Manipulating Y receptor subtype activation of short neuropeptide Y analogs by introducing carbaboranes

Short selective neuropeptide Y (NPY) analogs are highly attractive because of their facile synthesis. Based on the reduced-size NPY analog [Pro(30), Nle(31), Bpa(32), Leu(34)]NPY 28-36 position 32 was identified as a key position to alter the preferential activation pattern of the human neuropeptide Y receptors (hYRs). By replacing benzoylphenylalanine (Bpa) by a biphenylalanine (Bip) the photostability was first improved while the biological activity was maintained. SAR-studies showed that both aromatic rings have a high influence on the preferential hYR subtype activation. Interestingly, replacement of Bpa(32) by a strongly hydrophobic moiety changed the hYR subtype preference of the analog. Whereas the parent compound is able to activate the human neuropeptide Y-1 receptor (hY(1)R) subtype, the introduction of an N-epsilon-ortho-carbaboranyl propionic acid modified lysine resulted in a loss of activity at the hY(1)R but in an increased activity at both the hY(2)R and the hY(4)R. However, subsequent receptor internalization studies with this novel analog revealed that receptor internalization can neither be triggered at the hY(2)R nor at the hY(4)R suggesting a biased ligand. Surprisingly, investigations by H-1 NMR spectroscopy revealed structural changes in the side chains of residues Pro(30) and Leu(34) which nicely correlates with the shift from hY(1)R/hY(4)R to hY(2)R/hY(4)R activation preference. Thus, position 32 has been identified to switch the bioactive conformation and subsequently influences receptor subtype activation behavior. (C) 2013 Elsevier Ltd. All rights reserved.