Cyanide Trapping of Iminium Ion Reactive Metabolites: Implications for Clinical Hepatotoxicity

Reactive metabolite formation is a major mechanism of hepatotoxicity. Although reactive electrophiles can be soft or hard in nature, screening strategies have generally focused on the use of glutathione trapping assays to screen for soft electrophiles, with many data sets available to support their use. The use of a similar assay for hard electrophiles using cyanide as the trapping agent is far less common, and there is a lack of studies with sufficient supporting data. Using a set of 260 compounds with a defined hepatotoxicity status by the FDA, a comprehensive literature search yielded cyanide trapping data on an unbalanced set of 20 compounds that were all clinically hepatotoxic. Thus, a further set of 19 compounds was selected to generate cyanide trapping data, resulting in a more balanced data set of 39 compounds. Analysis of the data demonstrated that the cyanide trapping assay had high specificity (92%) and a positive predictive value (83%) such that hepatotoxic compounds would be confidently flagged. Structural analysis of the adducts formed revealed artifactual methylated cyanide adducts to also occur, highlighting the importance of full structural identification to confirm the nature of the adduct formed. The assay was demonstrated to add the most value for compounds containing typical structural alerts for hard electrophile formation: half of the severe hepatotoxins with these structural alerts formed cyanide adducts, while none of the severe hepatotoxins with no relevant structural alerts formed adducts. The assay conditions used included cytosolic enzymes (e.g., aldehyde oxidase) and an optimized cyanide concentration to minimize the inhibition of cytochrome P450 enzymes by cyanide. Based on the demonstrated added value of this assay, it is to be initiated for use at GSK as part of the integrated hepatotoxicity strategy, with its performance being reviewed periodically as more data is generated.

Role of microsomal metabolism in bromfenac-induced cytotoxicity

This study delves into the intricate mechanisms underlying drug-induced liver injury (DILI) with a specific focus on bromfenac, the withdrawn nonsteroidal anti-inflammatory drug. DILI is a pervasive concern in drug development, prompting market withdrawals and posing significant challenges to healthcare. Despite the withdrawal of bromfenac due to DILI, the exact role of its microsomal metabolism in inducing hepatotoxicity remains unclear. Herein, employing HepG2 cells with human liver microsomes and UDP-glucuronic acid (UDPGA), our investigation revealed a substantial increase in bromfenac-induced cytotoxicity in the presence of UDPGA, pointing to the significance of UDP-glucuronosyltransferase (UGT)-dependent metabolism in augmenting toxicity. Notably, among the recombinant UGTs examined, UGT2B7 emerged as a pivotal enzyme in the metabolic activation of bromfenac. Metabolite identification studies disclosed the formation of reactive intermediates, with bromfenac indolinone (lactam) identified as a potential mediator of hepatotoxic effects. Moreover, in cytotoxicity experiments, the toxicity of bromfenac lactam exhibited a 34-fold increase, relative to bromfenac. The toxicity of bromfenac lactam was mitigated by nicotinamide adenine dinucleotide phosphate-dependent metabolism. This finding underscores the role of UGT-dependent metabolism in generating reactive metabolites that contribute to the observed hepatotoxicity associated with bromfenac. Understanding these metabolic pathways and the involvement of specific enzymes, such as UGT2B7, provides crucial insights into the mechanisms of bromfenac-induced liver injury. In conclusion, this research sheds light on the metabolic intricacies leading to cytotoxicity induced by bromfenac, especially emphasizing the role of UGT-dependent metabolism and the formation of reactive intermediates like bromfenac lactam. These findings offer insight into the mechanistic basis of DILI and emphasize the importance of understanding metabolism-mediated toxicity.

Species differences in small intestinal exposure-related epithelial vacuolation in rats and dogs treated with a heteroaryldihydropyrimidine molecule

Small intestinal epithelial vacuolation induced by a heteroaryldihydropyrimidine compound (HAP-1) was observed in rats but not in dogs at termination in screening toxicity studies, despite the plasma exposure being higher in dogs. To understand the species differences, investigational studies with multiple time points following single dose (SD) and 7-day repeated dose (RD) were conducted in both species at doses resulting in comparable plasma exposures. In rats, epithelial vacuolation in the duodenum and jejunum were observed at all time points. In dogs, transient vacuolation was noted at 8 h post-SD (SD_8h) and 4 h post-RD (RD_4 h), but not at termination (RD_24 h). Special stains demonstrated lipid accumulation within enterocytes in both species and intracytoplasmic inclusion bodies in rats. Transmission electron microscopy identified these inclusion bodies as endoplasmic reticulum (ER) membranous structures. Transcriptomic analysis on jejunal mucosa at SD_8 h and RD_24 h revealed perturbations of lipid metabolism-related genes at SD_8 h in both species, but not at RD_24 h in dogs. ER stress-related gene changes at both time points were observed in rats only. Despite comparable HAP-1 plasma exposures, the duodenum and jejunum tissue concentrations of HAP-1 and acyl glucuronide metabolite were >5- and >30-fold higher in rats than in dogs, respectively. In vitro, similar cytotoxicity was observed in rat and dog duodenal organoids treated with HAP-1. In conclusion, HAP-1-induced intestinal epithelial vacuolation was related to lipid metabolism dysregulation in both species and ER-related injuries in rats only. The species differences were likely related to the difference in intestinal exposure to HAP-1 and its reactive metabolite.

Patients with naproxen-induced liver injury display T-cell memory responses toward an oxidative (S)-O-desmethyl naproxen metabolite but not the acyl glucuronide

BACKGROUND

Exposure to nonsteroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen (IBU) and naproxen (NAP) is associated with idiosyncratic drug-induced liver injury (DILI). Carboxylate bioactivation into reactive metabolites (e.g., acyl glucuronides, AG) and resulting T-cell activation is hypothesized as causal for this adverse event. However, conclusive evidence supporting this is lacking.

METHODS

In this work, we identify CD4+ and CD8+ T-cell hepatic infiltration in a biopsy from an IBU DILI patient. Lymphocyte transformation test and IFN-γ ELIspot, conducted on peripheral blood mononuclear cells (PBMCs) of patients with NAP-DILI, were used to explore drug-specific T-cell activation. T-cell clones (TCC) were generated and tested for drug specificity, phenotype/function, and pathways of T-cell activation. Cells were exposed to NAP, its oxidative metabolite 6-O-desmethyl NAP (DM-NAP), its AG or synthesized NAP-AG human-serum albumin adducts (NAP-AG adduct).

