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

We previously reported that the retroviral vector (LNAFW0.3tk) expressing t he 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 c onstructed the retroviral vector (LNANM0.3TK) in which the HSVtk gene expre ssion is regulated by the variant-type of the 0.3 kb human AFP promoter wit h a G-to-A substitution at nucleotide -119, a point mutation responsible fo r hereditary persistence of human AFP and the vector was applied to three h uman 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-typ e 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 an d PLC/PRF/5 cells to GCV, but did not affect cell growth of nonhepatoma cel ls (HeLa). In addition, the bystander effect was achieved more efficiently by LNAFM0.3TK infection than LNAFW0.3TK infection in HuH-7 cells. These res ults suggest that the variant-type of the human AFP promoter ensures the th erapeutic gene expression in gene therapy particularly for the low AFP-prod ucing hepatoma cells.