VALIDATED ASSAYS FOR HUMAN CYTOCHROME P450 ACTIVITIES

In vitro and in vivo preclinical pharmacokinetic characterization of aficamten, a small molecule cardiac myosin inhibitor

Aficamten, a small molecule selective inhibitor of cardiac myosin, was characterised in preclinical in vitro and in vivo studies.Protein binding in human plasma was 10.4% unbound and ranged from 1.6% to 24.9% unbound across species. Blood-to-plasma ratios ranged from 0.69 to 1.14 across species. Aficamten hepatic clearance in human was predicted to be low from observed high metabolic stability in vitro in human liver microsomes. Aficamten demonstrated high permeability in Caco-2 cell monolayers.Aficamten in vivo clearance was low across species at 8.8, 2.1, 3.3, and 11 mL/min/kg in mouse, rat, dog, and monkey, respectively. The volume of distribution was low-to-high ranging from 0.53 in rat to 11 L/kg in dog. Oral bioavailability ranged from 41% in monkey to 98% in mouse.Aficamten was metabolised in vitro to eight metabolites with hydroxylated metabolites M1a and M1b predominating. CYP phenotyping indicated multiple CYPs (2C8, 2C9, 2D6, and 3A4) contributing to the metabolism of aficamten.Human clearance (1.1 mL/min/kg) and volume of distribution (6.5 L/kg) were predicted using 4-species allometry employing 'rule-of-exponents'. A predicted 69 hour half-life is consistent with observed half-life in human Phase-1.No CYP-based drug-drug interaction liability as a precipitant was predicted for aficamten.

A Second-Generation Oral SARS-CoV-2 Main Protease Inhibitor Clinical Candidate for the Treatment of COVID-19

Despite the record-breaking discovery, development and approval of vaccines and antiviral therapeutics such as Paxlovid, coronavirus disease 2019 (COVID-19) remained the fourth leading cause of death in the world and third highest in the United States in 2022. Here, we report the discovery and characterization of PF-07817883, a second-generation, orally bioavailable, SARS-CoV-2 main protease inhibitor with improved metabolic stability versus nirmatrelvir, the antiviral component of the ritonavir-boosted therapy Paxlovid. We demonstrate the in vitro pan-human coronavirus antiviral activity and off-target selectivity profile of PF-07817883. PF-07817883 also demonstrated oral efficacy in a mouse-adapted SARS-CoV-2 model at plasma concentrations equivalent to nirmatrelvir. The preclinical in vivo pharmacokinetics and metabolism studies in human matrices are suggestive of improved oral pharmacokinetics for PF-07817883 in humans, relative to nirmatrelvir. In vitro inhibition/induction studies against major human drug metabolizing enzymes/transporters suggest a low potential for perpetrator drug-drug interactions upon single-agent use of PF-07817883.

HLM chip - A microfluidic approach to study the mechanistic basis of cytochrome P450 inhibition using immobilized human liver microsomes

Cytochrome P450 (CYP) system is a critical elimination route to most pharmaceuticals in human, but also prone to drug-drug interactions arising from the fact that concomitantly administered pharmaceuticals inhibit one another's CYP metabolism. The most severe form of CYP interactions is irreversible inhibition, which results in permanent inactivation of the critical CYP pathway and is only restored by de novo synthesis of new functional enzymes. In this study, we conceptualize a microfluidic approach to mechanistic CYP inhibition studies using human liver microsomes (HLMs) immobilized onto the walls of a polymer micropillar array. We evaluated the feasibility of these HLM chips for CYP inhibition studies by establishing the stability and the enzyme kinetics for a CYP2C9 model reaction under microfluidic flow and determining the half-maximal inhibitory concentrations (IC50) of three human CYP2C9 inhibitors (sulfaphenazole, tienilic acid, miconazole), including evaluation of their inhibition mechanisms and nonspecific microsomal binding on chip. Overall, the enzyme kinetics of CYP2C9 metabolism on the HLM chip (KM = 127 ± 55 µM) was shown to be similar to that of static HLM incubations (KM = 114 ± 14 µM) and the IC50 values toward CYP2C9 derived from the microfluidic assays (sulfaphenazole 0.38 ± 0.09 µM, tienilic acid 3.4 ± 0.6 µM, miconazole 0.54 ± 0.09 µM) correlated well with those determined using current standard IC50 shift assays. Most importantly, the HLM chip could distinguish between reversible (sulfaphenazole) and irreversible (tienilic acid) enzyme inhibitors in a single, automated experiment, indicating the great potential of the HLM chip to simplify current workflows used in mechanistic CYP inhibition studies. Furthermore, the results suggest that the HLM chip can also identify irreversible enzyme inhibitors, which are not necessarily resulting in a time-dependent inhibition (like suicide inhibitors), but whose inhibition mechanism is based on other kind of covalent or irreversible interaction with the CYP system. With our HLM chip approach, we could identify miconazole as such a compound that nonselectively inhibits the human CYP system with a prolonged, possibly irreversible impact in vitro, even if it is not a time-dependent inhibitor according to the IC50 shift assay.

Identification of New Substrates and Inhibitors of Human CYP2A7

CYP2A7 is one of the most understudied human cytochrome P450 enzymes and its contributions to either drug metabolism or endogenous biosynthesis pathways are not understood, as its only known enzymatic activities are the conversions of two proluciferin probe substrates. In addition, the CYP2A7 gene contains four single-nucleotide polymorphisms (SNPs) that cause missense mutations and have minor allele frequencies (MAFs) above 0.5. This means that the resulting amino acid changes occur in the majority of humans. In a previous study, we employed the reference standard sequence (called CYP2A7*1 in P450 nomenclature). For the present study, we created another CYP2A7 sequence that contains all four amino acid changes (Cys311, Glu169, Gly479, and Arg274) and labeled it CYP2A7-WT. Thus, it was the aim of this study to identify new substrates and inhibitors of CYP2A7 and to compare the properties of CYP2A7-WT with CYP2A7*1. We found several new proluciferin probe substrates for both enzyme variants (we also performed in silico studies to understand the activity difference between CYP2A7-WT and CYP2A7*1 on specific substrates), and we show that while they do not act on the standard CYP2A6 substrates nicotine, coumarin, or 7-ethoxycoumarin, both can hydroxylate diclofenac (as can CYP2A6). Moreover, we found ketoconazole, 1-benzylimidazole, and letrozole to be CYP2A7 inhibitors.

High-throughput assay to simultaneously evaluate activation of CYP3A and the direct and time-dependent inhibition of CYP3A, CYP2C9, and CYP2D6 using liquid chromatography-tandem mass spectrometry

In the early stages of drug discovery, adequate evaluation of the potential drug-drug interactions (DDIs) of drug candidates is important. Several CYP3A activators are known to lead to underestimation of DDIs. These compounds affect midazolam 1'-hydroxylation but not midazolam 4-hydroxylation.We used both metabolic reactions of midazolam to evaluate the activation and inhibition of CYP3A activators simultaneously. For our CYP inhibition assay using cocktail probe substrates, simultaneous liquid chromatography-tandem mass spectrometry monitoring of 1'-hydroxymidazolam and 4-hydroxymidazolam for CYP3A was established in addition to monitoring of 4-hydroxydiclofenac and 1'-hydroxybufuralol for CYP2C9 and CYP2D6.The results of our cocktail inhibition assay were well correlated with those of a single inhibition assay, as were the estimated inhibition parameters for typical CYP3A inhibitors. In our assay, a proprietary compound that activated midazolam 1'-hydroxylation and tended to inhibit 4-hydroxylation was evaluated along with known CYP3A activators. All compounds were well characterised by comparison of the results of midazolam 1'- and 4-hydroxylation.In conclusion, our CYP cocktail inhibition assay can detect CYP3A activation and assess the direct and time-dependent inhibition potentials for CYP3A, CYP2C9, and CYP2D6. This method is expected to be very efficient in the early stages of drug discovery.

A Review of CYP-Mediated Drug Interactions: Mechanisms and In Vitro Drug-Drug Interaction Assessment

Drug metabolism is a major determinant of drug concentrations in the body. Drug-drug interactions (DDIs) caused by the co-administration of multiple drugs can lead to alteration in the exposure of the victim drug, raising safety or effectiveness concerns. Assessment of the DDI potential starts with in vitro experiments to determine kinetic parameters and identify risks associated with the use of comedication that can inform future clinical studies. The diverse range of experimental models and techniques has significantly contributed to the examination of potential DDIs. Cytochrome P450 (CYP) enzymes are responsible for the biotransformation of many drugs on the market, making them frequently implicated in drug metabolism and DDIs. Consequently, there has been a growing focus on the assessment of DDI risk for CYPs. This review article provides mechanistic insights underlying CYP inhibition/induction and an overview of the in vitro assessment of CYP-mediated DDIs.