RESULTS

CD4+ and CD8+ T-cells from patients expressing a range of different Vβ receptors were stimulated to proliferate and secrete IFN-γ and IL-22 when exposed to DM-NAP, but not NAP, NAP-AG or the NAP-AG adduct. Activation of the CD4+ TCC was HLA-DQ-restricted and dependent on antigen presenting cells (APC); most TCC were activated with DM-NAP-pulsed APC, while fixation of APC blocked the T-cell response. Cross-reactivity was not observed with structurally-related drugs.

CONCLUSION

Our results confirm hepatic T-cell infiltrations in NSAID-induced DILI, and show a T-cell memory response toward DM-NAP indicating an immune-mediated basis for the adverse event. Whilst bioactivation at the carboxylate group is widely hypothesized to be pathogenic for NSAID associated DILI, we found no evidence of this with NAP.

Bioactivation and reactivity research advances - 2022 year in review‡

With the 50th year mark since the launch of Drug Metabolism and Disposition journal, the field of drug metabolism and bioactivation has advanced exponentially in the past decades (Guengerich 2023).This has, in a major part, been due to the continued advances across the whole spectrum of applied technologies in hardware, software, machine learning (ML), and artificial intelligence (AI). LC-MS platforms continue to evolve to support key applications in the field, and automation is also improving the accuracy, precision, and throughput of these supporting assays. In addition, sample generation and processing is being aided by increased diversity and quality of reagents and bio-matrices so that what is being analyzed is more relevant and translatable. The application of in silico platforms (applied software, ML, and AI) is also making great strides, and in tandem with the more traditional approaches mentioned previously, is significantly advancing our understanding of bioactivation pathways and how these play a role in toxicity. All of this continues to allow the area of bioactivation to evolve in parallel with associated fields to help bring novel or improved medicines to patients with urgent or unmet needs.Shuai Wang and Cyrus Khojasteh, on behalf of the authors.

Development of a fluorescent-labeled trapping reagent to evaluate the risk posed by acyl-CoA conjugates

Although acyl-CoA conjugates are known to have higher reactivity than acyl glucuronides, few studies have been conducted to evaluate the risk of the conjugates. In the present study, we aimed to develop a trapping assay for acyl-CoA conjugates using trapping reagents we have developed previously. It was revealed that Cys-Dan, which has both a thiol and an amino group, was the most effective in forming stable adducts containing an amide bond after intramolecular acyl migration. Additionally, we also developed a hepatocyte-based trapping assay in the present study to overcome the shortcomings of liver microsomes. Although liver microsomes are commonly used as enzyme sources in trapping assays, they lack some of the enzymes required for drug metabolism and detoxification systems. In human hepatocytes, our three trapping reagents, CysGlu-Dan, Dap-Dan and Cys-Dan, captured CYP-dependent reactive metabolites, reactive acyl glucuronides, and reactive acyl-CoA conjugates, respectively. The work suggests that the trapping assay with the reagents in hepatocytes is useful to evaluate the risk of reactive metabolites in drug discovery.

Preclinical evaluation of chemically reactive metabolites and mitigation of bioactivation in drug discovery

The formation of reactive metabolites (RMs) is thought to be one of the pathogeneses for some idiosyncratic adverse drug reactions (IADRs) which are considered one of the leading causes of some drug attritions and/or recalls. Minimizing or eliminating the formation of RMs via chemical modification is a useful tactic to reduce the risk of IADRs and time-dependent inhibition (TDI) of cytochrome P450 enzymes (CYPs). The RMs should be carefully handled before making a go-no-go decision. Herein, we highlight the role of RMs in the occurrence of IADRs and CYP TDI, the risk of structural alerts, the approaches of RM assessment at the discovery stage and strategies to minimize or eliminate RM liability. Finally, some considerations for developing a RM-positive drug candidate are suggested.

Investigation of the Pharmacokinetics and Metabolic Fate of Fasiglifam (TAK-875) in Male and Female Rats Following Oral and Intravenous Administration

The metabolism and pharmacokinetics of fasiglifam (TAK-875, 2-[(3S)-6-[[3-[2,6-dimethyl-4-(3-methylsulfonylpropoxy)phenyl]phenyl]methoxy]-2,3-dihydro-1-benzofuran-3-yl]acetic acid), a selective free fatty acid receptor 1 (FFAR1)/GPR40 agonist, were studied following intravenous (5 mg/kg) and oral administration (10 and 50 mg/kg) to male and female Sprague Dawley rats.Following intravenous dosing at 5 mg/kg, peak observed plasma concentrations of 8.8/9.2 μg/ml were seen in male and female rats respectively.Following oral dosing, peak plasma concentrations at 1 h of ca. 12.4/12.9 μg/ml for 10 mg/kg and 76.2/83.7 μg/ml for 50 mg/kg doses were obtained for male and female rats respectively. Drug concentrations then declined in the plasma of both sexes with t_1/2's of 12.4 (male) and 11.2 h (female). Oral bioavailability was estimated to be 85-120% in males and females at both dose levels.Urinary excretion was low, but in a significant sex-related difference, female rats eliminated ca. 10-fold more drug-related material by this route.Fasiglifam was the principal drug-related compound in plasma, with 15 metabolites, including the acyl glucuronide, also detected. In addition to previously identified metabolites, a novel biotransformation, that produced a side-chain shortened metabolite via elimination of CH₂ from the acetyl side chain was noted with implications for drug toxicity.

Acyl Glucuronide and Coenzyme A Thioester Metabolites of Carboxylic Acid-Containing Drug Molecules: Layering Chemistry with Reactive Metabolism and Toxicology

Glucuronidation and CoA (coenzyme A) conjugation are common pathways for the elimination of carboxylic acid-containing drug molecules. In some instances, these biotransformations have been associated with toxicity (such as idiosyncratic hepatic injury, renal impairment, hemolytic anemia, gastrointestinal inflammation, and bladder cancer) attributed to, in part, the propensity of acyl glucuronides and acyl CoA thioesters to covalently modify biological macromolecules such as proteins and DNA. It is to be noted that, while acyl glucuronidation and CoA conjugation are indeed implicated in adverse effects, there are many safe drugs in the market that are cleared by these reactive pathways. It is therefore important that new molecular entities with carboxylic acid groups are evaluated for toxicity in a manner that is not unreasonably risk-averse. In the absence of truly predictable methods, therefore, the general approach is to apply a set of end points to generate a weight-of-evidence evaluation. In practice, the focus is to identify structural liabilities and provide structure-activity recommendations early in the program, at a stage where an attempt to improve reactive metabolism does not deoptimize other critical drug-quality criteria. This review will present a high-level overview of the chemistry of glucuronidation and CoA conjugation and provide a discussion of the possible mechanisms of adverse effects that have been associated with these pathways, as well as how such potential hazards are addressed while delivering a new chemical entity for clinical evaluation.

