Accurately measuring metabolites is crucial to understand the complex biochemical processes within tissues and organisms. Traditionally, this measurement is achieved by mechanical or chemical disruption of cells to release metabolites into an extraction solution. Careful formulation of this solution enables enrichment of specific classes of molecules while reducing the abundance of others. Such reduction in matrix complexity favours efficient ionization of molecules of interest during mass spectrometry (MS), thereby improving detectability. However, information on the specific metabolome of different cell populations or on spatial metabolite distribution is typically lost in such bulk tissue analyses. Yet, capturing metabolic heterogeneity is essential when studying cell type-specific rewiring and metabolic crosstalk. Mass spectrometry imaging (MSI) addresses this challenge by enabling the reconstruction of detailed metabolic maps with preserved spatial information, to gain insights into cellular and even subcellular processes.

Deregulating cellular metabolism is a hallmark of cancer and targeting metabolic pathways represents a backbone of cancer treatment. Vande Voorde et al. used a combination of HPLC-MS, matrix-assisted laser desorption ionization (MALDI) and desorption electrospray ionization (DESI) MSI to identify vulnerabilities of KRAS-mutant colorectal cancers (CRC), which are refractory to targeted approaches and have a poor response to chemotherapy. Analysis of tissues from genetically engineered mouse models of CRC revealed pronounced metabolic differences between the tumour epithelial and stromal cell populations, which highlights the limitations of bulk metabolomics in capturing tumour heterogeneity. An MSI-guided approach showed specific depletion of glutamine in KRAS-mutant versus KRAS wild-type tumour cells. This finding can be attributed to the transcriptional upregulation of the amino acid transporter encoded by Slc7a5 in KRAS-mutant CRC; SLC7A5 imports essential amino acids in exchange for glutamine, a process that is crucial for colorectal tumorigenesis in preclinical models, as reported by Najumudeen et al.