DNDI-6174 is a preclinical candidate for visceral leishmaniasis that targets the cytochrome bc1

New drugs for visceral leishmaniasis that are safe, low cost, and adapted to the field are urgently required. Despite concerted efforts over the last several years, the number of new chemical entities that are suitable for clinical development for the treatment of Leishmania remains low. Here, we describe the discovery and preclinical development of DNDI-6174, an inhibitor of Leishmania cytochrome bc1 complex activity that originated from a phenotypically identified pyrrolopyrimidine series. This compound fulfills all target candidate profile criteria required for progression into preclinical development. In addition to good metabolic stability and pharmacokinetic properties, DNDI-6174 demonstrates potent in vitro activity against a variety of Leishmania species and can reduce parasite burden in animal models of infection, with the potential to approach sterile cure. No major flags were identified in preliminary safety studies, including an exploratory 14-day toxicology study in the rat. DNDI-6174 is a cytochrome bc1 complex inhibitor with acceptable development properties to enter preclinical development for visceral leishmaniasis.

Novel Approaches to Characterize Individual Drug Metabolism and Advance Precision Medicine

Interindividual variability in drug metabolism can significantly affect drug concentrations in the body and subsequent drug response. Understanding an individual's drug metabolism capacity is important for predicting drug exposure and developing precision medicine strategies. The goal of precision medicine is to individualize drug treatment for patients to maximize efficacy and minimize drug toxicity. While advances in pharmacogenomics have improved our understanding of how genetic variations in drug-metabolizing enzymes (DMEs) affect drug response, nongenetic factors are also known to influence drug metabolism phenotypes. This minireview discusses approaches beyond pharmacogenetic testing to phenotype DMEs-particularly the cytochrome P450 enzymes-in clinical settings. Several phenotyping approaches have been proposed: traditional approaches include phenotyping with exogenous probe substrates and the use of endogenous biomarkers; newer approaches include evaluating circulating noncoding RNAs and liquid biopsy-derived markers relevant to DME expression and function. The goals of this minireview are to 1) provide a high-level overview of traditional and novel approaches to phenotype individual drug metabolism capacity, 2) describe how these approaches are being applied or can be applied to pharmacokinetic studies, and 3) discuss perspectives on future opportunities to advance precision medicine in diverse populations. SIGNIFICANCE STATEMENT: This minireview provides an overview of recent advances in approaches to characterize individual drug metabolism phenotypes in clinical settings. It highlights the integration of existing pharmacokinetic biomarkers with novel approaches; also discussed are current challenges and existing knowledge gaps. The article concludes with perspectives on the future deployment of a liquid biopsy-informed physiologically based pharmacokinetic strategy for patient characterization and precision dosing.

Assessment of the potential of the MET inhibitor tepotinib to affect the pharmacokinetics of CYP3A4 and P-gp substrates

Tepotinib is a highly selective, potent, mesenchymal-epithelial transition factor (MET) inhibitor, approved for the treatment of non-small cell lung cancer harboring MET exon 14 skipping alterations. The aims of this work were to investigate the potential for drug-drug interactions via cytochrome P450 (CYP) 3A4/5 or P-glycoprotein (P-gp) inhibition. In vitro studies were conducted in human liver microsomes, human hepatocyte cultures and Caco-2 cell monolayers to investigate whether tepotinib or its major metabolite (MSC2571109A) inhibited or induced CYP3A4/5 or inhibited P-gp. Two clinical studies were conducted to investigate the effect of multiple dose tepotinib (500 mg once daily orally) on the single dose pharmacokinetics of a sensitive CYP3A4 substrate (midazolam 7.5 mg orally) and a P-gp substrate (dabigatran etexilate 75 mg orally) in healthy participants. Tepotinib and MSC2571109A showed little evidence of direct or time-dependent CYP3A4/5 inhibition (IC50 > 15 μM) in vitro, although MSC2571109A did show mechanism-based CYP3A4/5 inhibition. Tepotinib did not induce CYP3A4/5 activity in vitro, although both tepotinib and MSC2571109A increased CYP3A4 mRNA. In clinical studies, tepotinib had no effect on the pharmacokinetics of midazolam or its metabolite 1'-hydroxymidazolam. Tepotinib increased dabigatran maximum concentration and area under the curve extrapolated to infinity by 38% and 51%, respectively. These changes were not considered to be clinically relevant. Tepotinib was considered safe and well tolerated in both studies. The potential of tepotinib to cause clinically relevant DDI with CYP3A4- or P-gp-dependent drugs at the clinical dose is considered low. Study 1 (midazolam): NCT03628339 (registered 14 August 2018). Study 2 (dabigatran): NCT03492437 (registered 10 April 2018).

A Comparative Genomic and Phylogenetic Investigation of the Xenobiotic Metabolism Enzymes of Cytochrome P450 in Elephants Shows Loss in CYP2E and CYP4A

Cytochrome P450 is an important enzyme that metabolizes a variety of chemicals, including exogenous substances, such as drugs and environmental chemicals, and endogenous substances, such as steroids, fatty acids, and cholesterol. Some CYPs show interspecific differences in terms of genetic variation. As little is known about the mechanisms of elephant metabolism, we carried out a comparative genomic and phylogenetic analysis of CYP in elephants. Our results suggest that elephant CYP genes have undergone independent duplication, particularly in the CYP2A, CYP2C, and CYP3A genes, a unique cluster specific to elephant species. However, while CYP2E and CYP4A were conserved in other Afrotheria taxa, their decay in elephants resulted in genetic dysfunction (pseudogene). These findings outline several remarkable characteristics of elephant CYP1-4 genes and provide new insights into elephant xenobiotic metabolism. Further functional investigations are necessary to characterize elephant CYP, including expression patterns and interactions with drugs and sensitivities to other chemicals.

Rationally Engineered CYP3A4 Fluorogenic Substrates for Functional Imaging Analysis and Drug-Drug Interaction Studies

Cytochrome P450 3A4 (CYP3A4) is a key xenobiotic-metabolizing enzyme-mediated drug metabolism and drug-drug interaction (DDI). Herein, an effective strategy was used to rationally construct a practical two-photon fluorogenic substrate for hCYP3A4. Following two-round structure-based substrate discovery and optimization, we have successfully constructed a hCYP3A4 fluorogenic substrate (F8) with desirable features, including high binding affinity, rapid response, excellent isoform specificity, and low cytotoxicity. Under physiological conditions, F8 is readily metabolized by hCYP3A4 to form a brightly fluorescent product (4-OH F8) that can be easily detected by various fluorescence devices. The practicality of F8 for real-time sensing and functional imaging of hCYP3A4 has been examined in tissue preparations, living cells, and organ slices. F8 also demonstrates good performance for high-throughput screening of hCYP3A4 inhibitors and assessing DDI potentials in vivo. Collectively, this study develops an advanced molecular tool for sensing CYP3A4 activities in biological systems, which strongly facilitates CYP3A4-associated fundamental and applied research studies.

Rottlerin renders a selective and highly potent CYP2C8 inhibition to impede EET formation for implication in cancer therapy

CYP2C8 is a crucial CYP isoform responsible for the metabolism of xenobiotics and endogenous molecules. CYP2C8 converts arachidonic acid to epoxyeicosatrienoic acids (EETs) that cause cancer progression. Rottlerin possess significant anticancer actions. However, information on its CYP inhibitory action is lacking in the literature and therefore, we aimed to explore the same using in silico, in vitro, and in vivo approaches. Rottlerin showed highly potent and selective CYP2C8 inhibition (IC₅₀ < 0.1 μM) compared to negligible inhibition (IC₅₀ > 10 μM) for seven other experimental CYPs in human liver microsomes (HLM) (in vitro) using USFDA recommended index reactions. Mechanistic studies reveal that rottlerin could reversibly (mixed-type) block CYP2C8. Molecular docking (in silico) results indicate a strong interaction could occur between rottlerin and the active site of human CYP2C8. Rottlerin boosted the plasma exposure of repaglinide and paclitaxel (CYP2C8 substrates) by delaying their metabolism using the rat model (in vivo). Multiple-dose treatment of rottlerin with CYP2C8 substrates lowered the CYP2C8 protein expression and up-regulated & down-regulated the mRNA for CYP2C12 and CYP2C11 (rat homologs), respectively, in rat liver tissue. Rottlerin substantially hindered the EET formation in HLM. Overall results of rottlerin on CYP2C8 inhibition and EET formation insinuate further exploration for targeted cancer therapy.