Exploratory toxicology studies of 2,3-substituted imidazo[1,2-a]pyridines with antiparasitic and anti-inflammatory properties

Background

Trichomoniasis and amoebiasis are neglected diseases and still remain as a global health burden not only for developing countries, from where are endemic, but also for the developed world. Previously, we tested the antiparasitic activity of a number of imidazo[1,2-a]pyridine derivatives (IMPYs) on metronidazole-resistant strains of Entamoeba Hystolitica (HM1:IMSS), and Trichomonas Vaginalis (GT3). Their anti-inflammatory activity was also evaluated.

Objective

The present work is a part of a project whose aim is to find new alternatives to standard treatments for these maladies, and to address the current concern of emerging resistant parasite strains. Here we report a non-clinical study focused on exploratory toxicology assays of seven IMPYs that showed the best antiparasitic and/or anti-inflammatory properties.

Methods

Acute, and subacute toxicity tests were carried out. After 14-day oral treatment, liver and kidney functionality assays in combination with chemometric methods were implemented to detect hepatic and/or kidney damage.

Results

Some compounds produced off-target effects. Vehicle effects were also detected. However, no signs of hepatic or renal toxicity were observed for any IMPY.

Conclusion

These compounds can continue non-clinical evaluations, and if possible, clinical trials as new candidates to treat trichomoniasis and amoebiasis, and inflammatory diseases. Further studies are also needed to fully elucidate a proposed dual effect that may exert these molecules against trichomoniasis and amoebiasis, which may also signify a novel mechanism of action to treat these infections.

18O-Enabled High-Throughput Acyl Glucuronide Stability Assay

Acyl glucuronides (AGs) are common metabolites of carboxylic acid-containing compounds. In some circumstances, AGs are suspected to be involved in drug toxicity due to formation of acyl migration products that bind covalently to cellular components. The risk of this adverse effect has been found to be correlated with the chemical stability of the AG, and assays have been described that monitor acyl migration by liquid chromatography coupled with mass spectrometry (LC-MS). This analysis can be challenging as it requires baseline chromatographic separation of the unmigrated 1-β-acyl glucuronide from the migrated isomers and thus needs to be individually optimized for each aglycone. Therefore, a high-throughput assay that eliminates LC method development is desirable. Herein, we report an improved acyl glucuronide stability assay based on the rate of ¹⁸O-incorporation from [¹⁸O] water, which is compatible with high-throughput bioanalytical LC-MS workflows. Synthetic AGs with shorter migration half-lives showed faster incorporation of ¹⁸O. The level of differential incorporation of ¹⁸O following a 24 h incubation correlates well with the migration tendency of AGs. This assay was developed further, exploring in situ generation of AGs by human hepatic microsomal fraction. The results from 18 in situ-formed acyl glucuronides were similar to those obtained using authentic reference standards. In this format, this new ¹⁸O-labeling method offers a simplified workflow, requires no LC method development or AG reference standard, and thus facilitates AG liability assessment in early drug discovery.

Species differences in liver microsomal hydrolysis of acyl glucuronide in humans and rats

Acyl glucuronides (AGs) are known as one of the causes of idiosyncratic drug toxicity (IDT). Although AGs can be enzymatically hydrolysed by β-glucuronidase and esterase, much information on their characteristics and species differences is lacking. This study was aimed to clarify species differences in AG hydrolysis between human and rat liver microsomes (HLM and RLM).To evaluate the AG hydrolysis profile, and the contribution of β-glucuronidase and esterase towards AG hydrolysis in HLM and RLM, nonsteroidal anti-inflammatory drugs (NSAIDs) were used. AGs were incubated with 0.1 M Tris-HCl buffer (pH 7.4) and 0.3 mg/mL HLM or RLM in the absence or presence of β-glucuronidase inhibitor, D-saccharic acid 1,4-lactone (D-SL) and esterase inhibitor, phenylmethylsulfonyl fluoride (PMSF).AGs of mefenamic acid (MEF-AG) and etodolac (ETO-AG) showed significantly higher AG hydrolysis rates in RLM than in HLM. Esterases were found to serve as AG hydrolases dominantly in HLM, whereas both esterases and β-glucuronidase equally contribute to AG hydrolysis in RLM. However, MEF-AG and ETO-AG were hydrolysed only by β-glucuronidase.We demonstrated for the first time that the activity of AG hydrolases towards NSAID-AGs differs between humans and rats.

Stereoselective Covalent Adduct Formation of Acyl Glucuronide Metabolite of Nonsteroidal Anti-Inflammatory Drugs with UDP-Glucuronosyltransferase

A reactive metabolite of nonsteroidal anti-inflammatory drugs (NSAIDs), acyl-β-D-glucuronide (AG), covalently binds to endogenous proteins. The covalent adduct formation of NSAIDs-AG may lead to the dysfunction of target proteins. Therefore, it is important to clarify the detailed characterization of the formation of covalent protein adducts of NSAID-AG. UDP-glucuronosyltransferase (UGT) catalyzes the conversion of NSAIDs to NSAIDs-AG. The aim of this study was to perform a quantitative analysis of the covalent adduct formation of NSAIDs-AG with UGT. Diclofenac-AG and ketoprofen-AG formed covalent adducts with organelle proteins. Next, the number of covalent adducts formed between NSAIDs-AG and UGT isoforms (UGT1A1, UGT1A9, UGT2B4, and UGT2B9) was determined. The capacity of diclofenac-AG to form covalent adducts with UGT1A9 or UGT2B7 was approximately 10 times higher than that of mefenamic acid-AG. The amounts of covalent adducts of AG of propionic acid derivative NSAIDs with UGT2B were higher than those with UGT1A. Stereoselectivity was observed upon covalent binding to UGT. A significant negative correlation between the half-lives of NSAIDs-AG in phosphate buffers and the amount of covalent adduct with UGT2B7 was observed, suggesting the more labile NSAID-AG forms higher irreversible bindings to UGT. This report provides comprehensive information on the covalent adduct formation of NSAIDs-AGs with UGT.

