Identification of approved drugs as potent inhibitors of pregnane X receptor activation with differential receptor interaction profiles
Activation of pregnane X receptor (PXR) results in the induction of first-pass metabolism and drug efflux. Hereby, PXR may cause adverse drug reactions or therapeutic failure of drugs. PXR inhibition is thus an attractive option to minimise adverse effects or to improve therapeutic efficiencies; however, only a limited number of antagonists have been identified so far. We performed a cell-based high-throughput screen to identify PXR antagonists, using a library of approved and investigational drugs. Two approved drugs, pimecrolimus and pazopanib, emerged as novel potent antagonists of PXR activation, with IC50 values of 1.2 and 4.1 µM, respectively. We further characterised these with respect to receptor specificity, assembly of the PXR ligand-binding domain (LBD) and interactions with co-factors. In vitro and in silico assays were carried out to identify the site(s) of interaction with the PXR LBD. Primary human hepatocytes were used to investigate antagonism of the induction of endogenous PXR target genes. Pimecrolimus and pazopanib did not affect the transcriptional activity of other nuclear receptors. Both induced the release of co-repressor from PXR and likewise interfered with agonist-induced recruitment of co-activator. Cumulative evidence from cellular and in vitro assays, as well as molecular docking, suggested additional or exclusive binding outside the PXR ligand-binding pocket for both. The compounds differentially antagonised the induction of PXR-regulated genes by rifampicin in primary human hepatocytes. In conclusion, we here have identified two approved drugs as novel potent PXR inhibitors with differential receptor interaction profiles and gene selectivity in primary human hepatocytes.
KeywordsPregnane X Receptor Antagonist High-throughput screening Pimecrolimus Pazopanib
We appreciate the expert technical assistance of K. Abuazi-Rincones. The non-profit foundation Human Tissue and Cell Research (Regensburg, Germany), which holds human tissue on trust, making it broadly available for research on an ethical and legal basis, kindly provided liver tissue for the preparation of human primary hepatocytes. Primary human hepatocytes were kindly prepared by M. Demmel (Hepacult GmbH, München, Germany). This work was supported by the São Paulo state funding agency FAPESP (Grants 2014/03644-9, 2014/27313-1) and CNPq-DAAD Science Without Borders programme (T.K.), by the Robert Bosch Foundation, Stuttgart, Germany (O.B., M.S.), the Horizon 2020-PHC-2015 Grant U-PGx 668353 (M.S.) and by the Interfaculty Center for Pharmacogenomics and Pharma Research of the University of Tübingen, Germany (O.B., J.J.).
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards.
Human and animal rights statement
This article does not contain any studies with animals performed by any of the authors.
Informed consent was obtained from all individual participants included in the study.
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