal Findings

We investigated the immunogenicity of an attenuated strain of vaccinia virus engineered to inactivate the N1L gene (vGK5). Using the intranasal route, this recombinant virus was 2 logs less virulent compared to the wildtype VACV-WR. Infection by the intranasal, intraperitoneal, and tail scarification routes resulted in the robust induction of cytolytic virus-specific CD8 T cells in the spleens and the lungs. VACV-specific antibodies were also detected in the sera of mice infected 3–5 months prior with the attenuated vGK5 virus. Finally, mice immunized with vGK5 were significantly protected when challenged with a lethal dose of VACV-WR.

Conclusions

These results indicate that the attenuated vGK5 virus protects against subsequent infection and suggest that the N1L protein limits the strength of the early antiviral CD8 T cell response following respiratory infection.

Differential pathogenesis of cowpox virus intranasal infections in mice induced by low and high inoculum volumes and effects of cidofovir treatment

The causes of death from intranasal cowpox virus infections in mice remain unclear. Hypotheses include severe pneumonitis, hepatitis and/or hyperproduction of cytokines and chemokines. This work explores these hypotheses by studying the influence of low- and high-volume virus inocula on viral pathogenesis. BALB/c mice were infected intranasally with a syncytium-forming variant of cowpox virus in 5 microL or 50 microL volumes containing the same infectious virus challenge dose. The 50 microL infection produced a more rapidly lethal disease associated with severe pneumonitis, high lung and nasal virus titres and increased cytokine and chemokine levels in the lungs and nasal tissue, whilst liver infection was minimal. The 5 microL inoculum infection was also lethal, but the infection was primarily confined to the upper respiratory tract and included elevated nasal cytokine and chemokine levels. Levels of the pro-inflammatory cytokine interleukin-6 were particularly high in both infections. Treatment of the infections with cidofovir (100mg/kg/day for 2 days starting 24h after virus exposure) led to survival and suppression of tissue virus titres. Treatment reduced pneumonitis in the 50 microL infection and lessened cytokine hyperproduction in both infections. We conclude that a 5 microL volume inoculum of cowpox virus causes a lethal upper respiratory tract infection, whilst the 50 microL inoculum targets both upper and lower respiratory tracts, with excessive release of systemic pro-inflammatory factors. Cidofovir effectively treated both infections and slowed viral replication sufficiently to subdue the exaggerated release of pro-inflammatory mediators.

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-W-(3,3a,4,4a,5,5a,6,6a-octahydro-1,3-dioxo-4,6-ethenocycloprop [f]isoindol-2(1H)-yl)-benza-mide] 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 VV protein and to protect mice from VV, CPV and ECTV orthopoxvirus-induced disease.

Methods

The antiviral activity of ST-246 was assessed against extracellular and intracellular VV, 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 VV) and in PHK cells (for CMLV). In organotypic epithelial raft cultures, ST-246 at 20 μg/ml inhibited extracellular VV 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 μg/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 VV-, CPV- and CMLV-infected cells treated with 10 μg/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.

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.

The design and development of drugs acting against the smallpox virus

The eradication of smallpox was announced by the WHO in 1980. However, smallpox has not totally disappeared from people's minds because of its potential use as a biological weapon. Further outbreaks of smallpox would, needless to say, be devastating in a population, which has little or no immune defence against the virus. The real concerns come from the fact that the previously used vaccine would not be tolerated today by a number of patients and, more worryingly, there are no approved antiviral drugs against smallpox. This review is focused on the antiviral research, which has been stimulated to deliver potent inhibitors of the replication of the causative agent of smallpox, variola virus.

Intranasal cowpox virus infection of the mouse as a model for preclinical evaluation of smallpox vaccines

The intranasal infection of mice with cowpox virus (CPXV) has been evaluated as a model for smallpox infection in man. Administration of a lethal dose of CPXV allowed time for development of T-cell responses but antibodies could not be detected before death occurred. In contrast, infection with a sublethal dose was associated with an early T-cell response followed by neutralising antibodies which correlated with virus clearance. Comparison of two first generation smallpox vaccines revealed no significant differences in terms of immunogenicity, protection and post-challenge virus clearance. These studies show that the CPXV/mouse model is valuable for the initial assessment of smallpox vaccines.

