Cell-permeable iron inhibits vascular endothelial growth factor receptor-2 signaling and tumor angiogenesis

// Devika Kir 1, 2 , Manju Saluja 1 , Shrey Modi 2 , Annapoorna Venkatachalam 1 , Erica Schnettler 1 , Sabita Roy 1, 2, 3 , Sundaram Ramakrishnan 1, 3 1 Department of Pharmacology, Masonic Comprehensive Cancer Center, Minneapolis, MN 55455, USA 2 Department of Surgery, University of Minnesota, Minneapolis, MN 55455, USA 3 Present address: Department of Surgery, University of Miami, FL 33136, USA Correspondence to: Sundaram Ramakrishnan, email: sunda001@umn.edu Keywords: cell-permeable iron, ferric ammonium citrate, angiogenesis, vascular endothelial growth factor, receptor phosphorylation Received: March 25, 2016      Accepted: July 19, 2016      Published: August 30, 2016 ABSTRACT Angiogenesis is important for tumor growth and metastasis. Hypoxia in tumors drives this angiogenic response by stabilizing Hypoxia Inducible Factors (HIF) and target genes like Vascular Endothelial Growth Factor (VEGF). HIF stability is regulated by Prolylhydroxylases (PHD)-mediated modification. Iron is an important cofactor in regulating the enzymatic activity of PHDs. Reducing intracellular iron, for instance, mimics hypoxia and induces a pro-angiogenic response. It is hypothesized that increasing the intracellular iron levels will have an opposite, anti-angiogenic effect. We tested this hypothesis by perturbing iron homeostasis in endothelial cells using a unique form of iron, Ferric Ammonium Citrate (FAC). FAC is a cell-permeable form of iron, which can passively enter into cells bypassing the transferrin receptor mediated uptake of transferrin-bound iron. Our studies show that FAC does not decrease the levels of HIF-1α and HIF-2α in endothelial cells but inhibits the autocrine stimulation of VEGF-Vascular Endothelial Growth Factor Receptor-2 (VEGFR-2) system by blocking receptor tyrosine kinase phosphorylation. FAC inhibits VEGF-induced endothelial cell proliferation, migration, tube formation and sprouting. Finally, systemic administration of FAC inhibits VEGF and tumor cell-induced angiogenesis in vivo . In conclusion, our studies show that cell-permeable iron attenuates VEGFR-2 mediated signaling and inhibits tumor angiogenesis.