The pregnane X receptor (PXR) is an important regulator of hepatic metabolism, yet mechanistic insights into the effects of pharmacological inhibition using PXR inverse agonists or antagonists on critical genes involved in both xenobiotic and endobiotic metabolism remain limited. Here, we discovered a novel PXR inverse agonist/antagonist, MI891, which binds to the ligand-binding domain of PXR. Furthermore, we computationally designed and synthesized the proteolysis-targeting chimera molecule, MI1013, based on the PXR antagonist SPA70, which degrades PXR in HepaRG hepatic cells. Using these tools, we investigated the regulation of key PXR target genes in HepaRG cells and human hepatocytes. Our findings indicate that PXR antagonism or degradation suppresses basal and rifampicin-induced expression of selected ADME genes. Moreover, the PXR antagonists and PROTAC degrader downregulate the expression of several key genes involved in gluconeogenesis, cholesterol homeostasis, bile acid synthesis, and proliferation in hepatocyte cells, suggesting their potential therapeutic applications for metabolic diseases.

• MeSH
• Hepatocytes metabolism   drug effects   MeSH
• Liver * metabolism   drug effects   MeSH
• Humans MeSH
• Drug Discovery * MeSH
• Pregnane X Receptor * antagonists & inhibitors   metabolism   MeSH
• Cell Proliferation drug effects   MeSH
• Gene Expression Regulation * drug effects   MeSH
• Structure-Activity Relationship MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Pregnane X Receptor * MeSH

The pregnane X receptor (PXR, NR1I2) is a xenobiotic-activated transcription factor with high levels of expression in the liver. It not only plays a key role in drug metabolism and elimination, but also promotes tumor growth, drug resistance, and metabolic diseases. It has been proposed as a therapeutic target for type II diabetes, metabolic syndrome, and inflammatory bowel disease, and PXR antagonists have recently been considered as a therapy for colon cancer. There are currently no PXR antagonists that can be used in a clinical setting. Nevertheless, due to the large and complex ligand-binding pocket (LBP) of the PXR, it is challenging to discover PXR antagonists at the orthosteric site. Alternative ligand binding sites of the PXR have also been proposed and are currently being studied. Recently, the AF-2 allosteric binding site of the PXR has been identified, with several compounds modulating the site discovered. Herein, we aimed to summarize our current knowledge of allosteric modulation of the PXR as well as our attempt to unlock novel allosteric sites. We describe the novel binding function 3 (BF-3) site of PXR, which is also common for other nuclear receptors. In addition, we also mention a novel allosteric site III based on in silico prediction. The identified allosteric sites of the PXR provide new insights into the development of safe and efficient allosteric modulators of the PXR receptor. We therefore propose that novel PXR allosteric sites might be promising targets for treating chronic metabolic diseases and some cancers.

• Keywords
• AF-2 site, BF-3 site, CAR, PAM-antagonist, PXR, allosteric site, pregnane X receptor,
• MeSH
• Allosteric Site MeSH
• Diabetes Mellitus, Type 2 * MeSH
• Furylfuramide MeSH
• Humans MeSH
• Ligands MeSH
• Pregnane X Receptor MeSH
• Receptors, Cytoplasmic and Nuclear MeSH
• Receptors, Steroid * metabolism   MeSH
• Xenobiotics MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Review MeSH
• Names of Substances
• Furylfuramide MeSH
• Ligands MeSH
• Pregnane X Receptor MeSH
• Receptors, Cytoplasmic and Nuclear MeSH
• Receptors, Steroid * MeSH
• Xenobiotics MeSH

Pregnane X Receptor (PXR) is a ligand-activated transcription factor which binds many structurally different molecules. The receptor is able to regulate the expression of a wide array of genes and is involved in cancer and different key physiological processes such as the metabolism of drugs/xenobiotics and endogenous compounds including lipids and carbohydrates, and inflammation. Algae, sponges, sea squirts, and other marine organisms are some of the species from which structurally new molecules have been isolated that have been subsequently identified in recent decades as ligands for PXR. The therapeutic potential of these natural compounds is promising in different areas and has recently resulted in the registration of trabectedin by the FDA as a novel antineoplastic drug. Apart from being potentially novel drugs, these compounds can also serve as models for the development of new molecules with improved activity. The aim of this review is to succinctly summarize the currently known natural molecules isolated from marine organisms with a proven ability to interact with PXR.

