Utilization of variant-type of human α-fetoprotein promoter in gene therapy targeting for hepatocellular carcinoma

We previously reported that the retroviral vector (LNAFW0.3tk) expressing the herpes simplex thymidine kinase (HSVtk) gene under the control of the 0.3 kb human alpha-fetoprotein (AFP) promoter provided the ganciclovir (GCV)-mediated cytotoxicity in the high AFP-producing (HuH-7) hut not in the low AFP-producing (huH-1/cl.2) human hepatoma cells, in the present study, we constructed the retroviral vector (LNANM0.3TK) in which the HSVtk gene expression is regulated by the variant-type of the 0.3 kb human AFP promoter with a G-to-A substitution at nucleotide -119, a point mutation responsible for hereditary persistence of human AFP and the vector was applied to three human hepatoma cell lines, HuH-7, huH-1/c1.2 and intermediate AFP-producing cells (PLC/PRF/5). By the reporter gene transfection assay, the activity of the variant-type of the promoter was much higher than that of the wild-type of the promoter in both HuH-7 and huH-1/cl.2 cells. consistent with this, LNAFM0.3TK infection could sensitize huH-1/cl.2 cells, as well as HuH-7 and PLC/PRF/5 cells to GCV, but did not affect cell growth of nonhepatoma cells (HeLa). In addition, the bystander effect was achieved more efficiently by LNAFM0.3TK infection than LNAFW0.3TK infection in HuH-7 cells. These results suggest that the variant-type of the human AFP promoter ensures the therapeutic gene expression in gene therapy particularly for the low AFP-producing hepatoma cells.