Bombesin is a 14-residue peptide ligand that was initially isolated from the frog B. bombina. There are also mammalian versions of this signaling peptide that bind to their respective receptor subtypes. In addition to governing various processes in the central nervous system, bombesin receptors are overexpressed on a variety of tumor cell types. Bombesin and bombesin-like peptides have therefore proven useful as tumor markers, and radiolabeled bombesin peptides have been used in radiotherapy and as imaging tracers. However, high abdominal uptake of these peptides has hindered their effectiveness.

Dirk Tourwé and colleagues, Vrije Universiteit Brussel, Belgium, along with collaborators at the Paul Scherrer Institute, Villigen, and the ETH, Zurich, Switzerland, report the synthesis of bombesin analogues conjugated to triazole-based chelating groups for labeling with the ^99mTc(CO)₃ tracer core. These compounds do not suffer the high abdominal uptake that conventional compounds do, and thus show greater potential for both imaging and radiotherapeutic targeting of bombsin-receptor-positive tumors.

• Synthesis and Evaluation of Bombesin Analogues Conjugated to Two Different Triazolyl-Derived Chelators for ^99mTc Labeling
  L. Brans, E. García-Garayoa, C. Schweinsberg, V. Maes, H. Struthers, R. Schibli, D. Tourwé,
  ChemMedChem 2010, 5(10).
  DOI: 10.1002/cmdc.201000191