Laser Interstitial Thermal Therapy Enhances Bidirectional Blood-Brain Barrier Permeability in Glioblastoma

BACKGROUND: Laser interstitial thermal therapy (LITT) is a minimally invasive treatment for glioblastoma that increases blood-brain barrier (BBB) permeability. However, the mechanisms and spatiotemporal features of this effect remain unclear. It is also unknown whether LITT promotes release of circulating tumor DNA (ctDNA). METHODS: Using our previously developed LITT mouse model, we employed single-cell RNA sequencing (scRNAseq) to investigate gene expression changes in endothelial cells following LITT in naïve mouse brain. Brains were also harvested at multiple time points to assess LITT effects on tight junction (TJ) integrity and transcytosis via immunofluorescence and transmission electron microscopy. Human glioblastoma tissues were analyzed to monitor ambient caveolae-mediated transcytosis in tumor regions. Finally, ctDNA levels in mouse plasma were quantified using digital droplet PCR following LITT. RESULTS: LITT triggered downregulation of pathways related to cell-cell junctions and upregulation of transcytosis. LITT transiently disrupted TJ integrity for 7 days up to 100 µm away from the ablation zone. Further, LITT increased caveolae-mediated transcytosis in endothelial cells for 21 days, peaking at 14 days, in part due to suppression of the transcytosis inhibitor Mfsd2a. LITT facilitated ctDNA detection in mouse plasma at 1 hour, 3 days, 7 days, and 14 days post-procedure. CONCLUSIONS: Our study demonstrates that LITT transiently disrupts the BBB in the periphery of the ablation with endothelial TJ disruption and transcytosis upregulation following distinct time courses. LITT effects on the BBB are bidirectional and enhance ctDNA release in addition to enabling brain entry of agents.