PACM-10 CELLULAR CROSSTALK IN THE BRAIN MICROENVIRONMENT PROMOTES MELANOMA INVASION AND GROWTH

Abstract

Melanoma exhibits dynamic transcriptional adaptations to microenvironmental cues. Phenotypic heterogeneity impacts treatment response, particularly in melanoma brain metastasis (MBM), where therapeutic resistance is common. To interrogate MBM cellular ecosystem, we profiled 114,455 single-cell transcriptomes from publicly available dataset. Melanoma cells were dichotomized by WNT5A expression levels to proliferative and invasive subtypes. Intercellular communication networks were inferred using CellChat, with top predicted interactions validated in vivo and in vitro. Invasive melanoma (WNT5A-high) showed strongest interactions with endothelial cells through laminin-integrin signaling. Proliferative melanoma (WNT5A-low) interacted most strongly with microglia, which induced a shift toward an invasive tumor state through MCAM activation. To assess melanoma phenotype—microenvironment interactions, control and WNT5A-overexpressing cells were injected intracranially into C57BL/6J mice. WNT5A tumors demonstrated significantly faster growth and shorter survival. Histologic examination revealed significantly greater proportion of invasive infiltrates in WNT5A tumors, frequently tracking along native vasculature. In vitro, WNT5A-overexpressing cells showed increased adhesion to endothelial cells and perivascular matrix, and ex vivo brain slice co-cultures demonstrated greater perivascular localization. Immunofluorescent imaging of microglia revealed three morphologies: homeostatic microglia in non‑tumor regions, enlarged intratumoral microglia, and elongated microglia within invasive infiltrates aligned with MCAM‑positive tumor tracks. While immunohistochemistry confirmed higher overall WNT5A expression in WNT5A-overexpressing tumors, melanoma cells within invasive infiltrates of control tumors exhibited comparable WNT5A expression, suggesting local microenvironmental induction of an invasive phenotype. Single-cell RNA sequencing of tumor-associated microglia identified three subclusters, including one with elevated WNT5A expression. Ongoing spatial transcriptomic analyses in human MBM aim to validate the spatial organization of melanoma phenotypes and their interactions with microglia and other brain cell types. Integrated analyses show that MBM exhibits dynamic bidirectional signaling across tumor cells, endothelium, and microglia, collectively driving invasion and proliferation. Targeting these communication networks may offer a promising therapeutic strategy.