RETROVIRUS-MEDIATED GENE-THERAPY FOR HEPATOCELLULAR-CARCINOMA - SELECTIVE AND ENHANCED SUICIDE GENE-EXPRESSION REGULATED BY HUMAN ALPHA-FETOPROTEIN ENHANCER DIRECTLY LINKED TO ITS PROMOTER

We have previously reported that a retrovirus vector (LNAF0.3TK) carry ing a herpes simplex virus thymidine kinase gene regulated only by the 0.3-kb human alpha-fetoprotein (AFP) promoter provides ganciclovir (G CV)-mediated cytotoxicity in high AFP-producing human hepatoma cells b ut not in low AFP-producing cells. in the present study, a retrovirus vector (LNAF0.3(E+)TK), in which herpes simplex virus thymidine kinase gene expression is under the control of a human AFP enhancer directly linked to its promoter, was constructed and compared with LNAF0.3(E-) TK. In the intermediate and low AFP-producing human hepatoma cells PLC /PRF/5 and huH1/cl.2, respectively, as well as in the high AFP-produci ng human hepatoma cells (HepG2), LNAF0.3(E+)TK sensitized these cells to GCV in vitro but did not affect cell growth in nonhepatoma cells (H eLa). In an animal model using athymic mice harboring PLC/PRF/5 cells, GCV treatment resulted in more pronounced growth inhibition in the LN AF0.3(E+)TK virus-infected cells than in the LNAF0.3(E-)TK virus-infec ted cells. These results indicate that the human AFP enhancer that is directly linked to its promoter involves selective and enhanced tumori cidal activity in gene therapy for hepatocellular carcinoma.