P02.04.B TARGETING METABOLIC VULNERABILITIES IN GLIOBLASTOMA

Abstract

Abstract BACKGROUND Glioblastoma is the most common and aggressive primary brain cancer, with a median survival of 16 months. A subset of cells within these tumours, termed glioblastoma stem cells (GSCs), displays high tumourigenic capacity and resistance to conventional therapies, and are responsible for tumour recurrence. Glioblastomas have been initially shown to mainly rely on glycolysis as a source of energy. However, a growing body of literature reports that GSCs are less glycolytic than their differentiated progeny and can thrive on oxidative phosphorylation (OXPHOS) to survive, sustain stemness and fuel tumourigenic potential. Thus, targeting OXPHOS could be a promising strategy to halt energy production and starve GSCs to death. However, under metabolic stress, GSCs can also switch to a more glycolytic phenotype, suggesting a metabolic plasticity in GSCs, and thus adding a layer of complexity to target GSC metabolism. In the current study, we have investigated the impact of compound X (CX), recently shown to impair mitochondrial respiration, on the fate and tumourigenesis of GSCs. MATERIAL AND METHODS Multiple patient-derived and murine GSC models were used to test the impact of CX on GSCs in vitro. The effect of CX on glioblastoma tumors was evaluated using patient-derived xenografts and syngeneic mouse models. RESULTS We have established that CX inhibits GSC proliferation and impairs stemness-related pathways in vitro. CX delays glioblastoma tumourigenesis in vivo. While a drastic decrease in cell proliferation was observed, cell death assays revealed that CX does not induce cell death. This suggests that GSCs gain a slow-cycling phenotype to resist energy depletion. Mechanistically, we have established that CX targets complex I of the mitochondrial respiratory chain, leading to an impairment of OXPHOS. Interestingly, inhibition of OXPHOS by CX was associated with an extensive production of extracellular lactate, indicating that at least, a subset of GSCs gain metabolic adaptability by co-opting glycolysis to survive. Thus, to tackle this metabolic plasticity in GSCs, we adopted a new strategy that involves sequestration of the lactic acid intracellularly via disruption of lactate transporters. Treatment of GSCs with monocarboxylate transporter inhibitors, AZD3965 and syrosingopine, alone did not significantly impact GSC growth and viability. Strikingly, combined CX treatment with either AZD3965 or syrosingopine resulted in high intracellular lactate buildup, increased reactive oxygen species, and led to drastic cell lethality in multiple GSC models. CONCLUSION This study highlights that re-routing the OXPHOS-dependent GSCs to glycolysis offers a vulnerability to sensitize GSCs to cell death. Dual inhibition of OXPHOS and lactate export could be a promising therapeutic approach to deplete malignant GSCs and suppress glioblastoma tumourigenesis.