TY - JOUR T1 - Identification and Quantitation of the <em>N</em>-Acetyl-L-cysteine <em>S</em>-Conjugates of Bendamustine and Its Sulfoxides in Human Bile after Administration of Bendamustine Hydrochloride JF - Drug Metabolism and Disposition JO - Drug Metab Dispos SP - 292 LP - 301 DO - 10.1124/dmd.108.022855 VL - 37 IS - 2 AU - Jens Teichert AU - Reinhard Sohr AU - Lothar Hennig AU - Frank Baumann AU - Konrad Schoppmeyer AU - Ulrich Patzak AU - Rainer Preiss Y1 - 2009/02/01 UR - http://dmd.aspetjournals.org/content/37/2/292.abstract N2 - We recently reported the detection of mercapturic acid pathway metabolites of bendamustine, namely, cysteine S-conjugates in human bile, which are supposed to subsequently undergo further metabolism. In this study, we describe the identification and quantitation of consecutive bendamustine metabolites occurring in human bile using authentic reference standards and the synthesis and structural confirmation of these compounds. Mass spectrometry data along with high-performance liquid chromatography retention data (fluorescence detection) of the synthetic reference standards were consistent with those of the metabolites found in human bile after administration of bendamustine hydrochloride to cancer patients. Analysis of the purified synthetic reference compounds showed a purity of at least 95%. Structural confirmation was achieved by one- and two-dimensional proton as well as carbon-13 NMR spectroscopy and mass spectrometry. A total of 16 bendamustine-related compounds were detected in the bile of patients, 11 of them were recovered as conjugates. Eight conjugates have been structurally confirmed as novel mercapturic acids and sulfoxides. Biliary excretion of the sulfoxides was twice that of the mercapturate precursors. Glutathione S-conjugates of bendamustine have not been detected in bile samples, indicating rapid enzymatic cleavage in humans. Both the lack of glutathione (GSH) conjugates and occurrence of diastereomeric sulfoxides emphasize species-related differences in the GSH conjugation of bendamustine between humans and rats. The total amount recovered in the bile as the sum of all conjugates over the period of 24 h after dosing averaged 5.2% of the administered dose. The question of whether the novel metabolites contribute to urinary excretion should be a target of future investigations. The American Society for Pharmacology and Experimental Therapeutics ER -