Abstract
Three methods for estimating the inhibitory activity of IDU against herpes simplex virus were compared. The first method measured the CPE caused by virus in tube-cultured HeLa cells; the minimal effective concentration of IDU as estimated by this method was approximately 0.001%. Toxicity of the drug could not be determined with HeLa cells, because IDU was more toxic to HeLa cells than to non-malignant cells such as primary chick embryo cells. The second method utilized the plaque reduction in primary chick embryo cells due to presence of IDU in the overlay medium; 0.01% IDU completely suppressed viral plaques but no reduction was seen with 0.001%. In the last method, virus-infected primary chick embryo cells were overlaid with a penicillin cup placed in the center, and the plaque inhibition zone caused by diffusion of the drug was measured. When diffusion of the drug was allowed to take place at 20°C for 2 days before bringing the dishes to the 37°C CO2-incubator, efficiency of this method to assay the effect of IDU was increased; concentrations of IDU higher than 0.001% placed in the cup resulted in exhibition of inhibition zones whose diameters were in proportion to the log of the drug. Since the last method was simplest in manipulation and no lass sensitive than the other methods, it was thought recommendable for screening of anti-herpes drugs. This was further ascertained by comparing it with the plaque reduction method using several newly synthesized thymidine derivatives. It should be cautioned, however, that cytotoxicity of a new drug must be examined in tube-cultured primary chick embryo cells in parallel with this screening.
