Considerations for Human ADME Strategy and Design Paradigm Shift(s) - An Industry White Paper

Human absorption, distribution, metabolism, and excretion studies: Conventional or microtracer?

A human absorption, distribution, metabolism, and excretion (hADME) study is an essential clinical pharmacology study for small-molecule drugs. The study provides insights into circulating drug-related materials and the drug's elimination pathways in humans, which can guide future studies on safety and drug-drug interaction of metabolites as well as organ impairment and drug-drug interaction of the parent drug. The 2 hADME study types, namely conventional and microtracer, are comprehensively compared in this manuscript. A review of literature found that conventional hADME studies were approximately 7 times that of microtracer hADME studies for small molecule and peptide drugs based on publications in 3 peer-reviewed journals from 2010 to 2024. Each study type has advantages and disadvantages. The advantages of conventional hADME studies primarily include the ease, low cost, and flexibility of radiometric sample analysis. In contrast, the advantages of microtracer hADME studies primarily include exemption from prerequisite studies and use of non-good manufacturing practice 14C-labeled materials. The disadvantages of each study type are essentially the advantages of the other. The manuscript also discusses scenarios where a microtracer hADME study may be preferable. Finally, recommendations are provided on selecting the appropriate hADME study type for an investigational drug. SIGNIFICANCE STATEMENT: The manuscript discusses 2 primary human absorption, distribution, metabolism, and excretion study types: conventional and microtracer. It covers published literature studies, the pros and cons of each type, scenarios for conducting microtracer studies, and a recommended decision tree for selecting the appropriate human absorption, distribution, metabolism, and excretion study type.

Optical 14C Tracing for Biological and Pharmaceutical Applications Using Two-Color Cavity Ringdown Spectroscopy

Laser-based 14C quantitation has been proposed as a more affordable, higher-throughput, table-top alternative to accelerator mass spectrometry (AMS). Here, we demonstrate the feasibility of a mid-IR 14C detector based on two-color cavity ringdown spectroscopy (2C-CRDS) for low-level 14C isotope tracing in biological studies. The 2C-CRDS technique quantifies the sample 14C content by measuring the 14CO2 absorption signals from the combusted samples with mid-IR lasers. With 2C-CRDS, we previously demonstrated the most sensitive and accurate optical measurements of 14CO2. The current detection sensitivity and quantitation accuracy of the instrument, at a few parts per quadrillion (where a quadrillion = 1015) 14C/C mole fraction, is competitive against AMS. Here, by applying the 2C-CRDS 14C sensor to two applications relevant to 14C-labeled biochemical analysis and pharmaceutical studies, we demonstrate sub-fCi level (where 1 fCi = 10-15 Ci) quantitation of sample 14C activity, with a minimum sample-size requirement of 3 mg of carbon. The current measurement throughput, ∼25 min/sample, is largely limited by the sampling efficiency of the online combustion and CO2 processing interface to the 2C-CRDS instrument. The possibility of a significantly improved measurement throughput of a few minutes per sample is suggested by the results of a flow-through 14CO2 sampling scheme. This improved measurement efficiency, combined with the relatively low cost and compact size of a 2C-CRDS sensor, could potentially revolutionize high-sensitivity 14C tracing in biological, pharmaceutical, and clinical studies.

Cross-industry demonstration of the validity of the mixed matrix method for the assessment of cross-species exposure coverage of human circulating drug metabolites

