Adriana Albini, Francesca Tosetti, Ulrich Pfeffer, Davide Bisacchi, Silvio De Flora1 and Nicoletta Ferrari

Laboratory of Molecular Biology, Istituto Nazionale per la Ricerca sul Cancro, 1Department of Health Sciences, University of Genoa, Genoa, Italy

The concept that angiogenesis appears to be a key factor in both tumor growth and metastasis formation initiated the development of several new strategies for cancer therapy and management based on antiangiogenesis. The generation of a new blood vessel network occurs through a series of distinct steps. First, factors released by the tumor cells stimulate neighboring endothelial cells to release proteases that degrade the extracellular matrix (ECM). The endothelial cells then migrate towards the source of the stimulus, proliferate, and finally differentiate into mature blood vessels. Several studies have indicated that until a tumor acquires the potential to induce angiogenesis, it is trapped in a dormant state, where the enhanced proliferation of the transformed cells is counterbalanced by concurrent death due inadequate diffusion of nutrients and oxygen. This concept is known as the angiogenic switch hypothesis, and implies that early angiogenesis control can prevent or delay tumor insurgence. Matrix metalloproteinases (MMPs), angiogenic growth factors (AGFs), and their receptors have been the main targets of an increasing number of clinical trials approved to test the tolerance and therapeutic efficacy of anti-angiogenic agents. Since anti-angiogenesis inhibits tumor growth but does not eliminate tumor cells, these agents must have low toxicity permitting chronic administration. We noted that several cancer chemopreventive agents show anti-angiogenic properties when tested in in vitro and in vivo models. We have demonstrated that N-acetyl-L-cysteine (NAC) is able to reduce the invasive and metastatic potential of melanoma cells, and to inhibit endothelial cell invasion by direct inhibition of MMP activity. Epigallocatechin gallate (EGCG), a flavonoid from green tea which possesses chemopreventive activity in experimental and epidemiological studies and to inhibit angiogenesis in vivo, is a potent inhibitor of MMP-2 and MMP-9. Angiogenesis has also been demonstrated to be a target for nonsteroidal anti-inflammatory drugs (NSAIDs) with chemopreventive activity. Most recently we have shown that the synthetic retinoid N-(4-hydroxyphenyl)retinamide (fenretinide) inhibits angiogenesis in different in vivo models. Other chemopreventive agents, including steroid hormone antagonists, peroxisome proliferator-activated receptor g ligands, vitamin D, and protease inhibitors, also most likely have anti-angiogenic properties. Our hypothesis is that effective chemopreventive agents all have a common and key target: angiogenesis inhibition, a concept that we term "angioprevention". Chemoprevention agents, through their angioprevention activity, appear to suppress the angiogenic switch associated with conversion to benign microscopic lesions to malignancy. Testing for and improving the anti-angiogenic activity of chemopreventive compounds should lead to increased efficacy without excessive toxicity. Several effective angiogenesis inhibitors are proteins, however, the problems associated with production and long-term administration of proteins led us to test delivery of angiostatic proteins through a gene transfer strategy. We have demonstrated that local gene transfer of class I interferons by retroviral vectors effectively inhibits angiogenesis in Kaposis sarcoma models in vivo. Further, we have investigated the effects of murine angiostatin gene transfer in in vitro and in vivo models of KS induced neovascularization. Stable gene transfer of the angiostatin cDNA by retroviral vectors in the KS-IMM cell line resulted in delayed tumor growth in nude mice that was associated with constant angiostatin expression and reduced vascularization.

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Paper presented at the International Symposium on Predictive Oncology and Intervention Strategies; Paris, France; February 9 - 12, 2002; in the section on Novel Molecular Therapies.