Adenovirus-mediated gene transfer to orthotopic hepatocellular carcinomas in athymic nude mice

Gene therapy may become an option for the treatment of malignant tumors suc h as hepatocellular carcinoma (HCC), once safe and efficient vector systems have been established. Due to their stability in vivo, recombinant adenovi ral vectors are promising vectors for gene delivery to HCC. To study the ch aracteristics of gene delivery into HCCs by recombinant adenoviral vectors in vivo, we established an in situ HCC model in the livers of athymic nude mice by intrahepatic injection of human HCC cells. Recombinant adenovirus v ectors expressing beta -galactosiclase (Ad2CMV beta gal) were injected via the tail vein of mice bearing HCC or directly into intrahepatic tumors. Lev els of beta -galactosiclase expression in tumor tissue and surrounding norm al liver were analyzed by histochemistry or for quantification by a chemi l uminescence assay in tissue homogenates. Following tail vein injection, hig h levels of beta -galactosidase expression were found in the liver, but vir tually no gene expression could be detected in the tumor tissue. In contras t, after direct injection of Ad2CM beta gal into intrahepatic HCCs, high le vels of beta -galactosiclase expression were detected in the tumor tissue. However, single transdced hepatocytes scattered throughout the normal liver could also be identified. These results indicate that barriers such as the endothelial lining of the tumor vasculature impair the efficiency of adeno viral vectors for gene delivery into HCCs by intravenous administration, wh ich can be overcome by direct injection into the tumor tissue. However, due to the observed transduction of disseminated hepatocytes following intratu moral administration, additional HCC-specific targeting to further enhance the safety of adenoviral vectors may be required.