Role of cytochrome P450 enzymes in drug-drug interactions

Possible Side Effects of Polyphenols and Their Interactions with Medicines

Polyphenols are an important component of plant-derived food with a wide spectrum of beneficial effects on human health. For many years, they have aroused great interest, especially due to their antioxidant properties, which are used in the prevention and treatment of many diseases. Unfortunately, as with any chemical substance, depending on the conditions, dose, and interactions with the environment, it is possible for polyphenols to also exert harmful effects. This review presents a comprehensive current state of the knowledge on the negative impact of polyphenols on human health, describing the possible side effects of polyphenol intake, especially in the form of supplements. The review begins with a brief overview of the physiological role of polyphenols and their potential use in disease prevention, followed by the harmful effects of polyphenols which are exerted in particular situations. The individual chapters discuss the consequences of polyphenols’ ability to block iron uptake, which in some subpopulations can be harmful, as well as the possible inhibition of digestive enzymes, inhibition of intestinal microbiota, interactions of polyphenolic compounds with drugs, and impact on hormonal balance. Finally, the prooxidative activity of polyphenols as well as their mutagenic, carcinogenic, and genotoxic effects are presented. According to the authors, there is a need to raise public awareness about the possible side effects of polyphenols supplementation, especially in the case of vulnerable subpopulations.

Ferroptosis and Tumor Drug Resistance: Current Status and Major Challenges

Ferroptosis is a novel type of regulated cell death, whose unique metabolic characteristics are commonly used to evaluate the conditions of various diseases especially in tumors. Accumulating evidence supports that ferroptosis can regulate tumor development, metastasis, and therapeutic responses. Considering to the important role of chemotherapy in tumor treatment, drug resistance has become the most serious challenge. Revealing the molecular mechanism of ferroptosis is expected to solve tumor drug resistance and find new therapies to treat cancers. In this review, we discuss the relationship between ferroptosis and tumor drug resistance, summarize the abnormal ferroptosis in tissues of different cancer types and current research progress and challenges in overcoming treatment resistance, and explore the concept of targeting ferroptosis to improve tumor treatment outcomes.

Novel Small-Molecule Inhibitor of NLRP3 Inflammasome Reverses Cognitive Impairment in an Alzheimer's Disease Model

Aberrant activation of the Nod-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome plays an essential role in multiple diseases, including Alzheimer's disease (AD) and psoriasis. We report a novel small-molecule inhibitor, NLRP3-inhibitory compound 7 (NIC7), and its derivative, which inhibit NLRP3-mediated activation of caspase 1 along with the secretion of interleukin (IL)-1β, IL-18, and lactate dehydrogenase. We examined the therapeutic potential of NIC7 in a disease model of AD by analyzing its effect on cognitive impairment as well as the expression of dopamine receptors and neuronal markers. NIC7 significantly reversed the associated disease symptoms in the mice model. On the other hand, NIC7 did not reverse the disease symptoms in the imiquimod (IMQ)-induced disease model of psoriasis. This indicates that IMQ-based psoriasis is independent of NLRP3. Overall, NIC7 and its derivative have therapeutic prospects to treat AD or NLRP3-mediated diseases.

Cocktail Method: Effect of the Bletilla striata Extracts on CytochromeP450 Activity in Rat

Bletilla striata is a dried tuber of B striata (Thunb.) Reichb.f. of Orchidaceae plant, which is mainly used for hemoptysis, vomiting blood, trauma bleeding, sore swollen poison, and cracked skin. There have been few research reports on the effect of this herb on cytochrome P450 (CYP), therefore, the study was aimed to investigate the effects of the B striata extracts on the activity of 6 subtypes (CYP2D6, 1A2, 2C19, 2E1, 3A4, and 2C9) using a cocktail method. The B striata extracts were administrated to rats in 0.21 or 0.63 g/kg once a day for 7 or 14 days. The 3 control groups were used to ensure the accuracy of the results. Subsequently, a cocktail of tolbutamide, chlorzoxazone, midazolam, metoprolol, omeprazole, and caffeine was injected. A ultra performance liquid chromatography–tandem mass spectrometer was developed and validated to investigate the concentration of the probes and the pharmacokinetic parameters were calculated to investigate the effects of the extracts on the activity of 6 enzymes under different doses and different dosing periods. The results suggested that the B striata extracts could induce the activities of CYP2D6, 1A2, and 2C19 and could inhibit the activities of CYP2E1, 3A4, and 2C9. When used in combination with drugs that are metabolized by CYP2D6, 1A2, 2C19, 2E1, 3A4, and 2C9, appropriate dose adjustments were needed to avoid toxic side effects caused by drug interactions.

Evaluation of the Pharmacokinetics of Trazpiroben (TAK-906), a Peripherally Selective D2/D3 Dopamine Receptor Antagonist, in the Presence and Absence of Itraconazole, a Potent CYP 3A4 Inhibitor

Purpose

Treatment options for gastroparesis, such as metoclopramide and domperidone, are limited because of safety concerns, which may be exacerbated in the presence of inhibitors of drug metabolism. This study evaluated the effect of itraconazole on the pharmacokinetics, safety, and tolerability of trazpiroben (previously TAK-906), a novel, peripherally selective D₂/D₃ dopamine receptor antagonist.

Methods

This was a phase 1, two-period, crossover trial in healthy participants (NCT03161405). On day 1, period 1 (days 1–3), participants received a single oral dose of trazpiroben 25 mg. During period 2 (days 4–9), participants received oral itraconazole 200 mg once daily (days 1–5) and one oral dose of trazpiroben 25 mg post itraconazole on day 4. Trazpiroben pharmacokinetics were assessed. Safety assessments included triplicate electrocardiograms.

Results

Twelve healthy males (24–45 years old) were studied. Co-administration of itraconazole increased trazpiroben area under the concentration–time curve from time 0 to infinity by 1.28-fold (90% confidence interval: 1.10, 1.49) and maximum plasma concentration (C_max) by 1.98-fold (1.64, 2.39) versus trazpiroben alone. Placebo-corrected, change from baseline in corrected QT interval at the observed geometric mean C_max for trazpiroben alone (9.53 ng/mL) and with itraconazole (18.00 ng/mL) was estimated at 1.31 ms (−0.39, 3.01) and 1.54 ms (−0.15, 3.24), respectively. There were no clinically relevant abnormalities in any safety parameters.

Conclusion

These results indicate that TAK‑906 is relatively insensitive to inhibition of cytochrome P450 3A4, and cardiovascular safety concerns associated with domperidone are unlikely to be elicited by trazpiroben under similar conditions.

