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      Insights into CYP2B6-mediated drug–drug interactions

      , , *

      Acta Pharmaceutica Sinica. B

      Elsevier

      CAR, constitutive androstane receptor, C/EBP, CCAAT/enhancer-binding protein, CHOP, cyclophosphamide–doxorubicin–vincristine–prednisone, CITCO, (6-(4-chlorophenyl)imidazo[2,1-b][1,3]thiazole-5-carbaldehyde-O-(3,4-dichlorobenzyl)oxime), COUP-TF, chicken ovalbumin upstream promoter-transcription factor, CPA, cyclophosphamide, 4-OH-CPA, 4-hydroxycyclophosphamide, CYP, cytochrome P450, DDI, drug–drug interaction, DEX, dexamethasone, EFV, efavirenz, E2, estradiol, ERE, estrogen responsive element, GR, glucocorticoid receptor, GRE, glucocorticoid responsive element, HAART, highly active antiretroviral therapy, HNF, hepatocyte nuclear factor, IFA, Ifosfamide, MAOI, monoamine oxidase inhibitor, NNRTI, non-nucleotide reverse-transcriptase inhibitor, NR1/2, nuclear receptor binding site 1/2, NVP, nevirapine, PB, phenobarbital, PBREM, phenobarbital-responsive enhancer module, PCN, pregnenolone 16 alpha-carbonitrile, PXR, pregnane X receptor, RIF, rifampin, SNP, single nucleotide polymorphism, TCPOBOP, 1,4-bis[3,5-dichloropyridyloxy]benzene, UGT, UDP-glucuronosyl transferase, CYP2B6, CAR, PXR, Polymorphism, Drug–drug interaction, Cyclophosphamide, Efavirenz

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          Abstract

          Mounting evidence demonstrates that CYP2B6 plays a much larger role in human drug metabolism than was previously believed. The discovery of multiple important substrates of CYP2B6 as well as polymorphic differences has sparked increasing interest in the genetic and xenobiotic factors contributing to the expression and function of the enzyme. The expression of CYP2B6 is regulated primarily by the xenobiotic receptors constitutive androstane receptor (CAR) and pregnane X receptor (PXR) in the liver. In addition to CYP2B6, these receptors also mediate the inductive expression of CYP3A4, and a number of important phase II enzymes and drug transporters. CYP2B6 has been demonstrated to play a role in the metabolism of 2%–10% of clinically used drugs including widely used antineoplastic agents cyclophosphamide and ifosfamide, anesthetics propofol and ketamine, synthetic opioids pethidine and methadone, and the antiretrovirals nevirapine and efavirenz, among others. Significant inter-individual variability in the expression and function of the human CYP2B6 gene exists and can result in altered clinical outcomes in patients receiving treatment with CYP2B6-substrate drugs. These variances arise from a number of sources including genetic polymorphism, and xenobiotic intervention. In this review, we will provide an overview of the key players in CYP2B6 expression and function and highlight recent advances made in assessing clinical ramifications of important CYP2B6-mediated drug–drug interactions.

          Graphical abstract

          CYP2B6 is a highly inducible and polymorphic enzyme which plays a significant role in human drug metabolism. Variations in the expression and function of CYP2B6 significantly alter the metabolism and pharmacokinetics of many drugs. These alterations may result in significant drug–drug interactions which may lead to improved therapy or toxicity.

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          Most cited references 157

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          Nuclear receptor response elements mediate induction of intestinal MDR1 by rifampin.

          Intestinal P-glycoprotein, which is encoded by the MDR1 gene, plays an important role in the absorption and presystemic elimination of many xenobiotics. Hence, an understanding of the factors regulating its expression and function is of substantial interest. In addition to genetic factors, exposure to drugs such as rifampin can profoundly affect its expression. So far, the mechanisms by which rifampin induces MDR1 expression are poorly understood. Recent studies demonstrate that the nuclear receptor PXR (pregnane X receptor) is involved in xenobiotic induction of CYP3A4. Because CYP3A4 and MDR1 are often co-induced, we investigated whether a similar mechanism is also involved in MDR1 induction. The human colon carcinoma cell line LS174T was used as an intestinal model to study induction because in these cells the endogenous MDR1 gene is highly inducible by rifampin. The 5'-upstream region of human MDR1 was examined for the presence of potential PXR response elements. Several binding sites were identified that form a complex regulatory cluster at about -8 kilobase pairs. Only one DR4 motif within this cluster is necessary for induction by rifampin. We conclude that induction of MDR1 is mediated by a DR4 motif in the upstream enhancer at about -8 kilobase pairs, to which PXR binds.
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            Comparison of cytochrome P450 (CYP) genes from the mouse and human genomes, including nomenclature recommendations for genes, pseudogenes and alternative-splice variants.

