AbstractThe 2-oxidation, 3-methyl hydroxylation, and 6-hydroxylation of skatole (a contributor to boar taint) mediated by minipig liver microsomes and recombinant P450 enzymes expressed in bacterial membranes were investigated.At low substrate concentrations of 10 µM, the formation rates of indole-3-carbinol, 6-hydroxyskatole, and the sum of 3-methyloxindole, indole-3-carbinol, and 6-hydroxyskatole in male minipig liver microsomes were significantly lower than those in female minipig liver microsomes.Compensatory 3-methyloxindole and indole-3-carbinol formation in minipig liver microsomes, which lack 6-hydroxyskatole formation in males, was mediated partly by liver microsomal P450 1A2 and P450 1A2/2E1, respectively. These enzymes were suppressed by typical P450 inhibitors in female minipig liver microsomes.Among the 14 pig P450 forms evaluated, P450 2A19 was the dominant form mediating 3-methyloxindole, indole-3-carbinol, and 6-hydroxyskatole formation from skatole at substrate concentrations of 100 µM. Positive cooperativity was observed in 3-methyloxindole formation from skatole mediated by male minipig liver microsomes and by pig P450 3A22 with Hill coefficients of 1.2–1.5.These results suggest high skatole 2-oxidation, 3-methyl hydroxylation, and 6-hydroxylation activities of pig P450 2A19 and compensatory skatole oxidations mediated by pig P450 1A2, 2E1, or 3A22 in male minipig liver microsomes.

AbstractUnderstanding compound metabolism in early drug discovery aids medicinal chemistry in designing molecules with improved safety and ADME properties. While advancements in metabolite prediction brings increased confidence, structural decisions require experimental data. In vitro metabolism studies using liquid chromatography and high-resolution mass spectrometry (LC–MS) are generally resource intensive and performed on very few compounds, limiting the chemical space that can be examined.Here, we describe a novel metabolism strategy increasing compound throughput using residual in vitro clearance samples conducted at drug concentrations of 0.5 µM. Analysis by robust ultra high-performance liquid chromatography separation and accurate-mass MS detection ensures major metabolites are identified from a single injection. In silico prediction (parent cLogD) tailors chromatographic conditions, with data-dependent tandem mass spectroscopy targeting predicted metabolites. Software-assisted data mining, structure elucidation and automatic reporting are used.Confidence in the globally aligned workflow is demonstrated with 16 marketed drugs. The approach is now implemented routinely across our laboratories. To date, the success rate for identification of at least one major metabolite is 85%. The utility of these data has been demonstrated across multiple projects, allowing earlier medicinal chemistry decisions to increase efficiency and impact of the design–make–test cycle thus improving the translatability of early in vitro metabolism data.

Abstract  The therapeutic concept of antibody drug conjugates (ADCs) is to selectively target tumour cells with small molecule cytotoxic drugs to maximise cell kill benefit and minimise healthy tissue toxicity.An ADC generally consists of an antibody that targets a protein on the surface of tumour cells chemically linked to a warhead small molecule cytotoxic drug.To deliver the warhead to the tumour cell, the antibody must bind to the target protein and in general be internalised into the cell. Following internalisation, the cytotoxic agent can be released in the endosomal or lysosomal compartment (via different mechanisms). Diffusion or transport out of the endosome or lysosome allows the cytotoxic drug to express its cell-killing pharmacology. Alternatively, some ADCs (e.g. EDB-ADCs) rely on extracellular cleavage releasing membrane permeable warheads.One potentially important aspect of the ADC mechanism is the ‘bystander effect’ whereby the cytotoxic drug released in the targeted cell can diffuse out of that cell and into other (non-target expressing) tumour cells to exert its cytotoxic effect. This is important as solid tumours tend to be heterogeneous and not all cells in a tumour will express the targeted protein.The combination of large and small molecule aspects in an ADC poses significant challenges to the disposition scientist in describing the ADME properties of the entire molecule.This article will review the ADC landscape and the ADME properties of successful ADCs, with the aim of outlining best practice and providing a perspective of how the field can further facilitate the discovery and development of these important therapeutic modalities.

