Details of a Researcher - Ohtani, Hisakazu

Papers - Ohtani, Hisakazu

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医薬品情報の科学的な収集、評価、活用

大谷壽一

The Annual Meeting of Japanese Society of Pharmaceutical Health Care and Sciences (Japanese Society of Pharmaceutical Health Care and Sciences) 32 ( 0 ) 99 - 99 2022.09

Research paper (other academic)

Inhibitory Effects of Cranberry Juice and Its Components on Intestinal OATP1A2 and OATP2B1: Identification of Avicularin as a Novel Inhibitor

Morita T., Akiyoshi T., Tsuchitani T., Kataoka H., Araki N., Yajima K., Katayama K., Imaoka A., Ohtani H.

Journal of Agricultural and Food Chemistry (Journal of Agricultural and Food Chemistry) 70 ( 10 ) 3310 - 3320 2022.03

Research paper (scientific journal), Joint Work, Last author, Corresponding author, Accepted, ISSN 00218561

Organic anion-transporting polypeptide (OATP) 1A2 and OATP2B1 mediate the intestinal absorption of drugs. This study aimed to identify fruit juices or fruit juice components that inhibit OATPs and assess the risk of associated food-drug interactions. Inhibitory potency was assessed by examining the uptake of [3H]estrone 3-sulfate and [3H]fexofenadine into HEK293 cells expressing OATP1A2 or OATP2B1. In vivo experiments were conducted using mice to evaluate the effects of cranberry juice on the pharmacokinetics of orally administered fexofenadine. Of eight examined fruit juices, cranberry juice inhibited the functions of both OATPs most potently. Avicularin, a component of cranberry juice, was identified as a novel OATP inhibitor. It exhibited IC50values of 9.0 and 37 μM for the inhibition of estrone 3-sulfate uptake mediated by OATP1A2 and OATP2B1, respectively. A pharmacokinetic experiment revealed that fexofenadine exposure was significantly reduced (by 50%) by cranberry juice. Cranberry juice may cause drug interactions with OATP substrates.

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Analysis of inhibition kinetics of three beverage ingredients, bergamottin, dihydroxybergamottin and resveratrol, on CYP2C9 activity

Akiyoshi T., Uchiyama M., Inada R., Imaoka A., Ohtani H.

Drug Metabolism and Pharmacokinetics (Drug Metabolism and Pharmacokinetics) 42 100429 2022.02

Research paper (scientific journal), Joint Work, Last author, Corresponding author, Accepted, ISSN 13474367

Some grapefruit juice (GFJ) ingredients and resveratrol, a fruit-derived phytoalexin, are known to inhibit cytochrome P450 (CYP) 2C9. However, their inhibition modes and detailed inhibition kinetics remain undetermined. This study aimed to investigate the inhibitory effects of two GFJ ingredients, bergamottin (BG) and dihydroxybergamottin (DHB), and resveratrol on CYP2C9 activity in vitro. DHB inhibited CYP2C9 activity, as assessed by warfarin 7-hydroxylation, in a preincubation time-dependent manner (i.e., mechanism-based inhibition; MBI), in the same manner as CYP2C19 and CYP3A4. The maximal inactivation rate (kinact,max) was 0.0638 min−1 and 0.12- and 0.26-fold of that for CYP2C19 and CYP3A4, respectively. BG showed both MBI and time-independent competitive inhibition. Resveratrol showed non-competitive inhibition with an inhibition constant (Ki) of 3.64 μM. Unlike the inhibition of CYP2C19 and CYP3A4, resveratrol did not induce MBI. These findings are important for estimating the risk of drug interactions between CYP2C9 substrates and some beverages. (146 words)

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Evaluation of hepatic CYP3A enzyme activity using endogenous markers in lung cancer patients treated with cisplatin, dexamethasone, and aprepitant.

