Phosphoinositide 3-Kinase Signalling Pathways in Tumor Progression, Invasion and Angiogenesis

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Abstract
Aims and background: The PI3 kinase signalling pathway is now accepted as being at least as important as the ras-MAP kinase pathway in cell survival and proliferation, and hence its potential role in cancer is of great interest1. The purpose of this review is briefly to examine evidence for an involvement of PI3K in human cancers, discuss the mechanisms by which its activation promotes tumor progression, and consider its utility as a novel target for anticancer therapy. Methods and study design: A Medline review of recent literature concerning the role of PI3 kinase in tumor progression -mechanisms of action and clinical implications. Results: Evidence is presented that misregulation of the PI3 kinase pathway is a feature of many common cancers, either by loss of the suppressor protein PTEN, or by constitutive activation of PI3 kinase isoforms or downstream elements such as AKT and mTOR. This activation potentiates not only cell survival and proliferation, but also cytoskeletal deformability and motility; key elements in tumor invasion. In addition the PI3K pathway is implicated in many aspects of angiogenesis, including upregulation of angiogenic cytokines due to tumor hypoxia or oncogene activation and endothelial cell responses to them. These cytokines signal though receptors such as VEGF-R, FGF-R and Tie-2 and potentiate processes essential for neoangiogenesis including cell proliferation, migration, differentiation into tubules and “invasion” of these capillary sprouts into extracellular matrix (ECM). Conclusions: A more complete understanding of the role of the PI3 kinase pathway in cancer will lead the way to the development of more potent and selective inhibitors which should be a useful adjunct to conventional therapies, potentially interfering with tumor progression at several pivotal points; in particular cell survival, invasion and angiogenesis.