AbstractThe past two decades have seen diversification of drug development pipelines and approvals from traditional small molecule therapies to alternative modalities including monoclonal antibodies, engineered proteins, antibody drug conjugates (ADCs), oligonucleotides and gene therapies. At the same time, physiologically based pharmacokinetic (PBPK) models for small molecules have seen increased industry and regulatory acceptance.This review focusses on the current status of the application of PBPK models to these newer modalities and give a perspective on the successes, challenges and future directions of this field.There is greatest experience in the development of PBPK models for therapeutic proteins, and PBPK models for ADCs benefit from prior experience for both therapeutic proteins and small molecules. For other modalities, the application of PBPK models is in its infancy.Challenges are discussed and a common theme is lack of availability of physiological and experimental data to characterise systems and drug parameters to enable a priori prediction of pharmacokinetics. Furthermore, sufficient clinical data are required to build confidence in developed models.The PBPK modelling approach provides a quantitative framework for integrating knowledge and data from multiple sources and can be built on as more data becomes available.

AbstractUridine diphosphate glucuronosyltransferase (UGT) enzymes conjugate many lipophilic chemicals, such as drugs, environmental contaminants, and endogenous compounds, promoting their excretion. The complexity of UGT kinetics, and the location of enzyme active site in endoplasmic reticulum lumen, requires an accurate optimisation of enzyme assays.In the present study, we characterised UGT activity in liver microsomes of green turtles (Chelonia mydas), an endangered species. The conditions for measuring UGT activity were standardised through spectrofluorimetric methods, using the substrates 4-methylumbelliferone (4-MU) and uridine diphosphate glucuronic acid (UDPGA) at 30 °C and pH 7.4.The green turtles showed UGT activity at the saturating concentrations of substrates of 250 µM to 4-MU and 7 mM to UDPGA. The alamethicin, Brij®58, bovine serum albumin (BSA), and magnesium increased UGT activity. The assay using alamethicin (22 µg per mg of protein), magnesium (1 mM), and BSA (0.25%) reached the highest Vmax (1203 pmol·min−1mg·protein−1). Lithocholic acid and diclofenac inhibited UGT activity in green turtles.This study is the first report of UGT activity in the liver of green turtles and provides a base for future studies to understand the mechanisms of toxicity by exposure to contaminants in this charismatic species.

ABSTRACT We investigated the changes in the expression of drug-metabolising enzymes and drug transporters in the liver, small intestine and kidney of mice with collagen antibody-induced arthritis (CAIA) to determine whether changes in these expressions affect pharmacokinetics of drugs in patients with rheumatoid arthritis.mRNA expression levels of cytochrome P450 (Cyp) 2b10, Cyp2c29 and Cyp3a11 were observed to be lower in the liver and small intestine of CAIA mice than in control mice. Compared with control mice, mRNA expression levels of multidrug resistance 1b, peptide transporter 2 and organic anion transporter (Oat) 2 were high in the liver of CAIA mice. Changes in these expression levels were different among organs. However, elevated expression of Oat2 mRNA was not associated with an increase in protein expression and transport activity evaluated using [3H]cGMP as a substrate.These results suggest that arthritis can change the expression of pharmacokinetics-related genes, but the changes may not necessarily be linked to the pharmacokinetics in patients with rheumatoid arthritis. On the other hand, we found Oat2 mRNA expression level was positively correlated with plasma interleukin-6 level, indicating that transcriptional activation of Oat2 may occur in inflammatory state.

