Mutations conferring resistance to viral DNA polymerase inhibitors in camelpox virus give different drug-susceptibility profiles in vaccinia virus

J Virol. 2012 Jul;86(13):7310-25. doi: 10.1128/JVI.00355-12. Epub 2012 Apr 24.


Cidofovir or (S)-HPMPC is one of the three antiviral drugs that might be used for the treatment of orthopoxvirus infections. (S)-HPMPC and its 2,6-diaminopurine counterpart, (S)-HPMPDAP, have been described to select, in vitro, for drug resistance mutations in the viral DNA polymerase (E9L) gene of vaccinia virus (VACV). Here, to extend our knowledge of drug resistance development among orthopoxviruses, we selected, in vitro, camelpox viruses (CMLV) resistant to (S)-HPMPDAP and identified a single amino acid change, T831I, and a double mutation, A314V+A684V, within E9L. The production of recombinant CMLV and VACV carrying these amino acid substitutions (T831I, A314V, or A314V+A684V) demonstrated clearly their involvement in conferring reduced sensitivity to viral DNA polymerase inhibitors, including (S)-HPMPDAP. Both CMLV and VACV harboring the A314V change showed comparable drug-susceptibility profiles to various antivirals and similar impairments in viral growth. In contrast, the single change T831I and the double change A314V+A684V in VACV were responsible for increased levels of drug resistance and for cross-resistance to viral DNA polymerase antivirals that were not observed with their CMLV counterparts. Each amino acid change accounted for an attenuated phenotype of VACV in vivo. Modeling of E9L suggested that the T→I change at position 831 might abolish hydrogen bonds between E9L and the DNA backbone and have a direct impact on the incorporation of the acyclic nucleoside phosphonates. Our findings demonstrate that drug-resistance development in two related orthopoxvirus species may impact drug-susceptibility profiles and viral fitness differently.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Substitution
  • Animals
  • Antiviral Agents / pharmacology*
  • Cell Line
  • Cidofovir
  • Cytosine / analogs & derivatives
  • Cytosine / pharmacology
  • DNA-Directed DNA Polymerase / genetics*
  • DNA-Directed DNA Polymerase / metabolism
  • Drug Resistance, Viral*
  • Humans
  • Microbial Sensitivity Tests
  • Molecular Structure
  • Mutant Proteins / genetics
  • Mutant Proteins / metabolism
  • Mutation, Missense*
  • Organophosphonates / pharmacology
  • Orthopoxvirus / drug effects*
  • Orthopoxvirus / enzymology
  • Recombinant Proteins / genetics
  • Recombinant Proteins / metabolism
  • Selection, Genetic
  • Vaccinia virus / drug effects*
  • Vaccinia virus / enzymology
  • Viral Plaque Assay


  • Antiviral Agents
  • Mutant Proteins
  • Organophosphonates
  • Recombinant Proteins
  • Cytosine
  • DNA-Directed DNA Polymerase
  • Cidofovir