Exploration of xenobiotic metabolism within cell lines used for Tox21 chemical screening

The Tox21 Program has investigated thousands of chemicals with high-throughput screening assays using cell-based assays to link thousands of chemicals to individual molecular targets/pathways. However, these systems have been widely criticized for their suspected lack of 'metabolic competence' to bioactivate or detoxify chemical exposures. In this study, 9 cell line backgrounds used in Tox21 assays (i.e., HepG2, HEK293, Hela, HCT116, ME180, CHO-K1, GH3.TRE-Luc, C3H10T1/2 and MCF7) were evaluated via metabolite formation rates, along with metabolic clearance and metabolite profiling for HepG2, HEK293, and MCF-7aroERE, in comparison to pooled donor (50) suspensions of primary human hepatocytes (PHHs). Using prototype clinical drug substrates for CYP1A2, CYP2B6, and CYP3A4/5, extremely low-to-undetectable CYP450 metabolism was observed (24 h), and consistent with their purported 'lack' of metabolic competence. However, for Phase II metabolizing enzymes and metabolic clearance, surprisingly proficient metabolism was observed for bisphenol AF, bisphenol S, and 7-hydroxycoumarin. Here, comparatively low glucuronidation relative to sulfation was observed in contrast to equivalent levels in PHHs. Overall, while a lack of CYP450 metabolism was confirmed in this benchmarking effort, Tox21 cell lines were not 'incompetent' for xenobiotic metabolism, and displayed surprisingly high proficiency for sulfation that rivaled PHHs. These findings have implications for the interpretation of Tox21 assay data, and establish a framework for evaluating of 'metabolic competence' with in vitro models.

Homotropic Cooperativity of Midazolam Metabolism by Cytochrome P450 3A4: Insight from Computational Studies

Human cytochrome P450 3A4 (CYP3A4) is responsible for the metabolism of ∼50% clinically used drugs. Midazolam (MDZ) is a commonly used sedative drug and serves as a marker substrate for the CYP3A4 activity assessment. MDZ is metabolized by CYP3A4 to two hydroxylation products, 1′-OH-MDZ and 4-OH-MDZ. It has been reported that the ratio of 1′-OH-MDZ and 4-OH-MDZ is dependent on the MDZ concentration, which reflects the homotropic cooperative behavior in MDZ metabolism by CYP3A4. Here, we used quantum chemistry (QC), molecular docking, conventional molecular dynamics (cMD), and Gaussian accelerated molecular dynamics (GaMD) approaches to investigate the mechanism of the interactions between CYP3A4 and MDZ. QC calculations suggest that C1′ is less reactive for hydroxylation than C4, which is a pro-chirality carbon. However, the 4-OH-MDZ product is likely to be racemic due to the chirality inversion in the rebound step. The MD simulation results indicate that MDZ at the peripheral allosteric site is not stable and the binding modes of the MDZ molecules at the productive site are in line with the experimental observations.

Molecular modeling approaches to address drug-metabolizing enzymes (DMEs) mediated chemoresistance: a review

Resistance against clinically approved anticancer drugs is the main roadblock in cancer treatment. Drug metabolizing enzymes (DMEs) that are capable of metabolizing a variety of xenobiotic get overexpressed in malignant cells, therefore, catalyzing drug inactivation. As evident from the literature reports, the levels of DMEs increase in cancer cells that ultimately lead to drug inactivation followed by drug resistance. To puzzle out this issue, several strategies inclusive of analog designing, prodrug designing, and inhibitor designing have been forged. On that front, the implementation of computational tools can be considered a fascinating approach to address the problem of chemoresistance. Various research groups have adopted different molecular modeling tools for the investigation of DMEs mediated toxicity problems. However, the utilization of these in-silico tools in maneuvering the DME mediated chemoresistance is least considered and yet to be explored. These tools can be employed in the designing of such chemotherapeutic agents that are devoid of the resistance problem. The current review canvasses various molecular modeling approaches that can be implemented to address this issue. Special focus was laid on the development of specific inhibitors of DMEs. Additionally, the strategies to bypass the DMEs mediated drug metabolism were also contemplated in this report that includes analogs and pro-drugs designing. Different strategies discussed in the review will be beneficial in designing novel chemotherapeutic agents that depreciate the resistance problem.

Discovery of GLPG2451, a Novel Once Daily Potentiator for the Treatment of Cystic Fibrosis

Cystic fibrosis (CF) is a life-threatening recessive genetic disease caused by mutations in the gene encoding for the cystic fibrosis transmembrane conductance regulator (CFTR). With the discovery of Ivacaftor and Lumacaftor, it has been shown that administration of one or more small molecules can partially restore the CFTR function. Correctors are small molecules that enhance the amount of CFTR on the cell surface, while potentiators improve the gating function of the CFTR channel. Herein, we describe the discovery and optimization of a novel potentiator series. Scaffold hopping, focusing on retaining the different intramolecular contacts, was crucial in the whole discovery process to identify a novel series devoid of genotoxic liabilities. From this series, the clinical candidate GLPG2451 was selected based on its pharmacokinetic properties, allowing QD dosing and based on its low CYP induction potential.

CYP2J2 Molecular Recognition: A New Axis for Therapeutic Design

Cytochrome P450 (CYP) epoxygenases are a special subset of heme-containing CYP enzymes capable of performing the epoxidation of polyunsaturated fatty acids (PUFA) and the metabolism of xenobiotics. This dual functionality positions epoxygenases along a metabolic crossroad. Therefore, structure-function studies are critical for understanding their role in bioactive oxy-lipid synthesis, drug-PUFA interactions, and for designing therapeutics that directly target the epoxygenases. To better exploit CYP epoxygenases as therapeutic targets, there is a need for improved understanding of epoxygenase structure-function. Of the characterized epoxygenases, human CYP2J2 stands out as a potential target because of its role in cardiovascular physiology. In this review, the early research on the discovery and activity of epoxygenases is contextualized to more recent advances in CYP epoxygenase enzymology with respect to PUFA and drug metabolism. Additionally, this review employs CYP2J2 epoxygenase as a model system to highlight both the seminal works and recent advances in epoxygenase enzymology. Herein we cover CYP2J2's interactions with PUFAs and xenobiotics, its tissue-specific physiological roles in diseased states, and its structural features that enable epoxygenase function. Additionally, the enumeration of research on CYP2J2 identifies the future needs for the molecular characterization of CYP2J2 to enable a new axis of therapeutic design.

