Acquisition of Chemoresistance in Gliomas Is Associated with Increased Mitochondrial Coupling and Decreased ROS Production

Abstract

Temozolomide (TMZ) is an alkylating agent used for treating gliomas. Chemoresistance is a severe limitation to TMZ therapy; there is a critical need to understand the underlying mechanisms that determine tumor response to TMZ. We recently reported that chemoresistance to TMZ is related to a remodeling of the entire electron transport chain, with significant increases in the activity of complexes II/III and cytochrome c oxidase (CcO). Moreover, pharmacologic and genetic manipulation of CcO reverses chemoresistance. Therefore, to test the hypothesis that TMZ-resistance arises from tighter mitochondrial coupling and decreased production of reactive oxygen species (ROS), we have assessed mitochondrial function in TMZ-sensitive and -resistant glioma cells, and in TMZ-resistant glioblastoma multiform (GBM) xenograft lines (xenolines). Maximum ADP-stimulated (state 3) rates of mitochondrial oxygen consumption were greater in TMZ-resistant cells and xenolines, and basal respiration (state 2), proton leak (state 4), and mitochondrial ROS production were significantly lower in TMZ-resistant cells. Furthermore, TMZ-resistant cells consumed less glucose and produced less lactic acid. Chemoresistant cells were insensitive to the oxidative stress induced by TMZ and hydrogen peroxide challenges, but treatment with the oxidant L-buthionine-S,R-sulfoximine increased TMZ-dependent ROS generation and reversed chemoresistance. Importantly, treatment with the antioxidant N-acetyl-cysteine inhibited TMZ-dependent ROS generation in chemosensitive cells, preventing TMZ toxicity. Finally, we found that mitochondrial DNA-depleted cells (ρ°) were resistant to TMZ and had lower intracellular ROS levels after TMZ exposure compared with parental cells. Repopulation of ρ° cells with mitochondria restored ROS production and sensitivity to TMZ. Taken together, our results indicate that chemoresistance to TMZ is linked to tighter mitochondrial coupling and low ROS production, and suggest a novel mitochondrial ROS-dependent mechanism underlying TMZ-chemoresistance in glioma. Thus, perturbation of mitochondrial functions and changes in redox status might constitute a novel strategy for sensitizing glioma cells to therapeutic approaches.

Function of neuronal nitric oxide synthase enzyme in temozolomide-induced damage of astrocytic tumor cells

“…1). Corroborating previous studies, cell groups with increased levels of ROS exhibited a lower cell viability than those with reduced ROS levels (33,34).…”

“…TMZ also reduces the membrane potential of the mitochondrion, releases cytochrome c from this organelle, and increases activated caspases 3 and 9 cell content (32). Oliva et al (2011) suggested that U251MG cells demonstrated an increase in ROS production at 2 and 4 h post-TMZ (33), which indicated that oxidative stress contributed to the TMZ effects on astrocytoma tumor cells, as confirmed by a protective effect obtained with the antioxidant N-acetylcysteine. Indeed, TMZ at 300 µM caused a 10-fold increase in ROS levels in TMZ-sensitive U251MG cells, but no effect occurred on resistant cells (33).…”

Downregulation of cytochrome c oxidase 1 induced radioresistance in esophageal squamous cell carcinoma

“…Aichler et al (18) reported that knockdown of MT-CO7A2 with siRNA increased chemosensitivity after chemotherapy with cisplatin and 5-flurouracil in esophageal adenocarcinoma cells. Oliva et al (19,20) revealed that pharmacologic and genetic manipulation of cytochrome c oxidase restored chemosensitivity in chemoresistant glioma cells. From these and our results, cytochrome c oxidase seems to be a significant gene which induces chemo or radioresistance, and it may be a target gene for treatment to improve chemo or radiosensitivity.…”

Exploring Melissa Officinalis Properties for Glioblastoma Multiforme Treatment

“…Thus, although the BBB may be disrupted at the tumor core, it is intact at other tumor areas where the presence of tight junctions and transporter proteins of the ABC family prevents access of chemotherapeutics drugs to tumor cells. The alkylating agent temozolomide (TMZ), the front-line drug used for GBM treatment induces mitochondria uncoupling, ROS production, DNA strand breaks in GBM cells [10,11] and show a modest increase in patents survival rate [6]. However, a great number of patients with recurrent GBM develop resistance to the second cycle of TMZ and the treatment Chemotherapy : Open Access efficacy is further decreased.…”

“…However, a great number of patients with recurrent GBM develop resistance to the second cycle of TMZ and the treatment Chemotherapy : Open Access efficacy is further decreased. Expression of ATP-dependent drug efflux pumps, increase in mitochondria function and decrease of ROS production are just some of the mechanisms responsible for TMZ resistance [11,12].…”