RGD integrin radioligands

The tripeptide motif arginine-glycine-aspartate (RGD) binds integrins, and cyclic RGD peptides are selective for integrin alphavbeta3, which is expressed on activated endothelium in tumour neovasculature and on some tumour cells. Haubner and colleagues (Technical University of Munich, PLoS Medicine 2005) showed with [18F]Galacto-RGD that PET can assess alphavbeta3 expression non-invasively in patients with cancer, with tumour uptake correlating with expression measured afterwards, and proposed it for planning and monitoring anti-angiogenic therapy. Later studies imaged the neovasculature of head and neck squamous cell carcinoma and of malignant glioma.

Several RGD tracers have been studied in people, but none is approved, and therapeutic RGD radioconjugates have remained largely preclinical. Uptake reflects both vessels and tumour cells, which makes the signal hard to interpret.