Selective suicide gene therapy of colon cancer cell lines exploiting fibroblast growth factor 18 promoter

Fibroblast growth factor 18 (FGF18) is one of the genes downstream of Wnt, one of the most important signaling pathways activated in colon cancer. An FGF18 promoter containing a single T-cell factor/lymphocyte enhancing factor 1 (TCF/LEF1) binding site was inserted upstream of a thymidine kinase (TK) suicide gene module, while a bacterial beta-Gal (LacZ) element served as the reporter gene. Following transient transfection with pUCFGF18LacZ, beta-Gal staining showed that 5% of SW480, 10% of HCT116, 0% of human umbilical vein endothelial cells (HUVECs) and 0% of normal colon cells (NCCs) had expressed LacZ. beta-Gal enzyme-linked immunosorbent assay revealed that the ratio of pUCFGF18LacZ activity to that of positive control was 0.09 and 0.25 in SW480 and HCT116, respectively (significantly higher than mock plasmid), while there were no significant changes in the beta-Gal expression in HUVEC and NCC cells transfected with pUCFGF18LacZ or mock plasmid. Following transfection with pUCFGF18TK and pUCCMVTK (positive control), cytotoxicity analysis of transfected cells showed that treatment with ganciclovir (GCV) significantly decreased SW480 and HCT116 cell survival at GCV concentrations above 20 microg/mL. An inverse correlation between GCV concentration and cell viability was evident in both colon cancer cell lines following transfection with these suicide plasmids. pUCFGF18TK and pUCCMVTK induced apoptosis after the administration of GCV in HCT116, but not in SW480, as demonstrated by M30 cytodeath antibody. This discrepancy may stem from differences in the mechanisms of TK/GCV-induced apoptosis in p53-proficient (HCT116) and -deficient (SW480) cells. The specific activity of the FGF18 promoter in HCT116 and SW480 may reflect the advantage of this promoter over artificial promoters containing artificial TCF/LEF binding sites.