Impact of microsampling on toxicological evaluation in rodent safety studies.

Recently, animal welfare has been attracting worldwide attention, and implementation of 3Rs (replacement, reduction, and refinement) is prioritized in every way possible in the drug development. Microsampling, in which small amounts of blood are collected, is attracting attention in this context. ICH S3A Q&A focused on microsampling was published in November 2017 to help accelerate the application of microsampling for toxicokinetic assessment. The increased sensitivity of drug measurement apparatuses such as mass spectrometers has made it possible to measure drug concentrations with small amounts of blood samples. In this review, we summarized the reports on toxicological influence of microsampling in rodents (rats and mice) with or without drug administration or recovery period after blood collection and influences that may arise from differences in the blood sampling site or blood sampling volume. We also summarized some perspectives on further implementation of microsampling in toxicology studies. The use of microsampling in regulatory toxicology studies has gradually increased, although at a lower rate than in discovery studies. Since more animals are used in GLP toxicology studies than in discovery studies, the effect of reducing the number of animals by microsampling is expected to be greater in the toxicology studies. This report aims to promote the application of microsampling to nonclinical studies, as it is beneficial for improving animal welfare and can contribute to the 3Rs.

No obvious toxicological influences of 50 µL microsampling from rats administered phenacetin as a drug with hematological toxicity.

According to ICH S3A Q&A focusing on microsampling, its application should be avoided in main study animals for test drugs that could exacerbate hematological parameters with frequent blood sampling. However, no study has reported the effects of microsampling on toxicity parameters of drugs known to induce hematological toxicity. Therefore, we assessed the toxicological effects of serial microsampling on rats treated with phenacetin as a model drug. In a common 28-day study, 50 µL of microsampling was performed at 6-time points on days 1 to 2 and 7-time points on days 27 to 28 from the jugular vein of Sprague Dawley rats. The study was performed independently by two organizations. The toxicological influence of microsampling was evaluated on body weight, food consumption, hematology, blood clinical chemistry, urine parameters, organ weights, and tissue pathology. Phenacetin treatments induced significant changes of various hematological parameters (including hemoglobin and reticulocytes), some organ weights (including liver and spleen), and some hematology-related pathological parameters in the liver, spleen and bone marrow. Meanwhile, serial microsampling exhibited minimal influence on the assessed parameters, although 20 parameters showed statistical differences mostly at one organization. The current results support the notion that serial 50 µL microsampling from the jugular vein had minimal impacts on overall toxicological profiles even in rats treated with a drug inducing hematological toxicity, but the potential adverse effect on certain parameters could not be fully excluded. Accordingly, this microsampling technique has possibility to be employed even for non-clinical rat toxicity studies using drugs with potentially hematological toxicity.

Lack of toxicological influences by microsampling (50 µL) from jugular vein of rats in a collaborative 28-day study.

Due to finalization of the ICH S3A Q&A focusing on microsampling, application of microsampling technique to regular non-clinical animal studies is expected for non-clinical safety assessment of pharmaceuticals. In Europe, microsampling from the tail vein or saphenous vein has often been used, whereas sampling from the jugular vein is thought to be more common for non-clinical studies in Japan. Therefore, we assessed the toxicological effects of serial microsampling from the jugular vein of SD rats in a common 28-day study at 4 independent organizations. Fifty microliter sampling was performed at 6 timepoints on day 1 to 2 and 7 timepoints on day 27 to 28 and its toxicological influences on body weight, food consumption, hematological and clinical chemistry parameters, and organ weights (on day 29 for 3 and day 28 for 1 organizations) were evaluated. The serial microsampling was shown to have no or minimal influences on the assessed parameters. The observed statistical differences for the 18 parameters were sporadic and did not appear to be systemically associated with microsampling. However, the sporadic changes were more often observed in females (14/18 parameters) than in males (6/18), suggesting the possibility that female rats were more susceptible to treatment-based influences. The current results indicate that serial 50 µL sampling from the jugular vein of SD rats had no or very slight toxicological effects, suggesting that this microsampling condition is applicable for toxicokinetic evaluation of non-clinical rat toxicity studies.

