Inhibitors of vascular endothelial growth factor in cancer.

Angiogenesis is a complex process that is regulated by pro- and antiangiogenic factors. These factors can emanate from diverse sources including cancer cells, stromal cells, blood and extracellular matrix. Their relative contribution is likely to change with tumor type and tumor site. Vascular endothelial growth factor (VEGF) is now well confirmed as the primary and the most potent inducer of angiogenesis. To activate cellular signaling pathways, VEGF binds to receptor kinases VEGF-R1, R2 and R3. It then promotes several events required for the formation of new blood vessels, such as endothelial cell survival, proliferation, migration and vascular permeability. Activation of endothelial cells, leads to the secretion of enzymes which degrade the extracellular matrix (ECM) and hence promote metastasis. Similarly it promotes survival by inducing Bcl-2 expression on VEGF receptor positive leukemia. Besides being a potent mitogen for macrovascular cells derived from arteries, veins and lymphatics, it is also highly involved in a number of angiogenic related disorders including inflammatory diseases, rheumatoid arthritis, psoriasis, retinopathies and age related macular degeneration. Neovascularization and increased vessel permeability are being recognized as major causes of VEGF related pathogenesis. Therefore, inhibition of VEGF pathway is a strategy being widely pursued to provide new therapeutics for the treatment of VEGF related disorders. Over twenty compounds with anti-angiogenic properties ranging from VEGF neutralizing antibody, soluble receptors, receptor antagonists or tyrosine kinase inhibitors (TKIs) are either approved or are currently under clinical (phase I - III) study. This review aims to provide an updated account of how VEGF inhibitors are shaping up to become an important class of drugs used in the treatment of cancer.