P-24 薬用植物由来MEK核外移行阻害物質(ポスター発表の部)

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MEK is a member of MAPK cascade playing an important role of cell proliferation. MEK is anchored in cytosol because of contained specific amino acid sequence called as NES with the aid of carrier protein CRM1. Nuclear export of MEK is essential stage for signal transduction of MAPK cascade and MEK was reported to be activated potently in many cancer cell lines, thus inhibitors for nuclear export of MEK would be anti-tumor seed candidates. In this context, we have searched for inhibitors for nuclear export of MEK from medicinal plants. By using the fission yeast expressing fusion protein NES-GFP-NLS for bioassay, 1'-acetoxychavicol acetate (1) and valtrate (2) were isolated as active principles. The mechanism of action of 1 and 2 were analyzed by use of biotinylated probe (3) derived from leptomycin B. A competitive experiment between each inhibitor and 3 revealed that both 1 and 2 bound to the SH group of 529-Cys in CRM1 to inhibit nuclear export of MEK through NES antagonism in the same fashion as leptomycin B. Additionally, the reactants of N-acetyl-L-cystein methyl ester with 1 or 2 clarified respective pharmacophore to be the 1-acetoxy-2-ene and epoxy moiety. As a result of evaluation of cytotoxicity of 1 and 2 against four tumor cell lines, they exhibited the selective growth inhibition against tumor cell lines with enhanced MEK activity. In order to explore inhibitors for MEK nuclear export through NES non-antagonistic mode, we surveyed the extracts of medicinal plants, showing little activity in the fission yeast assay, by detecting localization of MEK in HeLa cells directly by indirect fluorescent antibody method. Consequently, we found two kaurenols (4, 5) and a new principle named peumusolide A (6) as inhibitors for MEK nuclear export. The gross structure of 6 was constructed from HRFAB-MS, IR, NMR and correlation between H-3 and H-7 on NOESY determined E configuration double bond attached lactone ring. The position of olefin in side chain was clarified by analysis for EI-MS of bismethylsulfide derivative and chemical degradation to 1-pentanol. In addition, these active principles were confirmed not to affect the nuclear export of NES-contained fusion protein in yeast. A competitive experiment was also conducted for three compounds (4, 5, and 6) in the presence of the biotinylated probe (3). No interference for the binding of probe (3) to 529-Cys in CRM1 established these compounds to inhibit the nuclear export of MEK through NES non-antagonistic mode. In the cytotoxicity test, 6 displayed selective cytotoxicity for MEK activated tumor cells, however 4 showed little selectivity.
天然有機化合物討論会の論文
2005-09-15

P-24 薬用植物由来MEK核外移行阻害物質(ポスター発表の部)

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