Trastuzumab Deruxtecan Dosing in Human Epidermal Growth Factor Receptor 2-Positive Gastric Cancer: Population Pharmacokinetic Modeling and Exposure-Response Analysis.

This study evaluated the benefit/risk of trastuzumab deruxtecan (T-DXd) 6.4 mg/kg in patients with human epidermal growth factor receptor 2 (HER2)-positive gastric cancer using pharmacometrics. A population pharmacokinetic (PopPK) model was developed using data from patients with gastric cancer, breast cancer, or other tumors in T-DXd clinical trials, primarily conducted in Asia. Post hoc model-estimated pharmacokinetic metrics were used in exposure-efficacy (objective response rates, ORRs) and exposure-safety analyses. The PopPK analysis included 808 patients (217 with gastric cancer, 512 with breast cancer, and 79 with other cancers). In gastric cancer, the T-DXd 6.4 mg/kg steady-state exposure metrics were lower compared with 6.4 mg/kg in breast cancer, but were similar to 5.4 mg/kg in breast cancer. Tumor type was selected as a significant covariate on T-DXd clearance. In exposure-efficacy analysis among 160 patients with gastric cancer, the T-DXd steady-state minimum concentration was associated with a confirmed ORR in univariate logistic regression analysis (P = .023). The model-predicted confirmed ORRs in gastric cancer were 36.0% (90%CI 29.3% to 43.7%) with 5.4 mg/kg and 40.0% (90%CI 33.1% to 47.6%) with 6.4 mg/kg. Among 808 patients in the exposure-safety analyses, the model-predicted estimates for the rates of any-grade interstitial lung disease (ILD) over a period of 180 days were 10.2% (90%CI 8.7% to 12.8%) with 6.4 mg/kg in gastric cancer and 9.7% (90%CI 8.2% to 11.8%) with 5.4 mg/kg in breast cancer. In gastric cancer, the efficacy of T-DXd was higher at 6.4 mg/kg than at 5.4 mg/kg. Exposure and ILD rates were comparable between 6.4 mg/kg in gastric cancer and 5.4 mg/kg in breast cancer. This study identified T-DXd 6.4 mg/kg as the recommended dose in HER2-positive gastric cancer.

Effect of Trastuzumab Deruxtecan on QT/QTc Interval and Pharmacokinetics in HER2-Positive or HER2-Low Metastatic/Unresectable Breast Cancer.

HER2-targeted anticancer therapies may be associated with cardiovascular adverse events. This study evaluated effects of the HER2-targeted antibody-drug conjugate trastuzumab deruxtecan (T-DXd, DS-8201a) on QT/QTc interval and its pharmacokinetics. Patients with heavily pretreated, metastatic HER2-expressing breast cancer were enrolled at seven study sites in Japan. T-DXd was administered intravenously at 6.4 mg/kg on day 1 of each 21-day cycle. Primary end points were baseline-adjusted QTcF interval and pharmacokinetics parameters. Key secondary end points included safety events, serum concentration of T-DXd and DXd at the time of electrocardiographic measurements, and antitumor activity parameters. Among 51 total patients, 47 (92.2%) had HER2-low breast cancer (immunohistochemistry 1+ or 2+ and in situ hybridization-negative/equivocal/missing). Pharmacokinetic parameters after a single dose of T-DXd were consistent with previous studies. After multiple doses, T-DXd showed moderate accumulation (accumulation ratio (cycle 3/cycle 1), 1.35), but DXd showed minimal accumulation (1.09). The upper bound of the 90% confidence interval for mean ΔQTcF interval was < 10 ms at all timepoints, and at mean maximum serum concentration was also < 10 ms. Based on concentration-QT analysis, ΔQTcF increased with increasing concentrations of T-DXd and DXd. No clinically meaningful QTcF prolongation was observed. T-DXd had a manageable safety profile and showed antitumor activity in HER2-low breast cancer. In this study, a T-DXd dose of 6.4 mg/kg, higher than the 5.4-mg/kg dose currently approved for breast cancer, was not associated with clinically relevant QTcF prolongation in heavily pretreated patients with HER2-expressing metastatic breast cancer. This study adds to our understanding of T-DXd for treatment of HER2-low breast cancer.

