Pathogenesis and chemotherapy of a thymidine kinase deficient mutant strain of HSV‐1 in a murine zosteriform infection model.

Abstract

Type I and II Herpesvirus simplex virus [HSV] are contagious and cause oral (cold sores) and genital ulcers (genital HSV) before becoming latent in trigeminal ganglia (oral HSV) or sacral ganglia (genital HSV), and can reactivate and cause disease almost at the same spot of the initial virus exposure. Acyclovir is one of the gold standard treatments for labial and genital HSV for decades. Topical Acyclovir and penciclovir and their prodrugs act on thymidine kinase (TK) and are viral DNA chain inhibitor agents and hence inhibit virus replication. In TK deletion mutants, drugs which interact with TK enzyme and inhibit virus replication do not have any inhibitory effect. TK deletion mutants also replicate at slower rates and therefore take longer to make plaques in tissue culture compared to wild type strains. Resistant virus could also arise due to suboptimal treatment regimens although it is not a great problem currently in immunocompetent patients. However resistant HSV could be a major challenge to treat in immunocompromised and immunosuppressed patients as not many options are available to use antiviral drugs whose mode of action is to work on TK inhibition. In this study pathogenesis of TK deletion mutant resistant strains of HSV were used in a immunocompetent neck-ear zosteriform infection mouse model and efficacy of prodrugs on zoster spread was studied. Resistant strains of HSV mutants received were originally raised in vitro and plaques purified. These strains were then grown in tissue culture and working stock was produced. We observed that rate of replication of these mutant viruses was slower as they took longer to make plaque in tissue culture compared to wild type strains. Resistant strain of HSV were used in the immunocompetent murine zosteriform infection model along with the wild strain and efficacy of prodrugs was studied to see if murine immunocompetent natural defense will have any effect on the pathogenicity and if antiviral agents have any effect in vivo. A murine neck ear zosteriform infection model was used and development of zosteriform lesion were noted on the ear pinna along with ear thickness and body weight. Mutant viruses show delayed zosteriform spread. It was noticed that though lesions were not completely inhibited by prodrugs, zosteriform lesion and intensity was lower after antiviral treatment. This was not expected so we tend to believe that either immunocompetent immune defense system of mice were providing extra help to reduce the virus lesion or a possibility of helper virus in the murine model. In order to see the effect of TK activity in resistant mutants original stock was further analyzed by radiolabeled C-14 TK assay to confirm the deletion mutants status. In this communication In vivo results of zoster spread, radiolabeled C-14 TK assays to identify TK deletion mutant, purified cloning, other antiviral which can have an effect on TK deletion resistant HSV in immunocompromised and immunosuppressed patients will be discussed.