Effect of Itraconazole, a Potent CYP3A4 Inhibitor, on the Steady-State Pharmacokinetics of Vemurafenib in Patients With BRAFV600 Mutation-Positive Malignancies

The effects of itraconazole, a strong CYP3A4 inhibitor, on the steady-state pharmacokinetics of vemurafenib were evaluated in a phase 1, multicenter, open-label, fixed-sequence study. Patients with BRAF^V600 mutation-positive metastatic malignancies received oral vemurafenib 960 mg twice daily on days 1 to 20 (period A) and oral vemurafenib 960 mg twice daily with oral itraconazole 200 mg once daily on days 21 to 40 (period B). A mixed-effects analysis of variance model was used to compare log-transformed area under the concentration-time curve during the dosing interval and maximum plasma concentration values for vemurafenib in 8 patients between period B (vemurafenib plus itraconazole) and period A (vemurafenib alone). Multiple doses of itraconazole increased steady-state exposure of vemurafenib by approximately 40%, with geometric least squares mean ratios (period B/period A) of 140% (90% confidence interval, 121-161) for both maximum plasma concentration and area under the concentration-time curve during the dosing interval. There was no apparent increase in incidence or severity of adverse events during coadministration of vemurafenib with itraconazole. In conclusion, coadministration of itraconazole with vemurafenib resulted in a modest increase in exposure of vemurafenib at steady state and was generally well tolerated.

In vitro metabolic characterization of orbitazine, a novel derivative of the PAC-1 anticancer agent

OBJECTIVES

The in vitro evaluation of new drugs is an important step in the drug development pipeline. Orbitazine is a derivative of PAC-1 that has substituted the functional group homopiperazine ring with a piperazine ring. The purpose of this study was to assess the metabolic profile of orbitazine.

METHODS

Metabolism was characterized in vitro by incubating liver microsomes with metabolize orbitazine or the classical metabolic enzyme substrates. High performance liquid chromatography (HPLC) and LC-MS/MS were used to identify the parent drugs and metabolites of orbitazine or metabolic enzyme substrates.

KEY FINDINGS

There was no difference in metabolic stability or metabolites across different species. The metabolites included a debenzyl compound and several hydroxyl compounds, defined as M1(316), M2(440), M3(422), M4(422) and M5(422). We found that orbitazine was metabolized by CYP3A4, CYP2C9 and CYP2D6 in a human liver microsomes incubation system. Orbitazine had no significant inhibitory effect on CYP1A2, CYP2B6, CYP2C9, or CYP2C19 in human liver microsomes, but showed a dose-dependent inhibition of CYP2C8, CYP2D6 and CYP3A4; and there was no orbitazine-mediated induction of CYP1A2, CYP2B6, CYP3A4 or mRNA expression in hepatocytes.

CONCLUSIONS

This in vitro data on the metabolism of orbitazine may provide valuable information to support further clinical progression as a potential therapeutic molecule.

Metabolism of JQ1, an inhibitor of bromodomain and extra terminal bromodomain proteins, in human and mouse liver microsomes†

JQ1 is a small-molecule inhibitor of the bromodomain and extra terminal (BET) protein family that potently inhibits the bromodomain testis-specific protein (BRDT), which is essential for spermatogenesis. JQ1 treatment produces a reversible contraceptive effect by targeting the activity of BRDT in mouse male germ cells, validating BRDT as a male contraceptive target. Although JQ1 possesses favourable physical properties, it exhibits a short half-life. Because the details of xenobiotic metabolism play important roles in the optimization of drug candidates and in determining the role of metabolism in drug efficacy, we investigated the metabolism of JQ1 in human and mouse liver microsomes. We present the first comprehensive view of JQ1 metabolism in liver microsomes, distinguishing nine JQ1 metabolites, including three monohydroxylated, one de-tert-butylated, two dihydroxylated, one monohydroxylated/dehydrogenated, one monohydroxylated-de-tert-butylated and one dihydroxylated/dehydrogenated variant of JQ1. The dominant metabolite (M1) in both human and mouse liver microsomes is monohydroxylated on the fused three-ring core. Using recombinant cytochrome P450 (CYP) enzymes, chemical inhibitors and the liver S9 fraction of Cyp3a-null mice, we identify enzymes that contribute to the formation of these metabolites. Cytochrome P450 family 3 subfamily A member 4 (CYP3A4) is the main contributor to the production of JQ1 metabolites in vitro, and the CYP3A4/5 inhibitor ketoconazole strongly inhibits JQ1 metabolism in both human and mouse liver microsomes. Our findings suggest that JQ1 half-life and efficacy might be improved in vivo by co-administration of a selective CYP inhibitor, thereby impacting the use of JQ1 as a probe for BRDT activity in spermatogenesis and as a probe or therapeutic in other systems.

Structure-Based Site of Metabolism (SOM) Prediction of Ligand for CYP3A4 Enzyme: Comparison of Glide XP and Induced Fit Docking (IFD)

Metabolism is one of the prime reasons where most of drugs fail to accomplish their clinical trials. The enzyme CYP3A4, which belongs to the superfamily of cytochrome P450 enzymes (CYP), helps in the metabolism of a large number of drugs in the body. The enzyme CYP3A4 catalyzes oxidative chemical processes and shows a very broad range of ligand specificity. The understanding of the compound’s structure where oxidation would take place is crucial for the successful modification of molecules to avoid unwanted metabolism and to increase its bioavailability. For this reason, it is required to know the site of metabolism (SOM) of the compounds, where compounds undergo enzymatic oxidation. It can be identified by predicting the accessibility of the substrate’s atom toward oxygenated Fe atom of heme in a CYP protein. The CYP3A4 enzyme is highly flexible and can take significantly different conformations depending on the ligand with which it is being bound. To predict the accessibility of substrate atoms to the heme iron, conventional protein-rigid docking methods failed due to the high flexibility of the CYP3A4 protein. Herein, we demonstrated and compared the ability of the Glide extra precision (XP) and Induced Fit docking (IFD) tool of Schrodinger software suite to reproduce the binding mode of co-crystallized ligands into six X-ray crystallographic structures. We extend our studies toward the prediction of SOM for compounds whose experimental SOM is reported but the ligand-enzyme complex crystal structure is not available in the Protein Data Bank (PDB). The quality and accuracy of Glide XP and IFD was determined by calculating RMSD of docked ligands over the corresponding co-crystallized bound ligand and by measuring the distance between the SOM of the ligand and Fe atom of heme. It was observed that IFD reproduces the exact binding mode of available co-crystallized structures and correctly predicted the SOM of experimentally reported compounds. Our approach using IFD with multiple conformer structures of CYP3A4 will be one of the effective methods for SOM prediction.