Pharmacokinetics, Safety, and Efficacy of Trastuzumab Deruxtecan with Concomitant Ritonavir or Itraconazole in Patients with HER2-Expressing Advanced Solid Tumors.

PURPOSE: To evaluate drug-drug interactions between the human epidermal growth factor receptor 2 (HER2)-targeted antibody-drug conjugate trastuzumab deruxtecan (T-DXd; DS-8201a) and the OATP1B/CYP3A inhibitor ritonavir or the strong CYP3A inhibitor itraconazole. PATIENTS AND METHODS: Patients with HER2-expressing advanced solid tumors were enrolled in this phase I, open-label, single-sequence crossover study (NCT03383692) and received i.v. T-DXd 5.4 mg/kg every 3 weeks. Patients received ritonavir (cohort 1) or itraconazole (cohort 2) from day 17 of cycle 2 through the end of cycle 3. Primary endpoints were maximum serum concentration (C max) and partial area under the concentration-time curve from beginning of cycle through day 17 (AUC17d) for T-DXd and deruxtecan (DXd) with (cycle 3) and without (cycle 2) ritonavir or itraconazole treatment. RESULTS: Forty patients were enrolled (cohort 1, n = 17; cohort 2, n = 23). T-DXd C max was similar whether combined with ritonavir [cohort 1, cycle 3/cycle 2; 90% confidence interval (CI): 1.05 (0.98-1.13)] or itraconazole [cohort 2, 1.03 (0.96-1.09)]. T-DXd AUC17d increased from cycle 2 to 3; however, the cycle 3/cycle 2 ratio upper CI bound remained at ≤1.25 for both cohorts. For DXd (cycle 3/cycle 2), C max ratio was 0.99 (90% CI, 0.85-1.14) for cohort 1 and 1.04 (0.92-1.18) for cohort 2; AUC17d ratio was 1.22 (1.08-1.37) and 1.18 (1.11-1.25), respectively. The safety profile of T-DXd plus ritonavir or itraconazole was consistent with previous studies of T-DXd monotherapy. T-DXd demonstrated promising antitumor activity across HER2-expressing solid-tumor types. CONCLUSIONS: T-DXd was safely combined with ritonavir or itraconazole without clinically meaningful impact on T-DXd or DXd pharmacokinetics.

[Pharmacological and clinical study results of trastuzumab deruxtecan (T-DXd, ENHERTU®)].

Antibody-drug conjugates (ADCs) combine the specific antibody and cytotoxic agent by a linker and represent a promising drug class with a wider therapeutic window than conventional chemotherapeutic agents by substantiating efficient and specific drug delivery to antigen-expressing tumor cells. However, there are rooms for improvement in terms of efficacy, safety, physicochemical property; therefore, the development of promising ADC drugs across multiple indications are eagerly awaited. In 2015, Daiichi Sankyo initiated the first-in-human study of HER2 ADC, trastuzumab deruxtecan (T-DXd, ENHERTU®) which possesses DNA topoisomerase I inhibitor, exatecan derivative and proprietary linker, in Japan. Based on the provocative results in phase 1 study, the global development program has been accelerated to show the high and durable efficacy in patients with HER2 positive breast cancer pretreated with trastuzumab emtansine. As a result, T-DXd was approved based on single arm phase 2 study in the US (Dec 2019) and Japan (March 2020) by leveraging the breakthrough designation and conditional early approval system, respectively, at the first time for the HER2 positive breast cancer. In addition, T-DXd was recently approved in gastric cancer through Sakigake designation in Japan based on a randomized phase 2 study. T-DXd is also being developed in the earlier lines or other indications where no anti-HER2 therapies were approved to date. Combination studies with other agents, such as immune checkpoint inhibitors are underway. In the near future, we hope that more patients worldwide can enjoy the therapeutic benefits of T-DXd through our continuous efforts to expand its indications.

