Targeted label-free approach for quantification of epoxide hydrolase and glutathione transferases in microsomes

NAD (P)H Quinone Dehydrogenase 1-Targeting Triptolide Analogue Causes Tumor Regression and Sensitizes Cisplatin-Resistant Lung Cancer to Chemotherapy

Cisplatin (DDP) is a first-line chemotherapeutic drug against lung cancer. Nonetheless, the effectiveness of this drug is hampered by drug resistance. Overcoming drug resistance is crucial for improving the outcomes of lung cancer treatment. Here, we reported the effect of CX-23, an activated triptolide analogue that targets NAD (P)H quinone dehydrogenase 1 (NQO1), on DDP-resistant lung cancer and sensitizes DDP-resistant lung cancer to chemotherapy. Our findings unveiled the antiproliferative activity of CX-23 against both A549- and DDP-resistant A549 (A549/DDP) cells while enhancing the chemosensitivity of these cells to DDP. Notably, CX-23 demonstrated no toxicity toward normal lung cells. Further investigations revealed that CX-23 exerts its effects by blocking AKT phosphorylation, leading to reduced expression of Mcl-1 and Bcl-2, and upregulating cleaved-caspase-3 levels, ultimately inducing apoptosis in cancer cells. CX-23 can be rapidly transformed in both A549 and A549/DDP cell lysates while remaining stable in mouse plasma and normal lung tissues. Pharmacokinetic analysis showed that CX-23 can distribute to lung tissues. Moreover, in vivo studies showed that CX-23 can prevent DDP-resistant lung cancer progression without causing any toxicity in the liver, kidneys, or lungs after 6 weeks of treatment. The combination of CX-23 and DDP not only significantly inhibited tumor progression compared to DDP alone but also attenuated DDP-induced kidney toxicity. These findings suggest that CX-23 alone or in combination with DDP may provide an alternative therapeutic option for DDP-resistant lung cancer.

Identification and cross-species comparison of in vitro phase I brevetoxin (BTX-2) metabolites in northern Gulf of Mexico fish and human liver microsomes by UHPLC-HRMS(/MS)

Brevetoxins (BTX) are a group of marine neurotoxins produced by the harmful alga Karenia brevis. Numerous studies have shown that BTX are rapidly accumulated and metabolized in shellfish and mammals. However, there are only limited data on BTX metabolism in fish, despite growing evidence that fish serve as vectors for BTX transfer in marine food webs. In this study, we aimed to investigate the in vitro biotransformation of BTX-2, the major constituent of BTX profiles in K. brevis, in several species of northern Gulf of Mexico fish. Metabolism assays were performed using hepatic microsomes prepared in-house as well as commercially available human microsomes for comparison, focusing on phase I reactions mediated by cytochrome P450 monooxygenase (CYP) enzymes. Samples were analyzed by UHPLC-HRMS(/MS) to monitor BTX-2 depletion and characterize BTX metabolites based on MS/MS fragmentation pathways. Our results showed that both fish and human liver microsomes rapidly depleted BTX-2, resulting in a 72-99% reduction within 1 h of incubation. We observed the simultaneous production of 22 metabolites functionalized by reductions, oxidations, and other phase I reactions. We were able to identify the previously described congeners BTX-3 and BTX-B5, and tentatively identified BTX-9, 41,43-dihydro-BTX-2, several A-ring hydrolysis products, as well as several novel metabolites. Our results confirmed that fish are capable of similar BTX biotransformation reactions as reported for shellfish and mammals, but comparison of metabolite formation across the tested species suggested considerable interspecific variation in BTX-2 metabolism potentially leading to divergent BTX profiles. We additionally observed non-enzymatic formation of BTX-2 and BTX-3 glutathione conjugates. Collectively, these findings have important implications for determining the ecotoxicological fate of BTX in marine food webs.

Parameterization of Microsomal and Cytosolic Scaling Factors: Methodological and Biological Considerations for Scalar Derivation and Validation

Mathematical models that can predict the kinetics of compounds have been increasingly adopted for drug development and risk assessment. Data for these models may be generated from in vitro experimental systems containing enzymes contributing to metabolic clearance, such as subcellular tissue fractions including microsomes and cytosol. Extrapolation from these systems is facilitated by common scaling factors, known as microsomal protein per gram (MPPG) and cytosolic protein per gram (CPPG). Historically, parameterization of MPPG and CPPG has employed the use of recovery factors, commonly benchmarked to cytochromes P450 which work well in some contexts, but could be problematic for other enzymes. Here, we propose absolute quantification of protein content and supplementary assays to evaluate microsomal/cytosolic purity that should be employed. Examples include calculation of microsomal latency by mannose-6-phosphatase activity and immunoblotting of subcellular fractions with fraction-specific markers. Further considerations include tissue source, as disease states can affect enzyme expression and activity, and the methodology used for scalar parameterization. Regional- and organ-specific expression of enzymes, in addition to differences in organ physiology, is another important consideration. Because most efforts have focused on the liver that is, for the most part, homogeneous, derived scalars may not capture the heterogeneity of other major tissues contributing to xenobiotic metabolism including the kidneys and small intestine. Better understanding of these scalars, and how to appropriately derive them from extrahepatic tissues can provide support to the inferences made with physiologically based pharmacokinetic modeling, increase its accuracy in characterizing in vivo drug pharmacokinetics, and improve confidence in go-no-go decisions for clinical trials.