Design, Synthesis, and Pharmacological Evaluation of Embelin-Aryl/alkyl Amine Hybrids as Orally Bioavailable Blood-Brain Barrier Permeable Multitargeted Agents with Therapeutic Potential in Alzheimer's Disease: Discovery of SB-1448

The complex and multifaceted nature of Alzheimer's disease has brought about a pressing demand to develop ligands targeting multiple pathways to combat its outrageous prevalence. Embelin is a major secondary metabolite of Embelia ribes Burm f., one of the oldest herbs in Indian traditional medicine. It is a micromolar inhibitor of cholinesterases (ChEs) and β-site amyloid precursor protein cleaving enzyme 1 (BACE-1) with poor absorption, distribution, metabolism, and excretion (ADME) properties. Herein, we synthesize a series of embelin-aryl/alkyl amine hybrids to improve its physicochemical properties and therapeutic potency against targeted enzymes. The most active derivative, 9j (SB-1448), inhibits human acetylcholinesterase (hAChE), human butyrylcholinesterase (hBChE), and human BACE-1 (hBACE-1) with IC₅₀ values of 0.15, 1.6, and 0.6 μM, respectively. It inhibits both ChEs noncompetitively with k_i values of 0.21 and 1.3 μM, respectively. It is orally bioavailable, crosses blood-brain barrier (BBB), inhibits Aβ self-aggregation, possesses good ADME properties, and protects neuronal cells from scopolamine-induced cell death. The oral administration of 9j at 30 mg/kg attenuates the scopolamine-induced cognitive impairments in C57BL/6J mice.

Contribution of UGT Enzymes to Human Drug Metabolism Stereoselectivity: A Case Study of Medetomidine, RO5263397, Propranolol, and Testosterone

The enantiomeric forms of chiral compounds have identical physical properties but may vary greatly in their metabolism by individual enzymes. Enantioselectivity in UDP-glucuronosyl transferase (UGT) metabolism has been reported for a number of compounds and with different UGT isoforms involved. However, the impact of such individual enzyme results on overall clearance stereoselectivity is often not clear. The enantiomers of medetomidine, RO5263397, and propranolol and the epimers testosterone and epitestosterone exhibit more than a 10-fold difference in glucuronidation rates by individual UGT enzymes. In this study, we examined the translation of human UGT stereoselectivity to hepatic drug clearance considering the combination of multiple UGTs to overall glucuronidation, the contribution of other metabolic enzymes such as cytochrome P450s (P450s), and the potential for differences in protein binding and blood/plasma partitioning. For medetomidine and RO5263397, the high individual enzyme (UGT2B10) enantioselectivity translated into ∼3- to >10-fold differences in predicted human hepatic in vivo clearance. For propranolol, the UGT enantioselectivity was irrelevant in the context of high P450 metabolism. For testosterone, a complex picture emerged due to differential epimeric selectivity of various contributing enzymes and potential for extrahepatic metabolism. Quite different patterns of P450- and UGT-mediated metabolism were observed across species, as well as differences in stereoselectivity, indicating that extrapolation from human enzyme and tissue data are essential when predicting human clearance enantioselectivity. SIGNIFICANCE STATEMENT: Individual enzyme stereoselectivity illustrates the importance of three-dimensional drug-metabolizing enzyme-substrate interactions and is essential when considering the clearance of racemic drugs. However, translation from in vitro to in vivo can be challenging as contributions from multiple enzymes and enzyme classes must be combined with protein binding and blood/plasma partitioning data to estimate the net intrinsic clearance for each enantiomer. Preclinical species may be misleading as enzyme involvement and metabolism stereoselectivity can differ substantially.

Effects of chronic cirrhosis induced by intraperitoneal thioacetamide injection on the protein content and Michaelis-Menten kinetics of cytochrome P450 enzymes in the rat liver microsomes

Chronic intraperitoneal injection of thioacetamide (TAA) in rats has been used as an animal model of human cirrhosis to study the effects of the disease on drug metabolism. However, TAA inhibits P450 enzymes directly and independently of cirrhosis. We investigated the effects of chronic cirrhosis in rats, induced by 10 weeks of intraperitoneal TAA, on the P450 enzymes after a 10-day washout period to eliminate TAA. Liver histology and serum biomarkers of hepatic function confirmed cirrhosis in all animals. Microsomal total P450 content, P450 reductase activity and ethoxycoumarin O-deethylase activity, a general marker of P450 activity, were significantly reduced by 30%-50% in cirrhotic animals. Additionally, the protein content and Michaelis-Menten kinetics of the activities of CYP2D, CYP2E1 and CYP3A were investigated. Whereas cirrhosis reduced the microsomal protein contents of CYP2D and CYP3A by 70% and 30%, respectively, the protein contents of CYP2E1 were not affected. However, the activities of all the tested isoenzymes were substantially lower in the cirrhotic livers. It is concluded that the TAA model of cirrhosis that incorporates a 10-day washout period after intraperitoneal injection of the chemical to rats produces isoenzyme-selective reductions in the P450 proteins or activities, which are independent of the direct inhibitory effects of TAA.

Formation of CYP3A-specific metabolites of ibrutinib in vitro is correlated with hepatic CYP3A activity and 4β-hydroxycholesterol/cholesterol ratio

Ibrutinib is an orally administered Bruton's tyrosine kinase inhibitor approved for the treatment of B-cell malignancies, including chronic lymphocytic leukemia. Ibrutinib is metabolized primarily via oxidation by cytochrome P450 (CYP) 3A4/5 to M37 (the primary active metabolite), M34, and M25. The objectives of this study were to assess the relationship between formation of the major CYP3A-specific ibrutinib metabolites in vitro and hepatic CYP3A activity and protein abundance, and to evaluate the utility of the endogenous CYP3A biomarker, plasma 4β-hydroxycholesterol (4β-HC) to cholesterol ratio, to predict ibrutinib metabolite formation in individual cadaveric donors with matching hepatocytes. Ibrutinib (5 μM) was incubated with single-donor human liver microsomes (n = 20) and primary human hepatocytes (n = 15), and metabolites (M37, M34, and M25) were measured by liquid chromatography-tandem mass spectrometry analysis. CYP3A4/5 protein concentrations were measured by quantitative targeted absolute proteomics, and CYP3A activity was measured by midazolam 1'-hydroxylation. Ibrutinib metabolite formation positively correlated with midazolam 1'-hydroxylation in human liver microsomes and hepatocytes. Plasma 4β-HC and cholesterol concentrations were measured in plasma samples obtained at the time of liver harvest from the same 15 donors with matching hepatocytes. Midazolam 1'-hydroxylation in hepatocytes correlated with plasma 4β-HC/cholesterol ratio. When an infant donor (1 year old) was excluded based on previous ontogeny studies, M37 and M25 formation correlated with plasma 4β-HC/cholesterol ratio in the remaining 14 donors (Spearman correlation coefficients [r] 0.62 and 0.67, respectively). Collectively, these data indicate a positive association among formation of CYP3A-specific ibrutinib metabolites in human hepatocytes, hepatic CYP3A activity, and plasma 4β-HC/cholesterol ratio in the same non-infant donors.

Qualification of Human Liver Microsomes for Antibacterial Activity Screening of Drug Metabolites

Microsomes are commonly used to perform in vitro drug metabolism, predominantly to form phase I drug metabolites. Pooled microsomes from multiple donors can contain microorganisms from underlying microbial diseases. Exposure to microbes can also occur during extraction if aseptic processing is compromised. Although microbial presence does not affect the metabolic activity of microsomes, presence of unwanted microorganisms can cause interference if the downstream application of microsomal drug metabolites is screening for antibacterial activity. In this work, traditional biochemical tests and advanced proteomics-based identification techniques were used to identify two gram-negative bacteria in pooled human liver microsomes. Several decontamination procedures were assessed to eradicate these two bacteria from the microsomes without affecting its metabolic capacity, and organic extraction was found to be the most convenient and efficient approach to decontaminate microsomes and screen drug metabolites for antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA).

What Is Known about Midazolam? A Bibliometric Approach of the Literature

Midazolam is a drug with actions towards the central nervous system producing sedative and anticonvulsants effects, used for sedation and seizures treatments. A better understanding about its effects in the different scenarios presented in the literature could be helpful to gather information regarding its clinical indications, pharmacological interactions, and adverse events. From this perspective, the aim of this study was to analyze the global research about midazolam mapping, specifically the knowledge of the 100 most-cited papers about this research field. For this, a search was executed on the Web of Science-Core Collection database using bibliometric methodological tools. The search strategy retrieved 34,799 articles. A total of 170 articles were evaluated, with 70 articles being excluded for not meeting the inclusion criteria. The 100 most-cited articles rendered 42,480 citations on WoS-CC, ranging from 253 to 1744. Non-systematic review was the most published study type, mainly from North America, during the period of 1992 to 2002. The most frequent keywords were midazolam and pharmacokinetics. Regarding the authors, Thummel and Kunze were the ones with the greatest number of papers included. Our findings showed the global research trends about midazolam, mainly related to its different effects and uses throughout the time.

