title: Metabolic activation of zebularine, a novel DNA methylation inhibitor, in human bladder carcinoma cells.
abstract: Zebularine (2(1H)-pyrimidinone riboside, Zeb), a synthetic analogue of cytidine that is a potent inhibitor of cytidine deaminase, has been recently identified as a general inhibitor of DNA methylation. This inhibition of DNA methyltransferase (DNMT) is hypothesized to be mechanism-based and result from formation of a covalent complex between the enzyme and zebularine-substituted DNA. Metabolic activation of Zeb thus requires that it be phosphorylated and incorporated into DNA. We have quantitatively assessed the phosphorylation and DNA incorporation of Zeb in T24 cells using 2-[(14)C]-Zeb in conjunction with gradient anion-exchange HPLC and selected enzymatic and spectroscopic analyses. The corresponding 5'-mono-, di- and triphosphates of Zeb were readily formed in a dose- and time-dependent manner. Two additional Zeb-containing metabolites were tentatively identified as diphosphocholine (Zeb-DP-Chol) and diphosphoethanolamine adducts. Intracellular concentrations of Zeb-TP and Zeb-DP-Chol were similar and greatly exceeded those of other metabolites. DNA incorporation occurred but was surpassed by that of RNA by at least seven-fold. Equivalent levels and similar intracellular metabolic patterns were also observed in the Molt-4 (human T-lymphoblasts) and MC38 (murine colon carcinoma) cell lines. For male BALB/c nu/nu mice implanted s.c. with the EJ6 variant of T24 bladder carcinoma and treated i.p. with 500mg/kg 2-[(14)C]-Zeb, the in vivo phosphorylation pattern of Zeb in tumor tissue examined 24h after drug administration was similar to that observed in vitro. The complex metabolism of Zeb and its limited DNA incorporation suggest that these are the reasons why it is less potent than either 5-azacytidine or 5-aza-2'-deoxycytidine and requires higher doses for equivalent inhibition of DNMT.
authors.affiliation: Department of Clinical Pharmacology, Faculty of Health Sciences, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel.
authors.forename: Tsipi
authors.initials: T
authors.lastname: Ben-Kasus
authors.forename: Zvi
authors.initials: Z
authors.lastname: Ben-Zvi
authors.forename: Victor E
authors.initials: VE
authors.lastname: Marquez
authors.forename: James A
authors.initials: JA
authors.lastname: Kelley
authors.forename: Riad
authors.initials: R
authors.lastname: Agbaria
mesh_terms: D000818:Animals; D001711:Biotransformation; D002455:Cell Division / Q000187:drug effects; D045744:Cell Line, Tumor; D003562:Cytidine / Q000031:analogs & derivatives* / Q000493:pharmacokinetics* / Q000494:pharmacology; D004247:DNA / Q000378:metabolism; D019175:DNA Methylation / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000493:pharmacokinetics*; D006801:Humans; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D010766:Phosphorylation; D012313:RNA / Q000378:metabolism; D001749:Urinary Bladder Neoplasms / Q000378:metabolism* / Q000473:pathology
chemical_list: D004791:Enzyme Inhibitors; D003562:Cytidine; D012313:RNA; C009131:pyrimidin-2-one beta-ribofuranoside; D004247:DNA