[show abstract][hide abstract] ABSTRACT: The alpha2beta1 integrin receptor plays a key role in angiogenesis. Here we investigated the effects of small molecule inhibitors (SMIs) designed to disrupt integrin alpha2 I or beta1 I-like domain function on angiogenesis. In unchallenged endothelial cells, fibrillar collagen induced robust capillary morphogenesis. In contrast, tube formation was significantly reduced by SMI496, a beta1 I-like domain inhibitor and by function-blocking anti-alpha2beta1 but not -alpha1beta1 antibodies. Endothelial cells bound fluorescein-labeled collagen I fibrils, an interaction specifically inhibited by SMI496. Moreover, SMI496 caused cell retraction and cytoskeletal collapse of endothelial cells as well as delayed endothelial cell wound healing. SMI activities were examined in vivo by supplementing the growth medium of zebrafish embryos expressing green fluorescent protein under the control of the vascular endothelial growth factor receptor-2 promoter. SMI496, but not a control compound, interfered with angiogenesis in vivo by reversibly inhibiting sprouting from the axial vessels. We further characterized zebrafish alpha2 integrin and discovered that this integrin is highly conserved, especially the I domain. Notably, a similar vascular phenotype was induced by morpholino-mediated knockdown of the integrin alpha2 subunit. By live videomicroscopy, we confirmed that the vessels were largely nonfunctional in the absence of alpha2beta1 integrin. Collectively, our results provide strong biochemical and genetic evidence of a central role for alpha2beta1 integrin in experimental and developmental angiogenesis.
American Journal Of Pathology 09/2009; 175(3):1338-47. · 4.52 Impact Factor
[show abstract][hide abstract] ABSTRACT: Endorepellin, a C-terminal fragment of the vascular basement membrane proteoglycan perlecan, inhibits angiogenesis via the alpha2beta1-integrin receptor. Because this integrin is also implicated in platelet-collagen responses and because endorepellin or its fragments are generated in response to injury and inflammation, we hypothesized that endorepellin could also affect platelet biology. We discovered that endorepellin supported alpha2beta1-dependent platelet adhesion, without appreciably activating or aggregating platelets. Notably, endorepellin enhanced collagen-evoked responses in platelets, in a src kinase-dependent fashion, and enhanced the collagen-inhibitory effect of an alpha2beta1-integrin function-blocking antibody. Collectively, these results suggest that endorepellin/alpha2beta1-integrin interaction and effects are specific and dependent on cell type, differ from those emanated by exposure to collagen, and may be due to cellular differences in alpha2beta1-integrin activation/ligand affinity state. These studies also suggest a heretofore unrecognized role for angiostatic basement membrane fragments in platelet biology.
[show abstract][hide abstract] ABSTRACT: The antiangiogenic approach to controlling cancer requires a better understanding of angiogenesis and the discovery of new compounds that modulate this key biological process. Here we investigated the role of endorepellin, an angiostatic protein fragment that is derived from the C-terminus of perlecan, a heparan sulfate proteoglycan, in controlling tumor angiogenesis in vivo.
We administered human recombinant endorepellin systemically to mice bearing orthotopic squamous carcinoma xenografts or syngeneic Lewis lung carcinoma tumors. We monitored tumor growth, angiogenesis, metabolism, hypoxia, and mitotic index by using quantitative immunohistochemistry and positron emission tomography scan imaging. In addition, we determined the localization of injected endorepellin using near-infrared labeling and immunohistochemistry of frozen tumor sections. Finally, we isolated tumor-derived endothelial cells and tested whether endorepellin could interact with these cells and disrupt in vitro capillary morphogenesis. All statistical tests were two-sided.
Endorepellin specifically targeted the tumor vasculature as determined by immunohistochemical analysis and accumulated in the tumor perivascular zones where it persisted for several days as discrete deposits. This led to inhibition of tumor angiogenesis (as measured by decreased CD31-positive cells, mean control = 1902 CD31-positive pixels, mean endorepellin treated = 343.9, difference between means = 1558, 95% confidence interval [CI] = 1296 to 1820, P<.001), enhanced tumor hypoxia, and a statistically significant decrease in tumor metabolism and mitotic index (as measured by decreased Ki67-positive cells, mean control Ki67 pixels = 5970, mean endorepellin-treated Ki67 pixels = 3644, difference between means = 2326, 95% CI = 1904 to 2749, P<.001) compared to untreated controls. Endorepellin was actively internalized by tumor-derived endothelial cells causing a redistribution of alpha2beta1 integrin such that both proteins colocalized to punctate deposits in the perivascular region. Endorepellin treatment inhibited in vitro capillary morphogenesis of both normal and tumor-derived endothelia.
Our results provide support for the hypothesis that endorepellin is an effective antitumor vasculature agent that could be used as a therapeutic modality to combat cancer.