The Immunosuppressive Function of Checkpoint Kinase 2 in Gliomas

Project Abstract Whereas the contribution of tumor microenvironment to the profound immune suppression of glioblastoma (GBM) is clear, tumor-cell intrinsic mechanisms that regulate resistance to CD8 T cell mediated killing are less studied. We performed an in vivo CRISPR screen to identify glioma intrinsic kinases that contribute to evasion of tumor cells from CD8 T cell recognition. The screen revealed checkpoint kinase 2 (Chek2) to be the most important kinase contributing to escape from CD8 T-cell recognition. Genetic depletion or pharmacological inhibition of Chek2 with blood-brain-barrier permeable drugs that are in the clinical trials, in combination with PD-1/PD-L1 blockade, led to survival benefit in preclinical glioma models. Furthermore, our experiment using ex vivo gliomas showed that glioma tumor cell intrinsic Chek2 interacts with Y-Box Binding Protein 1 and 3 (YBX1&3). The YBX1&3 are DNA/RNA binding proteins implicated in transcriptional regulation of immune-modulatory genes. However, the mechanism underlying the immunosuppressive function of Chek2 in gliomas is unknown. Therefore, in this proposal, we propose to determine the Chek2-YBX1&3 interaction mediated transcriptional changes that modulate CD8 T cell response using chromatin immunoprecipitation sequencing and CD8 T cell -mediated tumor cell killing assay (Aim 1). As an independent mechanism, we will investigate the contribution of Chek2 inhibition/depletion dependent STING pathway activation in enhancing CD8 T cell response by inhibiting STING pathway and studying its impact on CD8 T cell proliferation using OT- 1 CD8 T cell assay (Aim 2). As a potential novel therapeutic approach, we will test if targeting YBX1 enhances response to PD-1 blockade by determining the effect of this treatment strategy on the survival of preclinical glioma models (Aim 3). Together, this project will elucidate the mechanism underlying the immunosuppressive function of Chek2 and will provide a novel therapeutic strategy combining YBX1 inhibition, Chek2 inhibition and PD-1 blockade for testing in GBM patients.