Abstract1. The metabolism of most medications approved for the treatment of ADHD is not fully understood.2. In vitro studies using cryopreserved, plated human hepatocytes (cPHHs) and pooled human liver microsomes (HLMs) were performed to more thoroughly characterise the metabolism of several ADHD medications.3. The use of enzyme-specific chemical inhibitors indicated a role for CYP2D6 in atomoxetine metabolism, and roles for CYP3A4/5 in guanfacine metabolism.4. The 4-hydroxy-atomoxetine and N-desmethyl-atomoxetine pathways represented 98.4% and 1.5% of atomoxetine metabolism in cPHHs, respectively. The 3-OH-guanfacine pathway represented at least 2.6% of guanfacine metabolism in cPHHs, and 71% in HLMs.5. The major metabolizing enzyme for methylphenidate and dexmethylphenidate could not be identified using these methods because these compounds were too unstable. Hydrolysis of these medications was spontaneous and did not require the presence of protein to occur.6. Clonidine, amphetamine, and dextroamphetamine did not deplete substantially in cPHHs nor HLMs, suggesting that these compounds may not undergo considerable hepatic metabolism. The major circulating metabolites of amphetamine and dextroamphetamine (benzoic acid and hippuric acid) were not observed in either system, and therefore could not be characterised. Additionally, inhibition experiments suggested a very minimal role for CYP2D6 in clonidine and amphetamine metabolism.

AbstractCefixime is an antibiotic from the cephalosporin class used to treat various bacterial infections. The purpose of performing this review is to thoroughly evaluate the pharmacokinetic (PK) data on cefiximeFive databases were systematically searched to identify studies on the PK of cefixime.A total of 38 articles meeting the eligibility criteria were included that provide data on concentration-time profiles or PK parameters such as peak plasma and serum concentration (Cmax), area under the curve (AUC), clearance (CL), and time to reach Cmax (tmax). A dose-dependent increase in AUC and Cmax of cefixime was depicted in healthy volunteers. The clearance of cefixime decreased according to the degree of renal insufficiency among haemodialysis patients. A significant difference in CL was found in comparing fasted and fed states. A biphasic decline in serum concentrations of cefixime was reported when it was taken without probenecid.This review compiles all the reports on the PK of cefixime in healthy and really impaired patients; the summarised information can be used to optimise cefixime dosing in different disease states. Moreover, cefixime has increased time above MIC value suggesting that it may be an effective treatment for infections caused by certain pathogens.

AbstractThe co-administration of losartan and puerarin in hypertension rat models was investigated aiming to evaluate their interaction and potential mechanism.Hypertension rat models were established with N (omega)-nitro-L-arginine methyl ester and the pharmacokinetics and antihypertensive effect of losartan were analyzed in normal and hypertension rats. In vitro, the metabolic stability of losartan was evaluated in rat liver microsomes, and the effect of puerarin on the activity of CYP2C9 and 3A4 was assessed in human liver microsomes.Puerarin significantly changed the pharmacokinetic profiling of losartan in hypertension rats, with the behaviour of increasing AUC, AUMC, Cmax, and prolonged t1/2. The antihypertensive effect of losartan was enhanced by the co-administration of puerarin, which reduced the systolic blood pressure and diastolic blood pressure below normal levels. In vitro, puerarin significantly improved the metabolic stability of losartan with a reduced intrinsic clearance rate. Puerarin also showed significant inhibitory effects on the activity of CYP2C9 and 3A4 with the IC50 of 17.15 and 7.69 μM, respectively.Losartan co-administered with puerarin increased the system exposure and metabolic stability of losartan and enhanced its antihypertensive effect. The inhibition of CYP2C9 and 3A4 by puerarin was the potential mechanism mediating their interaction.

