Abstract 3335: Characterization and analysis of the complement immune system in glioblastoma (GBM)

The purpose of this study is to determine the role of the complement immune system in glioma and/or glioma therapy. Glioblastoma (GBM) is the most common primary malignant brain tumor in adults. It is accompanied by a devastating prognosis; the median survival is 12-14 months, with less than 10 percent of patients living for more than two years after diagnosis. Unfortunately, current treatment options are limited, and many initially promising drugs have failed phase three clinical trials. One potential and relatively unexplored target for co-therapy in GBM is the complement immune system. Historically, the focus of work with complement has been on its role in innate immunity, where it can aid in the recognition and elimination of pathogens or undesired host material. More recent work, however, has revealed a key function of complement as a “double-edged sword” in the CNS. While the cascade is necessary for CNS development and homeostasis, overactive complement can lead to the hallmark neuroinflammation and neurodegeneration seen in conditions like Alzheimer's, multiple sclerosis, and traumatic brain injuries. Yet despite the presence of complement receptors on nearly all CNS cells and the direct role that complement plays in multiple neuroinflammatory diseases, very few studies have examined complement expression in brain tumors. The current project seeks to bridge this gap in knowledge by assessing the impact of complement on glioma. This effort began by selecting candidate genes, as the complement family contains over 50 members. To do so, data from the publicly available Cancer Genome Atlas (TCGA) was mined, providing 14 targets of interest for further analysis. Cell-based experiments were performed in three GBM patient-derived xenolines (PDx): XD456, JX6, and JX10. mRNA expression was determined via TaqMan real-time PCR. Protein levels were assessed via Western blot. Overall, seven of the 14 initial targets demonstrated clear over-expression in all three human GBM PDx cell lines. This expression was not changed upon treatment with glioma growth factors such as epidermal or fibroblast growth factor (EGF or FGF). Intriguingly, however, the degree of over-expression varied by cell line, even when these lines were derived from patients assigned to the same molecular GBM subtype. For example, at the RNA level and in comparison to other cell lines, complement factor H (a C3 inhibitor) was up to six times higher in XD456, and clusterin (a MAC inhibitor) was n