Pathogeneses of respiratory infections with virulent and attenuated vaccinia viruses

BACKGROUND

Respiratory infection with the neurovirulent vaccinia virus (VV) strain Western Reserve (WR) results in an acute infection of the lung followed by dissemination of the virus to other organs and causes lethality in mice. The mechanisms of lethality are not well-understood. In this study, we analyzed virus replication and host immune responses after intranasal infection with lethal and non-lethal doses of VV using the WR strain and the less virulent Wyeth strain.

RESULTS

The WR strain replicated more vigorously in the lung and in the brain than the Wyeth strain. There were, however, no differences between the virus titers in the brains of mice infected with the higher lethal dose and the lower non-lethal dose of WR strain, suggesting that the amount of virus replication in the brain is unlikely to be the sole determining factor of lethality. The WR strain grew better in primary mouse lung cells than the Wyeth strain. Lethal infection with WR strain was associated with a reduced number of lymphocytes and an altered phenotype of the T cells in the lung compared to non-lethal infections with the WR or Wyeth strains. Severe thymus atrophy with a reduction of CD4 and CD8 double positive T cells was also observed in the lethal infection.

CONCLUSION

These results suggest that the lethality induced by intranasal infection with a high dose of the WR strain is caused by the higher replication of virus in lung cells and immune suppression during the early phase of the infection, resulting in uncontrolled virus replication in the lung.

Mutations in the E9L polymerase gene of cidofovir-resistant vaccinia virus strain WR are associated with the drug resistance phenotype

Cidofovir (CDV) is an effective drug against viruses of the Orthopoxviridae family and is active in vitro against variola virus, the cause of smallpox. However, CDV-resistant poxviruses can be generated by repeated in vitro passage in the presence of suboptimal concentrations of CDV. To determine if mutations in the E9L polymerase gene could confer resistance to this nucleoside analog, this gene was sequenced from CDV-resistant vaccinia virus and found to encode five amino acid changes, centered on an N-terminal region associated with 3'-->5' exonuclease activity. Transfer of this mutant E9L gene into wild-type vaccinia virus by marker rescue sufficed to confer the resistance phenotype. E9L polymerase mutations occurred sequentially during passage in CDV, and an H296Y/S338F double mutant that conferred an intermediate CDV resistance phenotype was identified. In vitro, the marker-rescued CDV-resistant vaccinia virus containing all five mutations grew nearly as well as wild-type vaccinia virus. However, the virulence of this virus for mice was reduced, as 10- to 30-fold more CDV-resistant virus than wild-type virus was required for lethality following intranasal challenge. Cidofovir and hexadecyloxypropyl-cidofovir gave partial protection to mice infected with the virus when used at 50 and 100 mg/kg of body weight given as single treatments 24 h after virus exposure, whereas 2-amino-7-[(1,3-dihydroxy-2-propoxy)methyl]purine (compound S2242) was completely protective at 25, 50, and 100 mg/kg/day when given daily for 5 days. These findings suggest that drug therapy for poxviruses may be complicated by drug resistance but that treatment of the infection with currently known compounds is possible.

Cell line dependency for antiviral activity and in vivo efficacy of N-methanocarbathymidine against orthopoxvirus infections in mice