Structural and clinical impact of anti-allergy agents: An overview

Allergic disorders are markedly rising in industrialized countries. The identification of compounds that trigger the immunoglobulin E (IgE)-dependent allergic reaction remain the means to improve the quality of life by limiting patient's exposure to critical allergens. Information concerning the treatment and onset of allergic disorders including atopic dermatitis, allergic rhinitis, and bronchial asthma has been provided by the research over the past decade. Recent studies also indicated that allergic inflammation is associated closely with their exacerbation and progression and indeed is the basic pathophysiology of allergic diseases. As a result of immunological and molecular biological studies our understanding of the mechanism of allergic inflammation with regard to therapeutic agents has improved. While much effort has been paid to developing a new anti-allergic agent, the allergic disease has yet to be completely conquered. The more extensive research will allow the development of new therapeutics to combat allergic diseases. Currently, with respect to mechanism of action anti-allergy drugs are classified into five types including histamine H₁ antagonists, leukotriene antagonists, Th₂ cytokine inhibitors, thromboxane A₂ inhibitors and mediator-release inhibitors. The use of two or more anti-allergy agents together is not acknowledged at present, but this will be the subject of research in the future because with different mechanisms of action anti-allergy agents used at the same time will theoretically increase their effects. This review article focuses on anti-allergy agents highlighting their applications, clinical trials and recent advancement on drugs.

Microbial Bioconversion: A Regio-specific Method for Novel Drug Design and Toxicological Study of Metabolites

The methods of chemical structural alteration of small organic molecules by using microbes (fungi, bacteria, yeast, etc.) are gaining tremendous attention to obtain structurally novel and therapeutically potential leads. The regiospecific mild environmental friendly reaction conditions with the ability of novel chemical structural modification in compounds categorize this technique; a distinguished and unique way to obtain medicinally important drugs and their in vivo mimic metabolites with costeffective and timely manner. This review article shortly addresses the immense pharmaceutical importance of microbial transformation methods in drug designing and development as well as the role of CYP450 enzymes in fungi to obtain in vivo drug metabolites for toxicological studies.

Drug-Drug Interaction Discovery: Kernel Learning from Heterogeneous Similarities

We develop a pipeline to mine complex drug interactions by combining different similarities and interaction types (molecular, structural, phenotypic, genomic etc). Our goal is to learn an optimal kernel from these heterogeneous similarities in a supervised manner. We formulate an extensible framework that can easily integrate new interaction types into a rich model. The core of our pipeline features a novel kernel-learning approach that tunes the weights of the heterogeneous similarities, and fuses them into a Similarity-based Kernel for Identifying Drug-Drug interactions and Discovery, or SKID3. Experimental evaluation on the DrugBank database shows that SKID3 effectively combines similarities generated from chemical reaction pathways (which generally improve precision) and molecular and structural fingerprints (which generally improve recall) into a single kernel that gets the best of both worlds, and consequently demonstrates the best performance.

Rosehip inhibits xanthine oxidase activity and reduces serum urate levels in a mouse model of hyperuricemia

Rosehip, the fruit of Rosa canina L., has traditionally been used to treat urate metabolism disorders; however, its effects on such disorders have not been characterized in detail. Therefore, the present study investigated the effects of hot water, ethanol and ethyl acetate extracts of rosehip on xanthine oxidase (XO) activity in vitro. In addition, the serum urate lowering effects of the rosehip hot water extract in a mouse model of hyperuricemia (male ddY mice, which were intraperitoneally injected with potassium oxonate) were investigated. Furthermore, the influence of rosehip hot water extract on CYP3A4 activity, which is the most important drug-metabolizing enzyme from a herb-drug interaction perspective, was investigated. Rosehip extracts of hot water, ethanol and ethyl acetate inhibited XO activity [half maximal inhibitory concentration (IC50) values: 259.6±50.6, 242.5±46.2 and 1,462.8±544.2 µg/ml, respectively]. Furthermore, the administration of 1X rosehip hot water extract significantly reduced the levels of serum urate at 8 h, which was similar when compared with the administration of 1 mg/kg allopurinol. Rosehip hot water extract only marginally affected CYP3A4 activity (IC50 value, >1 mg/ml). These findings indicate that rosehip hot water extract may present as a functional food for individuals with a high urate level, and as a therapeutic reagent for hyperuricemic patients.

Application of multi-target phytotherapeutic concept in malaria drug discovery: a systems biology approach in biomarker identification

There is an urgent need for new anti-malaria drugs with broad therapeutic potential and novel mode of action, for effective treatment and to overcome emerging drug resistance. Plant-derived anti-malarials remain a significant source of bioactive molecules in this regard. The multicomponent formulation forms the basis of phytotherapy. Mechanistic reasons for the poly-pharmacological effects of plants constitute increased bioavailability, interference with cellular transport processes, activation of pro-drugs/deactivation of active compounds to inactive metabolites and action of synergistic partners at different points of the same signaling cascade. These effects are known as the multi-target concept. However, due to the intrinsic complexity of natural products-based drug discovery, there is need to rethink the approaches toward understanding their therapeutic effect. This review discusses the multi-target phytotherapeutic concept and its application in biomarker identification using the modified reverse pharmacology - systems biology approach. Considerations include the generation of a product library, high throughput screening (HTS) techniques for efficacy and interaction assessment, High Performance Liquid Chromatography (HPLC)-based anti-malarial profiling and animal pharmacology. This approach is an integrated interdisciplinary implementation of tailored technology platforms coupled to miniaturized biological assays, to track and characterize the multi-target bioactive components of botanicals as well as identify potential biomarkers. While preserving biodiversity, this will serve as a primary step towards the development of standardized phytomedicines, as well as facilitate lead discovery for chemical prioritization and downstream clinical development.