Safety, tolerability, pharmacokinetics, and pharmacodynamics of the afucosylated, humanized anti-EPHA2 antibody DS-8895a: a first-in-human phase I dose escalation and dose expansion study in patients with advanced solid tumors.

BACKGROUND: Erythropoietin-producing hepatocellular receptor A2 (EPHA2) is overexpressed on the cell surface in many cancers and predicts poor prognosis. DS-8895a is a humanized anti-EPHA2 IgG1 monoclonal antibody afucosylated to enhance antibody-dependent cellular cytotoxicity activity. We conducted a two-step, phase I, multicenter, open-label study to determine the safety, tolerability, and pharmacokinetics of DS-8895a in patients with advanced solid tumors. METHODS: Step 1 was a dose escalation cohort in advanced solid tumor patients (six dose levels, 0.1-20 mg/kg) to determine Step 2 dosing. Step 2 was a dose expansion cohort in EPHA2-positive esophageal and gastric cancer patients. DS-8895a was intravenously administered every 2 weeks for the duration of the study, with a 28-day period to assess dose-limiting toxicity (DLT). Safety, pharmacokinetics, tumor response, and potential biomarkers were evaluated. RESULTS: Thirty-seven patients (Step 1: 22, Step 2: 15 [9: gastric cancer, 6: esophageal cancer]) were enrolled. Although one DLT (Grade 4 platelet count decreased) was observed in Step 1 (dose level 6, 20 mg/kg), the maximum tolerated dose was not reached; the highest dose (20 mg/kg) was used in Step 2. Of the 37 patients, 24 (64.9%) experienced drug-related adverse events (AEs) including three (8.1%) with Grade ≥ 3 AEs. Infusion-related reactions occurred in 19 patients (51.4%) but were manageable. All patients discontinued the study (evident disease progression, 33; AEs, 4). Maximum and trough serum DS-8895a concentrations increased dose-dependently. One gastric cancer patient achieved partial response and 13 patients achieved stable disease. Serum inflammatory cytokines transiently increased at completion of and 4 h after the start of DS-8895a administration. The proportion of CD16-positive natural killer (NK) cells (CD3-CD56+CD16+) decreased 4 h after the start of DS-8895a administration, and the ratio of CD3-CD56+CD137+ to CD3-CD56+CD16+ cells increased on day 3. CONCLUSIONS: Twenty mg/kg DS-8895a infused intravenously every 2 weeks was generally safe and well tolerated in patients (n = 21) with advanced solid tumors. The exposure of DS-8895a seemed to increase dose-dependently and induce activated NK cells. TRIAL REGISTRATION: Phase 1 Study of DS-8895a in patients with advanced solid tumors ( NCT02004717 ; 7 November 2013 to 2 February 2017); retrospectively registered on 9 December 2013.

Effect of DS-8500a, a Novel G Protein-Coupled Receptor 119 Agonist, on the Pharmacokinetics of Rosuvastatin and Atorvastatin in Healthy Subjects.

