A novel U2OS/tGFP-KOR cell line has been developed through stable transfection to modulate the internalization of the Human Kappa Opioid Receptor (KOR) complex in living cells and to assay for compounds inducing tGFP-KOR redistribution inside the cells. Fluorescent KOR Internalization Assay cell line was obtained by stable transfection of an expression vector for a fusion protein of tGFP and human kappa-opioid receptor, as well as G418 into U2OS cells. Single cells with strong green fluorescence were selected by flow cytometry, and allowed to expand. These cells constitutively express the tGFP-KOR fusion protein.Assay Details: Innoprot KOR Internalization Cell Line has been designed to assay compounds or analyze stimuli for their ability to modulate kappa-opioid receptor activation and the following redistribution process inside the cells. This highly reproducible assay allows monitoring KOR receptor activation and redistribution process in High Content Analysis and fluorescence microscope applications. This internalization assay was validated with an average Z prime of 0.84 +/- 0.02 for High Content Screening.