TMIC-47. INHIBITION OF MIR-146A-5P DECREASES PROGRESSION OF MELANOMA BRAIN METASTASIS VIA NOTCH PATHWAY DYSREGULATION IN ASTROCYTES

Abstract Melanoma has a high propensity for brain metastasis, occurring in 40% of late-stage patients. The progression of secondary tumors in the brain depends on the support of the surrounding microenvironment, emphasizing the importance of modulating neighboring cells for successful metastasis. Tumor-derived extracellular vesicles (EVs) play a crucial role in creating a pre-metastatic niche for tumor growth by transferring proteins, RNA, and DNA. This study aims to explore the involvement of melanoma brain metastasis (MBM)-derived EVs in MBM development and identify a target miRNA for potential therapeutic intervention. In an in vivo metastatic model, MBM-EV pre-treated mice exhibited significantly increased MBM tumor burden compared to non-primed mice. In vitro co-cultures of MBM-derived EVs with astrocytes led to astrocyte activation characterized by enhanced proliferation, invasion, cytokine production, and upregulation of GFAP. Microarray analysis revealed significant upregulation of miR-146a-5p in MBM-EVs compared to healthy astrocyte and melanocyte EVs. In situ hybridization of clinical MBM samples showed significantly elevated miR-146a-5p expression compared to healthy brain controls. Sequencing of NHA after co-culture with miR-146a-5p mimic revealed NUMB, a Notch signaling pathway inhibitor, as a miR-146a-5p target. Expression levels of Numb and other downstream Notch proteins were significantly altered in NHA in the presence of MBM-derived EVs and miR-146a. Deserpidine was identified as a potential inhibitor of miR-146a-5p through a drug docking study, and qPCR analysis confirmed reduced miR-146a-5p expression in deserpidine-treated MBM cells and EVs in vitro. In an MBM in vivo model, deserpidine-treated mice exhibited significantly increased survival, reduced tumor burden, and decreased astrocyte activation in both tumor and non-tumor brain tissues. In conclusion, EVs are important regulators of MBM and establish tumor-supporting reactive astrocytes by delivery of miR-146a. Elevated miR-146a levels in patients suggests a potential clinical intervention, and our results indicate deserpidine as a promising candidate for adjuvant therapy.