Hidetaka Kamimura

Astellas Pharmaceutical, Northbrook, Illinois, Japan

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Publications (64)135.61 Total impact

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    ABSTRACT: The ability to predict circulating human metabolites of a candidate drug before first-in-man studies are carried out would provide a clear advantage in drug development. A recent report demonstrated that while in vitro studies using human liver preparations reliably predict primary human metabolites in plasma, the predictability of secondary metabolites, formed by multiple reactions, was low, with total success rates of < or =65%. Here, we assess the use of chimeric mice with humanized liver as an animal model for the prediction of human metabolism in vivo. Metabolism studies with debrisoquine and (S)-warfarin demonstrated significantly higher concentrations of their primary human abundant metabolites in serum or plasma in chimeric mice than in control mice. Humanized chimeric mice were also capable of producing human-specific metabolites of several in-house compounds which were generated through more than one metabolism reaction. This model is closer to in vivo human physiology and therefore appears to have an advantage over in vitro systems in predicting complex metabolites in human plasma. However, prediction of human metabolites failed for other compounds which were highly metabolized in mice. Although requiring careful consideration of compound suitability, this model represents a potential tool for predicting human metabolites in combination with conventional in vitro systems.
    Drug Metabolism and Pharmacokinetics 01/2010; 25(3):223-35. · 2.07 Impact Factor
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    ABSTRACT: We investigated the inhibitory effects of (1R,9S,12S,13R,14S,17R,18E,21S,23S,24R,25S,27R)-1, 14-dihydroxy-12-(E)-2-[(1R,3R,4R)-4-hydroxy-3-methoxycyclohexyl]-1-methylvinyl-23,25-dimethoxy-13,19,21,27-tetramethyl-17-(2-oxopropyl)-11,28-dioxa-4-azatricyclo []octacos-18-ene-2,3,10,16-tetrone (FK1706), a novel nonimmunosuppressive immunophilin ligand, on CYP3A4/5 in in vitro and in vivo settings. First, the inhibitory effects of FK1706 (preincubation dependence, inactivation rate estimation, and reversibility) were tested using human liver microsomes. Second, the effect of repeated oral doses of FK1706 (60 mg q.d. for 14 days) on the pharmacokinetics of midazolam (single oral 2-mg dose) was tested in healthy volunteers. Finally, pharmacokinetic modeling and simulation were performed. In vitro experiments showed that FK1706 inhibited CYP3A4/5 in a time-dependent and irreversible manner. The in vitro maximum inactivation rate constant (k(inact)) and concentration of inhibitor that gave half-maximal k(inact) (K(I)) were estimated to be 10.1 h(-1) and 2050 ng/ml, respectively. In the clinical study, FK1706 produced a 2-fold increase in the area under the time-concentration curve (AUC) of midazolam. A pharmacokinetic model developed for this study, which described the time course of concentrations of both FK1706 and midazolam and incorporated CYP3A4/5 inactivation in the liver and intestine, successfully predicted the change in the pharmacokinetics of midazolam using in vitro k(inact) and K(I) values (1.66- to 2.81-fold increases in AUC predicted) and estimated the in vivo inactivation rate to be 0.00404 to 0.0318 h(-1) x ml/ng. In conclusion, FK1706 weakly or moderately inhibited the activity of CYP3A4/5 in vitro and vivo at the tested dose. The model developed here would be helpful in predicting drug-drug interactions and in the design of dose regimens that avoid drug-drug interactions.
