In Vitro Assay for the Evaluation of Cytotoxic Effects Provided by a Combination of Suicide and Killer Genes in a Bicistronic Vector

When using bicistronic expression constructs the issue arises concerning proper evaluation of the cytotoxic efficiency of a combination of therapeutic genes. For this purpose, an approach can be applied based on the transient transfection of cultured human cells with a specifically designed set of mono- and bicistronic expression constructs and on the comparison of their cytotoxic effects. Here the application of this approach is described using an example of the evaluation of the combined cytotoxic action of bifunctional yeast cytosine deaminase/uracil phosphoribosyltransferase fusion protein (FCU1) and hepatitis A virus 3C protease in a bicistronic plasmid construct.

Cytotoxic effect of co-expression of human hepatitis A virus 3C protease and bifunctional suicide protein FCU1 genes in a bicistronic vector

Recent reports on various cancer models demonstrate a great potential of cytosine deaminase/5-fluorocytosine suicide system in cancer therapy. However, this approach has limited success and its application to patients has not reached the desirable clinical significance. Accordingly, the improvement of this suicide system is an actively developing trend in gene therapy. The purpose of this study was to explore the cytotoxic effect observed after co-expression of hepatitis A virus 3C protease (3C) and yeast cytosine deaminase/uracil phosphoribosyltransferase fusion protein (FCU1) in a bicistronic vector. A set of mono- and bicistronic plasmid constructs was generated to provide individual or combined expression of 3C and FCU1. The constructs were introduced into HEK293 and HeLa cells, and target protein synthesis as well as the effect of 5-fluorocytosine on cell death and the time course of the cytotoxic effect was studied. The obtained vectors provide for the synthesis of target proteins in human cells. The expression of the genes in a bicistronic construct provide for the cytotoxic effect comparable to that observed after the expression of genes in monocistronic constructs. At the same time, co-expression of FCU1 and 3C recapitulated their cytotoxic effects. The combined effect of the killer and suicide genes was studied for the first time on human cells in vitro. The integration of different gene therapy systems inducing cell death (FCU1 and 3C genes) in a bicistronic construct allowed us to demonstrate that it does not interfere with the cytotoxic effect of each of them. A combination of cytotoxic genes in multicistronic vectors can be used to develop pluripotent gene therapy agents.