Carbaboranylation of Truncated C-Terminal Neuropeptide Y Analogue Leads to Full hY1 Receptor Agonism.

The human Y1 receptor is overexpressed in breast tumour cells and is, therefore, a valuable target for site-selective drug delivery. The well-established hY1 R-selective ligand [Phe7,Pro34]NPY has been used to couple to drugs but its length of 36 amino acids also implies complex synthesis and high production costs. Therefore, shorter ligands are desirable. However, truncated versions of neuropeptide Y (NPY) usually result in reduced binding, antagonists, or only partial G-protein-biased agonists. Herein, we report on a nonamer peptide derived from the C terminus of NPY that is modified by a carbaborane, which is able to activate hY1 R fully in terms of G-protein activation but also arrestin recruitment and internalisation. We provide evidence that this unique behaviour is due to the bulky nature of the carbaborane cluster, which might address a specific second binding pocket in hY1 R that is crucial for arrestin recruitment. Thus, this study helps in deciphering ligand-induced onset of different pathways in hY1 R mediated signalling.