The mixed matrix method (MmM) is a widely used approach by the pharmaceutical industry for early assessment of whether exposures to major human circulating metabolites, of traditional small-molecule drugs, are adequately covered by the species used for toxicology assessment, which is a key requirement of the safety testing of drug metabolites (metabolites in safety testing guidelines). However, questions remain regarding its accuracy and utility in replacing conventional bioanalytical approaches. Furthermore, the available literature on the topic is not fully consistent in terms of how the assay should be conducted. As a result, encouraged by health authority advice on this topic, a cross-industry group under the European Federation of Pharmaceutical Industries and Associations was formed to: (1) further investigate the MmM accuracy, including a robust statistical analysis covering a diverse chemical space of commercially available drugs and drug candidates as well as their metabolites; (2) propose recommendations for best practice including a decision tree that the industry should consider when using the MmM; and (3) discuss whether the MmM could be used to support metabolites in safety testing assessment and could potentially be included into new drug application submissions without the need for additional measurements using the conventional bioanalytical approach. The outcome of this European Federation of Pharmaceutical Industries and Associations assessment shows that MmM measured exposure ratios of 1.9 and 1.4 are statistically sufficient to demonstrate adequate exposure coverage of human metabolites above 50% or between 10% and 50% of drug-related exposure, respectively, by toxicology species. The aim is to encourage both industry and regulatory agencies to consider MmM as an acceptable approach to compare major human circulating metabolite exposures across species. SIGNIFICANCE STATEMENT: The outcome of our mixed matrix method assessment showed that measured exposure ratios of 1.9 and 1.4 are adequate to demonstrate coverage of human metabolites above or below 50% drug-related exposure by toxicology species. Recommendations for best practice and a decision tree for conducting metabolites in safety testing evaluations are proposed. Our investigations show that mixed matrix method data are sufficiently robust for the intended purpose and that the assay provides an opportunity to streamline drug development and reduce the need for resource-intensive bioanalysis and certain animal studies.

Pharmacokinetics and absorption, distribution, metabolism and excretion profiling of tanimilast following an intravenous 14C-microtracer coadministered with an inhaled dose in healthy male individuals

Tanimilast is an inhaled phosphodiesterase-4 inhibitor currently in phase III clinical development for treating chronic obstructive pulmonary disease and asthma. This trial aimed to characterize the pharmacokinetics, mass balance, and metabolite profiling of tanimilast. Eight healthy male volunteers received a single dose of nonradiolabeled tanimilast via powder inhaler (Chiesi NEXThaler [3200 μg]), followed by a concomitant intravenous infusion of a microtracer ([14C]-tanimilast: 18.5 μg and 500 nCi). Plasma, whole blood, urine, and feces samples were collected up to 240 hours after dose to quantify nonradiolabeled tanimilast, [14C]-tanimilast, and total-[14C]. The inhaled absolute bioavailability of tanimilast was found to be approximately 50%. Following intravenous administration of [14C]-tanimilast, plasma clearance was 22 L/h, the steady-state volume of distribution was 201 L, and the half-life was shorter compared to inhaled administration (14 vs 39 hours, respectively), suggesting that plasma elimination is limited by the absorption rate from the lungs. Seventy-nine percent (71% in feces; 8% in urine) of the intravenous dose was recovered in excreta as total-[14C]. [14C]-tanimilast was the major radioactive compound in plasma, whereas no recovery was observed in urine and only 0.3% was recovered in feces, indicating predominant elimination through metabolic route. Importantly, as far as no metabolites accounting for more than 10% of the circulating drug-related exposure in plasma or the administered dose in excreta were detected, no further qualification is required according to regulatory guidelines. This study design successfully characterized the absorption, distribution, and elimination of tanimilast, providing key pharmacokinetic parameters to support its clinical development and regulatory application. SIGNIFICANCE STATEMENT: This trial investigates pharmacokinetic and absorption, distribution, metabolism and excretion profile of tanimilast, an inhaled phosphodiesterase-4 inhibitor for chronic obstructive pulmonary disease and asthma. Eight male volunteers received a dose of nonradiolabeled tanimilast via Chiesi NEXThaler and a microtracer intravenous dose. Results show pivotal pharmacokinetic results for the characterization of tanimilast, excretion route and quantification of significant metabolites, facilitating streamlined clinical development and regulatory approval.

