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Featured researches published by Akio Hayashi.
Nuclear Medicine and Biology | 2003
Jun Toyohara; Akio Hayashi; Mikiko Sato; Akie Gogami; Hiromichi Tanaka; Kazuhiro Haraguchi; Yuichi Yoshimura; Hiroki Kumamoto; Yoshiharu Yonekura; Yasuhisa Fujibayashi
The aim of this study was to determine the most suitable iodonucleoside analogs for use in tissue proliferation imaging by means of single photon emission tomography (SPECT). In this study, 5-[(125)I]iodo-(2-deoxy-2-fluoro-4-thio-beta-D-arabinofuranosyl)uracil ([(125)I]FITAU, 1E) and 5-[(125)I]iodo-1-methyl-(2-deoxy-2-bromo-beta-D-arabinofuranosyl)uracil ([(125)I]IMBAU, 1F) were synthesized and their biological data were compared with previously published results regarding 4-thio nucleoside analogs and the reference compound 5-[(125)I]iodo-(2-deoxy-2-fluoro-beta-D-arabinofuranosyl)uracil ([(125)I]FIAU, 1D). 5-Iodo-(2-deoxy-2-fluoro-beta-D-arabinofuranosyl)uracil (FIAU, 2D), 5-iodo-(2-deoxy-2-fluoro-4-thio-beta-D-arabinofuranosyl)uracil (FITAU, 2E), and 5-iodo-1-methyl-(2-deoxy-2-bromo-beta-D-arabinofuranosyl)uracil (IMBAU, 2F) were successfully labeled with (125)I and their in vitro cytosolic thymidine kinase (TK(1)) phosphorylation, recombinant thymidine phosphorylase enzymatic catabolism, TK(1)-dependent cell uptake, and in vivo biodistribution in normal mice were evaluated. Five compounds (1B, 1C, 1D, 1E, and 1F) were stable against C-N glycoside degradation induced by recombinant thymidine phosphorylase. However, 5-[(125)I]iodo-2-deoxyuridine ([(125)I]IUdR, 1A) was not shown to be stable against such degradation. The TK(1) assay showed that [(125)I]FIAU (1D) expressed 16% of the phosphorylation potential of [(125)I]IUdR (1A). Furthermore, [(125)I]FITAU (1E) was shown to have reduced phosphorylation potential, in comparison with that of [(125)I]IUdR (1A) (<0.01). [(125)I]IMBAU (1F) did not show any phosphorylation. In vitro cell uptake and in vivo proliferation-selective uptake of each nucleoside was largely dependent on its potential as a TK(1) substrate. Neither [(125)I]FITAU (1E) nor [(125)I]IMBAU (1F) were shown to have distinct TK(1)-dependent cell uptake and retention in the proliferating tissues. From these results, we concluded that [(125)I]FITAU (1E) and [(125)I]IMBAU (1F) are not effective as imaging agents of cell proliferation. The biological data obtained with these nucleosides were compared, and requirements for the design of pharmaceutically useful radioiodinated nucleoside analogs were also considered.
The Journal of Nuclear Medicine | 2002
Jun Toyohara; Akio Hayashi; Mikiko Sato; Hiromichi Tanaka; Kazuhiro Haraguchi; Yuichi Yoshimura; Yoshiharu Yonekura; Yasuhisa Fujibayashi
The Journal of Nuclear Medicine | 2003
Jun Toyohara; Akie Gogami; Akio Hayashi; Yoshiharu Yonekura; Yasuhisa Fujibayashi
Archive | 2002
Jun Toyohara; Akio Hayashi
Nuclear Medicine and Biology | 2006
Jun Toyohara; Akio Hayashi; Akie Gogami; Yasuhisa Fujibayashi
Nuclear Medicine and Biology | 2006
Jun Toyohara; Akio Hayashi; Akie Gogami; Masahiro Hamada; Yoshio Hamashima; Takahiro Katoh; Manabu Node; Yasuhisa Fujibayashi
Nuclear Medicine and Biology | 2006
Jun Toyohara; Akio Hayashi; Akie Gogami; Yasuhisa Fujibayashi
Archive | 2006
Jun Toyohara; Akio Hayashi
The Journal of Nuclear Medicine | 2012
Norihito Nakata; Yuki Okumura; Eriko Nagata; Masato Kiriu; Akio Hayashi; Ken-ichi Nishijima; Songji Zhao; Nagara Tamaki; Yuji Kuge; Hiroki Matsumoto
Society of Nuclear Medicine Annual Meeting Abstracts | 2006
Jun Toyohara; Akio Hayashi; Akie Gogami; Masahiro Hamada; Yoshio Hamashima; Takahiro Kato; Manabu Node; Yasuhisa Fujibayashi