Prospective Prediction of Dapaconazole Clinical Drug-Drug Interactions Using an In Vitro to In Vivo Extrapolation Equation and PBPK Modeling

This study predicted dapaconazole clinical drug−drug interactions (DDIs) over the main Cytochrome P450 (CYP) isoenzymes using static (in vitro to in vivo extrapolation equation, IVIVE) and dynamic (PBPK model) approaches. The in vitro inhibition of main CYP450 isoenzymes by dapaconazole in a human liver microsome incubation medium was evaluated. A dapaconazole PBPK model (Simcyp version 20) in dogs was developed and qualified using observed data and was scaled up for humans. Static and dynamic models to predict DDIs following current FDA guidelines were applied. The in vitro dapaconazole inhibition was observed for all isoforms investigated, including CYP1A2 (IC50 of 3.68 µM), CYP2A6 (20.7 µM), 2C8 (104.1 µM), 2C9 (0.22 µM), 2C19 (0.05 µM), 2D6 (0.87 µM), and 3A4 (0.008−0.03 µM). The dynamic (PBPK) and static DDI mechanistic model-based analyses suggest that dapaconazole is a weak inhibitor (AUCR > 1.25 and <2) of CYP1A2 and CYP2C9, a moderate inhibitor (AUCR > 2 and <5) of CYP2C8 and CYP2D6, and a strong inhibitor (AUCR ≥ 5) of CYP2C19 and CYP3A, considering a clinical scenario. The results presented may be a useful guide for future in vivo and clinical dapaconazole studies.

Discovery of Ervogastat (PF-06865571): A Potent and Selective Inhibitor of Diacylglycerol Acyltransferase 2 for the Treatment of Non-alcoholic Steatohepatitis

Discovery efforts leading to the identification of ervogastat (PF-06865571), a systemically acting diacylglycerol acyltransferase (DGAT2) inhibitor that has advanced into clinical trials for the treatment of non-alcoholic steatohepatitis (NASH) with liver fibrosis, are described herein. Ervogastat is a first-in-class DGAT2 inhibitor that addressed potential development risks of the prototype liver-targeted DGAT2 inhibitor PF-06427878. Key design elements that culminated in the discovery of ervogastat are (1) replacement of the metabolically labile motif with a 3,5-disubstituted pyridine system, which addressed potential safety risks arising from a cytochrome P450-mediated O-dearylation of PF-06427878 to a reactive quinone metabolite precursor, and (2) modifications of the amide group to a 3-THF group, guided by metabolite identification studies coupled with property-based drug design.

Metabolic clearance of select opioids and opioid antagonists using hepatic spheroids and recombinant cytochrome P450 enzymes

The opioid crisis is a pressing public health issue, exacerbated by the emergence of more potent synthetic opioids, particularly fentanyl and its analogs. While competitive antagonists exist, their efficacy against synthetic opioids is largely unknown. Furthermore, due to the short durations of action of current antagonists, renarcotization remains a concern. In this study, metabolic activity was characterized for fentanyl-class opioids and common opioid antagonists using multiple in vitro systems, namely, cytochrome P450 (CYP) enzymes and hepatic spheroids, after which an in vitro-in vivo correlation was applied to convert in vitro metabolic activity to predictive in vivo intrinsic clearance. For all substrates, intrinsic hepatic metabolism was higher than the composite of CYP activities, due to fundamental differences between whole cells and single enzymatic reactions. Of the CYP isozymes investigated, 3A4 yielded the highest absolute and relative metabolism across all substrates, with largely negligible contributions from 2D6 and 2C19. Comparative analysis highlighted elevated lipophilicity and diminished CYP3A4 activity as potential considerations for the development of more efficacious opioid antagonists. Finally, antagonists with a high degree of molecular similarity exhibited comparable clearance, providing a basis for structure-metabolism relationships. Together, these results provide multiple screening criteria for early stage drug discovery involving opioid countermeasures.

The Anti-Fungal Activity of Nitropropenyl Benzodioxole (NPBD), a Redox-Thiol Oxidant and Tyrosine Phosphatase Inhibitor

Phylogenetically diverse fungal species are an increasing cause of severe disease and mortality. Identification of new targets and development of new fungicidal drugs are required to augment the effectiveness of current chemotherapy and counter increasing resistance in pathogens. Nitroalkenyl benzene derivatives are thiol oxidants and inhibitors of cysteine-based molecules, which show broad biological activity against microorganisms. Nitropropenyl benzodioxole (NPBD), one of the most active antimicrobial derivatives, shows high activity in MIC assays for phylogenetically diverse saprophytic, commensal and parasitic fungi. NPBD was fungicidal to all species except the dermatophytic fungi, with an activity profile comparable to that of Amphotericin B and Miconazole. NPBD showed differing patterns of dynamic kill rates under different growth conditions for Candida albicans and Aspergillus fumigatus and was rapidly fungicidal for non-replicating vegetative forms and microconidia. It did not induce resistant or drug tolerant strains in major pathogens on long term exposure. A literature review highlights the complexity and interactivity of fungal tyrosine phosphate and redox signaling pathways, their differing metabolic effects in fungal species and identifies some targets for inhibition. A comparison of the metabolic activities of Amphotericin B, Miconazole and NPBD highlights the multiple cellular functions of these agents and the complementarity of many mechanisms. The activity profile of NPBD illustrates the functional diversity of fungal tyrosine phosphatases and thiol-based redox active molecules and contributes to the validation of tyrosine phosphatases and redox thiol molecules as related and complementary selective targets for antimicrobial drug development. NPBD is a selective antifungal agent with low oral toxicity which would be suitable for local treatment of skin and mucosal infections.

Cytochromes P450 2C8 and 3A Catalyze the Metabolic Activation of the Tyrosine Kinase Inhibitor Masitinib

Masitinib is a small molecule tyrosine kinase inhibitor under investigation for the treatment of amyotrophic lateral sclerosis, mastocytosis, and COVID-19. Hepatotoxicity has been reported in some patients while taking masitinib. The liver injury is thought to involve hepatic metabolism of masitinib by cytochrome P450 (P450) enzymes to form chemically reactive, potentially toxic metabolites. The goal of the current investigation was to determine the P450 enzymes involved in the metabolic activation of masitinib in vitro. In initial studies, masitinib (30 μM) was incubated with pooled human liver microsomes in the presence of NADPH and potassium cyanide to trap reactive iminium ion metabolites as cyano adducts. Masitinib metabolites and cyano adducts were analyzed using reversed-phase liquid chromatography-tandem mass spectrometry. The primary active metabolite, N-desmethyl masitinib (M485), and several oxygenated metabolites were detected along with four reactive metabolite cyano adducts (MCN510, MCN524, MCN526, and MCN538). To determine which P450 enzymes were involved in metabolite formation, reaction phenotyping experiments were conducted by incubation of masitinib (2 μM) with a panel of recombinant human P450 enzymes and by incubation of masitinib with human liver microsomes in the presence of P450-selective chemical inhibitors. In addition, enzyme kinetic assays were conducted to determine the relative kinetic parameters (apparent K_m and V_max) of masitinib metabolism and cyano adduct formation. Integrated analysis of the results from these experiments indicates that masitinib metabolic activation is catalyzed primarily by P450 3A4 and 2C8, with minor contributions from P450 3A5 and 2D6. These findings provide further insight into the pathways involved in the generation of reactive, potentially toxic metabolites of masitinib. Future studies are needed to evaluate the impact of masitinib metabolism on the toxicity of the drug in vivo.

Evaluation of Zuo-Gui Yin Decoction Effects on Six CYP450 Enzymes in Rats Using a Cocktail Method by UPLC-MS/MS

Background. Zuo-Gui Yin Decoction (ZGYD), a traditional Chinese prescription, is mainly used in various kinds of andrology and gynecology diseases. However, the study on the interaction of ZGYD and drugs has not been reported. Therefore, evaluating the interaction between ZGYD and metabolic enzymes is helpful to guide rational drug use. Objective. This study was conducted to explore the effects of ZGYD on the activity and mRNA expressions of six Cytochrome P450 (CYP450) enzymes in rats and to provide a basis for its rational clinical use. Methods. Sprague-Dawley rats were randomly divided into control, ZGYD high, medium, and low-dose group ( $n=6$ ). The concentrations of six probe substrates in plasma of rats in each group were determined by UPLC-MS/MS. In addition, RT-PCR and Western blot were used to determine the effects of ZGYD on the expression of CYP450 isoforms in the liver. Results. Compared with the control group, the main pharmacokinetic parameters AUC(0-t), AUC (0~∞), of omeprazole, dextromethorphan, and midazolam in the high-dose group were significantly decreased, while the CL of these were significantly increased. The gene expressions of CYP2C11 and CYP3A1 were upregulated in the ZGYD medium, high-dose group. The protein expression of CYP2C11 was upregulated in the high-dose group, and the protein expression of CYP3A1 was upregulated in the medium, high-dose group. Conclusion. The results showed that ZGYD exhibited the induction effects on CYP2C11 and CYP3A1 (CYP2C19 and CYP3A4 in humans) in rats. However, no significant change in CYP1A2, CYP2B1, CYP2C7, and CYP2D2 activities was observed. It would be useful for the safe and effective usage of ZGYD in clinic.

