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 2

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C6 gliomas initiate vascularly after implantation into muscle tissue. (a...
C6 gliomas initiate vascularly after implantation into muscle tissue. (a) C6 glioma spheroid on day 0. Note the smooth edge of the microtumor, lacking early passive detachment of individual tumor cells. (b) C6 glioma spheroid on day 3. Detachment and migration of glioma cells from the spheroid. (c) Histology of C6 glioma spheroid on day 6 shows tumor cell invasion into adjacent muscle and subcutaneous tissue. Arrows indicate blood vessels. t, tumor mass; m, striated muscle; s, subcutaneous tissue. (d–f) C6 glioma spheroid on day 6. Same region of interest as assessed by using the two filter systems to detect DiI-labeled tumor cells (d) and FITC-Dextran–labeled blood vessels (e and f) and focusing into tumor mass (d and f) and host tissue (e). Tumor cells do not home in on the parallel host blood vessels (indicated by c) (d vs. e) but induce tumor angiogenesis (e and f). Arrows indicate sprouts originating from host blood vessels (e) and growing into tumor tissue to form a new microvascular system (f). (g and h) Microvasculature of C6 glioma on day 10 after implantation of a cell suspension (g) and spheroid (h), demonstrating comparable tumor-specific angioarchitecture. (i–k) Quantitative analysis of tumor size (i), vessel density (j), and vessel diameter (k). For the host tissue, the range of values is indicated. Bars represent 100 μm (a) and 50 μm (b–h). SUS, cell suspension group; SPH, spheroid group; host, peritumoral host tissue.