P10.03.B MOLECULAR REGULATION OF BLOOD TUMOR BARRIER IN SONIC HEDGEHOG SUBGROUP OF MEDULLOBLASTOMA

Abstract BACKGROUND Target inhibitors of SHH signaling pathway have entered clinical trials, but the efficacy is poor and the mechanism is unclear. Studies have shown that remodeling of the Blood Tumor Barrier (BTB) in brain tumors is closely related to the effectiveness of chemotherapy. The formation of BTB is not a simple destruction and reconstruction of the Blood Brain Barrier (BBB), but the result of structural remodeling of the interaction between tumor cells and the cells that make up the BBB. The permeability and regulatory mechanism of BTB in SHH-MB remain to be determined. The purpose of this study was to explore the integrity of BTB in SHH-MB and the potential molecular mechanism of tumor cells affecting BTB remodeling, so as to provide new target for improving the therapeutic strategy. MATERIAL AND METHODS A transgenic mouse model of SHH-MB was used to observe the permeability of BTB after injection of FITC-Dextran with different molecular sizes in the tail vein by two-photon microscopy. The structure and integrity of BTB were verified by immunofluorescence and electron microscope staining. The differential expression of BTB-related molecules in SHH-MB tumor tissues was compared and analyzed by transcriptome sequencing data, and further verified in vivo and in vitro BTB models. At the same time, by establishing the co-culture system of SHH-MB and BTB cells, the regulatory molecular mechanism of SHH-MB tumor cells on BTB was explored. RESULTS In vivo two-photon microscopy imaging showed that the permeability of FITC-Dextran with different molecular sizes was different in SHH-MB mice. Compared with BBB, the BTB permeability of SHH-MB was increased. The results of tissue immunofluorescence and transmission electron microscopy showed that the tight connections between endothelial cells in BTB of SHH-MB were destroyed. Western Blot results showed that the expression of tight junction related proteins in SHH-MB showed heterogeneity, in which the expression of Occludin decreased, while the expression of JAM-A increased. In vitro cell experiment results showed that SHH-MB tumor cells could up-regulate the expression of JAM-A and Claudin-5 in microvascular endothelial cells, and down-regulate the expression of Occludin at the same time. CONCLUSION In this study, the remodeling of BTB in SHH-MB was investigated in depth for the first time. Compared with BBB, the BTB permeability of SHH-MB was not significantly increased because the expression of JAM-A and Claudin-5 in microvascular endothelial cells was upregulated, although the expression of Occludin, another tight junction related protein, was decreased paradoxically. The results of this study provide potential therapeutic targets and new ideas for improving the permeability of SHH-MB chemotherapy drugs.