Targeting the pancreatic "tumor vessel interface": strategies based on engineered mesenchymal stem cell biology

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We have recently shown that the mTOR inhibitor rapamycin inhibits tumor growth via an anti-angiogenic mechanism that involves blockage of VEGF signaling in endothelial cells. Interestingly, we have also observed local microthromboses in the tumor microvasculature following rapamycin treatment suggesting that mTOR inhibition also inhibits tumor growth via a tumor-specific anti-vascular effect. In the first part of the present research project, we will explore the downstream signal transduction pathways and the underlying mechanism of mTOR inhibition in the developing as well as already existing tumor vasculature. These experiments will take into consideration the complex interactions between tumor cells, endothelial cells, and pericytes. Since ionizing radiation therapy is an effective modality for the treatment of a wide range of tumors, but is certainly hampered by a high rate of radioinsensitivity, our experiments will also cover this aspect. Specifically, we will investigate a potential sensitizing effect of mTOR inhibition on radiation therapy. These experiments will involve co-culture systems, spheroid assays, intravital microscopy of tumor bearing dorsal skinfold chambers, orthotopic and ectopic, heterogeneic and syngeneic tumor animal models (colon, pancreatic, gastric cancer), flow cytometry analysis, imrnunohistochemistry as well as western blot analysis. In the second part of the project, we want to investigate the effect of mTOR inhibition on lymphangiogenesis. These studies are based on our observation that in orthotopic pancreatic and colon cancer animal experiments we observed a reduction of lymph node metastases following mTOR inhibition. Clinical observations for the use of rapamycin in transplant patients also suggest that rapamycin might impede lymphangiogenesis. Therefore, we would like to explore the effect of mTOR inhibition on lymphangiogenesis in vitro and in vivo. We will use FACS analysis, proliferation assays, and immunohistochemical analysis of isolated lymphatic endothelial cells and tumor tissue, respectively. For the in vivo experiments, we have already established two distinct lymphangiogenesis models: a skin flap model for studies of regenerative lymphangiogenesis and a subcutaneous tumor model for studies of tumor-driven lymphangiogenesis.