Relationship between the risk of idiosyncratic drug toxicity and formation and degradation profiles of acyl-glucuronide metabolites of nonsteroidal anti-inflammatory drugs in rat liver microsomes

Acyl glucuronides (AGs) are considered to cause idiosyncratic drug toxicity (IDT), and evaluating the chemical instability of AGs may be useful for predicting the IDT risk of novel drug candidates. However, AGs show variations in their chemical instability, degree of formation, and enzymatic hydrolysis. Therefore, we evaluated the degree of AG formation, enzymatic hydrolysis, and chemical instability in liver microsomes and their relationship with IDT risk. Nonsteroidal anti-inflammatory drugs (NSAIDs) were classified into three categories in terms of their IDT risk as parent drugs: safe (SA), warning (WA), and withdrawn (WDN). To evaluate the enzymatic and non-enzymatic degradation of AG, the parent drugs were incubated with rat liver microsomes in the absence or presence of AG hydrolase inhibitors. The degree of AG formation and disappearance was considered as the rate constant. For all NSAIDs investigated, the number of AGs formed notably increased following addition of AG hydrolase inhibitors. Particularly, AG was produced by WDN drugs at a lower level than that produced by WA and SA drugs in the absence of AG hydrolase inhibitors but was significantly increased after adding AG hydrolase inhibitors. The rate constants of AG formation and non-enzymatic AG disappearance did not significantly differ among the WDN, WA, and SA drugs, whereas the rate constant of enzymatic AG disappearance of WDN drugs tended to be higher than those of WA and SA drugs. In conclusion, we evaluated the enzymatic degradation and chemical instability of AG by simultaneously producing it in liver microsomes. This method enables evaluation of AG degradation without preparing AG. Moreover, we determined the relationship between enzymatic AG degradation in rat liver microsomes and IDT risk.

Driving to a Better Understanding of Acyl Glucuronide Transformations Using NMR and Molecular Modeling

Acyl glucuronide (AG) metabolites of carboxylic acid-containing drugs and products of their transformations have long been implicated in drug-induced liver injury (DILI). To inform on the DILI risk arising from AG reactive intermediates, a comprehensive mechanistic study of enzyme-independent AG rearrangements using nuclear magnetic resonance (NMR) and density functional theory (DFT) was undertaken. NMR spectroscopy was utilized for structure elucidation and kinetics measurements of nine rearrangement and hydrolysis products of 1β-O-acyl glucuronide of ibufenac. To extract rate constants of rearrangement, mutarotation, and hydrolysis from kinetic data, 11 different kinetic models were examined. Model selection and estimated rate constant verification were supported by measurements of H/D kinetic isotope effects. DFT calculations of ground and transition states supported the proposed kinetic mechanisms and helped to explain the unusually fast intramolecular transacylation rates found for some of the intermediates. The findings of the current study reinforce the notion that the short half-life of parent AG and slow hydrolysis rates of AG rearrangement products are the two key factors that can influence the in vivo toxicity of AGs.

A cysteine trapping assay for risk assessment of reactive acyl CoA metabolites

1. Some drugs with carboxylic acid moieties can potentially cause rare but severe hepatotoxicity. The reactive chemical species generated by drug metabolism are thought to be one reason for this event. Although the phase II conjugation metabolism of carboxylic acids generally renders a compound more polar and inactive, it is also responsible for the formation of reactive metabolites.2. This study aimed to provide a new approach toward the risk assessment of carboxylic acids in the aspect of reactive acyl CoA metabolites.3. Although acyl CoA metabolites have been concerned, it is difficult to detect them because of its instability. We investigated the trapping agents for acyl CoA metabolites. We found that cysteine is a good trapping agent and developed an assay method for the reactivity of acyl CoA metabolites. We evaluated 17 drugs with carboxylic acid moieties, all drugs concerned with hepatotoxicity displayed reactive potential. With a consideration of the exposure of each parent drug, the correlation between drug labels and the calculated risk of carboxylic drugs was improved.4. These evaluations can be conducted without radiochemical reagents or the authentic standards of metabolites. We believe that the method will be beneficial for drug discovery.

Development of a Fluorescent-Labeled Trapping Reagent to Detect Reactive Acyl Glucuronides

Acyl glucuronides are common metabolites of carboxylic acid-containing compounds. Since acyl glucuronides sometimes show high reactivity, they are considered to be involved in drug toxicity. Therefore, it is important to evaluate the risk posed by acyl glucuronides in the development of safe drugs; however, there are no suitable evaluation methods for the early stages of drug discovery. We aimed to develop a trapping reagent that detects reactive acyl glucuronides to assess their risk. We designed a diamine-structured trapping reagent, Dap-Dan, and compared its trapping ability with the reported one that has an amino group, and results showed that Dap-Dan showed higher accuracy. In the trapping assay with 17 medicines containing a carboxylic acid, Dap-Dan trapped acyl glucuronides that had a higher risk of toxicity. In conclusion, Dap-Dan can be useful for evaluating the risk of reactive acyl glucuronides.

Evaluation of the hepatotoxicity of the novel GPR40 (FFAR1) agonist CPL207280 in the rat and monkey

GPR40 (FFAR1) is a promising target for the managing type 2 diabetes (T2D). The most advanced GPR40 agonist TAK-875 exhibited satisfactory glucose-lowering effects in phase II and III studies. However, the phase III studies of TAK-875 revealed drug-induced liver injury (DILI). It is unknown whether DILI is a consequence of a specific GPR40 agonist or is an inherent feature of all GPR40 agonists. CPL207280 is a novel GPR40 agonist that improves diabetes in Zucker Diabetic Fatty (ZDF) rats, Goto Kakizaki (GK) rats and db/db mice. In this report, the DILI-related toxicity of CPL207280 was compared directly with that of TAK-875. In vitro studies evaluating hepatic biliary transporter inhibition, mitochondrial function, and metabolic profiling were performed in hepatocytes from different species. The long term toxicity of CPL207280 was studied in vivo in rats and monkeys. Activity of CPL207280 was one order of magnitude lesser than that of TAK-875 for the inhibition of bile acid transporters. CPL207280 had a negligible effect on the hepatic mitochondria. In contrast to TAK-875, which was metabolized through toxic glucuronidation, CPL207280 was metabolized mainly through oxidation. No deleterious hepatic effects were observed in chronically treated healthy and diabetic animals. The study presents promising data on the feasibility of creating a liver-safe GPR40 agonist. Additionally, it can be concluded that DILI is not a hallmark of GPR40 agonists; it is linked to the intrinsic properties of an individual agonist.

Recent Developments in the Practical Application of Novel Carboxylic Acid Bioisosteres

BACKGROUND

The carboxylic acid is an important functional group which features in the pharmacophore of some 450 drugs. Unfortunately, some carboxylic acid-containing drugs have been withdrawn from market due to unforeseen toxicity issues. Other issues associated with the carboxylate moiety include reduced metabolic stability or limited passive diffusion across biological membranes. Medicinal chemists often turn to bioisosteres to circumvent such obstacles.

OBJECTIVE

The aim of this review is to provide a summary of the various applications of novel carboxylic acid bioisosteres which have appeared in the literature since 2013.

RESULTS

We have summarised the most recent developments in carboxylic acid bioisosterism. In particular, we focus on the changes in bioactivity, selectivity or physiochemical properties brought about by these substitutions, as well as the advantages and disadvantages of each isostere.