A novel carbocyclic thymidine analog, N-methanocarbathymidine [(N)-MCT], was evaluated for inhibition of orthopoxvirus infections. Efficacy in vitro was assessed by plaque reduction assays against wild-type and cidofovir-resistant strains of cowpox and vaccinia viruses in nine different cell lines. Minimal differences were seen in antiviral activity against wild-type and cidofovir-resistant viruses. (N)-MCT's efficacy was affected by the cell line used for assay, with 50% poxvirus-inhibitory concentrations in cells as follows: mouse=0.6-2.2 microM, rabbit=52-90 microM, monkey=87 to >1000 microM, and human=39-220 microM. Limited studies performed with carbocyclic thymidine indicated a similar cell line dependency for antiviral activity. (N)-MCT did not inhibit actively dividing uninfected cells at 1000 microM. The potency of (N)-MCT against an S-variant thymidine kinase-deficient vaccinia virus was similar to that seen against S-variant and wild-type viruses in mouse, monkey, and human cells, implicating a cellular enzyme in the phosphorylation of the compound. Mice were intranasally infected with cowpox and vaccinia viruses followed 24h later by intraperitoneal treatment with (N)-MCT (twice a day for 7 days) or cidofovir (once a day for 2 days). (N)-MCT treatment at 100 and 30 mg/kg/day resulted in 90 and 20% survival from cowpox virus infection, respectively, compared to 0% survival in the placebo group. Statistically significant reductions in lung virus titers on day 5 occurred in 10, 30, and 100mg/kg/day treated mice. These same doses were also active against a lethal vaccinia virus (WR strain) challenge, and protection was seen down to 10mg/kg/day against a lethal vaccinia virus (IHD strain) infection. Cidofovir (100mg/kg/day) protected animals from death in all three infections.

Using the TAP component of the antigen-processing machinery as a molecular adjuvant

We hypothesize that over-expression of transporters associated with antigen processing (TAP1 and TAP2), components of the major histocompatibility complex (MHC) class I antigen-processing pathway, enhances antigen-specific cytotoxic activity in response to viral infection. An expression system using recombinant vaccinia virus (VV) was used to over-express human TAP1 and TAP2 (VV-hTAP1,2) in normal mice. Mice coinfected with either vesicular stomatitis virus plus VV-hTAP1,2 or Sendai virus plus VV-hTAP1,2 increased cytotoxic lymphocyte (CTL) activity by at least 4-fold when compared to coinfections with a control vector, VV encoding the plasmid PJS-5. Coinfections with VV-hTAP1,2 increased virus-specific CTL precursors compared to control infections without VV-hTAP1,2. In an animal model of lethal viral challenge after vaccination, VV-hTAP1,2 provided protection against a lethal challenge of VV at doses 100-fold lower than control vector alone. Mechanistically, the total MHC class I antigen surface expression and the cross-presentation mechanism in spleen-derived dendritic cells was augmented by over-expression of TAP. Furthermore, VV-hTAP1,2 increases splenic TAP transport activity and endogenous antigen processing, thus rendering infected targets more susceptible to CTL recognition and subsequent killing. This is the first demonstration that over-expression of a component of the antigen-processing machinery increases endogenous antigen presentation and dendritic cell cross-presentation of exogenous antigens and may provide a novel and general approach for increasing immune responses against pathogens at low doses of vaccine inocula.

Reemergence of monkeypox: prevalence, diagnostics, and countermeasures

Human monkeypox is a viral zoonotic disease that occurs mostly in the rain forests of central and western Africa. However, the disease recently emerged in the United States in imported wild rodents from Africa. Monkeypox has a clinical presentation very similar to that of ordinary forms of smallpox, including flulike symptoms, fever, malaise, back pain, headache, and characteristic rash. Given this clinical spectrum, differential diagnosis to rule out smallpox is very important. There are no licensed therapies for human monkeypox; however, the smallpox vaccine can protect against the disease. The discontinuation of general vaccination in the 1980s has given rise to increasing susceptibility to monkeypox virus infection in the human population. This has led to fears that monkeypox virus could be used as a bioterrorism agent. Effective prevention relies on limiting the contact with infected patients or animals and limiting the respiratory exposure to infected patients.

