P02.25.B DECREASED GLIOBLASTOMA GROWTH AND MACROPHAGE INFILTRATION IN A DISINTEGRIN AND METALLOPROTEINASE DOMAIN-CONTAINING PROTEIN 8 KNOCK-OUT MICE

Abstract BACKGROUND Proteases are pivotal drivers of solid tumor progression, facilitating invasiveness and modulating immune responses. A disintegrin and metalloproteinase domain-containing protein 8 (ADAM8) is expressed by both tumor and diverse immune cell subsets and may regulate their migratory behavior. Although elevated ADAM8 levels have been reported in glioblastoma (GBM) and correlated with unfavorable prognosis, its specific role in shaping the tumor immune microenvironment remains unclear. This study aimed to characterize the cellular expression profile of ADAM8 on stromal cells in GBM and to investigate its functional impact on tumor growth and macrophage recruitment using an orthotopic murine GBM model. MATERIAL AND METHODS Single-cell RNA sequencing (scRNA-seq) data from human GBM (Darmanis et al., 2017; www.gbmseq.org) were analyzed to determine ADAM8 expression across different cell types. Additionally, scRNA-seq data from CD45⁺ immune cells (Antunes et al., 2021) were examined to assess Adam8 expression in immune subsets from healthy mouse brain and GL261 tumors. To evaluate the functional role of Adam8 in stromal cells, syngeneic GL261 glioma cells were implanted orthotopically into Adam8 wild-type (wt) and knock-out (ko) mice. After three weeks, tumor volume was assessed using hematoxylin and eosin staining and analyzed with the Volumest plugin in ImageJ. Immune cell infiltration was evaluated via immunohistochemical staining for CD45 and F4/80 markers. RESULTS In human GBM, ADAM8 expression was primarily detected in myeloid cells. Analysis of murine CD45⁺ immune cells revealed cell type specific expression patterns of Adam8, with highest levels observed in dendritic cells and tumor-associated macrophages. In vivo, Adam8 ko mice exhibited significantly reduced tumor volumes compared to wt controls. Immunohistochemical analysis further demonstrated a decrease in F4/80⁺ macrophage infiltration in tumors from Adam8 ko mice. CONCLUSION ADAM8 is predominantly expressed in myeloid cells within the GBM microenvironment, particularly in dendritic cells and tumor-infiltrating macrophages. Loss of Adam8 in a murine model led to reduced tumor growth and macrophage infiltration, suggesting ADAM8’s role in GBM progression and its potential as a therapeutic target. ACKNOWLEDGMENT This work was supported by the National Institute for Cancer Research (LX22NPO5102), the Center for Tumor Ecology (CZ.02.1.01/0.0/0.0/16_019/0000785), Charles University project GAUK 365022 and Cooperatio Program,,Oncology and Haematology”. Adam8 ko mice were a kind gift from professor Jörg W. Bartsch, Head of Neurosurgery Lab at Philipps University of Marburg.