A Physiologically Based Pharmacokinetic and Pharmacodynamic Model of the CYP3A4 Substrate Felodipine for Drug-Drug Interaction Modeling

The antihypertensive felodipine is a calcium channel blocker of the dihydropyridine type, and its pharmacodynamic effect directly correlates with its plasma concentration. As a sensitive substrate of cytochrome P450 (CYP) 3A4 with high first-pass metabolism, felodipine shows low oral bioavailability and is susceptible to drug–drug interactions (DDIs) with CYP3A4 perpetrators. This study aimed to develop a physiologically based pharmacokinetic/pharmacodynamic (PBPK/PD) parent–metabolite model of felodipine and its metabolite dehydrofelodipine for DDI predictions. The model was developed in PK-Sim^® and MoBi^® using 49 clinical studies (94 plasma concentration–time profiles in total) that investigated different doses (1–40 mg) of the intravenous and oral administration of felodipine. The final model describes the metabolism of felodipine to dehydrofelodipine by CYP3A4, sufficiently capturing the first-pass metabolism and the subsequent metabolism of dehydrofelodipine by CYP3A4. Diastolic blood pressure and heart rate PD models were included, using an E_max function to describe the felodipine concentration–effect relationship. The model was tested in DDI predictions with itraconazole, erythromycin, carbamazepine, and phenytoin as CYP3A4 perpetrators, with all predicted DDI AUC_last and C_max ratios within two-fold of the observed values. The model will be freely available in the Open Systems Pharmacology model repository and can be applied in DDI predictions as a CYP3A4 victim drug.

Defining the Selectivity of Chemical Inhibitors Used for Cytochrome P450 Reaction Phenotyping: Overcoming Selectivity Limitations with a Six-Parameter Inhibition Curve-Fitting Approach

The utility of chemical inhibitors in cytochrome P450 (CYP) reaction phenotyping is highly dependent on their selectivity and potency for their target CYP isoforms. In the present study, seventeen inhibitors of CYP1A2, 2B6, 2C8, 2C9, 2C19, 2D6, and 3A4/5 commonly used in reaction phenotyping were evaluated for their cross-enzyme selectivity in pooled human liver microsomes. The data were evaluated using a statistical desirability analysis to identify (1) inhibitors of superior selectivity for reaction phenotyping and (2) optimal concentrations for each. Among the inhibitors evaluated, α-naphthoflavone, furafylline, sulfaphenazole, tienilic acid, N-benzylnirvanol, and quinidine were most selective, such that their respective target enzymes were inhibited by ~95% without inhibiting any other CYP enzyme by more than 10%. Other commonly employed inhibitors, such as ketoconazole and montelukast, among others, were of insufficient selectivity to yield a concentration that could adequately inhibit their target enzymes without affecting other CYP enzymes. To overcome these shortcomings, an experimental design was developed wherein dose response data from a densely sampled multi-concentration inhibition curve are analyzed by a six-parameter inhibition curve function, allowing accounting of the inhibition of off-target CYP isoforms inhibition and more reliable determination of maximum targeted enzyme inhibition. The approach was exemplified using rosiglitazone N-demethylation, catalyzed by both CYP2C8 and 3A4, and was able to discern the off-target inhibition by ketoconazole and montelukast from the inhibition of the targeted enzyme. This methodology yields more accurate estimates of CYP contributions in reaction phenotyping. Significance Statement Isoform-selective chemical inhibitors are important tools for identifying and quantifying enzyme contributions as part of a CYP reaction phenotyping assessment for projecting drug-drug interactions. However, currently employed practices fail to adequately compensate for shortcomings in inhibitor selectivity and the resulting confounding impact on estimates of the CYP enzyme contribution to drug clearance. In this report, we describe a detailed IC50 study design with 6-parameter modeling approach that yields more accurate estimates of enzyme contribution.

"Commandeuring" Xenobiotic Metabolism: Advances in Understanding Xenobiotic Metabolism

The understanding of how exogenous chemicals (xenobiotics) are metabolized, distributed, and eliminated is critical to determine the impact of the chemical and its metabolites to the (human) organism. This is part of the research and educational discipline ADMET (absorption, distribution, metabolism, elimination, and toxicity). Here, we review the work of Jan Commandeur and colleagues who have not only made a significant impact in understanding of phase I and phase II metabolism of several important compounds but also contributed greatly to the development of experimental techniques for the study of xenobiotic metabolism. Jan Commandeur’s work has covered a broad area of research, such as the development of online screening methodologies, the use of a combination of enzyme mutagenesis and molecular modeling for structure–activity relationship (SAR) studies, and the development of novel probe substrates. This work is the bedrock of current activities and brings the field closer to personalized (cohort-based) pharmacology, toxicology, and hazard/risk assessment.

Assessment of the CYP1A2 Inhibition-Mediated Drug Interaction Potential for Pinocembrin Using In Silico, In Vitro, and In Vivo Approaches

Pinocembrin, a bioflavonoid, is extensively used in complementary/alternative medicine. It turns out as a promising candidate against neurodegenerative diseases because of its multifaceted pharmacological action toward neuroprotection. However, literature evidence is still lacking for its inhibitory action on CYP1A2, which is responsible for xenobiotic metabolism leading to the generation of toxic metabolites and bioactivation of procarcinogens. In the present study, our aim was to evaluate the CYP1A2 inhibitory potential of pinocembrin via in silico, in vitro, and in vivo investigations. From the results of in vitro studies, pinocembrin is found to be a potent and competitive inhibitor of CYP1A2. In vitro-in vivo extrapolation results indicate the potential of pinocembrin to interact with CYP1A2 substrate drugs clinically. Molecular docking-based in silico studies demonstrate the strong interaction of pinocembrin with human CYP1A2. In in vivo investigations using a rat model, pinocembrin displayed a marked alteration in the plasma exposure of CYP1A2 substrate drugs, namely, caffeine and tacrine. In conclusion, pinocembrin has a potent CYP1A2 inhibitory action to cause drug interactions, and further confirmatory study is warranted at the clinical level.

Interindividual Variability in Cytochrome P450 3A and 1A Activity Influences Sunitinib Metabolism and Bioactivation

Sunitinib is an orally administered tyrosine kinase inhibitor associated with idiosyncratic hepatotoxicity; however, the mechanisms of this toxicity remain unclear. We have previously shown that cytochromes P450 1A2 and 3A4 catalyze sunitinib metabolic activation via oxidative defluorination leading to a chemically reactive, potentially toxic quinoneimine, trapped as a glutathione (GSH) conjugate (M5). The goals of this study were to determine the impact of interindividual variability in P450 1A and 3A activity on sunitinib bioactivation to the reactive quinoneimine and sunitinib N-dealkylation to the primary active metabolite N-desethylsunitinib (M1). Experiments were conducted in vitro using single-donor human liver microsomes and human hepatocytes. Relative sunitinib metabolite levels were measured by liquid chromatography-tandem mass spectrometry. In human liver microsomes, the P450 3A inhibitor ketoconazole significantly reduced M1 formation compared to the control. The P450 1A2 inhibitor furafylline significantly reduced defluorosunitinib (M3) and M5 formation compared to the control but had minimal effect on M1. In CYP3A5-genotyped human liver microsomes from 12 individual donors, M1 formation was highly correlated with P450 3A activity measured by midazolam 1'-hydroxylation, and M3 and M5 formation was correlated with P450 1A2 activity estimated by phenacetin O-deethylation. M3 and M5 formation was also associated with P450 3A5-selective activity. In sandwich-cultured human hepatocytes, the P450 3A inducer rifampicin significantly increased M1 levels. P450 1A induction by omeprazole markedly increased M3 formation and the generation of a quinoneimine-cysteine conjugate (M6) identified as a downstream metabolite of M5. The nonselective P450 inhibitor 1-aminobenzotriazole reduced each of these metabolites (M1, M3, and M6). Collectively, these findings indicate that P450 3A activity is a key determinant of sunitinib N-dealkylation to the active metabolite M1, and P450 1A (and potentially 3A5) activity influences sunitinib bioactivation to the reactive quinoneimine metabolite. Accordingly, modulation of P450 activity due to genetic and/or nongenetic factors may impact the risk of sunitinib-associated toxicities.

