Development and characterization of a 99m Tc-labeled Neuropeptide Y short analog with potential application in breast cancer imaging.

The aim of this work was to develop and evaluate a 99m Tc-labeled neuropeptide Y derivative with affinity toward Y1-receptor. The selected amino acid sequence included nine amino acids derived from the C-terminal portion of the NPY complemented with the addition of one cysteine-mercaptoacetic acid moiety to bind the radiometal. Labeling was achieved through the preparation of a 3 + 1 nitrido complex. Physicochemical evaluation, cell uptake, internalization and externalization studies, and competitive assays were performed. Biodistribution experiments were carried out in normal and tumor-bearing mice. A single product with radiochemical purity >90% and high stability was obtained. In vitro analysis showed specific cellular uptake, IC50 of 73.2 nM, and a high internalization rate (80%). Biodistribution studies showed low blood and renal uptake and combined hepatobiliary and urinary elimination. Preliminary studies in mice bearing induced breast tumors rendered promising uptake values.