Characterization and treatment of cidofovir-resistant vaccinia (WR strain) virus infections in cell culture and in mice

The wild-type (WT) vaccinia (WR strain) virus is highly virulent to mice by intranasal inoculation, yet death can be prevented by cidofovir treatment. A cidofovir-resistant (CDV-R) mutant of the virus was developed by 15 Vero cell culture passages in order to determine cross-resistance to other inhibitors, growth characteristics, virulence in infected mice, and suitability of the animal model for studying antiviral therapies. Comparisons were made to the original WT virus and to a WT virus passaged 15 times in culture (WTp15 virus). Cidofovir inhibited WT, WTp15, and CDV-R viruses by 50% at 61, 56 and 790 microM, respectively, in plaque reduction assays, with similar inhibition seen in virus yield studies. Cross-resistance occurred with compounds related to cidofovir, but not with unrelated nucleosides. The resistant virus produced 300-fold fewer infectious particles (PFU) than WT and WTp15 viruses in mouse C1271 cells, yet replicated similarly in Vero (monkey) cells. The CDV-R virus was completely attenuated for virulence at 10(7) PFU per mouse in normal BALB/c mice and in severe combined immunodeficient (SCID) mice. The WTp15 virus was 100-fold less virulent than WT virus in BALB/c mice. Thus, the lack of virulence of the resistant virus in the animal model is explained partly by its reduced ability to replicate in mouse cells and by attenuation occurring as a result of extensive cell culturing (inferred from what occurred with the WTp15 virus). Lung and snout virus titre reduction parameters were used to assess antiviral activity of compounds in BALB/c mice infected intranasally with the CDV-R virus. Cidofovir, HDP-cidofovir and arabinofuranosyladenine treatments reduced lung virus titres <fourfold, and snout virus titres > or = eight-fold. The animal model appears to have limited utility in drug efficacy testing.

Particulate delivery systems for biodefense subunit vaccines

Expanding identification of potentially protective subunit antigens and correlates of protection has provided a basis for the introduction of safer vaccines. Despite encouraging results in animal models, the significant potential of particulate delivery systems in vaccine design has not yet translated into effective vaccines available for use in humans. This review article will focus on the current status of the development of particulate vaccines, mainly liposomes and bio-degradable polymers, against potential agents for biowarfare: plague, anthrax, botulinum, and smallpox; and filoviruses: Marburg and Ebola.

A rapid detection method for Vaccinia virus, the surrogate for smallpox virus

Prior to the World Health Organization’s announcement of total eradication in 1977 [J. Am. Med. Assoc. 281 (1999) 1735], smallpox was a worldwide pathogen. Vaccinations were ceased in 1980 and now with a largely unprotected world population, smallpox is considered the ideal biowarfare agent [Antiviral Res. 57 (2002) 1]. Infection normally occurs after implantation of the virus on the oropharyngeal or respiratory mucosa [J. Am. Med. Assoc. 281 (1999) 2127]. Smallpox virus can be detected from the throats of exposed individuals prior to onset of illness and prior to the infectious stage of the illness. A rapid, sensitive real-time assay to detect Variola virus (smallpox) has been developed using the Vaccinia virus, a surrogate of smallpox, as a target. Cyanine 5 dye-labeled anti-Vaccinia antibody was used in a sandwich immunoassay to produce a fluorescent signal in the presence of the Vaccinia virus. The signal was detected using the Analyte 2000 biosensor (Research International, Monroe, WA). The Analyte 2000 uses a 635 nm laser diode to provide excitation light that is launched into a polystyrene optical waveguide. Fluorescent molecules within the evanescent wave are excited and a portion of their emission energy recouples into the waveguide. A photodiode quantifies the emission light at wavelengths between 670 and 710 nm. The biosensor was able to detect a minimum of 2.5×10⁵ pfu/ml of Vaccinia virus in seeded throat culture swab specimens.

Effects of four antiviral substances on lethal vaccinia virus (IHD strain) respiratory infections in mice

