The Time to Move Cytochrome P450 Induction into Mainstream Pharmacology Is Long Overdue

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122

ABSTRACT:Induction of cytochrome P450 (P450) activity in the clinic can result in therapeutic failure such as tissue rejection in transplant patients or unwanted pregnancy, among others. CYP3A4 is by far the most abundant isoform and is responsible for the majority of P450-related metabolism of all marketed drugs. However, it is of importance to understand the significance of induction mediated through other P450 enzymes. The objective of this investigation was to evaluate several known inducers in vitro using cryopreserved human hepatocytes, with the aim of assessing the relevant induction of CYP3A4, CYP2B6, CYP2C9, CYP2C19, and CYP3A5, based on mRNA expression. CYP3A4 induction was also assessed based on enzymatic activity in three different lots to investigate whether mRNA expression data have any advantages over enzymatic activity. In general, the mRNA fold-induction data results were more sensitive compared with activity data, and more informative in cases in which the drug is also a P450 inhibitor. The induction of transcription of other drug-metabolizing enzymes including CYP2B6 and CYP2C enzymes occurred every time that CYP3A4 mRNA levels increased, but to a lesser extent, indicating that measurement of CYP3A4 mRNA is a sensitive marker for the induction of these other enzymes. This was the case even for enzymes and inducers that are known to also act via the constitutive androstane receptor pathway. Finally, the utility of in vitro induction measurements in the identification of clinically meaningful inducers was tested by using two simple binary classification approaches: 1) fold-induction versus vehicle control and 2) induction response relative to rifampin. The best classification was observed when the cutoff criteria based on fold induction relative to the vehicle control, using mRNA data are used.

Section: Discussionmentioning

confidence: 99%

Cytochrome P450 3A4 mRNA Is a More Reliable Marker than CYP3A4 Activity for Detecting Pregnane X Receptor-Activated Induction of Drug-Metabolizing Enzymes

Fahmi¹,

Kish²,

Boldt³

et al. 2010

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122

“…), the character of the receptor agonism (full or partial agonist), and the capability of the putative inducer to enter the cell. These have been recently discussed in the context of characterizing induction in a manner similar to other pharmacological responses (Smith et al, 2007). Nevertheless, combining in vitro induction data (potency, degree of agonism) with other parameters (in vivo pharmacokinetics of the inducer, target tissue penetration, free fraction, etc.)…”

Section: Resultsmentioning

confidence: 99%

Prediction of Drug-Drug Interactions From in Vitro Induction Data

Fahmi

Boldt²,

Kish³

et al. 2008

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ABSTRACT:Cytochrome P450 induction-mediated drug-drug interaction (DDI) is one of the major concerns in clinical practice and for the pharmaceutical industry. Previously, a novel approach [the relative induction score (RIS)] was developed using the Fa2N-4 immortalized human hepatocyte line and proposed as a tool for predicting magnitude of clinical DDIs caused by induction of CYP3A. The approach is based on combining in vitro induction parameters (EC 50 and E max ) with the efficacious free plasma concentrations to calculate a relative induction score, which is correlated to the magnitude of clinical DDI for midazolam or ethinyl estradiol. To expand the applicability of the RIS model, we have measured induction caused by ten drugs in two different lots of human cryopreserved hepatocytes and correlated the data to clinical DDIs using the RIS. The results demonstrated that, as with Fa2N-4 hepatocytes, sigmoidal relationships can be derived between RIS and magnitude of induction of midazolam and ethinyl estradiol clearance in cryopreserved human hepatocytes. This study demonstrates the general applicability of the relative induction score approach using the human cryopreserved hepatocyte model to predict clinical DDI.The induction of cytochrome CYP3A4 can have important clinical significance. CYP3A4 gene expression is inducible by numerous xenobiotics, resulting in altered drug metabolism and drug-drug interactions in addition to enhanced metabolism of endogenous substrates including cortisol. CYP3A4 is predominantly expressed in the liver and the small intestine and is known to metabolize the majority of drugs whose biotransformation is known (Guengerich, 1996;Rendic and Di Carlo, 1997). Induction of CYP3A activity in the clinic can result in therapeutic failure such as tissue rejection in transplant patients caused by increased clearance of cyclosporine or unwanted pregnancy caused by increased clearance of oral contraceptive agents, among others (Mannel, 2004;Huwyler et al., 2006). Therefore, different models to study CYP3A4 induction have been developed to allow the selection and development of safer compounds and aid in the design of more efficient clinical trials.During the past several years, important advances have been made in our understanding of the mechanisms that regulate the expression of genes that determine drug clearance, including drug-metabolizing enzymes and drug transporters. Nuclear receptors, such as the pregnane X receptor (PXR) and constitutive androstane receptor (CAR), have been recognized as key mediators of drug-induced changes in the expression of CYP2B, CYP2C, and CYP3A, as well as of phase II enzymes and transporters. Moreover, it has been documented that hCAR and hPXR are both responsible for coordinating the regulation of a large number of drug metabolizing enzymes and drug transporter genes (Faucette et al., 2006;Konno et al., 2008).Considerable effort has been expended in an attempt to predict the magnitude of in vivo metabolic drug-drug interactions using in vitro data. A number...