BACKGROUND: Non-clinical study data suggest that DS-8500a, a G protein-coupled receptor 119 agonist, exhibits antidiabetic activity, inhibition of some transporters and induction of cytochrome P450 (CYP) 3A. Statins are substrates for some transporters and CYP3A that may be coadministered with DS-8500a in clinical practice. OBJECTIVE: To determine the potential effects of DS-8500a on the pharmacokinetics of statins, we evaluated the effects of repeated oral administration of DS-8500a 75 mg on the pharmacokinetics of rosuvastatin and atorvastatin in healthy adults. METHODS: We performed two single-center, open-label, single-sequence studies. In Study I, subjects received single-dose rosuvastatin 10 mg (Period A) and DS-8500a 75 mg once daily + single-dose rosuvastatin 10 mg (Period B). In Study II, subjects received single-dose atorvastatin 10 mg (Period A) and DS-8500a 75 mg once daily + single-dose atorvastatin 10 mg (Period B). Primary pharmacokinetic endpoints were maximum plasma concentration (Cmax) and area under the plasma concentration-time curve (AUC) of rosuvastatin and atorvastatin. Safety was evaluated. RESULTS: In Study I, the Cmax and AUC of rosuvastatin increased by 66% and 33%, respectively, when coadministered with DS-8500a, versus rosuvastatin alone. In Study II, the Cmax of atorvastatin increased by 28%, but AUC remained unchanged following coadministration with DS-8500a, versus atorvastatin alone. Treatment-emergent adverse events were mild to moderate and mostly unrelated to the study drugs. CONCLUSIONS: Multiple doses of DS-8500a increased exposure to rosuvastatin and atorvastatin. This short-term study suggests that the impact of DS-8500a coadministration on atorvastatin exposure is limited and may not be clinically relevant. Nevertheless, caution may be necessary when patients are coadministered rosuvastatin with DS-8500a. CLINICALTRIALS. GOV IDENTIFIER: NCT03699774. JAPAN PHARMACEUTICAL INFORMATION CENTER IDENTIFIER: JapicCTI-152878.

Pharmacokinetics and Safety of DS-8500a, an Antidiabetic Drug, in Japanese Subjects with Hepatic or Renal Impairment: A Single-Center, Open-Label, Single-Dose Study.

INTRODUCTION: The pharmacokinetics, safety, and tolerability of DS-8500a (a G protein receptor 119 agonist) up to 100 mg have been investigated in healthy Japanese adults. The objective of this study was to evaluate the effects of hepatic or renal impairment on the pharmacokinetics of a single 25-mg oral dose of DS-8500a. METHODS: This single-center, open-label study enrolled subjects into eight groups according to hepatic function (normal; mild or moderate impairment) and renal function [normal; mild, moderate, or severe impairment; and end-stage renal disease (ESRD)]. Drug concentrations were measured by liquid-chromatography tandem mass spectrometry. Pharmacokinetic parameters were evaluated by non-compartmental analysis. Adverse events (AEs) were evaluated for safety. RESULTS: The hepatic and renal groups enrolled 15 and 30 subjects, respectively. Pharmacokinetic parameters of DS-8500a were comparable between the normal hepatic function and mild hepatic impairment groups, but the mean area under the concentration-time curve (AUC) was 1.37-fold higher, and the half-life was longer in the moderate hepatic impairment group compared with the normal hepatic function group. The maximum concentration (Cmax) and AUC values were 0.704- and 0.609-fold lower, respectively, in the ESRD group compared with the values in the other renal impairment groups; no clear differences in AUC and time to Cmax were observed in the normal function and mild, moderate, and severe renal impairment groups. There was no relationship between apparent total body clearance and estimated glomerular filtration rate. The incidence of AEs was similar among all groups. CONCLUSION: DS-8500a exposure in the mild hepatic impairment and mild to severe renal impairment groups was similar to that in the corresponding normal hepatic and renal function groups, but dose adjustments may be required in those with moderate hepatic impairment and ESRD. TRIAL REGISTRATION: Japic CTI-No. 163135. FUNDING: Daiichi Sankyo Co. Ltd., Tokyo, Japan.

Safety and Pharmacokinetics of DS-8500a, a Novel GPR119 Agonist, After Multiple Oral Doses in Healthy Japanese Males.