    Drug metabolism and disposition: the biological fate of chemicals 11/2009; 38(2):249-59. · 3.74 Impact Factor
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    ABSTRACT: 1-(2-Methoxyethyl)-2-methyl-4,9-dioxo-3-(pyrazin-2-ylmethyl)-4,9-dihydro-1H-naphtho[2,3-d]imidazolium bromide (YM155 monobromide) is a novel small-molecule survivin suppressant that induces the down-regulation of survivin and exhibits potent antitumor activity in nude mice bearing human hormone refractory prostate carcinoma cell line PC-3. Although YM155, which has a cationic moiety in its structure, is influxed into its pharmacologically effective site (cancer cells) and one of its eliminating organs (hepatocytes) in a transporter-mediated manner, the mechanism seems to be different between the two cell types. The other eliminating organ is the kidney. In this study, the transport of [(14)C]YM155 was characterized by using human embryonic kidney 293 cells expressing organic cation transporter 1 (OCT1/SLC22A1), OCT2 (SLC22A2), and OCT3 (SLC22A3). YM155 inhibited the uptake of a typical substrate [(3)H]1-methyl-4-phenylpyridinium via OCT1, OCT2, and OCT3 with IC(50) values of 23.8, 15.9, and 108 microM, respectively. The time- and saturable concentration-dependent uptake of [(14)C]YM155 was observed in cells expressing OCT1 and OCT2 with K(m) values of 22.1 and 2.67 microM, respectively, but not in cells expressing OCT3. By taking into consideration the tissue distribution and localization of each transporter, these results suggest that, in humans, YM155 is taken up from the blood into hepatocytes and proximal tubular cells via OCT1 and OCT2, respectively. The comparison of the IC(50) values of OCT inhibitors and K(m) values for the uptake of YM155 into cells expressing OCTs with those into cancer cell lines indicated that transporter(s) other than OCT1 and OCT2 are involved in the uptake of YM155 into cancer cell lines.
    Drug metabolism and disposition: the biological fate of chemicals 10/2009; 38(1):1-4. · 3.74 Impact Factor
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    ABSTRACT: (-)-N-{2-[(R)-3-(6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline-2-carbonyl)piperidino]ethyl}-4-fluorobenzamide (YM758), a novel "funny" If current channel inhibitor, was being developed as a treatment for stable angina and atrial fibrillation. After a single oral administration of (14)C-YM758, extensive accumulation and long-term retention of radioactivity were observed in the eyeballs of nonalbino rats and in the thoracic aorta of albino/nonalbino rats. Radioluminograms of the eyeballs of nonalbino rats indicated that the radioactivity was localized to the uveal tract, which suggests that the radioactivity may be positively charged and bound mainly to the melanins. Treatment with a mixture of 2 mol/l hydrochloric acid and methanol (5:95, v/v) allowed for the recovery of the major portion of radioactivity from the eyeball, which suggests reversible binding. The radioactive constituents in eyeballs consisted of the unchanged drug (YM758) and three metabolites [mainly 6,7-dimethoxy-2-[(3R)-piperidin-3-ylcarbonyl]-1,2,3,4-tetrahydroisoquinoline (YM-252124)]. Using the organic solvent mixture described above, almost all of the radioactivity was not collected from the thoracic aorta, and approximately 90% was recovered by treatment with elastase, which suggests that some metabolites covalently bind to the elastin fiber localized in the tunica media.
    Drug metabolism and disposition: the biological fate of chemicals 09/2009; 37(11):2137-44. · 3.74 Impact Factor
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    ABSTRACT: 1-(2-Methoxyethyl)-2-methyl-4,9-dioxo-3-(pyrazin-2-ylmethyl)-4,9-dihydro-1H-naphtho[2,3-d]imidazolium bromide (YM155 monobromide), which is a hydrophilic and cationic compound, exhibits antitumor activity in experimental human hormone refractory prostate carcinoma models. Urinary excretion was 18.3 to 28.6% of the dose in the clinical phase I study, and nonrenal elimination may be explained by the biliary excretion of YM155 in its unchanged form. Because the penetration through the sinusoidal membrane of the hepatocytes is the first step and an important part of biliary excretion, we evaluated the uptake of [(14)C]YM155 into human cryopreserved hepatocytes. YM155 was taken up into hepatocytes in a temperature- and concentration-dependent manner. The saturable uptake component was much higher than the nonsaturable passive diffusion component. In vitro hepatic uptake clearance was consistent with the in vivo hepatic intrinsic clearance calculated using clinical study data. Hepatic uptake of YM155 was inhibited by organic cation transporter (OCT) inhibitors, and the IC(50) values for YM155 uptake were comparable to those reported for human OCT1-mediated transport. The interaction of YM155 with candidate transporter, OCT1, was also characterized using S2 cells stably expressing human OCT1 (OCT1-S2) cells. In OCT1-expressing S2 cells, YM155 inhibited the OCT1-mediated uptake of a typical OCT1 substrate, [(14)C]tetraethylammonium. In addition, YM155 was taken up into OCT1-S2 cells These results indicated that OCT1 was the predominant transporter for the hepatic uptake of YM155, and the transporter-mediated uptake clearance observed in vitro may account for the in vivo intrinsic hepatic clearance.