• Keywords
• CYP450, PXR, cancer, gene regulation, inflammation, marine origin, natural compound,
• MeSH
• Biological Products chemistry   isolation & purification   pharmacology   MeSH
• Humans MeSH
• Ligands MeSH
• Molecular Structure MeSH
• Porifera chemistry   MeSH
• Pregnane X Receptor metabolism   MeSH
• Gene Expression Regulation drug effects   MeSH
• Urochordata chemistry   MeSH
• Aquatic Organisms chemistry   MeSH
• Drug Development * MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Review MeSH
• Names of Substances
• Biological Products MeSH
• Ligands MeSH
• Pregnane X Receptor MeSH

The constitutive androstane receptor (CAR) is a nuclear receptor involved mainly in xenobiotic and endobiotic metabolism regulation. CAR is activated directly by its ligands via the ligand binding domain (LBD) or indirectly by inhibition of the epidermal growth factor (EGF) signaling. We found that leflunomide (LEF) and its main metabolite teriflunomide (TER), both used for autoimmune diseases treatment, induce the prototype CAR target gene CYP2B6 in primary human hepatocytes. As TER was discovered to be an EGF receptor antagonist, we sought to determine if TER is an indirect activator of CAR. In primary human hepatocytes and in differentiated HepaRG cells, we found that LEF and TER up-regulate CAR target genes CYP2B6 and CYP3A4 mRNAs and enzymatic activities. TER stimulated CAR+A mutant translocation into the nucleus but neither LEF nor TER activated the CAR LBD, CAR3 variant or pregnane X receptor (PXR) in gene reporter assays. Interestingly, TER significantly up-regulated CAR mRNA expression, a result which could be a consequence of both EGF receptor and ELK-1 transcription factor inhibition by TER or by TER-mediated activation of glucocorticoid receptor (GR), an upstream hormonal regulator of CAR. We can conclude that TER is a novel indirect CAR activator which through EGF inhibition and GR activation controls both detoxification and some intermediary metabolism genes.

• Keywords
• CAR, cytochrome P450, gene regulation, metabolism, nuclear receptor,
• Publication type
• Journal Article MeSH

Pregnane X receptor is a ligand-activated nuclear receptor (NR) that mainly controls inducible expression of xenobiotics handling genes including biotransformation enzymes and drug transporters. Nowadays it is clear that PXR is also involved in regulation of intermediate metabolism through trans-activation and trans-repression of genes controlling glucose, lipid, cholesterol, bile acid, and bilirubin homeostasis. In these processes PXR cross-talks with other NRs. Accumulating evidence suggests that the cross-talk is often mediated by competing for common coactivators or by disruption of coactivation and activity of other transcription factors by the ligand-activated PXR. In this respect mainly PXR-CAR and PXR-HNF4α interference have been reported and several cytochrome P450 enzymes (such as CYP7A1 and CYP8B1), phase II enzymes (SULT1E1, Gsta2, Ugt1a1), drug and endobiotic transporters (OCT1, Mrp2, Mrp3, Oatp1a, and Oatp4) as well as intermediate metabolism enzymes (PEPCK1 and G6Pase) have been shown as down-regulated genes after PXR activation. In this review, I summarize our current knowledge of PXR-mediated repression and coactivation interference in PXR-controlled gene expression regulation.

• Keywords
• PXR, cross-talk, gene regulation, metabolism, nuclear receptor,
• Publication type
• Journal Article MeSH
• Review MeSH