title: Cellular and biochemical mechanisms of the resistance of human cancer cells to a new anticancer ribo-nucleoside, TAS-106.
abstract: We have established variants of DLD-1 human colon carcinoma and HT-1080 human fibrosarcoma cells resistant to the new anticancer ribo-nucleosides, 1-(3-C-ethynyl-beta-D-ribo-pentofuranosyl)-cytosine (ECyd, TAS-106) and 1-(3-C-ethynyl-beta-D-ribo-pentofuranosyl)uracil (EUrd). Both variants were shown to have decreased (3- to 24-fold decrease) uridine-cytidine kinase (UCK) activity, and exhibited cross-resistance to EUrd and TAS-106. Based on the IC(50) values determined by chemosensitivity testing, a 41- to 1102-fold resistance to TAS-106 was observed in the resistant cells. TAS-106 concentration-dependently inhibited RNA synthesis, while its effect on DNA synthesis was negligible. The degree of resistance (14- to 3628-fold resistance) calculated from the inhibition of RNA synthesis tended to be close to the degree of chemoresistance of tested cells to TAS-106. The experiments on the intracellular metabolism of TAS-106 in the parental cells revealed a rapid phosphorylation to its nucleotides, particularly the triphosphate (ECTP), its major active metabolite. The amount of TAS-106 transported into the resistant cells was markedly reduced and the intracellular level of ECTP was decreased from 1/19 to below the limit of detection; however, the unmetabolized TAS-106 as a percentage of the total metabolite level was high as compared with the parental cells. The ratio of the intracellular level of ECTP between parental and resistant cells tended to approximate to the degree of resistance calculated from the inhibitory effect on RNA synthesis. These results indicate that the TAS-106 sensitivity of cells is correlated with the intracellular accumulation of ECTP, which may be affected by both the cellular membrane transport mechanism and UCK activity.
authors: Hanno Research Center, Taiho Pharmaceutical Co., Ltd., Hanno, Saitama 357-8527, Japan. simamoto@taiho.co.jp
authors: Yuji
authors: Y
authors: Shimamoto
authors: Hiromi
authors: H
authors: Kazuno
authors: Yuko
authors: Y
authors: Murakami
authors: Atsushi
authors: A
authors: Azuma
authors: Katsuhisa
authors: K
authors: Koizumi
authors: Akira
authors: A
authors: Matsuda
authors: Takuma
authors: T
authors: Sasaki
authors: Masakazu
authors: M
authors: Fukushima
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D001692:Biological Transport; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D003562:Cytidine / Q000031:analogs & derivatives* / Q000494:pharmacology*; D004247:DNA / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D019008:Drug Resistance, Neoplasm; D006801:Humans; D020128:Inhibitory Concentration 50; D008954:Models, Biological; D008956:Models, Chemical; D009703:Nucleoside-Phosphate Kinase / Q000378:metabolism; D010766:Phosphorylation; D012313:RNA / Q000378:metabolism; D013997:Time Factors; D014541:Uridine Kinase / Q000378:metabolism*
chemical_list: C103084:1-(3-C-ethynylribopentofuranosyl)cytosine; D000970:Antineoplastic Agents; D003562:Cytidine; D012313:RNA; D004247:DNA; D014541:Uridine Kinase; C019979:cytidylate kinase; D009703:Nucleoside-Phosphate Kinase