Intranasal infection of BALB/c mice with the IHD strain of vaccinia virus was found to cause pneumonia, profound weight loss and death. Cidofovir, hexadecyloxypropyl-cidofovir (HDP-CDV), the diacetate ester prodrug of 2-amino-7-[(1,3-dihydroxy-2-propoxy)methyl]purine (HOE961), and ribavirin were used to treat the infections starting 24h after virus exposure. Single intraperitoneal (i.p.) cidofovir treatments of 100 and 30 mg/kg led to 90-100% survival compared with no survivors in the placebo group, whereas a 10 mg/kg dose was ineffective. The 100 mg/kg treatment reduced lung and snout virus titres on day 3 of the infection by 20- and 8-fold, respectively. Mean arterial oxygen saturation levels in these two cidofovir treatment groups were significantly higher than placebo on days 4 through 6 of the infection, indicating an improvement in lung function. Effects of cidofovir on viral pathogenesis were studied on days 1, 3 and 5 of the infection, and demonstrated statistically significant reductions in lung consolidation scores, lung weights, lung virus titre and snout virus titres on days 3 and 5. Cidofovir treatment also reduced virus titres in other tissues and body fluid, including blood, brain, heart, liver, salivary gland and spleen. HDP-CDV was given by oral gavage at 100, 50 and 25mg/kg doses one time only, resulting in 80-100% survival. Lower daily oral doses of 10 and 5mg/kg per day given for 5 days protected only 30% of animals from death. Oral doses (100, 50 and 25 mg/kg per day) of HOE961 for 5 days protected all animals, whereas equivalent oral doses of ribavirin were completely ineffective. The rapidity of recovery from weight loss during the infection was a function of dose of compound administered. These data indicate the utility of parenteral cidofovir, oral HDP-CDV and oral HOE961 in treating severe respiratory infections caused by this virus.

Anti-cowpox virus activities of certain adenosine analogs, arabinofuranosyl nucleosides, and 2'-fluoro-arabinofuranosyl nucleosides

Nucleoside analogs were investigated for their potential to inhibit cowpox virus (a surrogate for variola and monkeypox viruses) in cell culture and in lethal respiratory infections in mice. Cell culture antiviral activity was determined by plaque reduction assays, with cytotoxicity determined by cell proliferation assays. Selectivity indices (SI's, 50% cytotoxic concentration divided by 50% virus-inhibitory concentration) were determined for 15 compounds. Three arabinofuranosyl (Ara) nucleosides showed activity in mouse mammary tumor (C127I) cells: guanine (Ara-G), thymine (Ara-T), and adenine (Ara-A) with SI's of 113, 61, and 95, respectively. The 2'-fluoro-Ara nucleosides of 5-F-cytosine (FIAC), 5-methyluracil (FMAU), and 5-iodouracil (FIAU) exhibited SI's of 148, 77, and 29, respectively. Other potent compounds included cidofovir (a positive control) and 3'-O-methyladenosine, with SI values of 164 and 56, respectively. In general, assays performed in African green monkey kidney (Vero) cells produced lower SI's than in C127I cells, except for 5-iodo-2'-deoxyuridine (IDU) which had an SI of > 71 in Vero cells and 3.1 in C127I cells. Intranasal infection of mice with cowpox virus was followed a day later by twice daily intraperitoneal treatment with compounds for 5 days. Ara-A was active at 300 mg/kg/day (40% survival), FMAU at 100 mg/kg/day (70% survival), and cidofovir (given for 1 day only) at 100 mg/kg (80-100% survival). None of the other compounds, including IDU, prevented death nor delayed the time to death. Cidofovir had the best potential for treating orthopoxvirus infections of those tested.

Prevention of lethal respiratory vaccinia infections in mice with interferon-alpha and interferon-gamma

The antiviral efficacy of interferons (IFNs) was evaluated using a vaccinia intranasal infection model in mice in this study. We provide evidence that intranasal administration of IFN-alpha and IFN-gamma (days -1 to +3) resulted in 100 and 90% survival against a lethal respiratory vaccinia infection (8 LD50) in mice, respectively; whereas no animals in the placebo group survived through the study period (21 days). The IFN treatment consisted of a single daily dose of 5x10(3) U per mouse for 5 consecutive days. The efficacy of IFN-gamma was evident even when the IFN-gamma treatments started 1-2 days after infection and when a lower dose (2x10(3) U per mouse) was used. The treatment of IFN-alpha and IFN-gamma reduced the virus titers in the lungs of infected mice by 1000-10,000-fold, when the administration started 1 day after infection. Our data suggest that IFN-alpha and IFN-gamma are effective in protecting vaccinia-infected mice from viral replication in lungs and mortality, and may be beneficial in other human orthopoxvirus infections.