Dietary Polyphenols Inhibit the Cytochrome P450 Monooxygenase Branch of the Arachidonic Acid Cascade with Remarkable Structure-Dependent Selectivity and Potency

The products of the cytochrome P450 monooxygenase (CYP)-catalyzed oxidation of arachidonic acid (AA), that is, epoxy- and hydroxy-fatty acids, play a crucial role in the homeostasis of several physiological processes. In a liver microsome-based multienzyme assay using AA as natural substrate, we investigated how polyphenols inhibit different oxylipin-forming CYP in parallel but independently from each other. The ω-hydroxylating CYP4F2 and CYP4A11 were investigated, as well as the epoxidizing CYP2C-subfamily and CYP3A4 along with the (ω-n)-hydroxylating CYP1A1 and CYP2E1. The oxylipin formation was inhibited by several polyphenols with a remarkable selectivity and a potency comparable to known CYP inhibitors. The flavone apigenin inhibited the epoxidation, ω-hydroxylation, and (ω-n)-hydroxylation of AA with IC₅₀ values of 4.4-9.8, 2.9-10, and 10-25 μM, respectively. Other flavones such as wogonin selectively inhibited CYP1A1-catalyzed (ω-n)-hydroxylation with an IC₅₀ value of 0.10-0.22 μM, while the isoflavone genistein was a selective ω-hydroxylase inhibitor (IC₅₀: 5.5-46 μM). Of note, the flavanone naringenin and the anthocyanidin perlargonidin did not inhibit CYPs of the AA cascade. Moderate permeability of apigenin as tested in the Caco-2 model of intestinal absorption (P_app: 4.5 ± 1 × 10^-6 cm/s) and confirmation of the inhibition of 20-HETE formation by apigenin in the colorectal cancer-derived cell line HCT 116 (IC₅₀: 1.5-8.8 μM) underline the possible in vivo relevance of these effects. Further research is needed to better understand how polyphenols impact human health by this newly described molecular mode of action.

Dataset from proteomic analysis of human liver, lung, kidney and intestine microsomes

We provide detailed datasets from our analysis of proteins that are identified in human liver, lung, kidney and intestine microsomes by MS-based proteomics. Also included is a set of CYP450 enzymes and microsomal glutathione-S-transferase (MGSTs) activities in human liver microsomes. The data presented in this paper support the research article "Targeted label-free approach for quantification of epoxide hydrolase and glutathione transferases in microsomes" (Song et al., 2015) [1]. We expect that the data will contribute to the study of metabolism enzymes.

Oxetane Substrates of Human Microsomal Epoxide Hydrolase

Oxetanyl building blocks are increasingly used in drug discovery because of the improved drug-like properties they confer on drug candidates, yet little is currently known about their biotransformation. A series of oxetane-containing analogs was studied and we provide the first direct evidence of oxetane hydrolysis by human recombinant microsomal epoxide hydrolase (mEH). Incubations with human liver fractions and hepatocytes were performed with and without inhibitors of cytochrome P450 (P450), mEH and soluble epoxide hydrolase (sEH). Reaction dependence on NADPH was investigated in subcellular fractions. A full kinetic characterization of oxetane hydrolysis is presented, in both human liver microsomes and human recombinant mEH. In human liver fractions and hepatocytes, hydrolysis by mEH was the only oxetane ring-opening metabolic route, with no contribution from sEH or from cytochrome P450-catalyzed oxidation. Minimally altering the structural elements in the immediate vicinity of the oxetane can greatly modulate the efficiency of hydrolytic ring cleavage. In particular, higher pKa in the vicinity of the oxetane and an increased distance between the oxetane ring and the benzylic nitrogen improve reaction rate, which is further enhanced by the presence of methyl groups near or on the oxetane. This work defines oxetanes as the first nonepoxide class of substrates for human mEH, which was previously known to catalyze the hydrolytic ring opening of electrophilic and potentially toxic epoxide-containing drugs, drug metabolites, and exogenous organochemicals. These findings will be of value for the development of biologically active oxetanes and may be exploited for the biocatalytic generation of enantiomerically pure oxetanes and diols.

