Targeting tumor vasculature with homing peptides from phage display

Tumor vasculature expresses a number of molecular markers at much lower levels than those seen in the blood vessels of normal tissues, and in some cases, such markers are undetectable. The presence of these markers relates to angiogenesis; the same markers are shared by all blood vessels undergoing angiogenesis. The endothelial cells, pericytes and smooth muscle cells, and the vascular extracellular matrix in angiogenic vessels can each express such markers. Molecularly, they represent vascular growth factor receptors, cell adhesion, proteins and their receptors. Screening of phage display libraries for peptides that home to tumor vasculature when injected into mice has recently provided a new tool for analyzing the distinguishing features of tumor vasculature. Tumor-homing peptides isolated in this manner, as well as an antibody against a form of fibronectin expressed in tumor blood vessels, have been found to serve as targeting devices to concentrate drugs and other therapeutic materials to tumors in in vivo models. Such a targeting strategy can therefore potentially improve the efficacy of drugs and reduce their side effects.