REDD1 is a determinant of low-dose metronomic doxorubicin-elicited endothelial cell dysfunction through downregulation of VEGFR-2/3 expression

Low-dose metronomic chemotherapy (LDMC) inhibits tumor angiogenesis and growth by targeting tumor-associated endothelial cells, but the molecular mechanism has not been fully elucidated. Here, we examined the functional role of regulated in development and DNA damage responses 1 (REDD1), an inhibitor of mammalian target of rapamycin complex 1 (mTORC1), in LDMC-mediated endothelial cell dysfunction. Low-dose doxorubicin (DOX) treatment induced REDD1 expression in cultured vascular and lymphatic endothelial cells and subsequently repressed the mRNA expression of mTORC1-dependent translation of vascular endothelial growth factor receptor ( Vegfr )- 2/3 , resulting in the inhibition of VEGF-mediated angiogenesis and lymphangiogenesis. These regulatory effects of DOX-induced REDD1 expression were additionally confirmed by loss- and gain-of-function studies. Furthermore, LDMC with DOX significantly suppressed tumor angiogenesis, lymphangiogenesis, vascular permeability, growth, and metastasis in B16 melanoma-bearing wild-type but not Redd1 -deficient mice. Altogether, our findings indicate that REDD1 is a crucial determinant of LDMC-mediated functional dysregulation of tumor vascular and lymphatic endothelial cells by translational repression of Vegfr-2/3 transcripts, supporting the potential therapeutic properties of REDD1 in highly progressive or metastatic tumors. Cancer: Stress protein implicated in effects of low-dose metronomic chemotherapy Sustained low-dose metronomic chemotherapy impairs the function of tumor-associated blood vessels and lymphatic tissues due to the action of a stress response protein called REDD1. A research team from South Korea led by Young-Myeong Kim of Kangwon National University School of Medicine in Chuncheon showed that low doses of doxorubicin, a widely used anti-cancer drug, induces the expression of REDD1. This in turn inhibits the activity of vascular endothelial growth factor receptors-2/-3 that are needed for the formation of blood and lymphatic vessels, both of which can promote tumor growth. Cancer-bearing mice that lacked a working version of REDD1 did not respond to continuous low-dose treatment with doxorubicin, demonstrating the critical nature of this protein in mediating the drug regimen’s effects. The authors propose that pharmacologically enhancing REDD1 activity could help combat highly aggressive or metastatic tumors.