Computational discovery of novel low micromolar human pregnane X receptor antagonists

Sean Ekins, Vladyslav Kholodovych, Ni Ai, Michael Sinz, Joseph Gal, Lajos Gera, William J. Welsh, Kenneth Bachmann, Sridhar Mani

Research output: Contribution to journalArticlepeer-review

61 Scopus citations


Very few antagonists have been identified for the human pregnane X receptor (PXR). These molecules may be of use for modulating the effects of therapeutic drugs, which are potent agonists for this receptor (e.g., some anticancer compounds and macrolide antibiotics), with subsequent effects on transcriptional regulation of xenobiotic metabolism and transporter genes. A recent novel pharmacophore for PXR antagonists was developed using three azoles and consisted of two hydrogen bond acceptor regions and two hydrophobic features. This pharmacophore also suggested an overall small binding site that was identified on the outer surface of the receptor at the AF-2 site and validated by docking studies. Using computational approaches to search libraries of known drugs or commercially available molecules is preferred over random screening. We have now described several new smaller antagonists of PXR discovered with the antagonist pharmacophore with in vitro activity in the low micromolar range [S-p-tolyl 3′,5-dimethyl-3,5′-biisoxazole-4′-carbothioate (SPB03255) (IC50, 6.3 μM) and 4-(3-chlorophenyl)-5-(2,4-dichlorobenzylthio)- 4H-1,2,4-triazol-3-ol (SPB00574) (IC50, 24.8 μM)]. We have also used our computational pharmacophore and docking tools to suggest that most of the known PXR antagonists, such as coumestrol and sulforaphane, could also interact on the outer surface of PXR at the AF-2 domain. The involvement of this domain was also suggested by further site-directed mutagenesis work. We have additionally described an FDA approved prodrug, leflunomide (IC50, 6.8 μM), that seems to be a PXR antagonist in vitro. These observations are important for predicting whether further molecules may interact with PXR as antagonists in vivo with potential therapeutic applications.

Original languageEnglish (US)
Pages (from-to)662-672
Number of pages11
JournalMolecular Pharmacology
Issue number3
StatePublished - Sep 2008

ASJC Scopus subject areas

  • Molecular Medicine
  • Pharmacology


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