Hibino H, Sakiyama N, Makino Y, Makihara-Ando R, Horinouchi H, Fujiwara Y, Kanda S, Goto Y, Yoshida T, Okuma Y, Shinno Y, Murakami S, Hashimoto H, Akiyoshi T, Imaoka A, Ohe Y, Yamaguchi M, Ohtani H

European Journal of Clinical Pharmacology (Eur J Clin Pharmacol) 78 ( 4 ) 613 - 621 2022

Research paper (scientific journal), Joint Work, Accepted, ISSN 00316970

Purpose: Aprepitant is used with dexamethasone and 5-HT3 receptor antagonists as an antiemetic treatment for chemotherapy, including cisplatin. Aprepitant is a substrate of cytochrome P450 (CYP) 3A4 and is known to cause its inhibition and induction. In addition, dexamethasone is a CYP3A4 substrate that induces CYP3A4 and CYP3A5 expression. In this study, we aimed to quantitatively evaluate the profile of CYP3A activity using its endogenous markers in non-small cell lung cancer patients receiving a standard cisplatin regimen with antiemetics, including aprepitant. Methods: Urinary 11β-hydroxytestosterone (11β-OHT)/testosterone concentration ratio and plasma 4β-hydroxycholesterol (4β-OHC) concentrations were measured before and after cisplatin treatment (days 1, 4, and 8). CYP3A5 was genotyped, and plasma aprepitant concentrations were measured on day 4 to examine its influence on CYP3A endogenous markers. Results: The urinary 11β-OHT/testosterone concentration ratio in the 35 patients included in this study increased by 2.65-fold and 1.21-fold on days 4 and 8 compared with day 1, respectively. Their plasma 4β-OHC concentration increased by 1.46-fold and 1.66-fold, respectively. The mean plasma aprepitant concentration on day 4 was 1,451 ng/mL, which is far lower than its inhibitory constant. The allele frequencies of CYP3A5*1 and CYP3A5*3 were 0.229 and 0.771, respectively. In patients with the CYP3A5*1 allele, the plasma 4β-OHC concentration was significantly lower at baseline but more potently increased with chemotherapy. Conclusion: CYP3A activity was significantly induced from day 4 to day 8 in patients receiving cisplatin and three antiemetic drugs.

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Mechanistic bottom-up estimation of passive drug absorption from the gastrointestinal tract– Comparison among primary cultured human intestinal cells, Caco-2 cells, artificial membranes, and animal scale-up

Tsuchitani T, Akiyoshi T, Imaoka A, Ohtani H

Int J Clin Pharmacol Ther (International Journal of Clinical Pharmacology and Therapeutics) 60 ( 5 ) 217 - 224 2022

Research paper (scientific journal), Joint Work, Last author, Corresponding author, Accepted, ISSN 0946-1965

Objective: The fraction of drug absorbed (Fa) from the intestine is an important parameter to characterize the pharmacokinetics of a drug. We aimed to search for an experimental system that provides the best parameters for estimating the effective permeability (Peff) used for the bottom-up prediction of Fa. Materials and methods: The absorption kinetics of 12 passively absorbed drugs were simulated by a compartment absorption transit (CAT) model using absorption parameters from four different experimental systems: human intestinal epithelial cell (HIEC) monolayer, Caco-2 monolayer, parallel artificial membrane permeability assay (PAMPA), and in situ rat intestinal perfusion. All absorption parameters were obtained from the literature. The in vitro apparent permeability coefficient (Papp) and rat in situ Peff were converted to human Peff using a bottom-up approach for each region, based on the morphological features of the human intestine. The simulated Fa values were compared to the respective observed values. Furthermore, plasma concentration profiles of the drugs were simulated by convolution using the time-course of the absorption rate simulated using the Peff values calculated from the HIEC Papp. Results: The Fa values were best predicted by using the Peff values calculated from HEIC, within a 1.3-fold range of observed Fa in 11 out of 12 drugs. The simulated Cmax values of pharmacokinetic simulation using HIEC Papp fell within a 1.5-fold range of observed values for all the drugs examined. Conclusion: The HIEC monolayer was identified as the most suitable permeation parameter for estimating Fa and Cmax using a morphological feature-based bottom-up approach.

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Comparison of the inhibitory properties of the fruit component naringenin and its glycosides against OATP1A2 genetic variants.

Araki N, Morita T, Akiyoshi T, Kataoka H, Yajima K, Katayama K, Imaoka A and Ohtani H.

