The role of αv integrins during angiogenesis: insights into potential mechanisms of action and clinical development

Angiogenesis depends on specific molecular interactions between vascular cells and components of the extracellular matrix (ECM). This Perspective focuses on the functional role of integrins in angiogenesis and neovascularization. Specifically, we discuss the mechanism by which antagonists of αv integrins disrupt angiogenesis in vivo and how they may impact patients with cancer and inflammatory disease. Role of ECM and integrins during angiogenesis and vasculogenesis. Angiogenesis depends not only on growth factors and their receptors but is also influenced by receptors for ECM proteins. In general, cell adhesion to the ECM is mediated by integrins, heterodimeric transmembrane proteins that comprise a diverse family of over 15 α and 8 β subunits. Integrin subunits can heterodimerize in over 20 combinations. Different integrin combinations may recognize a single ECM ligand, while others bind several different ECM proteins. Integrin-mediated adhesion leads to intracellular signaling events that regulate cell survival, proliferation, and migration (1). These signals include elevation in intracellular pH and calcium, inositol lipid synthesis, and the tyrosine phosphorylation of a wide range of nonreceptor tyrosine kinases such as focal adhesion kinase and Src kinases, as well as adaptor proteins such as Shc, p130 CAS, and Crk II. These signaling events trigger a number of downstream signals, including activation of the Ras/mitogen-activated protein (MAP) kinase pathway (1).