The effect of elevated α1-acid glycoprotein on the pharmacokinetics of TAK-272 (SCO-272), an orally active renin inhibitor, in rats.

The pharmacokinetics of TAK-272 (SCO-272), an orally active renin inhibitor, was investigated in rats with subcutaneously injected turpentine oil, which was an inflammation animal model. Following intravenous administration of TAK-272 to the turpentine-treated rats, the systemic clearance and volume of distribution decreased with the elevated plasma α1-acid glycoprotein (AGP) levels. The elevated plasma AGP levels were negatively correlated with the plasma unbound fraction of TAK-272 in the rats. Although the AUCs of total TAK-272 in the turpentine-treated rats were higher than those in the control rats after intravenous and oral administration, those of unbound TAK-272, which seem to directly contribute to the pharmacological effect and safety, were nearly equal between the turpentine-treated and control rats in the respective dose routes. TAK-272 has been shown to primarily bind to AGP in the human plasma. These results strongly suggested that the pharmacokinetic of TAK-272 in humans would also be affected by the variation in the plasma AGP levels and should be discussed with not only the total concentrations but also the unbound concentrations in the clinical trial for patients with elevated plasma AGP levels.

Differences in nonclinical pharmacokinetics between species and prediction of human pharmacokinetics of TAK-272 (SCO-272), a novel orally active renin inhibitor.

In the search for orally available drugs, the prediction of human pharmacokinetics (PK) is essential for successfully selecting compounds that will be clinically useful. This report describes the selection of TAK-272 (SCO-272), a novel orally active renin inhibitor, as a clinical candidate via the detailed investigation of nonclinical PK data and human PK prediction. The bioavailability (BA) of TAK-272 after oral administration to rats and monkeys was low, especially in fasted monkeys, and the systemic exposure of TAK-272 was highly variable in monkeys. The results of mass balance studies in animals suggested that the absorbed TAK-272 was largely eliminated by metabolism. In vitro studies revealed that TAK-272 was mainly metabolized by CYP3A4/5 in humans, and it was a P-glycoprotein substrate. PK analysis suggested that the factors responsible for the low BA were different in rats and monkeys. First-pass hepatic extraction was high in rats, while the fraction absorbed from the gastrointestinal tract (Fa * Fg ) was low in monkeys. It was predicted that humans would have a higher BA and a longer half-life in the plasma compared with the animals by a simple calculation using intrinsic hepatic clearance in monkeys, which correlates well with human values for CYP3A4 substrates, and Fa * Fg in rats, which correlates relatively well with human values. TAK-272 was finally selected as a clinical candidate based on the result of human PK prediction. The actual human PK after oral administration of TAK-272 was comparable to the predicted profile and was preferable for clinical usage.

Bioanalysis of farnesyl pyrophosphate in human plasma by high-performance liquid chromatography coupled to triple quadrupole tandem mass spectrometry and hybrid quadrupole Orbitrap high-resolution mass spectrometry.

The isoprenoids farnesyl pyrophosphate (FPP) and geranylgeranyl pyrophosphate (GGPP) are pivotal intermediates for cholesterol homeostasis and cell signaling in the mevalonate pathway. We developed a sensitive and selective high-performance liquid chromatography tandem triple quadrupole mass spectrometry (LC-QQQ-MS) method for FPP in human plasma without the need for a derivatization process. We optimized the sample preparation procedure to extract FPP and 13C5-FPP (as internal standard) from sample fluids using methanol. Phosphate-buffered saline was used as the surrogate matrix for the preparation of calibration curves and quality control samples. Using an XBridge C18 column (3.5 µm, 2.1 × 100-mm ID) with gradient elution composed of 10 mmol/L ammonium carbonate/ammonium hydroxide (1000:5, v/v) and acetonitrile/ammonium hydroxide (1000:5, v/v) provided the sharp peaks of FPP and 13C5-FPP in human plasma. The calibration curve ranged from 0.2 to 20 ng/mL in human plasma with acceptable intra-day and inter-day precision and accuracy. The sensitivity of this bioanalytical method was sufficient for clinical analysis. The endogenous FPP plasma concentrations in 40 human healthy volunteers ascertained by LC-QQQ-MS and high-performance liquid chromatography tandem hybrid quadrupole Orbitrap high-resolution mass spectrometry (LC-Q-Orbi-MS) were comparable. Furthermore, the endogenous GGPP in human plasma was selectively detected for the first time by LC-Q-Orbi-MS. In conclusion, a sensitive bioanalytical method for FPP in human plasma by means of LC-QQQ-MS and LC-Q-Orbi-MS was developed in this study. Taking into account the versatility of LC-Q-Orbi-MS, the simultaneous detection of FPP and GGPP may be feasible in clinical practice.

