Glioblastoma multiforme (GBM) is the most common malignant glioma and has an extremely invasive phenotype. The ability of glioblastoma cells to diffusely infiltrate healthy tissue is the major obstacle for current treatments, including surgery and radiotherapy. Over the years, established human glioblastoma cell lines were used as models to study molecular mechanisms of invasion; however, these mechanisms remain elusive since established lines are not invasive in vivo. In contrast to established lines, primary non-established glioblastomas, including GBM6 and GBM12 cells, are invasive in vivo, and thus can be successfully used to study growth, motility, and invasion. Recently, an elevated expression of sphingosine kinase 1 (SphK1), an enzyme that generates sphingosine 1-phosphate (S1P), was correlated with poor prognosis of patients with GBM. S1P is a potent lipid mediator important for cancer growth, survival, migration, and invasion. In the brain, S1P is present at high concentrations, and has been shown to stimulate migration and invasion of established glioblastoma lines in vitro. The activity of SphK1 is rapidly and transiently stimulated by various growth factors and cytokines; however, mechanisms of the transcriptional regulation of the sphk1 gene are not understood and the factors enhancing SphK1 expression in GBM patients have not been identified. Recently, inflammation has been linked to the development and progression of many cancers with inflammatory cytokines involved in these processes. IL-1 is one of the major regulators of inflammation in the brain, which can induce the secretion of other proinflammatory cytokines and also promote proliferation of glioblastoma cells in vitro. More importantly, glioblastoma cells secrete significant amounts of IL-1. In preliminary studies, we show that IL-1 is coexpressed with SphK1 in GBMs, exogenous IL-1 increases expression of SphK1, and both IL-1 and S1P enhance invasion and proliferation of glioblastoma cells. More importantly, neutralizing anti-IL-1 antibodies inhibit proliferation of glioblastoma cells in vitro, while a novel SphK1 inhibitor (SKI) reduces xenografted glioblastoma tumor growth in mice. It is our hypothesis that the IL-1-mediated stimulation of SphK1 expression leads to the production of S1P, which in turn activates proliferation, motility, and invasion of GBMs. We propose to study SphK1 functions and its regulation in primary GBM cells. Moreover, development of potent and specific SphK1 inhibitors that are active in animal models could pave the way for new therapeutics for treatment of GBM.
Our specific aims are as follows:
Aim 1. To determine the role of SphK1 expression and the effect of its inhibition on proliferation, motility, and invasion of primary non-established GBMs in vitro, and xenografts implanted in the brains of athymic mice.
Aim 2. To identify the mechanisms that control endogenous SphK1 expression in response to IL-1.
Glioblastoma multiforme (GBM) has an extremely invasive phenotype, which is the major obstacle for current treatments. It is our hypothesis that the IL-1-mediated stimulation of SphK1 (sphingosine kinase 1) expression plays an important role in GBM growth and invasiveness, and may be a potential therapeutic target. Therefore, we propose to study SphK1 functions and its regulation in primary non-established GBM cells. Moreover, development of potent and specific SphK1 inhibitors that are active in animal models could pave the way for new therapeutics for treatment of GBM. ? ? ? ?
