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Identification of Compounds from the Tox21 10K Compound Library which Modulate CYP3A4 Gene Expression through Activation of the Pregnane X Receptor
Citation:
Lynch, C., S. Sakamuru, R. Huang, K. Houck, S. Ferguson, AND M. Xia. Identification of Compounds from the Tox21 10K Compound Library which Modulate CYP3A4 Gene Expression through Activation of the Pregnane X Receptor. Keystone Symposia: Gene Regulation: From Mechanisms to Disease, Keystone, CO, January 26 - 30, 2020.
Impact/Purpose:
The pregnane X receptor (PXR; NR1I2) is an important nuclear receptor whose classic function is to regulate drug metabolizing enzymes (DMEs). Cytochrome P450 (CYP) 3A4, the main DME controlled partially by PXR, accounts for the metabolism of nearly 50% of all marketed drugs. Recently, there have been newly identified functions of PXR, such as playing a role in energy homeostasis, immune response, and in certain types of cancer. Due to its involvement with these important roles, alongside its drug-drug interaction effects, it is imperative to identify compounds which can modulate this essential nuclear receptor. In this study, we screened the Tox21 10,000 compound collection with a reporter gene assay to identify novel or not well-characterized hPXR agonists. From this primary screen, we identified a group of potentially active PXR agonists belonging to structural clusters as well as singletons not found in a structural cluster but still showing potential strong PXR agonist activity. Among 83 potential PXR agonists identified from the primary screening, 21 compounds were further explored by studying the induction of CYP3A4 mRNA expression in differentiated HepaRG cells, an immortalized cell line which has a metabolically competent system. The 14 compounds with promising induction of CYP3A4 in HepaRG cells were treated in HepaRG PXR-knockout cells to determine their true effect on PXR. Twelve of the 14 compounds had significantly reduced CYP3A4 mRNA expression, indicating that these compounds modulate expression of CYP3A4 mRNA through PXR activity. Further studies will need to be conducted to identify the implications that these compounds have on PXR in an in vivo condition.
Description:
The pregnane X receptor (PXR; NR1I2) is an important nuclear receptor whose classic function is to regulate drug metabolizing enzymes (DMEs). Cytochrome P450 (CYP) 3A4, the main DME controlled partially by PXR, accounts for the metabolism of nearly 50% of all marketed drugs. Recently, there have been newly identified functions of PXR, such as playing a role in energy homeostasis, immune response, and in certain types of cancer. Due to its involvement with these important roles, alongside its drug-drug interaction effects, it is imperative to identify compounds which can modulate this essential nuclear receptor. In this study, we screened the Tox21 10,000 compound collection with a reporter gene assay to identify novel or not well-characterized hPXR agonists. From this primary screen, we identified a group of potentially active PXR agonists belonging to structural clusters as well as singletons not found in a structural cluster but still showing potential strong PXR agonist activity. Among 83 potential PXR agonists identified from the primary screening, 21 compounds were further explored by studying the induction of CYP3A4 mRNA expression in differentiated HepaRG cells, an immortalized cell line which has a metabolically competent system. The 14 compounds with promising induction of CYP3A4 in HepaRG cells were treated in HepaRG PXR-knockout cells to determine their true effect on PXR. Twelve of the 14 compounds had significantly reduced CYP3A4 mRNA expression, indicating that these compounds modulate expression of CYP3A4 mRNA through PXR activity. Further studies will need to be conducted to identify the implications that these compounds have on PXR in an in vivo condition. The views expressed in this publication are those of the authors and do not necessarily represent the views or policies of the U.S. EPA.