Human cytomegalovirus UL27 is not required for viral replication in human tissue implanted in SCID mice

Inhibition of the human cytomegalovirus UL97 kinase by maribavir is thought to be responsible for the antiviral activity of this compound. Some mutations that confer resistance to maribavir map to UL97, however additional mutations that also confer resistance to the drug were mapped to UL27. These open reading frames share a low level of homology, yet the function of pUL27 remains unknown. A recombinant virus with a deletion in the UL27 open reading frame was reported previously to exhibit a slight replication deficit, but a more important function in vivo was hypothesized given its homology to the UL97 kinase. The potential for an important function in vivo was investigated by determining if these knockout viruses could replicate in human tissue implanted in SCID mice. None of the AD169 derived viruses replicated well in the implanted thymus/liver tissue, and is consistent with previous observations, although all of the viruses replicated to some degree in retinal tissue implants. Replication of the parent viruses was observed at 7 days post inoculation, whereas no replication was detected with any of the recombinant viruses with deletions in UL27. By day 14, replication was detected in two of the three knockout viruses and in all of the viruses by day 42. These data are consistent with minimal defects observed in cell culture, but are not consistent with an important role for UL27 in vivo. We conclude that UL27 is not required for viral replication in vivo

Isolation and characterization of cidofovir resistant vaccinia viruses

© 2008 Becker et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution Licens

Treatment of Vaccinia and Cowpox Virus Infections in Mice with CMX001 and ST-246

Although a large number of compounds have been identified with antiviral activity against orthopoxviruses in tissue culture systems, it is highly preferred that these compounds have activity in vivo before they can be seriously considered for further development. One of the most commonly used animal models for the confirmation of this activity has been the use of mice infected with either vaccinia or cowpox viruses. These model systems have the advantage that they are relatively inexpensive, readily available and do not require any special containment facilities; therefore, relatively large numbers of compounds can be evaluated in vivo for their activity. The two antiviral agents that have progressed from preclinical studies to human safety trials for the treatment of orthopoxvirus infections are the cidofovir analog, CMX001, and an inhibitor of extracellular virus formation, ST-246. These compounds are the ones most likely to be used in the event of a bioterror attack. The purpose of this communication is to review the advantages and disadvantages of using mice infected with vaccinia and cowpox virus as surrogate models for human orthopoxvirus infections and to summarize the activity of CMX001 and ST-246 in these model infections

Treatment of Vaccinia and Cowpox Virus Infections in Mice with CMX001 and ST-246

Although a large number of compounds have been identified with antiviral activity against orthopoxviruses in tissue culture systems, it is highly preferred that these compounds have activity in vivo before they can be seriously considered for further development. One of the most commonly used animal models for the confirmation of this activity has been the use of mice infected with either vaccinia or cowpox viruses. These model systems have the advantage that they are relatively inexpensive, readily available and do not require any special containment facilities; therefore, relatively large numbers of compounds can be evaluated in vivo for their activity. The two antiviral agents that have progressed from preclinical studies to human safety trials for the treatment of orthopoxvirus infections are the cidofovir analog, CMX001, and an inhibitor of extracellular virus formation, ST-246. These compounds are the ones most likely to be used in the event of a bioterror attack. The purpose of this communication is to review the advantages and disadvantages of using mice infected with vaccinia and cowpox virus as surrogate models for human orthopoxvirus infections and to summarize the activity of CMX001 and ST-246 in these model infections

Activity and Mechanism of Action of N-Methanocarbathymidine against Herpesvirus and Orthopoxvirus Infections

N-Methanocarbathymidine [(N)-MCT] is a conformationally locked nucleoside analog that is active against some herpesviruses and orthopoxviruses in vitro. The antiviral activity of this molecule is dependent on the type I thymidine kinase (TK) in herpes simplex virus and also appears to be dependent on the type II TK expressed by cowpox and vaccinia viruses, suggesting that it is a substrate for both of these divergent forms of the enzyme. The drug is also a good inhibitor of viral DNA synthesis in both viruses and is consistent with inhibition of the viral DNA polymerase once it is activated by the viral TK homologs. This mechanism of action explains the rather unusual spectrum of activity, which is limited to orthopoxviruses, alphaherpesviruses, and Epstein-Barr virus, since these viruses express molecules with TK activity that can phosphorylate and thus activate the drug. The compound is also effective in vivo and reduces the mortality of mice infected with orthopoxviruses, as well as those infected with herpes simplex virus type 1 when treatment is initiated 24 h after infection. These results indicate that (N)-MCT is active in vitro and in vivo, and its mechanism of action suggests that the molecule may be an effective therapeutic for orthopoxvirus and herpesvirus infections, thus warranting further development

Oral Activity of a Methylenecyclopropane Analog, Cyclopropavir, in Animal Models for Cytomegalovirus Infections

We reported previously that purine 2-(hydroxymethyl)methylenecyclopropane analogs have good activity against cytomegalovirus infection. A second-generation analog, (Z)-9-{[2,2-bis-(hydroxymethyl)cyclopropylidene]methyl}guanine (ZSM-I-62, cyclopropavir [CPV]), has particularly good activity against murine and human cytomegaloviruses (MCMV and HCMV) in vitro. To determine the oral activity of this compound in vivo, BALB/c or severe combined immunodeficient (SCID) mice infected with MCMV and two models using SCID mice implanted with human fetal tissue and subsequently infected with HCMV were used. In MCMV-infected normal mice, CPV at 10 mg/kg of body weight was highly effective in preventing mortality when administered at 24, 48, or 72 h post-viral inoculation and reduced titers of virus in tissues of SCID mice by 2 to 5 log(10). In one HCMV model, human fetal retinal tissue was implanted into the anterior chamber of the mouse eye and inoculated with the Toledo strain of HCMV, and in the second, human fetal thymus and liver tissues were implanted under the kidney capsule of mice and then inoculated with HCMV. In general, replication of HCMV in both types of implant tissue increased from 7 through 21 to 28 days and then gradually decreased to undetectable levels by 8 weeks postinfection. Oral treatment with 45 or 15 mg of CPV/kg initiated 24 h after infection was highly effective in reducing replication to undetectable levels in both models and was generally more effective than ganciclovir. These data indicate that the methylenecyclopropane analog, CPV, was highly efficacious in these four animal models and should be evaluated for use in HCMV infections in humans

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