BACKGROUND AND OBJECTIVES: G protein-coupled receptor 119 (GPR119) agonists reduce plasma glucose by promoting insulin secretion in a glucose-dependent manner. We evaluated the safety and pharmacokinetics of multiple oral doses of DS-8500a, a GPR119 agonist, under fed conditions in healthy adult Japanese male subjects. METHODS: In this Phase 1, randomized, placebo-controlled, double-blind, multiple oral dose study, participants were aged ≥ 20 and ≤ 45 years with a body mass index ≥ 18.5 and < 25.0 kg/m2. DS-8500a 50 and 100 mg or placebo were administered orally, once daily, 30 min after breakfast for 7 days. The primary endpoints were pharmacokinetics and safety. RESULTS: Twenty-four subjects were included (6, 9, and 9 in the placebo, 50-, and 100-mg groups, respectively). On Day 7, the mean maximum plasma concentration (Cmax) was 812 ng/mL in the 50-mg group and 1310 ng/mL in the 100-mg group. The mean area under the plasma concentration-time curve during dosing interval (AUCtau) was 7910 and 13,200 ng·h/mL in the two treatment groups, respectively. The observed accumulation ratio was 1.25 in the 50-mg group and 1.32 in the 100-mg group. All adverse events were mild and judged unrelated to the study drug. CONCLUSIONS: DS-8500a plasma concentrations reached steady state from Day 3, and Cmax and AUCtau increased in a less than dose-proportional manner. After repeated doses of DS-8500a at 100 mg, the DS-8500a trough concentration was expected to reach a pharmacologically active dose. DS-8500a was well tolerated up to 100 mg after a 7-day administration. STUDY REGISTRY IDENTIFICATION: JAPIC ID: JapicCTI-173550 (registered retrospectively on 30 March 2017).

Phase 1 study of new formulation of patritumab (U3-1287) Process 2, a fully human anti-HER3 monoclonal antibody in combination with erlotinib in Japanese patients with advanced non-small cell lung cancer.

BACKGROUND: This phase 1 study evaluated the safety, tolerability, pharmacokinetics and efficacy of patritumab (U3-1287) Process 2, a new formulation of fully human anti-HER3 monoclonal antibody in combination with erlotinib, an epidermal growth factor receptortyrosine kinase inhibitor (EGFR-TKI) in prior chemotherapy treated Japanese patients with advanced non-small cell lung cancer (NSCLC). METHODS: Patients received intravenous patritumab Process 2 formulation at 9 mg/kg every 3 weeks after initiation of 18 mg/kg loading dose combined with continuous daily dose of erlotinib (150 mg QD) until any of the withdrawal criteria are met. Adverse events (AEs) were assessed using CTCAE v4.0 and tumor response was assessed using RECIST v1.1. Full pharmacokinetic sampling and serum biomarker analyses were mainly performed during cycle 1 and 2. RESULTS: Total of six EGFR-mutant NSCLC patients including one EGFR-TKI naïve patient received patritumab Process 2 formulation combined with erlotinib. No dose-limiting toxicities were observed. The most frequent AEs were gastrointestinal or skin toxicities, which were generally mild and manageable. One patient discontinued from study due to reversible grade 3 interstitial lung disease. The mean area under the curve (AUC) value was 2640 µg/day/mL; the Cmax value was 434 µg/mL, respectively. The median progression-free survival (95% confidence interval) was 220.0 (100.0-363.0) days. HER3 ligand heregulin was detected in serum from only a patient that maintained most durable stable disease. CONCLUSIONS: Patritumab Process 2 formulation in combination with erlotinib was well tolerated compatible with favorable PK profile in Japanese patients with advanced NSCLC.

Metabolism and disposition of [(14)C]tivantinib after oral administration to humans, dogs and rats.

