Bioenergetics pathways and therapeutic resistance in gliomas: emerging role of mitochondria.

Cancer metabolism has gained considerable interest, since significant studies have indicated a close relationship between the activation of various oncogenes and alterations of cellular metabolism. Furthermore, several lines of evidence have shown that metabolic imaging can significantly impact malignant glioma patient management and monitoring of tumor response to therapy. In this context, mitochondria play a central role in cellular energy production, apoptosis and free radical generation. Mitochondrial malfunctions have been associated with development of many cancers, including brain tumors. Glioblastoma multiforme (GBM) is the most common primary intracranial neoplasm and its almost uniform lethality is exemplified by a median survival of 12-15 months. Current management consists of a combination of surgery, radiotherapy and chemotherapy. Despite aggressive treatment approaches, recurrence occurs in 90% of GBM patients. One cause of this poor outcome is development of a multidrug-resistance (MDR) phenotype. We and others have described in detail the bioenergetic pathways central to glioma growth and progression. One of the most striking observations is that glioma cells which rely on glycolytic metabolism readily adapt to bioenergetic stress by engaging their mitochondrial pathway in order to survive and grow. This suggests that mitochondrial function plays a critical role in the biology of gliomas. Still, the role that mitochondrial function has in development of chemoresistance in malignant brain tumors is largely unknown. Our goal in this review is to describe the current knowledge on the role of mitochondria function in the development of chemoresistance in glioma. Particular emphasis will be on ABC transporters. We will discuss the significance of these research areas in the context of development of more effective, targeted therapeutic modalities and diagnostic strategies for malignant glioma patients.