A Novel Suicide Gene Therapy System for p53-Mutated Cells Using a Wild-Type p53-Specific Promoter and Cre/loxP Switch

Abstract

Approximately half of all malignant tumors have a mutation or deficiency in the p53 tumor suppressor gene. The present study was designed to develop a p53-mutated cancer cell-specific suicide gene therapy system using p53 as a transcriptional activating factor. We introduced the promoter containing the wild-type p53-specific binding sequence (p53SP) and the Cre/loxP exchange system to induce specific expression of the herpes simplex viral thymidine hinase (HSV-tk) gene in p53-mutated cells. The transfection of an enhanced green fluorescent protein (EGFP) reporter gene expression vector containing p53SP resulted in selective EGFP expression in wild-type p53-producing cells, but not in p53-mutated cells. To express HSV-tk alone in the p53-mutated cells, two plasmid vectors were prepared: one regulator plasmid vector to express Cre under the control of the p53SP promoter (p53Cre), and another tk expression vector driven by the CAG promoter containing loxP sites at both ends of the HSV-tk gene (pCALtkL). The cotransfection of p53Cre with pCALtkL preferentially reduced the expression of HSV-tk in the wild-type p53-producing cells, but not in the p53-mutated cells. This cotransfection led to selective growth inhibition in the cotransfected p53-mutated cells mediated by ganciclovir, whereas a single transfection of pCALtkL caused nonselective growth inhibition in both cell lines following ganciclovir treatment. Thus, the HSV-tk expression system containing the wild-type p53-specific promoter and the Cre/loxP switch endabled the selective growth inhibition of p53-mutated cancer cells.