Endeavours made by trade associations, pharmaceutical companies and regulators in the replacement, reduction and refinement of animal experimentation in safety testing of pharmaceuticals

Following the European Commission decision to develop a roadmap to phase out animal testing and the signing of the US Modernisation Act, there is additional pressure on regulators and the pharmaceutical industry to abandon animal experimentation in safety testing. Often, endeavours already made by governments, regulators, trade associations, and industry to replace, reduce and refine animal experimentation (3Rs) are unnoticed. Herein, we review such endeavours to promote wider application and acceptance of 3Rs. ICH guidelines have stated 3Rs objectives and have enjoyed many successes driven by global consensus. Initiatives driven by US and European regulators such as the removal of the Abnormal Toxicity Test are neutralised by reticent regional regulators. Stream-lined testing requirements have been proposed for new modalities, oncology, impurity management and animal pharmacokinetics/metabolism. Use of virtual controls, value of the second toxicity species, information sharing and expectations for life-threatening diseases, human specific or well-characterised targets are currently being scrutinised. Despite much effort, progress falls short of the ambitious intent of decisionmakers. From a clinical safety and litigation perspective pharmaceutical companies and regulators are reluctant to step away from current paradigms unless replacement approaches are validated and globally accepted. Such consensus has historically been best achieved through ICH initiatives.

Metabolite analysis of 14C-labeled chloromethylisothiazolinone/methylisothiazolinone for toxicological consideration of inhaled isothiazolinone biocides in lungs

5-Chloro-2-methyl-4-isothiazolin-3-one (CMIT) and 2-methyl-4-isothiazolin-3-one (MIT) used as preservatives in various products, including humidifier disinfectants, presents substantial health hazards. This research delves into the toxicological assessments of CMIT/MIT in the respiratory system using animal models. Through the synthesis of radiolabeled [14C]CMIT and [14C]MIT, we investigated the biological uptake and in vivo behaviors of CMIT/MIT in the respiratory tissues following intratracheal exposure. Quantitative whole-body autoradiography (QWBA) revealed significant persistence of CMIT/MIT in lung tissue. In addition, radio high-performance liquid chromatography (radio-HPLC) with tandem mass spectrometry (LC-MS/MS) was employed for metabolite profiling and identification. Notably, around 28% of the radiolabel was retained in tissue after the extraction step, suggesting covalent binding of CMIT/MIT and their metabolites with pulmonary biomolecules. This observation demonstrates the propensity of the electrophilic isothiazolinone ring in CMIT/MIT to undergo chemical interactions with biothiols in proteins and enzymes, fostering irreversible alterations of biomolecules. Such accumulations of transformations could result in direct toxicity at both cellular and organ levels. Additionally, the detection of metabolites, including a MIT dimer conjugated with glutathione (GSH), as analyzed by mass spectrometry indicates the possible reduction of cellular GSH levels and subsequent oxidative stress. This investigation offers an in-depth insight into the toxic mechanisms of CMIT/MIT, underlying their capability to engage in complex formations with biomacromolecules and induce pronounced respiratory toxicity. These results highlight the imperative for stringent safety assessments of these chemicals, advocating for improved public health and safety measures in the use of chemicals.

Alpibectir: Early Qualitative and Quantitative Metabolic Profiling from a First-Time-in-Human Study by Combining 19F-NMR (Nuclear Magnetic Resonance), 1H-NMR, and High-Resolution Mass Spectrometric Analyses

