title: Comparison of methods for identifying resistant herpes simplex virus and measuring antiviral susceptibility.
abstract: BACKGROUND
  A number of in vitro assays are used to determine susceptibility of HSV to antiviral agents, but results from these in vitro assays do not necessarily correlate with treatment outcome.
  
  
  OBJECTIVE
  A method with improved capability for identifying an isolate as acyclovir (ACV) or penciclovir (PCV) resistant when resistance is borderline could greatly improve the management of HSV disease.
  
  
  METHODS
  A comparative evaluation of four in vitro assays, plaque reduction (PRA), DNA hybridization, plating efficiency (PEA) and plaque autoradiography (PAR) was performed to accurately identify and measure resistance of a TK-altered clinical HSV isolate (HSV-1 N4) from a patient who was non-responsive to ACV treatment. Two established criteria for the prediction of antiviral resistance, IC(50)> or =2.0 microg/ml or an IC(50) greater than 10x above a sensitive virus IC(50), as well as testing in human (MRC-5) and nonhuman (Vero and CV-1 monkey kidney) cell lines were evaluated.
  
  
  RESULTS
  The PRA and DNA hybridization assays accurately identified HSV-1 N4 as ACV(r) in human cells when using the 10x above sensitive virus IC(50) resistance criterion. Moreover, the PEA and PAR assays failed to classify HSV-1 N4 as drug resistant and indicate that these technologies alone are inadequate for identifying resistant virus.
  
  
  CONCLUSIONS
  The data presented herein indicate that the PRA and DNA hybridization assays most accurately identified an otherwise borderline-resistant isolate as drug resistant: (i) when a sensitive virus is used within each individual assay as a control, (ii) when ACV and PCV susceptibility is evaluated in human cells, and (iii) when the 10x above sensitive IC(50) criterion is used to classify a virus as drug-resistant. Testing of additional clinical samples is warranted to further confirm these findings.
authors.affiliation: Department of Host Defense, The Antimicrobial and Host Defense Center of Excellence for Drug Discovery, GlaxoSmithKline Pharmaceuticals, 1250 South Collegeville Road, UP 1450, Collegeville, PA 19426-0989, USA. robert_t_sarisky@gsk.com
authors.forename: Robert T
authors.initials: RT
authors.lastname: Sarisky
authors.forename: Paul
authors.initials: P
authors.lastname: Crosson
authors.forename: Rachel
authors.initials: R
authors.lastname: Cano
authors.forename: Matthew R
authors.initials: MR
authors.lastname: Quail
authors.forename: Tammy T
authors.initials: TT
authors.lastname: Nguyen
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Wittrock
authors.forename: Teresa H
authors.initials: TH
authors.lastname: Bacon
authors.forename: Stephen L
authors.initials: SL
authors.lastname: Sacks
authors.forename: Laure
authors.initials: L
authors.lastname: Caspers-Velu
authors.forename: Richard L
authors.initials: RL
authors.lastname: Hodinka
authors.forename: Jeffry J
authors.initials: JJ
authors.lastname: Leary
mesh_terms: D000212:Acyclovir / Q000031:analogs & derivatives* / Q000494:pharmacology; D000998:Antiviral Agents / Q000494:pharmacology*; D001345:Autoradiography; D024882:Drug Resistance, Viral; D006147:Guanine; D008826:Microbial Sensitivity Tests; D009693:Nucleic Acid Hybridization; D018139:Simplexvirus / Q000187:drug effects* / Q000201:enzymology; D013937:Thymidine Kinase / Q000378:metabolism; D010948:Viral Plaque Assay
chemical_list: D000998:Antiviral Agents; C053539:penciclovir; D006147:Guanine; D013937:Thymidine Kinase; D000212:Acyclovir