Extracellular Vesicle-Mediated Nucleolin Transfer in Glioblastoma: A Targetable Axis Driving Blood-Tumour Barrier Formation

Glioblastoma (GBM) remains a significant therapeutic challenge. While GBM-derived extracellular vesicles (EVs) are known to remodel the normal blood-brain barrier (BBB) into a blood-tumour barrier (BTB), the underlying mechanism is largely not understood. Here, we reveal that nucleolin (NCL) is transferred via GBM-derived EVs to the surface of brain endothelial cells, where it promotes BTB formation. Furthermore, the NCL-specific aptamer AS1411 exploits this pathway, crossing the BTB through receptor-mediated transcytosis and selectively entering GBM cells in an NCL-dependent manner. Proteolysis-targeting chimeras (PROTACs), heterobifunctional molecules that recruit E3 Ligases to degrade target proteins, show therapeutic potential but are hindered by inefficient brain penetration in GBM. Capitalizing on the BTB-penetrating capability of AS1411 and our prior finding that AS1411 can intracellularly recruit the E3 Ligase MDM2 via employing NCL as a molecular bridge, we engineered AS1411-based PROTACs against VEGFR2 and EGFR. These PROTACs induced NCL- and MDM2-dependent ubiquitination and degradation of VEGFR2 or EGFR in GBM cells, demonstrating potent anti-tumour activity. Collectively, our findings identify EV-transferred NCL as a key mediator of BTB formation and a functional transcytosis receptor for AS1411, providing a promising strategy for developing BTB-permeable, targeted therapy for GBM.