Targeting of Mitochondrial Lon Protease as a Novel Therapy for Glioblastoma

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PROJECT SUMMARY Glioblastoma (GBM) is the most aggressive primary brain tumor with a two years survival rate of less than 50% following surgical resection, radiation, and chemotherapy. Recurrence is nearly universal after the first-line treatment, and there is currently no therapy proven to prolong survival after tumor recurrence. Thus, there is an urgent need for more effective GBM therapies. The overarching goal of this project is to further develop and validate new chemotherapeutic agents for the treatment of GBM. GBM's resistance to radiation and chemotherapy heavily correlates with extensive hypoxia-induced, mitochondria-dependent phenotypic changes such as glycolytic respiration, decreased the ability to undergo apoptosis and extensive invasiveness. Mitochondrial LonP1 is an ATP-stimulated protease, directly up-regulated by HIF-1α. LonP1 is overexpressed in human malignant gliomas and its elevated expression levels are associated with high glioma tumor grade and poor patient survival. Therefore, regulation of mitochondrial function by inhibiting LonP1 protease could represent a novel approach for GBM and potentially other fast-growing malignancies which heavily depend on hypoxic adaptation. The proposed project is based on our published and preliminary results obtained from in vitro (cell- based) studies with LonP1 inhibition using siRNA and the inhibitor compounds CC4 and BT317 and in vivo LonP1-overexpression xenograft models studies. BT317 is a small molecule compound, able to cross the blood- brain barrier and to achieve promising concentrations in the brain. BT317 is highly effective in inducing cell death in multiple glioma lines and patient-derived glioblastoma stem cell cultures, with an IC50 value of 60-100 µM (temozolomide – the main FDA approved therapy and has minimal toxicity in normal lines. identifying BT317 as a potentially new therapy for this universally fatal disease. In this project, we propose to: (1) examine the effect of mitochondrial LonP1 knockout in distinct patient-derived primary glioma stem-like cells (GSC), glioblastoma cell lines and xenograft models, (2) identify microenvironment cues and LonP1-induced mitochondrial changes that drive GSC invasiveness, and (3) examine the drug-target inhibition and molecular mechanisms for anti- cancer efficacy of the LonP1 inhibitor, BT317. The studies outlined here are the first to explore a very promising avenue – mitochondrial Lon protease inhibition – as a treatment for GBM.