Characterization of an herpes simplex virus type 2 mutant, which is resistant to acycloguanosine and causes fusion of BSC1 cells

Isolation and characterization of herpes simplex virus resistant to nucleoside analogs

Herpes simplex virus type 1 was isolated from nine patients with herpes labialis who were not previously exposed to any antiviral agent. A significant variation in the growth of these isolates in BSC1 cells in the presence of 5-iodo-2'-deoxyuridine and acyclovir was observed. One of the isolates was highly resistant to 5-iodo-2'-deoxyuridine and acyclovir and failed to induce significant activity of thymidine kinase in cultures. Herpesvirus reisolated from the same patient 3 1/2 years later did not show significant changes in its resistance to acyclovir, suggesting that the patient has a latent infection with a drug-resistant virus.

Perspectives in antiviral chemotherapy

The current progress in antiviral therapy is related to our better understanding of the viral multiplication, with potential targets for specific antiviral action at each step of the multiplication cycle inside the infected cell. Amantadine and Rimantadine are anti-influenza A drugs interfering with the penetration and the release of the virus. Most of the other antiviral drugs which are clinically available have the same target in common, namely the viral DNA polymerase. This holds true for modified nucleosides such as Acycloguanosine (Acyclovir), DHPG, Adenine-Arabinoside, Azidothymidine as well as pyrophosphate derivatives such as phosphonoformic acid. Unfortunately the antiviral chemotherapy must confront 3 obstacles: 1) a possible interference with the normal cellular metabolism, leading to residual cytotoxic side effects; 2) the genetic variability of the viruses, producing drug-resistant mutants and 3) the inability of any antiviral chemotherapeutic agent known to date to eradicate latent viral infection. A new approach of the control of latent infection is suggested with anti sense oligonucleotides of hybridons.

An acyclovir-resistant strain of herpes simplex virus type 2 which is highly virulent for mice

Herpes simplex virus type 2 (HSV-2), strain YS-4 C-1, isolated by plaque cloning from a clinical isolate was found to be resistant to acyclovir (ACV; acycloguanosine) in vitro. It was sensitive to phosphonoacetic acid and 9-beta-D-arabinofuranosyladenine. Thymidine kinase (TK) activity of YS-4 C-1 was less than 1% of that of other strains from the same clinical source. However, thymidine plaque autoradiography showed that YS-4 C-1 was not completely deficient in TK activity. YS-4 C-1 showed high virulence for mice like other HSV-2 strains which were sensitive to ACV. YS-4 C-1 was able to establish latent infection in mice. Virus isolated from the brain of a mouse died after being inoculated with YS-4 C-1 was also resistant to ACV. ACV was not effective in mice inoculated with YS-4 C-1. This study shows that not all ACV-resistant strains are avirulent for mice.

Sensitivity in vitro of herpes simplex virus isolates to human fibroblast interferon

Sensitivity of herpes simplex virus (HSV) isolates, from patients with recurrent infections, to human fibroblast beta interferon (IFN), was tested in vitro. Among 25 HSV strains, 12 were HSV-1, isolated from facial and labial lesions, and 13 were HSV-2 isolated from genital lesions. Viral sensitivity to IFN was examined on epithelial MB cell line by yield reduction and plaque reduction and close correspondence between the two methods was observed. Most of HSV-1 isolates were in the same range of sensitivity to IFN, while HSV-2 isolates varied in sensitivity and differences approached statistical significance (P = 0.14). No correlation was found between various biological properties, such as plaque size, virulence in baby mice, growth at different temperatures, thymidine kinase activity in the presence or absence of IFN and sensitivity to IFN. Application of beta IFN containing cream reduced clinical symptoms in most of the patients. However, larger numbers of patients should be evaluated in order to conclude whether in vitro sensitivity correlates to clinical improvement.

Antiviral activity of SK&F 21681 against herpes simplex virus

SK&F 21681 (3,10-dimethyl-10-H-s-triazolo[4',3':2,3]-as-triazino-[ 5,6-b]indole) is an inhibitor of the growth of herpes simplex viruses types 1 and 2 at a concentration of 60 micrograms/ml. It inhibits the synthesis of the viral DNA and the formation of virus particles, although the viral polypeptide synthesis is not significantly affected by this compound. Mutants of herpes simplex viruses types 1 and 2 which are able to grow in the presence of SK&F 21681 were isolated. They induced normal levels of thymidine kinase and DNA polymerase activities in the infected cells and did not show resistance to either 9-[2-hydroxyethoxymethyl] guanine or phosphonoacetic acid.