Patupilone-induced apoptosis is mediated by mitochondrial reactive oxygen species through Bim relocalization to mitochondria.

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.

Microtubules in apoptosis induction: are they necessary?

Microtubule-Targeting Agents (MTAs) constitute a class of drugs largely used in cancer treatment. Among them, both taxanes and Vinca-alkaloids are known to inhibit cancer cell proliferation by inducing cell cycle arrest and subsequent apoptosis. These agents modify the cytoskeleton by affecting the tubulin/microtubule system. In cancer cells, both classes suppress microtubule dynamics through inhibition of microtubule dynamic instability and treadmilling, and commonly induce diverse signals responsible for cell death initiation and execution via the mitochondrial intrinsic pathway. However, links between microtubule network disturbance and the involvement of mitochondria in apoptosis are not obvious, and one may think that they could be independent. Nevertheless, several intracellular proteins could connect microtubules and the apoptotic machinery. The aim of the present review is to provide elements that could answer to the question: is microtubule disruption dispensable for MTA-induced apoptosis? The first section is focused on the mechanisms responsible for the MTA-mediated apoptosis. Then, links between cell cycle regulators and apoptosis are underlined since MTA induce cell cycle arrest by inhibiting microtubules. In the third part, the potential involvement of microtubule-sequestered and/or -transported proteins in apoptotic signalisation is discussed. Lastly, the possible role of the tubulin/microtubule system in direct effects of MTAs on mitochondria is summarized. Thus, it becomes clear that microtubule network and apoptosis are deeply linked in MTA effectiveness, through a cascade of cellular events. It could lead to identification of new biomarkers of MTA effectiveness, that could improve combinatorial therapy with MTAs and provide crucial arms to circumvent resistance of cancer cells.

Pericarditis causing exercise test induced ST-elevations.

Pericarditis has not been well associated with exercise test induced ST-elevations. This case report of a pericarditis patient who underwent exercise stress testing and other similar cases found in the literature suggest that this is an unrecognized clinical manifestation of pericarditis.

Side-branch occlusion with directional coronary atherectomy: incidence and risk factors.

Side-branch occlusion is a recognized complication of directional coronary atherectomy (DCA). To evaluate the incidence, risk factors, and clinical outcome of side-branch compromise, we analyzed our first 100 consecutive atherectomies of native coronary arteries. Seventy-eight patients had 122 side branches at risk, 21 (17%) of which demonstrated compromised flow after DCA. Origin of the side branch from the culprit atheroma and preexisting side-branch ostial stenosis were highly predictive of this complication in 20 of 55 (p < 0.05) and 14 of 31 (p < 0.05) lesions, respectively. There was one non-Q-wave myocardial infarction, no emergency surgeries, and no deaths. In conclusion, side-branch loss after DCA occurs with a frequency similar to balloon angioplasty and was well tolerated in our patient population. Side branches that originate directly from culprit lesions or that have significant ostial narrowing have a higher incidence of this complication.