title: Possible antitumor activity of 1-(3-C-ethynyl-beta-D-ribo-pentofuranosyl)cytosine (ECyd, TAS-106) against an established gemcitabine (dFdCyd)-resistant human pancreatic cancer cell line.
abstract: We established a variant of MIAPaCa-2 human pancreatic cancer cells that is resistant to 2',2'-difluorodeoxycytidine (gemcitabine, dFdCyd), MIAPaCa-2/dFdCyd, and elucidated the biochemical characteristics and mechanism of dFdCyd-resistance in these cells. We also evaluated 1-(3-C-ethynyl-beta-D-ribo-pentofuranosyl)cytosine (ECyd, TAS-106, RNA polymerase inhibitor), a new anticancer ribonucleoside, for antitumor activity against the resistant cells in vitro and in vivo. MIAPaCa-2/dFdCyd cells were 2541-fold more resistant to dFdCyd than parental MIAPaCa-2 cells, and the major mechanism of the dFdCyd-resistance was found to be a decrease in the intracellular pool of dFdCyd and its active metabolites, which would result in a decrease in incorporation of dFdCyd triphosphate into DNA. This finding was confirmed by the discovery of decreased deoxycytidine kinase activity, increased cytidine deaminase and ribonucleotide reductase activity, and increased 5'-nucleotidase mRNA expression in the MIAPaCa-2/dFdCyd cells. The cytotoxicity of TAS-106 as an antitumor nucleoside analog was similar in both parental and dFdCyd-resistant cells, with IC(50) values of 6.25 and 6.27 nM, respectively, and this finding was supported by similar intracellular uptake and metabolism of TAS-106 in both cell lines. We also evaluated the in vivo antitumor activity of TAS-106 against MIAPaCa-2 and dFdCyd-resistant MIAPaCa-2/dFdCyd tumors implanted into nude mice. The tumor growth inhibition rate of weekly additions of TAS-106 (7 mg/kg, iv) against parental and dFdCyd-resistant tumors was 73% and 76%, respectively, while that of dFdCyd administered twice a week (240 mg/kg, iv) was 84% and 34%, respectively. These results suggest that TAS-106 would contribute to the treatment of patients with advanced pancreatic carcinomas in whom dFdCyd-based chemotherapy has failed.
authors.affiliation: Advanced Research Laboratory, Hanno Research Center, Taiho Pharmaceutical Co., Hanno-city, Saitama 357-8527, Japan. h-kazuno@taiho.co.jp
authors.forename: Hiromi
authors.initials: H
authors.lastname: Kazuno
authors.forename: Kazuki
authors.initials: K
authors.lastname: Sakamoto
authors.forename: Akio
authors.initials: A
authors.lastname: Fujioka
authors.forename: Masakazu
authors.initials: M
authors.lastname: Fukushima
authors.forename: Akira
authors.initials: A
authors.lastname: Matsuda
authors.forename: Takuma
authors.initials: T
authors.lastname: Sasaki
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D045744:Cell Line, Tumor; D003562:Cytidine / Q000031:analogs & derivatives* / Q000494:pharmacology*; D003841:Deoxycytidine / Q000031:analogs & derivatives* / Q000494:pharmacology*; D003854:Deoxyribonucleotides / Q000378:metabolism; D019008:Drug Resistance, Neoplasm; D006801:Humans; D020128:Inhibitory Concentration 50; D008297:Male; D051379:Mice; D008819:Mice, Nude; D010190:Pancreatic Neoplasms / Q000188:drug therapy / Q000201:enzymology / Q000235:genetics / Q000473:pathology*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012265:Ribonucleotides / Q000378:metabolism; D023041:Xenograft Model Antitumor Assays; D000093542:Gemcitabine
chemical_list: C103084:1-(3-C-ethynylribopentofuranosyl)cytosine; D000970:Antineoplastic Agents; D003854:Deoxyribonucleotides; D012333:RNA, Messenger; D012265:Ribonucleotides; D003841:Deoxycytidine; D003562:Cytidine; D000093542:Gemcitabine