Alpibectir (also known as BVL-GSK098 and GSK3729098) is a new chemical entity (NCE) with a novel mechanism for the treatment of tuberculosis. The disposition of alpibectir was determined in subjects from a first-time-in-human trial after a single oral dose of 40 mg and after 7 days repeat dosing at 30 mg. Here we present a combined approach of 19F-NMR (nuclear magnetic resonance), 1H-NMR, and high-resolution mass spectrometry (HRMS) to confidently determine the human metabolic fate of alpibectir. Utilizing multiple sites of fluorination in the molecule, it was possible to fractionate human urine and plasma to confidently detect and quantify the metabolite responses using 19F-NMR. Qualitative detection and structural characterization of F-containing NMR fractions were performed using complementary high-resolution ultra-high performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) analyses to further add confidence to the metabolite responses in these fractions. Subsequent 1H-NMR then provided unequivocal standard-free structural confirmation for key metabolites, which would not be possible with conventional radioactivity detection and LC-MS/MS techniques. Alpibectir was shown to undergo extensive hydrolysis of the central amide moiety, where the resultant N-dealkylated amine and trifluorobutyric acid products were detected initially by unbiased 19F-NMR detection along with major downstream biotransformations to form a carbamoyl glucuronide conjugate and trifluoroacetic acid, respectively. Parallel UHPLC-MS/MS analyses provided confirmatory or additional structural characterization only where relevant. These concerted data allowed for the qualitative metabolic profile and quantitative determination of drug-related material (DRM) in urine and plasma, along with the percentage of dose excreted in urine, to be reported in a comprehensive, efficient, and data-led manner. SIGNIFICANCE STATEMENT: Combining the selectivity of 19F-NMR (nuclear magnetic resonance) for unfractionated samples as first-intent, data-led sample fractionation prior to 19F-NMR and structure-rich 1H-NMR detection, along with the sensitivity of high-resolution ultra-high performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS), a novel alternative for time-efficient detection and quantification of drug-related material (DRM) in human without use of radiolabeled drug is reported. This allowed more complete data rationalization of human metabolism, permitting early risk assessment and progression of the development of antitubercular agent, alpibectir.

Non-Labeled, Stable Labeled, or Radiolabelled Approaches for Provision of Intravenous Pharmacokinetics in Humans: A Discussion Piece

A review of the use of microdoses and isotopic microtracers for clinical intravenous pharmacokinetic (i.v. PK) data provision is presented. The extent of application of the varied approaches available and the relative merits of each are highlighted with the aim of assisting practitioners in making informed decisions on the most scientifically appropriate design to adopt for any given new drug in development. It is envisaged that significant efficiencies will be realized as i.v. PK data in humans becomes more routinely available for suitable assets in early development, than has been the case prior to the last decade.

Metabolite Bioanalysis in Drug Development: Recommendations from the IQ Consortium Metabolite Bioanalysis Working Group

The intent of this perspective is to share the recommendations of the International Consortium for Innovation and Quality in Pharmaceutical Development Metabolite Bioanalysis Working Group on the fit-for-purpose metabolite bioanalysis in support of drug development and registration. This report summarizes the considerations for the trigger, timing, and rigor of bioanalysis in the various assessments to address unique challenges due to metabolites, with respect to efficacy and safety, which may arise during drug development from investigational new drug (IND) enabling studies, and phase I, phase II, and phase III clinical trials to regulatory submission. The recommended approaches ensure that important drug metabolites are identified in a timely manner and properly characterized for efficient drug development.

Small molecule drug metabolite synthesis and identification: why, when and how?

The drug discovery and development process encompasses the interrogation of metabolites arising from the biotransformation of drugs. Here we look at why, when and how metabolites of small-molecule drugs are synthesised from the perspective of a specialist contract research organisation, with particular attention paid to projects for which regulatory oversight is relevant during this journey. To illustrate important aspects, we look at recent case studies, trends and learnings from our experience of making and identifying metabolites over the past ten years, along with with selected examples from the literature.