Stable isotope biomarker breath tests for human metabolic and infectious diseases: a review of recent patent literature

INTRODUCTION

Stable isotope breath tests can rapidly and quantitatively report metabolic phenotypes and disease in both humans and microbes in situ. The labelled compound is administered and acted upon by human or microbial metabolism, producing a labelled gas that is detected in exhaled breath. Areas covered: This review details the unique advantages (and disadvantages) of phenotypic stable isotope based breath tests. A review of recent US patent applications and prosecutions since 2010 is conducted. Finally, current clinical trials, product pipelines and approved products are discussed. Expert opinion: Stable isotope breath tests offer new approaches for rapid and minimally invasive detection and study of metabolic phenotypes, both human and microbial. The patent literature has developed considerably in the last 6 years, with over 30 patent applications made. Rates of issuance remain high, although rejections citing 35 U.S.C. §101(subject matter eligibility), §102 (novelty), §103 (obviousness) and §112 (description, enablement and best mode) have occurred. The prior art is significantly greater for human metabolism than microbial, and may drive differing rates of future issuance. These biomarker and diagnostic tools can enable optimization of drug doses, diagnosis of metabolic disease and its progression, and detection of infectious disease and optimize its treatment.

Frequency and clinical relevance of potential cytochrome P450 drug interactions in a psychiatric patient population - an analysis based on German insurance claims data

BACKGROUND

Numerous drugs used in the treatment of psychiatric disorders are substrates of cytochrome P450 enzymes and are potential candidates for drug-drug interactions (DDIs).

METHODS

Claims data of a German statutory health insurance company from severely mentally ill patients who registered in an integrated care contract from August 2004 to December 2009 were analysed. We measured time periods of concomitant prescription of drugs that have been reported to interact via cytochrome P450, with a focus on drugs acting as strong inhibitors. Such drug-drug exposure (DDE) is an incontrovertible precursor of DDIs. We assessed whether potential DDIs were considered clinically relevant based on the prescribing information of the respective drugs.

RESULTS

Among all 1221 patients, 186 patients (15.2 %; Clopper-Pearson 95 % confidence interval (CI): 13.3-17.4 %) had at least one DDE prescription, and 58 patients (4.8 %; 95 % CI 3.6-6.1) had at least one DDE prescription involving a strong cytochrome P450 inhibitor. In 59 patients, (4.8 %; 95 % CI: 3.7-6.2 %) five or more DDEs were identified, and five or more DDEs with a strong inhibitor were identified in 18 patients (1.5 %; 95 % CI: 0.9-2.3). The rates of DDEs were 0.27 (Garwood 95%CI: 0.25-0.28) per person-year and 0.07 (95 % CI: 0.07-0.08) for strong-inhibitor DDEs. Four of the ten most frequent DDEs were identified as clinically relevant, and seven of the eight most frequent DDEs involving a strong inhibitor were clinically relevant.

CONCLUSIONS

The number of patients with DDEs was not alarmingly high in our sample. Nevertheless, prescription information showed that some prescribed drug combinations could result in serious adverse consequences that are known to weaken or strengthen the effect of the drugs and should therefore be avoided.

In Silico Prediction of Cytochrome P450-Drug Interaction: QSARs for CYP3A4 and CYP2C9

Cytochromes P450 (CYP) are the main actors in the oxidation of xenobiotics and play a crucial role in drug safety, persistence, bioactivation, and drug-drug/food-drug interaction. This work aims to develop Quantitative Structure-Activity Relationship (QSAR) models to predict the drug interaction with two of the most important CYP isoforms, namely 2C9 and 3A4. The presented models are calibrated on 9122 drug-like compounds, using three different modelling approaches and two types of molecular description (classical molecular descriptors and binary fingerprints). For each isoform, three classification models are presented, based on a different approach and with different advantages: (1) a very simple and interpretable classification tree; (2) a local (k-Nearest Neighbor) model based classical descriptors and; (3) a model based on a recently proposed local classifier (N-Nearest Neighbor) on binary fingerprints. The salient features of the work are (1) the thorough model validation and the applicability domain assessment; (2) the descriptor interpretation, which highlighted the crucial aspects of P450-drug interaction; and (3) the consensus aggregation of models, which largely increased the prediction accuracy.

Reductive metabolism of oxymatrine is catalyzed by microsomal CYP3A4

Oxymatrine (OMT) is a pharmacologically active primary quinolizidine alkaloid with various beneficial and toxic effects. It is confirmed that, after oral administration, OMT could be transformed to the more toxic metabolite matrine (MT), and this process may be through the reduction reaction, but the study on the characteristics of this transformation is limited. The aim of this study was to investigate the characteristics of this transformation of OMT in the human liver microsomes (HLMs) and human intestinal microsomes (HIMs) and the cytochrome P450 (CYP) isoforms involved in this transformation. The current studies demonstrated that OMT could be metabolized to MT rapidly in HLMs and HIMs and CYP3A4 greatly contributed to this transformation. All HLMs, HIMs, and CYP3A4 isoform mediated reduction reaction followed typical biphasic kinetic model, and Km, Vmax, and CL were significant higher in HLMs than those in HIMs. Importantly, different oxygen contents could significantly affect the metabolism of OMT, and with the oxygen content decreased, the formation of metabolite was increased, suggesting this transformation was very likely a reduction reaction. Results of this in vitro study elucidated the metabolic pathways and characteristics of metabolism of OMT to MT and would provide a theoretical basis and guidance for the safe application of OMT.

The Effect of MGCD0103 on CYP450 Isoforms Activity of Rats by Cocktail Method

MGCD0103, an isotype-selective histone deacetylase inhibitor (HDACi), has been clinically evaluated for the treatment of hematologic malignancies and advanced solid tumors, alone and in combination with standard-of-care agents. In order to investigate the effects of MGCD0103 on the metabolic capacity of cytochrome P450 (CYP) enzymes, a cocktail method was employed to evaluate the activities of human CYP2B1, CYP1A2, CYP2C11, CYP2D6, CYP3A4, and CYP2C9. The rats were randomly divided into MGCD0103 group (Low, Medium, and High) and control group. The MGCD0103 group rats were given 20, 40, and 80 mg/kg (Low, Medium, and High) MGCD0103 by continuous intragastric administration for 7 days. Six probe drugs, bupropion, phenacetin, tolbutamide, metoprolol, testosterone, and omeprazole, were given to rats through intragastric administration, and the plasma concentrations were determined by UPLC-MS/MS. Statistical pharmacokinetics difference for tolbutamide in rats were observed by comparing MGCD0103 group with control group. Continuous 7-day intragastric administration of MGCD0103 slightly induces the activities of CYP2C11 of rats.

