Antiangiogenic Gene Therapy in Cancer

One of the most recent and exciting approaches in cancer gene therapy is the ability to target the developing blood supply of the tumor. An appealing feature of antiangiogenic gene therapy is that the tumor vasculature is a readily accessible target, particularly when the carrier and its gene are administered systemically. This is in contrast to several other gene therapy approaches in which the tumor vasculature represents a major obstacle to achieving high levels of transfection of the tumor cells. Several gene-based viral or non-viral therapies that target tumor angiogenesis have shown efficacy in pre-clinical models. Genes that encode antiangiogenic polypeptides such as angiostatin and endostatin have significantly inhibited tumor growth, inducing a microscopic dormant state. The products of these genes are thought to act extracellularly to inhibit angiogenesis. An alternative approach that investigators have used successfully in tumor-bearing mice is to target angiogenic growth factors or their receptors that are essential for tumor growth. Levels of angiogenic factors such as vascular endothelial growth factor (VEGF) have been reduced by either antisense methods or the use of genes encoding truncated angiogenic decoy receptors. Despite these promising findings of tumor reduction with antiangiogenic gene therapy, advances in the viral and/or non-viral delivery systems are essential for this therapy to have clinical utility. In this review, we will discuss the mechanisms of angiogenesis/antiangiogenesis, and the current status and future directions of antiangiogenic gene therapy.