CONCLUSION

The topics discussed herein highlight the continued interest in carboxylate bioisosteres. The development of novel carboxylic acid substitutes which display improved pharmacological profiles is testament to the innovation and creativity required to overcome the challenges faced in modern drug design.

Discovery and Optimization of Highly Potent and Selective AT2R Antagonists to Relieve Peripheral Neuropathic Pain

The angiotensin II type 2 receptor (AT2R) has attracted much attention as a potential target for the relief of neuropathic pain, which represents an area of unmet clinical need. A series of 1,2,3,4-tetrahydroisoquinolines with a benzoxazole side-chain were discovered as potent AT2R antagonists. Rational optimization resulted in compound 15, which demonstrated both excellent antagonistic activity against AT2R in vitro and analgesic efficacy in a rat chronic constriction injury model. Its favorable physicochemical properties and oral bioavailability make it a promising therapeutic candidate for neuropathic pain.

Impacts of diphenylamine NSAID halogenation on bioactivation risks

Diphenylamine NSAIDs are highly prescribed therapeutics for chronic pain despite causing symptomatic hepatotoxicity through mitochondrial damage in five percent of patients taking them. Differences in toxicity are attributed to structural modifications to the diphenylamine scaffold rather than its inherent toxicity. We hypothesize that marketed diphenylamine NSAID substituents affect preference and efficiency of bioactivation pathways and clearance. We parsed the FDA DILIrank hepatotoxicity database and modeled marketed drug bioactivation into quinone-species metabolites to identify a family of seven clinically relevant diphenylamine NSAIDs. These drugs fell into two subgroups, i.e., acetic acid and propionic acid diphenylamines, varying in hepatotoxicity risks and modeled bioactivation propensities. We carried out steady-state kinetic studies to assess bioactivation pathways by trapping quinone-species metabolites with dansyl glutathione. Analysis of the glutathione adducts by mass spectrometry characterized structures while dansyl fluorescence provided quantitative yields for their formation. Resulting kinetics identified four possible bioactivation pathways among the drugs, but reaction preference and efficiency depended upon structural modifications to the diphenylamine scaffold. Strikingly, diphenylamine dihalogenation promotes formation of quinone metabolites through four distinct metabolic pathways with high efficiency, whereas those without aromatic halogen atoms were metabolized less efficiently through two or fewer metabolic pathways. Overall metabolism of the drugs was comparable with bioactivation accounting for 4-13% of clearance. Lastly, we calculated daily bioload exposure of quinone-species metabolites based on bioactivation efficiency, bioavailability, and maximal daily dose. The results revealed stratification into the two subgroups; propionic acid diphenylamines had an average four-fold greater daily bioload compared to acetic acid diphenylamines. However, the lack of sufficient study on the hepatotoxicity for all drugs prevents further correlative analyses. These findings provide critical insights on the impact of diphenylamine bioactivation as a precursor to hepatotoxicity and thus, provide a foundation for better risk assessment in drug discovery and development.

Use of Cyclic Ion Mobility Spectrometry (cIM)-Mass Spectrometry to Study the Intramolecular Transacylation of Diclofenac Acyl Glucuronide

1-β-O-Acyl-glucuronides (AGs) are common metabolites of carboxylic acid-containing xenobiotics, including, e.g., many nonsteroidal anti-inflammatory drugs (NSAIDs). They are of concern to regulatory authorities because of the association of these metabolites with the hepatotoxicity that has resulted in drug withdrawal. One factor in assessing the potential risk posed by AGs is the rate of transacylation of the biosynthetic 1-β-O-acyl form to the 2-, 3-, and 4-O-acyl isomers. While transacylation can be measured using ¹H NMR spectroscopy or liquid chromatography-mass spectrometry (LC-MS), the process can be time consuming and involve significant method development. The separation of these positional isomers by ion mobility spectrometry (IMS) has the potential to allow their rapid analysis, but conventional instruments lacked the resolving power to do this. Prediction of the collision cross section (CCS) using a machine learning model suggested that greater IMS resolution might be of use in this area. Cyclic IMS was evaluated for separating mixtures of isomeric AGs of diclofenac and was compared with a conventional ultraperformance liquid chromatography (UPLC)-MS method as a means for studying transacylation kinetics. The resolution of isomeric AGs was not seen using a conventional traveling wave IMS device; however, separation was seen after several passes around a cyclic IMS. The cyclic IMS enabled the degradation of the 1-β-O-acyl-isomer to be analyzed much more rapidly than by LC-MS. The ability of cyclic IMS to monitor the rate of AG transacylation at different pH values, without the need for a prior chromatographic separation, should allow high-throughput, real-time, monitoring of these types of reactions.

Enzyme Kinetics of Uridine Diphosphate Glucuronosyltransferases (UGTs)

Glucuronidation, catalyzed by uridine diphosphate glucuronosyltransferases (UGTs), is an important process for the metabolism and clearance of many lipophilic chemicals, including drugs, environmental chemicals, and endogenous compounds. Glucuronidation is a bisubstrate reaction that requires the aglycone and the cofactor, UDP-GlcUA. Accumulating evidence suggests that the bisubstrate reaction follows a compulsory-order ternary mechanism. To simplify the kinetic modeling of glucuronidation reactions in vitro, UDP-GlcUA is usually added to incubations in large excess. Many factors have been shown to influence UGT activity and kinetics in vitro, and these must be accounted for during experimental design and data interpretation. While the assessment of drug-drug interactions resulting from UGT inhibition has been challenging in the past, the increasing availability of UGT enzyme-selective substrate and inhibitor "probes" provides the prospect for more reliable reaction phenotyping and assessment of drug-drug interaction potential. Although extrapolation of the in vitro intrinsic clearance of a glucuronidated drug often underpredicts in vivo clearance, careful selection of in vitro experimental conditions and inclusion of extrahepatic glucuronidation may improve the predictivity of in vitro-in vivo extrapolation. Physiologically based pharmacokinetic (PBPK) modeling has also shown to be of value for predicting PK of drugs eliminated by glucuronidation.

