Meeting report: metabolites in safety testing (MIST) symposium-safety assessment of human metabolites: what's REALLY necessary to ascertain exposure coverage in safety tests?

Absorption, distribution, metabolism and excretion of 14C-Emvododstat following a single oral dose in rats and dogs

Emvododstat is a potent inhibitor of dihydroorotate dehydrogenase and is now in clinical development for the treatment of acute myeloid leukaemia and COVID-19.Following an oral dose administration in Long-Evans rats, ¹⁴C-emvododstat-derived radioactivity was widely distributed throughout the body, with the highest distribution in the endocrine, fatty, and secretory tissues and the lowest in central nervous system.Following a single oral dose of ¹⁴C-emvododstat in rats, 54.7% of the dose was recovered in faeces while less than 0.4% of dose was recovered in urine 7 days post-dose. Emvododstat was the dominant radioactive component in plasma and faeces.Following a single oral dose of ¹⁴C-emvododstat in dogs, 75.2% of the dose was recovered in faeces while 0.5% of dose was recovered in urine 8 days post-dose. Emvododstat was the dominant radioactive component in faeces, while emvododstat and its two metabolites (O-desmethyl emvododstat and emvododstat amide bond hydrolysis product) were the major circulating radioactivity in dog plasma.

Quantification of abemaciclib and metabolites: evolution of bioanalytical methods supporting a novel oncolytic agent

Aim: Bioanalytical methods undergo many revisions and modifications throughout drug development to meet the objectives of the study and development program. Results: Validated LC-MS/MS methodology used to quantify abemaciclib and four metabolites in human plasma is described. The method, initially validated to support the first-in-human study, was successfully modified to include additional metabolites as in vitro and in vivo information about the activity and abundance of human metabolites became available. Consistent performance of the method over time was demonstrated by an incurred sample reanalysis passing rate exceeding 95%, across clinical studies. An overview of the numerous methods involved during the development of abemaciclib, including the quantification of drugs evaluated as combination regimens and used as substrates during drug-drug interaction studies, is presented. Conclusion: Robust bioanalytical methods need to be designed with the flexibility required to support the evolving study objectives associated with registration and post-registration trials.

Effects of Analyte Concentration on the Protonation Sites of 4-Aminobenzoic Acid upon Atmospheric Pressure Chemical Ionization As Revealed by Gas-Phase Ion-Molecule Reactions

The most basic site of 4-aminobenzoic acid in aqueous solution is the amino nitrogen, while the carbonyl oxygen is calculated to be the most basic site in the gas phase. However, the preferred protonation site of 4-aminobenzoic acid upon electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) depends upon the ionization solvent and ion source parameters. The influence of the concentration of the analyte on the manifested protonation sites upon APCI has not been investigated and is reported here. Gas-phase ion-molecule reactions of trimethoxymethylsilane were used to identify the protonation sites of 4-aminobenzoic acid ionized using APCI with methanol or acetonitrile-water as the solvent. The nitrogen-protomer was found to be about twice as abundant as the oxygen-protomer at low analyte concentrations (10^-9-10^-6 M) in methanol solvent. This finding was rationalized on the basis of a previous finding that when the O-protomer is surrounded by more than eight methanol molecules in the gas phase it starts behaving as if it were in an aqueous solution and converts to the N-protomer. At greater analyte concentrations (≥10^-4 M), the amino group was predominantly protonated, which was rationalized based on the formation of a particularly stable proton-bound dimer of 4-aminobenzoic acid that preferentially dissociates to form the N-protomer. The above findings suggest that solution processes are much more important in APCI than commonly assumed, in agreement with recent literature. Indeed, when 1:1 (v/v) acetonitrile-water was used as the solvent system for 4-aminobenzoic acid, the N-protomer was predominantly generated at all analyte concentrations.

