title: Patupilone-induced apoptosis is mediated by mitochondrial reactive oxygen species through Bim relocalization to mitochondria.
abstract: Among the new microtubule-targeted agents, the epothilone family of molecules has shown promising anticancer potential, and clinical trials are currently underway for patupilone (epothilone B) in various cancer indications. In this study, we characterized novel aspects of patupilone's cellular action that may underlie its potent cytotoxicity in human neuroblastoma cells. Patupilone induced mitochondrial membrane potential collapse, mitochondrial morphological changes, and cytochrome c release, leading to apoptosis. Within the first 2 h, patupilone increased the generation of reactive oxygen species (ROS; i.e., superoxides and hydrogen peroxide, 33+/-6 and 51+/-3% increase, respectively), specifically from mitochondria. ROS scavengers and mitochondrial DNA depletion [rho(-) cells] significantly protected cells against patupilone cytotoxicity, indicating that ROS generation is a key event in the initial phase of apoptosis. Although the Bim expression level was not modified by patupilone, this proapoptotic protein accumulated in the mitochondrial compartment (2.4-fold increase at IC70) after only a 6-h treatment. In contrast, Bax and Bcl-2 mitochondrial levels were not changed during treatment. It is noteworthy that ROS inhibition prevented Bim relocalization to mitochondria and mitochondrial membrane changes induced by patupilone. Altogether, our data reveal that patupilone-mediated ROS production by mitochondria initiates the intrinsic signaling cascade by inducing Bim accumulation in mitochondria. These results might explain the superior activity of patupilone in tumor cells compared with paclitaxel that is, until now, the clinical reference among microtubule-stabilizing agents. Furthermore, our data highlight the importance of mitochondria that simultaneously assume the role of activator and integrator of apoptotic signals triggered by patupilone.
authors.affiliation: INSERM UMR911, Faculté de Pharmacie, 27 Bd Jean Moulin, 13385 Marseille Cedex 05, France.
authors.forename: N R
authors.initials: NR
authors.lastname: Khawaja
authors.forename: M
authors.initials: M
authors.lastname: Carré
authors.forename: H
authors.initials: H
authors.lastname: Kovacic
authors.forename: M A
authors.initials: MA
authors.lastname: Estève
authors.forename: D
authors.initials: D
authors.lastname: Braguer
mesh_terms: D017209:Apoptosis / Q000187:drug effects*; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D045304:Cytochromes c / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D034261:Epothilones / Q000494:pharmacology*; D006801:Humans; D007202:Indicators and Reagents / Q000378:metabolism; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects; D008928:Mitochondria / Q000378:metabolism* / Q000502:physiology; D009447:Neuroblastoma / Q000188:drug therapy; D017382:Reactive Oxygen Species / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology; D013778:Tetrazolium Salts / Q000378:metabolism; D013997:Time Factors; D050257:Tubulin Modulators / Q000494:pharmacology*; D051028:bcl-2-Associated X Protein / Q000378:metabolism
chemical_list: D034261:Epothilones; D007202:Indicators and Reagents; D017382:Reactive Oxygen Species; D013778:Tetrazolium Salts; D050257:Tubulin Modulators; D051028:bcl-2-Associated X Protein; D045304:Cytochromes c; C093788:epothilone B