(A) Chemical structures of carapin, santonin and isokobusone, along with those of the typical PXR and CAR agonists rifampicin, PCN, TCPOBOP, and CITCO. (B and C) CV-1 cells were cotransfected with the tk-CYP3A23-Luc reporter gene, together with the wild-type and mutant hPXR (B) or rPXR (C). Transfected cells were treated with the vehicle or the indicated compounds (10 μM each) for 24 h before luciferase assay. Rifampicin (RIF) and prenenolon-16α-carbonitrile (PCN) were included as the positive control ligands for hPXR and rPXR, respectively. Results are shown as fold induction over vehicle control and represent the average from triplicate assays. *, P < 0.05, vs the vehicle control group of each WT and mutant receptors.