    Drug metabolism and disposition: the biological fate of chemicals 07/2009; 37(9):1856-63. · 3.74 Impact Factor
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    ABSTRACT: (-)-N-{2-[(R)-3-(6,7-Dimethoxy-1,2,3,4-tetrahydroisoquinoline-2-carbonyl)piperidino]ethyl}-4-fluorobenzamide (YM758) is a novel inhibitor of the "funny" If current channel (If channel) that is expressed in the sinus node of heart and is being developed as a treatment for stable angina and atrial fibrillation. Its metabolites were identified in human urine, plasma, and feces by radio-high-performance liquid chromatography and liquid chromatography-tandem mass spectrometry analyses after oral administration of [(14)C]YM758. 6,7-Dimethoxy-2-[(3R)-piperidin-3-ylcarbonyl]-1,2,3,4-tetrahydroisoquinoline (YM-252124), (5R)-5-[(6,7-dimethoxy-3,4-dihydroisoquinolin-2(1H)-yl)carbonyl]piperidin-2-one (YM-385459), 2-{[(3R)-1-{2-[(4-fluorobenzoyl)amino]ethyl}piperidin-3-yl]carbonyl}-7-methoxy-1,2,3,4-tetrahydroisonolin-6-yl beta-D-glucopyranosiduronic acid (AS2036329), and the unchanged drug were detected as major constituents in both urine and plasma, whereas N-(4-fluorobenzoyl)glycine (YM-385461) was detected in plasma, but not in urine. The renal and hepatic uptake transporters for these metabolites were investigated by assessing their inhibitory effect on uptake activity in human (h) organic cation transporter (OCT) 1-3/rat (r) Oct1-3, human organic anion transporter (OAT) 1/rOat1, hOAT3/rOat3, and organic anion-transporting protein 1B1/1B3-expressing HEK293 cells. IC(50) values of YM-252124 for 1-methyl-4-phenylpyridinium uptake via hOCT2 and rOct2 were 93.9 and 1700 microM, respectively, suggesting that this metabolite is secreted into urine via hOCT2/rOct2 and that the large difference in the inhibitory potentials between hOCT2 and rOct2 explains the species difference in the urinary excretion ratio of the radioactivity. The renal secretion of YM-385461, one derivative of p-aminohippuric acid, via hOAT1/rOat1, and hepatic uptake of YM-252124 via hOCT1/rOct1 was also expected. This kind of study was useful in investigating the relationship between the urinary/hepatic elimination and the transport activity for metabolites.
    Drug metabolism and disposition: the biological fate of chemicals 06/2009; 37(8):1646-57. · 3.74 Impact Factor
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    ABSTRACT: (-)-N-{2-[(R)-3-(6,7-Dimethoxy-1,2,3,4-tetrahydroisoquinoline-2-carbonyl)piperidino]ethyl}-4-fluorobenzamide (YM758), a novel "funny" If current channel (If channel) inhibitor, is developed as a treatment for stable angina and atrial fibrillation. In this study, the pharmacokinetic/pharmacodynamic (PK/PD) relationship after intravenous administration of YM758 to tachycardia-induced dogs was investigated and described based on the simplified compartment model. The PK of YM758 in dogs did not differ between the nontreated and tachycardia-induced groups. A drug-induced reduction in heart rate (HR) was clearly observed, and the half-life of the duration of the effect (approximately 4.0 h) was longer than that of the plasma concentration of the unchanged drug. The fitting and simulation procedure from the PK/PD relationship between the time profiles for YM758 plasma concentration and HR reduction had an ECe(50) value (YM758 concentration in the effective compartment resulting in a 50% decrease of the maximum effect) of 6.0 ng/ml, which did not agree with the results of the in vitro experiment using right atria isolated from guinea pigs (EC(30), 70.4 ng/ml). In addition, in the in vitro experiments, YM758 metabolites had a weak inhibitory effect, if any, on the spontaneous beat rate of the right atria from guinea pigs. These data, along with the previous finding that YM758 and its metabolites are eliminated rapidly from rat hearts, indicate that the duration of the pharmacological effect of YM758 (compared with the rapid elimination of the plasma drug concentration) may be the result of strong binding and/or slower dissociation of YM758 in the If channel. Such PK/PD analyses allow the pharmacological profiles of many drugs, especially cardiovascular drugs, to be more readily understood and better predicted during the clinical stages.
