Acyclovir-resistant Varicella-Zoster virus: Phenotypic and genetic characterization

Abstract

A man with acquired immunodeficiency syndrome (AIDS) developed zoster of the right arm which was resistant clinically to acyclovir. Varicella-zoster virus (VZV) was cultured from a skin biopsy performed at the beginning of acyclovir therapy (isolate 1) and after its failure (isolate 2). The emergence of acyclovir resistance during treatment was investigated by developing a simple and rapid drug sensitivity assay based on the plaque reduction reference method. This late-antigen synthesis reduction assay involved serial dilutions of cell-associated virus. The 50% inhibitory concentration (IC50) of acyclovir was 16 +/- 7.5 microM for the susceptible reference strain OKA, in agreement with published data. The acyclovir IC50 increased from 6.5 microM for isolate 1 to 100 microM for isolate 2. In comparison with the sequence of isolate 1, isolate 2 had a single mutation consisting of a C to T change at position 907 of the thymidine kinase gene, which changed a glutamine codon into a stop codon at position 303 of the thymidine kinase protein. These results show the emergence of acyclovir resistance through a single previously undescribed mutation in the thymidine kinase gene, and confirm the heterogeneity of mutations inducing acyclovir resistance.

In Vitro -Selected Drug-Resistant Varicella-Zoster Virus Mutants in the Thymidine Kinase and DNA Polymerase Genes Yield Novel Phenotype-Genotype Associations and Highlight Differences between Antiherpesvirus Drugs

“…In several studies, laboratory and clinical ACV r VZV mutants were reported (8,14,28,62). However, investigations correlating a detailed phenotype with specific mutations in the VZV TK and DNA Pol genes are lacking.…”

A Rapid Phenotypic Assay for Detection of Acyclovir-Resistant Varicella-Zoster Virus with Mutations in the Thymidine Kinase Open Reading Frame

“…However, this is not the case. Indeed, one can expect that most strains will be correctly identified by the colony reduction assay, for only a few strains with mutations in pol (4,14,28) have been reported, and these represent no more than 5% of all ACV r VZV strains (3,4,13,14,20,21,23,24,26,28,30,33,36,37,42,46). In addition, VZV TK mutations selected in tdk mutant bacteria can confer either deficient or altered TK phenotypes (40).…”

“…Rapid assays for the detection of resistant VZV or HSV have been reported (1,11,13,38,41,44), and all these assays depend on cell culture methods to obtain the initial virus sample for analysis. This may be limiting and time-consuming, in particular, for VZV.…”

“…Mutations in tk are found at least 20 times more often than mutations in pol in viruses from patients with ACV r HSV (7,27). Resistant VZV strains which presumably contain DNA polymerase mutations are also rarely found in patients with suspected clinical resistance (3,4,13,14,20,21,23,24,26,28,30,33,36,37,42,46). Thus, like in HSV infections, most mutations associated with the clinical resistance of VZV to ACV are within tk.…”

Point Mutations and Antiviral Drug Resistance

“…Sauerbrei et al, 2011 analyzed genotypically 16 VZV strains with clinical diagnosis of ACV-resistance, finding seven strains with alterations in the TK gene: three were associated to amino acid substitutions (L73I, W225R, T256M), three with stop codon generation (A163-, Q303-, N334-) and one frameshift due to a deletion of nucleotides 19-223. All of them were not previously reported, except the Q303-mutation, which has been reported in two patients with AIDS treated with ACV to control persistent zoster (Fillet et al, 1998;Saint-Léger et al, 2001). …”