809. Suppression of Human Pancreatic Cancer Growth by Lentiviral Vector-Mediated Gene Transfer of Pigment Epithelium Derived Factor (PEDF)

Pancreatic cancer is the fourth leading cause of cancer death. Most patients are diagnosed after metastasis to adjacent organs and blood vessels. Angiogenesis, which is required to for solid tumor growth beyond 1-2 mm3, plays a critical role in pancreatic cancer. Pigment epithelium-derived factor (PEDF) has been identified as the main inhibitor of retinal angiogenesis. Subsequently, PEDF has been shown to critically regulate the vasculature and mass of the pancreas. Here we examined the feasibility of using lentiviral vector-expressed human PEDF gene to treat human pancreatic tumor cell line-derived tumors in a murine model. Mono-cistronic FIV vectors encoding human PEDF or a control protein (eGFP) with each gene linked to neoR via an IRES, were used. PEDF protein produced from transduced cells and direct application of PEDF vector significantly reduced angiogenesis (63% inhibition compared to control) in a capillary formation assay using human umbilical vascular endothelial cells (HUVECs) and in a chick chorioallantoic membrane assay (14% angiogenesis index compared to control index of 64%). Enhanced HUVEC apoptosis was also observed. We examined the therapeutic efficacy of injected PEDF and control vectors on established human pancreatic tumor xenografts in nude mice. Significant anti-tumor effects and prolonged overall survival benefit was observed in PEDF vector-treated mice (> 80% tumor reduction after 1- 2 x 10^7 TU at day 30 post injection). PEDF vector-treated animals survived 52±2 days compared to 30±3 days with control vector, n = 16 in each group. Tumors treated with PEDF vector had enhanced apoptosis and vascular endothelial growth factor receptor-1 expression. We also studied tumor formation by stable pancreatic cell lines derived by transduction with PEDF and control vectors and G418 selection. PEDF secreted from these stable tumor cell lines was shown to be biologically active in the in vitro assays and a significant antitumor effect and prolonged overall survival benefit was seen. However, injection of vectors into established tumors had a better therapeutic effect than pre-transducing and selecting cells prior to establishing tumors, and this correlated with up-regulation of VEGFR-1 in the stable tumor cell lines. PEDF is a promising transgene for pancreatic cancer gene therapy.