Fig. 2.

Relative PXR reporter activity and firefly or Renilla luminescence with an PXR activator exhibiting high cytotoxicity. Idealized model (upper panels): a ① Proliferation is decreased concentration-dependently, ② Relative PXR activity seems well enhanced by the drug of interest, reaching a certain maximum effect. b ① Initial sigmoidal increase of the firefly luminescence due to reporter activation. ② Renilla luminescence remains initially constant. ③ However, the parallel decrease of the firefly and Renilla luminescence maintain the impression of a relative PXR activity plateau. Experimental data (lower panels): c Dovitinib effect on cell proliferation and relative PXR activity after 24 h drug exposure, normalized to untreated control. d Firefly and Renilla luminescence normalized to untreated control. Data shown are the mean ± SEM of three independent biological replicates with n = 4 (reporter data) or n = 8 (proliferation data) replicates for each concentration/replicate. Whenever data could not be fitted to a sigmoidal Emax model (four parameter-logistic equation; variable slope), data points are simply connected (here: dovitinib effect on firefly luminescence). 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