Fluorescence- and luminescence-based methods for the determination of affinity and activity of neuropeptide Y2 receptor ligands

With respect to the discovery and characterization of neuropeptide Y2 receptor ligands as pharmacological tools or potential drugs, fluorescence- and luminescence-based assays were developed to determine both the affinity and the activity of receptor agonists and antagonists. A flow cytometric binding assay is described for the hY2 receptor stably expressed in CHO cells using cy5-labeled porcine neuropeptide Y and compared with a radioligand binding assay. Binding of the fluorescent ligand was visualized by confocal microscopy. Stable co-transfection with the chimeric G protein Gqi5 enabled the establishment of a spectrofluorimetric fura-2 and a flow cytometric fluo-4 calcium assay. Further stable expression of apoaequorin targeted to the mitochondria allowed the establishment of an aequorin assay which could be performed in the 96-well format. The shape of the concentration–response curves of porcine neuropeptide Y in the presence of the Y2-selective receptor antagonist BIIE0246, characteristic of either competitive or insurmountable antagonism, depended on the period of incubation with the cells. Functional data of Y2 receptor agonists and antagonists determined in the fluorescence- and luminescence-based assays were in good agreement.