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Blood, 1 September 2008, Vol. 112, No. 5, pp. 1904-1911. Prepublished online as a Blood First Edition Paper on June 24, 2008; DOI 10.1182/blood-2007-11-126045.
NEOPLASIA Dll4 activation of Notch signaling reduces tumor vascularity and inhibits tumor growth1 Laboratory of Cellular Oncology and 2 Molecular Imaging Program, Center for Cancer Research, National Cancer Institute (NCI), National Institutes of Health (NIH), Bethesda, MD; 3 Laboratory Animal Science Program, SAIC-Frederick, NCI-Frederick, Frederick, MD; and 4 Flow Cytometry Core Facility, National Institutes of Neurological Disorders and Stroke, NIH, Bethesda, MD Gene targeting experiments have shown that Delta-like 4 (Dll4) is a vascular-specific Notch ligand critical to normal vascular development. Recent studies have demonstrated that inhibition of Dll4/Notch signaling in tumor-bearing mice resulted in excessive, yet nonproductive tumor neovascularization and unexpectedly reduced tumor growth. Because nonfunctional blood vessels have the potential to normalize, we explored the alternative approach of stimulating Notch signaling in the tumor vasculature to inhibit tumor growth. Here we show that retrovirus-induced over-expression of Dll4 in tumor cells activates Notch signaling in cocultured endothelial cells and limits vascular endothelial growth factor (VEGF)–induced endothelial cell growth. Tumors produced in mice by injection of human and murine tumor cells transduced with Dll4 were significantly smaller, less vascularized and more hypoxic than controls, and displayed evidence of Notch activation. In addition, tumor blood perfusion was reduced as documented by vascular imaging. These results demonstrate that Notch activation in the tumor microenvironment reduces tumor neovascularization and blood perfusion, and suggest that Dll4-induced Notch activation may represent an effective therapeutic approach for the treatment of solid tumors.
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