Abstract1. Cytochrome P450 2J2 (CYP2J2) shows high expression in extrahepatic tissues, including the heart and kidney and in tumours. Inhibition of CYP2J2 has attracted attention for cancer treatment because it metabolizes arachidonic acid (AA) to epoxyeicosatrienoic acid (EET), which inhibits apoptosis and promotes tumour growth. Multi-kinase inhibitor (MKI) is a molecular-targeted drug with antitumor activities. This study aimed to clarify the inhibitory effects of MKIs on CYP2J2 activity. We also investigated whether MKIs affected CYP2J2-catalysed EET formation from AA.2. Twenty MKIs showed different inhibitory potencies against astemizole O-demethylation in CYP2J2. In particular, apatinib, motesanib, and vatalanib strongly inhibited astemizole O-demethylation. These three MKIs exhibited competitive inhibition with inhibition constant (Ki) values of 9.3, 15.4, and 65.0 nM, respectively. Apatinib, motesanib, and vatalanib also inhibited CYP2J2-catalysed 14,15-EET formation from AA.3. In simulations of docking to CYP2J2, the U energy values of apatinib, motesanib, and vatalanib were low, and measured -84.5, -69.9, and -52.3 kcal/mol, respectively.4. In conclusion, apatinib, motesanib, and vatalanib strongly inhibited CYP2J2 activity, suggesting that the effects of a given CYP2J2 substrate may be altered upon the administration of these MKIs.

AbstractBictegravir (BIC) is a potent small-molecule integrase strand-transfer inhibitor (INSTI) and a component of Biktarvy®, a single-tablet combination regimen that is currently approved for the treatment of human immunodeficiency virus type 1 (HIV-1) infection. The in vitro properties, pharmacokinetics (PK), and drug-drug interaction (DDI) profile of BIC were characterised in vitro and in vivo.BIC is a weakly acidic, ionisable, lipophilic, highly plasma protein-bound BCS class 2 molecule, which makes it difficult to predict human PK using standard methods. Its systemic plasma clearance is low, and the volume of distribution is approximately the volume of extracellular water in nonclinical species. BIC metabolism is predominantly mediated by cytochrome P450 enzyme (CYP) 3A and UDP-glucuronosyltransferase 1A1. BIC shows a low potential to perpetrate clinically meaningful DDIs via known drug metabolising enzymes or transporters.The human PK of BIC was predicted using a combination of bioavailability and volume of distribution scaled from nonclinical species and a modified in vitro-in vivo correlation (IVIVC) correction for clearance. Phase 1 studies in healthy subjects largely bore out the prediction and supported the methods used. The approach presented herein could be useful for other drug molecules where standard projections are not sufficiently accurate.

AbstractDrug oxidations are mediated mainly by cytochromes P450 (P450s or CYPs). CYP3As are an important P450 subfamily and include liver-specific CYP3A12 and intestine-specific CYP3A98 in dogs. Individual differences in drug oxidation activities were investigated, including correlations with immunoreactive CYP3A protein intensities and CYP3A mRNA expression levels in livers.Pooled and individual dog liver microsomes showed activities towards nifedipine, midazolam, alprazolam, and estradiol, but the levels of catalytic activities varied approximately twofold among the individual dogs. One dog harboured a CYP1A2 variant causing protein deletion but showed higher activities than the other dogs towards nifedipine oxidation, midazolam 1′-hydroxylation, alprazolam 4-hydroxylation, estradiol 16α-hydroxylation activities, and caffeine C8-hydroxylation; the latter is used as a reference reaction for CYP1A.In individual dog liver microsomes, the intensities of the immunochemical bands with anti-human CYP3A4 and anti-rat CYP3A2 antibodies along with CYP3A12 and CYP3A26 mRNA expression levels showed good correlations (p < 0.05) with nifedipine oxidation, midazolam 1′- and 4-hydroxylation, alprazolam 1′- and 4-hydroxylation, and estradiol 16α-hydroxylation activities.These results suggest that the oxidation activities of dog liver microsomes towards nifedipine and other typical CYP3A-catalyzed drugs exhibit approximately twofold individual differences and were predominantly mediated by liver-specific CYP3A12 in the dogs.

