Insulinoma-induced hypoglycemic death in mice is prevented with beta cell-specific gene therapy

Objective and Summary Background Data Tumor-specific gene therapy can be ac hieved if a tumor-specific promoter can be identified. In this study the au thors investigated the use of the rat insulin promoter (RIP) for insulinoma -specific expression of a reporter gene. Insulinoma-specific cytotoxicity u sing the suicide gene thymidine kinase (tk) was studied both in vitro and i n vivo, RIPtk gene therapy, delivered by a nontoxic, noninflammatory liposo mal delivery system, was used in an insulinoma ICR/SCID mouse model to prev ent hypoglycemic death. Methods Rat insulin promoter (0.502 kb) was ligated to the reporter gene la cZ and ligated to the tk gene. These two genes were transfected into a mous e insulinoma (NIT) cell line to ascertain insulinoma-specific expression an d insulinoma-specific cytotoxicity in vitro. Reverse transcriptase-polymera se chain reaction and electrophoretic mobility-shift assays were performed on NIT-I cell RNA and nuclear extract, respectively, to determine the trans cription factors present and responsible for RIP activation in NIT-1 cells. A mouse insulinoma model was created with NIT-1 cells. These mice were tre ated with the RiPtk gene, and both blood sugars and animal viability were m onitored. Results Only NIT-1 cells stained blue after X-gal staining or had detectabl e levels of beta -galactosidase protein. A significant decrease in cell sur vival was observed in NIT-1 cells transfected with RIPtk in vitro. Messenge r RNA for both BETA2 and PDX-1 was found in NIT-1 cells, and a supershift w as observed for both BETA2 and PDX-1. Experimental mice treated with the RI Ptk gene, delivered by a liposomal gene delivery system, maintained their b lood glucose levels, and the animals did not die of hypoglycemia. Conclusions The data suggest that the RIP is an insulinoma-specific promote r. An ICR/SCID mouse insulinoma model was used to show that insulinoma-spec ific cytotoxicity can be accomplished by RIP coupled to a suicide gene in v ivo, preventing hypoglycemic death.