Microtumor growth initiates angiogenic sprouting with simultaneous expression of VEGF, VEGF receptor-2, and angiopoietin-2
Peter Vajkoczy, … , Michael D. Menger, Georg Breier
Peter Vajkoczy, … , Michael D. Menger, Georg Breier
Published March 15, 2002
Citation Information: J Clin Invest. 2002;109(6):777-785. https://doi.org/10.1172/JCI14105.
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Microtumor growth initiates angiogenic sprouting with simultaneous expression of VEGF, VEGF receptor-2, and angiopoietin-2

Abstract

Tumors have been thought to initiate as avascular aggregates of malignant cells that only later induce vascularization. Recently, this classic concept of tumor angiogenesis has been challenged by the suggestion that tumor cells grow by co-opting preexisting host vessels and thus initiate as well-vascularized tumors without triggering angiogenesis. To discriminate between these two mechanisms, we have used intravital epifluorescence microscopy and multi-photon laser scanning confocal microscopy to visualize C6 microglioma vascularization and tumor cell behavior. To address the mechanisms underlying tumor initiation, we assessed the expression of VEGF, VEGF receptor-2 (VEGFR-2), and angiopoietin-2 (Ang-2), as well as endothelial cell proliferation. We show that multicellular aggregates (<< 1 mm3) initiate vascular growth by angiogenic sprouting via the simultaneous expression of VEGFR-2 and Ang-2 by host and tumor endothelium. Host blood vessels are not co-opted by tumor cells but rather are used as trails for tumor cell invasion of the host tissue. Our data further suggest that the established microvasculature of growing tumors is characterized by a continuous vascular remodeling, putatively mediated by the expression of VEGF and Ang-2. The results of this study suggest a new concept of vascular tumor initiation that may have important implications for the clinical application of antiangiogenic strategies.

Authors

Peter Vajkoczy, Mohammad Farhadi, Andreas Gaumann, Regina Heidenreich, Ralf Erber, Andreas Wunder, Jörg C. Tonn, Michael D. Menger, Georg Breier

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Figure 4

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C6 gliomas initiate vascularly after intracranial implantation. (a) C6 g...
C6 gliomas initiate vascularly after intracranial implantation. (a) C6 glioma spheroid on day 3 revealing a central solid tumor mass and individual tumor cells actively spreading over the cerebral tissue. Square indicates area of interest detailed in b and c. (b and c) Glioma cells (arrows) migrate along peritumoral cerebral blood vessels. (d) Histological examination of C6 glioma spheroid on day 6 shows perivascular tumor cell invasion into adjacent brain tissue. Arrows indicate groups of tumor cells localized next to cerebral blood vessels. (e and f) C6 glioma spheroid initiates vascularly on day 3 by inducing angiogenic sprouting. Arrows in f indicate sprouts originating from host blood vessels and vascularizing the multicellular aggregate shown in e. (g) Quantitative analysis of blood-brain barrier function of peritumoral host blood vessels from day 3 to day 14 after spheroid implantation, versus control cerebral vessels (CON). (h and i) Established neovasculature of C6 glioma spheroid on day 6 with tumor-specific angioarchitecture. (j–l) Quantitative analysis of tumor size (j), vessel density (k), and vessel diameter (l). The range of values is indicated for the host tissue. SUS, cell suspension group; SPH, spheroid group; host, peritumoral host tissue. Bars represent 400 μm (a) and 50 μm (b–f, h, and i).