Abstracts Category : Other

Molecular Tools for the NPY Y Receptor Derived from the C-Terminus of hPP and from Argininamide-type YR Antagonists

by Kilian Kuhn

The neuropeptide Y family comprises three 36-amino acid peptides, namely neuropeptide Y (NPY), peptide YY (PYY) and pancreatic polypeptide (PP). In humans, the three peptides activate four functionally expressed G-protein coupled receptors (Y1R, Y2R, Y4R and Y5R) and contribute to the regulation of numerous (patho)physiological processes such as feeding behavior, pain sensitivity or the formation of mental disorders. Among the NPY receptors, the Y4R is unique, because it preferentially binds PP over NPY or PYY. Recently, Y4R agonists were proposed as anti-obesity agents. However, due to the lack of appropriate pharmacological tools, the physiological role of the Y4R is still far from being understood. Therefore, this work aimed at the development of selective high affinity Y4R ligands, agonists and antagonists, and labeled Y4R ligands.Bivalent, NG-carbamoylated argininamides such as UR-MK188 represent the only class of Y4R antagonists with affinities in the nanomolar range known so far. UR-MK188 (Ki = 130 nM, Kb = 20 nM) was used as a lead structure for the development of truncated, centrally constrained dimeric ligands. Aromatic substructures in the core of the linker were tolerated. Bivalent ligands with a central bent 1,7-disubstituted imidazo[4,5-f]benzimidazol moiety had slightly higher affinities than those with a 4,4-disubstituted biphenyl moiety. A truncation of the linker length from 39 to 21 atoms did not compromise the Y4R affinity of the investigated ligands. An exchange of the linker attachment position from the guanidine group to the carboxylic acid of the argininamides improved the synthetic availability, but resulted in Y4R bivalent ligands with slightly reduced affinities.The diastereomeric mixture of D/L-2,7-diaminooctanedioyl-bis(YRLRY-NH2) (BVD-74D) was described as a high affinity Y4R agonist. The pure diastereomers (2R,7R)-BVD-74D and (2S,7S)-BVD-74D and a series of homo- and heterodimeric analogs in which octanedioic acid was used as an achiral linker were prepared. To investigate the role of the amino acid residues, selected amino acids were replaced by Ala. (2R,7R)-BVD-74D was superior to (2S,7S)-BVD-74D in binding and functional cellular assays, and the presence of at least one unaltered tetrapeptide sequence Arg-Leu-Arg-Tyr-NH2 was indispensable with regard to Y4R affinity. [3H]Propionylation of one amino group in the linker of (2R,7R)-BVD-74D resulted in the high affinity Y4R radioligand [3H]UR-KK193 (Kd (Y4R) = 0.67 nM), a useful new tool for the Y4R. Binding experiments with [3H]UR-KK193 revealed that the affinity of peptide Y4R agonists may be considerably higher in the absence of sodium ions, conditions widely used for the investigation of NPY receptor ligands.Recently, analogs of the C-terminus of PP containing artificial cyclic -amino acids such as [cpen34]pNPY(32-36), were described as partial Y4R agonists. With respect to the development of Y4R antagonists, aza-amino acids and D-amino acids where introduced into peptide agonist precursors. The incorporation of aza-aminoAdvisors/Committee Members: Buschauer, A. (advisor).