GPNMB Drives Brain Metastasis by Sculpting a Pathologic Endothelial–Immune Interactome

Brain metastasis remains a devastating disease with dismal prognosis. How circulating tumor cells (CTC) penetrate the blood-brain barrier (BBB) and reprogram the brain microenvironment remains unclear. Using spatially resolved multi-omics profiling of CTCs and brain metastases, integrated with experimental and clinical analyses, we identified glycoprotein nonmetastatic melanoma protein B (GPNMB) as a CTC-secreted driver of vascular disruption and brain colonization. CBX3 upregulation induced GPNMB expression, which bound endothelial EGFR, triggering CBL-mediated ubiquitination and degradation. Attenuated EGFR signaling suppressed FTO and disrupted endothelial junctions via YTHDF2-dependent TJP1 m6A methylation. Remarkably, GPNMB-induced BBB remodeling promoted immune infiltration via the CXCL12-CXCR4 axis and induced time-course-dependent T-cell exhaustion within the brain microenvironment. Clinically, elevated CBX3+GPNMB+ CTCs and plasma CXCL12 were significantly associated with brain metastasis progression in lung cancer and melanoma. Therapeutically, dual blockade of GPNMB and PD1 enhanced anti-brain metastasis efficacy in mice, unveiling GPNMB as a promising target for precision immunotherapy. SIGNIFICANCE: GPNMB is a CTC-secreted driver of BBB disruption and brain colonization via the CBX3-GPNMB-EGFR-FTO-TJP1 axis. GPNMB-induced BBB remodeling promotes CXCL12-CXCR4-mediated immune infiltration and enhances T-cell exhaustion, sensitizing brain metastasis tumors to GPNMB/PD1 dual blockade. CBX3+GPNMB+ CTCs and plasma CXCL12 may serve as noninvasive biomarkers for brain metastasis management.