A validated simultaneous quantification method for vonoprazan (TAK-438F) and its 4 metabolites in human plasma by the liquid chromatography-tandem mass spectrometry.

Vonoprazan fumarate (TAK-438) is a potassium-competitive acid blocker which was approved in Japan for a treatment of acid-related diseases. In this study a simple and validated bioanalytical method, which can simultaneously determine vonoprazan (TAK-438F) and its four metabolites (M-I, M-II, M-III and M-IV-Sul) in human plasma, was developed. The method is based on protein precipitation and subsequent ultra-high performance liquid chromatography separation followed by tandem mass spectrometry detection. The mass spectrometric parameters for detection of TAK-438F, M-I, M-III and M-IV-Sul were modified from their optimum values in order to achieve a simultaneous quantification while retaining enough sensitivity and wide dynamic ranges for all the target analytes. The validity and robustness of the method was verified through a validation study as per the regulatory guidance on bioanalytical method validation. The calibration ranges are 0.1-100 ng/mL for TAK-438F and M-III, and 1-1000 ng/mL for M-I, M-II and M-IV-Sul using the 100 µL of human plasma. The total run time per sample is 5 min. The working solution for M-III was recommended to be prepared separately, especially for the long-term use, in order to avoid the instability of M-III in the mixed working solutions, which could cause the high consumption of reference standards. The established method was applied to clinical pharmacokinetic studies and concentrations of all the analytes in human plasma were successfully determined with high reproducibility ensured by incurred sample reanalysis, indicating the suitableness of the established method.

Method development for the determination of D- and L-isomers of leucine in human plasma by high-performance liquid chromatography tandem mass spectrometry and its application to animal plasma samples.

We developed a highly sensitive and specific high-performance liquid chromatography tandem mass spectrometry method with an electrospray ionization for the determination of D- and L-isomers of leucine in human plasma. Phosphate-buffered saline was used as the surrogate matrix for preparation of calibration curves and quality control samples. The extraction of D- and L-leucine in plasma samples (100 µL) was performed using cationic exchange solid-phase extraction. The enantiomer separation of D- and L-leucine was successfully achieved without derivatization using a CHIRALPAK ZWIX(-) with an isocratic mobile phase comprised of methanol/acetonitrile/1 mol/L ammonium formate/formic acid (500:500:25:2, v/v/v/v) at a flow rate of 0.5 mL/min. In addition, the discrimination of DL-leucine from structural isomers DL-isoleucine and DL-allo-isoleucine was performed using the unique precursor and product ion pair transition of DL-leucine (m/z 132.1 > 43.0) and DL-leucine-d 7 (m/z 139.2 > 93.0) in positive electrospray ionization mode. The standard curves were linear throughout the calibration range from 0.001 to 1 µg/mL for D-leucine and from 1 to 1000 µg/mL for L-leucine, respectively, with acceptable intra- and inter-day precision and accuracy. The stability of D- and L-leucine in human plasma and solvents was confirmed. The endogenous level of D- and L-leucine in human plasma was 0.00197~0.00591 and 9.63~24.7 µg/mL, respectively. This method was also successfully applied to investigate the species difference in the ratios of D-leucine to total leucine from individual plasma concentrations in humans and various animals. The plasma D-leucine concentrations or their ratio to total leucine in rodents was much higher than that in humans.

