Abstract 3451: Microglial phagocytosis suppressed the development of metastatic tumors in the imaging model of brain metastasis

Abstract

Abstract Brain metastasis of lung cancer is a crucial problem that causes poor clinical outcomes and alters patient quality of life. Previous evidence showed that lung cancer cells (LUCs) may escape from host immunity to form distant metastases. We previously used an original imaging model of brain metastasis (IBrM) to show a heterogeneous interaction between microglia, the tissue macrophages in the brain, and LUCs in the brain niche. The findings confirmed that microglia can phagocytose metastatic cancer cells. Here, we show that genetic deletion of the “don’t eat me” signals of cancer cells can promote phagocytic activity of microglia against LUCs. We injected an adenocarcinoma lung cancer cell line expressing mCherry (CMT167mC) via the internal carotid artery of the CX3CR1-EGFP mice, whose microglia had been specifically labeled with EGFP. The microglia and LUCs were visualized in vivo simultaneously by two-photon microscopy for 14 days. The tumor fate and microglial response against cancer cells were evaluated at single cell resolution in the IBrM. CD24, CD47, and/or PDL1 were deleted in CMT167mC cells using CRISPR/Cas9 to examine the effect of the “don’t eat me” signals. The dynamic behavior of LUCs and the microglial phagocytosis activity against LUCs were visualized in living mice. Microglial phagocytosis was significantly increased by single deletion of CD47 or CD24 compared with WT cells. Combined deletion of CD47 and CD24 also synergically increased microglial phagocytosis, resulting in reduced IBrM and prolonged mouse survival. By contrast, deletion of PD-L1 did not enhance microglial phagocytosis or prolong survival. The pharmacological or genetic conditional depletion of microglia canceled both the increased phagocytosis and the extended survival time, suggesting that the effect of “don't eat me” signals was microglia-dependent. These results indicate that suppression of both CD24 and CD47 in LUCs enhances microglial phagocytic activity and suppresses the metastatic formation of LUCs. Furthermore, the combined use of CRISPR/Cas9 in LUCs and in vivo imaging allows us to evaluate potential therapeutic targets associated with microglial phagocytosis. We are currently using single cell RNA-seq and cell-to-cell communication analysis of the brain tumor and surrounding niche to explore other signal pathways that regulate tumor phagocytosis by microglia and to identify potential therapeutic targets. Citation Format: Takahiro Tsuji, Hiroaki Wake, Mariko Shindo, Daisuke Kato, Hiroaki Ozasa, Toyohiro Hirai. Microglial phagocytosis suppressed the development of metastatic tumors in the imaging model of brain metastasis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3451.