Effect of Myricetin on CYP2C8 Inhibition to Assess the Likelihood of Drug Interaction Using In Silico, In Vitro, and In Vivo Approaches

Myricetin, a bioflavonoid, is widely used as functional food/complementary medicine and has promising multifaceted pharmacological actions against therapeutically validated anticancer targets. On the other hand, CYP2C8 is not only crucial for alteration in the pharmacokinetics of drugs to cause drug interaction but also unequivocally important for the metabolism of endogenous substances like the formation of epoxyeicosatrienoic acids (EETs), which are considered as signaling molecules against hallmarks of cancer. However, there is hardly any information known to date about the effect of myricetin on CYP2C8 inhibition and, subsequently, the CYP2C8-mediated drug interaction potential of myricetin at the preclinical/clinical level. We aimed here to explore the CYP2C8 inhibitory potential of myricetin using in silico, in vitro, and in vivo investigations. In the in vitro study, myricetin showed a substantial effect on CYP2C8 inhibition in human liver microsomes using CYP2C8-catalyzed amodiaquine-N-deethylation as an index reaction. Considering the Lineweaver-Burk plot, the Dixon plot, and the higher α-value, myricetin is found to be a mixed type of CYP2C8 inhibitor. Moreover, in vitro-in vivo extrapolation data suggest that myricetin is likely to cause drug interaction at the hepatic level. The molecular docking study depicted a strong interaction between myricetin and the active site of the human CYP2C8 enzyme. Moreover, myricetin caused considerable elevation in the oral exposure of amodiaquine as a CYP2C8 substrate via a slowdown of amodiaquine clearance in the rat model. Overall, the potent action of myricetin on CYP2C8 inhibition indicates that there is a need for further exploration to avoid drug interaction-mediated precipitation of obvious adverse effects as well as to optimize anticancer therapy.

In vitro cell-based models of drug-induced hepatotoxicity screening: progress and limitation

Drug-induced liver injury (DILI) is one of the major causes of post-approval withdrawal of therapeutics. As a result, there is an increasing need for accurate predictive in vitro assays that reliably detect hepatotoxic drug candidates while reducing drug discovery time, costs, and the number of animal experiments. In vitro hepatocyte-based research has led to an improved comprehension of the underlying mechanisms of chemical toxicity and can assist the prioritization of therapeutic choices with low hepatotoxicity risk. Therefore, several in vitro systems have been generated over the last few decades. This review aims to comprehensively present the development and validation of 2D (two-dimensional) and 3D (three-dimensional) culture approaches on hepatotoxicity screening of compounds and highlight the main factors affecting predictive power of experiments. To this end, we first summarize some of the recognized hepatotoxicity mechanisms and related assays used to appraise DILI mechanisms and then discuss the challenges and limitations of in vitro models.

In vitro evaluation of the inhibition potential of echinacoside on human cytochrome P450 isozymes

Background

Echinacoside (ECH) possesses a wide range of biological activity. This present study analyzes the effect of ECH on cytochrome P450 isozymes (CYPs) activities of human liver microsomes.

Methods

The effect of ECH on CYPs enzyme activities were studied using the enzyme-selective substrates phenacetin (1A2), chlorzoxazone (2E1), S-mephenytoin (2C19), testosterone (3A4), coumarin (2A6), diclofenac (2C9), paclitaxel (2C8), and dextromethorphan (2D6). The IC50 values for CYP1A2, CYP2E1, CYP2C19, and CYP3A4 isoforms were examined to express the strength of inhibition. Further, the inhibition of CYPs was checked for time-dependent or not, and then fitted with competitive or non-competitive inhibition models. The corresponding parameters were also obtained.

Results

ECH caused inhibitions on CYP1A2, CYP2E1, CYP2C19 and CYP3A4 enzyme activities in HLMs with IC50 of 21.23, 19.15, 8.70 and 55.42 μM, respectively. The obtained results showed that the inhibition of ECH on CYP3A4 was time-dependent with the KI/K_inact value of 6.63/0.066 min^− 1·μM^− 1. Moreover, ECH inhibited the activity of CYP1A2 and CYP2E1 via non-competitive manners (K_i = 10.90 μM and K_i = 14.40 μM, respectively), while ECH attenuated the CYP2C19 activity via a competitive manner (K_i = 4.41 μM).

Conclusions

The results of this study indicate that ECH inhibits CYP1A2, CYP2E1, CYP2C19 and CYP3A4 activities in vitro. In vivo and clinical studies are warranted to verify the relevance of these interactions.

LC-MS-based assay of granisetron 7-hydroxylation activity for the evaluation of CYP1A1 induction from diesel particulate matter-exposed hepatic and respiratory cell lines

Particulate matter (PM) generally consists of aggregated particles containing trace metals and polycyclic aromatic hydrocarbons (PAHs). Cytochrome P450 (CYP) 1A1, one of the extensively investigated biomarkers, is highly inducible when PAHs activate the aryl hydrocarbon receptor (AhR). The present study focused on developing a LC-MS/MS-based assay to evaluate CYP1A1 induction potential following PM exposure. This assay adapted a CYP1A1 selective reaction of granisetron 7-hydroxylation in response to an AhR inducer, 6-formylindolo[3,2-b]carbazole (FICZ), in HepaRG and A549 cell lines. Exposure to FICZ (10 nM) increased the levels of granisetron 7-hydroxylation significantly, whereas no elevation of ethoxyresorufin-O-deethylation (EROD) activity was found in HepaRG cells. In A549 cells, granisetron 7-hydroxylation showed a better dose-response from 0 to 10000 nM FICZ treatment than EROD. EROD Additionally, the application of the assay with diesel PM exposure showed a concentration-dependent induction of CYP1A1 in HepaRG, A549, and human nasal epithelial cells. The granisetron assay has better selectivity for CYP1A1 than the conventional EROD assay, which is overlapped reaction with CYP1A2 and CYP1B1, with high correlations between AhR activation and CYP1A1 mRNA levels. Accompanying the great application potential to different organs and cell culture systems, future studies will implement the granisetron assay for the respiratory toxicity evaluation.

Assessment of drug-drug interactions of CC-90001, a potent and selective inhibitor of c-Jun N-terminal kinase

CC-90001 is predominantly metabolised via glucuronidation, while oxidative metabolism is a minor pathway in human hepatocytes and liver microsomes. In vitro, CC-90001 glucuronidation was catalysed by UGT1A9, UGT1A4, and UGT1A1, while oxidative metabolism was primarily mediated by CYP3A4/5 with minor contributions from CYP1A2, CYP2C9, CYP2B6, and CYP2D6.CC-90001 in vitro inhibits CYP2A6, CYP2B6, CYP2C8, CYP2C9, CYP2C19, and CYP3A4 ≤ 55% at 100 μM, and the inhibition was negligible at ≤30 μM. CC-90001 is not a time-dependent CYP inhibitor.In human hepatocytes CC-90001 is an inducer of CYP2B6 and CYP3A, with mRNA levels increased 34.4% to 52.8% relative to positive controls.In vitro CC-90001 is a substrate of P-gp, and an inhibitor of P-gp, BCRP, OAT3, OATP1B1, OATP1B3, OCT2, MATE1, and MATE2k with IC₅₀ values of 30.3, 25.8, 17.7, 0.417, 19.9, 0.605, 4.17, and 20 μM, respectively.A clinical study demonstrated that CC-90001 has no or little impact on the exposure of warfarin (CYP2C9), omeprazole (CYP2C19), midazolam (CYP3A) or metformin (OCT2, MATE1/2k). CC-90001 co-administration increases the AUC_t and C_max 176% and 339% for rosuvastatin (BCRP/OATP1B1/3), 116% and 171% for digoxin (P-gp), and 266% and 321% for nintedanib (CYP3A & P-gp), respectively.In conclusion, CC-90001 in unlikely to be a victim or perpetrator of clinically relevant interactions involving CYPs or UGTs. Weak to moderate interactions are expected in clinic with substrates of P-gp and OATP1B1 due to CC-90001 inhibition of these transporters.

Optimization of the CYP inhibition assay using LC-MS/MS

The data presented in this article are related to the research article entitled “Cytochrome P450 inhibition activities of non-standardized botanical products” [1], in which the possible CYP inhibitory properties of botanical products were investigated. This article describes the optimization and bioanalytical method validation of the CYP (Cytochrome P450 inhibition assay) inhibition assays, namely, phenacetin O-deethylase assay, testosterone 6β-hydroxylase assay, felodipine dehydrogenase assay and midazolam 1’-hydroxylase assay using LC-MS/MS.

Physiologically based pharmacokinetic/pharmacodynamic modeling to evaluate the absorption of midazolam rectal gel

OBJECTIVE

We aimed to 1) develop physiologically based pharmacokinetic/pharmacodynamic (PBPK/PD) models of a novel midazolam rectal gel in healthy adults, 2) assess the contribution of different physiologically relevant factors in rectal absorption, and 3) to provide supports for future clinical studies of midazolam rectal gel.

