Much evidence indicates that various naturally occurring compounds have an anti-cancer effect, but the detailed mechanisms are not well understood. In this study, we selected anti-cancer phytochemicals such as epigallocatechin-3-gallate (EGCG), resveratrol (RES) and α-mangostin (α-M), all of which are well-characterized chemopreventive agents. We sought to elucidate the mechanism of their anti-cancer effects and the synergistic effects obtained by combined treatment with the anti-cancer drug 5-fluorouracil (5-FU) in three human colon cancer cell lines. The numbers of viable cells were consistently decreased by the treatment with EGCG, RES or α-M at more than 10 μM in all three cell lines tested. All compounds mainly induced apoptosis and suppressed the PI3K/Akt signaling pathway. Additionally, α-M, which had the greatest PI3K/Akt-suppressing activity, also suppressed MAP kinase (MAPK)/Erk1/2 signaling. Importantly, the combination treatment with RES and 5-FU induced a remarkably synergistic enhancement of growth inhibition and apoptosis through the additional suppression of the MAPK/Erk1/2 signaling pathway in colon cancer DLD-1 cells. Interestingly, RES increased the intracellular expression level of miR-34a, which down-regulated the target gene E2F3 and its downstream Sirt1, resulting in growth inhibition. These findings indicate that these compounds functioned as chemosensitizers when combined with anti-cancer drugs through the modulation of apoptotic and growth-related signaling pathways. Also, RES exerted its anti-cancer activity in part through a newly defined mechanism, i.e., the miR-34a/E2F3/Sirt1 cascade.

译文

许多证据表明,各种天然存在的化合物具有抗癌作用,但详细的机制尚不清楚。在这项研究中,我们选择了抗癌植物化学物质,例如epigallocatechin-3-gallate (EGCG),白藜芦醇 (RES) 和 α-甘露素 (α-M),它们都是特征良好的化学预防剂。我们试图阐明其抗癌作用的机制以及通过与抗癌药物5-氟尿嘧啶 (5-FU) 联合治疗在三种人结肠癌细胞系中获得的协同作用。在所有测试的三种细胞系中,通过使用超过10μm的EGCG,RES或 α-M处理,活细胞的数量持续减少。所有化合物均主要诱导细胞凋亡并抑制PI3K/Akt信号通路。此外,具有最大PI3K/Akt抑制活性的 α-M也抑制了MAP激酶 (MAPK)/Erk1/2信号传导。重要的是,RES和5-FU的联合治疗通过额外抑制结肠癌DLD-1细胞中的MAPK/Erk1/2信号通路,诱导生长抑制和凋亡的显著协同增强。有趣的是,RES增加了miR-34a的细胞内表达水平,从而下调了靶基因E2F3及其下游Sirt1,从而导致生长抑制。这些发现表明,当这些化合物与抗癌药物结合时,通过调节凋亡和与生长相关的信号通路发挥化学增敏作用。此外,RES部分地通过新定义的机制,即miR-34a/E2F3/Sirt1级联发挥其抗癌活性。

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