Key Laboratory for Molecular Enzymology, Engineering of the Ministry of Education, Jilin University, Changchun, China.
Mol Carcinog. 2010 Jul;49(7):630-40. doi: 10.1002/mc.20638.
We examined whether betulin, a naturally abundant compound, has anticancer functions in human cancer cells. The results showed that betulin significantly inhibited cell viability in cervix carcinoma HeLa cells, hepatoma HepG2 cells, lung adenocarcinoma A549 cells, and breast cancer MCF-7 cells with IC(50) values ranging from 10 to 15 microg/mL. While betulin exhibited only moderate anticancer activity in other human cancer cells such as hepatoma SK-HEP-1 cells, prostate carcinoma PC-3, and lung carcinoma NCI-H460, with IC(50) values ranging from 20 to 60 microg/mL, it showed minor growth inhibition in human erythroleukemia K562 cells (IC(50) > 100 microg/mL). We further investigated the mechanism of anticancer activity by betulin, using HeLa cells as an experimental model. Betulin (10 microg/mL) induces apoptotic cell death, as evidenced by morphological characteristics such as membrane phosphatidylserine translocation, nuclear condensation/fragmentation, and apoptotic body formation. A kinetics analysis showed that the depolarization of mitochondrial membrane potential and the release of mitochondrial cytochrome c occurred as early as 30 min after treatment with betulin. Betulin, unlike its chemical derivative betulinic acid, did not directly trigger mitochondrial cytochrome c release in isolated mitochondria. Importantly, Bax and Bak were rapidly translocated to the mitochondria 30 min after betulin treatment. The sequential activation of caspase-9 and caspase-3/-7 and the cleavage of poly(ADP-ribose) polymerase (PARP) were observed behind those mitochondrial events. Furthermore, specific downregulation of either caspase-9, Bax, or Bak by siRNA effectively reduced PARP cleavage and caspase-3 activation. Taken together, the lines of evidence demonstrate that betulin triggers apoptosis of human cancer cells through the intrinsic apoptotic pathway.
我们研究了桦木醇（一种天然存在的丰富化合物）在人类癌细胞中的抗癌功能。结果表明，桦木醇显著抑制宫颈癌 HeLa 细胞、肝癌 HepG2 细胞、肺腺癌 A549 细胞和乳腺癌 MCF-7 细胞的细胞活力，IC50 值在 10 到 15 微克/毫升之间。虽然桦木醇在其他人类癌细胞（如肝癌 SK-HEP-1 细胞、前列腺癌 PC-3 和肺癌 NCI-H460）中的抗癌活性仅为中度，IC50 值在 20 到 60 微克/毫升之间，但它对人类红白血病 K562 细胞的生长抑制作用较小（IC50 > 100 微克/毫升）。我们进一步研究了桦木醇的抗癌活性机制，以 HeLa 细胞为实验模型。桦木醇（10 微克/毫升）诱导细胞凋亡死亡，这表现为膜磷酯酰丝氨酸易位、核浓缩/碎裂和凋亡小体形成等形态特征。动力学分析表明，线粒体膜电位去极化和线粒体细胞色素 c 释放早在桦木醇处理 30 分钟后就发生了。与化学衍生物桦木酸不同，桦木醇不会直接触发分离的线粒体中线粒体细胞色素 c 的释放。重要的是，Bax 和 Bak 在桦木醇处理 30 分钟后迅速转运到线粒体。在线粒体事件之后，观察到 caspase-9 和 caspase-3/-7 的顺序激活以及聚（ADP-核糖）聚合酶（PARP）的裂解。此外，siRNA 特异性下调 caspase-9、Bax 或 Bak 有效减少了 PARP 裂解和 caspase-3 激活。总之，这些证据表明桦木醇通过内在的凋亡途径触发人类癌细胞的凋亡。
