Oral Presentation 26th Annual Lorne Proteomics Symposium 2021

Illuminating the dark lipidome of cancer using isomer-resolved lipidomics (#24)

Reuben SE Young 1 , Andrew P Bowman 2 , Kaylyn D Tousignant 3 , David L Marshall 4 , Shane R Ellis 2 5 , Berwyck LJ Poad 4 , Martin C Sadowski 3 6 , Stephen J Blanksby 1 4
  1. School of Chemistry and Physics, Queensland University of Technology, Brisbane, QLD, Australia
  2. The Maastricht MultiModal Molecular Imaging Institute (M4I), Maastricht University, Maastricht, Netherlands
  3. Australian Prostate Cancer Research Centre - Queensland, Institute of Health and Biomedical Innovation, School of Biomedical Sciences, Faculty of Health, Queensland University of Technology/Translational Research Institute, Brisbane, QLD, Australia
  4. Central Analytical Research Facility - Institute for Future Environments, Queensland University of Technology, Brisbane, Not US or Canada, Australia
  5. Molecular Horizons and School of Chemistry and Molecular Bioscience, University of Wollongong, Woolongong, NSW, Australia
  6. Institute of Pathology, University of Bern, Bern, Switzerland

One hallmark of cancer metabolism is the increased production of membrane lipids during cellular proliferation. This characteristic necessitates a transition from the predominant supply of fatty acids from extracellular sources to their generation through de novo synthesis mechanisms. It follows therefore, that the cancer lipidome should carry signatures of this metabolic shift. Recent research has highlighted that significant variation within the cellular lipidome of cancer can remain ‘dark’ to conventional lipidomics. In contrast, isomer-resolved lipidomics can illuminate the once ‘dark lipidome’ and reveal otherwise hidden changes in cancer cells lipid metabolism. Here we deploy these next-generation technologies to trace the metabolic fate of exogenously supplied fatty acids in prostate cancer cell lines.

Using a combination of stable isotope labelled fatty acids with high-resolution mass spectrometry that combines collision- and ozone-induced dissociation modes, we trace metabolic end-products of extracellular fatty acids and contrast these with isotopologues derived from de novo synthesis. These isomer-resolved strategies elucidate full molecular structure(s) of labelled glycerophospholipids, including assignment of fatty acyl chain position on the glycerol-backbone (sn-position) and carbon-carbon double bond location(s). This analysis reveals that glycerophospholipids carrying labelled-extracellular fatty acids (or their metabolites) have distinctive regiochemical profiles. Notably, extracellular palmitic acid and its desaturated progeny are enriched at the sn-1 position on the glycerol-backbone compared to de novo-derived isotopologues. This trait is also shared by extracellular stearic acid, however metabolites of stearic acid display enrichment at the sn-2 position. Probing these ratiometric isomer changes can therefore provide signatures of de novo and extracellular sourcing of fatty acids.

Unlike in vitro cell models, the reduced blood flow (and hence restricted nutrient supply) that is common to in vivo tumours will limit extracellular fatty acid supply for uptake. Based on the regioisomeric changes observed within the in vitro LNCaP cell experiments, we hypothesised that exploring the dark lipidome of tumour tissues would reveal otherwise hidden fatty acid metabolic behaviours. To test this, we obtained resected LNCaP xenograft tumours and combined isomer-resolved lipidomics with mass spectrometry imaging to monitor the regioisomeric lipid distribution across the tissues. This analysis revealed distinct domains across the tumour, indicating changes to fatty acid supply. Regions marred with the isomeric-signature of extracellular uptake were also found to contain high levels of arachidonic acid and DHA containing glycerophospholipids – fatty acids that must be exogenously sourced within mammals. Together, these findings implicate the lipase enzyme, PLA2, may have a unique influence on tumour lipid remodelling.