    Drug metabolism and disposition: the biological fate of chemicals 05/2009; 37(7):1427-33. · 3.74 Impact Factor
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    ABSTRACT: 1-(2-Methoxyethyl)-2-methyl-4,9-dioxo-3-(pyrazin-2-ylmethyl)-4,9-dihydro-1H-naphtho[2,3-d]imidazolium bromide (YM155 monobromide) is a novel small-molecule survivin suppressant that induces the down-regulation of survivin and exhibits potent antitumor activity in nude mice bearing the human hormone refractory prostate carcinoma cell line PC-3. In this study, radioluminographic determination of the in vivo distribution of radioactivity after administration of [(14)C]YM155 to PC-3-xenografted nude mice revealed a relatively high level of radioactivity in the PC-3 xenograft. Therefore, the uptake of [(14)C]YM155 was further characterized in vitro using PC-3, lung cancer (Calu-6 and NCI-H358), malignant melanoma (A375 and SK-MEL-5), and non-Hodgkin's lymphoma (RL and Ramos) cell lines. The uptake of [(14)C]YM155 in these cell lines was dependent on incubation time, temperature, and drug concentration. The Michaelis-Menten constant values were similar among the seven cell lines (0.189-0.367 microM). The effects of various compounds on the uptake of [(14)C]YM155 were tested in PC-3, Calu-6, A375, RL, and Ramos cell lines. Of the compounds tested, the cationic transporter substrates/inhibitors (tetraethylammonium, 1-methyl-4-phenylpyridium, cimetidine, prazosin, corticosterone, verapamil, amantadine, procainamide, and N-methylnicotinamide) inhibited the uptake of [(14)C]YM155 to a similar extent among the five cell lines. The half-maximal inhibitory concentration values (IC(50)) of several compounds for the uptake of [(14)C]YM155 into PC-3 differed from those reported in the literature for human organic cation transporter 1 (OCT1/SLC22A1), OCT2 (SLC22A2), and OCT3 (SLC22A3). To summarize, YM155 was taken up into cancer cells in a carrier-mediated manner and with a similar affinity among all the cancer cell lines tested. An influx transporter(s) may contribute to this process.
    Drug metabolism and disposition: the biological fate of chemicals 01/2009; 37(3):619-28. · 3.74 Impact Factor
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    ABSTRACT: The inhibitory effects of cationic drugs (beta-adrenoreceptor antagonists, calcium (Ca)-channel blocker, I(f) channel inhibitor, antiarrhythmic drugs, and antibacterial drugs) that inhibit 1-methyl-4-phenylpyridinium (MPP) and/or metformin uptake into hOCT1-3/rOct1-3-expressing cells and human/rat hepatocytes were investigated in this study. The drug-drug interaction (DDI) potential of these drugs for the hOCT/rOct-mediated hepatic/renal uptake process was also assessed. The IC(50) values of cardiovascular drugs, including an I(f) channel inhibitor with a new mechanism of action, were greater for hOCT2/rOct2 than those for hOCT1/rOct1 or hOCT3/rOct3. No species differences in these values were observed between hOCTs and rOcts. As for hOCT2-mediated uptake, the IC(50) values of quinidine and the I(f) channel inhibitor for metformin uptake were lower than those for MPP uptake. However, previous clinical studies found that the IC(50) values of these drugs for hOCT1/rOct1 and hOCT2/rOct2 were much greater than their unbound plasma concentrations, which suggests that the DDIs of these cationic compounds may not be related to hOCT/rOct-mediated hepatic/renal uptake pathways. In addition, investigation of the luminal transporters of cationic compounds in the kidney, as well as the in vitro DDI potential of their inhibitors, is important for the clarification of cationic compound DDIs in humans.
