Abstract 1509: Microglial dominance in glioma dissemination: Unraveling TAMs' impact and therapeutic implications through modulating cathepsin activity

Abstract Introduction: It is well known that tumor-associated macrophages/microglia (TAMs) play a vital role in brain tumor progression. Our previous studies suggested that the activated microglia could reduce the cytotoxic effect of chemotherapeutic drugs on glioma cells in a 2D/3D model. This study delves into TAMs within diverse brain TME regions, emphasizing the distinction of resident microglia from infiltrating macrophages in invasion areas and their role in glioma migration and invasion. Material and Method: We employed the murine orthotopic astrocytoma model (ALTS1C1), dissecting brain tumor tissues into normal, invasion, edge, and core regions. Immunofluorescence staining, utilizing TMEM119 and CD68 markers to identify resident microglia and infiltrating macrophages, respectively. The IHC results were analyzed with QuPath software and validated via flow cytometry. Microglia (BV2) and macrophage (RAW264.7) cell lines were directly co-cultured with ALTS1C1 in 2D and 3D migration/invasion models. Bulk RNA sequencing analysis unraveled the differences between BV2 and RAW264.7. Bone marrow-derived macrophages (BMDM) were used for the TAMs activation test, and the cathepsin inhibitor, E64, was applied to elucidate cathepsin's role in microglia within co-culture models. Results: The IHC results reveal more TMEM119+ microglia than CD68+ infiltrating macrophages in the tumor invasion area. On the other hand, there are more CD68+ infiltrating macrophages than TMEM119+ microglia in the tumor core regions, signifying a specific role of microglia in tumor invasion. Flow cytometry further supported that more CD11b+CD45low microglia prevalence in tumor surrounding tissues than in tumor core. ALTS1C1 astrocytoma cells, in the presence of microglia, exhibited more increased invasion and migration ability than the presence of macrophages in 2D/3D models. RNA sequencing highlighted M2 activation and cathepsin gene upregulation in microglia over macrophages. M2-polarized TAMs enhanced 2D migration, while cathepsin inhibition significantly decreased glioma's 3D invasion potential. Conclusion: This study identifies microglia as primary TAMs in brain tumor invasion areas and their roles in glioma cell survival and dissemination. Notable differences in activation states and the critical impact of cathepsin in microglia for their roles on brain tumor invasion and survival offer promising therapeutic avenues. Targeting cathepsin in microglia emerges as a novel glioma prevention and treatment strategy. These findings contribute valuable insights to enhance clinical interventions for glioma patients. Citation Format: Sheng-Yan Wu, Chi-Shiun Chiang. Microglial dominance in glioma dissemination: Unraveling TAMs' impact and therapeutic implications through modulating cathepsin activity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1509.