Microsomal and Cytosolic Scaling Factors in Dog and Human Kidney Cortex and Application for In Vitro-In Vivo Extrapolation of Renal Metabolic Clearance

In vitro-in vivo extrapolation of drug metabolism data obtained in enriched preparations of subcellular fractions rely on robust estimates of physiologically relevant scaling factors for the prediction of clearance in vivo. The purpose of the current study was to measure the microsomal and cytosolic protein per gram of kidney (MPPGK and CPPGK) in dog and human kidney cortex using appropriate protein recovery marker and evaluate functional activity of human cortex microsomes. Cytochrome P450 (CYP) content and glucose-6-phosphatase (G6Pase) activity were used as microsomal protein markers, whereas glutathione-S-transferase activity was a cytosolic marker. Functional activity of human microsomal samples was assessed by measuring mycophenolic acid glucuronidation. MPPGK was 33.9 and 44.0 mg/g in dog kidney cortex, and 41.1 and 63.6 mg/g in dog liver (n = 17), using P450 content and G6Pase activity, respectively. No trends were noted between kidney, liver, and intestinal scalars from the same animals. Species differences were evident, as human MPPGK and CPPGK were 26.2 and 53.3 mg/g in kidney cortex (n = 38), respectively. MPPGK was 2-fold greater than the commonly used in vitro-in vivo extrapolation scalar; this difference was attributed mainly to tissue source (mixed kidney regions versus cortex). Robust human MPPGK and CPPGK scalars were measured for the first time. The work emphasized the importance of regional differences (cortex versus whole kidney-specific MPPGK, tissue weight, and blood flow) and a need to account for these to improve assessment of renal metabolic clearance and its extrapolation to in vivo.

Database of Optimized Proteomic Quantitative Methods for Human Drug Disposition-Related Proteins for Applications in Physiologically Based Pharmacokinetic Modeling

The purpose of this study was to create an open access repository of validated liquid chromatography tandem mass spectrometry (LC‐MS/MS) multiple reaction monitoring (MRM) methods for quantifying 284 important proteins associated with drug absorption, distribution, metabolism, and excretion (ADME). Various in silico and experimental approaches were used to select surrogate peptides and optimize instrument parameters for LC‐MS/MS quantification of the selected proteins. The final methods were uploaded to an online public database (QPrOmics; www.qpromics.uw.edu/qpromics/assay/), which provides essential information for facile method development in triple quadrupole mass spectrometry (MS) instruments. To validate the utility of the methods, the differential tissue expression of 107 key ADME proteins was characterized in the tryptic digests of the pooled subcellular fractions of human liver, kidneys, intestines, and lungs. These methods and the data are critical for development of physiologically based pharmacokinetic (PBPK) models to predict xenobiotic disposition.

Differential protein expression and localization of CYP450 enzymes in three species of earthworm; is this a reflection of environmental adaptation?

Cytochrome P450 (CYP450) is a hemoprotein superfamily, among which CYP1, CYP2 and CYP3 play a major role in the metabolism of vast array of xenobiotics and endobiotics. This paper reports on three CYP enzyme variants (CYP1A2, CYP2E1 and CYP3A4) in three species of earthworm (Eisenia fetida, Metaphire guillelmi and Amynthas carnosus). The relative expression levels and localization of the three associated proteins were investigated at three life-cycle points (juvenile, sub-adult and adult), through comparison of anterior and posterior body tissue and between specific organs (body wall, intestine and reproductive tissues) using western blot analysis. This study confirmed the presence of CYP3A4, CYP1A2 and CYP2E1 in all three species of earthworm tested. The levels of expression varied with earthworm species, age, and body location. These differences in occurrence of the three CYP enzymes appeared to reflect the ecological niche (the spatial and temporal location and functional relationship of each individual or population in populations or communities), and the likelihood of contact with soil contaminants of the respective species. These results may help to explain why earthworms are capable of adapting to very different and extensively polluted soil environments and provide important data for subsequent ecotoxicology and ecological adaptability studies.

Cytochrome P450 and Non-Cytochrome P450 Oxidative Metabolism: Contributions to the Pharmacokinetics, Safety, and Efficacy of Xenobiotics

The drug-metabolizing enzymes that contribute to the metabolism or bioactivation of a drug play a crucial role in defining the absorption, distribution, metabolism, and excretion properties of that drug. Although the overall effect of the cytochrome P450 (P450) family of drug-metabolizing enzymes in this capacity cannot be understated, advancements in the field of non-P450-mediated metabolism have garnered increasing attention in recent years. This is perhaps a direct result of our ability to systematically avoid P450 liabilities by introducing chemical moieties that are not susceptible to P450 metabolism but, as a result, may introduce key pharmacophores for other drug-metabolizing enzymes. Furthermore, the effects of both P450 and non-P450 metabolism at a drug's site of therapeutic action have also been subject to increased scrutiny. To this end, this Special Section on Emerging Novel Enzyme Pathways in Drug Metabolism will highlight a number of advancements that have recently been reported. The included articles support the important role of non-P450 enzymes in the clearance pathways of U.S. Food and Drug Administration-approved drugs over the past 10 years. Specific examples will detail recent reports of aldehyde oxidase, flavin-containing monooxygenase, and other non-P450 pathways that contribute to the metabolic, pharmacokinetic, or pharmacodynamic properties of xenobiotic compounds. Collectively, this series of articles provides additional support for the role of non-P450-mediated metabolic pathways that contribute to the absorption, distribution, metabolism, and excretion properties of current xenobiotics.