title: Cancer cells metabolically "fertilize" the tumor microenvironment with hydrogen peroxide, driving the Warburg effect: implications for PET imaging of human tumors.
abstract: Previously, we proposed that cancer cells behave as metabolic parasites, as they use targeted oxidative stress as a "weapon" to extract recycled nutrients from adjacent stromal cells. Oxidative stress in cancer-associated fibroblasts triggers autophagy and  mitophagy, resulting in compartmentalized cellular catabolism, loss of mitochondrial function, and the onset of aerobic glycolysis, in the tumor stroma. As such, cancer-associated fibroblasts produce high-energy nutrients (such as lactate and ketones) that fuel mitochondrial biogenesis, and oxidative metabolism in cancer cells. We have termed this new energy-transfer mechanism the "reverse Warburg effect." To further test the validity of this hypothesis, here we used an in vitro MCF7-fibroblast co-culture system, and quantitatively measured a variety of metabolic parameters by FACS analysis (analogous to laser-capture micro-dissection).  Mitochondrial activity, glucose uptake, and ROS production were measured with highly-sensitive fluorescent probes (MitoTracker, NBD-2-deoxy-glucose, and DCF-DA). Interestingly, using this approach, we directly show that cancer cells initially secrete hydrogen peroxide that then triggers oxidative stress in neighboring fibroblasts. Thus, oxidative stress is contagious (spreads like a virus) and is propagated laterally and vectorially from cancer cells to adjacent fibroblasts. Experimentally, we show that oxidative stress in cancer-associated fibroblasts quantitatively reduces mitochondrial activity, and increases glucose uptake, as the fibroblasts become more dependent on aerobic glycolysis.  Conversely, co-cultured cancer cells show significant increases in mitochondrial activity, and corresponding reductions in both glucose uptake and GLUT1 expression. Pre-treatment of co-cultures with extracellular catalase (an anti-oxidant enzyme that detoxifies hydrogen peroxide) blocks the onset of oxidative stress, and potently induces the death of cancer cells, likely via starvation.  Given that cancer-associated fibroblasts show the largest increases in glucose uptake, we suggest that PET imaging of human tumors, with Fluoro-2-deoxy-D-glucose (F-2-DG), may be specifically detecting the tumor stroma, rather than epithelial cancer cells.
authors.affiliation: The Jefferson Stem Cell Biology and Regenerative Medicine Center, Kimmel Cancer Center, Thomas Jefferson University, Philadelphia, PA, USA.
authors.forename: Ubaldo E
authors.initials: UE
authors.lastname: Martinez-Outschoorn
authors.forename: Zhao
authors.initials: Z
authors.lastname: Lin
authors.forename: Casey
authors.initials: C
authors.lastname: Trimmer
authors.forename: Neal
authors.initials: N
authors.lastname: Flomenberg
authors.forename: Chenguang
authors.initials: C
authors.lastname: Wang
authors.forename: Stephanos
authors.initials: S
authors.lastname: Pavlides
authors.forename: Richard G
authors.initials: RG
authors.lastname: Pestell
authors.forename: Anthony
authors.initials: A
authors.lastname: Howell
authors.forename: Federica
authors.initials: F
authors.lastname: Sotgia
authors.forename: Michael P
authors.initials: MP
authors.lastname: Lisanti
mesh_terms: D017209:Apoptosis; D001943:Breast Neoplasms / Q000000981:diagnostic imaging / Q000378:metabolism*; D002374:Catalase / Q000494:pharmacology; D002460:Cell Line; D018920:Coculture Techniques; D005260:Female; D005347:Fibroblasts / Q000378:metabolism; D005456:Fluorescent Dyes / Q000737:chemistry; D051272:Glucose Transporter Type 1 / Q000378:metabolism; D006019:Glycolysis; D006801:Humans; D006861:Hydrogen Peroxide / Q000378:metabolism*; D008928:Mitochondria / Q000378:metabolism; D018384:Oxidative Stress; D049268:Positron-Emission Tomography; D017382:Reactive Oxygen Species / Q000378:metabolism; D059016:Tumor Microenvironment
chemical_list: D005456:Fluorescent Dyes; D051272:Glucose Transporter Type 1; D017382:Reactive Oxygen Species; D006861:Hydrogen Peroxide; D002374:Catalase