In Vitro Investigation, Pharmacokinetics, and Disposition of Imeglimin, a Novel Oral Antidiabetic Drug, in Preclinical Species and Humans

Imeglimin is a novel oral antidiabetic drug for treatment of type 2 diabetes that targets mitochondrial bioenergetics. Its pharmacokinetics absorption characteristics, metabolism, distribution, and elimination were assessed through several in vitro and in vivo experiments in both animals and humans. Its potential to induce drug-drug interactions was also extensively assessed. Imeglimin is a small cationic compound with an intermediate intestinal permeability. Its absorption mechanism involves an active transport process in addition to passive paracellular absorption. Absorption was good (50%-80%) in vivo across several species but decreased with increasing dose, probably because of saturation of active transport. After absorption, imeglimin was rapidly and largely distributed to internal organs. Plasma protein binding was low, which can explain the rapid distribution to organs observed in all species. In animals and humans, imeglimin was largely excreted unchanged in urine, indicating a low extent of metabolism. Unchanged drug was the main circulating entity in plasma, and none of the identified metabolites were unique to human. Imeglimin renal clearance was higher than creatinine clearance, indicating that it was actively secreted into urine. There was no evidence that it had the potential to cause cytochrome P450 inhibition or induction. It was shown to be a substrate of organic cation transporter (OCT) 1, OCT2, multidrug and toxin extrusion (MATE) 1, and MATE2-K and an inhibitor of OCT1, OCT2, and MATE1; as a consequence, corresponding clinical drug-drug interaction studies were performed and confirmed the absence of relevant interactions with substrates or inhibitors of these transporters. SIGNIFICANCE STATEMENT: Imeglimin is absorbed through a passive and active mechanism, which can be saturated. It is rapidly and largely distributed to internal organs and mainly excreted unchanged in urine. It is poorly metabolized and has no cytochrome P450 inhibition or induction potential. Imeglimin is a substrate of MATE2-K and also a substrate and an inhibitor of OCT1, OCT2, and MATE1 transporters; however, there are no clinically significant interactions when imeglimin is coadministered with either a substrate or an inhibitor of these transporters.

Validation and reproducibility of an LC-MS/MS method for emixustat and its three deaminated metabolites in human plasma

Aim: A sensitive method to quantify emixustat and its rapidly formed three major deaminated metabolites in human plasma was necessary to determine exposure in clinical trials. Methods: An LC-MS/MS method was validated for accuracy and precision, linearity, carry over, selectivity, recovery, matrix effects, hematocrit effects and stability. Results: A quantitative procedure for the determination of emixustat, ACU-5116, ACU-5124 and ACU-5149 in human plasma over the concentration range of 0.0500/1.00/1.00/1.00-10.0/1000/1000/1000 ng/ml, was successfully validated and has been used to successfully analyze samples in three clinical trials. Incurred sample reanalysis was performed for all four analytes in each study with >92% of the repeat results and original results within 20% of the mean of the two values.

Characterization of Cytochrome P450 Enzymes and Their Applications in Synthetic Biology

The cytochrome P450 monooxygenase enzymes (P450s) catalyze a diverse array of chemical transformations, most originating from the insertion of an oxygen atom into a substrate that binds close to the P450 heme. The oxygen is delivered by a highly reactive heme iron-oxo species (compound I) and, according to the chemical nature of the substrate and its position in the active site, the P450 can catalyze a wide range of reactions including, e.g., hydroxylation, reduction, decarboxylation, sulfoxidation, N- and O-demethylation, epoxidation, deamination, CC bond formation and breakage, nitration, and dehalogenation. In this chapter, we describe the structural, biochemical, and catalytic properties of the P450s, along with spectroscopic and analytical methods used to characterize P450 enzymes and their redox partners. Important uses of P450 enzymes are highlighted, including how various P450s have been exploited for applications in synthetic biology.

Biotransformation of 4-fluoro-N-(1-{2-[(propan-2-yl)phenoxy]ethyl}-8-azabicyclo[3.2.1]octan-3-yl)-benzenesulfonamide, a novel potent 5-HT7 receptor antagonist with antidepressant-like and anxiolytic properties: In vitro and in silico approach

