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 previously 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. The role that mitochondrial dysfunction has in development of the MDR phenotype in brain tumors is unknown. Our goal in this exploratory grant is to confirm and extend our preliminary findings that defective mitochondrial function supports development of the MDR phenotype that leads to progression of malignant brain tumors. Long-term, we believe this will inform development of rational therapeutic and diagnostic strategies that can be applied effectively to this disease. We will test our central hypothesis that impairment of mitochondrial function drives development of the MDR phenotype in glioma by achieving three Specific Aims: (1) We will use human glioma cells and isogenic A0 (mtDNA-depleted) derivatives that display increased MDR phenotype to determine: i) relative cellular sensitivities to temozolomide (TZM) and carmustine (BCNU), by investigating drug effects on cell growth and survival, apoptosis and cell cycle distribution;ii) expression pattern of MDR-associated proteins in particular Major Vault Protein (MVP), highly expressed in the A0 model, and;iii) contribution of MVP to MDR. (2) We will examine established, temozolomide-resistant human glioma cells to determine whether mitochondrial function is impaired in chemoresistant glioma cells compared to chemosensitive isogenic cells. We will quantify and compare: i) respiration rates;ii) enzymatic activities of mitochondrial complexes;iii) mitochondrial proteome and iv) MDR associated proteins. (3) We will determine whether mitochondrial dysfunction results in increased expression of MDR-associated proteins via HIF-11 transcriptional activity. These studies will critically examine the contribution of mitochondrial function in development of multidrug- resistance in gliomas and the findings will produce a foundation for future studies to address development of more effective, targeted therapeutic modalities and diagnostic strategies for malignant glioma patients.
It is well-established that malignant gliomas are generally very resistant to chemotherapeutic modalities with minimal improvement in patient progression-free or overall survivals following aggressive regimens. An essential impediment to effective therapy is believed to reside in the Multi-Drug Resistant Phenotype expressed by these cells. Our preliminary data has revealed that impairment of mitochondrial function in glioma cell lines results in a MDR-like phenotype. The relevance of this research lies in our plan to develop a more detailed understanding of the role that mitochondria have in regulation of multidrug-resistance. This information will provide the foundation for subsequent studies designed to develop rational means to improve chemotherapy regimens for brain tumor patients and as such is highly significant.