Risk factors associated with adverse reactions to antituberculosis drugs

This review sought to identify the available scientific evidence on risk factors associated with adverse reactions to antituberculosis drugs. We performed a systematic review of studies published in the 1965-2012 period and indexed in the MEDLINE and LILACS databases. A total of 1,389 articles were initially selected. After reading their abstracts, we selected 85 studies. Of those 85 studies, 16 were included in the review. Risk factors for adverse reactions to antituberculosis drugs included age > 60 years, treatment regimens, alcoholism, anemia, and HIV co-infection, as well as sodium, iron, and albumin deficiency. Protective factors against hepatic adverse effects of antituberculosis drugs included being male (combined OR = 0.38; 95% CI: 0.20-0.72) and showing a rapid/intermediate N-acetyltransferase 2 acetylator phenotype (combined OR = 0.41; 95% CI: 0.18-0.90). There is evidence to support the need for management of adverse reactions to antituberculosis drugs at public health care facilities.

Mechanism-based inhibition of Alantolactone on human cytochrome P450 3A4 in vitro and activity of hepatic cytochrome P450 in mice

ETHNOPHARMACOLOGICAL RELEVANCE

Alantolactone (AL), one of the main active ingredients in Inula helenium L., has been included in various prescriptions of traditional Chinese medicine. The effects of AL on cytochrome P450 (CYP450) were still unclear. This study evaluated the inhibitory effect of AL on cytochrome P450s in vitro and in vivo.

MATERIALS AND METHODS

The inhibitory effects of AL on the CYPs activity were evaluated in human liver microsomes (HLMs) and recombinant cDNA-expressed enzymes incubation system, and then determined by LC-MS/MS based CYPs probe substrate assay. C57BL/6 mice were treated AL orally (0, 25, 50, 100 mg/kg) for 15 days. The inhibitory effects of AL on major Cyps in mice were examined at both the mRNA and enzyme activity levels.

RESULTS

AL showed a potent inhibitory effect on CYP3A4 activity with IC50 values of 3.599 (HLMs) and 3.90 (recombinant CYP3A4) μM, respectively. AL strongly decreased CYP3A4 activity in a dose-dependent but not time-dependent way in HLMs. Results from typical Lineweaver-Burk plots showed that AL could inhibit CYP3A4 activity noncompetitively, with a Ki value of 1.09 μM in HLMs. Moreover, activity of CYP2C19 could also be inhibited by AL with IC50 of 36.82 μM. Other CYP450 isoforms were not markedly affected by AL. The inhibition was also validated by in vivo study of mice. AL significantly decreased mRNA expression of Cyp2c and 3a family.

CONCLUSION

The study indicates that herb-drug interaction should be paid more attention between AL and drugs metabolized by CYP3A4.

Evaluation of the impact of Polygonum capitatum, a traditional Chinese herbal medicine, on rat hepatic cytochrome P450 enzymes by using a cocktail of probe drugs

ETHNOPHARMACOLOGICAL RELEVANCE

Polygonum capitatum is a well-known Miao medicinal plant that has been used for many years for its unique therapeutic effects on various urological disorders, including urinary calculus and urinary tract infections. To investigate the effect of Polygonum capitatum on cytochrome P450 (CYP) isoforms (CYP1A2, CYP2C9, CYP2C19, CYP2E1, and CYP3A4) in vivo using a "cocktail" approach by administering five probe drugs to rats. This study assessed the potential of Polygonum capitatum to interact with co-administered drugs.

MATERIALS AND METHODS

An aqueous extract of dried whole Polygonum capitatum was prepared and administered orally to rats at a dose of 0.58g/kg or 1.74g/kg twice daily for 7 or 14 consecutive days. A cocktail of caffeine (1.0mg/kg), tolbutamide (1.0mg/kg), omeprazole (2.0mg/kg), chlorzoxazone (4.0mg/kg) and midazolam (4.0mg/kg) was then administered on the eighth or fifteenth day to evaluate the effects of Polygonum capitatum on CYP1A2, 2C9, 2C19, 2E1, and 3A4, respectively. Blood samples were collected at a range of time-points and the plasma concentrations of the probe drugs were simultaneously quantified using ultra high-performance liquid chromatography-tandem mass spectrometry. Pharmacokinetic parameters were calculated to evaluate the effects of Polygonum capitatum on the activities of these CYP enzymes in rats.

RESULTS

Polygonum capitatum pre-treatment had no significant effect on the pharmacokinetic parameters of caffeine, omeprazole or chlorzoxazone. However, the pharmacokinetics of tolbutamide and midazolam were affected significantly (P<0.05) by Polygonum capitatum, which induced more rapid metabolism of these probe compounds.

CONCLUSIONS

These results suggested that Polygonum capitatum could induce CYP2C9 and CYP3A4, and did not influence CYP1A2, CYP2C19 or CYP2E1. Therefore, the clinical dose of drugs metabolized by human CYP2C9 or CYP3A4 may need to be adjusted in patients taking Polygonum capitatum, as this herbal medication may result in reduced effective concentrations of these drugs.

Role of CYP3A in regulating hepatic clearance and hepatotoxicity of triptolide in rat liver microsomes and sandwich-cultured hepatocytes

Triptolide (TP) is an active component of Tripterygium wilfordii Hook. F and widely used to treat autoimmune and inflammatory diseases. It has been demonstrated that cytochrome P450 (CYP) are involved in the metabolism of TP. However, the underlying mechanisms of TP-induced toxicity mediated by hepatic CYP have not been well delineated. In this study, rat liver microsomes (RLM) and sandwich-cultured rat hepatocytes (SCRH) were used to identify the mechanism involving the CYP3A inhibition by TP and to evaluate TP-induced liver damage after CYP3A modulation by the known inhibitor, ketoconazole, and the known inducer, dexamethasone. The results showed that TP itself had a time- and concentration-dependent inhibitory effect on CYP3A. When the CYP3A inhibitor and inducer were added, the enzyme activity and hepatotoxicity changed significantly. The enzyme inducer increased CYP3A activity and decreased the metabolic half life (t1/2) of TP when compared to the control group, while the enzyme inhibitor had an opposite effect. Our findings reveal that TP is a weak CYP3A inhibitor involving the time-dependent inhibition mechanism. The induction or inhibition of CYP3A played an important role in TP-induced hepatotoxicity. Clinicians should be aware of the metabolic characteristics of TP to maximize therapeutic efficacy and reduce TP-induced toxicity.

