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vessel-like tube structures

Using tumour models to study tumour angiogenesis is an advance on assays such as the CAM assay, as it allows study of the uptake and distribution of a drug candidate, as well as its efficacy, in the same experiment. Furthermore, it is also possible to use such models to determine whether a new drug is anti-angiogenic or anti-vascular in action. If the former, the drug will prevent or greatly reduce the growth of new blood vessels to the tumour; if the latter, it will damage the endothelial cell lining of the existing tumour blood vessels. However, the local environment of experimental tumours, especially those growing subcutaneously, differs from that of tumours growing orthotopically, and this may impinge on the results obtained. Furthermore, the visualization of angiogenesis requires animal killing followed (usually) by lengthy histological preparation, making real-time noninvasive studies impossible


Green fluorescent protein (GFP), isolated from the jellyfish Aequorea victoria, has been used to image tumours during progression and metastasisthe technique has recently been adapted for the study of in vivo tumour angiogenesis . GFP expression in primary tumours and in their metastases can be detected by an intense green fluorescence, which can be imaged by fluorescence stereo microscopy and then captured on camera. New blood vessels, formed by angiogenesis, are not fluorescent and, consequently, are imaged as well-defined dark networks against the bright green background. Total vessel length can be measured in areas with maximum vessel development and the microvessel density determined using the appropriate software. Using GFP is noninvasive, and it allows for the real-time imaging of angiogenesis. The main disadvantage with GFP is that its sensitivity is limited due to light absorption by the surrounding tissues, especially skin. However, the use of a reversible skin flap has been found to increase sensitivity by at least an order of magnitude Here, an arc-shaped incision is made in the skin of an anaesthetized animal to produce a small flap; this can then be repeatedly opened and closed to image GFP fluorescence through the nearly transparent body walls or skull.