Molecular imaging of avb3 expression in cancer patients

Angiogenesis, the formation of new blood vessels, is a key process in the growth of solid tumors. Thus this process could potentially be utilized for diagnosis of malignancies by molecular imaging on the one hand and for tumor treatment on the other hand. Imaging of angiogenesis has become increasingly important with the rising use of targeted antiangiogenic therapies, like bevacizumab (Avastin). Non-invasive assessment of angiogenic activity is in this respect interesting e.g. for response assessment of such targeted antiangiogenic therapies. Several methods have been employed for imaging of angiogenesis in vivo. Mostly these approaches measure physical parameters of the tissue, e.g. blood flow, blood volume and vessel permeability. Another approach of angiogenesis imaging is imaging of specific molecular markers of the angiogenic cascade. Integrins, like avb3, but also avb5 and a5b1, play a central role in the angiogenic process and integrin avb3 binding substances can be used as imaging probes to assess integrin expression. For clinical applications, the use of radiolabeled integrin binding substances is favorable, as radiotracers can be detected with very high sensitivities in vivo. As the radiotracer approach for molecular imaging of avb3 expression is by now the only approach used in the clinical setting, it will be the focus of this review. We will summarize the current data on imaging of avb3 expression in the clinical arena using single photon emission computed tomography (SPECT) and positron emission tomography (PET). Moreover, an outlook will be presented on potential clinical applications of imaging of avb3 expression.