Efficacy of cidofovir in a murine model of disseminated progressive vaccinia

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.

Flow cytometric quantitation of the protective efficacy of dendritic cell based vaccines in a human papillomavirus type 16 murine challenge model

A murine model for the assessment of protective immunity to human papillomavirus (HPV) type 16, a virus that does not naturally infect mice, is described. In this system, protection was tested following intranasal challenge of mice with a recombinant vaccinia virus expressing both the selected HPV antigen and a beta-galactosidase (beta-gal) reporter. The extent of viral infectivity was determined by measuring beta-gal positive lung cells using flow cytometry. The efficacy of this model to measure protective immunity was evaluated by priming mice with the beta-gal vaccinia virus then challenging the mice with the same virus. Vaccinia primed mice had negligible numbers of beta-gal positive cells in the lung 5 days following viral challenge indicating protection, whereas around 50% of cells were infected in immunologically naive, challenged mice. The protective efficacy of two dendritic cell vaccines for HPV16 was measured in this model. Both vaccines provided some protection to subsequent viral challenge, compared with their controls. Although this protection model was applied to HPV in this study, it may also have broad application to other viruses that do not infect mice naturally.

Oral treatment of cowpox and vaccinia virus infections in mice with ether lipid esters of cidofovir

Four newly synthesized ether lipid esters of cidofovir (CDV), hexadecyloxypropyl-CDV (HDP-CDV), octadecyloxyethyl-CDV (ODE-CDV), oleyloxypropyl-CDV (OLP-CDV), and oleyloxyethyl-CDV (OLE-CDV), were found to have enhanced activities against vaccinia virus (VV) and cowpox virus (CV) in vitro compared to those of CDV. The compounds were administered orally and were evaluated for their efficacies against lethal CV or VV infections in mice. HDP-CDV, ODE-CDV, and OLE-CDV were effective at preventing mortality from CV infection when treatments were initiated 24 h after viral inoculation, but only HDP-CDV and ODE-CDV maintained efficacy when treatments were initiated as late as 72 h postinfection. Oral pretreatment with HDP-CDV and ODE-CDV were also effective when they were given 5, 3, or 1 day prior to inoculation with CV, even when each compound was administered as a single dose. Both HDP-CDV and ODE-CDV were also effective against VV infections when they were administered orally 24 or 48 h after infection. In animals treated with HDP-CDV or ODE-CDV, the titers of both CV and VV in the liver, spleen, and kidney were reduced 3 to 7 log(10). In contrast, virus replication in the lungs was not significantly reduced. These data indicate that HDP-CDV or ODE-CDV given orally is as effective as CDV given parenterally for the treatment of experimental CV and VV infections and suggest that these compounds may be useful for the treatment of orthopoxvirus infections in humans.

Efficacy of multiple- or single-dose cidofovir against vaccinia and cowpox virus infections in mice

Orthopoxviruses, including variola and monkeypox, pose risks to human health through natural transmission or potential bioterrorist activities. Since vaccination has not recently been utilized for control of these infections, there is renewed effort in the development of antiviral agents not only for postexposure smallpox therapy but also for treatment of adverse reactions following vaccination. The objectives of this study were to expand on the results of others that cidofovir (CDV) is effective in mice inoculated with cowpox virus (CV) or vaccinia virus (VV) and to document the efficacy of single and interval dosing beginning prior to or after infection, particularly including evaluations using suboptimal doses of CDV. We utilized BALB/c or SCID mice inoculated with CV or VV as models for systemic poxvirus infections. BALB/c mice were inoculated intranasally with CV or VV and treated with CDV prior to or after virus inoculation. CDV, at concentrations as low as 0.7 to 6.7 mg/kg of body weight/day for 5 days, conferred significant protection when treatment was initiated as late as 72 to 96 h postinfection. A single-dose pretreatment or posttreatment with CDV at 3 to 100 mg/kg was effective when given as early as 5 days prior to infection or as late as 3 days after infection with either VV or CV. Interval treatments given every third day beginning 72 h postinfection using 6.7 or 2 mg of CDV/kg also proved effective against CV infections. When SCID mice were inoculated intraperitoneally with CV or VV and treated for 7 to 30 days with CDV, all the mice eventually died during or after cessation of treatment; however, significant delays in time to death and reduction of virus replication in organs occurred in most treated groups, and no resistance to CDV was detected.

