ABSTRACT:Imatinib mesylate (GLEEVEC, GLIVEC, formerly STI571) has demonstrated unprecedented efficacy as first-line therapy for treatment for all phases of chronic myelogenous leukemia and metastatic and unresectable malignant gastrointestinal stromal tumors. Disposition and biotransformation of imatinib were studied in four male healthy volunteers after a single oral dose of 239 mg of 14 C-labeled imatinib mesylate. Biological fluids were analyzed for total radioactivity, imatinib, and its main metabolite CGP74588. Metabolite patterns were determined by radio-high-performance liquid chromatography with off-line microplate solid scintillation counting and characterized by liquid chromatography-mass spectrometry. Imatinib treatment was well tolerated without serious adverse events. Absorption was rapid (t max 1-2 h) and complete with imatinib as the major radioactive compound in plasma. Maximum plasma concentrations were 0.921 ؎ 0.095 g/ml (mean ؎ S.D., n ‫؍‬ 4) for imatinib and 0.115 ؎ 0.026 g/ml for the pharmacologically active N-desmethyl metabolite (CGP74588). Mean plasma terminal elimination half-lives were 13.5 ؎ 0.9 h for imatinib, 20.6 ؎ 1.7 h for CGP74588, and 57.3 ؎ 12.5 h for 14 C radioactivity. Imatinib was predominantly cleared through oxidative metabolism. Approximately 65 and 9% of total systemic exposure [AUC 0-24 h (area under the concentration time curve) of radioactivity] corresponded to imatinib and CGP74588, respectively. The remaining proportion corresponded mainly to oxidized derivatives of imatinib and CGP74588. Imatinib and its metabolites were excreted predominantly via the biliary-fecal route. Excretion of radioactivity was slow with a mean radiocarbon recovery of 80% within 7 days (67% in feces, 13% in urine). Approximately 28 and 13% of the dose in the excreta corresponded to imatinib and CGP74588, respectively.

ABSTRACT:Fingolimod [(FTY720), Gilenya; 2-amino-2-[2-(4-octylphenyl)ethyl]-1,3-propanediol], a new drug for the treatment of relapsing multiple sclerosis, acts through its phosphate metabolite, which modulates sphingosine 1-phosphate receptors. This represents a novel mechanism of action. In the present work, the absorption and disposition of 14 C-labeled fingolimod were investigated in healthy male volunteers after a single oral dose of 4.5 mg. Total radioactivity was determined in blood, urine, and feces. Fingolimod was quantified in blood. Metabolite profiles were determined in blood and excreta, and metabolite structures were elucidated by mass spectrometry, wet-chemical methods, and comparison with reference compounds. Fingolimod was absorbed slowly but almost completely. The biotransformation of fingolimod involved three main pathways: 1) reversible phosphorylation to fingolimod phosphate [(S)-enantiomer, active principle]; 2) -hydroxylation at the octyl chain, catalyzed predominantly by CYP4F enzymes, followed by further oxidation to a carboxylic acid and subsequent ␤-oxidation; and 3) formation of ceramide analogs by conjugation with endogenous fatty acids. This metabolism is quite unusual because it follows metabolic pathways of structurally related endogenous compounds rather than biotransformations typical for xenobiotics. The elimination of fingolimod was slow and occurred predominantly by oxidative metabolism whereas fingolimod phosphate was eliminated mainly by dephosphorylation back to fingolimod. Drug-related material was excreted mostly in the urine in the form of oxidation products.

ABSTRACT:The immunosuppressant macrolide everolimus was found to be metabolized in animals and humans to a phosphocholine ester (ATG181), a hitherto unknown type of conjugate in xenobiotic metabolism. The structure of ATG181 was elucidated by mass spectrometry and confirmed by synthesis. ATG181 was among the most prominent metabolites of everolimus in rat, monkey, and human blood and was found also in various tissues of the rat, whereas no ATG181 was identified in the urine and feces of the species investigated. The metabolite showed binding to FK506 binding protein with a 2-to 3-fold higher affinity than everolimus. However, ATG181 exhibited only marginal in vitro immunosuppressive activity and is therefore very unlikely to contribute in a relevant manner to the immunosuppressive effect of everolimus.