    Xenobiotica 10/2008; 38(9):1203-18. · 1.98 Impact Factor
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    ABSTRACT: In this study the tissue distribution of radioactivity in pregnant and lactating rats was investigated by quantitatively determining radioactivity concentrations and by whole-body autoradioluminograms after a single oral administration of 14C-YM758. In addition, the transfer of radioactivity into the reproductive tissues, foetus, and milk is discussed in terms of the localization of transporters in syncytiotrophoblast and mammary gland. The radioactivity concentrations in the liver were the highest of all the tissues and organs tested at all the sampling times. The radioactivity in main tissues (liver and kidney), including reproductive tissues (amniotic fluid, placenta, ovary, and uterus), was not retained for a long time, as in the plasma. The tissue/plasma (T/P) ratio of radioactivity in the foetus was below 1.0, which might be due to Mdr1-mediated export of YM758 into blood via the blood-placenta barrier since YM758 is a substrate for hMDR1, not for hBCRP/rBcrp. The T/P ratio of radioactivity in the maternal milk 1 and 4 h after oral administration of 14C-YM758 was 7.2 and 11.0, respectively. To understand better the distribution of new drugs into the reproductive tissues/milk, and to interpret further the results of reproductive safety studies for drug development, the contribution of transporters expressed in the blood-placenta barrier and mammary gland to the drug-transfer into placenta and milk should be considered.
    Xenobiotica 10/2008; 38(10):1274-88. · 1.98 Impact Factor
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    ABSTRACT: Zonampanel monohydrate ([2,3-dioxo-7-(1H-imidazol-1-yl)-6-nitro-1,2,3,4-tetrahydro-1-quinoxalinyl] acetic acid monohydrate, YM872) is a novel alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptor antagonist. In humans, almost all administered zonampanel is excreted in the urine unchanged. Furthermore, zonampanel is transported by human organic anion transporter (OAT) 1, and OAT3 but not by OAT2, suggesting the contribution of OATs to renal excretion. In rats also, zonampanel is predominantly eliminated via urine but partly also via bile as the unchanged form. In this study, the molecular mechanism of the excretion of zonampanel was elucidated using cells expressing rat Oat1, Oat2, and Oat3. Furthermore, zonampanel (15 mg/kg) was given i.v. to rats with or without probenecid (50 mg/kg) or cimetidine (40 mg/kg), and pharmacokinetic parameters were compared. Zonampanel inhibited the uptake of typical substrates by Oat1, Oat2, and Oat3 with inhibition constant (K(i)) values of 7.02 to 10.4 microM. A time- and saturable concentration-dependent increase in [14C]zonampanel uptake was observed in these cells [Michaelis-Menten constant (K(m)) values: 13.4 to 53.6 microM]. Probenecid and cimetidine inhibited [14C]zonampanel uptake by Oats. In in vivo experiments, probenecid and cimetidine decreased intrinsic clearance for both the renal secretion and biliary excretion of zonampanel. Considering the tissue distribution and localization of each transporter, these results suggest that in rats zonampanel is taken up from the blood into proximal tubular cells via Oat1 and Oat3 and, unlike the case in humans, also into hepatocytes via Oat2 and Oat3. The interspecies differences in the excretion of zonampanel between rats and humans may thus be explained by those in the substrate selectivity and tissue distribution of OATs.
    Drug metabolism and disposition: the biological fate of chemicals 09/2008; 36(8):1496-504. · 3.74 Impact Factor
  • Yuji Mano, Takashi Usui, Hidetaka Kamimura
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    ABSTRACT: Differences in the inhibitory potentials against UDP-glucuronosyltransferase (UGT) between species have been reported only rarely, even though the information would be useful for the precise characterization of drug candidates. In this study, the inhibition potentials of nonsteroidal anti-inflammatory drugs (NSAIDs) against UGT-catalyzed estradiol 3beta-glucuronidation (E3G) in the liver microsomes of rats, dogs, and humans were compared. Rat liver microsomes (RLMs) and human liver microsomes (HLMs) exhibited homotropic activation kinetics with S(50) values of 22 and 12 microM, respectively. However, dog liver microsomes (DLMs), exhibited Michaelis-Menten kinetics with no activation. Among the NSAIDs investigated (diclofenac, diflunisal, fenoprofen, flurbiprofen, ibuprofen, indomethacin, ketoprofen, mefenamic acid, niflumic acid, and sulindac), only niflumic acid and mefenamic acid inhibited E3G potently in all three species. The IC(50) values of NSAIDs against E3G in RLMs and HLMs were within a threefold difference of each other, while those in DLMs was more than three times higher than the other two. In conclusion, RLMs showed an inhibitory pattern similar to that of HLMs, whereas DLMs presented a distinct pattern. These results indicate that a rat animal model would be useful for evaluating the inhibitory potentials of drugs against estradiol glucuronidation, but a dog model would not.