1. The biotransformation and disposition of tivantinib in humans, dogs and rats was examined after a single oral administration of [(14)C]tivantinib. Tivantinib constituted no more than one-third of the plasma radioactivity in all species, demonstrating significant contribution of the metabolites to plasma radioactivity. The major circulating metabolites in all species were M4 and M5, hydroxylated metabolites at the benzyl position of the tricyclic ring, accounting for 19.3 and 12.2% of the AUC of the total radioactivity, respectively, in humans. 2. The majority of radioactivity was excreted to the feces via bile. Tivantinib was detected at trace levels in urine, feces and bile, demonstrating extensive metabolism prior to biliary excretion and nearly complete tivantinib absorption under fed conditions. 3. Seven metabolic pathways were identified for tivantinib and included six oxidations (M4, M5, M7, M8, M9 and M11) and one glucuronidation (M23). The major metabolic and excretory pathways were found to be common among all species. Species differences in the metabolic pathways included lactam metabolite (M8) formation in humans and dehydrogenated metabolite (M11) formation in animals. 4. None of the metabolites identified in this work are believed to significantly impact the efficacy or toxicity of tivantinib in humans.

Human small intestinal and colonic tissue mounted in the Ussing chamber as a tool for characterizing the intestinal absorption of drugs.

The purpose of this study was to validate human small intestinal and colonic tissue mounted in the Ussing chamber as a tool for predicting the oral drug absorption in humans with the main focus on moderately and poorly permeable compounds. The obtained apparent permeability coefficient (P(app)) of eleven test compounds was compared to their fraction absorbed (Fa) in humans taken from the literature. Beside the conventional P(app) a new parameter, the apparent permeability coefficient total (P(app,total)), involving both the apical-to-basolateral permeability and the time-dependent compound accumulation in the tissue was established. The permeability of lucifer yellow (LY), a fluorescent marker of the paracellular pathway and the test compounds showed no obvious differences between small intestine and colon. Furthermore, small intestinal and colonic tissue from a single donor showed similar permeability of both LY and a transcellularly transported compound metoprolol. All test compounds including low molecular weight hydrophilic compounds such as metformin, atenolol, sulpiride and famotidine showed adequate permeability reflecting human Fa values (R(2)=0.87). The P(app) values of digoxin, a P-glycoprotein (P-gp) substrate, were not significantly affected by the addition of verapamil, a P-gp inhibitor. In contrast, the P(app,total) values of digoxin increased approximately threefold in the presence of verapamil. In conclusion, both small intestinal and colonic tissue mounted in the Ussing chamber provide a good opportunity to predict the oral drug absorption rate in humans even for moderately and poorly absorbed compounds. The novel calculation of P(app,total) allows the study of the carrier-mediated drug-drug interactions in human intestine.

Synthesis and evaluation of CS-2100, a potent, orally active and S1P(3)- sparing S1P(1) agonist.

Modulators of sphingosine phosphate receptor-1 (S1P(1)) have recently been focused as a suppressant of autoimmunity. We have discovered a 4-ethylthiophene-based S1P(1) agonist 1-({4-Ethyl-5-[5-(4-phenoxyphenyl)-1,2,4-oxadiazol-3-yl]-2-thienyl}methyl)azetidine-3-carboxylic acid (CS-2100, 8) showing potent S1P(1) agonist activity against S1P(3) and an excellent in vivo potency. We report herein the synthesis of CS-2100 (8) and pharmacological effects such as S1P(1) and S1P(3) agonist activity in vitro, peripheral blood lymphocyte lowering effects and the suppressive effects on adjuvant-induced arthritis and experimental autoimmune encephalomyelitis (EAE) in animal models. The pharmacokinetic data were also reported. CS-2100 (8) had >5000-fold greater agonist activity for human S1P(1) (EC(50); 4.0 nM) relative to S1P(3) (EC(50); >20,000 nM). Following administration of single oral doses of 0.1 and 1 mg/kg of CS-2100 (8) in rats, lymphocyte counts decreased significantly, with a nadir at 8 and/or 12 h post-dose and recovery to vehicle control levels by 24-48 h post-dose. CS-2100 (8) is efficacious in the adjuvant-induced arthritis model in rats (ID(50); 0.44 mg/kg). In the EAE model compared to the vehicle-treated group, significant decreases in the cumulative EAE scores were observed for 0.3 and 1 mg/kg CS-2100 (8) groups in mice. While CS-2100 (8) showed potent efficacy in various animal disease models, it was also revealed that the central 1,2,4-oxadiazole ring of CS-2100 (8) was decomposed by enterobacteria in intestine of rats and monkeys, implicating the latent concern about an external susceptibility in its metabolic process in the upcoming clinical studies.