Clinical potential of the acyclic nucleoside phosphonates cidofovir, adefovir, and tenofovir in treatment of DNA virus and retrovirus infections

The acyclic nucleoside phosphonates HPMPC (cidofovir), PMEA (adefovir), and PMPA (tenofovir) have proved to be effective in vitro (cell culture systems) and in vivo (animal models and clinical studies) against a wide variety of DNA virus and retrovirus infections: cidofovir against herpesvirus (herpes simplex virus types 1 and 2 varicella-zoster virus, cytomegalovirus [CMV], Epstein-Barr virus, and human herpesviruses 6, 7, and 8), polyomavirus, papillomavirus, adenovirus, and poxvirus (variola virus, cowpox virus, vaccinia virus, molluscum contagiosum virus, and orf virus) infections; adefovir against herpesvirus, hepadnavirus (human hepatitis B virus), and retrovirus (human immunodeficiency virus types 1 [HIV-1] and 2 [HIV-2], simian immunodeficiency virus, and feline immunodeficiency virus) infections; and tenofovir against both hepadnavirus and retrovirus infections. Cidofovir (Vistide) has been officially approved for the treatment of CMV retinitis in AIDS patients, tenofovir disoproxil fumarate (Viread) has been approved for the treatment of HIV infections (i.e., AIDS), and adefovir dipivoxil (Hepsera) has been approved for the treatment of chronic hepatitis B. Nephrotoxicity is the dose-limiting side effect for cidofovir (Vistide) when used intravenously (5 mg/kg); no toxic side effects have been described for adefovir dipivoxil and tenofovir disoproxil fumarate, at the approved doses (Hepsera at 10 mg orally daily and Viread at 300 mg orally daily).

Human monkeypox: an emerging zoonosis

Human monkeypox is a rare viral zoonosis endemic to central and western Africa that has recently emerged in the USA. Laboratory diagnosis is important because the virus can cause disease that is clinically indistinguishable from other pox-like illnesses, particularly smallpox and chickenpox. Although the natural animal reservoir of the monkeypox virus is unknown, rodents are the probable source of its introduction into the USA. A clear understanding of the virulence and transmissibility of human monkeypox has been limited by inconsistencies in epidemiological investigations. Monkeypox is the most important orthopoxvirus infection in human beings since the eradication of smallpox in the 1970s. There is currently no proven treatment for human monkeypox, and questions about its potential as an agent of bioterrorism persist.

[Seeds against smallpox: Joaquim Vás and the scientific translation of bananeira brava seeds in Goa, India (1894-1930)]

In 1914, in the former Portuguese colony of Goa, India, the physician António Joaquim Vás announced the discovery of a wonderful treatment for smallpox, entailing clinical application of seeds from the bananeira brava (Heliconia biabi Sw.m.), a plant remedy allegedly derived from Indian medical practices. The present article explores the circumstances surrounding the successes and failures of this discovery. The concept of scientific translation is used to interpret the transformation of bananeira brava seeds into an early twentieth-century remedy for smallpox. This transfer from indigenous use to scientific therapeutic constitutes the creation of a quasi-medicine, that is, a case of 'medium translation'. Although these seeds occupy a problematic place within the program of scientific translation, they enjoyed active circulation within science and remained a part of medical practices for combating smallpox.

Preventive and therapeutic approaches to viral agents of bioterrorism

Certain viruses, such as those that cause smallpox and hemorrhagic fevers, have been identified as possible bioterrorism agents by the Centers for Disease Control and Prevention. They have been designated as potential threats because large quantities can be propagated in cell culture, they are transmissible as aerosols and, for the most part, there are only limited vaccine and pharmaceutical strategies for either prevention or treatment of established infection. An additional concern is the potential to genetically modify these agents to enhance virulence or promote resistance to vaccines or identified antivirals. Although the major impact of these agents is human illness, the release of zoonotic agents, such as the Nipah virus, would have consequences for both humans and animals because infected and noninfected animals might need to be sacrificed to control the spread of infection. Continued research is necessary to develop effective strategies to limit the impact of these biological threats.

