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Angiogenesis starts with the separation of endothelial cells from pericytes cells that are located within the basement Ciclopirox membrane of capillary vessels stabilizing the vessel wall and the vascular basement membrane, processing of the vascular ECM, cell invasion and migration across the basement membranes, and results in novel vascular extensions into the tumor body. Angiogenesis depends plausibly on a delicate balance between endogenous stimulators and inhibitors.In adult individuals the normal physiological status of the Betamethasone angiogenic switch is either off or at balance and thus angiogenesis does not occur.It is speculated that some individuals might be more susceptible to turn the angiogenic switch on in pathological conditions depending on whether their physiological angiogenic state is at balance rather than completely off. Therefore it is crucially important to understand how the angiogenic switch is maintained at balance or off, and what happens when it is pathologically turned on.Different types of tumor cells use distinct molecular mechanisms to activate the angiogenic switch. The vascular system is highly heterogeneous in different organs and tissues.The organ microenvironment can directly contribute to the maintenance and induction of the angiogenic factors. It has been shown that the phenotype of tumorassociated microvessels is different from both normal and nontumorassociated angiogenic vessels.Thus, it seems possible to target the antiangiogenic therapy to the tumor vasculature without any harmful effects on the normal vasculature.The predominant mode of action of the antiangiogenic agents clinically tested to date has been cytostatic; the inhibition of tumor vasculature causes tumor dormancy.Many of these cytostatic agents have been shown to have reversibility of their activity upon removal of the agent.Knowing the speed of vascular regrowth in tumors after cessation of treatment is therefore of high clinical relevance.A recent article determined how rapidly and to what extent tumor blood vessels regrow after removal of antiVEGF therapy.As fast as one day after drug removal, endothelial sprouts started growing into the empty sleeves of basement membranes that were not destroyed by the antiangiogenic treatment.Furthermore, also pericytes survived the treatment.This suggests that antiangiogenic therapy could be more effective if pericytes and basement membrane sleeves could be targeted as well. The endogenous molecules affecting the angiogenic balance are released by the tumor cells and various other cell types or the extracellular matrix in the tumor microenvironment.In addition to the above proangiogenic factors, the angiogenic phenotype is characterized by tumor expression of proangiogenic proteins such as interleukin. Various endogenous antiangiogenic factors have been described, many of which are fragments of naturally occurring basement membrane and extracellular matrix components.Particularly the noncollagenous parts of many basement membrane collagens function as inhibitors of angiogenesis once they are cleaved from the parent molecule. In addition, there are many so called nonclassic endogenous regulators of angiogenesis that will be only briefly mentioned here.Basement membranes are specialized sheetlike extracellular matrix structures that are closely attached to cells.They function as barriers, polarize cells, shape tissue structures, guide and support migrating cells. In addition to providing structural and functional support, vascular basement membrane components can modulate endothelial cell behavior. The main constituent of basement membranes is type IV collagen that forms a network together with other basement membrane molecules, such as laminins, nidogens, fibulins, SPARC, fibronectin, type XV and XVIII collagens, and heparan sulphate proteoglycans.

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