Interaction of angiotensin II type 1 receptor blockers with P-gp substrates in Caco-2 cells and hMDR1-expressing membranes.

AIMS: The inhibitory effect of angiotensin II type 1 receptor blockers (ARBs) on P-glycoprotein (P-gp) was examined to evaluate their clinical drug-drug interaction (DDI) potential. MAIN METHODS: We performed an inhibition study on the vectorial transport of digoxin, a typical substrate for P-gp, using a human colonic adenocarcinoma cell line, Caco-2 cells, and verapamil-stimulated ATPase activity using human multidrug resistance 1 (hMDR1)-expressing membrane. KEY FINDINGS: The vectorial transport of digoxin was inhibited by candesartan cilexetil, irbesartan and telmisartan with the IC(50) values of 14.7, 34.0 and 2.19microM, respectively. Those values were 7.4-426-fold higher than their theoretical clinical gastrointestinal concentration [I] at doses in clinical DDI studies. Other ARBs failed to show interaction with P-gp. SIGNIFICANCE: It was demonstrated that candesartan cilexetil, irbesartan and telmisartan had the potential to inhibit the transport of various drugs via P-gp. Telmisartan, which caused an increase in the serum digoxin concentration in humans, had a sufficiently high [I]/IC(50) value, suggesting that DDI between digoxin and telmisartan was caused by the inhibition of digoxin efflux via intestinal P-gp.

Culture period-dependent change of function and expression of ATP-binding cassette transporters in Caco-2 cells.

The objective of this study was to determine an appropriate culture period to assess whether a compound of interest is transported by efflux transporters such as human multidrug resistance 1 (hMDR1), human multidrug resistance-associated protein 2 (hMRP2), and human breast cancer resistance protein (hBCRP) in Caco-2 cells. Caco-2 cells were cultured on a Transwell for 1 to 6 weeks. The expression of these transporters in the mRNA and protein levels was examined using a real-time polymerase chain reaction and Western blotting, respectively. Transcellular transport activities using digoxin, ochratoxin A, olmesartan, and estrone-3-sulfate were also examined. Except for digoxin, the permeability coefficient (P(app)) ratio of the three compounds at 2 weeks was the highest in the periods tested. The P(app) ratio of digoxin at 2 weeks was higher than that at 3 weeks. The temporal expression profile of each transporter in the mRNA level was similar to that in the protein level, and the functions of hMRP2 and hBCRP were roughly correlated with the expression in the mRNA and protein levels, but that of hMDR1 was not. These data suggest that among all the culture periods evaluated a 2-week culture is the best culture period for transport studies to identify whether a compound is a substrate for hMDR1, hMRP2, and hBCRP.

Multiple human isoforms of drug transporters contribute to the hepatic and renal transport of olmesartan, a selective antagonist of the angiotensin II AT1-receptor.