“…), and an idea about actual clinical exposure are all needed to determine whether a compound will probably be an inducer of P450 enzymes in humans in vivo (Smith et al, 2007). The number of different published models to predict the clinical outcome of P450 induction are limited; however, the numbers of reports, particularly of modeling CYP3A induction in vivo, have increased very recently.…”

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confidence: 99%

In Vitro and in Vivo Induction of Cytochrome P450: A Survey of the Current Practices and Recommendations: A Pharmaceutical Research and Manufacturers of America Perspective

Chu¹,

Einolf²,

Evers³

et al. 2009

152

122

ABSTRACT:Cytochrome P450 (P450) induction is one of the factors that can affect the pharmacokinetics of a drug molecule upon multiple dosing, and it can result in pharmacokinetic drug-drug interactions with coadministered drugs causing potential therapeutic failures. In recent years, various in vitro assays have been developed and used routinely to assess the potential for drug-drug interactions due to P450 induction. There is a desire from the pharmaceutical industry and regulatory agencies to harmonize assay methodologies, data interpretation, and the design of clinical drug-drug interaction studies. In this article, a team of 10 scientists from nine Pharmaceutical Research and Manufacturers of America (PhRMA) member companies conducted an anonymous survey among PhRMA companies to query current practices with regards to the conduct of in vitro induction assays, data interpretation, and clinical induction study practices. The results of the survey are presented in this article, along with reviews of current methodologies of in vitro assays and in vivo studies, including modeling efforts in this area. A consensus recommendation regarding common practices for the conduct of P450 induction studies is included.The convergence of recent advances in molecular biology and genomics, higher throughput chemical synthesis, and automated highthroughput in vitro enzyme and cell-based assays to assess biological activity has led to shorter lead identification and optimization times in drug research. However, these breakthroughs have not yet translated into success in drug development. Surveys suggest that in the last several years, the number of New Drug Applications submitted to regulatory agencies has declined and that the poor success rate during drug development is to some extent due to late-stage failures. It is important that novel and innovative approaches are used for assessing the risks and benefits of new molecular entities (NMEs) early in the research and development life cycle to minimize late-stage attrition.Based on a survey conducted in 2004, the major factors for compound attrition during clinical development are lack of efficacy, toxicity, and safety, and suboptimal pharmacokinetics and/or bioavailability, with the remaining failures due to financial and/or commercial reasons (Kola and Landis, 2004). In that survey, one notable observation was the reduction of compound attrition due to pharmacokinetic and/or bioavailability issues from pre-1991 to the period be- ABBREVIATIONS: NME, new molecular entity; P450, cytochrome P450; DDI, drug-drug interaction; RIF, rifampicin; PhRMA, Pharmaceutical Research and Manufacturers of America; AhR, aryl hydrocarbon receptor; CAR, constitutive androstane receptor; PXR, pregnane X receptor; UGT, uridine diphosphate glucuronosyl transferase; FXR, farnesyl X receptor; PPAR, peroxisome proliferator-activated receptor; VDR, vitamin D receptor; Nrf2, nuclear factor erythroid 2-related factor 2; LBD, ligand binding domain; hPXR, human PXR; SR12813, tetra-ethyl 2-(3,5-di-tertbutyl...