Antagonist activity against human GPR10 receptor expressed in HEK293 cells assessed as inhibition of PrRP-induced intracellular calcium mobilization pre-incubated for 15 mins before PrRP addition by Fluo-8 dye based fluorescence imaging plate reader method
Inhibition Assay: Receptor-expressing HEK 293 cell membrane fraction was analyzed by modifying the methods of C. J. Langmead et al. (see Langmead C J, Szekeres P G; Chambers J K, Ratcliffe S J, Jones D N C, Hirst W D, et al. Characterization of the binding of [125I]-human prolactin releasing peptide (PrRP) to GPR10, a novel G protein coupled receptor. Br J Pharmacol 2000; 131: 683-688.). To each well of a 96-well plate, 150 μl of assay buffer (20 mM HEPES, 10 mM EDTA, 1 μl/ml protease inhibiting agent cocktail, pH 7.4), 20 μl of cell membrane fraction, 10 μl of test compound and [3H]-PrRP (final concentration 1 nM) were added and incubated at room temperature for 90 minutes. After completion of the reaction, using a cell harvester, the cell-membrane fraction sample product was filtered under aspiration by a glass fiber filter plate (Unifilter; GF/B) previously treated with 0.5% polyethylene imine. The filter was washed with a 50 mM Tris hydrochloric acid buffer (pH 7.4) three times.
Intracellular Calcium Mobilization Assay: HEK293 cells expressing human GPR10 were maintained in Dulbecco's Modified Eagles' medium supplemented with 10% fetal bovine serum, 1% penicillin-streptomycin and 20 mM HEPES at 37° C. in a 5% CO2 incubator. GPR10-expressing HEK293 cells were placed in poly-D-lysine coated 96-well culture plates and cultured for 18-24 hr before the test at a density of 3×104 cells/well. The cells were incubated with 2.5 nM Fluo-8 for 1 hr at room temperature in Recording Buffer containing 1% bovine serum albumin, 0.01% pluronic F-127 and 20 mM HEPES, Hanks Balanced Buffered Saline, pH 7.4. The cells were incubated with test compounds for 15 min at room temperature, and then PrRP (the final concentration, 1 nM) was added into the medium. The changes in intracellular calcium-dependent fluorescence were monitored using a fluorescence imaging plate reader (FDSS3000, Hamamatsu Photonics K.K.). Fluo-8 fluorescence was measured with excitation at 490 nm and emission at 520 nm.