Neutrophils as a key cellular target for angiostatin: implications for regulation of angiogenesis and inflammation

Abstract

Angiostatin effectively blocks tumor angiogenesis through still poorly understood mechanisms. Given the close association between immune and vascular regulation, we investigated the effects of angiostatin on angiogenesis-associated leukocytes. Angiostatin inhibited the migration of monocytes and, even more markedly, neutrophils. Angiostatin blocked chemotaxis of neutrophils to CXCR2 chemokine receptor agonists (IL-8, MIP-2, and GROalpha), formyl-Met-Leu-Phe (fMLP), and 12-O-tetradecanoylphorbol 13-acetate, and repressed fMLP-induced mitochondrial activity. Two different angiostatin forms (kringles 1-4 and 1-3) were effective, whereas whole plasminogen had no effect. IL-8, MIP-2, and GROalpha induced intense angiogenic reactions in vivo, but no angiogenic response to these factors was observed in neutropenic mice, demonstrating an essential role for neutrophils. Angiostatin potently inhibited chemokine-induced angiogenesis in vivo, and consistent with in vitro observations, both angiostatin forms were active and whole plasminogen had little effect. Angiostatin inhibition of angiogenesis in vivo was accompanied by a striking reduction in the number of recruited leukocytes. In vivo, the inflammatory agent lipopolysaccharide also induced extensive leukocyte infiltration and angiogenesis that were blocked by angiostatin. Neutrophils expressed mRNAs for ATP synthase and angiomotin, two known angiostatin receptors. These data show that angiostatin directly inhibits neutrophil migration and neutrophil-mediated angiogenesis and indicate that angiostatin might inhibit inflammation.

CXCL1/Macrophage Inflammatory Protein-2-Induced Angiogenesis In Vivo Is Mediated by Neutrophil-Derived Vascular Endothelial Growth Factor-A

“…1), as previously described (10). The intensity of the angiogenic response to CXCL1/MIP-2, as estimated by the hemoglobin content, was comparable to that induced by VTH, a mixture containing TNF-␣, which increases the expression of VEGFR2 on endothelial cells (27), and VEGF-A, a potent angiogenic factor acting directly on endothelial cells (Fig.…”

“…We have recently reported that the angiogenic activity of CXC-ELR ϩ chemokines in the Matrigel plug angiogenesis assay in vivo is neutrophil-dependent, as neutrophil depletion of the animals completely abrogated the angiogenic response to these agonists (10). In this study, we have identified a mechanism through which neutrophils exert this specific activity.…”

“…In this context, recent data clearly suggest that neutrophils can play a key role in the angiogenic process induced by CXC-ELR ϩ chemokines. We observed that the angiogenic activity of CXCL8/ IL-8, CXCL1/GRO, and CXCL1/MIP-2 in the Matrigel plug angiogenesis assay in vivo appears to be neutrophil dependent, as neutrophil depletion of these animals completely abrogated the angiogenic response (10). However, the mechanisms through which neutrophils induce neovascularization in this model have not been elucidated.…”

Transient inflammatory response induced by apoptotic cells is an important mediator of melanoma cell engraftment and growth

“…47 Although expression of CXCR2 has also been reported in endothelial cells, 48,49 evidence has clearly shown that neutrophils are necessary mediators of the angiogenic response induced by CXCR2 agonists in vivo. 50 In wound-healing studies, angiogenesis begins immediately after injury and peaks after 7 days. 51,52 Our histologic analysis of tissue sections 72 hr after coinoculation of apoptotic cells and viable tumor cells showed a great number of newly formed blood vessels, which followed the appearance of MRP-14-positive leukocyte infiltrate in that area.…”

A multiprong approach to cancer gene therapy by coencapsulated cells

“…When delivered concurrently with angiostatin, IL-2 accumulated less in the spleen while more was found in the kidneys, the tumor, and systemically (Fig 3a, b). This may be related to angiostatin's ability to alter neutrophil trafficking 34 or adhesion molecule expression on endothelial cells. Angiostatin, when bound to integrins, 35 may alter trafficking of lymphocytes, while the expression of hypoxic-induced proangiogenic factors in tumors can alter the expression of cell adhesion molecules involved in systemic cell trafficking.…”