Fig. 1.

SPA70 is a specific hPXR antagonist. a Chemical structure of SPA70. b–d Dose–response curves of SPA70 in various assays. b PXR-binding: hPXR TR-FRET-binding assay (T0901317 IC₅₀ = 96.1 nM); PXR-Anta and PXR-Ag: hPXR transactivation assay using the HepG2 stable cell line in antagonistic and agonistic modes (rifampicin EC₅₀ = 1.18 µM); CAR-Ag and CAR-IA: hCAR transactivation assay in agonistic and inverse agonistic modes (CITCO EC₅₀ = 60.8 nM in agonistic mode; PK11195 IC₅₀ = 247.2 nM in inverse agonistic mode); c FXR-Ag and FXR-Anta, GR-Ag and GR-Anta, LXRα-Ag and LXRα-Anta, LXRβ-Ag and LXRβ-Anta, PPARγ-Ag and PPARγ-Anta, RXRα-Ag and RXRα-Anta, RXRβ-Ag and RXRβ-Anta, and VDR-Ag and VDR-Anta: GeneBLAzer NR-UAS-bla HEK 293 T assays for FXR, GR, LXRα, LXRβ, PPARγ, RXRα, RXRβ, and VDR in agonistic (Ag) and antagonistic (Anta) modes; mPXR-Ag and mPXR-Anta: mPXR transactivation assay in agonistic and antagonistic modes. % Activity refers to the % inhibition or % activation as described for each assay (EC₅₀ = 77.1, 2.2, 21.3, 50.4, 5.0, 13.3, 7.6, 0.4 and 293.8 nM for GW4604/FXR, dexamethasone/GR, T0901317/LXRα, T0901317/LXRβ, rosiglitazone/PPARγ, 9-cis-retinoic acid/RXRα, 9-cis-retinoic acid/RXRβ, 1α, 25-dihydroxyvitamin D3/VDR and pregnenolone 16α-carbonitrile [PCN]/mPXR, respectively). d One- and 3-day cytotoxicity assays in HepG2, HEK293, and Hepa 1-6 cells. e SPA70 inhibits rifampicin-induced hPXR activation in a dose-responsive manner. Each data point represents the mean ± S.E.M. from quadruplicate measurements. Representative results from at least triplicated experiments are shown