Drug Metabol Pharmacokinet 46 2022

Research paper (scientific journal), Joint Work, Last author, Corresponding author, Accepted

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Dual kinetics of OATP2B1: Inhibitory potency and pH-dependence of OATP2B1 inhibitors

Sato R., Akiyoshi T., Morita T., Katayama K., Yajima K., Kataoka H., Imaoka A., Ohtani H.

Drug Metabolism and Pharmacokinetics (Drug Metabolism and Pharmacokinetics) 41 100416 2021.12

Research paper (scientific journal), Accepted, ISSN 13474367

Organic anion transporting polypeptide (OATP) 2B1 is expressed in the intestine and liver, and OATP2B1-mediated transport of estrone 3-sulfate is pH-dependent and consists of: the high-affinity component (Hc) and low-affinity component (Lc). This study aimed to evaluate the influence of pH on the transport kinetics of each component, along with the inhibitory nature of ten OATP2B1 inhibitors. The Michaelis constants (Km) were 4-fold and 1.5-fold lower at pH 6.3 than at pH 7.4, for Hc and Lc respectively. The inhibitory potencies of diclofenac, indomethacin, and ibuprofen towards Hc were 1.5–4.3 fold lower at pH 6.3 than at pH 7.4. Contrastingly, inhibitory potencies towards Lc were 9.0–52 fold lower at pH 7.4. Similarly, the inhibitory effect of naproxen was stronger towards Hc at pH 6.3 and towards Lc at pH 7.4. On the other hand, celecoxib selectively inhibited Lc transport at pH 7.4. Rifampicin inhibited both components at pH 6.3 and 7.4 to a similar extent, while bromosulphophthalein, naringin, and gefitinib selectively inhibited Hc irrespective of pH. Fexofenadine inhibited neither component. In conclusion, the transport affinities of both Hc and Lc were enhanced under acidic conditions. The influence of pH on the inhibitory potency towards each component varied among the inhibitors.

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Time-dependent inhibition of CYP3A4-mediated midazolam metabolism by macrolide antibiotics in CYP3A4 genetic variants: Comparison with testosterone metabolism

Akiyoshi Takeshi, Naitou Rina, Imaoka Ayuko, Miyazaki Mitsue, Guengerich F. Peter, Nakamura Katsunori, Yamamoto Koujiro, Ohtani Hisakazu

INTERNATIONAL JOURNAL OF CLINICAL PHARMACOLOGY AND THERAPEUTICS (International Journal of Clinical Pharmacology and Therapeutics) 59 ( 12 ) 745 - 752 2021.12

Research paper (scientific journal), Joint Work, Accepted, ISSN 0946-1965

Objectives: The present study aimed to evaluate the effects of CYP3A4 genetic variation on the kinetics of mechanismbased inhibition (MBI) of both inhibitors using midazolam as a substrate for comparison with our previous study, as midazolam and testosterone have different binding sites. Background: The genetic variation of cytochrome P450 (CYP) 3A4 affects MBI, expressed as the maximum inactivation rate constant (kinact,max) and the inhibitor concentration required to achieve half-maximal inactivation (KI). We previously showed, using testosterone as a substrate, that the MBI kinetics of erythromycin and clarithromycin differ among CYP3A4 variants. Materials and methods: Midazolam 1'-hydroxylation inactivation profiles of erythromycin and clarithromycin were assessed using recombinant CYP3A4.1, .2, .7, .16, and .18 expressed in Escherichia coli. MBI parameters were calculated from changes in the inactivation rate constant (Δkobs) by the inhibitors. Results: Both inhibitors increased Δkobs value in a concentration- and preincubation time-dependent manner, and MBI kinetics differed among variants. Trends of differences in MBI parameters among variants were similar to those assessed using testosterone as a substrate; KI decreased for CYP3A4.7, and kinact,max decreased for CYP3A4.2, .7, and .16. Conclusion: The genetic variation of recombinant CYP3A4 affects the MBI profile of CYP3A4 by erythromycin and clarithromycin, while the influence of genetic variation was similarly observed regardless of substrates. Our findings are of clinical relevance because the residual enzyme activity of CYP3A4 in the presence of inhibitor was estimated to vary among genetic variants.

