DDDR-06. THE SMOKING CESSATION AGENT LOBELINE DELAYS HYPOXIC STRESS RECOVERY RESULTING IN GLIOBLASTOMA CELL DEATH

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Abstract Glioblastoma (GBM) is the most common and aggressive primary malignant brain tumour with a universally fatal prognosis. GBM is characterized by extensive regions of hypoxia which adversely impacts clinical outcomes, as hypoxia promotes chemoresistance. Tumour cells can adapt to and survive hypoxic stress by inducing rapid changes in the translational landscape, facilitated in part by the formation of stress granules (SGs). SGs are cytoplasmic aggregates of untranslated mRNAs and RNA binding proteins formed in response to a variety of cellular stressors, that allow cells to temporarily prioritize translation of stress-related proteins. Previous work in our laboratory has shown that GBM cells form SGs in vitro and in vivo, and that pharmacologically altering SG dynamics to prevent their dissolution (effectively locking cells in a stressed state) increases GBM cell death. Here we have identified another compound that delays the dissolution of hypoxia-induced SGs in GBM cells, the smoking cessation agent lobeline. SG dissolution typically occurs within 15 minutes post-hypoxia, however pre-treatment of immortalized GBM cells with lobeline delays SG dissolution for up to 2 hours. This delay in SG dissolution is dose dependent, as higher lobeline concentrations resulted in corresponding increases in the percentage of cells containing SGs and the average number of SGs per cell post-hypoxia. Lobeline also led to sustained phosphorylation of eIF2a (a key regulator of translation initiation) with an accompanying decrease in global protein translation levels post-hypoxia. Importantly, the combination of lobeline and hypoxia led to synergistic cell death in both immortalized and primary GBM cells, specifically through increased necrosis. Lobeline acts as a VMAT2 ligand and can stimulate dopamine release. Interestingly, we have found miRNA related to dopamine metabolism pathways overrepresented in extracellular vesicles isolated from GBM patient plasma. We postulate that disrupting the balance of stress pathways may have therapeutic potential in the future.

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