Chelating Systems for 99mTc/188Re in the Development of Radiolabeled Peptide Pharmaceuticals

Currently, receptor based radiopharmaceuticals have received great attention in molecular imaging and radiotherapy of cancer, and provide a unique tool for target-specific delivery of radionuclides to pathological tissues. In this context, receptor binding peptides represent an attractive class of target vectors for Nuclear Medicine purposes. The rich chemistry of the group 7 elements elaborated in past years, has allowed the development of different procedures for the preparation of radiolabeled peptides in high yield. This, joint to the use of solid-phase peptide synthesis, has opened the possibility to explore new strategies for approaching the design of new class of radiolabeled receptor-targeted peptides, and to create new versatilities in targeting vehicle design e. g. in synthesis of metal-cyclized peptides or of multivalent targeting agents. This review provides an overview on several aspects of the development of new Tc-99m/Re-188-peptide based target specific radiopharmaceuticals, in particular on the synthetic strategies employed for modifying molecular vectors, and the application of the different metal-cores and/or building block for preparing high specific activity agents.