Mass Spectrometry Images Acylcarnitines, Phosphatidylcholines and Sphingomyelin in MDA-MB-231 Breast Tumor Models

The lipid compositions of different breast tumor microenvironments are largely unknown due to limitations in lipid imaging techniques. Imaging lipid distributions would enhance our understanding of processes occurring inside growing tumors such as cancer proliferation and metastasis. Recent developments in MALDI mass spectrometry imaging (MSI) enable rapid and specific detection of lipids directly from thin tissue sections. In this study, we performed multimodal imaging of acylcarnitines, phosphatidylcholines (PC), a lysophosphatidylcholine (LPC) and a sphingomyelin (SM) from different microenvironments of breast tumor xenograft models, which carried tdTomato red fluorescent protein as a hypoxia-response element driven reporter gene. The MSI molecular lipid images revealed spatially heterogeneous lipid distributions within tumor tissue. Five of the most abundant lipid species, namely PC(16:0/16:0), PC(16:0/18:1), PC(18:1/18:1) PC(18:0/18:1) and SM(d18:1/16:0) sodium adduct were localized in viable tumor regions, while PC(18:0/22:1) and LPC(16:0/0:0) were detected in necrotic tumor regions. We identified a heterogeneous distribution of palmitoyl- and stearoylcarnitine, which mostly colocalized with hypoxic tumor regions. For the first time, we have applied a multimodal imaging approach that has combined optical imaging and MALDI-MSI with ion mobility separation to spatially localize and structurally identify acylcarnitines and a variety of lipid species present in breast tumor xenograft models.