    Journal of Pharmaceutical Sciences 08/2008; 97(7):2805-10. · 3.13 Impact Factor
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    ABSTRACT: The aim of this study was to investigate the absorption, distribution, and excretion of radioactivity in male rabbits after a single or repeated instillation of (14)C-labeled tacrolimus (FK506) ophthalmic suspension or an intravenous (i.v.) administration of (14)C-FK506. The 0.3% (14)C-FK506 suspension was administered in single and repeated (three times, 5-min intervals) instillation studies, and 1 mg/kg of (14)C-FK506 was administered in the i.v. dose study. Results for single and repeated instillation studies were similar. In eyeball microautoradiograms, 15 min after dosing, the level of radioactivity in the cornea was the highest, followed by conjunctiva. After 1 h, little specific distribution was detected in the corneal epithelium, stroma, or Descemet's membrane. At 24 h, the level of radioactivity in the cornea decreased. Whole-body autoradiograms showed that the radioactivity was distributed to the digestive tract through the nasal meatus and esophagus and then was excreted into the feces. In the i.v. dose study, the distribution of radioactivity in whole-body autoradiographs was similar to that in quantitative tissue distribution measurements. The excretion of radioactivity in the urine and feces up to 168 h were 4.5 and 94.9%, respectively. After the ocular instillation, FK506 is first absorbed in the cornea, conjunctiva, and nasolacrimal duct, and then the rest is distributed to digestive tract through the nasal meatus and esophagus, after which it is excreted mainly into the feces.
    Journal of Ocular Pharmacology and Therapeutics 07/2008; 24(3):333-43. · 1.29 Impact Factor
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    ABSTRACT: This paper describes a sensitive and selective liquid chromatography with tandem mass spectrometry (LC-MS/MS) method for determination of the novel survivin suppressant YM155, 1-(2-methoxyethyl)-2-methyl-4,9-dioxo-3-(pyrazin-2-ylmethyl)-4,9-dihydro-1H-naphtho[2,3-d]imidazolium, which is developed for the treatment of solid tumors. This method uses a liquid-liquid extraction from 0.25 mL of dog plasma. LC separation was carried out on a Genesis Silica column (50 mm x 3.0 mm i.d.) at a flow-rate of 0.5 mL/min. Compounds were eluted using a mobile phase of 5 mm ammonium acetate and 0.1% formic acid in water-0.1% formic acid in acetonitrile, 17:83 (v/v). MS/MS detection was carried out with an MDS-Sciex API3000 triple quadrupole mass spectrometer in positive electrospray ionization mode. The standard curve was linear from 0.05 to 50 ng/mL (r > or = 0.9968). The lower limit of quantitation was 0.05 ng/mL. Good intra- and inter-day assay precision (within 7.4% RSD) and accuracy (within +/-12.3%) were obtained. The extraction recovery was 66.2%. The method was successfully applied to preclinical pharmacokinetic studies in dogs.
