Broad Application of CYP3A4 Liquid Chromatography-Mass Spectrometry Protein Quantification in Hepatocyte Cytochrome P450 Induction Assays Identifies Nonuniformity in mRNA and Protein Induction Responses

Screening for cytochrome P450 (CYP) induction potential is routine in drug development. Induction results in a net increase in CYP protein and is assessed typically by measuring indirect endpoints, i.e., enzyme activity and mRNA in vitro. Recent methodological advancements have made CYP protein quantification by liquid chromatography-mass spectrometry in vitro induction studies more accessible and amenable to routine testing. In this study, we evaluated CYP3A4 concentration dependence of induction response for 11 compounds (rifampin, rifabutin, carbamazepine, efavirenz, nitrendipine, flumazenil, pioglitazone, rosiglitazone, troglitazone, pazopanib, and ticagrelor) in plated hepatocytes from two or three donors incorporating in the assessment all three endpoints. In addition, the time-dependence of the induction was examined over 1, 2, or 3 days of treatment. For most compounds, mRNA, enzyme activity, and protein endpoints exhibited similarity in induction responses. Pazopanib and ticagrelor were notable exceptions as neither protein nor enzyme activity were induced despite mRNA induction of a magnitude similar to efavirenz, pioglitazone, or rosiglitazone, which clearly induced in all three endpoints. Static modeling of clinical induction responses supported a role for protein as a predictive endpoint. These data highlight the value of including CYP protein quantification as an induction assay endpoint to provide a more comprehensive assessment of induction liability. SIGNIFICANCE STATEMENT: Direct, liquid chromatography-mass spectrometry (LC-MS)-based quantification of cytochrome P450 (CYP) protein is a desirable induction assay endpoint; however such application has been limited due to inefficient workflows. Here, we incorporate recent advancements in protein quantitation methods to efficiently quantify CYP3A4 protein in in vitro induction assays with 11 compounds in up to 3 donors. The data indicate induction responses from mRNA do not always align with those of protein suggesting assessment of induction liability is more complex than thought previously.

Enrichment-free High-throughput Liquid Chromatography-Multiple-Reaction Monitoring Quantification of Cytochrome P450 Proteins in Plated Human Hepatocytes Direct from 96-Well Plates Enables Routine Protein Induction Measurements

Despite the availability of liquid chromatography (LC)-mass spectrometry (MS) methods for quantifying cytochrome P450 (P450) proteins, incorporation of P450 protein quantification into induction study workflows has not been widely adopted. To more readily enable P450 protein quantification in induction study workflows, DMPK research groups need a simple, robust, cost-effective, high-throughput method compatible with 96-well-plated human hepatocyte formats. Here, we provide such a methodology. Our method bypasses both microsomal enrichment and antibody-based enrichment to go directly from the plate to LC-MS/MS analysis. We use this "plate-to-peaks" approach for quantifying CYP3A4, CYP2B6, and CYP1A2, the major inducible hepatic P450s representative of pregnane X receptor-, constitutive androstane receptor-, and aryl hydrocarbon receptor-mediated induction, respectively. We leveraged our induction study-aligned assay format to assess induction across mRNA, protein, and enzyme activity using known induction control compounds. As expected, results from the three methods using model inducers were broadly concordant, but the magnitude of the induction response differed. Induction of CYP3A4 using 10 µM rifampicin was 12-fold for RNA, eightfold for protein, and threefold for activity; for CYP1A2 with 50 µM omeprazole, induction was 30-fold for RNA, 13-fold for protein, and 17-fold for activity; for CYP2B6 with 50 µM phenytoin, induction was 23-fold for RNA, twofold for protein, and fivefold for activity. Most importantly, we anticipate the relative ease of this method will enable researchers to routinely adopt P450 protein quantification as part of nonclinical evaluation of P450 induction. SIGNIFICANCE STATEMENT: Current methodologies for quantifying P450 proteins by liquid chromatography (LC)-tandem mass spectrometry are either cumbersome, too costly, or both to be widely adopted into induction study workflows by the ADME research community. We present a simplified LC-MS/MS methodology for quantifying P450 proteins directly from human hepatocytes, without any form of enrichment, in 96-well induction assay plate format that should be readily adoptable by any ADME laboratory with LC-multiple-reaction monitoring capabilities.

UDP-glucuronosyltransferases (UGTs) and their related metabolic cross-talk with internal homeostasis: A systematic review of UGT isoforms for precision medicine

UDP-glucuronosyltransferases (UGTs) are the primary phase II enzymes catalyzing the conjugation of glucuronic acid to the xenobiotics with polar groups for facilitating their clearance. The UGTs belong to a superfamily that consists of diverse isoforms possessing distinct but overlapping metabolic activity. The abnormality or deficiency of UGTs in vivo is highly associated with some diseases, efficacy and toxicity of drugs, and precisely therapeutic personality. Despite the great effects and fruitful results achieved, to date, the expression and functions of individual UGTs have not been well clarified, the inconsistency of UGTs is often observed in human and experimental animals, and the complex regulation factors affecting UGTs have not been systematically summarized. This article gives an overview of updated reports on UGTs involving the various regulatory factors in terms of the genetic, environmental, pathological, and physiological effects on the functioning of individual UGTs, in turn, the dysfunction of UGTs induced disease risk and endo- or xenobiotic metabolism-related toxicity. The complex cross-talk effect of UGTs with internal homeostasis is systematically summarized and discussed in detail, which would be of great importance for personalized precision medicine.