Bioactivation of lumiracoxib in human liver microsomes: Formation of GSH‐ and amino adducts through acyl glucuronide

Detection and identification of imperatorin metabolites in rat, dog, monkey, and human liver microsomes by ultra-high-performance liquid chromatography combined with high-resolution mass spectrometry and Compound Discoverer software

Imperatorin, a furanocoumarin that widely exists in many umbelliferous herbs, has been demonstrated to have a variety of pharmacological effects, including anti-inflammatory, antiosteoporosis, and antitumor activities. The purpose of this study was to investigate the metabolism of imperatorin using liver microsomes. The metabolites were generated by individually incubating imperatorin with rat, dog, monkey, and human liver microsomes. To trap the reactive metabolites during microsomal metabolism, glutathione (GSH) was included in the incubation. A LC technique coupled with benchtop orbitrap MS with full mass/data-dependent tandem mass spectrometry acquisition mode was used to detect and identify the generated metabolites. The possible structures of the metabolites were characterized according to their accurate masses and fragment ions. Under the current conditions, a total of 10 metabolites, including four GSH adducts, were identified. The results indicated that imperatorin underwent extensive metabolic reactions including hydroxylation, oxidation, glucuronidation, and GSH conjugation. This study provides essential data on the metabolism of imperatorin, which will be helpful for us to understand the safety and efficacy of this bioactive compound.

Preclinical evaluation of chemically reactive metabolites and mitigation of bioactivation in drug discovery

The formation of reactive metabolites (RMs) is thought to be one of the pathogeneses for some idiosyncratic adverse drug reactions (IADRs) which are considered one of the leading causes of some drug attritions and/or recalls. Minimizing or eliminating the formation of RMs via chemical modification is a useful tactic to reduce the risk of IADRs and time-dependent inhibition (TDI) of cytochrome P450 enzymes (CYPs). The RMs should be carefully handled before making a go-no-go decision. Herein, we highlight the role of RMs in the occurrence of IADRs and CYP TDI, the risk of structural alerts, the approaches of RM assessment at the discovery stage and strategies to minimize or eliminate RM liability. Finally, some considerations for developing a RM-positive drug candidate are suggested.

Identification and characterization of the metabolites of moscatilin in mouse, rat, dog, monkey and human hepatocytes by LC-Orbitrap-MS/MS combined with diagnostic fragment ions and accurate mass measurements

Moscatilin, a bibenzyl derivative from the stem of Dendrobium loddigesii, has been shown to have anticancer activity. The aim of this study was to identify and characterize the possible in vitro metabolites of moscatilin generated from hepatocytes. The metabolites generated in the hepatocytes of mouse, rat, dog, monkey and human were identified and characterized employing ultra-high-performance liquid chromatography coupled with quadrupole Orbitrap tandem mass spectrometry (LC-Orbitrap-MS/MS) based on diagnostic fragment ions and accurate mass measurements. A total of 18 metabolites were identified, among which seven were phase I and 11 were phase II metabolites. The plausible structures of the metabolites and the probable biotransformation pathways were proposed based on the diagnostic fragment ions, chemical formula and mass fragmentation pattern, as well as the accurate masses. The majority of phase I metabolites were generated by demethylation and hydroxylation, while phase II metabolites were mainly generated by glucuronidation, glutathione conjugation and sulfation. Our study first expounded the metabolites of moscatilin in mouse, rat, dog, monkey and human hepatocytes and provided a foundation for a further pharmacokinetic and toxicity study. More importantly, LC-Orbitrap-MS/MS combined with diagnostic fragment ions and accurate mass measurements has been proved to be an effective method for the rapid identification of bibenzyl derivatives and their metabolites.

