||This assay utilizes proprietary non-human mammalian cells that express isoform 1 of human constitutive androstane receptor (NR1I3), a ligand-dependent transcription factor referred to as CAR1. These reporter cells utilize a modified version of human CAR1 in which the N-terminal DNA binding domain (DBD) has been replaced with the GAL4-DBD. The human CAR1 ligand binding domain (LBD) is unaltered and fully functional. The reporter cells also incorporate a luciferase cDNA functionally linked to the GAL4-upstream activation sequence (UAS). Thus, quantifying expressed luciferase activity provides a sensitive surrogate measure of changes in CAR1 activity resulting from direct interaction between a treatment compound and the nuclear receptor. Because this assay system expresses a GAL4-DBD + hCAR1 LBD hybrid receptor, the bioactivity of activators that act through indirect mechanisms (such as those that alter the phosphorylation status of the native N-terminal amino acid sequence of CAR1) may be dampened or go undetected. Human CAR1 exhibits constitutive activity, but its activity can be further regulated through direct ligand interactions. The primary application of this reporter assay system is in the screening of test samples to quantify any functional inverse-agonist activity that they may exert on human CAR1. Reporter cells are prepared using the proprietary CryoMite process. This cryo-preservation method yields high cell viability post-thaw, and provides the convenience of immediately dispensing healthy, division-competent reporter cells into assay plates. There is no need for intermediate spin-and-wash steps, viability determinations, or cell titer adjustments. The nuclear receptor reporter assays are all-inclusive cell-based assay systems. In addition to CAR1 reporter cells, this kit provides two optimized media for use during cell culture and in diluting the user"s test samples, a positive-control inverse-agonist, luciferase detection reagent, and a cell culture-ready assay plate.