The aim of the study was to investigate the metabolism of 4-fluoro-N-(1-{2-[(propan-2-yl)phenoxy]ethyl}-8-azabicyclo[3.2.1]octan-3-yl)-benzenesulfonamide (PZ-1150), a novel 5-HT₇ receptor antagonist with antidepressant-like and anxiolytic properties, by the following three ways: in vitro with microsomes; in vitro employing Cunninghamella echinulata, and in silico using MetaSite. Biotransformation of PZ-1150 with microsomes resulted in five metabolites, while transformation with C. echinulata afforded two metabolites. In both models, the predominant metabolite occurred due to hydroxylation of benzene ring. In silico data coincide with in vitro experiments, as three MetaSite metabolites matched compounds identified in microsomal samples. In human liver microsomes PZ-1150 exhibited in vitro half-life of 64 min, with microsomal intrinsic clearance of 54.1 μL/min/mg and intrinsic clearance of 48.7 mL/min/kg. Therefore, PZ-1150 is predicted to be a high-clearance agent. The study demonstrated the applicability of using microsomal model coupled with microbial model to elucidate the metabolic pathways of compounds and comparison with in silico metabolite predictions.

Identification of Protonated Sulfone and Aromatic Carboxylic Acid Functionalities in Organic Molecules by Using Ion-Molecule Reactions Followed by Collisionally Activated Dissociation in a Linear Quadrupole Ion Trap Mass Spectrometer

Gas-phase reactivity of protonated model compounds with different functional groups toward trimethoxymethylsilane (TMMS) was studied to explore the utility of this reagent in mass spectrometric identification of specific functionalities for potentially rapid characterization of drug metabolites. Only protonated analytes with a carboxylic acid, a sulfone, or a sulfonamide functionality formed diagnostic adducts that had lost a methanol molecule upon reactions with TMMS. Collisionally activated dissociation (CAD) of these methanol-eliminated adduct ions (MS³ experiments) produced characteristic fragment ions of m/z 75, 105, and 123 for sulfones, while an additional methanol elimination was observed for carboxylic acids and sulfonamides. CAD of latter products (MS⁴ experiments) resulted in elimination of diagnostic neutral molecules CO₂ (44 Da) and C₂H₆O₂Si (90 Da) for aromatic carboxylic acids. Both aliphatic carboxylic acids and sulfonamides yield several fragment ions in these MS⁴ experiments that are different from those observed for sulfones or aromatic carboxylic acids. Potential energy surfaces were calculated (at the M06-2X/6-311++G(d,p) level of theory) to explore the mechanisms of various reactions. In summary, sulfones and aromatic carboxylic acids can be differentiated from each other and also from sulfonamides and aliphatic carboxylic acids based on reactions with TMMS and one or two CAD experiments. Aliphatic carboxylic acids and sulfonamides could not be differentiated from each other.

Absorption, Distribution, Metabolism, and Excretion of the Oral Prostaglandin D2 Receptor 2 Antagonist Fevipiprant (QAW039) in Healthy Volunteers and In Vitro

Fevipiprant is a novel oral prostaglandin D₂ receptor 2 (DP₂; also known as CRTh2) antagonist, which is currently in development for the treatment of severe asthma and atopic dermatitis. We investigated the absorption, distribution, metabolism, and excretion properties of fevipiprant in healthy subjects after a single 200-mg oral dose of [¹⁴C]-radiolabeled fevipiprant. Fevipiprant and metabolites were analyzed by liquid chromatography coupled to tandem mass spectrometry and radioactivity measurements, and mechanistic in vitro studies were performed to investigate clearance pathways and covalent plasma protein binding. Biotransformation of fevipiprant involved predominantly an inactive acyl glucuronide (AG) metabolite, which was detected in plasma and excreta, representing 28% of excreted drug-related material. The AG metabolite was found to covalently bind to human plasma proteins, likely albumin; however, in vitro covalent binding to liver protein was negligible. Excretion was predominantly as unchanged fevipiprant in urine and feces, indicating clearance by renal and possibly biliary excretion. Fevipiprant was found to be a substrate of transporters organic anion transporter 3 (OAT3; renal uptake), multidrug resistance gene 1 (MDR1; possible biliary excretion), and organic anion-transporting polypeptide 1B3 (OATP1B3; hepatic uptake). Elimination of fevipiprant occurs via glucuronidation by several uridine 5'-diphospho glucuronosyltransferase (UGT) enzymes as well as direct excretion. These parallel elimination pathways result in a low risk of major drug-drug interactions or pharmacogenetic/ethnic variability for this compound.

