Metabolism of [14C]gemopatrilat after oral administration to rats, dogs, and humans.

This study describes the pharmacokinetic parameters of gemopatrilat, a potent vasopeptidase inhibitor, in humans and the comparative biotransformation of the compound in rats, dogs, and humans after administration of a single oral dose of [14C]gemopatrilat. Gemopatrilat was rapidly absorbed in humans with an oral bioavailability of 49%. Within 5 h after dose, the mean concentrations of gemopatrilat were less than 1% of the mean Cmax values. The total area under the first-moment time curve extrapolated to infinity [AUC(INF)] value for gemopatrilat was only 2% of the AUC(INF) of radioactivity in plasma. Gemopatrilat showed a large apparent steady-state volume of distribution (2500 liters) and a prolonged terminal-phase decline in plasma concentration. These results are consistent with the idea that the free sulfhydryl group of gemopatrilat forms reversible disulfide linkages with plasma and tissue proteins and is thus eliminated from the body at a very slow rate. Approximately half of the drug-related radioactivity in 1-h plasma samples from rat, dog, and human was reduced chemically with dithiothreitol to gemopatrilat, suggesting that disulfide linkage occurred in all species. In addition, metabolites formed through S-methylation and amide hydrolysis were also detected in rat, dog, and human plasma. No gemopatrilat was detected in urine and fecal samples from all three species, indicating that the compound is extensively metabolized in vivo. The major metabolites identified in human urine and feces were also present in rat and dog. These data suggest that the metabolism of gemopatrilat in all three species were qualitatively very similar.

Protein covalent binding of maxipost through a cytochrome P450-mediated ortho-quinone methide intermediate in rats.

(3S)-(+)-(5-Chloro-2-methoxyphenyl)-1,3-dihydro-3-fluoro-6-(trifluoromethyl)-2H-indole-2-one) (MaxiPost, BMS-204352) is a potent and specific opener for maxi-K channels and has potential to prevent and treat ischemic stroke. Following single intravenous doses of [14C]BMS-204352 to rats, only 10 to 12% of radioactivity was extractable from plasma with organic solvents. The unextractable radioactivity remained associated with the proteins (mostly albumin) after SDS-polyacrylamide gel electrophoresis or dialysis. Following acid hydrolysis in 6 M HCl for 24 h at 110 degrees C from plasma proteins collected from nine rats dosed with [14C]BMS-204352, one major radioactive product was isolated and identified as a lysine-adduct of des-fluoro des-O-methyl BMS-204352 by liquid chromatography/mass spectrometry and NMR analyses as well as by comparison with the synthetic analog, lysine-adduct of des-fluoro BMS-204352 (BMS-349821). The covalent binding of BMS-204352 results from the displacement of the ring-fluorine atom of des-O-methyl BMS-204352 with the epsilon-amino group of a lysine residue. Microsomal incubations of [14C]BMS-204352 resulted in low levels of covalent binding of radioactivity to proteins. This in vitro covalent binding required cytochrome P450-reductase cofactor NADPH and was attenuated by glutathione. P4503A inhibitors ketoconazole and troleadomycin selectively prevented the covalent binding in vitro. Based on these observations, a two-step bioactivation process for the protein covalent binding of BMS-204352 was postulated: 1) P4503A-mediated O-demethylation leading to spontaneous release of HF and the formation of an ortho-quinone methide reactive metabolite and 2) nucleophilic addition of the epsilon-amino group of protein lysine residue(s) in protein to form des-fluoro des-O-methyl BMS-204352 lysine adduct.

Comparative biotransformation of radiolabeled [(14)C]omapatrilat and stable-labeled [(13)C(2)]omapatrilat after oral administration to rats, dogs, and humans.

Omapatrilat, a novel vasopeptidase inhibitor, is under development for the treatment of hypertension and congestive heart failure. This study describes the comparative biotransformation of radiolabeled [(14)C]- and stable-labeled [(13)C(2)]omapatrilat after administration of single oral doses to rats, dogs, and humans. The metabolites were identified by a combination of methods including reduction, hydrolysis, and comparison of high performance liquid chromatography retention times with those of the synthetic standards. Urinary metabolites were further characterized by liquid chromatography tandem mass spectrometry analysis. Prominent metabolites identified in human plasma, which were also present in rat and dog plasma, were S-methyl omapatrilat and S-2-thiomethyl-3-phenylpropionic acid. Omapatrilat accounted for only a small portion of the extractable radioactivity in plasma in all three species. A portion of the plasma radioactivity was unextractable in all three species (27-53%). The majority of unextractable radioactivity in plasma was characterized after dithiothreitol reduction to be omapatrilat and (S)-2-thio-3-phenylpropionic acid, both apparently bound to plasma proteins by reversible disulfide bonds. The major human urinary metabolites were the amine hydrolysis product, diasteromeric sulfoxide of (S)-2-thiomethyl-3-phenylpropionic acid, acyl glucuronide of S-methyl omapatrilat, and S-methyl omapatrilat. The minor metabolites were acyl glucuronide of (S)-2-thiomethyl-3-phenylpropionic acid, L-cysteine mixed disulfide of omapatrilat, diastereomers of S-methyl sulfoxide of omapatrilat, and S-methyl omapatrilat ring sulfoxide. The metabolic profiles of dog and human urine were qualitatively similar whereas rat urine showed only metabolites arising from hydrolysis of omapatrilat. Unchanged omapatrilat was not found in rat, dog, or human urine samples indicating extensive metabolism in vivo.