Abstract 6945: Targeting Chek2-YBX1&3 axis to enhance response to immune checkpoint blockade therapy in gliomas

Abstract Although the immunosuppressive microenvironment of glioblastoma (GBM) is well-established, the tumor-intrinsic mechanisms underlying resistance to CD8+ T cell-mediated killing remain incompletely understood. Our previous study identified Checkpoint Kinase 2 (Chek2) as the top contributor to CD8+ T cell resistance in GBM through an in vivo CRISPR screen. Therapeutic evaluation demonstrated that Chek2 inhibition, combined with PD-1/PD-L1 immune checkpoint blockade, significantly enhanced CD8+ T cell-mediated tumor killing and improved survival in preclinical glioma models. Here, we aimed to elucidate the immunosuppressive function of Chek2. Immunoprecipitation-mass spectrometry (IP-MS) and phosphoproteomics identified the transcriptional repressors and RNA-stabilizing proteins YBX1 and YBX3 as critical interactors of Chek2. Single-gene knockout and overexpression studies of Chek2, YBX1, and YBX3 in multiple glioma cell lines revealed that these proteins positively regulate each other’s expression at the protein level. RNA sequencing coupled with ChIP-seq analysis demonstrated that the Chek2-YBX1-YBX3 interaction represses the expression of inflammatory cytokines. Targeting Chek2, YBX1, and YBX3 with the small-molecule inhibitor SU056 enhanced antigen presentation and promoted CD8+ T cell proliferation. Moreover, combining SU056 with PD-1 blockade significantly improved survival in multiple glioma models. Collectively, these findings reveal an immunosuppressive mechanism mediated by the Chek2-YBX1-YBX3 axis and propose its inhibition as a promising therapeutic strategy to enhance responses to immune checkpoint blockade therapies in gliomas. Citation Format: Heba Ali, Ningjia Zhou, Li Chen, Vivekanudeep Karri, Mahalakshmi Harish, Yalu Zhou, Vasilios Kalas, Karl Habashy, Victor A. Arrieta, Kwang-Soo Kim, Si Wang, Joseph Duffy, Ragini Yeeravalli, Deanna M. Tiek, Xiao Song, Snehasis Mishra, Catalina Leechang, Atique Ahmed, Prasanna Venkatraman, Gabriel J. Rocklin, Adam M. Sonabend, Crismita Dmello. Targeting Chek2-YBX1&3 axis to enhance response to immune checkpoint blockade therapy in gliomas [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 6945.