The major scientific focus of this project is to determine the Ras-initiated signaling pathways and their relevant transcriptional targets that contribute to human epithelial cell transformation and metastasis. Ras is mutated in approximately one quarter of all human cancers with the highest incidence in pancreatic, lung, colon, and thyroid tumors. In addition, there is considerable experimental evidence that persistent upstream signaling in other epithelial cancers may activate Ras. Transformation functions associated with Ras effector pathways are being analyzed in experimental models of human prostate cancer. Because multiple autocrine or paracrine growth factor pathways contribute to the transformation of epithelial cells and their colonization of distant tissues during the development of metastasis, Ras signaling pathways are expected to provide broadly applicable diagnostic markers and therapeutic targets. Multiple downstream effectors mediate Ras signaling, and there is a growing appreciation that the signaling outcomes of Ras activation demonstrate species and cell context differences. We have shown that ectopic Ras activation leads to the new expression of a bone and brain metastatic phenotype in the DU145 xenograft model of human prostate cancer. Histopathological analyses identified robust angiogenesis associated with metastasis formation. In addition, gene and protein assays identified VEGF-A as an induced protein following Ras transformation. Late stage or aggressive cancers exhibit metastatic growth at multiple sites, and the characterization of treatment response in various organs to drugs with potentially wide-ranging efficacy is needed. Tumor cells that induce angiogenesis are a common characteristic of metastatic disease, and clinically, anti-angiogenic therapies have demonstrated value in the setting of advanced cancer. However, recent pre-clinical studies have suggested that exposure to anti-angiogenic drugs can increase tumor invasiveness and metastasis, making it important to determine in which contexts anti-angiogenic therapy is most appropriate. We describe here the effects of Cediranib, a receptor tyrosine kinase inhibitor, in a model of advanced prostate cancer metastatic to skeleton and brain. Treatment with Cediranib decreased metastatic tumor burden in the brain and bone, decreased cerebral vasogenic edema and improved survival, despite increasing the invasive histology of brain metastases. Short duration Cediranib treatment administered at the time of tumor cell dissemination was sufficient to inhibit the establishment and subsequent growth of bone metastases, although brain metastases were subject to rebound growth after the discontinuation of Cediranib. Distinct growth patterns at different organ sites in the same animal demonstrated that certain tumor microenvironments such as bone may be most amenable to interventions by anti-VEGF therapies. In addition, anti-VEGF treatment may be of utility in decreasing the rapid growth of solid brain metastases and vasogenic edema in patients with advanced cancer, leading to reduced morbidity and associated clinical benefit. A novel receptor-ligand pathway that was observed also to be overexpressed in correlation with bone metastasis is the Tweak/Tweak Receptor pathway. Loss of the Tweak receptor inhibits bone metastasis. Since NFkappaB activation is observed downstream of Tweak receptor ligation, we have determined that the canonical NF-kappaB pathway is both necessary and sufficient for promoting bone metastasis. Relatively little is known about the regulation of FN14 expression. We have determined that androgen receptor is a transcriptional repressor of FN14 expression, which correlates with high FN14 expression in clinical samples of prostate cancer with low AR transcriptional output. We have identified the EGR transcription factor family as one positively regulated transcriptional target of FN14 signaling. This is of importance because low AR output prostate cancers are the least treatable with standard androgen deprivation therapy. This suggests that FN14 may be a useful target for castration resistant bone metastasis. We are currently exploring the use of FN14 targeting antibodies for imaging or linked toxin mediated inhibition.