AbstractEvodol is one of the furanoids isolated from the fruits of Evodia rutaecarpa that has been widely prescribed for the treatment of gastrointestinal diseases in China. The aim of this study was to investigate the inhibitory effect of evodol on CYP3A.A 30-min preincubation of evodol with human liver microsomes raised an obvious left IC50 shift, 3.9-fold for midazolam 1’-hydroxylation and 3.2-fold for testosterone 6β-hydroxylation. Evodol inactivated CYP3A in a time-, concentration- and NADPH-dependent manner, with KI and kinact of 5.1 μM and 0.028 min−1 for midazolam 1’-hydroxylation and 3.0 μM and 0.022 min−1 for testosterone 6β-hydroxylation.Co-incubation of ketoconazole attenuated the inactivation while the inclusion of glutathione (GSH) and catalase/superoxide dismutase displayed no such protection.cis-Butene-1, 4-dial (BDA) intermediate derived from evodol were trapped by glutathione and N-acetyl-lysine in microsomes and characterised by HR-MS spectra. The BDA intermediate was believed to play a key role in CYP3A inactivation. CYP3A4 and 2C9 were the primary enzymes contributing to the bioactivation of evodol.To sum up, for the first time evodol was characterised as a mechanism-based inactivator of CYP3A.

AbstractChallenges, strategies and new technologies in the field of biotransformation were presented and discussed at the 3rd European Biotransformation Workshop which was held in collaboration with the DMDG on 5–6 October 2022 in Amsterdam. In this meeting report we summarise the presentations and discussions from this workshop. The topics covered are listed below:Accelerator mass spectrometry (AMS) for the support of microtracer studiesBiotransformation of the novel myeloperoxidase inhibitor AZD4831 in preclinical species and humansAMS in biotransformation studies: unusual case studiesDiscussion on new FDA draft guidance and AMSMultimodal molecular imaging and ion mobility applications in drug discovery and developmentMetabolites in Safety Testing considerations for large molecules

AbstractAs the Space Race or Formula 1 drives innovation, efficiency and progress in home technology and home car markets, Drug Metabolism and Pharmacokinetics (DMPK) drives scientific innovation and value for drug development companies. Stand still and fall behind as the saying goes, and these analogies are true as much in the design and conduct of DMPK studies as they are in the technology and manufacturing sectors.This short review showcases the impact that DMPK has had on drug development and how it has changed in the last 10 years, illustrating the value added scientific benefit, cost and time saving, that innovative DMPK program design and study conduct have. Examples and case studies spanning novel in vitro alternatives such as organ-on-a-chip (OOAC) developments; use of in vivo microsampling across small and large animal species; challenging historical paradigms in Absorption, Distribution, Metabolism and Excretion (ADME) studies; and embracing new technologies to address regulatory concerns, are presented.The continual pace of change has kept DMPK at the core of pharmaceutical, crop and chemical evaluation, and this is set to continue as regulators use this discipline to inform decision-making. With new modalities and new scientific questions, DMPK will continue to evolve, with the likes of new in vitro, in vivo and in silico models becoming central to candidate selection and progression.

Abstract Tree shrews have high phylogenetic affinity to humans and are used in various fields of biomedical research, especially hepatitis virus infection; however, cytochromes P450 (P450s or CYPs) have not been investigated in this species.In this study, tree shrew CYP2B6 and pig CYP2B6b were newly identified and contained amino acid sequences highly identical (80% and 78%, respectively) to human CYP2B6 and included sequence motifs characteristic of P450s.Phylogenetic analysis revealed that novel tree shrew CYP2B6 was more closely related to known human CYP2B6 than dog, pig, or rat CYP2Bs are.Among the tissue types analysed, tree shrew CYP2B6 mRNA was preferentially expressed in liver and lung, whereas pig CYP2B6b mRNA was preferentially expressed in jejunum and lung.Tree shrew CYP2B6 and pig CYP2B6b proteins heterologously expressed in Escherichia coli metabolized human CYP2B6 substrates efavirenz, ethoxycoumarin, propofol, and testosterone, suggesting that these novel CYP2Bs are functional drug-metabolizing enzymes in liver and/or lung.

