title: Isolation of human adenovirus type 5 variants resistant to the antiviral cidofovir.
abstract: OBJECTIVE
  Cidofovir (S-HPMPC) is a potent broad-spectrum antiviral drug with potential clinical application against infections caused by human cytomegalovirus, herpes simplex virus, and adenovirus (AD). This study sought to determine whether variants of AD5 could be isolated in vitro that demonstrated increased resistance to this new antiviral drug.
  
  
  METHODS
  Homogenous stocks of wild-type AD5 (ATCC strain VR-5) were generated from isolated plaques grown in A549 cells. The stocks subsequently were serially passaged in cells containing increasing levels (from 5 to 75 micrograms/ml) of cidofovir. The recovered virus either was passaged, titrated, or assayed for 50% inhibitory concentration (IC50) of cidofovir.
  
  
  RESULTS
  Three independently isolated variants were obtained that demonstrated increased resistance to cidofovir. Viral resistance to the drug increased on stepwise passage in higher concentrations. Compared to the ATCC AD5 reference (IC50 = 6.2 micrograms/ml), stable cidofovir-resistant variants showed fivefold to eightfold resistance (AD5 RI IC50 = 36.5 micrograms/ml; AD5 R2 IC50 = 36.7 micrograms/ml; and AD5 R3 IC50 = 32.6 micrograms/ml; analysis of variance, P = 0.000001). However, a variable number of passages (1 to 13) at each concentration of cidofovir was performed to obtain robust infectious virus suitable for testing at the next higher concentration. All resistant virus isolates grew to levels of virus titer comparable to the parental virus and showed no apparent phenotypic changes in growth rates, plaque size, or efficiency of plaque formation.
  
  
  CONCLUSIONS
  The successful isolation of AD5 variants in tissue culture resistant to cidofovir has important clinical implications with respect to the anticipated use of this antiviral drug in treating adenoviral ocular infections.
authors.affiliation: Department of Ophthalmology, Eye and Ear Institute, University of Pittsburgh Medical Center, Pennsylvania 15213, USA.
authors.forename: Y J
authors.initials: YJ
authors.lastname: Gordon
authors.forename: T P
authors.initials: TP
authors.lastname: Araullo-Cruz
authors.forename: Y F
authors.initials: YF
authors.lastname: Johnson
authors.forename: E G
authors.initials: EG
authors.lastname: Romanowski
authors.forename: P R
authors.initials: PR
authors.lastname: Kinchington
mesh_terms: D000260:Adenoviruses, Human / Q000187:drug effects / Q000302:isolation & purification* / Q000502:physiology; D000998:Antiviral Agents / Q000494:pharmacology*; D000077404:Cidofovir; D003588:Cytopathogenic Effect, Viral; D003596:Cytosine / Q000031:analogs & derivatives* / Q000494:pharmacology; D004352:Drug Resistance, Microbial; D006801:Humans; D008175:Lung Neoplasms / Q000821:virology; D008826:Microbial Sensitivity Tests; D063065:Organophosphonates; D009943:Organophosphorus Compounds / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
chemical_list: D000998:Antiviral Agents; D063065:Organophosphonates; D009943:Organophosphorus Compounds; D003596:Cytosine; D000077404:Cidofovir