    Biomedical Chromatography 07/2008; 22(7):763-9. · 1.95 Impact Factor
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    ABSTRACT: (-)-N-{2-[(R)-3-(6,7-Dimethoxy-1,2,3,4-tetrahydroisoquinoline-2-carbonyl)piperidino]ethyl}-4-fluorobenzamide (YM758), a novel "funny" If current channel (If channel) inhibitor, is being developed as a treatment for stable angina and atrial fibrillation. The hepatic uptake/excretion of YM758 was clarified using transporter-expressing mammalian cells and hepatocytes mainly in humans and partly in rats. cDNA-expressing human embryonic kidney 293 cells were used to determine that YM758 was greatly taken up via organic anion-transporting polypeptide (OATP) 1B1 and slightly via human organic cation transporter (hOCT) 1/rat organic cation transporter 1 but not via OATP1B3. In addition, the uptake of 17beta-estradiol-d-17beta-glucuronide via OATP1B1 was inhibited in the presence of YM758, whereas that via OATP1B3 was not. In contrast, time-dependent uptake of YM758 into rat/human hepatocytes at 37 degrees C was observed, as was concentration-dependent uptake into human hepatocytes (K(m) value of 87.9 microM). This saturable uptake of YM758 into human hepatocytes was inhibited in the presence of quinidine (an inhibitor for OATP1B1) but not cimetidine (an inhibitor for the hOCT family). Moreover, the permeation clearance ratios for the transcellular transport of YM758 across multidrug resistance (MDR) 1-expressing LLC-PK1 cells were extensively higher than those across LLC-PK1 cells, which indicate that MDR1-mediated transport is one of the possible pathways through which YM758 may be excreted into the bile. These results indicate that YM758 is taken up into hepatocytes mainly via OATP1B1, but not via hOCT1, and is excreted into the bile via MDR1 in humans; however, passive diffusion or an unknown uptake/excretion mechanism could be at work in the hepatocytes. This study is the first to clarify the saturable hepatic uptake and/or the excretion mechanism by the If channel inhibitor.
    Drug metabolism and disposition: the biological fate of chemicals 07/2008; 36(6):1030-8. · 3.74 Impact Factor
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    ABSTRACT: The aim of this study was to investigate the ocular distribution of tacrolimus (FK506) and absorption into the systemic circulation after a single or repeated topical instillation of FK506 ophthalmic suspension in male New Zealand white rabbits. In the single instillation study (group 1), 29.1-34.8 microL of a 0.1, 0.3, and 1% suspension was administered to each of the 15 rabbits. In the repeated instillation study (group 2), 27.1-39.5 microL of a 0.3% suspension was administered to 27 rabbits q.i.d. (i.e., at 3-h intervals) for 14 days. In the intravenous (i.v.) dose study (group 3), 1 mg/kg of FK506 was administered to 3 rabbits. The amount of FK506 was measured by using a competitive enzyme immunoassay. The results for single and repeated instillation studies were similar. In the single instillation study, blood T(max) after an instillation of the 0.1, 0.3, and 1% suspensions (at 0.8, 1.0, and 1.0 hours) did not differ significantly among these doses. One (1) h after an instillation of the 1% suspension, ocular tissue concentrations, except the retina/choroid, vitreous body, and lens, were higher than the blood concentration (C(max): 2.7 ng/mL). In particular, concentrations in the conjunctiva, cornea, iris, and anterior sclera were much higher than the blood concentration (148, 900, 120, and 145 ng/g tissue). In the repeated instillation study, concentrations in the blood and ocular tissues (except the lens) reached a steady state by the 7th day. In the i.v. dose study, AUC(0-24h) and T(1/2) were 1643 ng h/mL and 18.5 h, respectively. The high-level distribution of FK506 was observed in the conjunctiva, which is desirable because the conjunctiva is the target tissue for pharmacologic effect (i.e., efficacy).
    Journal of Ocular Pharmacology and Therapeutics 07/2008; 24(3):309-19. · 1.29 Impact Factor
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    ABSTRACT: 1. Zonampanel, a novel alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) receptor antagonist, is mainly excreted unchanged via renal tubular secretion. The renal apical transport transport of zonampanel was examined in this study using HEK293 cells expressing human organic anion transporter 4 (OAT4/SLC22A11), and membrane vesicles prepared from Sf-9 insect cells expressing human multidrug resistance-associated protein 2 (MRP2/ABCC2), MRP4 (ABCC4), and breast cancer resistance protein (BCRP/ABCG2). 2. Glutaric acid, a model dicarboxylate, trans-stimulated the uptake of [(14)C]zonampanel by OAT4, suggesting that zonampanel was transported by OAT4 via an exchange with dicarboxylate. Considering the endogenous dicarboxylate gradient, OAT4 seems to transport zonampanel in the direction of reabsorption rather than secretion. For MRP2, MRP4, and BCRP, zonampanel selectively inhibited the activity of MRP4 (K(i) = 41.3 microM). Marked transport of [(14)C]zonampanel was observed only for MRP4 (K(m) = 33.7 microM). 3. In conclusion, the data indicate that MRP4 was the apical efflux transporter that contributed to the active renal tubular secretion of zonampanel in humans, in concert with the apical reabsorption transporter OAT4 and basolateral uptake transporters.
