Drug metabolism and metabolite safety assessment in drug discovery and development

Pharmacokinetics and metabolism of GW9508 in rat by liquid chromatography/electrospray ionization tandem mass spectrometry

In this study, a simple, fast and sensitive LC/MS/MS method was developed and validated for the determination of GW9508 in rat plasma. The sample was precipitated with acetonitrile and subsequently separated on ZORBAX Eclipse XDB C₁₈ column (50 mm × 2.1 mm, 5 μm). Mobile phase was composed of 0.1% formic acid in water and acetonitrile with gradient elution, at a flow rate of 0.4 mL/min. The analyte and internal standard were quantitatively monitored with precursor-to-product transitions of m/z 348.2→183.1 and m/z 397.2→260.2, respectively. The linearity of the assay was evident in the range of 1-1000 ng/mL with correlation coefficient more than 0.998. The validation parameters were all within the acceptable limits. The validated method has been successfully applied to the pharmacokinetics study of GW9508 in rat plasma, and our results demonstrated that GW9508 showed low clearance, moderate half-life and ideal bioavailability (54.88%). Furthermore, metabolites stemmed from rat plasma, rat hepatocytes and human hepatocytes were analyzed by an LC-Q-Exactive-Orbitrap-MS assay, resulting in the identification of seven metabolites based on the accurate mass and fragment ions. Acylglucuronide conjugate (M6) was found as the most abundant metabolite in all tested matrices. The metabolic pathways were proposed as hydroxylation and glucuronidation. This study provided an overview of disposition of GW9508, which is highly instructive for better understanding the effectiveness and toxicity of this drug.

In vitro metabolic profiles of motolimod by using liquid chromatography tandem mass spectrometry: Metabolic stability, metabolite characterization and species comparison

Motolimod (VTX-2337) is an agonist of toll-like receptor 8 (TLR8) with potential immune-stimulating and antineoplastic activities. The purpose of this study was to investigate the in vitro metabolic profiles of VTX-2337. The average in vitro T_1/2 values were 6.93, 8.71, 7.39, 2.85, and 10.58 min in the liver microsomes of mouse, rat, dog, monkey and human respectively, suggesting that VTX-2337 suffered from extensive metabolism. The metabolites were further profiled and identified by using ultra-high performance liquid chromatography coupled with diode array detector and Q-Exactive-Orbitrap tandem mass spectrometer (UHPLC-DAD-Q-Exactive-Orbitrap-MS) operated in positive ion mode. A total of 20 metabolites were detected and their identities were characterized based on their accurate masses, fragment ions and retention times. M13 (depropylation) was the most abundant metabolite in all species. M14 (oxygenation) was also the major metabolite in the liver microsomes of mouse, rat, monkey and human. M1, M5, M10, M15, and M16 were specifically detected in mouse, while M6 and M17 were monkey-specific. All the metabolites present in human could be found in animal species. The metabolic pathways of VTX-2337 referred to oxygenation, hydrolysis, depropylation, and dehydrogenation. Rat had the similar metabolic profiles to humans. The current study provided overall metabolic profiles of VTX-2337, which would be of great help in predicting in vivo pharmacokinetic profiles and in understanding the effectiveness and safety of this drug.

Pharmacokinetics, bioavailability and metabolism of cligosiban, an antagonist of oxytocin receptor, in rat by liquid chromatography hyphenated with electrospray ionization tandem mass spectrometry

Cligosiban is a highly-affinity nonpeptide oxytocin receptor antagonist. In this study, a simple an sensitive LC-MS/MS method was developed and validated for the determination of cligosiban in rat plasma. The plasma samples were pretreated with acetonitrile as precipitant and then separated on an ACQUITY BEH C₁₈ column (2.1 × 50 mm, 1.7 μm) with 0.1% formic acid in water and acetonitrile as mobile phase. The analytes were monitored using selected reaction monitoring (SRM) mode with transitions at m/z 420.1→248.1 for cligosiban and m/z 304.1→161.1 for IS. The developed method showed good linearity over the concentration range of 1-1000 ng/mL with coefficient of correlation > 0.996. The lower limit of quantification (LLOQ) is 1 ng/mL. The method was validated for selectivity, precision, accuracy, recovery, and stability in accordance with FDA's guidance. The validated assay has been successfully applied to the pharmacokinetic study of cligosiban in rat plasma after intravenous and oral administration. According to the current results, the oral bioavailability of cligosiban was 63.82%. Furthermore, the metabolites present in rat liver microsomes (RLM), human liver microsomes (HLM) and rat plasma were analyzed by UHPLC-LTQ-Orbitrap-MS method, and four metabolites structurally identified based on their accurate masses, and fragment ions. The proposed metabolic pathways of cligosiban were demethylation and glucuronidation. This study is the first report on the pharmacokinetic and metabolic information of cligosiban, which would provide insights into the effectiveness and toxicity of cligosiban.