Human superoxide dismutase 1 attenuates quinoneimine metabolite formation from mefenamic acid

Mefenamic acid (MFA), one of the nonsteroidal anti-inflammatory drugs (NSAIDs), sometimes causes liver injury. Quinoneimines formed by cytochrome P450 (CYP)-mediated oxidation of MFA are considered to be causal metabolites of the toxicity and are detoxified by glutathione conjugation. A previous study reported that NAD(P)H:quinone oxidoreductase 1 (NQO1) can reduce the quinoneimines, but NQO1 is scarcely expressed in the human liver. The purpose is to identify enzyme(s) responsible for the decrease in MFA-quinoneimine formation in the human liver. The formation of MFA-quinoneimine by recombinant CYP1A2 and CYP2C9 was significantly decreased by the addition of human liver cytosol, and the extent of the decrease in the metabolite formed by CYP1A2 was larger than that by CYP2C9. By column chromatography, superoxide dismutase 1 (SOD1) was identified from the human liver cytosol as an enzyme decreasing MFA-quinoneimine formation. Addition of recombinant SOD1 into the reaction mixture decreased the formation of MFA-quinoneimine from MFA by recombinant CYP1A2. By a structure-activity relationship study, we found that SOD1 decreased the formation of quinoneimines from flufenamic acid and tolfenamic acid, but did not affect those produced from acetaminophen, amodiaquine, diclofenac, and lapatinib. Thus, SOD1 may selectively decrease the quinoneimine formation from fenamate-class NSAIDs. To examine whether SOD1 can attenuate cytotoxicity caused by MFA, siRNA for SOD1 was transfected into CYP1A2-overexpressed HepG2 cells. The leakage of lactate dehydrogenase caused by MFA treatment was significantly increased by knockdown of SOD1. In conclusion, we found that SOD1 can serve as a detoxification enzyme for quinoneimines to protect from drug-induced toxicity.

Identification of an isoform catalyzing the CoA conjugation of nonsteroidal anti-inflammatory drugs and the evaluation of the expression levels of acyl-CoA synthetases in the human liver

Nonsteroidal anti-inflammatory drugs (NSAIDs) containing carboxylic acid are conjugated with coenzyme A (CoA) or glucuronic acid in the body. It has been suggested that these conjugates are associated with toxicities, such as liver injury and anaphylaxis, through their binding via trans-acylation to cellular proteins. Although studies on glucuronidation have progressed, studies on CoA conjugation of drugs catalyzed by acyl-CoA synthetase (ACS) enzymes are still in the early stages. This study aimed to clarify the human ACS isoforms responsible for CoA-conjugation of NSAIDs through consideration of the hepatic expression levels of ACS isoforms. We found that among 10 types of NSAIDs, propionic acid-class NSAIDs, namely, alminoprofen, flurbiprofen, ibuprofen, ketoprofen, and loxoprofen, were conjugated with CoA in the human liver, whereas NSAIDs in the other classes, including diclofenac and mefenamic acid, were not. qRT-PCR revealed that among the 26 ACS isoforms, ACSL1 was the most highly expressed in the human liver, followed by ACSM2B. The propionic acid-class NSAIDs were conjugated with CoA by recombinant human ACSL1. The protein binding abilities of the CoA conjugates and the glucuronide forms of propionic acid-class NSAIDs were compared as an index of toxicity. The CoA conjugates had stronger adduct formation with liver microsomal proteins than glucuronides for all 5 propionic acid-class NSAIDs. In conclusion, we found that propionic acid-class NSAIDs could be conjugated to CoA by ACSL1 in the human liver to form CoA conjugates, which likely cause toxicity by protein adduct formation.

Models of Idiosyncratic Drug-Induced Liver Injury

Drug-induced liver injury (DILI) is a leading cause of attrition during the early and late stages of drug development and after a drug is marketed. DILI is generally classified as either intrinsic or idiosyncratic. Intrinsic DILI is dose dependent and predictable (e.g., acetaminophen toxicity). However, predicting the occurrence of idiosyncratic DILI, which has a very low incidence and is associated with severe liver damage, is difficult because of its complex nature and the poor understanding of its mechanism. Considering drug metabolism and pharmacokinetics, we established experimental animal models of DILI for 14 clinical drugs that cause idiosyncratic DILI in humans, which is characterized by the formation of reactive metabolites and the involvement of both innate and adaptive immunity. On the basis of the biomarker data obtained from the animal models, we developed a cell-based assay system that predicts the potential risks of drugs for inducing DILI. These findings increase our understanding of the mechanisms of DILI and may help predict and prevent idiosyncratic DILI due to certain drugs.

Acyl glucuronide reactivity in perspective

Acyl glucuronidation is a common metabolic fate for acidic drugs and their metabolites and, because these metabolites are reactive, they have been linked to adverse drug reactions (ADRs) and drug withdrawals. However, alternative routes of metabolism leading to reactive metabolites (e.g., oxidations and acyl-CoA thioesters) mean that unambiguous proof that acyl glucuronides are toxic is lacking. Here, we review the synthesis and reactivity of these metabolites, and describe the use of molecular modelling and in vitro and in vivo reactivity assessment of acyl glucuronide reactivity. Based on the emerging structure-dependent differences in reactivity and protein adduction methods for risk assessment for acyl glucuronide-forming acid drugs or drug candidates in drug discovery/development are suggested.

New Perspectives on Drug-Induced Liver Injury Risk Assessment of Acyl Glucuronides

Drug-induced liver injury (DILI) remains one of the key challenges in drug development due to the mechanisms of action being multifactorial in nature. This is particularly the case for idiosyncratic DILI which occurs in a very low frequency in humans (e.g., 1:10,000). Despite perceptions that acyl glucuronide metabolites are defacto risks for DILI, scientific evidence suggests that acyl glucuronide formation alone does not pose an increased risk compared to other drug metabolites. This applies in particular to those acyl glucuronides which are not reactive and do not form covalent adducts with proteins. The goal of this paper is to provide guidance on preclinical and clinical strategies to evaluate the potential for acyl glucuronide formation to contribute to DILI. A key element of our proposed safety assessment is to investigate whether a particular acyl glucuronide is reactive or not and whether systemic exposure in humans can be demonstrated in animal toxicology studies following administration of the parent drug. While standard animal toxicology studies can identify overtly hepatotoxic compounds, these studies are not predictive for drugs that produce idiosyncratic forms of DILI. In addition, we do not recommend conducting toxicology studies of administered individual acyl glucuronides due to differences in pharmacokinetic and dispositional properties from the endogenously produced metabolites. Once a drug candidate has entered clinical trials, the focus should be on clinical safety data and emerging risk-benefit analysis.

Drug Induced Liver Injury (DILI). Mechanisms and Medicinal Chemistry Avoidance/Mitigation Strategies

Adverse drug reactions (ADRs) are a common cause of attrition in drug discovery and development and drug-induced liver injury (DILI) is a leading cause of preclinical and clinical drug terminations. This perspective outlines many of the known DILI mechanisms and assessment methods used to evaluate and mitigate DILI risk. Literature assessments and retrospective analyses using verified DILI-associated drugs from the Liver Tox Knowledge Base (LTKB) have been used to derive the predictive value of each end point, along with combination approaches of multiple methods. In vitro assays to assess inhibition of the bile salt export pump (BSEP), mitotoxicity, reactive metabolite (RM) formation, and hepatocyte cytolethality, along with physicochemical properties and clinical dose provide useful DILI predictivity. This Perspective also highlights some of the strategies used by medicinal chemists to reduce DILI risk during the optimization of drug candidates.