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Digoxin absorption decreased independently of P-gp activity in rats with irinotecan-induced gastrointestinal damage

Tsuchitani Toshiaki, Akiyoshi Takeshi, Imaoka Ayuko, Ohtani Hisakazu

JOURNAL OF PHARMACEUTICAL HEALTH CARE AND SCIENCES (Journal of Pharmaceutical Health Care and Sciences) 7 ( 1 ) 24 2021.07

Research paper (scientific journal), Joint Work, Accepted, ISSN 2055-0294

Background: Irinotecan (CPT-11) is clinically known to cause severe diarrhea and gastrointestinal damage. Recently, we have reported that CPT-11-induced gastrointestinal damage is associated with the upregulation of intestinal P-glycoprotein (P-gp) expression and decreased absorption of its substrate, dabigatran etexilate (DABE), using a rat model. However, the P-gp activity or its contribution to the decreased absorption remains unclear. The aim of this study was to quantitatively evaluate how P-gp activity changes in rats with CPT-11-induced gastrointestinal damage, as assessed by the absorption of digoxin (DGX), a typical P-gp substrate. Methods: Male Sprague-Dawley rats were intravenously administered CPT-11 at a dose of 60 mg/kg/day for 4 days to induce gastrointestinal damage. Then, the rats were administered DGX orally (40 μg/kg), after some of them were orally administered clarithromycin (CAM; 10 mg/kg), a P-gp inhibitor. DGX (30 μg/kg) was administered intravenously to determine the bioavailability (BA). The rats’ DGX plasma concentration profiles were determined using LC-MS/MS. Results: CPT-11 treatment decreased the maximum concentration (Cmax) and area under the plasma concentration-time curve (AUCpo) of DGX, which does not contradict to the DABE study. Although in the CPT-11-treated group the BA of DGX was significantly decreased to 40% of the control value, CAM did not affect the BA of DGX in the CPT-11-treated group. Conclusions: Increased P-gp expression in rats with CPT-11-induced gastrointestinal damage is not necessarily associated with increased P-gp activity or contribution to the drug absorption in vivo. The decreased DGX absorption observed in this study might be attributable to other factors, such as a reduction in the absorptive surface area of the gastrointestinal tract.

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Estimation of absolute oral bioavailability without performing an intravenous clinical study

Ohtani H., Iwata R., Imaoka A., Akiyoshi T.

Drug Metabolism and Pharmacokinetics (Drug Metabolism and Pharmacokinetics) 38 100392 2021.06

Research paper (scientific journal), Accepted, ISSN 13474367

The absolute oral bioavailability (BA) of drugs are yet to be determined, and intravenous pharmacokinetic studies are currently considered indispensable for determining the BA values of oral drugs. The aim of this study was to develop and validate a novel approach to estimating BA values without intravenous pharmacokinetic data. Based on the drug inclusion criteria, such as exhibiting a urinary recovery rate of (Ru) of ≥20% in a clinical study, 13 drugs were included in the present study, and pharmacokinetic data for them were collected from the literature. The fraction excreted unchanged into urine (fe) was calculated for healthy subjects by dividing the Ru value by the total recovery rate. The contribution of renal excretion to total clearance from the systemic circulation (Rren) was estimated by subjecting oral clearance and creatinine clearance to regression in subjects with normal and impaired renal function. BA was estimated as fe/Rren and compared with the observed BA (BAobs). The predicted BA values for 9 drugs fell within ±20% of their BAobs. The examined approach makes it possible to estimate BA values for drugs with mean renal excretion values in healthy subjects and oral clearance in subjects with various renal function, without intravenous pharmacokinetic data.

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Comparison of the inhibitory effects of azole antifungals on cytochrome P450 3A4 genetic variants

Yamaguchi Y., Akiyoshi T., Kawamura G., Imaoka A., Miyazaki M., Guengerich F.P., Nakamura K., Yamamoto K., Ohtani H.

