First selective agonist of the neuropeptide Y 1 ‐receptor with reduced size

Selective NPY analogues are potent tools for tumour targeting. Their Y 1 ‐receptors are significantly over‐expressed in human breast tumours, whereas normal breast tissue only expresses Y 2 ‐receptors. The endogenous peptide consists of 36 amino acids, whereas smaller peptides are preferred because of better labelling efficiencies. As Y 1 ‐receptor agonists enhance the tumour to background ratio compared to Y 1 ‐receptor antagonists, we were interested in the development of Y 1 ‐receptor selective agonists. We designed 19 peptides containing the C ‐terminus of NPY (28–36) with several modifications. By using competition receptor binding affinity assays, we identified three NPY analogues with high Y 1 ‐receptor affinity and selectivity. Metabolic stability studies in human blood plasma of the N ‐terminally 5(6)‐carboxyfluorescein (CF) labelled peptides resulted in half‐lives of several hours. Furthermore, the degradation pattern revealed proteolytic degradation of the peptides by amino peptidases. The most promising peptide was further investigated in receptor activation and internalization studies. Signal transduction assays revealed clear agonistic properties, which could be confirmed by microscopy studies that showed clear Y 1 ‐receptor internalization. For the first time, here we show the design and characterization of a small Y 1 ‐receptor selective agonist. This agonist might be a useful novel ligand for NPY‐mediated tumour diagnostics and therapeutics. Copyright © 2009 European Peptide Society and John Wiley & Sons, Ltd.