Combining Chimeric Mice with Humanized Liver, Mass Spectrometry, and Physiologically-Based Pharmacokinetic Modeling in Toxicology

Species differences exist in terms of drug oxidation activities, which are mediated mainly by cytochrome P450 (P450) enzymes. To overcome the problem of species extrapolation, transchromosomic mice containing a human P450 3A cluster or chimeric mice transplanted with human hepatocytes have been introduced into the human toxicology research area. In this review, drug metabolism and disposition mediated by humanized livers in chimeric mice are summarized in terms of biliary/urinary excretions of phthalate and bisphenol A and plasma clearances of the human cocktail probe drugs caffeine, warfarin, omeprazole, metoprolol, and midazolam. Simulation of human plasma concentrations of the teratogen thalidomide and its human metabolites is possible with a simplified physiologically based pharmacokinetic model based on data obtained in chimeric mice, in accordance with reported clinical thalidomide concentrations. In addition, in vivo nonspecific hepatic protein binding parameters of metabolically activated ¹⁴C-drug candidate and hepatotoxic medicines in humanized liver mice can be analyzed by accelerator mass spectrometry and are useful for predictions in humans.

Low-Turnover Drug Molecules: A Current Challenge for Drug Metabolism Scientists

In vitro assays using liver subcellular fractions or suspended hepatocytes for characterizing the metabolism of drug candidates play an integral role in the optimization strategy employed by medicinal chemists. However, conventional in vitro assays have limitations in their ability to predict clearance and generate metabolites for low-turnover (slowly metabolized) drug molecules. Due to a rapid loss in the activity of the drug-metabolizing enzymes, in vitro incubations are typically performed for a maximum of 1 hour with liver microsomes to 4 hours with suspended hepatocytes. Such incubations are insufficient to generate a robust metabolic response for compounds that are slowly metabolized. Thus, the challenge of accurately estimating low human clearance with confidence has emerged to be among the top challenges that drug metabolism scientists are confronted with today. In response, investigators have evaluated novel methodologies to extend incubation times and more sufficiently measure metabolism of low-turnover drugs. These methods include plated human hepatocytes in monoculture, and a novel in vitro methodology using a relay of sequential incubations with suspended cryopreserved hepatocytes. In addition, more complex in vitro cellular models, such as HepatoPac (Hepregen, Medford, MA), a micropatterned hepatocyte-fibroblast coculture system, and the HµREL (Beverley Hills, CA) hepatic coculture system, have been developed and characterized that demonstrate prolonged enzyme activity. In this review, the advantages and disadvantages of each of these in vitro methodologies as it relates to the prediction of clearance and metabolite identification will be described in an effort to provide drug metabolism scientists with the most up-to-date experimental options for dealing with the complex issue of low-turnover drug candidates.

Lipid Peroxide-Mediated Oxidative Rearrangement of the Pyrazinone Carboxamide Core of Neutrophil Elastase Inhibitor AZD9819 in Blood Plasma Samples

This study focused on the mechanistic interpretation of ex vivo oxidation of a candidate drug in blood plasma samples. An unexpected lipid peroxide-mediated epoxidation followed by a dramatic rearrangement led to production of a five-membered oxazole derivative from the original six-membered pyrazinone-carboxamide core of a human neutrophil elastase inhibitor, 6-(1-(4-cyanophenyl)-1H-pyrazol-5-yl)-N-ethyl-5-methyl-3-oxo-4-(3-(trifluoromethyl)phenyl)-3,4-dihydropyrazine-2-carboxamide (AZD9819). The rearranged oxidation product 2-(1-(4-cyanophenyl)-1H-pyrazol-5-yl)-5-(N-ethylacetamido)-N-(3-(trifluoromethyl)phenyl)oxazole-4-carboxamide was characterized by accurate-mass tandem mass spectrometry fragmentations, by two-dimensional NMR and X-ray crystallography of an authentic standard, and by incorporation of an (18)O atom from molecular (18)O2 to the location predicted by our proposed mechanism. The lipid peroxide-mediated oxidation was demonstrated by using human low-density lipoprotein (LDL) in pH 7.4 phosphate buffer and by inhibiting the oxidation with ascorbic acid or l-glutathione, two antioxidants effective in both plasma and the LDL incubation. A nucleophilic mechanism for the epoxidation of AZD9819 by lipid hydroperoxides explains the prevention of its ex vivo oxidation by acidification of the plasma samples. The discovery of the lipid peroxide-dependent oxidation of an analyte and the means of prevention could provide valuable information for biotransformation and bioanalysis.

