title: Inhibitory mechanisms of 1-(3-C-ethynyl-beta-D-ribopentofuranosyl)uracil (EUrd) on RNA synthesis.
abstract: 1-(3-C-ethynyl-beta-D-ribo-pentofuranosyl)uracil (EUrd) is an antimetabolite that strongly inhibits RNA synthesis and shows a broad antitumor activity in vitro and in vivo. In mouse mammary tumor FM3A cells, EUrd is sequentially phosphorylated to its 5'-triphosphate, EUTP, a major metabolite, and the RNA synthesis is inhibited proportionally to its intracellular accumulation. To study the inhibitory mechanisms of EUrd on RNA synthesis, we have performed the kinetic analysis of EUTP on RNA polymerization using isolated nuclei RNA synthesis was inhibited competitively by EUTP. The inhibition constant, Ki was much lower than the Km value of UTP (Ki value of EUTP, 84 nM; Km value of UTP, 13 microM), indicating that the high affinity of EUTP could contribute to the specific inhibition of RNA synthesis. As a result of RNA synthesis inhibition, EUrd, but not ara-C, induced shrinkage of nucleoli, which are the main sites for RNA synthesis in FM3A cells. Thus, the strong affinity of EUTP to RNA polymerase and specific inhibition of RNA synthesis could contribute to its antitumor effect. EUrd is expected to be a new antitumor drug, possessing a strong inhibitory effect on the synthesis of RNA.
authors.affiliation: Faculty of Pharmaceutical Sciences, Okayama University, Okayama, Japan.
authors.forename: Tatsushi
authors.initials: T
authors.lastname: Yokogawa
authors.forename: Tomoharu
authors.initials: T
authors.lastname: Naito
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Kanda
authors.forename: Satoshi
authors.initials: S
authors.lastname: Takatori
authors.forename: Kiyoko
authors.initials: K
authors.lastname: Takenaka
authors.forename: Takuma
authors.initials: T
authors.lastname: Sasaki
authors.forename: Akira
authors.initials: A
authors.lastname: Matsuda
authors.forename: Masakazu
authors.initials: M
authors.lastname: Fukushima
authors.forename: Hye-Sook
authors.initials: HS
authors.lastname: Kim
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Wataya
mesh_terms: D000818:Animals; D045744:Cell Line, Tumor; D005260:Female; D007700:Kinetics; D051379:Mice; D019384:Nucleic Acid Synthesis Inhibitors / Q000378:metabolism / Q000494:pharmacology*; D012313:RNA / Q000096:biosynthesis* / Q000378:metabolism; D014529:Uridine / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology
chemical_list: C103085:1-(3-C-ethynylribopentofuranosyl)uracil; D019384:Nucleic Acid Synthesis Inhibitors; D012313:RNA; D014529:Uridine