Antiviral activity of the EB peptide against zoonotic poxviruses.

BACKGROUND: The EB peptide is a 20-mer that was previously shown to have broad spectrum in vitro activity against several unrelated viruses, including highly pathogenic avian influenza, herpes simplex virus type I, and vaccinia, the prototypic orthopoxvirus. To expand on this work, we evaluated EB for in vitro activity against the zoonotic orthopoxviruses cowpox and monkeypox and for in vivo activity in mice against vaccinia and cowpox. FINDINGS: In yield reduction assays, EB had an EC50 of 26.7 µM against cowpox and 4.4 µM against monkeypox. The EC50 for plaque reduction was 26.3 µM against cowpox and 48.6 µM against monkeypox. A scrambled peptide had no inhibitory activity against either virus. EB inhibited cowpox in vitro by disrupting virus entry, as evidenced by a reduction of the release of virus cores into the cytoplasm. Monkeypox was also inhibited in vitro by EB, but at the attachment stage of infection. EB showed protective activity in mice infected intranasally with vaccinia when co-administered with the virus, but had no effect when administered prophylactically one day prior to infection or therapeutically one day post-infection. EB had no in vivo activity against cowpox in mice. CONCLUSIONS: While EB did demonstrate some in vivo efficacy against vaccinia in mice, the limited conditions under which it was effective against vaccinia and lack of activity against cowpox suggest EB may be more useful for studying orthopoxvirus entry and attachment in vitro than as a therapeutic against orthopoxviruses in vivo.

Inhibition of cowpox virus and monkeypox virus infection by mitoxantrone.

Mitoxantrone, an FDA-approved therapeutic for the treatment of cancer and multiple sclerosis, was previously reported to exhibit antiviral activity against vaccinia virus. To determine whether this activity extends to other orthopoxviruses, mitoxantrone was tested against cowpox and monkeypox. Mitoxantrone demonstrated an EC(50) of 0.25 µM against cowpox and 0.8 µM against monkeypox. Intraperitoneal treatment of cowpox virus-challenged C57Bl/6 mice with 0.5 mg/kg mitoxantrone resulted in 25% survival and a significant increase in survival time. In an effort to improve its efficacy, mitoxantrone was tested for synergistic activity with cidofovir. In vitro tests demonstrated significant synergy between the two drugs against cowpox; however, no synergistic effect on animal survival or median time-to-death was seen in intranasally-infected BALB/c mice. Significantly fewer animals survived when treated with a combination of 0.5 mg/kg mitoxantrone and 100 mg/kg cidofovir than with 100 mg/kg cidofovir alone. This is, to our knowledge, the first report of limited anti-orthopoxvirus activity by mitoxantrone in an animal model.