Department of Biochemistry, College of Natural Sciences, Kangwon National University, Chuncheon, Korea.
Oncol Rep. 2010 Jan;23(1):229-37.
Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a promising candidate for cancer therapeutics due to its ability to induce apoptosis selectively in cancer cells. However, sensitivity of cancer cells for induction of apoptosis by TRAIL varies considerably. Therefore, it is important to develop agents that overcome this resistance. We show, for the first time, that eupatolide, the sesquiterpene lactone isolated from the medicinal plant Inula britannica, sensitizes human breast cancer cells to TRAIL-induced apoptosis. Treatment with TRAIL in combination with subtoxic concentrations of eupatolide enhanced the TRAIL-induced cytotoxicity in MCF-7, MDA-MB-231 and MDA-MB-453 breast cancer cells, whereas each reagent alone slightly induced cell death. The combination induced sub-G1 phase DNA content and annexin V-staining in MCF-7 cells, which are major features of apoptosis. Apoptotic characteristics induced by the combined treatment were significantly inhibited by a pan-caspase inhibitor. The sensitization to TRAIL-induced apoptosis was accompanied by the activation of caspase-8 and was concomitant with Bid and poly(ADP-ribose) polymerase (PARP) cleavage. Treatment of eupatolide alone significantly down-regulated the expression of cellular FLICE inhibitory protein (c-FLIP) in MCF-7 cells. Furthermore, enforced expression of c-FLIP significantly attenuated the apoptosis induced by this combination in MCF-7 cells, suggesting a key role for c-FLIP down-regulation in these events. We also observed that euaptolide inhibited AKT phosphorylation in a dose- and time-dependent manner. Moreover, inhibition of Akt by LY294002, a specific PI3K inhibitor, down-regulated c-FLIP expression in MCF-7 cells. Taken together, these results indicate that eupatolide could augment TRAIL-induced apoptosis in human breast cancer cells by down-regulating c-FLIP expression through the inhibition of AKT phosphorylation and be a valuable compound to overcome TRAIL resistance in breast cancer cells.
肿瘤坏死因子相关凋亡诱导配体（TRAIL）是一种很有前途的癌症治疗候选药物，因为它能够选择性地诱导癌细胞凋亡。然而，癌细胞对 TRAIL 诱导凋亡的敏感性差异很大。因此，开发克服这种耐药性的药物非常重要。我们首次表明，从药用植物旋覆花中分离得到的倍半萜内酯艾蒲醇能够使人类乳腺癌细胞对 TRAIL 诱导的凋亡敏感。用 TRAIL 联合亚毒性浓度的艾蒲醇处理 MCF-7、MDA-MB-231 和 MDA-MB-453 乳腺癌细胞，增强了 TRAIL 诱导的细胞毒性，而单独使用每种试剂则轻微诱导细胞死亡。联合处理诱导 MCF-7 细胞出现亚 G1 期 DNA 含量和膜联蛋白 V 染色，这是凋亡的主要特征。联合处理诱导的凋亡特征被泛半胱天冬酶抑制剂显著抑制。对 TRAIL 诱导的凋亡的敏感性增加伴随着 caspase-8 的激活，并伴有 Bid 和多聚（ADP-核糖）聚合酶（PARP）的切割。艾蒲醇单独处理可显著下调 MCF-7 细胞中细胞 FLICE 抑制蛋白（c-FLIP）的表达。此外，c-FLIP 的强制表达显著减弱了该组合在 MCF-7 细胞中诱导的凋亡，表明 c-FLIP 的下调在这些事件中起关键作用。我们还观察到，艾蒲醇以剂量和时间依赖的方式抑制 AKT 磷酸化。此外，PI3K 抑制剂 LY294002 抑制 Akt 可下调 MCF-7 细胞中 c-FLIP 的表达。综上所述，这些结果表明，艾蒲醇通过抑制 AKT 磷酸化下调 c-FLIP 的表达，可增强人乳腺癌细胞中 TRAIL 诱导的凋亡，并可能成为克服乳腺癌细胞中 TRAIL 耐药性的有价值化合物。