Gut Microbiome Integration in Drug Discovery and Development of Small Molecules

Human microbiomes, particularly in the gut, could have a major impact on the efficacy and toxicity of drugs. However, gut microbial metabolism is often neglected in the drug discovery and development process. Medicen, a Paris-based human health innovation cluster, has gathered more than 30 international leading experts from pharma, academia, biotech, clinical research organizations, and regulatory science to develop proposals to facilitate the integration of microbiome science into drug discovery and development. Seven subteams were formed to cover the complementary expertise areas of 1) pharma experience and case studies, 2) in silico microbiome-drug interaction, 3) in vitro microbial stability screening, 4) gut fermentation models, 5) animal models, 6) microbiome integration in clinical and regulatory aspects, and 7) microbiome ecosystems and models. Each expert team produced a state-of-the-art report of their respective field highlighting existing microbiome-related tools at every stage of drug discovery and development. The most critical limitations are the growing, but still limited, drug-microbiome interaction data to produce predictive models and the lack of agreed-upon standards despite recent progress. In this paper we will report on and share proposals covering 1) how microbiome tools can support moving a compound from drug discovery to clinical proof-of-concept studies and alert early on potential undesired properties stemming from microbiome-induced drug metabolism and 2) how microbiome data can be generated and integrated in pharmacokinetic models that are predictive of the human situation. Examples of drugs metabolized by the microbiome will be discussed in detail to support recommendations from the working group. SIGNIFICANCE STATEMENT: Gut microbial metabolism is often neglected in the drug discovery and development process despite growing evidence of drugs' efficacy and safety impacted by their interaction with the microbiome. This paper will detail existing microbiome-related tools covering every stage of drug discovery and development, current progress, and limitations, as well as recommendations to integrate them into the drug discovery and development process.

Recommendations on the Use of Multiple Labels in Human Mass Balance Studies

The administration of radiolabeled drug candidates is considered the gold standard in absorption, distribution, metabolism, and excretion studies for small-molecule drugs since it allows facile and accurate quantification of parent drug, metabolites, and total drug-related material independent of the compound structure. The choice of the position of the radiolabel, typically 14C or 3H, is critical to obtain relevant information. Sometimes, a biotransformation reaction may lead to cleavage of a part of the molecule. As a result, only the radiolabeled portion can be followed, and information on the fate of the nonlabeled metabolite may be lost. Synthesis and administration of two or more radiolabeled versions of the parent drug as a mixture or in separate studies may resolve this issue but comes with additional challenges. In this paper, we address the questions that may be considered to help make the right choice whether to use a single or multiple radiolabel approach and discuss the pros and cons of different multiple-labeling strategies that can be taken as well as alternative methods that allow the nonlabeled part of the molecule to be followed. SIGNIFICANCE STATEMENT: Radiolabeled studies are the gold standard in drug metabolism research, but molecules can undergo cleavage with loss of the label. This often results in discussions around potential use of multiple labels, which seem to be occurring with increased frequency since an increasing proportion of the small-molecule drugs are tending towards larger molecular weights. This review provides insight and decision criteria in considering a multiple-label approach as well as pros and cons of different strategies that can be followed.

The Importance of Tracking "Missing" Metabolites: How and Why?

Technologies currently employed to find and identify drug metabolites in complex biological matrices generally yield results that offer a comprehensive picture of the drug metabolite profile. However, drug metabolites can be missed or are captured only late in the drug development process. This could be due to a variety of factors, such as metabolism that results in partial loss of the molecule, covalent bonding to macromolecules, the drug being metabolized in specific human tissues, or poor ionization in a mass spectrometer. These scenarios often draw a great deal of attention from chemistry, safety assessment, and pharmacology. This review will summarize scenarios of missing metabolites, why they are missing, and associated uncovering strategies from deeper investigations. Uncovering previously missed metabolites can have ramifications in drug development with toxicological and pharmacological consequences, and knowledge of these can help in the design of new drugs.

The Changing Landscape for Human Absorption, Metabolism, and Excretion: Practical Experiences From a Data Analysis of 500 Studies

Coincidental with the intensified regulatory and industry focus on the design and conduct of human absorption, metabolism, and excretion (hAME) studies in the past 12 months, we have recently completed our 500th cohort involving radiolabeled test item administration to humans. Here, we build upon a recent industry white paper in this journal1 and share some of our own experiences as a Contract Research Organization based upon collaborations with numerous pharma companies and their differing approaches to design and timing, to add further context to the discussion regarding hAME studies and the pivotal role that drug metabolism and pharmacokinetics plays. In this article, we explore how both changing relationships within the industry and shifting regulatory guidelines are impacting strategies, and compare EU and US pre-study approval requirements, before evaluating the trends from over 500 studies conducted at our global facilities conducted over more than 30 years. We conclude with a review of how improved technical capabilities and strategies are influencing the design and conduct of hAME studies, before speculating on some of the driving factors which may shape the direction they take in the future.

