METB-11. On-tissue Spatial Profiling with Quantitative Mass Spectrometry Discovers Isomeric Lipid Alternations in Patient-derived Orthotopic Medulloblastoma Mouse Models

Abstract Medulloblastoma (MB) is the most common malignant pediatric brain tumor with the propensity to metastasis at both initial diagnosis and recurrence. Lipid metabolism is increasingly recognized as a critical role in cancer metastasis and therapeutic resistance, yet the structural diversity and spatial heterogeneity of lipid isomers in biological tissues limited our understanding of lipid reprogramming during these processes. To address this, we developed a novel platform that integrates aziridination-based isobaric mass tagging strategy with mass spectrometry imaging (MSI) techniques to achieve spatially resolved, C=C positional isomer-specific, and quantitative lipid profiling on tissues sections. Using patient-derived orthotopic medulloblastoma mouse models, we discovered distinct lipid isomer distributions between tumor cores and metastatic sites. We found that n-9 fatty acids and phosphatidylcholines were more abundant in tumor cores, whereas n-7 lipids were less rich, indicating a differential preference for lipid biosynthetic pathways. Specifically, tumor cores favor elongation by fatty acid elongase (Elovl) followed by stearoyl-CoA desaturase (SCD), while metastatic sites prefer the desaturation-first pathway. Notably, n-10 fatty acids and phosphatidylcholines were significantly enriched in metastatic regions. Unlike common unsaturated lipids formed via SCD, n-10 lipids arise from an alternative desaturation pathway that involves fatty acid desaturase 2 (FADS2), which has recently been reported to be abnormally expressed in cancer cells and is potential therapeutic target for treatment. Our results suggested aberrant FADS2 activity in metastatic MB. Additionally, we observed significant lipid accumulation in post-radiotherapy PDOX mouse models through quantitative lipid profiling, highlighting enhanced fatty acid synthesis and lipid droplet formation as adaptive responses to therapeutic stress. Our findings highlight the complexity of lipid reprogramming in MB and underscore the importance of analyzing isomeric lipids to gain deeper insight into tumor biology, biomarkers discovery and therapeutic strategies.