[Molecular imaging with new PET tracers]

Radiolabelled RGD peptides for imaging and therapy

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. One promising approach of angiogenesis imaging is imaging of specific molecular markers of the angiogenic cascade like the integrin α(v)β(3). For molecular imaging of integrin expression, the use of radiolabelled peptides is still the only approach that has been successfully translated into the clinic. In this review we will summarize the current data on imaging of α(v)β(3) expression using radiolabelled RGD peptides with a focus on tracers already in clinical use. A perspective will be presented on the future clinical use of radiolabelled RGD peptides including an outlook on potential applications for radionuclide therapy.

Expression of integrin alphavbeta3 in gliomas correlates with tumor grade and is not restricted to tumor vasculature

In malignant gliomas, the integrin adhesion receptors seem to play a key role for invasive growth and angiogenesis. However, there is still a controversy about the expression and the distribution of α_vβ₃ integrin caused by malignancy. The aim of our study was to assess the extent and pattern of α_vβ₃ integrin expression within primary glioblastomas (GBMs) compared with low‐grade gliomas (LGGs). Tumor samples were immunostained for the detection of α_vβ₃ integrin and quantified by an imaging software. The expression of α_vβ₃ was found to be significantly higher in GBMs than in LGGs, whereby focal strong reactivity was restricted to GBMs only. Subsequent analysis revealed that not only endothelial cells but also, to a large extent, glial tumor cells contribute to the overall amount of α_vβ₃ integrin in the tumors. To further analyze the integrin subunits, Western blots from histologic sections were performed, which demonstrated a significant difference in the expression of the β₃ integrin subunit between GBMs and LGGs. The presented data lead to new insights in the pattern of α_vβ₃ integrin in gliomas and are of relevance for the inhibition of α_vβ₃ integrin with specific RGD peptides and interfering drugs to reduce angiogenesis and tumor growth.