            Completion of both the mouse and human genome sequences in the private and public sectors has prompted comparison between the two species at multiple levels. This review summarizes the cytochrome P450 (CYP) gene superfamily. For the first time, we have the ability to compare complete sets of CYP genes from two mammals. Use of the mouse as a model mammal, and as a surrogate for human biology, assumes reasonable similarity between the two. It is therefore of interest to catalog the genetic similarities and differences, and to clarify the limits of extrapolation from mouse to human. Data-mining methods have been used to find all the mouse and human CYP sequences; this includes 102 putatively functional genes and 88 pseudogenes in the mouse, and 57 putatively functional genes and 58 pseudogenes in the human. Comparison is made between all these genes, especially the seven main CYP gene clusters. The seven CYP clusters are greatly expanded in the mouse with 72 functional genes versus only 27 in the human, while many pseudogenes are present; presumably this phenomenon will be seen in many other gene superfamily clusters. Complete identification of all pseudogene sequences is likely to be clinically important, because some of these highly similar exons can interfere with PCR-based genotyping assays. A naming procedure for each of four categories of CYP pseudogenes is proposed, and we encourage various gene nomenclature committees to consider seriously the adoption and application of this pseudogene nomenclature system.
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              Drugs behave as substrates, inhibitors and inducers of human cytochrome P450 3A4.

               Feng Zhou (2008)
              Human cytochrome P450 (CYP) 3A4 is the most abundant hepatic and intestinal phase I enzyme that metabolizes approximately 50% marketed drugs. The crystal structure of bound and unbound CYP3A4 has been recently constructed, and a small active site and a peripheral binding site are identified. A recent study indicates that CYP3A4 undergoes dramatic conformational changes upon binding to ketoconazole or erythromycin with a differential but substantial (>80%) increase in the active site volume, providing a structural basis for ligand promiscuity of CYP3A4. A number of important drugs have been identified as substrates, inducers and/or inhibitors of CYP3A4. The ability of drugs to act as inducers, inhibitors, or substrates for CYP3A is predictive of whether concurrent administration of these compounds with a known CYP3A substrate might lead to altered drug disposition, efficacy or toxicity. The substrates of CYP3A4 considerably overlap with those of P-glycoprotein (P-gp). To date, the identified clinically important CYP3A4 inhibitors mainly include macrolide antibiotics (e.g., clarithromycin, and erythromycin), anti-HIV agents (e.g., ritonavir and delavirdine), antidepressants (e.g. fluoxetine and fluvoxamine), calcium channel blockers (e.g. verapamil and diltiazem), steroids and their modulators (e.g., gestodene and mifepristone), and several herbal and dietary components. Many of these drugs are also mechanism-based inhibitors of CYP3A4, which involves formation of reactive metabolites, binding to CYP3A4 and irreversible enzyme inactivation. A small number of drugs such as rifampin, phenytoin and ritonavir are identified as inducers of CYP3A4. The orphan nuclear receptor, pregnane X receptor (PXR), have been found to play a critical role in the induction of CYP3A4. The inhibition or induction of CYP3A4 by drugs often causes unfavorable and long-lasting drug-drug interactions and probably fatal toxicity, depending on many factors associated with the enzyme, drugs and the patients. The study of interactions of newly synthesized compounds with CYP3A4 has been incorporated into drug development and detection of possible CYP3A4 inhibitors and inducers during the early stages of drug development is critical in preventing potential drug-drug interactions and side effects. Clinicians are encouraged to have a sound knowledge on drugs that behave as substrates, inhibitors or inducers of CYP3A4, and take proper cautions and close monitoring for potential drug interactions when using drugs that are CYP3A4 inhibitors or inducers.
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                Author and article information

                Contributors
                Journal
                Acta Pharm Sin B
                Acta Pharm Sin B
                Acta Pharmaceutica Sinica. B
                Elsevier
                2211-3835
                2211-3843
                09 August 2016
                September 2016
                09 August 2016
                : 6
                : 5
                : 413-425
                Affiliations
                Department of Pharmaceutical Sciences, University of Maryland School of Pharmacy, Baltimore, MD 21201, USA
                Author notes
                [* ]Corresponding author at: Department of Pharmaceutical Sciences, University of Maryland School of Pharmacy, 20 Penn Street, Baltimore, MD 21201, USA. Tel.: +1 410 706 1280; fax: +1 410 706 5017. hwang@ 123456rx.umaryland.edu
                Article
                S2211-3835(16)30253-2
                10.1016/j.apsb.2016.07.016
                5045548
                © 2016 Chinese Pharmaceutical Association and Institute of Materia Medica, Chinese Academy of Medical Sciences. Production and hosting by Elsevier B.V.

                This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

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