674. Improved Therapy of Prostate Carcinoma with TRAIL Gene Delivery Using Flt-1 Promoter Element in Combination with Ionizing Radiation
Authors: Sergey A. Kaliberov, Lyudmila N. Kaliberova, Donald J. Buchsbaum
Journal: Molecular Therapy (2004)

Tumor necrosis factor-related apoptosis inducing ligand (TRAIL/Apo2L) is of particular interest in the development of prostate carcinoma therapeutics as it preferentially induces apoptosis of tumor cells. Several potential problems for recombinant TRAIL, including requirements of large amounts for treatment, short circulating half-life, and cytotoxicity against normal human hepatocytes, could limit the effectiveness of this anti-cancer agent. One way to overcome these limitations is to employ adenoviral vectors for high-efficiency and specific TRAIL gene transfer into cancer cells. The vascular endothelial growth factor (VEGF) and its cognate receptors Flt-1 and Flk-1 are involved in regulation of angiogenesis and tumor growth, invasion and metastasis of prostate carcinoma. VEGF receptor Flt-1 expression is observed in both tumor endothelial cells and prostate cancer cells. We hypothesized that selective transcriptional targeting of TRAIL gene expression under control of the Flt-1 promoter would increase specificity and efficiency of prostate cancer therapy in combination with ionizing radiation. We developed an adenoviral vector encoding the TRAIL gene under control of the Flt-1 promoter element (AdFlt-TRAIL), which produced prostate cancer cell death as well as endothelial cell death. Our results reveal that prostate cancer cells were relatively resistant to soluble TRAIL protein. Cell viability of DU145 and PC-3 cells was 75% and 77% following incubation for 96 h with soluble TRAIL at 400 ng/ml, respectively. Although hormone-responsive LNCaP prostate cancer cells demonstrated a lower level of Flt-1 promoter activity in comparison with hormone-independent (DU145 and PC-3) human prostate cancer cells, AdFlt-TRAIL produced increased cytotoxicity to LNCaP (p53-wildtype) and DU145 (p53-mutant) cells in comparison with PC-3 (p53-negative). Ionizing radiation at 3 Gy increased LacZ expression driven by the Flt-1 promoter by 61 % in DU145 human prostate cancer cells and 48 % in SVEC 4-10 murine endothelial cells. The combination of radiation treatment and AdFlt-TRAIL transduced overexpression of TRAIL overcame TRAIL resistance of human prostate cancer cells in vitro. Relative cell viability of DU145 cells was 90% at 72 h after radiation treatment (2 Gy) alone, 46% at 96 h after AdFlt-TRAIL infection (100 MOI) alone, and 15% for their combination. AdFlt-TRAIL-mediated apoptosis involved cleavage of caspase-3, and PARP, and required caspase-8 and -9 activity. Furthermore, in vivo administration of AdFlt-TRAIL at the site of tumor growth in combination with radiation treatment produced significant suppression of the growth of DU145 human prostate tumor xenografts in athymic nude mice. Our results suggest that specific TRAIL delivery employing the Flt-1 promoter can effectively inhibit tumor growth and demonstrate the advantage of combination radiotherapy and gene therapy for the treatment of prostate cancer.