Mechanism and its regulation of tumor-induced angiogenesis

Tumor angiogenesis is the proliferation of a network of bloodvessels that penetrates into cancerous growths,supplyingnutrients and oxygen and removing waste products.Theprocess of angiogenesis plays an important role in manyphysiological and pathological conditions.Solid tumorsdepend on angiogenesis for growth and metastasis in ahostile environment.In the prevascular phase,the tumor israrely larger than 2 to 3 mm~3 and may contain a million ormore cells.Up to this size,tumor cells can obtain thenecessary oxygen and nutrient supplies required for growthand survival by simple passive diffusion.The properties oftumors to release and induce several angiogenic and anti-angiogenic factors which play crucial roles in regulatingendothelial cell (EC) proliferation,migration,apoptosis orsurvival,cell-cell and cell-matrix adhesion through differentintracellular signaling are thought to be the essentialmechanisms during tumor-induced angiogenesis.Tumorangiogenesis actually starts with tumor cells releasingmolecules that send signals to surrounding normal hosttissue.This signaling activates certain genes in the hosttissue that,in turn,make proteins to encourage growth ofnew blood vessels.In this review,we focus the mechanismsof tumor-induced angiogenesis,with an emphasis on theregulatory role of several angiogenic and anti-angiogenicagents during the angiogenic process in tumors.Advancesin understanding the mechanisms of tumor angiogenesishave led to the development of several most effective anti-angiogenic and anti-metastatictherapeutic agents and alsohave provided several techniques for the regulation ofcancer’s angiogenic switch.The suggestion is made thatstandard cytotoxic chemotherapy and angiogenesis inhibitorsused in combination may produce complementarytherapeutic benefits in the treatment of cancer.