School of Biomedical Sciences, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong, China.
Free Radic Biol Med. 2011 Oct 1;51(7):1365-75. doi: 10.1016/j.freeradbiomed.2011.06.016. Epub 2011 Jun 29.
Colorectal cancer is the second most common cause of cancer death in the world and about half of the patients with colorectal cancer require adjuvant therapy after surgical resection. Therefore, the eradication of cancer cells via chemotherapy constitutes a viable approach to treating patients with colorectal cancer. In this study, the effects of bufalin isolated from a traditional Chinese medicine were evaluated and characterized in HT-29 and Caco-2 human colon cancer cells. Contrary to its well-documented apoptosis-promoting activity in other cancer cells, bufalin did not cause caspase-dependent cell death in colon cancer cells, as indicated by the absence of significant early apoptosis as well as poly(ADP-ribose) polymerase and caspase-3 cleavage. Instead, bufalin activated an autophagy pathway, as characterized by the accumulation of LC3-II and the stimulation of autophagic flux. The induction of autophagy by bufalin was linked to the generation of reactive oxygen species (ROS). ROS activated autophagy via the c-Jun NH(2)-terminal kinase (JNK). JNK activation increased expression of ATG5 and Beclin-1. ROS antioxidants (N-acetylcysteine and vitamin C), the JNK-specific inhibitor SP600125, and JNK2 siRNA attenuated bufalin-induced autophagy. Our findings unveil a novel mechanism of drug action by bufalin in colon cancer cells and open up the possibility of treating colorectal cancer through a ROS-dependent autophagy pathway.
结直肠癌是全球第二大常见癌症死因，大约一半的结直肠癌患者在手术切除后需要辅助治疗。因此，通过化疗消除癌细胞是治疗结直肠癌患者的一种可行方法。在这项研究中，评估并描述了来源于一种传统中药的蟾毒灵在 HT-29 和 Caco-2 人结肠癌细胞中的作用。与在其他癌细胞中已被充分证实的促进凋亡活性相反，蟾毒灵并没有引起结肠癌细胞中 caspase 依赖性细胞死亡，这表明没有明显的早期凋亡以及多聚（ADP-核糖）聚合酶和 caspase-3 切割。相反，蟾毒灵激活了自噬途径，其特征是 LC3-II 的积累和自噬流的刺激。蟾毒灵诱导的自噬与活性氧（ROS）的产生有关。ROS 通过 c-Jun NH(2)-末端激酶（JNK）激活自噬。JNK 激活增加了 ATG5 和 Beclin-1 的表达。ROS 抗氧化剂（N-乙酰半胱氨酸和维生素 C）、JNK 特异性抑制剂 SP600125 和 JNK2 siRNA 减弱了蟾毒灵诱导的自噬。我们的研究结果揭示了蟾毒灵在结肠癌细胞中的一种新的药物作用机制，并为通过 ROS 依赖性自噬途径治疗结直肠癌开辟了可能性。
