Design and activities of hPXR modulators. (A) Design of the PXR modulators by a step-by-step structural optimization approach starting from the SPA70 scaffold. (B) Representative dose response curves of agonist (111), antagonist (97), partial agonist and partial antagonist (42), and dual antagonist and inverse agonist [SPA70, (10)]. hPXR TR-FRET assay was used to determine binding inhibitory activity. HepG2 hPXR-CYP3A4-luciferase stable cells were used to test compounds in either agonistic mode (“Ag”, test compound alone for activation of hPXR; %Activity = %Activation. Note that SPA70 is an inverse agonist that decreased the basal activity of hPXR) or antagonistic mode (“Anta”, test compound in the presence of 5 μM rifampicin for inhibition of rifampicin-mediated activation of hPXR; %Activity = %Inhibition), and also in an 1-day cytotoxicity assay. Dose curves for reference compounds (SPA70, rifampicin and T0901317) were shown.