18F-Labeled Peptides: The Future Is Bright

Radiolabeled peptides have been the subject of intense research efforts for targeted diagnostic imaging and radiotherapy over the last 20 years. Peptides offer several advantages for receptor imaging and targeted radiotherapy. The low molecular weight of peptides allows for rapid clearance from the blood and non-target tissue, which results in favorable target-to-non-target ratios. Moreover, peptides usually display good tissue penetration and they are generally non-immunogenic. A major drawback is their potential low metabolic stability. The majority of currently used radiolabeled peptides for targeted molecular imaging and therapy of cancer is labeled with various radiometals like Tc-99m, Ga-68, and Lu-177. However, over the last decade an increasing number of F-18-labeled peptides have been reported. Despite of obvious advantages of F-18 like its ease of production in large quantities at high specific activity, the low beta(+) energy (0.64 MeV) and the favorable half-life (109.8 min), F-18-labeling of peptides remains a special challenge. The first part of this review will provide a brief overview on chemical strategies for peptide labeling with F-18. A second part will discuss recent technological advances for F-18-labeling of peptides with special focus on microfluidic technology, automation, and kit-like preparation of F-18-labeled peptides.