title: Epothilone B analogue (BMS-247550)-mediated cytotoxicity through induction of Bax conformational change in human breast cancer cells.
abstract: 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.
authors.affiliation: Drug Discovery Program, H. Lee Moffitt Cancer Center and Research Institute, Tampa, Florida 33612, USA.
authors.forename: Hirohito
authors.initials: H
authors.lastname: Yamaguchi
authors.forename: Shanthi R
authors.initials: SR
authors.lastname: Paranawithana
authors.forename: Michael W
authors.initials: MW
authors.lastname: Lee
authors.forename: Ziwei
authors.initials: Z
authors.lastname: Huang
authors.forename: Kapil N
authors.initials: KN
authors.lastname: Bhalla
authors.forename: Hong-Gang
authors.initials: HG
authors.lastname: Wang
mesh_terms: D000970:Antineoplastic Agents / Q000633:toxicity*; D017209:Apoptosis / Q000187:drug effects; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D034261:Epothilones; D004852:Epoxy Compounds / Q000633:toxicity*; D016195:G2 Phase / Q000187:drug effects / Q000502:physiology; D006801:Humans; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism; D008938:Mitosis / Q000187:drug effects / Q000502:physiology; D011487:Protein Conformation / Q000187:drug effects; D011518:Proto-Oncogene Proteins / Q000378:metabolism* / Q000502:physiology; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000502:physiology; D013844:Thiazoles / Q000633:toxicity*; D014407:Tumor Cells, Cultured; D051028:bcl-2-Associated X Protein
chemical_list: D000970:Antineoplastic Agents; C494826:BAX protein, human; D034261:Epothilones; D004852:Epoxy Compounds; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D013844:Thiazoles; D051028:bcl-2-Associated X Protein; C430592:ixabepilone