Pretreatment with turmeric modulates the inhibitory influence of cisplatin and paclitaxel on CYP2E1 and CYP3A1/2 in isolated rat hepatic microsomes

Previous animal studies have shown that turmeric can significantly modulate the activity of several drug metabolizing enzymes, this may dramatically affect the bioavailability of several drugs resulting in over dose or less therapeutic effects. This study was directed to evaluate the inhibitory effects of cisplatin and paclitaxel on two CYP450 enzymes namely CYP2E1 and CYP3A1/2 in hepatic microsomes isolated from normal and turmeric pretreated rats. Cisplatin and paclitaxel were added by different concentrations to hepatic microsomes isolated from untreated and turmeric (100 mg/kg/day) pretreated rats for 15 days after receiving pyrazole or dexamethasone for induction of CYP2E1 and CYP3A1/2 respectively. The kinetic potency of these drugs as CYP inhibitors was determined by analysis of Lineweaver-Burk plot. Addition of cisplatin or paclitaxel by (10, 50 and 100 μM) to hepatic microsomes from normal or turmeric pretreated rats caused a concentration dependent inhibition of CYP2E1, with an evidence of less inhibition in turmeric pretreated microsomes particularly at higher concentration. Both drugs at 100 μM displayed a mixed type of inhibition of CYP2E1 in normal or turmeric pretreated microsomes where paclitaxel was the most potent inhibitor. Cisplatin (10, 50 and 100 μM) caused a concentration dependant inhibition of CYP3A1/2 that was enhanced by turmeric pretreatment. The inhibition of CYP3A1/2 by cisplatin (100 μM) was in non-competitive manner with a smaller Ki value in turmeric pretreated microsomes. The inhibitory influence of paclitaxel (10, 50 and 100 μM) on CYP3A1/2 decreased with increasing the drug concentration and this inhibition was augmented by turmeric pretreatment. Interestingly, the inhibition of this enzyme by paclitaxel (10 μM) was switched from mixed type in normal microsomes to competitive manner in turmeric pretreated ones with a marked reduction of Ki values reflecting greater inhibitory influence of paclitaxel on CYP3A1/2 by turmeric pretreatment. In conclusion, turmeric pretreatment attenuated the inhibitory influence of cisplatin and paclitaxel on CYP2E1 activity and magnified their inhibition on CYP3A1/2, thus the use of turmeric with drugs or other medications should raise concern for drugs-herb interactions.

The effect of the Pheroid delivery system on the in vitro metabolism and in vivo pharmacokinetics of artemisone

OBJECTIVES

The objectives were to determine the pharmacokinetics (PK) of artemisone and artemisone formulated in the Pheroid® drug delivery system in primates and to establish whether the formulation affects the in vitro metabolism of artemisone in human and monkey liver and intestinal microsomes.

METHODS

For the PK study, a single oral dose of artemisone was administered to vervet monkeys using a crossover design. Plasma samples were analyzed by means of liquid chromatography-tandem mass spectrometry. For the in vitro metabolism study, clearance was determined using microsomes and recombinant CYP3A4 enzymes, and samples were analyzed by means of ultra-performance liquid chromatography quadrupole time-of-flight mass spectrometry.

RESULTS

Artemisone and M1 plasma levels were unexpectedly low compared to those previously recorded in rodents and humans. The in vitro intrinsic clearance (CLint) of the reference formulation with monkey liver microsomes was much higher (1359.33 ± 103.24 vs 178.86 ± 23.42) than that of human liver microsomes. The in vitro data suggest that microsomal metabolism of artemisone is inhibited by the Pheroid delivery system.

CONCLUSIONS

The in vivo results obtained in this study indicate that the Pheroid delivery system improves the PK profile of artemisone. The in vitro results indicate that microsomal metabolism of artemisone is inhibited by the Pheroid delivery system.

A Comparison of the In Vitro Inhibitory Effects of Thelephoric Acid and SKF-525A on Human Cytochrome P450 Activity

Thelephoric acid is an antioxidant produced by the hydrolysis of polyozellin, which is isolated from Polyozellus multiplex. In the present study, the inhibitory effects of polyozellin and thelephoric acid on 9 cytochrome P450 (CYP) family members (CYP1A2, CYP2A6, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP2E1, and CYP3A4) were examined in pooled human liver microsomes (HLMs) using a cocktail probe assay. Polyozellin exhibited weak inhibitory effects on the activities of all 9 CYPs examined, whereas thelephoric acid exhibited dose- and time-dependent inhibition of all 9 CYP isoforms (IC50 values, 3.2-33.7 μM). Dixon plots of CYP inhibition indicated that thelephoric acid was a competitive inhibitor of CYP1A2 and CYP3A4. In contrast, thelephoric acid was a noncompetitive inhibitor of CYP2D6. Our findings indicate that thelephoric acid may be a novel, non-specific CYP inhibitor, suggesting that it could replace SKF-525A in inhibitory studies designed to investigate the effects of CYP enzymes on the metabolism of given compounds.

Traditional usage, phytochemistry and pharmacology of the South African medicinal plant Boophone disticha (L.f.) Herb. (Amaryllidaceae)

ETHNOPHARMACOLOGICAL RELEVANCE

Boophone disticha is the most common member of the South African Amaryllidaceae used extensively in traditional medicine of the various indigenous population groups, including the Sotho, Xhosa and Zulu as well as the San. This survey was carried out to identify and highlight areas relevant to the traditional usage of Boophone disticha. Pharmacological aspects were examined with the purpose of reconciling these with the traditional usage of the plant. In relation to phytochemical make-up, particular attention was paid on how its alkaloid constitution might corroborate the various biological effects manifested by the plant.

MATERIALS AND METHODS

Information gathering involved the use of four different database platforms, including Google Scholar, ScienceDirect, SciFinder(®) and Scopus. Arrangement and detailing of this information is as reflected in the various sections of the paper.

RESULTS

Sixteen categories were identified under which Boophone disticha finds use in traditional medicine. These were shown to include general usage purposes, such as 'cultural and dietary', 'well-being', 'personal injury', 'divinatory purposes', 'psychoactive properties' and 'veterinary uses'. Furthermore, traditional usage was seen to involve six body systems, including functions pertaining to the circulatory, gastrointestinal, muscular, neurological, respiratory and urinary systems. The four remaining categories relate to use for inflammatory conditions, cancer, malaria and tuberculosis. Overall, three areas were discernible in which Boophone disticha finds most usage, which are (i) ailments pertaining to the CNS, (ii) wounds and infections, and (iii) inflammatory conditions. In addition, several aspects pertaining to the toxic properties of the plant are discussed, including genotoxicity, mutagenicity and neurotoxicity.

CONCLUSION

The widespread ethnic usage of Boophone disticha has justified its standing as a flagship for the Amaryllidaceae and its relevance to South African traditional medicine. Furthermore, its promising pharmacological and phytochemical profiles have stimulated significant interest in the clinical realm, especially in the areas of cancer and motor neuron disease chemotherapy. These collective properties should prove useful in steering the progress of the plant towards a wider audience.

