title: Hyperactivation of oxidative mitochondrial metabolism in epithelial cancer cells in situ: visualizing the therapeutic effects of metformin in tumor tissue.
abstract: We have recently proposed a new mechanism for explaining energy transfer in cancer metabolism. In this scenario, cancer cells behave as metabolic parasites, by extracting nutrients from normal host cells, such as fibroblasts, via the secretion of hydrogen peroxide as the initial trigger. Oxidative stress in the tumor microenvironment then leads to autophagy-driven catabolism, mitochondrial dys-function, and aerobic glycolysis. This, in turn, produces high-energy nutrients (such as L-lactate, ketones, and glutamine) that drive the anabolic growth of tumor cells, via oxidative mitochondrial metabolism. A logical prediction of this new "parasitic" cancer model is that tumor-associated fibroblasts should show evidence of mitochondrial dys-function (mitophagy and aerobic glycolysis). In contrast, epithelial cancer cells should increase their oxidative mitochondrial capacity. To further test this hypothesis, here we subjected frozen sections from human breast tumors to a staining procedure that only detects functional mitochondria. This method detects the in situ enzymatic activity of cytochrome C oxidase (COX), also known as Complex IV. Remarkably, cancer cells show an over-abundance of COX activity, while adjacent stromal cells remain essentially negative. Adjacent normal ductal epithelial cells also show little or no COX activity, relative to epithelial cancer cells. Thus, oxidative mitochondrial activity is selectively amplified in cancer cells. Although COX activity staining has never been applied to cancer tissues, it could now be used routinely to distinguish cancer cells from normal cells, and to establish negative margins during cancer surgery. Similar results were obtained with NADH activity staining, which measures Complex I activity, and succinate dehydrogenase (SDH) activity staining, which measures Complex II activity. COX and NADH activities were blocked by electron transport inhibitors, such as Metformin. This has mechanistic and clinical implications for using Metformin as an anti-cancer drug, both for cancer therapy and chemo-prevention. We also immuno-stained human breast cancers for a series of well-established protein biomarkers of metabolism. More specifically, we now show that cancer-associated fibroblasts over-express markers of autophagy (cathepsin B), mitophagy (BNIP3L), and aerobic glycolysis (MCT4). Conversely, epithelial cancer cells show the over-expression of a mitochondrial membrane marker (TOMM20), as well as key components of Complex IV (MT-CO1) and Complex II (SDH-B). We also validated our observations using a bioinformatics approach with data from > 2,000 breast cancer patients, which showed the transcriptional upregulation of mitochondrial oxidative phosphorylation (OXPHOS) in human breast tumors (p < 10(-20)), and a specific association with metastasis. Therefore, upregulation of OXPHOS in epithelial tumor cells is a common feature of human breast cancers. In summary, our data provide the first functional in vivo evidence that epithelial cancer cells perform enhanced mitochondrial oxidative phosphorylation, allowing them to produce high amounts of ATP. Thus, we believe that mitochondria are both the "powerhouse" and "Achilles' heel" of cancer cells.
authors: The Jefferson Stem Cell Biology and Regenerative Medicine Center, Kimmel Cancer Center, Thomas Jefferson University, Philadelphia, PA, USA.
authors: Diana
authors: D
authors: Whitaker-Menezes
authors: Ubaldo E
authors: UE
authors: Martinez-Outschoorn
authors: Neal
authors: N
authors: Flomenberg
authors: Ruth C
authors: RC
authors: Birbe
authors: Agnieszka K
authors: AK
authors: Witkiewicz
authors: Anthony
authors: A
authors: Howell
authors: Stephanos
authors: S
authors: Pavlides
authors: Aristotelis
authors: A
authors: Tsirigos
authors: Adam
authors: A
authors: Ertel
authors: Richard G
authors: RG
authors: Pestell
authors: Paolo
authors: P
authors: Broda
authors: Carlo
authors: C
authors: Minetti
authors: Michael P
authors: MP
authors: Lisanti
authors: Federica
authors: F
authors: Sotgia
mesh_terms: D014408:Biomarkers, Tumor / Q000378:metabolism; D001943:Breast Neoplasms / Q000378:metabolism*; D045744:Cell Line, Tumor / Q000187:drug effects; D019295:Computational Biology; D003576:Electron Transport Complex IV / Q000378:metabolism; D004734:Energy Metabolism; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004847:Epithelial Cells / Q000187:drug effects*; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006019:Glycolysis; D006801:Humans; D008314:Malonates / Q000494:pharmacology; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism; D008687:Metformin / Q000494:pharmacology*; D008928:Mitochondria / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D024101:Mitochondrial Proteins / Q000235:genetics / Q000378:metabolism; D009362:Neoplasm Metastasis; D010085:Oxidative Phosphorylation; D018384:Oxidative Stress; D011956:Receptors, Cell Surface / Q000235:genetics / Q000378:metabolism; D059016:Tumor Microenvironment
chemical_list: D014408:Biomarkers, Tumor; D004791:Enzyme Inhibitors; D008314:Malonates; D026901:Membrane Transport Proteins; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D024101:Mitochondrial Proteins; D011956:Receptors, Cell Surface; C084008:TOMM20 protein, human; D008687:Metformin; C030290:malonic acid; D003576:Electron Transport Complex IV