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

Abstract

Varicella zoster virus (VZV) is usually associated with mild to moderate illness in immunocompetent patients. However, older age and immune deficiency are the most important risk factors linked with virus reactivation and severe complications. Treatment of VZV infections is based on nucleoside analogues, such as acyclovir (ACV) and its valyl prodrug valacyclovir, penciclovir (PCV) as its prodrug famciclovir, and bromovinyldeoxyuridine (BVDU; brivudin) in some areas. The use of the pyrophosphate analogue foscarnet (PFA) is restricted to ACV-resistant (ACV r ) VZV infections. Since antiviral drug resistance is an emerging problem, we attempt to describe the contributions of specific mutations in the viral thymidine kinase (TK) gene identified following selection with ACV, BVDU and its derivative BVaraU (sorivudine), and the bicyclic pyrimidine nucleoside analogues (BCNAs), a new class of potent and specific anti-VZV agents. The string of 6 Cs at nucleotides 493 to 498 of the VZV TK gene appeared to function as a hot spot for nucleotide insertions or deletions. Novel amino acid substitutions (G24R and T86A) in VZV TK were also linked to drug resistance. Six mutations were identified in the "palm domain" of VZV DNA polymerase in viruses selected for resistance to PFA, PCV, and the 2-phophonylmethoxyethyl (PME) purine derivatives. The investigation of the contributions of specific mutations in VZV TK or DNA polymerase to antiviral drug resistance and their impacts on the structures of the viral proteins indicated specific patterns of cross-resistance and highlighted important differences, not only between distinct classes of antivirals, but also between ACV and PCV.

Antiherpesvirus Activities of Two Novel 4′-Thiothymidine Derivatives, KAY-2-41 and KAH-39-149, Are Dependent on Viral and Cellular Thymidine Kinases

“…In this study, we found this mutation in HSV-1 and HSV-2 clones replicated under pressure of KAY-2-41. Other previously known drug resistance mutations mapped in the TK of HSV-1 and HSV-2 of clinical samples have been also identified here, such as the amino acid substitutions R51W, R222C, V187M, S182N, T288M, and Y173C (13,24,(34)(35)(36)(37)(38)(39)(40)(41). Three amino acid changes in the HSV TK were never reported before, i.e., I235F, Y88C, and M129T.…”

Drug Resistance of Clinical Varicella-Zoster Virus Strains Confirmed by Recombinant Thymidine Kinase Expression and by Targeted Resistance Mutagenesis of a Cloned Wild-Type Isolate

“…The present study forms the basis for a similar VZV database. Thus, this approach is valuable not only for the characterization of unclear resistance mutations but also for the analysis of novel drug candidates against herpesvirus infections (38)(39)(40).…”

Vaccine-associated varicella and rubella infections in severe combined immunodeficiency with isolated CD4 lymphocytopenia and mutations in IL 7 R detected by tandem whole exome sequencing and chromosomal microarray

“…Foscarnet, a direct viral DNA polymerase inhibitor, is the drug of choice for patients with disseminated acyclovir-resistant varicella [42]. Cidofovir is recommended for acyclovir-and foscarnet-resistant strains [43]. VZIG is a purified pooled anti-IgG to VZV, and prophylaxis is recommended up to 10 days following VZV exposure in immunocompromised patients [44].…”