Human cancer cells overexpress many peptide receptors as molecular targets. Radiolabeled peptides that bind with high affinity and specificity to the receptors on tumor cells hold great potential for both diagnostic imaging and targeted radionuclide therapy. The advantage of solid-phase peptide synthesis, the availability of different chelating agents and prosthetic groups and bioconjugation techniques permit the facile preparation of a wide variety of peptide-based targeting molecules with diverse biological and tumor targeting properties. Some of these peptides, including somatostatin, bombesin, vasoactive intestinal peptide, gastrin, neurotensin, exendin and RGD are currently under investigation. It is anticipated that in the near future many of these peptides may find applications in nuclear oncology. This article presents recent developments in the field of small peptides, and their applications in the diagnosis and treatment of cancer.

Nature has designed peptides to stimulate, inhibit or regulate many body functions. The development of radiolabelled peptide-based radiopharmaceuticals for imaging a variety of tumours, infection/inflammation and thrombus has seen a new era in nuclear medicine. Recently, a number of 99Tcm-labelled bioactive peptides have proven to be useful diagnostic imaging agents. Due to their small size, peptide molecules exhibit favourable pharmacokinetic characteristics, such as rapid uptake by target tissue and rapid blood clearance, which potentially allows images to be acquired earlier following the administration of a 99Tcm-labelled peptide radiopharmaceutical. The challenge is to label bioactive peptides with 99Tcm with high specific activity without impairing the biological properties of the peptides. Molecular engineering techniques now permit synthesis of a wide range of biologically active peptides that carry chelating groups in their structure without affecting their receptor binding properties, thus permitting a high specific activity product. This review presents recent developments in 99Tcm-labelled small peptides and their potential applications in the imaging of various types of diseases. In addition, the different techniques for radiolabelling small bioactive peptides, the pharmacokinetic properties of peptides, and their potential as diagnostic imaging agents are also addressed.