Evaluation of the drug disposition of RO7049389 with in vitro data and human mass balance supported by physiologically based pharmacokinetic modelling

AIMS

RO7049389 (linvencorvir) is a developmental oral treatment for chronic hepatitis B virus infection. The aim of this work was to conduct mass balance (MB) and absolute bioavailability (BA) analyses in healthy volunteers, alongside in vitro evaluations of the metabolism of RO7049389 and a major circulating active metabolite M5 in human hepatocytes, and physiologically based pharmacokinetic (PBPK) modelling to refine the underlying drug disposition paradigm.

METHODS

Participants in the clinical study (MB: Caucasian, male, n = 6; BA: Caucasian and Asian, male and female, n = 16, 8 in each ethnic groups) received oral [14 C] or unlabelled RO7049389 (600/1000 mg) followed by 100 μg intravenous [13 C]RO7049389. Metabolic pathways with fractions metabolized-obtained from the in vitro incubation results of 10 μM [14 C]RO7049389 and 1 μM M5 with (long-term cocultured) human hepatocytes in the absence and presence of the cytochrome P450 3A4 (CYP3A4) inhibitor itraconazole-were used to complement the PBPK models, alongside the clinical MB and BA data.

RESULTS

The model performance in predicting the pharmacokinetic profiles of RO7049389 and M5 aligned with clinical observations in Caucasians and was also successfully applied to Asians. Accordingly, the drug disposition pathways for RO7049389 were postulated with newly characterized estimates of the fractions: biliary excretion by P-glycoprotein (~41%), direct glucuronidation via uridine 5'-diphosphoglucuronosyltransferase 1A3 (~11%), hexose conjugation (~6%), oxidation by CYP3A4 (~28%) and other oxidation reactions (~9%).

CONCLUSION

These results support the ongoing clinical development program for RO7049389 and highlight the broader value of PBPK and MB analyses in drug development.

In Vitro and In Vivo Models for Drug Transport Across the Blood-Testis Barrier

The blood-testis barrier (BTB) is a selectively permeable membrane barrier formed by adjacent Sertoli cells (SCs) in the seminiferous tubules of the testes that develops intercellular junctional complexes to protect developing germ cells from external pressures. However, due to this inherent defense mechanism, the seminiferous tubule lumen can act as a pharmacological sanctuary site for latent viruses (e.g., Ebola, Zika) and cancers (e.g., leukemia). Therefore, it is critical to identify and evaluate BTB carrier-mediated drug delivery pathways to successfully treat these viruses and cancers. Many drugs are unable to effectively cross cell membranes without assistance from carrier proteins like transporters because they are large, polar, and often carry a charge at physiologic pH. SCs express transporters that selectively permit endogenous compounds, such as carnitine or nucleosides, across the BTB to support normal physiologic activity, although reproductive toxicants can also use these pathways, thereby circumventing the BTB. Certain xenobiotics, including select cancer therapeutics, antivirals, contraceptives, and environmental toxicants, are known to accumulate within the male genital tract and cause testicular toxicity; however, the transport pathways by which these compounds circumvent the BTB are largely unknown. Consequently, there is a need to identify the clinically relevant BTB transport pathways in in vitro and in vivo BTB models that recapitulate human pharmacokinetics and pharmacodynamics for these xenobiotics. This review summarizes the various in vitro and in vivo models of the BTB reported in the literature and highlights the strengths and weaknesses of certain models for drug disposition studies. SIGNIFICANCE STATEMENT: Drug disposition to the testes is influenced by the physical, physiological, and immunological components of the blood-testis barrier (BTB). But many compounds are known to cross the BTB by transporters, resulting in pharmacological and/or toxicological effects in the testes. Therefore, models that assess drug transport across the human BTB must adequately account for these confounding factors. This review identifies and discusses the benefits and limitations of various in vitro and in vivo BTB models for preclinical drug disposition studies.

