Assessment of TBK1 as a Novel Therapeutic Target in IDH Wild-Type Gliomas

Abstract

Previously we identified four putative therapeutic targets in glioma using a high-throughput molecular approach, SHOC2, TBK1, TMED2, and YY1. These targets have been shown to play critical roles in tumor progression via the PI3K-AKT and Ras-ERK pathways. TBK1 was further pursued due to its role in multiple cancer-associated pathways and it was found to be significantly overexpressed in IDH wild-type compared with IDH mutant lower-grade gliomas (LGGs) (P = 0.005). To assess the therapeutic potential of targeting TBK1, we evaluated the efficacy of TBK1 inhibitors and their synergy with temozolomide (TMZ) and/or radiation in preclinical in vitro glioblastoma (GBM) models.LGG patient samples from an institutional cohort and the TCGA (RNA-sequencing) were used for TBK1 expression analyses. Cell viability and colony formation assays were performed using GBM cell lines (LN18, U87, GBM30-luciferase). TBK1 siRNAs and commercially available pharmacologic inhibitors, Amlexanox and GSK8612, were purchased for in vitro studies. Cells were treated with TBK1 inhibitors alone or in combination with radiation and/or TMZ. TBK1, AKT, and ERK expression were evaluated using Western blot analyses RESULTS: TBK1 was found to be significantly upregulated in IDH wild-type versus IDH mutant LGGs. Inhibition of TBK1 by siRNA or pharmaceutical agent (Amlexanox or GSK8612) resulted in decreased cell viability and colony formation in vitro in a dose- and time-dependent manner. Importantly, a synergistic effect was observed when GBM cells were treated with Amlexanox or GSK8612 in combination with TMZ and/or radiation. Further downstream molecular analysis revealed that inhibition of TBK1 led to decreased AKT and ERK activation.In conclusion, our study showed that Amlexanox or GSK8612 was effective in inhibiting TBK1 expression leading to decreased cell proliferation and colony formation in GBM cell lines. A synergistic effect was observed with each of these TBK1 inhibitors plus radiation and/or TMZ. These results suggest that TBK1 may be a potential candidate to pursue as novel therapeutic target in IDH wild-type gliomas. Future work will focus on in vivo studies with Amlexanox or GSK8612 alone and in combination with TMZ and radiation AUTHOR DISCLOSURE: Z. Tong: None.