| Research Abstract |
We previously reported that the retroviral vector expressing the herpes simplex virus-thymidine kinase (HSV-tk) gene under the control of 0.3-kb human α-fetoprotein (AFP) gene promoter (AF0.3) provided the cytotoxicity to ganciclovir (GCV) in high-AFP-producing human hepatoma cells but not in low-AFP-producing cells. Therefore, specific enhancement of AFP promoter activity is likely to be required to induce enough cytotoxicity in low-AFP-producing hepatoma cells. In this study, we constructed a hybrid promoter, [HRE]AF, in which a 0.4-kb fragment of human vascular endothelial growth factor (VEGF) 5'-flanking sequences containing hypoxia responsive element (HRE) was fused to AF0.3 promoter. By means of the reporter gene transfection assay, hypoxia-inducible transcriptions that were mediated by [HRE]AF promoter were detected in low- and non-AFP-producing human hepatoma cells, but not in nonhepatoma cells. When the HSV-tk gene controlled by [HRE]AF promoter was transduced into hepatoma and nonhepatoma cells by a retroviral vector, the exposure to 1% O2 induced GCV-cytotoxicity specifically in the hepatoma cells. Moreover, in nude mice bearing solid tumor xenografts, only the tumors consisting of the virus-infected hepatoma cells gradually disappeared by GCV administration. These results indicate that the hypoxia-inducible enhancer of the human VEGF gene, which is directly linked to human AFP promoter, involves selective and enhanced tumoricidal activity in gene therapy for hepatocellular carcinoma.
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