Glioblastoma multiforme (GBM) is a highly aggressive malignant brain tumor. Despite some recent improvement in the treatment of this malignancy, life expectancy of GBM patients remains extremely low. Therefore, continuous efforts to develop new treatment modalities are mandatory. A novel approach to cancer treatment is the use of targeted treatments, alone and in combination with other therapies. In this study, we evaluated the effects of novel combinations of conventional anti-cancer treatments (temozolomide or irradiation) with the targeted drug, imatinib, or with psychotropic drugs, belonging to the selective serotonin reuptake inhibitors (SSRIs) and phenothiazine subclasses, as well as combination of imatinib with psychotropic agents, on a human U87 glioblastoma cell line. The combination of temozolomide with imatinib or the psychotropic drugs resulted in an additive anti-proliferative effect, while the combination of irradiation and the psychotropic agents resulted in a less than additive effect on cell proliferation. A marked synergistic anti-proliferative effect of imatinib combined with the psychotropic drugs fluoxetine, sertraline or perphenazine was demonstrated. None of the single or combined treatments led to a reduction in the expression of phosphorylated MAP kinase. However, a marked synergistic reduction in the expression of the key regulatory molecule, pAKT, was detected, following the combined treatment of the cells with the imatinib/psychotropics combination. This down-regulation of pAKT may mediate the synergistic anti-proliferative interaction of imatinib with the psychotropic agents. Although the concentrations of the psychotropic agents used in this and other in vitro studies were beyond the clinically relevant blood levels in humans, recent studies have demonstrated anti-proliferative effects in vivo, using sertraline in a human colon cancer model. Thus, it seems that further in vivo studies combining imatinib with psychotropic agents, especially fluoxetine and sertraline, are warranted.

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