Species differences in liver microsomal hydrolysis of acyl glucuronide in humans and rats

Acyl glucuronides (AGs) are known as one of the causes of idiosyncratic drug toxicity (IDT). Although AGs can be enzymatically hydrolysed by β-glucuronidase and esterase, much information on their characteristics and species differences is lacking. This study was aimed to clarify species differences in AG hydrolysis between human and rat liver microsomes (HLM and RLM).To evaluate the AG hydrolysis profile, and the contribution of β-glucuronidase and esterase towards AG hydrolysis in HLM and RLM, nonsteroidal anti-inflammatory drugs (NSAIDs) were used. AGs were incubated with 0.1 M Tris-HCl buffer (pH 7.4) and 0.3 mg/mL HLM or RLM in the absence or presence of β-glucuronidase inhibitor, D-saccharic acid 1,4-lactone (D-SL) and esterase inhibitor, phenylmethylsulfonyl fluoride (PMSF).AGs of mefenamic acid (MEF-AG) and etodolac (ETO-AG) showed significantly higher AG hydrolysis rates in RLM than in HLM. Esterases were found to serve as AG hydrolases dominantly in HLM, whereas both esterases and β-glucuronidase equally contribute to AG hydrolysis in RLM. However, MEF-AG and ETO-AG were hydrolysed only by β-glucuronidase.We demonstrated for the first time that the activity of AG hydrolases towards NSAID-AGs differs between humans and rats.

A validated UHPLC-MS/MS method for simultaneous determination of lumiracoxib and its hydroxylation and acyl glucuronidation metabolites in rat plasma: Application to a pharmacokinetic study

Lumiracoxib is a selective cyclooxygenase-2 (COX-2) inhibitor. The aim of this study was to develop a simple and sensitive ultra-high performance liquid chromatography tandem mass spectrometric method (UHPLC-MS/MS) for the simultaneous determination of lumiracoxib and its circulating metabolites 4'-Hydroxyl-lumiracoxib and lumiracoxib-acyl-glucuronide in rat plasma. The analytes and diclofenac (internal standard, IS) were extracted using acetonitrile containing 0.2 % formic acid. Chromatographic separation was executed on ACQUITY BEH C₁₈ column (2.1 × 50 mm, 1.7 μm) with water containing 0.2 % formic acid and acetonitrile as mobile phase. Mass detection was achieved in positive multiple reactions monitoring (MRM) mode, with precursor-to-product transitions at m/z 294.1 > 248.1, m/z 310.1 > 264.1, m/z 470.1 > 276.1 and m/z 296.0 > 250.0 for lumiracoxib, 4'-hydroxyl-lumiracoxib, lumiracoxib-acyl-glucuronide and for IS, respectively. The developed LC-MS/MS method was validated based on the guidance of U.S. Food and Drug Administration. The linearity was evident (r > 0.995) over the concentration ranges of 1-1000 ng/mL for lumiracoxib, 1-500 ng/mL for 4'-hydroxyl-lumiracoxib and 1-200 ng/mL for lumiracoxib-acyl-glucuronide, respectively. The precision (RSD) did not exceed 8.23 % and accuracy (RE) ranged from -7.85 % to 9.50 %. The extraction recovery was more than 80.54 %. All the analytes were demonstrated to be stable under the tested storage and processing conditions. The validated LC-MS/MS method has been successfully applied to the pharmacokinetic study of lumiracoxib and its metabolites in the rats after orally administered with lumiracoxib.

Models of Idiosyncratic Drug-Induced Liver Injury

Drug-induced liver injury (DILI) is a leading cause of attrition during the early and late stages of drug development and after a drug is marketed. DILI is generally classified as either intrinsic or idiosyncratic. Intrinsic DILI is dose dependent and predictable (e.g., acetaminophen toxicity). However, predicting the occurrence of idiosyncratic DILI, which has a very low incidence and is associated with severe liver damage, is difficult because of its complex nature and the poor understanding of its mechanism. Considering drug metabolism and pharmacokinetics, we established experimental animal models of DILI for 14 clinical drugs that cause idiosyncratic DILI in humans, which is characterized by the formation of reactive metabolites and the involvement of both innate and adaptive immunity. On the basis of the biomarker data obtained from the animal models, we developed a cell-based assay system that predicts the potential risks of drugs for inducing DILI. These findings increase our understanding of the mechanisms of DILI and may help predict and prevent idiosyncratic DILI due to certain drugs.