Phospholipid dynamics in ex vivo lung cancer and normal lung explants

Abstract

In cancer cells, metabolic pathways are reprogrammed to promote cell proliferation and growth. While the rewiring of central biosynthetic pathways is being extensively studied, the dynamics of phospholipids in cancer cells are still poorly understood. In our study, we sought to evaluate de novo biosynthesis of glycerophospholipids (GPLs) in ex vivo lung cancer explants and corresponding normal lung tissue from six patients by utilizing a stable isotopic labeling approach. Incorporation of fully 13 C-labeled glucose into the backbone of phosphatidylethanolamine (PE), phosphatidylcholine (PC), and phosphatidylinositol (PI) was analyzed by liquid chromatography/mass spectrometry. Lung cancer tissue showed significantly elevated isotopic enrichment within the glycerol backbone of PE, normalized to its incorporation into PI, compared to that in normal lung tissue; however, the size of the PE pool normalized to the size of the PI pool was smaller in tumor tissue. These findings indicate enhanced PE turnover in lung cancer tissue. Elevated biosynthesis of PE in lung cancer tissue was supported by enhanced expression of the PE biosynthesis genes ETNK2 and EPT1 and decreased expression of the PC and PI biosynthesis genes CHPT1 and CDS2 , respectively, in different subtypes of lung cancer in publicly available datasets. Our study demonstrates that incorporation of glucose-derived carbons into the glycerol backbone of GPLs can be monitored to study phospholipid dynamics in tumor explants and shows that PE turnover is elevated in lung cancer tissue compared to normal lung tissue. Lung cancer cells rewire their metabolism to produce more of a lipid, or fat, called phosphatidylethanolamine (PE), an important component of the cell membrane. The ways that cancer cells change their metabolism to support tumor growth have been studied, but how lipid metabolism is altered is not well understood. Katharina Leithner at the Medical University of Graz in Austria and co-workers fed healthy lung tissue explants (fragments) and lung cancer explants with isotopically labelled sugars, and traced the metabolic products of these sugars. They found that lung cancer tissue made more PE than healthy tissue, and that the genes for PE biosynthesis were highly activated. These results demonstrate a new method for studying how cancer cells rewire lipid metabolism, and may help reveal cancer cells’ metabolic vulnerabilities, opening the way to development of novel treatments.