Olmesartan, a novel angiotensin II AT1-receptor antagonist, is excreted into both bile and urine, with minimal metabolism. Because olmesartan is a hydrophilic anionic compound, some transporters could be involved in its hepatic and renal clearance. In this study, we characterized the role of human drug transporters in the pharmacokinetics of olmesartan and determined the contribution of each transporter to the overall clearance of olmesartan. Olmesartan was significantly taken up into human embryonic kidney 293 cells expressing organic anion-transporting polypeptide (OATP) 1B1, OATP1B3, organic anion transporter (OAT) 1, and OAT3. We also observed its saturable uptake into human hepatocytes and kidney slices. Estimated from the relative activity factor method and application of specific inhibitors, the relative contributions of OATP1B1 and OATP1B3 to the uptake of olmesartan in human hepatocytes were almost the same, whereas OAT3 was predominantly involved in its uptake in kidney slices. The vectorial transport of olmesartan was observed in OATP1B1/multidrug resistance-associated protein (MRP) 2 double transfectants, but not in OATP1B1/multidrug resistance (MDR) 1 and OATP1B1/breast cancer resistance protein (BCRP) transfectants. ATP-dependent transport into membrane vesicles expressing human MRP2 and MRP4 was clearly observed, with K(m) values of 14.9 and 26.2 microM, respectively, whereas the urinary excretion of olmesartan in Mrp4-knockout mice was not different from that of control mice. We also investigated the transcellular transport of olmesartan medoxomil, a prodrug of olmesartan. Vectorial basal-to-apical transport was observed in OATP1B1/MRP2, OATP1B1/MDR1 double, and OATP1B1/BCRP double transfectants, suggesting the possible involvement of MRP2, MDR1, and BCRP in the limit of intestinal absorption of olmesartan medoxomil. From these results, we suggest that multiple transporters make a significant contribution to the pharmacokinetics of olmesartan and its prodrug.

Inhibitory effects of angiotensin receptor blockers on CYP2C9 activity in human liver microsomes.

We investigated the inhibitory effects of the angiotensin receptor blockers (ARBs), candesartan, irbesartan, losartan, losartan active metabolite (EXP-3174), olmesartan, telmisartan and valsartan (0.3-300 microM), on the CYP2C9 activity in human liver microsomes using (S)-(-)-warfarin as a typical CYP2C9 substrate. Except for olmesartan and valsartan, these ARBs inhibited the activity of 7-hydroxylation of (S)-(-)-warfarin with IC50 values of 39.5-116 microM. Of six synthetic derivatives of olmesartan, five compounds which possess either alkyl groups or a chloro group at the same position as that of the hydroxyisopropyl group in olmesartan inhibited CYP2C9 activity with IC50 values of 21.7-161 microM. Olmesartan and the olmesartan analogue, RNH-6272, both having a hydroxyisopropyl group, showed no inhibition, indicating that the hydrophilicity of this group greatly contributes to the lack of CYP2C9 inhibition by these two compounds. A three-dimensional model for docking between EXP-3174 and CYP2C9 indicated that the chloro group of EXP-3174 is oriented to a hydrophobic pocket in the CYP2C9 active site, indicating that the lipophilicity of the group present in ARBs at the position corresponding to that of the hydroxyisopropyl group in olmesartan is important in inhibiting CYP2C9 activity.

Characterization of CS-023 (RO4908463), a novel parenteral carbapenem antibiotic, and meropenem as substrates of human renal transporters.

To characterize the renal handling of CS-023 (RO4908463), a novel parenteral carbapenem antibiotic, and meropenem in humans, we examined their affinities as substrates to human renal transporters. In vitro studies on the uptake of [14C]CS-023 and [14C]meropenem were conducted using HEK293 cells expressing human organic anion transporters (hOAT) 1, hOAT3, hOAT4, and the human organic cation transporters (hOCT) 1 and hOCT2. CS-023 did not serve as the substrate for any of the transporters tested. On the other hand, meropenem was transported by hOAT1 and hOAT3. The Km value of the hOAT3-mediated transport was 847 microM, and the uptake was inhibited by probenecid, p-aminohippurate and benzylpenicillin with Ki values of 3.76, 712, and 202 microM, respectively. One of the reasons why CS-023 is not a substrate of hOATs, and vice versa for meropenem, would be that a very small proportion of CS-023 exists as the anionic form at the physiological pH, whereas 50% of meropenem exists as the anionic form. These findings indicate that the lack of recognition of CS-023 by renal transporters is one of the reasons for its long plasma half-life in humans compared with meropenem which undergoes renal tubular secretion mediated by hOAT1 and hOAT3.