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Published on: November 15, 2013
Target Hopping from Protein Kinases to PXR: Identification of Small-Molecule Protein Kinase Inhibitors as Selective
Enni-Kaisa Mustonen1, Tatu Pantsar2,3, Azam Rashidian4
1Dr. Margarete Fischer-Bosch-Institute of Clinical Pharmacology, Stuttgart, and University of Tuebingen, 72074 Tuebingen, Germany.
Abstract:
Small-molecule protein kinase inhibitors are used for the treatment of cancer, but off-target effects hinder their clinical use. Especially off-target activation of the pregnane X receptor (PXR) has to be considered, as it not only governs drug metabolism and elimination, but also can promote tumor growth and cancer drug resistance. Consequently, PXR antagonism has been proposed for improving cancer drug therapy. Here we aimed to identify small-molecule kinase inhibitors of the Tübingen Kinase Inhibitor Collection (TüKIC) compound library that would act also as PXR antagonists. By a combination of in silico screen and confirmatory cellular reporter gene assays, we identified four novel PXR antagonists and a structurally related agonist with a common phenylaminobenzosuberone scaffold. Further characterization using biochemical ligand binding and cellular protein interaction assays classified the novel compounds as mixed competitive/noncompetitive, passive antagonists, which bind PXR directly and disrupt its interaction with coregulatory proteins. Expression analysis of prototypical PXR target genes ABCB1 and CYP3A4 in LS174T colorectal cancer cells and HepaRG hepatocytes revealed novel antagonists as selective receptor modulators, which showed gene- and tissue-specific effects. These results demonstrate the possibility of dual PXR and protein kinase inhibitors, which might represent added value in cancer therapy.
Insights
Researchers identified novel dual-acting compounds that inhibit protein kinases and pregnane X receptor (PXR) activity. These PXR antagonists may improve cancer drug efficacy by reducing tumor growth and resistance.
Area of Science:
- Pharmacology
- Oncology
- Molecular Biology
Background:
- Small-molecule kinase inhibitors are crucial cancer therapeutics but face limitations due to off-target effects.
- Pregnane X receptor (PXR) activation by kinase inhibitors can negatively impact drug metabolism, elimination, tumor growth, and cancer drug resistance.
- PXR antagonism is a potential strategy to enhance cancer drug therapy.
Purpose of the Study:
- To identify small-molecule kinase inhibitors with dual activity as PXR antagonists from the Tübingen Kinase Inhibitor Collection (TüKIC) library.
- To characterize the mechanism of action and selectivity of identified compounds on PXR.
- To evaluate the potential of dual inhibitors in cancer therapy.
Main Methods:
- In silico screening of the TüKIC compound library.
- Confirmatory cellular reporter gene assays to identify PXR antagonists and agonists.
- Biochemical ligand binding and cellular protein interaction assays for mechanistic characterization.
- Gene expression analysis of PXR target genes (ABCB1, CYP3A4) in cancer cells and hepatocytes.
Main Results:
- Four novel PXR antagonists and one agonist with a phenylaminobenzosuberone scaffold were identified.
- Compounds were classified as mixed competitive/noncompetitive, passive antagonists that directly bind PXR and disrupt coregulator interactions.
- Novel antagonists demonstrated selective PXR modulation with gene- and tissue-specific effects on ABCB1 and CYP3A4 expression.
Conclusions:
- Dual PXR and protein kinase inhibitors can be developed, offering potential advantages in cancer treatment.
- Identified compounds represent promising candidates for improving cancer drug therapy by targeting both kinase activity and PXR-mediated pathways.
- Selective modulation of PXR by these novel antagonists warrants further investigation for therapeutic applications in oncology.
