Yamaguchi Hirohito, Paranawithana Shanthi R, Lee Michael W, Huang Ziwei, Bhalla Kapil N, Wang Hong-Gang
Drug Discovery Program, H. Lee Moffitt Cancer Center and Research Institute, Tampa, Florida 33612, USA.
Cancer Res. 2002 Jan 15;62(2):466-71.
Epothilone B is a novel nontaxane antimicrotubule agent that is active even against paclitaxel (Taxol)-resistant cancer cells. The present study further explores the mechanisms underlying epothilone B-mediated cytotoxicity in human breast cancer cells. We show that BMS-247550 (EpoB), a novel epothilone B analogue, induces cell cycle arrest at the G(2)-M phase transition and subsequent apoptotic cell death of MDA-MB-468 (468) cells. Treating cells with EpoB triggers a conformational change in the Bax protein and its translocation from the cytosol to the mitochondria, which is accompanied by cytochrome c release from the inter-membrane space of mitochondria into the cytosol. Overexpression of Bcl-2 delays Bax conformational change, cytochrome c release, and apoptosis induced by EpoB. Conversely, the Bcl-2 antagonist Bak-BH3 peptide or HA14-1 compound abrogates the antiapoptotic effects of Bcl-2 and enhances apoptosis of 468 cells pretreated with EpoB (to induce mitotic arrest). In synchronized 468 cells, EpoB is more potent in inducing Bax conformational change and apoptosis at G(2)-M phase compared with G(1)-S phase of the cell cycle. Taken together, these findings demonstrate that EpoB induces apoptosis through a Bcl-2-suppressible pathway that controls a conformational change of the proapoptotic Bax protein. The enhanced cytotoxicity of EpoB by blocking Bcl-2 at mitochondria implies a potential application of the combination of EpoB and Bcl-2 antagonists in the treatment of human breast cancer.
埃坡霉素B是一种新型的非紫杉烷类抗微管药物，甚至对紫杉醇（泰素）耐药的癌细胞也具有活性。本研究进一步探讨了埃坡霉素B介导的人乳腺癌细胞毒性的潜在机制。我们发现，新型埃坡霉素B类似物BMS-247550（EpoB）可诱导MDA-MB-468（468）细胞在G（2）-M期转换时发生细胞周期阻滞，并随后引发凋亡性细胞死亡。用EpoB处理细胞会触发Bax蛋白的构象变化及其从胞质溶胶向线粒体的转位，同时伴随着细胞色素c从线粒体内膜间隙释放到胞质溶胶中。Bcl-2的过表达会延迟Bax的构象变化、细胞色素c的释放以及EpoB诱导的凋亡。相反，Bcl-2拮抗剂Bak-BH3肽或HA14-1化合物可消除Bcl-2的抗凋亡作用，并增强经EpoB预处理（以诱导有丝分裂阻滞）的468细胞的凋亡。在同步化的468细胞中，与细胞周期的G（1）-S期相比，EpoB在G（2）-M期更有效地诱导Bax构象变化和凋亡。综上所述，这些发现表明EpoB通过一种受Bcl-2抑制的途径诱导凋亡，该途径控制促凋亡Bax蛋白的构象变化。通过在线粒体水平阻断Bcl-2增强EpoB的细胞毒性，这意味着EpoB与Bcl-2拮抗剂联合应用在治疗人类乳腺癌方面具有潜在应用价值。
