Identification and characterization of metabolites of ASP015K, a novel oral Janus kinase inhibitor, in rats, chimeric mice with humanized liver, and humans.

1. Here, we elucidated the structure of metabolites of novel oral Janus kinase inhibitor ASP015K in rats and humans and evaluated the predictability of human metabolites using chimeric mice with humanized liver (PXB mice). 2. Rat biological samples collected after oral dosing of (14)C-labelled ASP015K were examined using a liquid chromatography-radiometric detector and mass spectrometer (LC-RAD/MS). The molecular weight of metabolites in human and the liver chimeric mouse biological samples collected after oral dosing of non-labelled ASP015K was also investigated via LC-MS. Metabolites were also isolated from rat bile samples and analyzed using nuclear magnetic resonance. 3. Metabolic pathways of ASP015K in rats and humans were found to be glucuronide conjugation, methyl conjugation, sulfate conjugation, glutathione conjugation, hydroxylation of the adamantane ring and N-oxidation of the 1H-pyrrolo[2,3-b]pyridine ring. The main metabolite of ASP015K in rats was the glucuronide conjugate, while the main metabolite in humans was the sulfate conjugate. Given that human metabolites were produced by human hepatocytes in chimeric mice with humanized liver, this human model mouse was believed to be useful in predicting the human metabolic profile of various drug candidates.