Drug Metabolism and Pharmacokinetics (Drug Metabolism and Pharmacokinetics) 38 100384 2021.06

Research paper (scientific journal), Accepted, ISSN 13474367

Cytochrome P450 (CYP) 3A4 is one of the major drug-metabolizing enzymes. Genetic variants of CYP3A4 with altered activity are one of the factors responsible for interindividual differences in drug metabolism. Azole antifungals inhibit CYP3A4 to cause clinically significant drug-drug interactions. In the present quantitative study, we investigated the inhibitory effects of three azole antifungals (ketoconazole, voriconazole, and fluconazole) on testosterone metabolism by recombinant CYP3A4 genetic variants (CYP3A4.1 (WT), CYP3A4.2, CYP3A4.7, CYP3A4.16, and CYP3A4.18) and compared them with those previously reported for itraconazole. The inhibition constants (Ki) of ketoconazole, voriconazole, and fluconazole for rCYP3A4.1 were 3.6 nM, 3.2 μM, and 16.1 μM, respectively. The Ki values of these azoles for rCYP3A4.16 were 13.9-, 13.6-, and 6.2-fold higher than those for rCYP3A4.1, respectively, whereas the Ki value of itraconazole for rCYP3A4.16 was 0.54-fold of that for rCYP3A4.1. The other genetic variants had similar effects on the Ki values of the three azoles, whereas a very different pattern was seen for itraconazole. In conclusion, itraconazole has unique characteristics that are distinct from those shared by the other azole anti-fungal drugs ketoconazole, voriconazole, and fluconazole with regard to the influence of genetic variations on the inhibition of CYP3A4.

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Exacerbation of atrioventricular block associated with concomitant use of amlodipine and aprepitant in a lung cancer patient: A case report

Hibino H., Makino Y., Sakiyama N., Makihara-Ando R., Hashimoto H., Akiyoshi T., Imaoka A., Fujiwara Y., Ohe Y., Yamaguchi M., Ohtani H.

International Journal of Clinical Pharmacology and Therapeutics (International Journal of Clinical Pharmacology and Therapeutics) 59 ( 4 ) 328 - 332 2021.04

Research paper (scientific journal), Accepted, ISSN 09461965

Objective: To report a case of second-degree atrioventricular block associated with concomitant use of aprepitant and amlodipine. Case: A 73-year-old man with lung cancer was treated with aprepitant for prophylactic use for the prevention of nausea and vomiting, concomitantly with cisplatin, gemcitabine, and an investigational drug (anti-epidermal growth factor receptor monoclonal antibody). He was diagnosed with first-degree atrioventricular block and was taking amlodipine for hypertension. During the first cycle of chemotherapy, 5 days after the start of aprepitant, he experienced Wenckebach second-degree atrioventricular block (Mobitz type I), and amlodipine was discontinued. After day 6, the atrioventricular block was not shown. According to the Naranjo adverse drug reaction scale, a score of 7 was obtained (causality: probable). In addition, using the Drug Interaction Probability Scale, a score of 6 was obtained (causality: probable). Conclusion: The drug-drug interaction between aprepitant and amlodipine was considered to have deteriorated his atrioventricular block, conceivably due to the inhibition of cytochrome P450 (CYP) 3A-mediated metabolism of amlodipine by aprepitant.

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Relative contributions of metabolic enzymes to systemic elimination can be estimated from clinical DDI studies - validation using an in silico approach -

Koinuma K., Tsuchitani T., Imaoka A., Akiyoshi T., Ohtani H.

International Journal of Clinical Pharmacology and Therapeutics (International Journal of Clinical Pharmacology and Therapeutics) 59 ( 3 ) 231 - 238 2021

Research paper (scientific journal), Joint Work, Accepted, ISSN 09461965

Objective: The contribution ratios (CR) of metabolic enzymes to the systemic clearance of a drug can be estimated from in vitro studies. Another feasible approach is to calculate them based on the increase in the area under the time-concentration curve (AUC) caused by the co-administration of a potent and selective inhibitor in a clinical drug-drug interaction (DDI) study. However, some factors, such as the inhibitory potency of the inhibitor and the inhibition of first-pass metabolism, might affect the estimation of CR based on clinical DDI studies. We aimed to validate the accuracy of the DDI-based estimation of CR using an in silico approach. Materials and methods: An in silico DDI study was conducted using a population-based physiological pharmacokinetic simulator to estimate the CR of cytochrome P450 (CYP)3A4 for zolpidem, sildenafil, omeprazole, triazolam, and repaglinide. The ratio of the AUC value seen in the presence of an inhibitor (ketoconazole or itraconazole) to that observed in the absence of the inhibitor (AUC ratio) was also calculated. The CR for CYP3A4 obtained using the simulator (CRdef) were compared with those calculated from the AUC ratio (CRest). Results: When ketoconazole was used, good correlations between the CRest and CRdef were obtained for all examined substrates (inconsistencies were seen in < 10% of subjects). CR estimates derived from the AUC ratio were found to be accurate. Some underestimation was observed, possibly due to incomplete inhibition, and some overestimation caused by extensive first-pass metabolism was noted. Conclusion: This study verified that CR obtained from AUC ratios in DDI studies are quite reliable.

