TR-05ER STRESS INDUCING DRUGS DOWNREGULATES MGMT AND MPG SENSITIZING PEDIATRIC GLIOMA CELL LINES TO TMZ

Pediatric patients with glioblastoma multiforme (pGBM) are in desperate need of new therapies. Temozolamide (TMZ) is one of the preferred treatments however its clinical benefit is meager. Salinomycin (SLM) is a potassium ionophore (K+) that has proven efficient against different type of tumors. However, its antitumor effect has never been evaluated in pGBM. The main goal of this work was to characterized the antitumor effect of SLM in pGBM cell lines and improve our understanding of its mechanism action. SLM induced a potent antitumor effect against pGBM cell lines. Moreover, treatment with this drug resulted in an aberrant autophagic flux that led to regulated necrosis cell death. Our data showed that the cell death was mediated by AIF release which induced lysosomal membrane permeability. Of importance, SLM induced a potent ER stress in pGBM cell lines which was accompanied by the downregulation of MGMT and MPG, both proteins are involve in the DNA damage response to TMZ. We observed the same phenomenon when we treated the cells with other ER stress inducing drugs (i.e.: thapsigergin and tunicamycin). Chemical inhibition of ER stress resulted in abrogation of MGMT and MPG downregulation suggesting a common mechanism to ER stress inducing drugs. The results prompted us to combined SLM with TMZ resulting in a synergistic antiglioma effect. SLM induced a significant increment in the amount of DNA damage induced by TMZ, probably mediated by the downregulation of MGMT and MPG. Similarly, to SLM alone combination with TMZ induced ER stress and aberrant autophagy due to impairment of lysosomal activity that in turn led to regulated necrosis undercovering the crosstalk between ER stress and regulated necrosis. These findings provide a strong rationale for further exploring the combination of TMZ with ER stress inducing drugs as a therapeutic strategy for pGBM.