Disruption of Endothelial Cell Interactions with the Novel HU177 Cryptic Collagen Epitope Inhibits Angiogenesis

Purpose: The importance of cellular communication with the extracellular matrix in regulating cellular invasion is well established. Selective disruption of communication links between cells and the local microenvironment by specifically targeting non-cellular matrix-immobilized cryptic extracellular matrix epitopes may represent an effective new clinical approach to limit tumor-associated angiogenesis. Therefore, we sought to determine whether the HU177 cryptic collagen epitope plays a functional role in regulating angiogenesis in vivo . Experimental Design: We examined the expression and characterized the HU177 cryptic collagen epitope in vitro and in vivo using immunohistochemistry and ELISA. We examined potential mechanisms by which this cryptic collagen epitope may regulate angiogenesis using in vitro cell adhesion, migration, proliferation, and biochemical assays. Finally, we examined the whether blocking cellular interactions with the HU177 cryptic epitope plays a role in angiogenesis and tumor growth in vivo using the chick embryo model. Results: The HU177 cryptic epitope was selectively exposed within tumor blood vessel extracellular matrix, whereas little was associated with quiescent vessels. An antibody directed to this cryptic site selectively inhibited endothelial cell adhesion, migration, and proliferation on denatured collagen type IV and induced increased levels of cyclin-dependent kinase inhibitor p27 KIP1 . Systemic administration of mAb HU177 inhibited cytokine- and tumor-induced angiogenesis in vivo . Conclusions: We provide evidence for a new functional cryptic regulatory element within collagen IV that regulates tumor angiogenesis. These findings suggest a novel and highly selective approach for regulating angiogenesis by targeting a non-cellular cryptic collagen epitope.