Non-clinical characterization of the disposition of EMA401, a novel small molecule angiotensin II type 2 receptor (AT2R) antagonist

EMA401, (the S-enantiomer of 5-(benzyloxy)-2-(2,2-diphenylacetyl)-6-methoxy-1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid), also known as Olodanrigan, is an orally active selective angiotensin II type 2 receptor (AT₂ R) antagonist that is in Phase IIb clinical development as a novel analgesic for the relief of chronic pain. The main purpose of the present work was to investigate the disposition of a single ¹⁴ C- labeled EMA401 in non-clinical studies. The in vitro metabolism studies of EMA401 were undertaken to understand the hepatic biotransformation pathways in animal species used in toxicology studies and how they compare to human. Furthermore, investigation of EMA401's PK was carried out in vivo in rats. The study demonstrates the rapid absorption and distribution of drug-related material mainly to the tissues associated with absorption and elimination (GI tract, liver, and kidney). EMA401was then readily eliminated metabolically via the bile (95% of dose) predominantly in the form of the direct acylglucuronide (40% of dose), which was further hydrolysed by the intestinal flora to the active parent drug. Other metabolic pathways such as dealkylations and hydroxylation were also involved in the elimination of EMA401 to a lesser extent. EMA401 was metabolically unstable in hepatocytes of all species investigated and the key metabolites produced in the in vitro model were also detected in vivo. Independent of the dosing route, the S-enantiomer EMA401 showed a good in vivo chiral stability. Overall, the present study provides the first full characterization of the disposition of EMA401 in preclinical species.

Biotransformation Pathways and Metabolite Profiles of Oral [14C]Alisertib (MLN8237), an Investigational Aurora A Kinase Inhibitor, in Patients with Advanced Solid Tumors

Alisertib (MLN8237) is an investigational, orally available, selective aurora A kinase inhibitor in clinical development for the treatment of solid tumors and hematologic malignancies. This metabolic profiling analysis was conducted as part of a broader phase 1 study evaluating mass balance, pharmacokinetics, metabolism, and routes of excretion of alisertib following a single 35-mg dose of [14C]alisertib oral solution (∼80 μCi) in three patients with advanced malignancies. On average, 87.8% and 2.7% of the administered dose was recovered in feces and urine, respectively, for a total recovery of 90.5% by 14 days postdose. Unchanged [14C]alisertib was the predominant drug-related component in plasma, followed by O-desmethyl alisertib (M2), and alisertib acyl glucuronide (M1), which were present at 47.8%, 34.6%, and 12.0% of total plasma radioactivity. In urine, of the 2.7% of the dose excreted, unchanged [14C]alisertib was a negligible component (trace), with M1 (0.84% of dose) and glucuronide conjugate of hydroxy alisertib (M9; 0.66% of dose) representing the primary drug-related components in urine. Hydroxy alisertib (M3; 20.8% of the dose administered) and unchanged [14C]alisertib (26.3% of the dose administered) were the major drug-related components in feces. In vitro, oxidative metabolism of alisertib was primarily mediated by CYP3A. The acyl glucuronidation of alisertib was primarily mediated by uridine 5'-diphospho-glucuronosyltransferase 1A1, 1A3, and 1A8 and was stable in 0.1 M phosphate buffer and in plasma and urine. Further in vitro evaluation of alisertib and its metabolites M1 and M2 for cytochrome P450-based drug-drug interaction (DDI) showed minimal potential for perpetrating DDI with coadministered drugs. Overall, renal elimination played an insignificant role in the disposition of alisertib, and metabolites resulting from phase 1 oxidative pathways contributed to >58% of the alisertib dose recovered in urine and feces over 192 hours postdose. SIGNIFICANCE STATEMENT: This study describes the primary clearance pathways of alisertib and illustrates the value of timely conduct of human absorption, distribution, metabolism, and excretion studies in providing guidance to the clinical pharmacology development program for oncology drugs, for which a careful understanding of sources of exposure variability is crucial to inform risk management for drug-drug interactions given the generally limited therapeutic window for anticancer drugs and polypharmacy that is common in cancer patients.

Kinetic modelling of acyl glucuronide and glucoside reactivity and development of structure–property relationships

Detailed kinetic and transition structure modelling to rationalise the differences in reactivity observed between the acyl glucuronide and glucoside metabolites of a series of phenylacetic acid analogues.

Designing around Structural Alerts in Drug Discovery

Cumulative research over several decades has implicated the involvement of reactive metabolites in many idiosyncratic adverse drug reactions (IADRs). Consequently, "avoidance" strategies have been inserted into drug discovery paradigms, which include the exclusion of structural alerts and possible termination of reactive metabolite-positive compounds. Several noteworthy examples where reactive metabolite-related liabilities have been resolved through structure-metabolism studies are presented herein. Considerable progress has also been made in addressing the limitations of the avoidance strategy and further refining the process of managing reactive metabolite issues in drug development. These efforts primarily stemmed from the observation that numerous drugs, which contain structural alerts and/or form reactive metabolites, are devoid of ADRs. The Perspective also dwells into an analysis of the structural alert/reactive metabolite concept with a discussion of risk mitigation tactics to support the progression of reactive metabolite-positive drug candidates.

Differentiation of Deprotonated Acyl-, N-, and O-Glucuronide Drug Metabolites by Using Tandem Mass Spectrometry Based on Gas-Phase Ion-Molecule Reactions Followed by Collision-Activated Dissociation

