An emerging paradigm is that fragments of plasma or extracellular proteins may regulate angiogenesis. A known plasma protein has recently been identified as having anti-angiogenic activity only after proteolytic activation. This protein has no homology to previously identified proteins with anti-angiogenic activity e.g. angiostatin, thrombospondin. The specific binding of this activated protein to endothelial cells has been demonstrated. This results in the inhibition of endothelial cell proliferation in vitro (IC50 = 10 nM) as well as angiogenesis in vivo in a Matrigel Plug model. The migration of endothelial cells is also inhibited by this activated protein with an IC50 = 100 nM. Peptides based on the sequence of this protein have been synthesized and tested and l6-mer peptides with anti- proliferative activity against endothelial cells have been identified. The goal of this Phase I proposal is to identify the minimal sequences required for the inhibition of endothelial cell proliferation and migration and to optimize these peptides from the standpoint of activity and stability. Structure-based drug design will be used in Phase II to develop peptidomimetics based on the optimized peptide sequences. The goal of Phase II will be to identify a drug candidate peptide or peptidomimetic based on the sequence(s) of the optimized peptides identified in Phase I. PROPOSED COMMERCIAL APPLICATIONS: Pathological angiogenesis has been implicated in several major human disease states including cancer, arthritis, atherosclerosis and retinopathy. We propose to create a drug candidate which would specifically inhibit the proliferation of endothelial cells and could be usefii1 clinically as an anti- angiogenic agent. The therapeutic targeting of angiogenesis has been validated in vivo and may have application in both the acute and chronic use setting.