Epen-18. Multi-Omics Approach Revealed a Tight Blood-Brain Barrier in Ependymoma

Abstract BACKGROUND A major challenge in the treatment of brain tumors is the limited penetration of many drugs through the blood-brain barrier (BBB). BBB characteristics include endothelial cells connected by tight junction proteins (e.g. Claudin5, ZO1, occludin) and the expression of efflux transporters (e.g. P-gp) with the physiological role to limit the accumulation of potentially toxic substances in brain tissue. Our study aims to enhance our understanding of the BBB composition across different molecular groups of ependymoma (EPN) with the goal of leveraging this knowledge to improve therapeutic strategies against these tumors. METHODS We applied a multi-omics approach integrating single-nuclear RNA sequencing and ultra-high content imaging to unravel BBB composition at both transcriptomic and proteomic levels. Patient-derived xenograft (PDX) models were utilized to explore differences in BBB penetration between tumor and healthy brain tissue following drug treatments. RESULTS Expression of tight junction and transporter proteins revealed strong dependencies specific to molecular groups, but were independent of the corresponding brain regions. Human tissue of ST-EPN-ZFTA exhibited highest expression of claudin5, while both ST-EPN-ZFTA and PF-EPN-A represented upregulation of occludin and ZO1 in comparison to healthy tissue. These findings on claudin5 and ZO1 were further confirmed in PDX models. Single-cell data analysis from patients localized the expression of relevant BBB factors to tumor-associated endothelial cells. Treatment of PDX models with drugs revealed disparities in drug penetration between EPN tumors and healthy brain regions. Notably, for most drugs BBB penetration was lower in ST-EPN-ZFTA tumors than healthy brain region. CONCLUSIONS Molecular BBB specifics may contribute to drug resistance of aggressive EPN particularly in ST-EPN-ZFTA tumors, which presented high tight junction expressions and lower drug penetration. This resource aims to improve BBB penetration prediction in EPN, to identify combination therapies targeting BBB components and to select innovative drug delivery approaches.