The PathHunter U2OS MC4R Bioassay Kit provides an easy-to-use cell based assay to measure drug potency and detect neutralizing antibodies. This bioassay asseses ligand (e.g. α-Melanocyte stimulating hormone) based on activation of MC4R GPCR activity via detection of β-Arrestin recruitment. The included cell line overexpresses ProLink-tagged MC4R and EA-tagged β-Arrestin-2. Activation of MC4R stimulates the recruitment of β-Arrestin-2 and produces EFC signal. Bioassay kits are a convenient, ready-to-use format which contains all materials needed to run the assay, including single-use vials of cryopreserved cells, cell plating media, control agonist, detection reagent, and assay plates.