Modulation of the sphingolipid metabolism with the sphingosine kinase inhibitor SKI-II to overcome hypoxia-induced chemotherapy resistance in glioblastoma cells

Abstract

Glioblastoma patients commonly develop resistance to temozolomide (TMZ) chemotherapy. Tumor hypoxia, which supports chemotherapy resistance, favors the expansion of glioblastoma stem cells (GSCs), contributing to tumor relapse. Because of a deregulated sphingolipid metabolism, glioblastoma tissues contain high levels of the pro-survival sphingosine-1-phosphate (S1P) and low levels of the pro-apoptotic ceramide. Ceramide can be metabolized to S1P by sphingosine kinase (SK) 1 that is overexpressed in glioblastoma. Thus, blocking SK might prevent this conversion and support the efficacy of TMZ. The small molecule SKI-II inhibits SK and dihydroceramide desaturase 1, which converts dihydroceramide to ceramide. Previous studies from the laboratory of Anne Régnier-Vigouroux reported that SKI-II combined with TMZ induces caspase-dependent cell death, preceded by dihydrosphingolipids accumulation and autophagy in normoxia. In the present study, I investigated the effects of a lower dose combination of TMZ and SKI-II under normoxia and hypoxia in human glioblastoma cells and patient-derived GSCs. I observed that TMZ resistance of glioblastoma cells was increased under hypoxia. However, combination of TMZ (48 μM) and SKI-II (2.66 μM) synergistically inhibited glioblastoma cell growth and potentiated glioblastoma cell death relative to single treatments under hypoxia. This lower dose combination did not induce dihydrosphingolipids accumulation, but a decrease in ceramide and its metabolites. It induced oxidative and endoplasmic reticulum stress and triggered caspase-independent cell death. It impaired the self-renewal capacity of TMZ-resistant GSCs, particularly under hypoxia. Furthermore, it decreased invasion of glioblastoma cell spheroids. This study provides novel insights on the interplay between the sphingolipid metabolism and invasion, a hallmark of cancer, and cancer stem cells, key drivers of cancer. It demonstrates the therapeutic potential of approaches that combine modulation of sphingolipid metabolism with first-line agent TMZ in overcoming tumor growth and relapse by reducing hypoxia-induced resistance to chemotherapy and by targeting both differentiated and stem-like glioblastoma cells.