title: Biochemical characterization of a virus isolate, recovered from a patient with herpes keratitis, that was clinically resistant to acyclovir.
abstract: In vitro susceptibility assays of herpes simplex virus (HSV) do not necessarily correlate with treatment outcome. An HSV type 1 (HSV-1) isolate, N4, recovered from a patient who presented with herpes keratitis with localized immunosuppression, was characterized for susceptibility. Although the 50% inhibitory concentration (IC(50)) for this isolate was less than the accepted breakpoint for defining resistance to acyclovir (>2.0 microg/mL), the following lines of evidence suggest that the isolate was acyclovir resistant: (1) the clinical history confirmed that the infection was nonresponsive to acyclovir; (2) the in vitro susceptibility was similar to that of a thymidine kinase (TK)-negative, acyclovir-resistant virus SLU360; (3) the IC(50) of acyclovir was more than 10 times the IC(50) for an acyclovir-susceptible control strain; (4) plaque-purified clonal isolates were resistant to acyclovir (IC(50)s, >2.0 microg/mL); and (5) biochemical studies indicated that the HSV-1 N4 TK was partially impaired for acyclovir phosphorylation. Although residue changes were found in both the viral tk and pol coding regions of HSV-1 N4, characterization of a recombinant virus expressing the HSV-1 N4 polymerase suggested that the TK and Pol together conferred the acyclovir-resistance phenotype.
authors.affiliation: Department of Host Defense, Antimicrobial and Host Defense Center of Excellence for Drug Discovery, GlaxoSmithKline Pharmaceuticals, Collegeville, PA, 19426-0989, USA. robert_t_sarisky@gsk.com
authors.forename: R T
authors.initials: RT
authors.lastname: Sarisky
authors.forename: R
authors.initials: R
authors.lastname: Cano
authors.forename: T T
authors.initials: TT
authors.lastname: Nguyen
authors.forename: R J
authors.initials: RJ
authors.lastname: Wittrock
authors.forename: K E
authors.initials: KE
authors.lastname: Duffy
authors.forename: P
authors.initials: P
authors.lastname: Clark
authors.forename: J O
authors.initials: JO
authors.lastname: Bartus
authors.forename: T H
authors.initials: TH
authors.lastname: Bacon
authors.forename: L
authors.initials: L
authors.lastname: Caspers-Velu
authors.forename: R L
authors.initials: RL
authors.lastname: Hodinka
authors.forename: J J
authors.initials: JJ
authors.lastname: Leary
mesh_terms: D000212:Acyclovir / Q000494:pharmacology*; D000368:Aged; D000998:Antiviral Agents / Q000494:pharmacology*; D004352:Drug Resistance, Microbial; D006561:Herpes Simplex / Q000821:virology*; D018259:Herpesvirus 1, Human / Q000187:drug effects* / Q000302:isolation & purification; D006801:Humans; D007634:Keratitis / Q000821:virology*; D008297:Male; D008826:Microbial Sensitivity Tests; D010641:Phenotype
chemical_list: D000998:Antiviral Agents; D000212:Acyclovir