Undermining tumor angiogenesis by gene therapy: an emerging field

The recent discovery of several molecules that negatively modulate the migration and growth of endothelial cells, collectively referred to as inhibitors of angiogenesis, has made it possible to test the hypothesis that control of angiogenesis might be an effective strategy in controlling tumor growth, as well as ameliorating the course of other life-threatening diseases. Angiogenesis inhibitors are heterogeneous in origin and potency, and their growing list includes products of the proteolysis of larger molecules with a different function, such as angiostatin and endostatin, natural modulators of vascular endothelial growth factor activity, such as sFLT-1, and some cytokines with a marked anti-endothelial activity, such as IL-12 and interferon-alpha. Pre-clinical studies have clearly indicated that most of these factors exert cytostatic rather than cytotoxic effects, thus implying the need for long-term administration in order to obtain a prolonged therapeutic effect. This feature of angiostatic therapy and the difficulty in synthesizing large amounts of recombinant functional proteins have prompted several studies, which have investigated their delivery by a gene therapy approach. This review addresses the several experimental approaches attempted to date, points out the constraints that have delayed clinical application, and envisions possible areas of integration between antiangiogenic gene therapy and other established therapeutic options against cancer.