Development, validation and application of the liquid chromatography tandem mass spectrometry method for simultaneous quantification of azilsartan medoxomil (TAK-491), azilsartan (TAK-536), and its 2 metabolites in human plasma.

Azilsartan medoxomil potassium salt (TAK-491) is an orally administered angiotensin II type 1 receptor blocker for the treatment of hypertension and is an ester-based prodrug that is rapidly hydrolyzed to the pharmacologically active moiety, azilsartan (TAK-536), during absorption. TAK-536 is biotransformed to the 2 metabolites M-I by decarboxylation and M-II by dealkylation. In this study, we developed and validated a LC/MS/MS method which can simultaneously determine 4 analytes, TAK-491, TAK-536, M-I and M-II. The bioanalytical method can be outlined as follows: two structural analogues are used as the internal standards. The analytes and the IS are extracted from human plasma using solid phase extraction. After evaporating, the residue is reconstituted and injected into a LC/MS/MS system with an ESI probe and analyzed in the positive ion mode. Separation is performed through a conventional reversed-phase column with a mobile phase of water/acetonitrile/acetic acid (40:60:0.05, v/v/v) mixture at a flow rate of 0.2mL/min. The total run time is 8.5min. The calibration range is 1-2500ng/mL in human plasma for all the analytes. Instability issues of the prodrug, TAK-491, were overcome and all the validation results met the acceptance criteria in accordance with the regulatory guideline/guidance. As a result of the clinical study, the human PK profiles of TAK-536, M-I and M-II were successfully obtained and also it was confirmed that TAK-491 was below the LLOQ (1ng/mL) in the human plasma samples.

Method development for the determination of 24S-hydroxycholesterol in human plasma without derivatization by high-performance liquid chromatography with tandem mass spectrometry in atmospheric pressure chemical ionization mode.

We developed a highly sensitive and specific high-performance liquid chromatography with tandem mass spectrometry method with an atmospheric pressure chemical ionization interface to determine 24S-hydroxycholesterol, a major metabolite of cholesterol formed by cytochrome P450 family 46A1, in human plasma without any derivatization step. Phosphate buffered saline including 1% Tween 80 was used as the surrogate matrix for preparation of calibration curves and quality control samples. The saponification process to convert esterified 24S-hydroxycholesterol to free sterols was optimized, followed by liquid-liquid extraction using hexane. Chromatographic separation of 24S-hydroxycholesterol from other isobaric endogenous oxysterols was successfully achieved with gradient mobile phase comprised of 0.1% propionic acid and acetonitrile using L-column2 ODS (2 µm, 2.1 mm id × 150 mm). This assay was capable of determining 24S-hydroxycholesterol in human plasma (200 µL) ranging from 1 to 100 ng/mL with acceptable intra- and inter-day precision and accuracy. The potential risk of in vitro formation of 24S-hydroxycholesterol by oxidation from endogenous cholesterol in human plasma was found to be negligible. The stability of 24S-hydroxycholesterol in relevant solvents and human plasma was confirmed. This method was successfully applied to quantify the plasma concentrations of 24S-hydroxycholesterol in male and female volunteers.

Bioanalytical method for the simultaneous determination of D- and L-serine in human plasma by LC/MS/MS.

D-Serine is an endogenous modulator of N-methyl-D-aspartate (NMDA) receptors. Plasma concentrations of D-serine and the ratio of D-serine to total serine may be used as clinically-translatable biomarkers in NMDA receptor-related disease. We developed a highly sensitive and specific method using high performance liquid chromatography tandem mass spectrometry (LC/MS/MS) for the simultaneous determination of the D- and L-isomers of serine in human plasma. Since D- and L-serine are endogenous components, phosphate buffered saline was used as the surrogate matrix. D- and L-serine in human plasma and PBS were treated by cationic exchange solid phase extraction. D-Serine (m/z 106.1 > 60.0), L-serine (m/z 106.1 > 60.1) and DL-serine-d3 (m/z 109.1 > 63.0) were detected using a multiple reaction monitoring. The enantiomer separation of D- and L-serine was successfully achieved without any derivatization step using tandemly-arranged and ice-cold CROWNPAK CR-I(+) columns with an isocratic mobile phase comprised of 0.3% trifluoroacetic acid in 10% acetonitrile. The standard curves were linear throughout the calibration range with 0.01-10 µg/mL (D-serine) and 0.1-100 µg/mL (L-serine), respectively. Intra-day and inter-day precision and accuracy of the quality control samples were within relative standard deviations of less than 15%. The endogenous concentrations of D- and L-serine in human plasma were 0.124-0.199 and 7.97-13.1 µg/mL, respectively.