    Xenobiotica 06/2008; 38(9):1191-202. · 1.98 Impact Factor
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    ABSTRACT: 1. YM758 is a novel If channel inhibitor for the treatment of stable angina and atrial fibrillation. The absorption, distribution, and excretion of YM758 have been investigated in albino and non-albino rats after a single oral administration of (14)C-YM758 monophosphate. 2. YM758 was well absorbed from all segments of the gastrointestinal tract except for the stomach. After oral administration, the ratio of AUC(0-1 h) between the plasma concentrations of radioactivity and the unchanged drug was estimated to be 17.7%, which suggests metabolism. 3. The distribution of the radioactivity derived from (14)C-YM758 in tissues was evaluated both in albino and non-albino rats. The radioactivity concentrations in most tissues were higher than those in plasma, which indicates that the radioactivity is well distributed to tissues. Extensive accumulation and slower elimination of radioactivity were noted in the thoracic aorta of albino and non-albino rats as well as in the eyeballs of non-albino rats. The recovery rates of radioactivity in urine and bile after oral dosing to bile duct-cannulated albino rats were 17.8% and 57.3%, respectively. 4. These results suggest that YM758 was extensively absorbed, subjected to metabolism, and excreted mainly into the bile after oral administration to rats, and extensive accumulation of the unchanged drug and/or metabolites into tissues such as the thoracic aorta and eyeballs was observed.
    Xenobiotica 06/2008; 38(5):527-39. · 1.98 Impact Factor
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    ABSTRACT: A high‐performance liquid chromatographic method with ultraviolet detection was developed for the determination of zonampanel monohydrate (YM872), a novel α‐amino‐3‐hydroxy‐5‐methylisoxazole‐4‐propionic acid (AMPA) receptor antagonist, in rat plasma. YM872 was extracted via solid‐phase extraction. To remove blank plasma derived endogenous peaks, the extract was further purified by washing with tri‐n‐butyl phosphate and injected onto reversed‐phase HPLC with ultraviolet detection at 333 nm. The precision and accuracy were less than 4.99% and within±7.89%, respectively. The limit of quantification was 10 ng/mL when 1 mL of plasma was used. The usefulness of this method was demonstrated by monitoring plasma concentrations after intravenous administration of YM872 to rats.
    Journal of Liquid Chromatography & Related Technologies - J LIQ CHROMATOGR RELAT TECHNO. 01/2008; 31(7):1072-1080.
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    ABSTRACT: This study examined the contribution made by organic cation transporters (hOCT/rOct) to the saturable component of the renal uptake of 1-methyl-4-phenylpyridinium, tetraethylammonium (TEA), cimetidine and metformin into rOct2-expressing HEK293 cells and rat kidney slices. All the test compounds accumulated in the rat kidney slices in a carrier-mediated manner. The Michaelis- Menten constant (K(m)) values for saturable uptake of TEA, cimetidine and metformin into rat kidney slices were relatively comparable with those for the rOct2-expressing HEK293 cells. In addition, the relative uptake activity values of TEA, cimetidine and metformin in rat kidney slices were similar to those in rOct2-expressing HEK293 cells. This suggests that the saturable components involved in the renal uptake of TEA, cimetidine and metformin are mediated mainly by rOct2. The saturable uptake profile of cationic compounds into rat kidney can be evaluated in both cDNA-expressing cells and rat kidney slices, as well as the transporter expression pattern. This approach can also be used to estimate the saturable uptake mechanism of cationic compounds into the human kidney when human kidney slices and hOCT2-expressing cells are used.
    The Journal of international medical research 01/2008; 36(1):123-36. · 0.96 Impact Factor