529. Oncolytic Virotherapy Employing flt-1 Driven mda-7/IL-24 Gene Delivery

Abstract

Top of pageAbstract Vascular-targeted anticancer therapy using conditionally replicating adenoviruses (CRAd) is an attractive strategy for cancer treatment. For specific retargeting of CRAd, selective transcription of viral genes utilizing tumor-specific promoters has been developed. CRAd targeting using insertion of the tumor-specific binding RGD ligand in the Ad fiber has shown increased infectivity. A cancer growth-suppressing gene, mda-7/IL-24, has demonstrated profound and selective anticancer activity. The central hypothesis of this study was that selective transcriptional and transductional targeting of CRAd encoding the mda-7/IL-24 gene using flt-1 promoter for specific E1a expression and RDG-4C modification of the Ad fiber-knob region can increase efficacy via direct killing of tumor endothelial cells and flt-1-positive cancer cells. Specific mda-7/IL-24 overexpression should enhance the anti-tumor efficacy of CRAd oncolytic virotherapy alone. The flt-1 promoter-driven firefly luciferase expression was determined using replication-defective Adflt-Luc and AdCMV-Luc vectors on a panel of human glioma, breast, ovarian and prostate cancer cells and human or mouse endothelial cells. The cytotoxicity of cancer and endothelial cells to CRAd infection was analyzed using the crystal violet inclusion assay. The CRAd progeny production was determined using real time PCR and a standard 50% tissue culture infectious dose assay. Tumor xenograft models were used to determinate the therapeutic efficacy of oncolytic virotherapy to treat human glioma, breast, ovarian and prostate tumors. Specificity of flt-1 promoter for human and mouse endothelial cells and U251MG glioma, PA-1 ovarian, LCC6 breast, and DU145 prostate cancer cells was demonstrated. We have developed a CRAd using the flt-1 promoter element for specific E1a gene expression, encoding the mda-7/IL-24 gene (CRAdRGDflt-mda-7) and a CDCGRDCFC-containing peptide in the HI loop of the fiber knob domain. The cancer cells demonstrated different levels of cytotoxicity after CRAdRGDflt-mda-7 infection. There was a significant decrease in viability of U251MG, PA-1, LCC6, and DU145 cells infected with CRAdRGDflt-mda-7. In vivo therapy studies demonstrated that intratumoral injection of CRAdRGDflt-mda-7 produced significant inhibition of subcutaneous LCC6 breast, OVCAR-3 ovarian, and DU145 prostate cancer xenografts and delay of D54MG human glioma tumor growth in athymic nude mice. These results suggest that selective targeting of oncolytic virotherapy with enhanced potency via mda-7/IL-24 pro-apoptotic/anti-angiogenic gene expression would be a superior strategy for treatment of human cancer.