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Novel method to estimate the appropriate dosing interval for activated charcoal to avoid interaction with other drugs

Ohtani H., Nakamura K., Imaoka A., Akiyoshi T.

European Journal of Clinical Pharmacology (European Journal of Clinical Pharmacology) 76 ( 11 ) 1529 - 1536 2020.11

Research paper (scientific journal), Accepted, ISSN 00316970

© 2020, Springer-Verlag GmbH Germany, part of Springer Nature. Purpose: Activated charcoal is known to adsorb a variety of drugs concomitantly administered and reduce their intestinal absorption, and separating the dosing is considered a practical approach to avoid this drug interaction. The aim of the present study was to develop and validate a simple method to estimate the sufficient dosing interval to avoid drug interaction using the pharmacokinetic profile of the subject drugs administered alone and the amplitude of interaction upon simultaneous administration with activated charcoal. Methods: For each subject drug, the pharmacokinetic profile and the amplitude of interaction, as assessed by AUCR (the ratio of area under the plasma concentration-time curve (AUC) in the presence of activated charcoal to that in its absence), were collected from previous reports. The AUCR value was estimated based on the compartment model under the assumption that the subject drug in the first gastrointestinal compartment is immediately adsorbed to a certain extent upon the administration of activated charcoal. The estimated AUCR (AUCRe) for each drug with certain dosing interval was compared with the respective AUCR value reported previously (AUCRobs). Results: Among twenty concentration profiles for 14 subject drugs obtained from previous reports, 15 AUCRe values fell in the range of 80–120% of the respective AUCRobs values. Conclusion: The developed method enabled estimation of the amplitude of DDI by activated charcoal administered in a certain dosing interval, whereas overestimation of AUCRe was observed for drugs that undergo extensive enterohepatic circulation.

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Profile of the inhibitory effects of gefitinib in CYP2D6 variants in vitro

Semba Y., Akiyoshi T., Hibino H., Imaoka A., Ohtani H.

International Journal of Clinical Pharmacology and Therapeutics (International Journal of Clinical Pharmacology and Therapeutics) 58 ( 10 ) 539 - 542 2020.10

Research paper (scientific journal), Accepted, ISSN 09461965

© 2020 Dustri-Verlag Dr. K. Feistle. Objective: CYP2D6 is a highly polymorphic metabolic enzyme with more than 100 genetic variants, some of which are associated with significantly altered enzyme activity, such as CYP2D6.2 (Arg296Cys, Ser486Thr), CYP2D6.10 (Pro34Ser, Ser486Thr), and CYP2D6.39 (Ser486Thr). Gefitinib is a tyrosine kinase inhibitor of the epidermal growth factor receptor (EGFR) and is used to treat non-small-cell lung cancer with EGFR mutations. Gefitinib is known to competitively inhibit CYP2D6 activity. The aim of this study was to quantitatively compare the inhibitory effects of gefitinib on CYP2D6 enzyme kinetics among CYP2D6 variants. Materials and methods: The enzymatic activity of several CYP2D6 genetic variants; i.e., CYP2D6.1 (wild type), CYP2D6.2, CYP2D6.10, and CYP2D6.39, was assessed by examining the O-demethylation of dextromethorphan. Results and conclusion: The intrinsic clearance of dextromethorphan (Vmax/Km) for CYP2D6.2, CYP2D6.10, and CYP2D6.39 were 0.565-, 0.0376-, and 0.470-fold of that for wild type, respectively. For all variants, the mixed inhibition model was better at explaining the nature of the inhibitory effects of gefitinib than the competitive inhibition model. However, the inhibitory potency of gefitinib varied among the CYP2D6 genetic variants. The Ki values for CYP2D6.2, CYP2D6.10, and CYP2D6.39 were 1.4-, 2.5- and 1.5-fold higher than that for wild type, respectively, implying that these variants are less susceptible to the inhibition by gefitinib. The genetic variations in CYP2D6 might be one of the factors responsible for inter-individual differences in the strength of CYP2D6-mediated drug interactions involving gefitinib.

