Tissue distribution of YM758, a novel If channel inhibitor, in pregnant and lactating rats.

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.

Pharmacokinetics of YK754, a novel If channel inhibitor in rats, dogs and humans.

The pharmacokinetics of YM758, a novel funny If current channel (If channel) inhibitor, was investigated after single intravenous (i.v.) and oral dosing to rats and dogs, and partially compared with the results in humans by using liver microsomes. After i.v. administration, the plasma YM758 concentrations decreased, with an elimination half-life (t(1/2)) of 1.14-1.16 h in rats and 1.10-1.30 h in dogs. Total body clearance (CL(tot)) was 5.71-7.27 and 1.75-1.90 L/h/kg in rats and dogs, respectively which was comparable to the hepatic blood flow rate. In dogs, the pharmacokinetic profiles for i.v. bolus administration and continuous infusion did not differ. After oral administration, the levels of YM758 in rat plasma increased more than dose-proportionally, whereas almost linear pharmacokinetics were observed in dogs. Absolute bioavailability was 7.5%-16.6% in rats and 16.1%-22.0% in dogs. The plasma protein binding saturation of YM758 was observed in dogs and humans; this finding is consistent with the result that the major binding protein of YM758 in plasma is alpha1-acid glycoprotein (AGP), in particular in humans. The blood-to-plasma partition coefficient values were 1.36-1.42 in rats, 0.95-1.15 in dogs and 0.71-0.85 in humans. The results of the metabolic study on liver microsomes indicated that the non-linear pharmacokinetics of YM758 observed in rats may be partially due to a first-pass effect in the gastrointestinal tract and the liver.

Effect of cationic drugs on the transporting activity of human and rat OCT/Oct 1-3 in vitro and implications for drug-drug interactions.

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.

Comparative evaluation of absorption, distribution, and excretion of YM758, a novel If channel inhibitor, between albino and non-albino rats.

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.

Functional involvement of the organic cation transporter 2 (rOct2) in the renal uptake of organic cations in rats.

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.

Evaluation of the inhibitory and induction potential of YM758, a novel If channel inhibitor, for human P450-mediated metabolism.

This study was designed to examine the in vitro metabolism of YM758, a novel cardiovascular agent, and to evaluate its potential to cause drug interactions and induction of CYP isozymes. After incubation with pooled human liver microsomes, YM758 was converted to two major metabolites (AS2036313-00, and YM-394111 or YM-394112). The formation of AS2036313-00, and YM-394111 or YM-394112 were mediated by CYP2D6 and CYP3A4, respectively, which was elucidated by using a bank of human liver microsomes and recombinant CYP enzymes in combination with the utilization of typical substrates and inhibitors. The Ki values of YM758 for midazolam, nifedipine, and metoprolol metabolism ranged from 59 to 340 microM, being much higher than the YM758 concentration in human plasma. The formation of AS2036313-00, and YM-394111 or YM-394112 was inhibited by quinidine and ketoconazole with Ki values of 140 and 0.24 microM, respectively, which indicates that YM758 metabolism may be affected by coadministration of strong CYP2D6 and 3A4 inhibitors in vivo, given the clinical plasma concentrations of quinidine and ketoconazole. After human hepatocytes were exposed to 10 microM YM758, microsomal activity and mRNA level for CYP1A2 were not induced while those for CYP3A4 were slightly induced. The tested concentration was much higher than that in human plasma, which suggests that the induction potential of YM758 is also negligible.

Functional involvement of organic cation transporter1 (OCT1/Oct1) in the hepatic uptake of organic cations in humans and rats.

The contribution of organic cation transporters to the saturable component in the hepatic uptake of 1-methyl-4-phenylpyridinium (MPP), tetraethylammonium (TEA), cimetidine, and metformin was examined by the use of human/rat organic cation transporter (hOCT1/rOct1)-expressing cells and human/rat hepatocytes. Transfection of rOct1 resulted in a considerable increase in the uptake of metformin, whereas that of hOCT1 resulted in only a slight increase. All test compounds (MPP, TEA, cimetidine, and metformin) accumulated in human and rat hepatocytes in a carrier-mediated manner. The Km values for the uptake of MPP, TEA, cimetidine, and metformin into human and rat hepatocytes were comparable with those into hOCT1 and rOct1-expressing cells, respectively. In addition, the relative uptake activities, which were obtained by normalizing the intrinsic uptake clearances of TEA, cimetidine, and metformin against those values of MPP in human and rat hepatocytes, were similar with the uptake activities in hOCT1 and rOct1, respectively. These results suggest that the saturable component in the hepatic uptake of these cationic compounds may be mediated mainly by hOCT1/rOct1; therefore, it is meaningful to evaluate the saturable uptake profile of cationic compounds by the liver using both hOCT1/rOct1-expressing cells and human/rat hepatocytes.

Comparison of the kinetic characteristics of inhibitory effects exerted by biguanides and H2-blockers on human and rat organic cation transporter-mediated transport: Insight into the development of drug candidates.

In this study, the comparison of the transport of substrates (1-methyl-4-phenylpydinium (MPP) and tetraethyl ammonium (TEA)) and the inhibition potency of the inhibitors (biguanides and H(2)-blockers) for human and rat organic cation transporters (hOCTs and rOcts), and the inhibition type of inhibitors for these transporters were investigated using HEK293 cells that stably express hOCT/rOct. The concentration-dependent uptake of [(3)H]-MPP and [(14)C]-TEA by hOCT1-3/rOct1-3 had K(m) values similar to those in the literature. It was also deduced that MPP and TEA are competitive inhibitors for hOCT1-2/rOct1-2. The K(i) values for phenformin inhibition of [(3)H]-MPP and [(14)C]-TEA uptake by hOCT1-3/rOct1-3 were lower than that for metformin. The [(3)H]-MPP uptake by hOCT1/rOct1 and hOCT3/rOct3 was inhibited by famotidine and ranitidine whereas that by hOCT2/rOct2 was not. The inhibitory potency of cimetidine for hOCT1-2 was very weak. In most cases, the differences in the V(max)/K(m) values of substrates and the K(i) values of inhibitors between hOCT and rOct were minor. The acquisition of information on OCT/Oct mediated-transport and/or inhibition such as that presented in this report is very useful for further understanding of certain aspects of uptake, distribution, and excretion for drug candidates.