We describe that galectin-1 (gal-1) is a receptor for the angiogenesis inhibitor anginex, and that the protein is crucial for tumor angiogenesis. gal-1 is overexpressed in endothelial cells of different human tumors. Expression knockdown in cultured endothelial cells inhibits cell proliferation and migration. The importance of gal-1 in angiogenesis is illustrated in the zebrafish model, where expression knockdown results in impaired vascular guidance and growth of dysfunctional vessels. The role of gal-1 in tumor angiogenesis is demonstrated in gal-1-null mice, in which tumor growth is markedly impaired because of insufficient tumor angiogenesis. Furthermore, tumor growth in gal-1-null mice no longer responds to antiangiogenesis treatment by anginex. Thus, gal-1 regulates tumor angiogenesis and is a target for angiostatic cancer therapy.angiostatic therapy ͉ endothelial cell ͉ galectin ͉ tumor models ͉ anginex A n adequate vasculature is a prerequisite for tumors to grow, and the need for neovessel formation (or angiogenesis) provides a target for treatment of cancer (1). Endothelial cells (EC) that line the tumor vasculature are particularly suitable target cells for therapeutic approaches, because they are easily accessible to agents delivered by the blood (2). However, to affect only tumor vasculature, specific targets on angiogenically active EC are essential. To date, only a few targets of tumor vasculature have been identified (3).We recently developed the specific angiostatic peptide anginex, which inhibits tumor growth through specific inhibition of angiogenesis (4-6). Although a broad profile of activities of anginex is known, such as prevention of EC adhesion and induction of apoptosis, the molecular target on tumor EC was never identified. In a receptor-finding study using a yeast twohybrid screening approach, we identified galectin-1 (gal-1) as a target protein of anginex.gal-1 belongs to a family of carbohydrate-binding proteins that share a conserved carbohydrate recognition domain of Ϸ130 aa (7-9). Over a dozen mammalian galectins have been described (10, 11), and members of this family are expressed in a wide range of species, suggesting an important role for galectins in basic cellular mechanisms. Galectins can be secreted and, depending on the cell type or state of differentiation, they have been found in the nucleus, cytoplasm, or extracellular matrix. It has been proposed that gal-1 mediates cell adhesion and migration (12) and is involved in several processes, including proliferation (13), apoptosis (14), and even mRNA splicing (15). The role of gal-1 in EC function or vascular biology has not been extensively studied.Here, we describe the function of gal-1 in angiogenesis. We provide direct functional evidence that gal-1 is required for tumor angiogenesis and outgrowth of tumors. Furthermore, we show that gal-1 is the target for the potent angiogenesis inhibitor anginex, thus establishing gal-1 as an important target for anticancer therapy.Results gal-1 Binds the Angiostatic Peptide Anginex...
The formation of new blood vessels, or angiogenesis, is a complex process that plays important roles in growth and development, tissue and organ regeneration, as well as numerous pathological conditions. Angiogenesis undergoes multiple discrete steps that can be individually evaluated and quantified by a large number of bioassays. These independent assessments hold advantages but also have limitations. This article describes in vivo, ex vivo, and in vitro bioassays that are available for the evaluation of angiogenesis and highlights critical aspects that are relevant for their execution and proper interpretation. As such, this collaborative work is the first edition of consensus guidelines on angiogenesis bioassays to serve for current and future reference.
Purpose: To test whether a direct antiangiogenic peptide (anginex) and a vascular endothelial growth factor antibody (bevacizumab, Avastin) can transiently normalize vasculature within tumors to improve oxygen delivery, alleviate hypoxia, and increase the effect of radiation therapy. Experimental Design: Tumor oxygenation levels, microvessel density and pericyte coverage were monitored in three different solid tumor models (xenograft human ovarian carcinoma MA148, murine melanoma B16F10, and murine breast carcinoma SCK) in mice. Multiple treatment schedules were tested in these models to assess the influence on the effect of radiation therapy. Results: In all three tumor models, we found that tumor oxygenation levels, monitored daily in real time, were increased during the first 4 days of treatment with both anginex and bevacizumab. From treatment day 5 onward, tumor oxygenation in treated mice decreased significantly to below that in control mice. This ''tumor oxygenation window'' occurred in all three tumor models varying in origin and growth rate. Moreover, during the treatment period, tumor microvessel density decreased and pericyte coverage of vessels increased, supporting the idea of vessel normalization. We also found that the transient modulation of tumor physiology caused by either antiangiogenic therapy improved the effect of radiation treatment. Tumor growth delay was enhanced when single dose or fractionated radiotherapy was initiated within the tumor oxygenation window as compared with other treatment schedules. Conclusions:The results are of immediate translational importance because the clinical benefits of bevacizumab therapy might be increased by more precise treatment scheduling to ensure radiation is given during periods of peak radiosensitivity. The oxygen elevation in tumors by nonĝ rowth factor^mediated peptide anginex suggests that vessel normalization might be a general phenomenon of agents directed at disrupting the tumor vasculature by a variety of mechanisms.
Crucial to designing angiostatic and vascular targeting agents is the identification of target molecules. Because angiogenesis is not limited to pathologic conditions, careful evaluation of putative therapeutic targets is warranted to prevent adverse effects associated with impaired physiologic angiogenesis. To identify tumor-specific angiogenesis markers, we compared transcriptional profiles of angiogenic endothelial cells isolated from malignant and nonmalignant tissues with those of resting endothelial cells. We identified 17 genes that showed specific overexpression in tumor endothelium but not in angiogenic endothelium of normal tissues, creating a therapeutic window for tumor vasculature-specific targeting. Antibody targeting of 4 cell-surface-expressed or secreted products (vimentin, CD59, HMGB1, IGFBP7) inhibited angiogenesis in vitro and in vivo. Finally, targeting endothelial vimentin in a mouse tumor model significantly inhibited tumor growth and reduced microvessel density. Our results demonstrate the usefulness of the identification and subsequent targeting of specific tumor endothelial markers for anticancer therapy.
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