The Oxidative Biotransformation of Losoxantrone (CI-941)

Abstract

ABSTRACT: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 highperformance 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 orthoand 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., is a member of the novel class of anthrapyrazole anticancer agents. This cytostatic compound is derived from anthracyclines (e.g., doxorubicin and daunorubicin) and mitoxantrone by chromophore modification of the anthracene-9,10-dione unit. In clinical trials (phase I and II), losoxantrone has been shown to be the most powerful anthrapyrazole. It was developed with the intention of diminishing the cardiotoxicity associated with anthracene-9,10-dione drugs. The cardiotoxicity represents the dosis-limiting side effect and is induced by free radicals created during the biotransformation of anthraquinonoid antitumor agents (Murdock et al., 1979;Smith, 1983;Zee-Cheng and Cheng, 1983) (Fig. 1).Both the synthetic preparation and the exceptional in vivo anticancer activity of losoxantrone are well known (Lown, 1983;Showalter et al., 1987;Reszka et al., 1988;Beylin et al., 1989;Fry, 1991;Calvert et al., 1994;Zhang et al., 1994). Several clinical studies of combination regimens with losoxantrone and paclitaxel in patients with advanced breast cancer were recently completed (Kaufman et al., 1998(Kaufman et al., , 1999Diab et al., 1999). Furthermore, the results of a phase II clinical trail in hormone-refractory metastatic prostate cancer were published (Huan et al., 2000).The antitumor activity of losoxantrone, among other biochemical effects against tumor cells, is based on inhibiting the enzyme topoisomerase II (Fry, 1991;Leteurtre et al., 1994). Although numerous studies analyzing the pharmacokinetic behavior of the drug under various conditions were published, the metabolism of anthrapyrazole CI-941 is almost unknown until now. Only a small part of the CI-941 biotransformation, proved by metabolites in human urine Richards and Sun, 1995) and feces (Joshi et al., 2001), was ...

<p>Metabolite Profiling in Anticancer Drug Development: A Systematic Review</p>

“…Not evaluated [43] (Continued) Not evaluated [66] (Continued) efficiency over other methods such as radioimmunoassay (RIA), gas chromatography/mass spectrometry (GC/MS), 44 and liquid chromatography (LC) with ultraviolet detection (UV), 19,76 fluorescence, 34,45 radioactivity 38,81 and mass spectrometry (MS) 13,18,64 detection. Most of the works in metabolite analysis were carried out using triple-quadrupole mass spectrometers.…”

“…Carbendazim [18] Apoptotic induction, Antitumor (Solid tumor) CI-941(losoxantrone) [19] Anticancer females. 100 In rat liver, the expression level of CYP2C12 is higher in females than males, while the level of CYP2C11 is higher in males than females.…”

Metabolism of Ebracteolata Compound B Studied In Vitro with Human Liver Microsomes, HepG2 Cells, and Recombinant Human Enzymes

“…In addition, compared with primary human hepatocytes, HepG2 is a relatively easy-to-handle tool. Accordingly, HepG2 is frequently used for human biotransformation studies (Renner et al, 2002;Yamamoto et al, 2002;Asai et al, 2004;Lançon et al, 2007).…”