CHEMBL3889153

Competitive Inhibition Binding Assay: A competitive inhibition binding assay was performed using membrane homogenates prepared from HEK-293 cells that express recombinant hMCR-1a or hMCR-4 (in each instance where the h prefix refers to human), or alternatively membrane homogenates from B16-F10 mouse melanoma cells containing endogenous murine MCR-1. In the examples that follow, all MCR-1 and MCR-4 values are for human recombinant receptors, unless otherwise noted. Assays were performed in 96 well polypropylene round-bottom plates (VWR catalog number 12777-030). Membrane homogenates were incubated with 0.1 nM [I125]-NDP-α-MSH (Perkin Elmer) and increasing concentrations of test peptides of the present invention in buffer containing 25 mM HEPES buffer (pH 7.5) with 100 mM NaCl, 2 mM CaCl2, 2 mM MgCl2, 0.3 mM 1,10-phenanthroline, and 0.2% bovine serum albumin. After incubation for 90 minutes at 37° C., the assay mixture was filtered onto GF/B Unifilter plates (Perkin-Elmer catalog number 6005177) and washed with 3 mL of ice-cold buffer per well. Filters were air dried and 35 uL of scintillation cocktail added to each well. Plates were counted in a Microbeta counter for bound radioactivity. Non-specific binding was measured by inhibition of binding of [I125]-NDP-α-MSH in the presence of 1 uM NDP-α-MSH. Maximal specific binding (100%) was defined as the difference in radioactivity (cpm) bound to cell membranes in the absence and presence of 1 uM NDP-α-MSH. Each assay was conducted in duplicate and the actual mean values are described, with results less than 0% reported as 0%. Ki values for peptides of the present invention were determined using Graph-Pad Prism curve-fitting software.