Vol. 30, Issue 4, 464-478, April 2002

The Oxidative Biotransformation of Losoxantrone (CI-941)

Ulf D. Renner, Georgios Piperopoulos, Rolf Gebhardt, Gerhard Ehninger, and Klaus-Peter Zeller

Medizinische Klinik I, Universitätsklinikum Carl Gustav Carus, Dresden, Germany (U.D.R., G.E.); Institut für Organische Chemie, Eberhard-Karls-Universität Tübingen, Tübingen, Germany (U.D.R., G.P., K.-P.Z.); and Institut für Biochemie, Universität Leipzig, Leipzig, Germany (R.G.)

The oxidative biotransformation of the anticancer drug 7-hydroxy-2-[2-[(2-hydroxyethyl)amino]ethyl]-5-[[2-[(2-hydroxyethyl)amino]ethyl]amino]anthra[1,9-cd]pyrazol-6(2H)-one dihydrochloride (losoxantrone, CI-941) after incubation of primary cultures of rat hepatocytes has been investigated. The structures of twelve losoxantrone metabolites have been elucidated by means of high-performance liquid chromatography-mass spectometry, tandem mass spectrometry, and two-dimensional NMR. In these mammalian hepatocytes, the CI-941 biotransformation includes a monohydroxylation of the phenolic substructure of the CI-941-chromophore via cytochrome P450 catalysis, resulting in metabolites having an ortho- and para-hydroquinonoid substructure, respectively. The identification of a glutathione conjugate as a follow-up metabolite confirms the oxidative activation of the ortho-hydroxylated losoxantrone metabolite. The oxidative activation establishes the ability of CI-941 to form covalent bonds to intracellular nucleophilic targets. Furthermore, the CI-941 metabolism was shown to be extremely suppressed in rat hepatocytes incubated with metyrapone. In contrast to these results, human tumor HepG2 cells did not show any CI-941 biotransformation after incubation.