CNSC-38. TARGETING UNC5B INDUCES BLOOD-BRAIN BARRIER PERMEABILITY AND IMPROVES CHEMOTHERAPY DELIVERY AND EFFICACY IN GLIOBLASTOMA

Abstract The blood-brain barrier (BBB) plays a critical role in protecting the central nervous system (CNS) from toxins and pathogens while maintaining CNS homeostasis and function. However, this tightly regulated impermeability also poses a major challenge for delivery of therapeutic agents during CNS pathologies, including glioblastoma (GBM), the most common and aggressive primary brain tumor. GBM is associated with a median survival of 12–15 months post-diagnosis and a five-year survival rate of less than 5%. Thus, developing strategies to safely and effectively overcome the restrictive nature of the BBB remains a major challenge and key objective in neuro-oncology. We have identified Unc5B as a key regulator of BBB integrity via modulation of the Wnt/β-catenin pathway. Systemic administration of an anti-Unc5B blocking antibody induced transient, size-selective BBB opening, suggesting that anti-Unc5B could serve as a transformative tool in neuropharmacology, enabling controlled CNS drug delivery. In this study, our main goal was to assess the therapeutic potential and mechanistic basis of anti-Unc5B-mediated BBB modulation in glioblastoma. To achieve this, we first characterized expression of the Unc5B receptor and associated pathways in GBM endothelial cells using single-cell RNA sequencing and RT-PCR of patient-derived GBM samples. We further utilized iDISCO/LSFM and two-photon live imaging to investigate the spatial distribution and temporal dynamics of BBB modulation following anti-Unc5B administration. Mechanistically, we found that anti-Unc5B treatment promotes ubiquitination, internalization, and degradation of Claudin-5 (Cldn5), mediated by E3 ubiquitin ligase Siah1. Importantly, we demonstrated for the first time that anti-Unc5B-induced BBB opening enhances delivery of both conventional chemotherapies, such as doxorubicin and temozolomide, and targeted therapies, including the EGFRvIII-specific inhibitor osimertinib, in GBM-bearing mice. This enhanced delivery resulted in reduced tumor burden, increased tumor cell apoptosis, and improved survival. These findings represent the first preclinical validation of anti-Unc5B monoclonal blocking antibody in glioblastoma models and highlight its potential to improve drug delivery and therapeutic efficacy in brain tumors.