Tumor angiogenesis and endothelial cell modulatory factors

Angiogenesis is the ability of preexisting vasculature to send out capillary sprouts leading to the formation of new vasculature. It is now a well-accepted idea that progression of solid tumors is intrinsically dependent on angiogenesis for growth of the primary tumor and metastatic lesions. Investigations into tumor angiogenesis have focused on inhibition of tumor neovasculature as yet another possible mechanism for impairing tumor progression. Numerous studies have characterized cellular and molecular factors important to vascular formation and development and have led to the identification and understanding of requisite interactions between endothelium, angiogenic cytokines, and the supporting matrix. These studies have also led to the identification of cytokines involved in the proteolytic disruption of the basement membrane, the migration of endothelial cells, and the proliferation and formation of neoendothelium into functional vasculature. As therapies based on antiangiogenic strategies continue to evolve and clinical trials are conducted, these agents may become an important part of the arsenal against tumor proliferation, especially given their favorable toxicity profile. This review discusses the angiogenic cytokines which have been most intensely studied and the receptors they act upon. Additionally, we discuss select proteases and their importance in the development of neovasculature. A better understanding of these components will help in the development of novel therapeutic strategies.