Abstract Although liquid chromatography-tandem mass spectrometry is the gold standard analytical platform for the quantification of drugs, metabolites, and biomarkers in biological samples, it cannot localise them in target tissues.The localisation and quantification of drugs and/or their associated metabolites in target tissues is a more direct measure of local drug exposure, biodistribution, efficacy, and regional toxicity compared to the traditional substitute studies using plasma.Therefore, combining high spatial resolution imaging functionality with the superior selectivity and sensitivity of mass spectrometry into one analytical technique will be a valuable tool for targeted localisation and quantification of drugs, metabolites, and biomarkers in tissues.Mass spectrometry imaging (MSI) is a tagless analytical technique that allows for the direct localisation and quantification of drugs, metabolites, and biomarkers in biological tissues, and has been used extensively in pharmaceutical research.The overall goal of this current review is to provide a detailed description of the working principle of MSI and its application in pharmacokinetic studies encompassing absorption, distribution, metabolism, excretion, and toxicity processes, followed by a discussion of the strategies for addressing the challenges associated with the functional utility of MSI in pharmacokinetic studies that support drug development.

AbstractBCRP (breast cancer resistance protein) is a crucial efflux transporter involved in the regulation of the pharmacokinetics and pharmacodynamics of a wide range of drugs. Herein, we aimed to investigate a potential role for the nuclear receptor REV-ERBα in the regulation of BCRP expression and sulfasalazine (a BCRP probe substrate) pharmacokinetics.Regulation of BCRP expression by REV-ERBα was assessed using Rev-erbα-/- mice and AML12 and CT26 cells. Pharmacokinetic analysis was performed with Rev-erbα-/- and wild-type mice after sulfasalazine administration.We found that the expression levels of BCRP mRNA and protein were downregulated in the liver and small intestine of Rev-erbα-dificient mice. In line with this, Rev-erbα ablation increased the systemic exposures of oral sulfasalazine.Positive regulation of BCRP expression and function by REV-ERBα was furtherly confirmed in AML12 and CT26 cells. Moreover, indirect regulation of Bcrp expression by REV-ERBα was potentially mediated by a negative transcription factor DEC2, which is a downstream target of REV-ERBα.In conclusion, REV-ERBα positively regulates BCRP expression in mice, thereby affecting sulfasalazine pharmacokinetics.

Published in Xenobiotica: the fate of foreign compounds in biological systems (Vol. 53, No. 1, 2023)

AbstractSH-1028 is a novel, potent, and highly selective epidermal growth factor receptor tyrosine kinase inhibitor (EGFR-TKI) developed for the treatment of T790M Mutation-positive non-small cell lung cancer (NSCLC). The objective was to develop an LC-MS/MS method for the simultaneous determination of SH-1028 and its metabolites, Imp2 and Imp3, in human plasma.The plasma samples were extracted through protein precipitation with acetonitrile on wet ice conditions. A rapid, sensitive, and specific method was developed and successfully applied to evaluate the pharmacokinetic (PK) properties of SH-1028 in patients with advanced NSCLC following single and multiple doses of SH-1028 (60 mg).After single-dose administration, the Cmax of SH-1028, Imp2, and Imp3 was 11.2, 50.2, and 7.99 ng/mL, respectively. The mean AUC0–24 h was 138, 602, and 76.7 h*ng/mL, respectively. And the terminal half-life time was 19.9, 14.4, and 26.1 h, respectively. After multiple-dose administration, SH-1028 exhibited a slight accumulation, with a mean accumulation ratio (RAUC) of 2.00.The study assessed the PK properties of SH-1028 following single and multiple doses in patients with advanced NSCLC and would provide meaningful information for the further development of SH-1028.