Antiangiogenic therapy: the problem of redundant pathways

Decades of research investigating the molecular basis of new blood vessel formation has identified a number of pathways that promote tumor angiogenesis. One of the major pathways involved in this process is the vascular endothelial growth factor (VEGF) family of proteins and receptors. Another receptor tyrosine kinase signaling pathway is mediated by tie-2, a receptor tyrosine kinase expressed principally on the vascular endothelium. There are two major ligands for tie-2, angiopoietin-1 (ang-1) and angiopoietin-2 (ang-2). Recent studies have implicated a pivotal new angiogenesis signaling pathway, notch-deltalik…