Esterification of cidofovir with alkoxyalkanols increases oral bioavailability and diminishes drug accumulation in kidney

Smallpox was eradicated by vaccination in the 1970s. However, concerns have arisen about the potential use of variola virus as a biological weapon. Most of the world's population has little residual immunity because systematic vaccination against smallpox ceased in the early 1970s. Vaccination of key elements of the population against smallpox is again being considered. However, there are now large numbers of persons who cannot be safely vaccinated with the current vaccine because of AIDS, immunosuppressive drugs, and certain common skin disorders. It would be useful to have a potent orally active drug as an alternative for these persons in case of an outbreak of smallpox. Alkoxyalkyl esters of cidofovir (CDV) have been shown to be highly active and selective against poxviruses in vitro with activities several logs greater than the activity of unmodified CDV. This is due in large part to increased cellular penetration and conversion to CDV-diphosphate, the active antiviral. In this paper, the oral pharmacokinetics of 14C-labeled hexadecyloxypropyl-cidofir (HDP-CDV), octadecyloxyethyl-cidofir (ODP-CDV), and oleyloxypropyl-cidofir (OLP-CDV) are examined and oral bioavailability and tissue distribution assessed and compared with parenteral CDV. The alkoxyalkyl CDVs are highly orally bioavailable and do not concentrate in kidney, the site of the dose-limiting toxicity of CDV. Plasma and tissue drug levels are many times greater than the in vitro EC(50s) for variola, cowpox, and vaccinia viruses. Thus, the compounds are good candidates for further development for prevention and treatment of smallpox infection and the complications of vaccination.

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.

Smallpox vaccination and the patient with an organ transplant

Organ transplant recipients are vulnerable to a variety of infections because of the immunosuppressed state required to prevent organ rejection. We review the recommendations of the Centers for Disease Control and Prevention (Atlanta, Georgia) for smallpox vaccination and the possible complications of vaccination in the population with organ transplants. The risk of these complications is presumably dependent on the extent of deficient cell-mediated immunity.

Increased antiviral activity of 1-O-hexadecyloxypropyl-[2-(14)C]cidofovir in MRC-5 human lung fibroblasts is explained by unique cellular uptake and metabolism

Recently, there has been renewed interest in finding orally active drugs against smallpox. Cidofovir (CDV) given by parenteral injection has been shown to protect against lethal poxvirus infection. We have been interested in the synthesis and evaluation of orally active derivatives of CDV. Previous studies showed that the CDV and cyclic cidofovir (cCDV) analogs 1-O-hexa-decyloxypropyl-CDV (HDP-CDV) and 1-O-hexadecyloxypropyl-cCDV (HDP-cCDV), show >100-fold increases in antiviral activity versus the unmodified nucleosides against cells infected with orthopoxviruses, cowpox, and vaccinia virus. In contrast to CDV, HDP-CDV is orally bioavailable and has been reported to be orally active in lethal cowpox virus infection in mice. To assess the metabolic basis for the increased antiviral activity of HDP-CDV in vitro, we studied the cellular uptake and anabolic metabolism of (14)C-labeled CDV, cCDV, and their alkoxyalkanol esters HDP-CDV and HDP-cCDV. HDP-CDV and HDP-cCDV were taken up rapidly by MRC-5 human lung fibroblasts in vitro, but uptake of CDV and cCDV was much slower. Analysis of cellular metabolites showed that levels of cidofovir diphosphate (CDV-DP), the active antiviral compound, were >100 times greater with HDP-CDV than levels observed with CDV. When cells were exposed to HDP-CDV, the intracellular half-life of CDV-DP was 10 days versus 2.7 days reported when cells are exposed to CDV. HDP-CDV seems to circumvent poor cellular uptake by rapid association with cellular membrane phospholipids, whereas CDV uptake proceeds via the slow process of fluid endocytosis.