P02.28.A FIBROBLAST ACTIVATION PROTEIN-EXPRESSING STROMAL CELLS IN GLIOBLASTOMA ANGIOGENESIS AND VASCULAR DESTABILIZATION.

Abstract BACKGROUND Glioblastoma (GBM) is characterized by a disorganized stroma, where malignant cells reprogram host-derived mesenchymal cells to establish a supportive tumor microenvironment. Similar to findings in carcinomas, recent studies have identified stromal cells expressing the transmembrane protease fibroblast activation protein (FAP) within the GBM microenvironment. In various cancer types, FAP expressing stromal cells have emerged as promising targets for both diagnostic and therapeutic interventions. Our analysis demonstrated that FAP-positive stromal cells are predominantly localized around aberrant blood vessels in GBM, with their abundance positively correlating with tumor vascularization. Moreover, FAP-positive cells isolated from human GBM promoted angiogenic sprouting. In this study we investigated the contribution of FAP-positive stromal cells to blood vessel destabilization in GBM. MATERIAL AND METHODS Expression of blood-brain barrier (BBB) markers was analyzed using publicly available IVY Glioblastoma Atlas. FAP-expressing stromal cell cultures were isolated from human GBM samples via magnetic-activated cell sorting using anti-human FAP antibody. Conditioned media from these cells were used in in vitro permeability assays and analyzed using xMAP® technology. RESULTS Analysis of the IVY Glioblastoma Atlas revealed that vascular regions with high FAP expression exhibited reduced levels of key proteins involved in maintaining BBB integrity compared to regions with low FAP expression. Additionally, our preliminary in vitro experiments demonstrated that conditioned media from patient-derived FAP-positive stromal cell cultures decreased the expression of BBB markers in endothelial monolayers and impaired barrier integrity. Furthermore, we identified alterations in the production of mediators relevant to both the maintenance and disruption of the BBB in the conditioned media. CONCLUSION Our findings indicate that FAP-positive stromal cells in GBM not only promote angiogenesis but also contribute to vascular destabilization. These results highlight their role as active drivers of GBM progression and underscore their potential as therapeutic targets. ACKNOWLEDGMENT This research was funded by the Program Cooperatio, research area,,Oncology and Haematology“; Ministry of Education, Youth and Sports of the Czech Republic - LM2023053 of EATRIS-CZ and project “Center of Tumor Ecology” (CZ.02.1.01/0.0/0.0/16_019/0000785) - Operational Program Research, Development and Education; project National Institute for Cancer Research (Programme EXCELES, ID Project No. LX22NPO5102) by the European Union - Next Generation EU.