Synthesis and preliminary evaluation of Tc-99m-labeled somatostatin analog(RC-160) using "3+1" mixed ligand approach

The success of In-111-pentetreotide as a cancer-imaging agent has given imp etus to the search for other peptide-based radiopharmaceuticals. The labeli ng with Tc-99m has become even more attractive because of the ready availab ility and near ideal physical properties. Additionally, the kinetics of the peptide-receptor interactions favors the radiolabeling with technetium-99m . A somatostatin analog RC-160 has been labeled with Tc-99m using the "3+1" mixed ligand approach utilizing the NNS/S coordination sites. The ternary complex was formed in greater than 95% within 30 min by simultaneous reduct ion and complexation of technetium-99m pertechnetate. The Tc-99m and the su rrogate rhenium complexes showed similar chromatographic behavior. The comp lex was evaluated by in vitro receptor binding studies carried out on HTB-1 21 breast cancer cell line and biodistribution studies performed in normal mice. Our findings suggest that RC-160 can be labeled by the mixed ligand a pproach with the complex retaining its biological activity and warrants fur ther studies. (C) 2001 Elsevier Science Inc. All rights reserved.