Abstract 3968: Canonical NFkB signaling in myeloid cells is required for the glioblastoma growth

Glioblastoma (GBM) development and therapeutic resistance has been accompanying with the tumor-associated macrophages (TAMs) in the tumor microenvironment (TME). TAMs are heterogeneous cell populations of immune regulatory myeloid-derived suppressor cells (MDSCs) and polarization of anti-tumor macrophages (M1) into pro-tumor macrophages (M2). We investigated the role of myeloid cell NF-κB signaling in orthotopic GBM model using immune deficient and immune competent hosts. Interestingly, conditional deletion of canonical NF-κB signaling (p65) with Lysm-Cre (p65 KO) in myeloid cells, significantly inhibited syngeneic GL261 tumor growth in immune-competent mice compared to control mice. We studied the TAMs recruitment to the tumor and their polarization under the influence of TME. P65 KO mice displayed decreasing trend of immune cell infiltration (CD45), which phenotyped as decreased F4/80+, CD68+, CD206+ (M2) and Gr1+CD11b+ (MDSCs) macrophages, compared to control mice. This was associated with the increased CD80+ (M1) macrophages, increasing trend of CD4+ and CD8+ cytotoxic T cells, and decreased CD44+ mesenchymal cancer stem cells (CSCs) populations in the TME. Cytokine array data indicated that loss of canonical NF-κB signaling within the TAMs was implicated in increased production of IFNγ, IGF1, MCP1, MIP1α, and TNFα cytokines. Co-culture of T cells with p65 KO or control MDSCs identified increased proliferation of T cells with p65 KO MDSCs compared to control MDSCs. Conversely, GBM patient-derived xenografts and U251 GBM cell line-derived tumors showed increasing trend of growth in immune-deficient mice, following the transplantation of p65 KO bone marrow (BM) compared to control BM. Pro-tumor macrophages and CSCs were increased and T cell populations were decreased in human tumors grown in immune deficient mice transplanted with p65 KO BM, compared with control BM. In addition, analysis of human data set revealed higher expression of p65 subunit of NF-κB complex in brain tumor stroma compared to the tumor cells. The study suggests that canonical NF-κB signaling in TAMs is required for the tumor-promoting macrophage polarization and GBM growth in immunocompetent host compared to immune deficient host. Therefore, targeting myeloid-specific NFκB signaling in GBM could inhibit the immune suppressive TAMs and improve the anti-tumor immunity. Citation Format: Bhagelu R. Achyut, Jennifer Bradford, Kartik Angara, Mohammad Rashid, Meenu Jain, Thaiz Borin, ASM Iskander, Roxan Ara, Ali Arbab. Canonical NFkB signaling in myeloid cells is required for the glioblastoma growth [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3968. doi:10.1158/1538-7445.AM2017-3968