FKK5 and FKK6 activate PXR.Figure 1(A) Histogram (mean, 95 %CI) of fold induction of PXR activity reporter assay (luc, luciferase) in LS180 cells transiently transfected with wild-type PXR and p3A4-luc reporter plasmids. Chemical structures of FKK5, FKK6 and FKK999 compounds are overlaid. The bar graph(s) depicts one representative experiment of a series of experiments (n > 3) performed in four consecutive passages of cells. *p < 0.05, one-way ANOVA with Dunnett's post hoc test. *significant over vehicle (DMSO) control. (B), same as (A), in HepG2 cells stably expressing pCYP1A1 luciferase plasmid (AhR reporter). Chemical structures of FKK5, FKK6 and FKK999 compounds are overlaid. Indole is colored blue. The bar graph(s) depicts one representative experiment of a series of experiments (n > 3) performed in four consecutive passages of cells. *p < 0.05, one-way ANOVA with Dunnett's post hoc test. *significant over vehicle (DMSO) control. C, Histogram (mean, 95 %CI) of fold mRNA expression, CYP1A1 (top panel), CYP3A4 (middle panel) and MDR1 (bottom panel) in LS180 cells with or without (mock) transfected PXR plasmid, HepaRG hepatic progenitor cells (PXR-knockout, PXR-KO; AhR-knockout, AhR-KO; parental control 5F clone) and primary human hepatocytes (HEP) from four donors is shown. The bar graph represents one experiment of a series of experiments (n > 3) performed in four consecutive passages of LS180 cells; n = 2 independent experiments with one well/compound and RT-PCR performed in triplicate for each HepaRG genotype; for each donor hepatocyte, n = 1 well/compound and RT-PCR performed in triplicate. *, #p < 0.05, two-way ANOVA with Tukey's post hoc test. *significant over vehicle control. #significant over the same treatment in corresponding mock transfected or knock-out cells. D, Chromatin Immunoprecipitation (ChIP) assay in LS174T cells. Top panel, PCR products cells exposed to vehicle or FKK6 and run on a 2% agarose gel. DNA 100 base pair marker; Vehicle,10% DMSO; FKK6 (10 μM); 1/10 Input - 0.2 million cells before IP; IgG - IP with polyclonal rabbit IgG; PXR - IP with PXR antibody. Bottom panel, quantitative PCR from the ChIP assay for compounds tested with the gene specific PCR amplicon normalized to GAPDH (fold expression). Dash line, 2-fold expression. The data is one representative experiment of two independent experiments (each n = 3 biological replicates, n = 4 technical replicates). Mean fold expression is expressed above each histogram (mean + SD). E, PXR TR-FRET assay. TR-FRET ratio 520/495 nm are plotted against concentration of compound(s). Half-maximal inhibitory concentrations IC50 were obtained from interpolated standard curves (sigmoidal, 4PL, variable slope); error bars show standard deviation of n = 2 independent experiments each with four technical replicates. F, Microcalorimetric titrations of PXR ligand binding domain (LBD) with FKK5 and FKK6. A single-site binding model was used for fitting the data. The upper panel shows the output signal, dQ/dt, as a function of time. The middle panel shows the integrated heats as a function of the ligand/PXR molar ratio in the cell. The solid line represents the best non-linear least-squares fit of the data. The lower panel shows respective thermodynamic signatures of binding to the PXR ligand binding domain.