BSBM-02 Wnt5a Mediates Melanoma Brain Metastasis

Melanoma brain metastasis (MBM) leads to significant morbidity and mortality. Building on previous findings that WNT5A regulates melanoma metastasis and dormancy in extracranial niches, we hypothesize that WNT5A signaling facilitates melanoma invasion across the blood-brain barrier, while its downregulation drives intracranial metastatic proliferation. To explore this, we conducted functional studies using human melanoma cell lines and an organotypic mouse brain xenograft system. Overexpression or pharmacologic induction of WNT5A increased melanoma migration and invasion toward brain explant conditioned media in transwell assays. Wholemount confocal imaging of brain explant cultures revealed distinct tumor colonization patterns mirroring clinical dormancy and proliferative outgrowth depending on WNT5A level: melanoma overexpressing WNT5A formed single-cell dispersions perivascularly, whereas silencing WNT5A in syngeneic cells produced proliferative clusters. Exogenous recombinant WNT5A also induced G1 cell cycle arrest in FUCCI-transduced melanoma cells, supporting its role in maintaining dormancy. Conversely, the WNT5A antagonist SFRP1 drove melanoma toward increased tumor size and accelerated tumor development. Interestingly, immunohistochemical analysis of postmortem human brain tissue demonstrated robust SFRP1 expression in cerebral endothelium and neurons, indicating a potential source promoting metastatic outgrowth. Integrin profiling revealed elevated expression of adhesion proteins in invasive melanoma compared to WNT5A-silenced syngeneic lines, suggesting an association with enhanced metastatic potential and tumor extravasation. WNT5A overexpression resulted in greater endothelial and extracellular matrix engagement by adhesion assay and live-cell tracking. These interactions were recapitulated in ex vivo xenografts, with WNT5A-high melanoma adhering to endothelial basement laminin. Together, these findings highlight the importance of WNT5A regulation through the metastatic cascade, from endothelial adhesion and establishment of a perivascular dormancy niche to metastatic outgrowth. Further integration of transcriptomics and proteomics on mouse models and clinical MBM samples aim to uncover key modulators of WNT signaling and associated pathways in MBM progression which might be targeted therapeutically.