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Quantitation of Endogenous Metabolites in Mouse Tumors Using Mass-Spectrometry Imaging

Swales, John G., Dexter, Alex, Hamm, Gregory, Nilsson, Anna, Strittmatter, Nicole, Michopoulos, Filippos, Hardy, Christopher, Morentin-Gutierrez, Pablo, Mellor, Martine, Andren, Per E., Clench, Malcolm R., Bunch, Josephine, Critchlow, Susan E., Goodwin, Richard J. A.
Analytical chemistry 2018 v.90 no.10 pp. 6051-6058
containers, glutamic acid, image analysis, lactic acid, mass spectrometry, metabolites, mice, models, neoplasms, phenotype, protocols, storage temperature
Described is a quantitative-mass-spectrometry-imaging (qMSI) methodology for the analysis of lactate and glutamate distributions in order to delineate heterogeneity among mouse tumor models used to support drug-discovery efficacy testing. We evaluate and report on preanalysis-stabilization methods aimed at improving the reproducibility and efficiency of quantitative assessments of endogenous molecules in tissues. Stability experiments demonstrate that optimum stabilization protocols consist of frozen-tissue embedding, post-tissue-sectioning desiccation, and storage at −80 °C of tissue sections sealed in vacuum-tight containers. Optimized stabilization protocols are used in combination with qMSI methodology for the absolute quantitation of lactate and glutamate in tumors, incorporating the use of two different stable-isotope-labeled versions of each analyte and spectral-clustering performed on each tissue section using k-means clustering to allow region-specific, pixel-by-pixel quantitation. Region-specific qMSI was used to screen different tumor models and identify a phenotype that has low lactate heterogeneity, which will enable accurate measurements of lactate modulation in future drug-discovery studies. We conclude that using optimized qMSI protocols, it is possible to quantify endogenous metabolites within tumors, and region-specific quantitation can provide valuable insight into tissue heterogeneity and the tumor microenvironment.