Potent and selective tools to investigate neuropeptide Y receptors in the central and peripheral nervous systems: BIBO3304 (Y1) and CGP71683A (Y5)

Abstract

We have evaluated 3 newly developed neuropeptide Y receptor antagonists in various in vitro binding and bioassays: BIBO3304 (Y1), T4[NPY33-36]4(Y2), and CGP71683A (Y5). In rat brain homogenates, BIBO3304 competes for the same population of [125I][Leu31,Pro34] peptide YY (PYY) binding sites (75%) as BIBP3226, but with a 10 fold greater affinity (IC50of 0.2 ± 0.04 nM for BIBO3304 vs. 2.4 ± 0.07 nM for BIBP3226),while CGP71683A has high affinity for 25% of specific [125I][Leu31,Pro34]PYY binding sites. Both BIBO3304 and CGP71683A (at 1.0 µM) were unable to compete for a significant proportion of specific [125I]PYY3-36/Y2sites. The purported Y2antagonist T4[NPY33-36]4competed against [125I]PYY3-36binding sites with an affinity of 750 nM. These results were confirmed in HEK 293 cells transfected with either the rat Y1, Y2, Y4, or Y5receptor cDNA. BIBO3304, but not CGP71683A, competed with high affinity for [125I][Leu31,Pro34]PYY binding sites in HEK 293 cells transfected with the rat Y1receptor cDNA, whereas the reverse profile was observed upon transfection with the rat Y5receptor cDNA. Additionally, both molecules were inactive at Y2and Y4receptor subtypes expressed in HEK 293 cells. Receptor autoradiographic studies revealed the presence of [125I][Leu31,Pro34]PYY/BIBO3304-insensitive sites in the rat brain as reported previously for BIBP3226. Finally, the selective antagonistic properties of BIBO3304 were demonstrated in a Y1bioassay (rabbit saphenous vein; pA2value of 9.04) while being inactive in Y2(rat vas deferens) and Y4(rat colon) bioassays. These results confirm the high affinity and selectivity of BIBO3304 and CGP71683A for the Y1and Y5receptor subtypes, respectively, while the purported Y2antagonist, T4[NPY33-36]4possesses rather low affinity for this receptor.Key words: NPY receptor antagonist, receptor subtypes, bioassays, receptor binding assays, autoradiographic studies, receptor distribution.