Retrospective data analysis and proposal of a practical acceptance criterion for inter-laboratory cross-validation of bioanalytical methods using liquid chromatography/tandem mass spectrometry.

The purpose of this study is to conduct a retrospective data analysis for inter-laboratory cross-validation studies to set a reasonable and practical acceptance criterion based on a number of cross-validation results. From the results of cross-validation studies for 16 compounds and their metabolites, analytical bias and variation were evaluated. The accuracy of cross-validation samples was compared with that of quality control (QC) samples with statistical comparison of the analytical variation. An acceptance criterion was derived with a confidential interval approach. As the results, while a larger bias was observed for the cross-validation samples, the bias was not fully caused by analytical variation or bias attributable to the analytical methods. The direction of the deviation between the cross-validation samples and QC samples was random and not concentration-dependent, suggesting that inter-laboratory variability such as preparation errors could be a source of bias. A derived acceptance criterion corresponds to one prescribed in the Guideline on bioanalytical method validation from the Ministry of Health, Labour and Welfare in Japan and is a little wider than one in the European Medical Agency. In conclusion, thorough retrospective data analysis revealed potential causes of larger analytical bias in inter-laboratory cross-validation studies. A derived acceptance criterion would be practical and reasonable for the inter-laboratory cross-validation study.

Highly sensitive liquid chromatography-tandem mass spectrometry method for quantification of TAK-448 in human plasma.

TAK-448 is a nonapeptide analogue and a novel metastin receptor agonist. The aim of this study was to develop a bioanalytical method for TAK-448F (the free base of TAK-448) in human plasma with LC/MS/MS that is sensitive and applicable for the clinical PK studies, and to evaluate the reliability and robustness of the developed method through a validation study in accordance with the regulatory guidance/guideline. The bioanalytical method developed in this study can be outlined as follows. The structural analogue, TAK-683, was used as the internal standard (IS). TAK-448F and the IS were extracted from human plasma using solid phase extraction (SPE) with a polymer-based weak cationic exchanger. After evaporating, the residue was reconstituted and injected into a LC-MS/MS system with ESI probe and analyzed by the selected reaction monitoring (SRM) in the positive ion mode. Separation was performed through an UPLC BEH Phenyl column with the mobile phase of water/methanol/formic acid mixture at a flow rate of 0.2 mL/min. The total run time was 10 minutes. The LLOQ was achieved to be 5 pg/mL with 0.5 mL of human plasma sample. All the validation results met the acceptance criteria in accordance with the regulatory guidance/guideline proving its reliability and robustness. As a result of the clinical study, the human PK profiles of TAK-448F were successfully obtained with this method.

Species differences of organic anion transporters involved in the renal uptake of 4-amino-3-chlorophenyl hydrogen sulfate, a metabolite of resatorvid, between rats and dogs.

