597. Combined Suicide/Cytokine Gene Therapy of Hepatocellular Carcinoma

Abstract

Gene therapy might be a promising approach for advanced hepatocellular carcinoma (HCC) not amenable to any effective treatment. Retroviral vectors could be safely delivered directly in the tumor mass by either a percutaneous or an intra-hepatic artery approach. Aim of the study was to evaluate in vitro and in vivo efficacy of gene therapy of HCC with different retroviral vectors (LXSN-, MFG-, and SFβ91-based vectors) containing combinations of suicide (thymidine kinase of HSV-1, HSV-TK, and a mutant variant of HSV-TK with high affinity for ganciclovir, GCV) and cytokine (IL-2, IL-12, GM-CSF) genes. Comparison of vectors demonstrated that SFβ91-based retroviral vectors were the most efficient in transduction of HCC cells and in transgene expression. In vitro experiments in human and murine HCC cell lines showed dose- and time-dependent cell killing of transduced cells and efficient bystander effect after GCV treatment. A murine model of HCC was obtained by s.c. inoculation of 107 transduced and non-transduced BNL1MEA7R.1 cells in syngenic balb/c mice. Treatment with GCV led to complete or near complete regression of transduced tumors (1% of the original mass). Histological analysis of GCV-treated tumors showed inflammatory infiltration, wide necrotic and sclerotic areas and significant increase of apoptosis. In vivo experiments confirmed the bystander effect with complete regression of tumor masses containing less than 25% transduced cells. In vivo experiments also demonstrated that the combination of a cytokine gene with a suicide gene was significantly more effective in eradicating HCC than each gene alone. Moreover, mice implanted with transduced and non-transduced tumors in both flanks showed not only complete regression of thymidine kinase-positive tumors, but also growth inhibition of non-transduced tumors. In conclusion, we demonstrated the in vitro and in vivo efficacy of combined retroviral-mediated gene therapy for HCC, with a significant local bystander effect, due to suicide gene expression, and systemic therapeutic efficacy in vivo, accounted to cytokine production. These results are of interest for gene therapy applications in patients with advanced HCC.