Investigation of Metabolite Profile of YM758, a Novel If Channel Inhibitor

Background

YM758 monophosphate is a novel If channel inhibitor that has an inhibitory action for If current and shows a strong and specific activity, selectively lowering the heart rate and decreasing oxygen consumption by heart muscle.

Objectives

The objectives of the current study were to investigate the in vivo metabolic profiles of YM758 in mice, rats, rabbits, dogs, and monkeys and to elucidate the structures of YM758 metabolites.

Methods

Biological samples were analyzed by liquid chromatography hyphenated with a radiometric detection system and liquid chromatography coupled with a mass spectrometer to clarify their metabolic patterns. To elucidate their structures, metabolites were isolated and analyzed by mass spectrometry and nuclear magnetic resonance spectroscopy.

Results

Our results from in vivo metabolic profiling in humans and animals indicated there is no significant species difference in the metabolism of YM758, and the metabolic pathways of YM758 are considered to be oxidation, hydration, and demethylation followed by sulfate or glucuronide conjugation.

Hepatic OATP and OCT uptake transporters: their role for drug-drug interactions and pharmacogenetic aspects

Uptake transporters in the basolateral membrane of hepatocytes are important for the hepatobiliary elimination of drugs. Further, since drug-metabolizing enzymes are located intracellularly, uptake into hepatocytes is a prerequisite for their subsequent metabolism. Therefore, alteration of uptake transporter function (e.g., by concomitantly administered drugs or due to functional consequences of genetic variations, leading to reduced transport function) may result in a change in drug pharmacokinetics. In this review, we focus on the hepatocellularly expressed members of the OATP and OCT family, their impact on transport-mediated drug-drug interactions, and on the functional consequences of variations in genes encoding these transporters.

Investigation of long-term retention of unchanged (-)-N-{2-[(R)-3-(6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline-2-carbonyl)piperidino]ethyl}-4-fluorobenzamide, a novel "funny" If current channel inhibitor, and its metabolites in the eyeball and thoracic aorta of rats

(-)-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.

Relationship between exposure of (-)-N-{2-[(R)-3-(6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline-2-carbonyl)piperidino]ethyl}-4-fluorobenzamide (YM758), a "funny" if current channel inhibitor, and heart rate reduction in tachycardia-induced beagle dogs

(-)-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.