High-throughput metabolic genotoxicity screening with a fluidic microwell chip and electrochemiluminescence

A high throughput electrochemiluminescent (ECL) chip was fabricated and integrated into a fluidic system for screening toxicity-related chemistry of drug and pollutant metabolites. The chip base is conductive pyrolytic graphite onto which are printed 64 microwells capable of holding one-μL droplets. Films combining DNA, metabolic enzymes and an ECL-generating ruthenium metallopolymer (Ru(II)PVP) are fabricated in these microwells. The system runs metabolic enzyme reactions, and subsequently detects DNA damage caused by reactive metabolites. The performance of the chip was tested by measuring DNA damage caused by metabolites of the well-known procarcinogen benzo[a]pyrene (B[a]P). Liver microsomes and cytochrome P450 (cyt P450) enzymes were used with and without epoxide hydrolase (EH), a conjugative enzyme required for multi-enzyme bioactivation of B[a]P. DNA adduct formation was confirmed by determining specific DNA-metabolite adducts using similar films of DNA/enzyme on magnetic bead biocolloid reactors, hydrolyzing the DNA, and analyzing by capillary liquid chromatography-mass spectrometry (CapLC-MS/MS). The fluidic chip was also used to measure IC50-values of inhibitors of cyt P450s. All results show good correlation with reported enzyme activity and inhibition assays.

Effects of aescin on cytochrome P450 enzymes in rats

ETHNOPHARMACOLOGICAL RELEVANCE

Aescin, the main active component found in extracts of horse chestnut (Aesculus hippocastanum) seed a traditional medicinal herb, is a mixture of triterpene saponins. It has been shown to be effective in inflammatory, chronic venous and edematous treatment conditions in vitro and in vivo, and is broadly used to treat chronic venous insufficiency. The purpose of this study was to find out whether aescin influences the effect on rat cytochrome P450 (CYP) enzymes (CYP1A2, CYP2C9, CYP2E1 and CYP3A4) by using cocktail probe drugs in vivo; the influence on the levels of CYP mRNA was also studied.

MATERIALS AND METHODS

A cocktail solution at a dose of 5mL/kg, which contained phenacetin (20mg/kg), tolbutamide (5mg/kg), chlorzoxazone (20mg/kg) and midazolam (10mg/kg), was given as oral administration to rats treated with a single dose or multiple doses of intravenous aescin via the caudal vein. Blood samples were collected at a series of time-points and the concentrations of probe drugs in plasma were determined by HPLC-MS/MS. The corresponding pharmacokinetic parameters were calculated by the software of DAS 2.0. In addition, real-time RT-PCR was performed to determine the effects of aescin on the mRNA expression of CYP1A2, CYP2C9, CYP2E1 and CYP3A4 in rat liver.

RESULTS

Treatment with a single dose or multiple doses of aescin had inductive effects on rat CYP1A2, while CYP2C9 and CYP3A4 enzyme activities were inhibited. Moreover, aescin has no inductive or inhibitory effect on the activity of CYP2E1. The mRNA expression results were in accordance with the pharmacokinetic results.

CONCLUSIONS

Aescin can either inhibit or induce activities of CYP1A2, CYP2C9 and CYP3A4. Therefore, caution is needed when aescin is co-administration with some CYP1A2, CYP2C9 or CYP3A4 substrates in clinic, which may result in treatment failure and herb-drug interactions.

Functional influence of human CYP2D6 allelic variations: P34S, E418K, S486T, and R296C

CYP2D6 is responsible for the oxidative metabolism of 20-25 % of clinical drugs and its genetic polymorphisms can significantly influence the drug metabolism. In this study, we analyzed the functional activities of four nonsynonymous single nucleotide polymorphisms from CYP2D6*52 allele, which were recently found, and one found frequently in CYP2D6 alleles. Recombinant variant enzymes of E418K, S486T, and R296C were successfully expressed in Escherichia coli and purified. However, a CYP holoenzyme spectrum of P34S variant was not detected in E. coli whole cell level. Structural analysis indicated that P34S mutation seemed to perturb a highly conserved proline-rich N-terminus of CYP2D6. Steady state kinetic analyses showed the significant reductions of enzymatic activities in E418K and R296C variants. In the case of bufuralol 1'-hydroxylation, a novel mutant, E418K, showed 32 % decrease in catalytic efficiency (k cat/K m) mainly due to the decrease of k cat value. R296C showed much greater reduction in the catalytic efficiency (9 % of wild-type) due to both of a decrease of k cat value and an increase of K m value. In the case of dextromethorphan O-demethylation, E418K showed both of a decrease of k cat value and an increase K m value to result in ~43 % reduction of catalytic efficiency. A highly decreased catalytic efficiency (~6 % of wild-type) in the mutant of R296C also was observed mainly due to the dramatic change of k cat value of dextromethorphan O-demethylation. These results suggested that individuals carrying these allelic variants are likely to have the altered metabolic abilities of many clinical drugs therefore, these polymorphisms of CYP2D6 should be much concerned for reliable drug treatment.

PXR antagonists and implication in drug metabolism

Adopted orphan nuclear receptor (NR), pregnane X receptor (PXR), plays a central role in the regulation of xeno- and endobiotic metabolism. Since the discovery of the functional role of PXR in 1998, there is evolving evidence for the role of PXR agonists in abrogating metabolic pathophysiology (e.g., cholestasis, hypercholesterolemia, and inflammation). However, more recently, it is clear that PXR is also an important mediator of adverse xeno- (e.g., enhances acetaminophen toxicity) and endobiotic (e.g., hepatic steatosis) metabolic phenotypes. Moreover, in cancer therapeutics, PXR activation can induce drug resistance, and there is growing evidence for tissue-specific enhancement of the malignant phenotype. Thus, in these instances, there may be a role for PXR antagonists. However, as opposed to the discovery efforts for PXR agonists, there are only a few antagonists described. The mode of action of these antagonists (e.g., sulforaphane) remains less clear. Our laboratory efforts have focused on this question. Since the original discovery of azoles analogs as PXR antagonists, we have preliminarily defined an important PXR antagonist pharmacophore and developed less-toxic PXR antagonists. In this review, we describe our published and unpublished findings on recent structure-function studies involving the azole chemical scaffold. Further work in the future is needed to fully define potent, more-selective PXR antagonists that may be useful in clinical application.