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pH-dependent transport kinetics of the human organic anion-transporting polypeptide 1A2

T. Morita, T Akiyoshi, R. Sato, K. Katayama, K. Yajima, H. Kataoka, A. Imaoka, Y. Sugimoto, H. Ohtani

Drug Metabolism and Pharmacokinetics (Drug Metabolism and Pharmacokinetics) 35 ( 2 ) 220 - 227 2020

Research paper (scientific journal), Joint Work, Accepted, ISSN 13474367

© 2019 The Japanese Society for the Study of Xenobiotics Organic anion-transporting polypeptide (OATP) 1A2 is expressed on the apical sides of intestinal and renal epithelial cells and considered to be involved in the intestinal absorption and renal reabsorption of drugs. Although the transport activity of OATP1A2 is considered to be pH-dependent, the effects of pH on its kinetic parameters and on the potency of OATP1A2 inhibitors are yet to be elucidated. Some OATP are known to have multiple binding sites (MBS), but it remains unclear whether OATP1A2 has MBS. In the present study, we evaluated the influence of pH on the OATP1A2-mediated uptake of estrone 3-sulfate using OATP1A2-expressing HEK293 cells. The uptake of 0.3 μM estrone 3-sulfate by HEK293-OATP1A2 cells was pH-dependent. OATP1A2 exhibited bimodal saturation kinetics at pH 6.3 and 7.4. Compared with that seen at pH 6.3 (5.62 μM), the Km value of the high-affinity site was 8-fold higher at pH 7.4 (43.2 μM). In addition, the influence of pH on the potency of inhibitors varied among the examined inhibitors. These results suggest that the transport properties of OATP1A2 under lower pH conditions, such as those found in the microenvironments of the small intestinal mucosa and distal tubules, differ from those seen under neutral pH conditions.

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Pharmacy Customers' Awareness of the Illegality of Transferring Drugs to a Third Party

Ohtani Hisakazu, Fujii Honomi, Imaoka Ayuko, Mochizuki Mayumi, Yamaura Katsunori, Akiyoshi Takeshi

Iyakuhin Johogaku (Japanese Society of Drug Informatics) 22 ( 1 ) 30 - 34 2020

Research paper (scientific journal), Joint Work, Accepted, ISSN 1345-1464

Background: Although transferring drugs to a third party, even in a personal capacity, is illegal in Japan, many drug transactions are carried out via internet auction sites. Pharmacy consumers might not be aware of the illegality of transferring drugs to others due to various factors. To clarify pharmacy consumers' awareness of this issue and its covariates, we carried out a questionnaire survey.Methods: A self-completed questionnaire, consisting of yes/no and multiple-choice questions, was used. The adult patients who visited Keio University Pharmacy were asked to fill out the questionnaire.Results and Discussion: One hundred and fifty-one response sheets were effectively collected from 173 responders. The subjects'awareness of the illegality of transferring drugs was significantly affected by the formulation (oral vs. patches) and pharmacological category of the drug, as well as the source of the drug (prescribed vs. over the counter). Patient education about the illegality of personally transferring drugs, especially patches, might be required to avoid illegal drug transfers, including via the internet.

The citrus fruit-derived flavanone glycoside narirutin is a novel potent inhibitor of organic anion-transporting polypeptides

Morita T, Akiyoshi T, Sato R, Uekusa Y, Katayama K, Yajima K, Imaoka A, Sugimoto Y, Kiuchi F, Ohtani H

Journal of Agricultural and Food Chemistry (Journal of Agricultural and Food Chemistry) 68 ( 48 ) 14182 - 14191 2020