Clinical pharmacokinetics, safety, and preliminary efficacy evaluation of icotinib in patients with advanced non-small cell lung cancer

OBJECTIVES

To receive pharmacokinetics, safety, and anti-tumor activity of icotinib, a novel epidermal growth factor receptor (EGFR)-tyrosine kinase inhibitor (TKI), in patients with advanced non-small-cell lung cancer (NSCLC).

MATERIALS AND METHODS

Patients (n=40) with advanced NSCLC were enrolled to receive escalating doses of icotinib, which was administrated on Day 1 followed by 28-day continuous dosing starting from Day 4. Four dosing regimens, 100mg b.i.d., 150 mg b.i.d., 125 mg t.i.d., and 200mg b.i.d. were studied. Pharmacokinetics (PK), safety, and efficacy of icotinib were evaluated.

RESULTS

Icotinib was well tolerated in Chinese patients with refractory NSCLC. No toxicity with >3 grades were reported in more than 2 patients under any dose levels. One complete response (3%) and 9 partial responses (23%) were received. Total disease control rate could reach at 73% and median progress-free survival (range) was 154 (17-462) days. PK exposure of icotinib increased with increase of dose in NSCLC patients. Food was suggested to increase PK exposure by ∼30%. Mean t1/2β was within 5.31-8.07 h. No major metabolite (>10% plasma exposure of icotinib) was found in NSCLC patients.

CONCLUSIONS

Icotinib with up to 400 mg/day exhibited good tolerance and preliminary antitumor activity in Chinese NSCLC patients. Pharmacokinetics of icotinib and 5 major metabolites were fully investigated in NSCLC patients. Optimized biologic dose (OBD) was finally recommended to be 125 mg t.i.d. for the later clinical study.

The debate on animal ADME studies in drug development: an update

The preparation and release of the International Conference on Harmonisation guideline on safety evaluation of human metabolites and the technical progresses in bioanalysis have triggered an intense debate on the value of absorption, distribution, metabolism and excretion radiolabelled studies in animals. Some authors have radically challenged the traditional approach whereas others, while accepting the need of significant changes, argue that these studies remain an irreplaceable component of the preclinical registration dossier. This paper reviews some of the representative positions and describes the potential evolution.

Data-driven approach for cross-species comparative metabolite exposure assessment: how to establish fundamental bioanalytical parameters for the peak area ratio method

We previously developed an high-performance LC–MS peak area ratio approach to demonstrate whether an animal species used in a toxicology study has greater exposures to drug metabolites relative to humans, meeting regulatory guidances regarding safety assessment of drug metabolites. Herein we explain the underlying bioanalytical principals, how to establish all fundamental bioanalytical parameters, and how to evaluate data quality in sample analysis, in the absence of authentic standards of analyte(s). A data-driven tiered approach was used in which data from the peak area ratio method can stand based on statistical analysis, as well as assuring that fundamental elements of bioanalytical method and bioanalysis are met. This strategy offers considerable time- and resource-saving advantage while providing high confidence in the safety assessment of human metabolites in drug development.

An industry perspective on tiered approach to the investigation of metabolites in drug development

Background: A tiered approach to drug metabolite measurement and identification is often used industry wide to fulfill regulatory requirements specified in recent US FDA and European Medicines Agency guidance. Although this strategy is structured in its intent it can be customized to address unique challenges which may arise during early and late drug development activities. These unconventional methods can be applied at any stage to facilitate metabolite characterization. Results: Two case studies are described NVS 1 and 2. NVS 1: plasma concentrations, measured using a radiolabeled MS-response factor exploratory method, were comparable to those from a validated bioanalytical method. The NVS 2 example showed how in vitro analysis helped to characterize an unexpectedly abundant circulating plasma metabolite M3. Conclusion: A tiered approach incorporating many aspects of conventional and flexible analytical methodologies can be pulled together to address regulatory questions surrounding drug metabolite characterization.

