Vascular Apoptosis and Involution in Gliomas Precede Neovascularization: A Novel Concept for Glioma Growth and Angiogenesis

Abstract

SUMMARY:Vascular changes in gliomas were analyzed by implanting fluorescent-labeled glioma 261 cells in the brains of 28 mice. Seven animals were killed each week for 4 weeks. We investigated the expression of angiopoietin-2 (Ang-2) by in situ hybridization and compared it with the distribution of apoptotic cells identified by DNA strand breaks (using the terminal deoxynucleotidyl transferase-mediated biotinylated deoxyuridine triphosphate nick end labeling [TUNEL] method) and transmission electron microscopy (TEM). As early as 1 week after implantation, tumor cells accumulated around vessels, which expressed Ang-2 and were TUNEL negative. TEM showed tumor cells adjacent to the vascular cells "lifting up" the normal astrocytic feet processes away from the endothelial cells and disrupting normal pericytic cuffing. After 2 weeks the number of perivascular glioma cells had increased. No increase in the number of blood vessels was detected at this time. Vascular cells remained positive for Ang-2 and rare ones were TUNEL positive. TEM showed closely packed proliferating perivascular tumor cells. After 3 weeks, there was vascular involution with scant zones of tumor necrosis. Ang-2 was still detected in vascular cells, but now numerous vascular cells were TUNEL positive. In addition, TEM showed apoptotic vascular cells. After 4 weeks, there were extensive areas of tumor necrosis with pseudopalisading and adjacent angiogenesis. Ang-2 was detected in vascular cells at the edge of the tumors in the invaded brain and in vessels surrounded by tumor cells. At both 3 and 4 weeks, most of the TUNEL-positive tumor cells lacked morphological features characteristic of apoptosis and displayed features consistent with necrotic cell death as determined by TEM. Only rare tumor cells appeared truly apoptotic. In contrast, the TUNEL-positive endothelial cells and pericytes were round and shrunken, with condensed nuclear chromatin by TEM, suggesting that vascular cells were undergoing an apoptotic cell death. These results suggest that vascular cell apoptosis and involution preceded tumor necrosis and that angiogenesis is a later event in tumor progression in experimental gliomas. Moreover, Ang-2 is detected prior to the onset of apoptosis in vascular cells and could be linked to vascular involution. (Lab Invest 2000, 80:837-849).A poptosis and angiogenesis are both critical events in the normal sequences of many biologic processes and play key roles in regulatory activities during normal and pathological processes including development and oncogenesis. Apoptosis and angiogenesis are as fundamental to cellular and tissue physiology as are cell division and differentiation. In contrast to necrosis, apoptosis may affect scattered individual cells rather than clusters of cells, entire tissues, or organ compartments (Majno and Joris, 1995). One of the key characteristics of apoptosis is cell shrinkage. Apoptosis represents a mechanism to remove damaged, infected, or unwanted cells selectively (Allen et al, 1998;Dinsdale et al, 1999;Payne ...

Flavopiridol Induces Mitochondrial-Mediated Apoptosis in Murine Glioma GL261 Cells via Release of Cytochrome c and Apoptosis Inducing Factor

“…13,14 Taken together, our data provide a rationale for use of this drug in the treatment of patients with GBM. …”

“…12 We have developed an experimental animal model for GBM using the murine glioma cell line GL261 as a novel in vivo system to screen potential therapeutic agents. 13,14 In this study we wished to characterize the activity of flavopiridol on the GL261 cells in vitro in order to evaluate its potential to inhibit GL261 tumor growth in vivo. Our results demonstrate that flavopiridol 1.…”

CD4+FoxP3+ regulatory T cells gradually accumulate in gliomas during tumor growth and efficiently suppress antiglioma immune responses in vivo

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Nonlinear Modeling and Simulation of Tumor Growth

“…These results are supported by well-known clinical observations (e.g., [148]). As the tumor grows and engulfs vessels in its vicinity, the tumor may compress the vessels [155] and disrupt flow of nutrients, leading to further necrosis and even temporary mass and vascular regression [211,99]. A growing tumor contends with increasing mechanical resistance from normal brain tissue, which has physical properties resembling a gel [153,68].…”