Pharmacophore models of PXR activators. Pharmacophore models of PXR activators of (A) human PXR, (B) zebrafish PXR, (C) mouse PXR, (D) rat PXR, (E) rabbit PXR, and (F) chicken PXR. The pharmacophores were generated from the same 16 molecules using Catalyst. The molecules mapped to each pharmacophore are TCDD (green) and 5β-pregnane-3,20-dione (grey). It should be noted that TCDD is inactive in rabbit PXR and only maps to the hydrophobic features. The pharmacophore features are hydrophobic (cyan), hydrogen bond acceptor and vector (green), and excluded volume (grey).