Reflecting on a decade of metabolite screening and monitoring

The last 10 years have witnessed robust debate within the bioanalytical community and regulatory authorities on the topic of metabolite monitoring and safety assessment. Of particular interest to regulated bioanalytical laboratories was the acceptance by the US FDA and other major regulatory bodies of a tiered approach to bioanalytical assay validation. The tiered approach defines a sliding scale of regulatory rigor for the evaluation of significant human metabolites that encompasses a range of assessments from semi-quantitative assays to fully validated assays, all of which can be used in support of regulatory submissions. This article describes the utilization of a tiered approach at Bristol-Myers Squibb and the decision trees guiding the selection of the appropriate level of assay qualification. Case studies illustrate how decisions are made, how different scientific situations influence the assay choice, and what criteria may be set to continue or discontinue metabolite monitoring in later drug development.

Metabolism and excretion of canagliflozin in mice, rats, dogs, and humans

Canagliflozin is an oral antihyperglycemic agent used for the treatment of type 2 diabetes mellitus. It blocks the reabsorption of glucose in the proximal renal tubule by inhibiting the sodium-glucose cotransporter 2. This article describes the in vivo biotransformation and disposition of canagliflozin after a single oral dose of [(14)C]canagliflozin to intact and bile duct-cannulated (BDC) mice and rats and to intact dogs and humans. Fecal excretion was the primary route of elimination of drug-derived radioactivity in both animals and humans. In BDC mice and rats, most radioactivity was excreted in bile. The extent of radioactivity excreted in urine as a percentage of the administered [(14)C]canagliflozin dose was 1.2%-7.6% in animals and approximately 33% in humans. The primary pathways contributing to the metabolic clearance of canagliflozin were oxidation in animals and direct glucuronidation of canagliflozin in humans. Unchanged canagliflozin was the major component in systemic circulation in all species. In human plasma, two pharmacologically inactive O-glucuronide conjugates of canagliflozin, M5 and M7, represented 19% and 14% of total drug-related exposure and were considered major human metabolites. Plasma concentrations of M5 and M7 in mice and rats from repeated dose safety studies were lower than those in humans given canagliflozin at the maximum recommended dose of 300 mg. However, biliary metabolite profiling in rodents indicated that mouse and rat livers had significant exposure to M5 and M7. Pharmacologic inactivity and high water solubility of M5 and M7 support glucuronidation of canagliflozin as a safe detoxification pathway.

Clinical pharmacokinetics of Icotinib, an anti-cancer drug: evaluation of dose proportionality, food effect, and tolerability in healthy subjects

PURPOSE

Icotinib, an oral epidermal growth factor receptor tyrosine kinase inhibitor, has proved effectiveness in xenografted nude mice. Purpose of the present studies was to investigate tolerability and pharmacokinetics of Icotinib in healthy subjects for the first time, including dose proportionality, food effect, and tolerability.

METHODS

Two studies were conducted in total of 22 healthy subjects: a randomized, two-Latin-square crossover, dose proportional study (n = 12) and a randomized two-way crossover food-effect study (n = 10).

RESULTS

Plasma concentration of Icotinib reached peak at a median Tmax of 0.75-3.5 h after single dose and then declined with a mean t1/2β of 6.02-7.83 h. Over the dose range of 100-600 mg, AUC values were proportional to dose and Cmax showed a slight saturation when dose increases. Only 0.2 % of the dose was excreted through kidney in unchanged Icotinib. After dosing 400 mg of Icotinib with high-fat and high-calorie meal, mean Cmax and AUC were significantly increased by 59 and 79 %, respectively. Three subjects experienced four adverse events (rash, increase in AST and ALT, and external injury). Rash and increased levels of AST and ALT were considered as drug-related. No serious adverse events were reported.

CONCLUSION

The current work demonstrated that Icotinib was well tolerated in healthy male subjects (n = 22) over the dose range of 100-600 mg with or without food. Icotinib exposure, expressed in AUC, was proportionally increased with dose over the above dose range. Food intake significantly increased the absorption and exposure of Icotinib in healthy subjects.