Previous studies on the metabolic fate of resatorvid (TAK-242) have shown that species differences in the pharmacokinetics of 4-amino-3-chlorophenyl hydrogen sulfate (M-III), a metabolite of TAK-242, between rats and dogs are mainly attributable to the urinary excretion process. In the present study, the renal uptake mechanism of M-III was investigated using kidney slices and Xenopus laevis oocytes expressing rat organic anion transporter 1 (rOat1; Slc22a6) and rOat3 (Slc22a8). The uptake of p-aminohippuric acid (PAH), a substrate for Oats, by kidney slices from rats and dogs increased at 37 °C and M-III inhibited the uptake. The initial uptake clearance of M-III by rat kidney slices was 0.295 and 0.0114 ml/min/g at 37 °C and 4 °C, respectively. The Eadie-Hofstee plot of M-III uptake at 37 °C revealed two-component transport processes with K(m) values being 6.48 and 724 µmol/l. The uptake was inhibited by probenecid (PBC), PAH and benzylpenicillin (PCG). In contrast, in dog kidney slices, the initial uptake clearance of M-III was 8.70 × 10(-3) and 9.00 × 10(-3) ml/min/g at 37 °C and 4 °C, respectively, and the uptake was not inhibited by PBC. Furthermore, rOat1- and rOat3-expressing oocytes mediated M-III uptake and the uptake was inhibited by PAH and PCG, respectively. These results suggest that rOat1 and rOat3 are responsible for the renal uptake of M-III in rats. Moreover, it is speculated that Oat(s) is unable to transport M-III in dogs and that the difference in the substrate recognition of Oat(s) contributes to the species difference in the pharmacokinetics of M-III between rats and dogs.

Application of high-resolution ESI and MALDI mass spectrometry to metabolite profiling of small interfering RNA duplex.

We investigated the application of a high-resolution Orbitrap mass spectrometer equipped with an electrospray ionization (ESI) source and a matrix-assisted laser desorption/ionization-time-of-flight (MALDI-TOF) mass spectrometer to the metabolite profiling of a model small interfering RNA (siRNA) duplex TSR#34 and compared their functions and capabilities. TSR#34 duplex was incubated in human serum in vitro, and the duplex and its metabolites were then purified by ion exchange chromatography in order to remove the biological matrices. The fraction containing the siRNA duplex and its metabolites was collected and desalted and then subjected to high-performance liquid chromatography (HPLC) equipped with a reversed phase column. The siRNA and its metabolites were separated into single strands by elevated chromatographic temperature and analyzed using the ESI-Orbitrap or the MALDI-TOF mass spectrometer. Using this method, the 5' and/or 3' truncated metabolites of each strand were detected in the human serum samples. The ESI-Orbitrap mass spectrometer enabled differentiation between two possible RNA-based sequences, a monoisotopic molecular mass difference which was less than 2 Da, with an intrinsic mass resolving power. In-source decay (ISD) analysis using a MALDI-TOF mass spectrometer allowed the sequencing of the RNA metabolite with characteristic fragment ions, using 2,4-dihydroxyacetophenone (2,4-DHAP) as a matrix. The ESI-Orbitrap mass spectrometer provided the highest mass accuracy and the benefit of on-line coupling with HPLC for metabolite profiling. Meanwhile, the MALDI-TOF mass spectrometer, in combination with 2,4-DHAP, has the potential for the sequencing of RNA by ISD analysis. The combined use of these methods will be beneficial to characterize the metabolites of therapeutic siRNA compounds.

Differences in the pharmacokinetics of 4-amino-3-chlorophenyl hydrogen sulfate, a metabolite of resatorvid, in rats and dogs.

The pharmacokinetics of 4-amino-3-chlorophenyl hydrogen sulfate, M-III of resatorvid, in rats and dogs were investigated using radiolabeled M-III ([(14)C]M-III). The elimination half-life of (14)C in the plasma of rats was approximately 1/30 of that of dogs after intravenous dosing of [(14)C]M-III at 0.5 mg/kg to rats and dogs. The in vitro and in vivo plasma protein binding ratios of M-III were relatively high and were the same in both species. The intrinsic clearance (CL(int)) of M-III in rats was much higher than the glomerular filtration rate in rats. Furthermore, the concentration of [(14)C]M-III in the kidney of rats was much higher than that in the plasma. On the contrary, in dogs, the concentration of [(14)C]M-III in the kidney was very much lower than that in the plasma. These results indicated that M-III was effectively taken up into the kidney and was excreted into the urine in rats; however, in dogs, ineffective renal uptake of M-III was presumed. When [(14)C]M-III and probenecid were simultaneously and continually infused intravenously to rats, the CL(int) of M-III decreased with increasing plasma concentrations of probenecid, indicating that kidney uptake of M-III in rats was inhibited by probenecid. It was also thought that uptake by the organic anion transport system(s) in the basolateral membrane is involved in the renal uptake of M-III in rats. The pharmacokinetic differences of M-III between rats and dogs are considered to be mainly caused by the difference in the urinary excretion via the renal distribution processes.

