Assay Report Card

ID: ALA3888445

Type: Binding

Description: Radioligand Binding Assay: Assessments of compound binding to human MC5R (hMC5R)) by displacement of an 125I-labeled NDP-MSH receptor ligand peptide were performed essentially as described in the data sheets produced by Perkin Elmer to accompany their frozen hMC5R membranes (Perkin Elmer catalog number RBXMC5M400UA). [125I] NDP-MSH: Radiolabeled in House and Purified by HPLC: Na125I (0.5 mCi, 17.4 Ci/mg) was added to 50 μL sodium phosphate (50 mM, pH 7.4) in an eppendorf tube precoated with IODOGEN. After incubation for 10 mins the phosphate buffer containing the iodine was added to NDP-MSH (10 μl at 1 mg/mL) in a separate eppendorf tube. This was incubated for a further 10 mins. The iodinated NDP-MSH was purified by HPLC on a Zorbax SB 300 column using solvent A: 0.05% TFA and solvent B: 90% acetonitrile 0.045% TFA with a linear gradient, 0-67% B over 60 mins. The 125I NDP-MSH eluted at 52 mins after the unlabeled starting material (48 min) and was counted and stored in the freezer. It was used within 48 hrs, as radioactive decay and ligand decomposition resulted in greatly reduced specific binding observed after 72 hrs. Incubation buffer: 25 mM HEPES-KOH (pH 7.0), 1.5 mM CaCl2, 1 mM MgSO4, 0.1 M NaCl, 1 mM 1,10-phenanthroline, and 1 Complete™ protease inhibitor tablet/100 mL (Roche, catalog number 1873580). Perkin Elmer frozen hMC5 membranes: catalog number RBXMC5M400UA, 0.4 mL/vial; 400 microassays/vial, 0.78 mg/mL protein concentration. Vials of frozen membranes were thawed rapidly immediately before use, diluted with binding buffer and vortexed. Resuspended membranes were kept on ice until they were added to the wells of the plate. Assays were performed in 96 well polypropylene plates. Membranes (0.78 μg 40 μL of a 1:40 dilution in incubation buffer) were added to [125I] NDP-MSH (0.84 nM; 2200 Ci/mmol) and test compounds in a total volume of 140 μL. This was incubated for 1 hr at 37° C. Non-specific binding was determined with 3 mM NDP-MSH. Plates were filtered using a Tomtec cell harvester with GF/A filters (Wallac) (presoaked in 0.6% polyethylenimine) and washed three times with 1.0 mL ice-cold wash buffer (the above incubation buffer without 1,10-phenanthroline and Complete™ protease inhibitor tablet). The filters were dried in a 37° C. oven, placed in a sample bag and 5 mL Betaplatescint (Wallac) was added. Prepared filters were counted in cassettes in a Microbeta Trilux (Wallac) for 1 min.