METHODS

We developed the rectal PBPK model after built the intravenous and the oral PBPK model. Then, the physiological progress of rectal route was described in terms of the drug release, the rectal absorption and the particle first-pass elimination. Next, the validated PBPK model was combined with the sigmoid E_max PD model. This PBPK/PD model was used to identify the dose range and the critical parameters to ensure safety sedation.

RESULTS

Based on the simulations, the recommended maximum dose for adults' sedation was 15 mg. And the retention time of midazolam rectal gel should be longer than 3 h to reach over 80% pharmacokinetics and pharmacodynamics effects.

CONCLUSION

We successfully developed a PBPK/PD model for the midazolam rectal gel, which accurately described the PK/PD behavior in healthy adults and indicated the transit time of rectum was the most sensitive parameter for absorption. This PBPK/PD model would be expected to support the future clinical studies and pediatric application.

Complex Cytochrome P450 Kinetics Due to Multisubstrate Binding and Sequential Metabolism. Part 1. Theoretical Considerations

Complexities in P450-mediated metabolism kinetics include multisubstrate binding, multiple-product formation, and sequential metabolism. Saturation curves and intrinsic clearances were simulated for single-substrate and multisubstrate models using derived velocity equations and numerical solutions of ordinary differential equations (ODEs). Multisubstrate models focused on sigmoidal kinetics because of their dramatic impact on clearance predictions. These models were combined with multiple-product formation and sequential metabolism, and simulations were performed with random error. Use of single-substrate models to characterize multisubstrate data can result in inaccurate kinetic parameters and poor clearance predictions. Comparing results for use of standard velocity equations with ODEs clearly shows that ODEs are more versatile and provide better parameter estimates. It would be difficult to derive concentration-velocity relationships for complex models, but these relationships can be easily modeled using numerical methods and ODEs. SIGNIFICANCE STATEMENT: The impact of multisubstrate binding, multiple-product formation, and sequential metabolism on the P450 kinetics was investigated. Numerical methods are capable of characterizing complicated P450 kinetics.

Pirfenidone 5-hydroxylation is mainly catalysed by CYP1A2 and partly catalysed by CYP2C19 and CYP2D6 in the human liver

Pirfenidone is a first-line drug for the treatment of idiopathic pulmonary fibrosis. The primary metabolic pathways of pirfenidone in humans are 5-hydroxylation and subsequent oxidation to 5-carboxylpirfenidone. The aims of this study were to determine the cytochrome P450 isoforms responsible for pirfenidone 5-hydroxylation and to evaluate their contributions in human liver microsomes (HLM).Among the recombinant P450 isoforms, CYP1A2, CYP2D6, CYP2C19, CYP2A6, and CYP2B6 were shown to catalyse the 5-hydroxylation of pirfenidone. Pirfenidone 5-hydroxylase activity by HLM was inhibited by α-naphthoflavone (by 45%), 8-methoxypsolaren (by 84%), tranylcypromine (by 53%), and quinidine (by 15%), which are CYP1A2, CYP1A2/CYP2A6/CYP2C19, CYP2A6/CYP2C19, and CYP2D6 inhibitors, respectively.In 17 individual HLM donors, pirfenidone 5-hydroxylase activity was significantly correlated with phenacetin O-deethylase (r = 0.89, P < 0.001) and S-mephenytoin 4'-hydroxylase activities (r = 0.51, P < 0.05), which are CYP1A2 and CYP2C19 marker activities, respectively.By using the relative activity factors, the contributions of CYP1A2, CYP2C19, and CYP2D6 to pirfenidone 5-hydroxylation in the human liver were 72.8%, 11.8%, and 8.9%, respectively.In conclusion, we clearly demonstrated the predominant P450 involved in pirfenidone 5-hydroxylation in the human liver is CYP1A2, with CYP2C19 and CYP2D6 playing a minor role.

An oral SARS-CoV-2 Mpro inhibitor clinical candidate for the treatment of COVID-19

[Figure: see text].

Unanticipated CNS Safety Signal in a Placebo-Controlled, Randomized Trial of Co-Administered Atovaquone-Proguanil and Amodiaquine

Atovaquone‐proguanil (ATV‐PG) plus amodiaquine (AQ) has been considered as a potential replacement for sulfadoxine‐pyrimethamine plus AQ for seasonal malaria chemoprevention in African children. This randomized, double‐blind, placebo‐controlled, parallel group study assessed the safety, tolerability, and pharmacokinetics (PKs) of ATV‐PG plus AQ in healthy adult males and females of Black sub‐Saharan African origin. Participants were randomized to four treatment groups: ATV‐PG/AQ (n = 8), ATV‐PG/placebo (n = 12), AQ/placebo (n = 12), and placebo/placebo (n = 12). Treatments were administered orally once daily for 3 days (days 1–3) at daily doses of ATV‐PQ 1000/400 mg and AQ 612 mg. Co‐administration of ATV‐PG/AQ had no clinically relevant effect on PK parameters for ATV, PG, the PG metabolite cycloguanil, AQ, or the AQ metabolite N‐desethyl‐amodiaquine. Adverse events occurred in 8 of 8 (100%) of participants receiving ATV‐PG/AQ, 11 of 12 (91.7%) receiving ATV‐PG, 11 of 12 (91.7%) receiving AQ, and 3 of 12 (25%) receiving placebo. The safety and tolerability profiles of ATV‐PG and AQ were consistent with previous reports. In the ATV‐PG/AQ group, 2 of 8 participants experienced extrapyramidal adverse effects (EPAEs) on day 3, both psychiatric and physical, which appeared unrelated to drug plasma PKs or cytochrome P450 2C8 phenotype. Although rare cases are reported with AQ administration, the high incidence of EPAE was unexpected in this small study. Owing to the unanticipated increased frequency of EPAE observed, the combination of ATV‐PQ plus AQ is not recommended for further evaluation in prophylaxis of malaria in African children.

Comparison of Pinoresinol and its Diglucoside on their ADME Properties and Vasorelaxant Effects on Phenylephrine-Induced Model

Pinoresinol (PINL) and pinoresinol diglucoside (PDG), two natural lignans found in Eucommia ulmoides Oliv. (Duzhong), have several pharmacological activities. However, there is no report available on their absorption, distribution, metabolism, and elimination (ADME) properties. Given the possible wide spectrum of their application in therapeutic areas, this area should be investigated. This work studied the in vitro ADME properties of PDG and PINL, including their kinetic solubility, permeability across monolayer cells (PAMPA), protein binding, and metabolic stabilities in liver microsomes. The in vivo pharmacokinetic study and in vitro vasorelaxant effects on isolated phenylephrine-induced aortic rings of PINL and PDG were also investigated. It was found that both of their kinetic solubility in PBS (pH 7.4) was greater than 100 μM, indicating that they are both soluble compounds. The permeability investigations (P_eff) by PAMPA indicated that PINL had higher permeability than PDG (p < 0.05). Both components represented moderate plasma protein binding activities (average binding rate in human plasma: PINL 89.03%, PDG 45.21%) and low metabolic rate (t_1/2 in human liver microsome: PINL 1509.5 min, PDG 1004.8 min). Furthermore, the results of pharmacokinetic studies indicated that PINL might be eliminated less quickly than PDG from the rat plasma, and its cumulative urinary excretion was much lower than that of PDG. The phenylephrine-induced aortic rings demonstrated concentration-dependent vasorelaxation in PDG, PINL, or their combination group. The vasorelaxant effects of PINL were more obvious than those of PDG, whereas the vasorelaxant effect of the combinations was significantly better than that of the single component (p < 0.05). The similarity or difference between PINL and its diglucoside in these pharmaceutical aspects may offer valuable insights into the further exploration of lignans and might contribute to relevant studies involving natural products with similar molecular structure and their glucosides.

Enzyme Kinetics of Oxidative Metabolism-Cytochromes P450

The cytochrome P450 enzymes (CYPs) are the most important enzymes in the oxidative metabolism of hydrophobic drugs and other foreign compounds (xenobiotics). The versatility of these enzymes results in some unusual kinetic properties, stemming from the simultaneous interaction of multiple substrates with the CYP active site. Often, the CYPs display kinetics that deviate from standard hyperbolic saturation or inhibition kinetics. Non-Michaelis-Menten or "atypical" saturation kinetics include sigmoidal, biphasic, and substrate inhibition kinetics (see Chapter 2 ). Interactions between substrates include competitive inhibition, noncompetitive inhibition, mixed inhibition, partial inhibition, activation, and activation followed by inhibition (see Chapters 4 and 6 ). Models and equations that can result in these kinetic profiles will be presented and discussed.

