EXTH-48. INHIBITION OF SREBP-1 IS SYNTHETICALLY LETHAL WITH BCL-XL/BCL-2 INHIBITION IN GLIOBLASTOMA IN VITRO

Abstract

Abstract OBJECTIVE A cellular homeostasis that is shifted away from apoptosis and a reprogramming of the lipid metabolism are both, features that are frequently encountered in glioblastoma. This study aimed at investigating whether interference with the lipid metabolism is synthetically lethal with inhibition of anti-apoptotic Bcl-2 family proteins in glioblastoma in vitro. METHODS Established (U251) and primary-cultured glioblastoma cells (PC38, PC40 and PC128) as well as glioblastoma stem-like cells (SC38 and SC40) were treated with the Bcl-xL/Bcl-2 inhibitor ABT-263 (navitoclax) and/or the SREBP-1 inhibitor Fatostatin. MTT-assays were performed to assess effects of the combination therapy on the cell viability. Isobolograms were calculated to characterize the drug-drug interaction. Spheroids were used to determine anti-proliferative effects in a 3-dimensional setting. Staining with annexin V/propidium iodide and flowcytometric analysis were performed to assess pro-apoptotic effects. For molecular analyses, Western blots and specific knock-down experiments with siRNA were performed. RESULTS Combined targeting of SREBP-1 and Bcl-xL/Bcl-2 led to a synergistic inhibitory effect on the cellular viability of established, primary-cultured and glioblastoma stem-like cells as well as spheroids. This effect was shown to be at least in part mediated by enhanced apoptosis and to occur in a caspase-dependent manner. On the molecular level, treatment with increasing concentrations of Fatostatin led to a downregulation of Mcl-1. CONCLUSION Our study indicates that combined inhibition of Bcl-xL/Bcl-2 and interference with the lipid metabolism targeting SREBP-1 synergistically induces caspase-dependent apoptosis in glioblastoma cells. This effect can also be observed in more complex 3-dimensional glioblastoma cell formations. Further studies will focus on deciphering the drug-induced alterations of the metabolic pathways that are responsible for the synergistic effect of this therapeutic strategy.