Evaluation and characterization of Salinomycin as a therapeutic strategy for glioma

Abstract

Temozolamide (TMZ) is the standard treatment against GBM unfortunately, its therapeutic effect is limited due to the expression of the DNA repair protein O6-methylguanine-DNA methyltransferase (MGMT). Therefore, approaches that overcome the resistance to TMZ could pose a feasible therapeutic alternative for this deadly disease. Endoplasmic reticulum (ER) stress suppresses several DNA damage proteins through the unfolding protein response. In this work we sought to evaluate whether ER-stress inducing drugs were able to downmodulate MGMT and sensitize GBM cells to TMZ treatment. Salinomycin (SLM) is a potassium ionophore that has proven effective against cancer stem cells and a possible candidate to induce ER stress. Our data showed that SLM triggered ER stress that was accompanied by the downregulation of MGMT, MPG, and Rad51. We obtained the same results with other ER stress inducing drugs (ie: thapsigergin, tunicamycin) suggesting that this is a general mechanism. Chemical inhibition of ER stress resulted in abrogation of DNA damage protein downregulation. Of importance, SLM induced an aberrant autophagic flux that led to regulated necrosis cell death, mediated by the action of AIF protein, which induce a DNA damage when is localized into the nucleus. Combination of TMZ and SLM displayed a potent antitumor effect in vitro and in vivo in mice bearing a GBM stem cell model. Animals treated with both drugs exhibit an increment of the median survival and led to long term survivors free of disease. Moreover, tissue analysis confirmed a dramatic increase in the level of DNA damage. Altogether our results showed that combination treatment induces a potent antiglioma effect in vitro and in vivo. Our data uncover the possibility to exploit ER stress and regulated necrosis as therapeutic strategies for GBM treatment.