Variability in Human In Vitro Enzyme Kinetics

There are many factors which are known to cause variability in human in vitro enzyme kinetic data. Factors such as the source of enzyme and how it was prepared, the genetics and background of the donor, how the in vitro studies are designed, and how the data are analyzed contribute to variability in the resulting kinetic parameters. It is important to consider not only the factors which cause variability within an experiment, such as selection of a probe substrate, but also those that cause variability when comparing kinetic data across studies and laboratories. For example, the artificial nature of the microsomal lipid membrane and microenvironment in some recombinantly expressed enzymes, relative to those found in native tissue microsomes, has been shown to influence enzyme activity and thus can be a source of variability when comparing across the two different systems. All of these factors, and several others, are discussed in detail in the chapter below. In addition, approaches which can be used to visualize the uncertainty arising from the use of enzyme kinetic data within the context of predicting human pharmacokinetics are discussed.

In vitro study on the effect of leonurine hydrochloride on the enzyme activity of cytochrome P450 enzymes in human liver microsomes

Leonurine hydrochloride (LH) is derived from an ingredient of Leonurus japonicus Houtt which is widely used for diseases in women.The influence of LH on the activity of cytochrome P450 (CYPs) enzymes was investigated in this study.The effect of LH on CYPs enzyme activities were studied using the enzyme-selective substrates phenacetin (1A2), coumarin (2A6), diclofenac (2C9), S-mephenytoin (2C19), paclitaxel (2C8), dextromethorphan (2D6), chlorzoxazone (2E1) and testosterone (3A4). The IC₅₀ value was calculated to express the strength of inhibition. The inhibition of CYPs was fitted with competitive or non-competitive inhibition models and corresponding parameters were also obtained.LH exerted inhibitory effects on the activity of CYP1A2, 2D6, and 3A4 with the IC₅₀ values of 18.05, 15.13, and 20.09 μM, respectively. The obtained results showed that LH inhibited the activity of CYP1A2 and CYP2D6 via competitive manners (K_i = 8.667 μM and K_i = 7.805 μM, respectively), while LH attenuated the CYP3A4 activity via a non-competitive manner (K_i = 9.507 μM). Moreover, LH showed time-dependent inhibition on CYP3A4 with the K_I/K_inact value of 4.31/0.044 min^-1·μM^-1.The inhibition of CYP1A2, CYP2D6, and CYP3A4 by LH, demonstrated in vitro, indicated the potential herb-drug interaction. Therefore, pharmacokinetic interactions involving LH and CYP1A2 or CYP2D6 or CYP1A2 substrates are likely to occur.

In vitro assessments predict that CYP3A4 contributes to a greater extent than CYP3A5 to prednisolone clearance

Because several steroid hormones are metabolized to their respective 6β-hydroxy forms by CYP3A4 and CYP3A5, these isoenzymes have been assumed to metabolize the immunosuppressive drug prednisolone, with conflicting results in the literature with respect to their relative importance. A direct study of the metabolism of prednisolone by microsomal CYP3A4 and CYP3A5 is missing. The aim of this in vitro study was to investigate the relative importance of recombinant CYP3A4 and recombinant CYP3A5 in the metabolism of prednisolone and to compare the extent of formation of 6β-OH-prednisolone by the two enzymes. Through in vitro incubations using rCYP3A4 and rCYP3A5 enzymes, intrinsic clearance (CL_int ) of prednisolone was determined by the substrate depletion approach. Formation of the metabolite 6β-OH-prednisolone by rCYP3A4 and rCYP3A5, respectively, were compared. Prednisolone concentrations were measured and its metabolite 6β-OH-prednisolone was identified using a HPLC-MS/MS in-house method. CL_int for prednisolone by rCYP3A5 was less than 26% relative to rCYP3A4. Formation of 6β -OH-prednisolone by rCYP3A5 was less than 11% relative to rCYP3A4. The study indicates that 6β-hydroxylation of prednisolone assessed in vitro in recombinant CYP enzymes depends on rCYP3A4 rather than rCYP3A5, and that CYP3A5 may be responsible for the formation of other prednisolone metabolite(s) in addition to 6β-OH-prednisolone.

Evaluation of the effect of Bovis Calculus Artifactus on eight rat liver cytochrome P450 isozymes using LC-MS/MS and cocktail approach

Bovis Calculus Artifactus (BCA) is the main substitute for natural Calculus bovis, a traditional drug in China used to treat high fever, convulsion, and sore throat. The effect of BCA on cytochrome P450 (CYP) activities is unknown. This study was to investigate the effect of BCA on eight rat hepatic microsomal CYPisozymes to evaluate the potential drug interactions using the cocktail approach.Metabolites of the eight isoform probe substrates of CYP isozymes were quantified by LC-MS/MS. The method was validated by incubating known CYP inhibitors α-naphthoflavone (CYP1A2), thiotepa (CYP2B1), quercetin (CYP2C7), sulfaphenazole (CYP2C6), ticlopidine (CYP2C11), quinidine (CYP2D1), ketoconazole (CYP3A1),4-methylpyrazole (CYP2E1) with individual probe substrate and rat liver microsomes. The formation rates of the corresponding metabolites of the eight probe substrates were determined to evaluate the activity of each isozyme.The results showed that BCA has different degrees of inhibitory effect on four CYP450 isoforms (CYP2C6, CYP2C11, CYP2D1, CYP3A1) (p < 0.05), but no significant influence on CYP1A2, 2B1, 2C7 or 2E1 (p > 0.05). Attention should be paid to the BCA-drug interactions by careful monitoring and appropriate dosage adjustments in the concurrent use of the drugs which are metabolized by CYP1A2, CYP2C19, and CYP3A4. Abbreviations: BCA, bovis calculus artifactus; CYP, cytochrome P450; DDIs, drug-drug interactions; ESI, electrospray ionization; MRM, multiple reaction monitoring; NBC, Natural Bovis Calculus; QC, quality control; T CM, traditional Chinese medicine.

Case Study 4: Application of Basic Enzyme Kinetics to Metabolism Studies-Real-Life Examples

An appreciation of enzyme kinetic principles can be applied in a number of drug metabolism applications. The concept for this chapter arose from a simple discussion on selecting appropriate time points to most efficiently assess metabolite profiles in a human Phase 1a clinical study (Subheading 4). By considering enzyme kinetics, a logical approach to the issue was derived. The dialog was an important learning opportunity for the participants in the discussion, and we have endeavored to capture this experience with other questions related to determination of K_m and V_max parameters, a consideration of the value of hepatocytes vs. liver microsomes, and enzyme inhibition parameters.

Cytochrome P450-Mediated Metabolism and CYP Inhibition for the Synthetic Peroxide Antimalarial OZ439

OZ439 is a potent synthetic ozonide evaluated for the treatment of uncomplicated malaria. The metabolite profile of OZ439 was characterized in vitro using human liver microsomes combined with LC/MS-MS, chemical derivatization, and metabolite synthesis. The primary biotransformations were monohydroxylation at the three distal carbon atoms of the spiroadamantane substructure, with minor contributions from N-oxidation of the morpholine nitrogen and deethylation cleavage of the morpholine ring. Secondary transformations resulted in the formation of dihydroxylation metabolites and metabolites containing both monohydroxylation and morpholine N-oxidation. With the exception of two minor metabolites, none of the other metabolites had appreciable antimalarial activity. Reaction phenotyping indicated that CYP3A4 is the enzyme responsible for the metabolism of OZ439, and it was found to inhibit CYP3A via both direct and mechanism-based inhibition. Elucidation of the metabolic pathways and kinetics will assist with efforts to predict potential metabolic drug-drug interactions and support physiologically based pharmacokinetic (PBPK) modeling.

Global spectrum of population-specific common missense variation in cytochrome P450 pharmacogenes

Next-generation sequencing technology has afforded the discovery of many novel variants that are of significance to inheritable pharmacogenomics (PGx) traits but a large proportion of them have unknown consequences. These include missense variants resulting in single amino acid substitutions in cytochrome P450 (CYP) proteins that can impair enzyme function, leading to altered drug efficacy and toxicity. While most unknown variants are rare, an overlooked minority are variants that are collectively rare but enriched in specific populations. Here, we analyzed sequence variation data in 141,456 individuals from across eight study populations in gnomAD for 38 CYP genes to identify such variants in addition to common variants. By further comparison with data from two PGx-specific databases (PharmVar and PharmGKB) and ClinVar, we identified 234 missense variants in 35 CYP genes, of which 107 were unknown to these databases. Most unknown variants (n = 83) were population-specific common variants and several (n = 7) were found in important CYP pharmacogenes (CYP2D6, CYP4F2, and CYP2C19). Overall, 29% (n = 31) of 107 unknown variants were predicted to affect CYP enzyme function although further biochemical characterization is necessary. These variants may elucidate part of the unexplained interpopulation differences observed in drug response.