Human Absorption, Distribution, Metabolism, and Excretion Studies: Origins, Innovations, and Importance

Human absorption, distribution, metabolism, and excretion (hADME) studies represent one of the most important clinical studies in terms of obtaining a comprehensive and quantitative overview of the total disposition of a drug. This article will provide background on the origins of hADME studies as well as provide an overview of technological innovations that have impacted how hADME studies are carried out and analyzed. An overview of the current state of the art for hADME studies will be provided, the impacts of advances in technology and instrumentation on the timing of and approaches to hADME studies will be discussed, and a summary of the parameters and information obtained from these studies will be offered. Additionally, aspects of the ongoing debate over the importance of animal absorption, distribution, metabolism, and excretion studies versus a "human-first, human-only strategy" will be presented. Along with the information above, this manuscript will highlight how, for over 50 years, Drug Metabolism and Disposition has served as an important outlet for the reporting of hADME studies. SIGNIFICANCE STATEMENT: Human absorption, distribution, metabolism, and excretion (hADME) studies have and will continue to be important to the understanding and development of drugs. This manuscript provides a historical perspective on the origins of hADME studies as well as advancements resulting in the current-state-of the art practice for these studies.

Application of Accelerator Mass Spectrometry to Characterize the Mass Balance Recovery and Disposition of AZD4831, a Novel Myeloperoxidase Inhibitor, following Administration of an Oral Radiolabeled Microtracer Dose in Humans

This study evaluated the mass balance and disposition of AZD4831, a novel myeloperoxidase inhibitor, in six healthy participants using a 14C-labeled microtracer coupled with analysis by accelerator mass spectrometry (AMS). A single oral dose of 10 mg 14C-AZD4831 (14.8 kBq) was administered as a solution, and 14C levels were quantified by AMS in blood, urine, and feces over 336 hours postdose. AZD4831 was rapidly absorbed, and AZD4831 plasma concentrations declined in a biphasic manner, with a long half-life of 52 hours. AZD4831 was eliminated via metabolism and renal excretion. An N-carbamoyl glucuronide metabolite of AZD4831 (M7), formed primarily via UGT1A1, was the predominant circulating metabolite. Presumably, M7 contributed to the long half-life of AZD4831 via biliary elimination and hydrolysis/enterohepatic recirculation of AZD4831. On average, ∼84% of administered 14C-AZD4831 was recovered by 336 hours postdose (urine, 51.2%; feces, 32.4%). Between 32%-44% of the dose was excreted as unchanged AZD4831 in urine, indicating renal elimination as the major excretory route. Only 9.7% of overall fecal recovery was recorded in the first 48 hours, with the remainder excreted over 48%-336 hours, suggesting that most fecal recovery was due to biliary elimination. Furthermore, only 6% of unchanged AZD4831 was recovered in feces. Overall, the fraction of the administered AZD4831 dose absorbed was high. 14C-AZD4831 was well tolerated. These findings contribute to increasing evidence that human absorption, distribution, metabolism, and excretion studies can be performed with acceptable mass balance recovery at therapeutically relevant doses and low radiolabel-specific activity using an AMS-14C microtracer approach. SIGNIFICANCE STATEMENT: In this study, the human absorption, distribution, metabolism, and excretion (hADME) of the novel myeloperoxidase inhibitor AZD4831 was assessed following oral administration. This included investigation of the disposition of M7, the N-carbamoyl glucuronide metabolite. Resolution of challenges highlighted in this study contributes to increasing evidence that hADME objectives can be achieved in a single study for compounds with therapeutically relevant doses and low radiolabel-specific activity by using an AMS-14C microtracer approach, thus reducing the need for preclinical radiolabeled studies.

Meeting report of the 3rd European Biotransformation Workshop

Challenges, 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.