Molecular imaging of αvß3 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 αvß3, but also αvß5 and α5ß1, play a central role in the angiogenic process and integrin αvß3 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 αvß3 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 αvß3 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 αvß3 expression.