Paper BI+AS-MoA5
Time-of-Flight Secondary Ion Mass Spectrometry Investigations of the Pancreatic Islet Tumor Microenvironment

Monday, October 19, 2015, 3:40 pm, Room 211D

Imaging time-of-flight secondary ion mass spectrometry (ToF-SIMS) provides chemical information with subcellular spatial resolution. In this work, imaging ToF-SIMS is used to analyze tumor microenvironments from mouse model (Myc/p53-/-) biopsies with Myc-dependent inducible and regressible pancreatic β-cell neoplasia. The Myc oncogene is overexpressed in many human cancers and has major effects on cellular metabolism, including lipid metabolism. While imaging ToF-SIMS analysis of tumor tissue will provide a new perspective by visualizing tumor progression/regression, the system itself can also act as a model system for investigating stroma-tumor interactions in cancerous tissues.

Pancreatic tissues were harvested and frozen in optimal cutting temperature (OCT) at 6 days post Myc induction. 4 µm cryosections were serially cut, with one used for H&E staining, one for ToF-SIMS analysis, and another for immunohistochemistry. High mass and high spatial resolution data was acquired with the pulsed 25 keV Bi₃⁺ ion beam rastered over a 1 mm x 1 mm area (1280 x 1280 pixels). ROIs of the tumor and stromal tissue were then investigated further with imaging principal components analysis (PCA) to identify peaks that correspond to species of interest. Regions identified by analysis and PCA were cross-referenced against immunohistochemical and H&E images to differentiate tumor areas from the surrounding tissue.

ToF-SIMS data suggests a preferential uptake of fatty acids 18:3 and 18:2 within the tumor. The 6 day Myc-induced islet tumor exhibits a signal of 14:0, possibly a product of de novo fatty acid synthesis within the tumor. The tumor also exhibits an increased localization of sphingomyelin fragments and vitamin E compared to the surrounding tissue. Interestingly, the data shows an absence of Mg⁺ within the islet tumor and small, higher signal regions on the periphery of the tumor. These peripheral tumor regions also show an increased, localized signal of CN^-, CNO^-, C₇H₁₀O⁺, and Fe⁺, but further histologic correlations are needed to discern if these structures are inflammatory zones, mitochondrial dense regions, or related to vasculature. Once these localized areas have been defined, a comparison to the chemistry identified by ToF-SIMS may aid in interpreting the Myc oncogene and its effect on pancreatic β-cell neoplasia. PCA was applied to image data and revealed different chemistries within the tumor and surrounding tissue. PCA was also applied to selected tumor region images to spatially and chemically analyze within the tumor to compare chemistries between different tumor sizes, where tumor size is potentially indicative of different tumor stage development.