Abstract 2984: Developing a new combinational therapy to combat temozolomide resistance in glioblastoma multiforme

Abstract

Abstract Background: Glioblastoma multiforme (GBM) is the most lethal central nervous system malignancy, and recurrence is seen in nearly all cases. Temozolomide (TMZ), a DNA alkylating agent, shows initial promise in eradicating primary GBM, but has little effect on recurrent GBM. Our previous work identified the Phosphatidylinositol 3-kinase Catalytic Subunit Beta (PIK3CB) of the PI3K pathway to be selectively important for the survival and progression of GBM (1). Other previous research also shows that a gap-junction protein, Connexin 43 (Cx43), promotes TMZ resistance in GBM by activating PI3K signaling and that this resistance can be reversed by treatment with a peptide compound named αCT1 (2). More recently, it was discovered that G-protein coupled receptors (GPCRs), specifically the Gβγ subunit, are upstream activators of Cx43/PI3K/AKT signaling in TMZ-resistant GBM cells. We believe that selectively targeting and blocking the activators of these signaling pathways will help to restore and enhance sensitivity to TMZ, yielding successful eradication of GBM cells. We therefore propose to test the effect of a quadruple combination of TMZ, αCT1, TGX-221, and gallein, a selective inhibitor of the Gβγ subunit of GPCRs, on GBM tumor growth. Hypothesis: Gβγ subunit inhibition will substantially increase GBM cytotoxicity in combination with αCT1, TGX-221 (a PIK3CB inhibitor), and TMZ. Methods: MTS cell viability assay was used to determine optimum gallein dosage both alone and in combinational therapies in experimental cell lines with variable Cx43 expression rates and TMZ sensitivities. This assay was also used to determine cell viability after treatment with an optimized quadruple combination therapy in these same lines. Current work is focused on quantifying Cx43/PIK3CB/AKT signaling inhibition via Western blot, as well as applying the optimized quadruple combination treatment in GBM stem cells, three-dimensional GBM tumor models, primary GBM patient samples, and healthy astrocytes. Results: Significant inhibitory effects have been shown with an optimized quadruple combination therapy compared to TMZ alone in TMZ-resistant experimental cell lines. Conclusions: While results in experimental lines have been favorable, additional work is still needed to elucidate the efficacy of the optimized quadruple combination therapy, which will include testing primary GBM patient samples, GBM stem cells, healthy astrocytes and three-dimensional tumor models.