Glucuronidation, a common phase II biotransformation reaction, is one of the major in vitro and in vivo metabolism pathways of xenobiotics. In this process, glucuronic acid is conjugated to a drug or a drug metabolite via a carboxylic acid, a hydroxy, or an amino group to form acyl-, O-, and/or N-glucuronide metabolites, respectively. This process is traditionally thought to be a detoxification pathway. However, some acyl-glucuronides react with biomolecules in vivo, which may result in immune-mediated idiosyncratic drug toxicity (IDT). In order to avoid this, one may attempt in early drug discovery to modify the lead compounds in such a manner that they then have a lower probability of forming reactive acyl-glucuronide metabolites. Because most drugs or drug candidates bear multiple functionalities, e.g., hydroxy, amino, and carboxylic acid groups, glucuronidation can occur at any of those. However, differentiation of isomeric acyl-, N-, and O-glucuronide derivatives of drugs is challenging. In this study, gas-phase ion-molecule reactions between deprotonated glucuronide metabolites and BF₃ followed by collision-activated dissociation (CAD) in a linear quadrupole ion trap mass spectrometer were demonstrated to enable the differentiation of acyl-, N-, and O-glucuronides. Only deprotonated N-glucuronides and deprotonated, migrated acyl-glucuronides form the two diagnostic product ions: a BF₃ adduct that has lost two HF molecules, [M - H + BF₃ - 2HF]^-, and an adduct formed with two BF₃ molecules that has lost three HF molecules, [M - H + 2BF₃ - 3HF]^-. These product ions were not observed for deprotonated O-glucuronides and unmigrated, deprotonated acyl-glucuronides. Upon CAD of the [M - H + 2BF₃ - 3HF]^- product ion, a diagnostic fragment ion is formed via the loss of 2-fluoro-1,3,2-dioxaborale (MW of 88 Da) only in the case of deprotonated, migrated acyl-glucuronides. Therefore, this method can be used to unambiguously differentiate acyl-, N-, and O-glucuronides. Further, coupling this methodology with HPLC enables the differentiation of unmigrated 1-β-acyl-glucuronides from the isomeric acyl-glucuronides formed upon acyl migration. Quantum chemical calculations at the M06-2X/6-311++G(d,p) level of theory were employed to probe the mechanisms of the reactions of interest.

New Perspectives on Acyl Glucuronide Risk Assessment in Drug Discovery: Investigation of In vitro Stability, In situ Reactivity, and Bioactivation

Background:

Acyl glucuronides of xenobiotics have been a subject of wide interest from the pharmaceutical industry with respect to biochemical reactivity, hepatic disposition, and enterohepatic cir-culation. The reactivity and lack of stability of an acyl glucuronide for a clinical candidate could pose ma-jor developability concerns. To date, multiple in vitro assays have been published to assess the risk asso-ciated with acyl glucuronides. Despite this fact, the translation of these findings to predicting clinical safe-ty remains poor.

Methods:

In the present investigation, we aimed to provide simplified in vitro strategy to understand the bioactivation potential of acyl glucuronides of 10 commercial, carboxylic acid containing drugs that have been categorized as “safe,” “warning,” or “withdrawn” with respect to their marketed use. Acyl migration was measured as a function of the number of peaks observed in LC-MSn analysis. In addition, we carried out reactive intermediate trapping studies with glutathione and methoxylamine to identify the key interme-diates in the transacylation bioactivation and glycation pathways, respectively. We also conducted reaction phenotyping with recombinant UDP-glucuronosyltransferase (UGT) Supersomes® to investigate if the formation of acyl glucuronides could be linked to specific UGT isoform(s).

Results:

Our results were in line with reported values in the literature. Our assay could be used in discov-ery research where half-life calculation completely eliminated the need to chemically synthesize the acyl glucuronide standard for risk assessment. We captured our results for risk assessment in a flow chart to simplify the various complex in vitro techniques historically presented.

Conclusion:

While the compounds tested from “withdrawn” and “warning category” all formed the glu-tathione adduct in buffer, none from “safe” category formed the glutathione adduct. In contrast, none of the compounds tested from any category formed methoxylamine conjugate, a reaction with putative alde-hyde moiety formed via acyl migration. These results, highly favor the nucleophilic displacement as a cause of the reactivity rather than the acyl migration via aldehyde formation. The workflow presented could also be applied in the discovery setting to triage new chemical entities of interest.

Discovery of a GPR40 Superagonist: The Impact of Aryl Propionic Acid α-Fluorination

GPR40 is a G-protein-coupled receptor which mediates fatty acid-induced glucose-stimulated insulin secretion from pancreatic beta cells and incretion release from enteroendocrine cells of the small intestine. GPR40 full agonists exhibit superior glucose lowering compared to partial agonists in preclinical species due to increased insulin and GLP-1 secretion, with the added benefit of promoting weight loss. In our search for potent GPR40 full agonists, we discovered a superagonist which displayed excellent in vitro potency and superior efficacy in the Gαs-mediated signaling pathway. Most synthetic GPR40 agonists have a carboxylic acid headgroup, which may cause idiosyncratic toxicities, including drug-induced-liver-injury (DILI). With a methyl group and a fluorine atom substituted at the α-C of the carboxylic acid group, 19 is not only highly efficacious in lowering glucose and body weight in rodent models but also has a low DILI risk due to its stable acylglucuronide metabolite.

Practical one-step glucuronidation via biotransformation

We herein report a practical one-step glucuronidation method by biotransformation using Streptomyces sp. SANK 60895. This novel direct method of biotransformation has been shown to be more practical and scalable for glucuronidation than previously reported chemical and enzymatic procedures given its simplicity, high β-selectivity, cost-effectiveness, and reproducibility. We applied the present method to the synthesis of acyl glucuronide and hydroxy-β-glucuronide of mycophenolic acid and compound 4, respectively. This method was also shown to be applicable to the N-glucuronidation of various compounds.

Chemo-Enzymatic Synthesis, Structural and Stereochemical Characterization, and Intrinsic Degradation Kinetics of Diastereomers of 1-β-O-Acyl Glucuronides Derived from Racemic 2-{4-[(2-Methylprop-2-en-1-yl)amino]phenyl}propanoic Acid

Alminoprofen, (RS)-2-{4-[(2-methylprop-2-en-1-yl)amino]phenyl}propanoic acid (ALP) 1, is a racemic drug categorized as a 2-arylpropanoic acid-class nonsteroidal anti-inflammatory drug. Pharmacokinetic studies of 1 in patients have revealed that the corresponding acyl glucuronide 5 is a major urinary metabolite, but little is known about the structure and stereochemistry of 5. The present work describes the synthesis of a diastereomeric mixture of 1-β-O-acyl glucuronides (2RS)-5 from 1 and methyl 2,3,4-tri-O-acetyl-1-bromo-1-deoxy-α-d-glucopyranuronate 2 using our chemo-enzymatic method that has complete specificity for the β-configuration. The structure of (2RS)-5 was characterized by ¹H and ¹³C NMR spectroscopy and high-resolution mass spectrometry as well as by complete hydrolysis by β-glucuronidase. The absolute stereochemistry of (2RS)-5 was determined by comparison with (2R)-5 synthesized alternatively from (2R)-1 and 2. Compound (2R)-1 was prepared in two steps starting from chiral (R)-2-(4-nitrophenyl)propanoic acid (2R)-6. Chiral resolution of (2RS)-1 was achieved using a chiral high-performance liquid chromatography column, and its stereochemistry was determined by comparison with (2R)-1. The intrinsic degradation rate constant of (2R)-5 was 0.405 ± 0.002 h^-1, which is approximately twice that of (2S)-5 (the k value was 0.226 ± 0.002 h^-1) under physiological conditions (pH 7.40, 37 °C).