Evaluation of disease and viral biomarkers as triggers for therapeutic intervention in respiratory mousepox - an animal model of smallpox.

The human population is currently faced with the potential use of natural or recombinant variola and monkeypox viruses as biological weapons. Furthermore, the emergence of human monkeypox in Africa and its expanding environs poses a significant natural threat. Such occurrences would require therapeutic and prophylactic intervention with antivirals to minimize morbidity and mortality of exposed populations. Two orally-bioavailable antivirals are currently in clinical trials; namely CMX001, an ether-lipid analog of cidofovir with activity at the DNA replication stage and ST-246, a novel viral egress inhibitor. Both of these drugs have previously been evaluated in the ectromelia/mousepox system; however, the trigger for intervention was not linked to a disease biomarker or a specific marker of virus replication. In this study we used lethal, intranasal, ectromelia virus infections of C57BL/6 and hairless SKH1 mice to model human disease and evaluate exanthematous rash (rash) as an indicator to initiate antiviral treatment. We show that significant protection can be provided to C57BL/6 mice by CMX001 or ST-246 when therapy is initiated on day 6 post infection or earlier. We also show that significant protection can be provided to SKH1 mice treated with CMX001 at day 3 post infection or earlier, but this is four or more days before detection of rash (ST-246 not tested). Although in this model rash could not be used as a treatment trigger, viral DNA was detected in blood by day 4 post infection and in the oropharyngeal secretions (saliva) by day 2-3 post infection - thus providing robust and specific markers of virus replication for therapy initiation. These findings are discussed in the context of current respiratory challenge animal models in use for the evaluation of poxvirus antivirals.

Inhibition of viral replication by interferon-gamma-induced nitric oxide synthase.

Interferons (IFNs) induce antiviral activity in many cell types. The ability of IFN-gamma to inhibit replication of ectromelia, vaccinia, and herpes simplex-1 viruses in mouse macrophages correlated with the cells' production of nitric oxide (NO). Viral replication was restored in IFN-gamma-treated macrophages exposed to inhibitors of NO synthase. Conversely, epithelial cells with no detectable NO synthesis restricted viral replication when transfected with a complementary DNA encoding inducible NO synthase or treated with organic compounds that generate NO. In mice, an inhibitor of NO synthase converted resolving ectromelia virus infection into fulminant mousepox. Thus, induction of NO synthase can be necessary and sufficient for a substantial antiviral effect of IFN-gamma.