CYTOTOXIC EFFECTS OF PERIFOSINE IN HUMAN GLIOBLASTOMA CELLSARE ASSOCIATED TO AN ALTERED CERAMIDE METABOLISM

Background: Glioblastoma multiforme (GBM) is the most malignant brain tumor and, despite aggressive therapy, prognosis for patients is poor. Temozolomide (TMZ), the chosen drug in GBM therapy, exerts cytotoxic effects also through an increase of ceramide levels. Perifosine (PF) is currently being tested for treatment of major human cancers, but little is known about its efficacy in gliomas. The aim of this work is to evaluate in GBM cell lines if PF is able to regulate sphingolipid metabolism and to enhance the cytotoxic effect of TMZ. Results: The results obtained demonstrated that in different GBM cell lines, the treatment with PF led to a dose-dependent decrease in cell viability. In all GBM cells lines, PF promoted a time-dependent decrease of p-Akt levels, with an about 50% decrease after 4 hour treatment. In these conditions, metabolic studies showed that treatment with PF significantly modified sphingolipid (SL) metabolism by inhibiting sphingomyelin (SM) and, in a lesser extent, glycosphingolipid (GSL) biosynthesis with a consequent accumulation of ceramide (Cer). In addition, PF weakly reduced sphingosine-1-phosphate (S1P) biosynthesis. The treatment with LY294002, in conditions giving an almost complete inhibition of the PI3K/Akt pathway, only partly mimicked the effects of PF on SL metabolism, suggesting that PF could regulate SL metabolism also through a mechanism other than Akt inhibition. In the same GBM cell lines, the treatment of PF in combination with TMZ had an additive, but not synergistic cytotoxic effect. More of interest, a TMZ resistant cell line, that is characterized by an altered SL profile, a high capacity to release S1P and in which TMZ is unable to accumulate Cer, was still sensitive to PF. Conclusions: These data suggest that PF can exert its anticancer activity through a marked modulation of sphingolipid metabolism with increased Cer/S1P ratio, where Cer acts as a pro-death and S1P as a survival factor. PF in combination with TMZ could thus improve the treatment efficacy in GBM.