Radio-labeled receptor-binding peptides: A new class of radiopharmaceuticals

Radio-labeled receptor-binding peptides have emerged as an important class of radiopharmaceuticals. In vertebrates, these peptides transmit their biol ogical function by binding to their specific receptor on the target cell su rface. This specific receptor-binding property is exploited when the radio- labeled peptide is used as a radiopharmaceutical. The high-binding affinity for its receptor facilitates retention of the peptide in receptor-expressi ng tissues, whereas its relatively small size facilitates rapid clearance f rom the blood and other nontarget tissues. Receptor-binding peptides labele d with gamma-emitters can be used to visualize receptor-positive cells in v ivo. In addition, when labeled with beta- or alpha-emitters, these peptides can be used for peptide-receptor radionuclide therapy. Various receptors a re overexpressed on particular tumor types, and peptides binding to these r eceptors can be used to visualize tumor lesions scintigraphically. Furtherm ore, peptides binding receptors on granulocytes can be used to image infect ious and inflammatory foci. whereas peptides binding receptors on activated thrombocytes can be used for thrombus imaging. Here, the peptide analogs t hat are under development for these applications are reviewed. Copyright (C ) 2000 by W.B. Saunders Company.