Investigation of the unique metabolic fate of ethyl (6R)-6- [N- (2-chloro-4-fluorophenyl) sulfamoyl] cyclohex-1-ene-1-carboxylate (TAK-242) in rats and dogs using two types of 14C-labeled compounds having different labeled positions.

The pharmacokinetics of TAK-242 (ethyl (6R)-6- [N-(2-chloro-4-fluorophenyl)sulfamoyl]cyclohex-1-ene-1-carboxylate, CAS 243984-11-4) and its metabolites were investigated in rats and dogs after intravenous (i.v.) dosing of TAK-242 using two types of radiolabeled TAK-242: [phenyl ring-U-14C]TAK-242 and [cyclohexene ring-U-14C]TAK-242. The phenyl ring moiety of TAK-242 yielded 2-chloro-4-fluoroaniline, M-I, and M-I was further acetylated and conjugated to form M-II and the glucuronide (M-I-G), respectively. M-I was also converted to M-III and M-IV by hydroxylation and subsequent sulfate conjugation. Meanwhile, the cyclohexene ring moiety of TAK-242 was metabolized to glutathione conjugate, M-SG, followed by further metabolism of M-SG to form cysteine conjugate (M-Cys) and mercapturic acid conjugate (M-Mer). After i.v. injection of [phenyl ring-U-14C]TAK-242 to rats and dogs, the 14C concentrations in dogs declined slowly with a half-life of about 1 week although that in rats was about 6 h. The predominant components in the plasma of rats and dogs were M-I-G and M-III, respectively. After i.v. injection of [cyclohexene ring-U-14C]TAK-242 to rats and dogs, 14C-components unextractable by organic solvents were observed in the plasma. These results indicated two unique metabolic fates of TAK-242. The phenyl ring moiety of TAK-242 showed species differences between rats and dogs in the metabolism and excretion kinetics and the cyclohexene ring moiety of TAK-242 showed potential for covalent binding to endogenous components such as plasma proteins.

Chemical reactivity of ethyl (6R)-6-[N-(2-chloro-4-fluorophenyl)sulfamoyl]cyclohex-1-ene-1-carboxylate (TAK-242) in vitro.

Ethyl (6R)-6-[N-(2-chloro-4-fluorophenyl)sulfamoyl]cyclohex-1-ene-1-carboxylate (TAK-242) was metabolized to cyclohexene and phenyl ring moieties in non-clinical pharmacokinetic studies and it was suggested that the cyclohexene ring moiety of TAK-242 is tightly bound to endogenous macromolecules. After incubation of TAK-242 and glutathione (GSH) in phosphate buffer (pH 7.4) at 37 °C, TAK-242 reacted with GSH to produce a glutathione conjugate of the cyclohexene ring moiety of TAK-242, which had been observed as a metabolite (M-SG) in non-clinical pharmacokinetic studies. Formation of M-SG was time dependent with a first order reaction and M-I, a metabolite from the phenyl ring moiety of TAK-242, was also produced in parallel. The formation of M-SG was accelerated with increasing pH, therefore it was indicated that TAK-242 reacted with GSH by a nucleophilic substitution reaction. Because glutathione transferase (GST) enhanced M-SG formation in vitro, it is expected that the conjugation of TAK-242 with GSH is also facilitated by GST in vivo in addition to a spontaneous chemical reaction. When radio-labeled TAK-242 ([cyclohexene ring-U-¹4C]TAK-242) was incubated with rat serum albumin (RSA) or human serum albumin (HSA) in vitro, the radioactive material was covalently bound to RSA and HSA, and M-I was generated simultaneously in the reaction mixture. The chemical structure of the TAK-242 adduct covalently bound to HSA was characterized by the accurate mass spectra that cyclohexene ring moiety of TAK-242 was covalently bound to the lysine residue in HSA. The adduct was also detected in the plasma of rats and humans after single i.v. dosing of TAK-242 (in vivo).