Radiation-induced tubulogenesis in endothelial cells is antagonized by the antiangiogenic properties of green tea polyphenol (-) epigallocatechin-3-gallate

Radiation therapy is a widely-used option for the treatment of a variety of solid tumors. Although effective, ionizing radiation (IR) may give rise to various side effects, including secondary tumors. In agreement with this, recent reports have demonstrated increased invasive potential in different tumor-derived cell lines following radiation treatment. Many of the molecular effects of IR specifically on the endothelial cells involved in tumor neovascularization remain unknown. In this study, we found that low sublethal single doses of IR applied to human umbilical vein endothelial cells stimulated cell migration and in vitro tubulogenesis. This correlated with an increase in membrane type-1 matrix metalloproteinase (MT1-MMP) protein expression, a crucial enzyme that promotes endothelial cell migration and tube formation, and of caveolin-1, a protein that regulates tube formation. Cell adhesion was also promoted by IR, reflected in increased gene expression levels of cell surface beta(3) integrin. Pretreatment of the cells with epigallocatechin-3-gallate (EGCg), a green tea catechin that possesses anti-angiogenic properties, prevented most of the IR-induced cellular and molecular events. These observations suggest that current protocols involving radiation therapy for the treatment of cancer can paradoxically promote angiogenesis, but can be improved by combination with anti-angiogenic molecules such as EGCg to target those tumor-derived endothelial cells that escaped IR-induced apoptosis.