COX-2 inhibition induces autophagic flux and influences extracellular vesicle profile in human glioblastoma U87MG cell line

Introduction: Glioblastoma Multiforme (GBM), a lethal primary tumor of the central nervous system, is characterized by a highly infiltrating capacity, striking cellular heterogeneity, relapsing ability, and resistance to therapy. At present, the standard of therapeutic protocol consists of maximum conceivable surgical resection, followed by radiotherapy plus parallel adjuvant chemotherapy with temozolomide. Despite this, resistance to therapy limits its effectiveness, and GBM cannot be effectively controlled, being characterized by an extremely broad set of genetic and epigenetic alterations and high rates of recurrences. Several studies have suggested that gliomas, similar to most established malignant tumors, are characterized by a moderately inflammatory environment. Growing evidence over the past decades indicates the involvement of COX-2 in the progression of a variety of tumors, including GBM. We analyzed the effect of NS398, a COX-2 inhibitor, on the autophagic flux and extracellular vesicle (EV) secretion in the human U87MG glioma cell line. The effects of glioma stem cells (GSC)-derived EVs on adherent U87MG were also evaluated. Methods: After treatments, cell morphology was assessed by optical microscopy and by SEM. Cell proliferation and migration were examined using CCK-8 and scratch wound healing assay. Cell cycle profile and apoptosis were analyzed by flow cytometry. Autophagy-associated acidic vesicular organelles were quantified by acridine orange staining. A nanoparticle tracking analysis was used to assess the number and size of EVs. EV ultrastructure was verified by TEM and protein levels analyzed by WB. Acid sphingomyelinase was determined through ceramide levels. Results: NS398 was able to induce autophagy in both adherent U87MG and GSCs and EV secretion in GSCs. EVs secreted by NS398-treated GSC, but not those from untreated cells, were able to inhibit adherent U87MG cell growth and migration while also inducing a consistent level of autophagy. Conclusions: The hypothesis of COX-2 expression as GBM profile marker or interesting therapeutic target is supported by our findings. Autophagy and EV release following treatment with the COX-2 inhibitor could represent useful elements to better understand the complex biomolecular frame of GBM.