Research paper (scientific journal), Joint Work, Accepted, ISSN 00218561

© Organic anion-transporting polypeptides (OATPs) 1A2 and OATP2B1 are expressed in the small intestine and are involved in drug absorption. We identified narirutin, which is present in grapefruit juice, as a novel OATP inhibitor. The citrus fruit jabara also contains high levels of narirutin; therefore, we investigated the inhibitory potency of jabara juice against OATPs. The inhibitory effects of various related compounds on the transport activity of OATPs were evaluated using OATP-expressing HEK293 cells. The IC50 values of narirutin for OATP1A2- and OATP2B1-mediated transport were 22.6 and 18.2 μM, respectively. Other flavanone derivatives from grapefruit juice also inhibited OATP1A2/OATP2B1-mediated transport (order of inhibitory potency: naringenin > narirutin > naringin). Five percent jabara juice significantly inhibited OATP1A2- and OATP2B1-mediated transport by 67 ± 11 and 81 ± 5.5%, respectively (p < 0.05). Based on their inhibitory potency and levels in grapefruit juice, the inhibition of OATPs by grapefruit juice is attributable to both naringin and narirutin. Citrus × jabara, which contains narirutin, potently inhibits OATP-mediated transport.

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Irinotecan-induced gastrointestinal damage impairs the absorption of dabigatran etexilate

Hattori T., Imaoka A., Akiyoshi T., Ohtani H.

Biopharmaceutics and Drug Disposition (Biopharmaceutics and Drug Disposition) 40 ( 9 ) 315 - 324 2019.11

Research paper (scientific journal), Accepted, ISSN 01422782

© 2019 John Wiley & Sons, Ltd. Irinotecan causes serious gastrointestinal damage. Dabigatran etexilate (DABE), an oral anticoagulant and substrate of P-glycoprotein (P-gp), is poorly absorbed and exhibits low bioavailability in humans. The aim of this study was to evaluate the effects of irinotecan-induced gastrointestinal damage on the pharmacokinetics/pharmacodynamics (PK/PD) of DABE. Irinotecan was administered intravenously to rats for 4 days to induce gastrointestinal damage. To investigate the PK profile of dabigatran (DAB), an active moiety of DABE, DABE was administered orally on day 5, and then DAB was administered intravenously on day 6. To evaluate the PD profile of DAB, the activated partial thromboplastin time (APTT) was measured. The protein expression level of intestinal P-gp was evaluated. In the irinotecan-treated rats, the area under the concentration–time curve of DAB after the oral administration of DABE and the bioavailability of DABE were decreased significantly. The APTT ratio also decreased, suggesting that the impaired efficacy of DABE was attributable to a reduction in its bioavailability. The expression of intestinal P-gp was higher in the irinotecan-treated rats. Taking into consideration the histological damage caused to the intestinal epithelium, both the increased P-gp expression and the reduced passive diffusion were considered to be responsible for the reduction in the bioavailability of DABE.

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Current Status of Unapproved Drug Transactions via Internet Auction in Japan

Ohtani Hisakazu, Fujii Honomi, Imaoka Ayuko, Akiyoshi Takeshi

Iryo Yakugaku (Japanese Journal of Pharmaceutical Health Care and Sciences) (Japanese Society of Pharmaceutical Health Care and Sciences) 45 ( 10 ) 591 - 595 2019.10

Research paper (scientific journal), Joint Work, Accepted, ISSN 1346-342X

In Japan, purchasing drugs via Internet auction is prohibited by law. The aim of the present study was to clarify the current status of unapproved drug transactions via Internet auction in Japan. We created five sets of keywords corresponding to five therapeutic categories, ie, hair growth, gastrointestinal treatment, skin care, anti-aging therapy, and anti-cancer therapy. The searches were first performed on the website "Yahoo-oku" (Yahoo auction, Japan) using the above sets of keywords within five days, followed by secondary searches in the same manner after a forty-day interval. The searched items together with their explanations were evaluated independently by two researchers to determine whether they were illegal. The illegal items in the anti-cancer category were further monitored after submitting violation reports to the website. In two search phases within five days each, 571 and 581 illegal items were identified, respectively. After submission of the violation reports, only 1.1％ and 3.4％ of the items in the anti-cancer category were withdrawn by the site administrator and seller, respectively, and 38％ of the monitored items were sold. Taken together, unapproved drug transactions via the Internet are a serious problem. The government and site administrators may need to take effective measures to monitor and avoid such transactions, as well as providing notices and education to customers.

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