Antiviral Chemistry & Chemotherapy 16:203–211
Characterization and treatment of cidofovir-resistant vaccinia (WR strain) virus infections in cell culture and in mice Donald F Smee1*, Miles K Wandersee1, Kevin W Bailey1, Karl Y Hostetler 2, Antonin Holy 3 and Robert W Sidwell1 1
Institute for Antiviral Research, Department of Animal, Dairy and Veterinary Sciences, Utah State University, Logan, UT, USA 2 Department of Medicine, San Diego VA Healthcare System and the University of California at San Diego, La Jolla, CA, USA 3 Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Prague, Czech Republic *Corresponding author: Tel: +1 435 797 2897; Fax: +1 435 797 3959; E-mail:
[email protected]
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 µM, respectively, in plaque reduction assays, with similar inhibition seen in virus yield studies. Crossresistance 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 C127I cells, yet replicated similarly in Vero (monkey) cells. The CDV-R virus was completely
attenuated for virulence at 107 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
