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

We have evaluated 3 newly developed neuropeptide Y receptor antagonists in various in vitro binding and bioassays: BIBO3304 (Y-1), T4[NPY33-36](4) (Y-2), and CGP71683A (Y-5). In rat brain homogenates, BIBO3304 competes for the same population of [I-125][Leu(31),Pro(34)] peptide YY (PYY) binding sites (75%) as BIBP3226, but with a 10 fold greater affinity (IC50 of 0.2 +/- 0.04 nM for BIBO3304 vs. 2.4 +/- 0.07 nM for BIBP3226),while CGP71683A has high affinity for 25% of specific [I-125][Leu(31),Pro(34)]PYY binding sites. Both BIBO3304 and CGP71683A (at 1.0 mu M) were unable to compete for a significant proportion of specific [I-125]PYY3-36/Y-2 sites. The purported Y-2 antagonist T4[NPY33-36](4) competed against [I-125]PYY3-36 binding sites with an affinity of 750 nM. These results were confirmed in HEK 293 cells transfected with either the rat Y-1, Y-2, Y-4, or Y-5 receptor cDNA. BIBO3304, but not CGP71683A, competed with high affinity for [I-125][Leu(31),Pro(34)]PYY binding sites in HEK 293 cells transfected with the rat Y-1 receptor cDNA, whereas the reverse profile was observed upon transfection with the rat Y-5 receptor cDNA. Additionally, both molecules were inactive at Y-2 and Y-4 receptor subtypes expressed in HEK 293 cells. Receptor autoradiographic studies revealed the presence of [I-125][Leu(31),Pro(34)]PYY/BIBO3304-insensitive sites in the rat brain as reported previously for BIBP3226. Finally, the selective antagonistic properties of BIBO3304 were demonstrated in a Y-1 bioassay (rabbit saphenous vein; pA(2) value of 9.04) while being inactive in Y-2 (rat vas deferens) and Y-4 (rat colon) bioassays. These results confirm the high affinity and selectivity of BIBO3304 and CGP71683A for the Y-1 and Y-5 receptor subtypes, respectively, while the purported Y-2 antagonist, T4[NPY33-36](4) possesses rather low affinity for this receptor.