Fig. 3.

Relative PXR reporter activity and firefly or Renilla luminescence with a PXR inhibitor exhibiting low cytotoxicity. Idealized model (upper panels): a ① Proliferation is neither affected by the activator alone (e.g., rifampicin) nor by the proposed PXR inhibitor being added to the activator; ② PXR ligand-mediated enhancement of relative PXR activity (e.g. threefold compared to untreated control, dashed line) is concentration-dependently abolished by proposed PXR inhibitor being added to the activator. Eventually, relative PXR activity returns to the baseline level. b ① Strong PXR activator-mediated increase of the firefly luminescence (white circle), but unchanged Renilla signal (white square); ② Addition of an inhibitor leads to a sigmoidal decrease of the firefly luminescence; ③ Renilla luminescence remains constant. Experimental data (lower panels): c Impact of triptolide on cell proliferation and relative PXR activity when added to 5 µM rifampicin (24 h drug exposure). d Firefly and Renilla luminescence normalized to untreated control. Data shown is the mean ± SEM of three independent biological replicates with n = 4 (reporter data) or n = 8 (proliferation data) replicates for each concentration/replicate. Impact of drug treatments on firefly or Renilla values was evaluated by ANOVA with non-parametric Kruskal–Wallis test and Dunn’s test compared to untreated control. *P < 0.05, **P < 0.01, ***P < 0.001