Budding Yeast as a Screening Tool for Discovery of Nucleoside Analogs for Use in HSV-1 TK Suicide-Gene Therapy

We present a fast, convenient and inexpensive method that allows the automated, large-scale screening of chemical libraries for compounds that are converted by the herpes simplex virus type 1 (HSV-1) thymidine kinase (TK) into inhibitors of cell growth. The method is based on the use of budding yeast (Saccharomyces cerevisiae) transformed with the HSV-1 TK gene on a multicopy plasmid. Eight nucleoside analogs (acyclovir, ganciclovir, penciclovir, lobucavir, brivudin, sorivudine, IVDU and ara-T), for which the cytostatic action against mammalian cells expressing the HSV-1 TK gene has been well documented, were studied for their inhibitory effect on the growth of yeast expressing the viral TK. These nucleoside analogs had little or no inhibitory effect on the growth of yeasts transformed with the empty vector, but inhibited to a significant extent the growth of yeast expressing the viral TK. Use of HSV-1 TK-expressing yeast allows quick screening in multi-well plate format for compounds with potential use in HSV-1 TK suicide gene therapy. The method may also be used as a tool to selectively suppress or arrest the growth of one population of yeast out of mixed yeast cell cultures.