Gluconeogenesis and antioxidant defense in lung cancer cells

In rapidly growing cancers, the microenvironment is often nutrient-poor, despite the growth of new blood vessels. There is still a lack of understanding, how cancer cells adapt to these harsh conditions, especially to a lack of glucose, an important precursor for biosynthetic pathways. Our group was the first to show that expression of phosphoenolpyruvate carboxykinase ( PEPCK) is activated under low glucose conditions in cancer cells and mediates an adaptiv e metabolic response. PEPCK, which exists in two isoforms, PCK1 and PCK2, is the central enzyme in gluconeogenesis, the biosynthesis of glucose from non-carbohydrate precursors in the liver and other organs. Gluconeogenesis is utilized to maintain blood glucose levels under starvation and had not been considered of importance in cancer cells. In the past years, a number of publications including our own highlighted a functional role of the mitochondrial isoform of PEPCK, PCK2, in the flexible utilization of small metabolites in cancer cells, promoting cancer cell survival and growth. However, the exact metabolic role of PCK2 in cancer cells is still unclear. In this project we address the role of PCK2 in regulating cellular respiration and mediating antioxidant responses in glucose-deprived lung cancer cells. Our study utilizes genetic approaches to investigate the role of PCK2 in mitochondrial respiration, metabolism, formation of oxygen radicals, proliferation and colony formation in cancer cells and tumor growth in a subcutaneous tumor model in mice. We will use stable isotopic precursors including amino acids and track their conversion into different downstream metabolites, including antioxidant molecules, both in cells and in the tumor tissue in mice. Thus, we will clarify whether PCK2 is indeed active in tumor tissue in the direction of gluconeogenesis and whether it promotes the scavenging of oxygen radicals. Moreover, by using shRNA- mediated suppression (silencing) of PCK2 in already established tumors, we will explore, whether PCK2 inhibition could be a potential strategy for the treatment of lung cancer in the future.

Cancer cells need to generate new biomass with every cell doubling. To this end they require metabolic precursors from the circulation, which is ensured by the activation of angiogenesis, the growth of new blood vessels. Moreover, cancer cells rewire their metabolism to promote the synthesis of important cellular building blocks. However, recent studies suggest that cancer cells in fact face a shortage of important precursors, like glucose, since their metabolic demand exceeds the supply. We are interested to identify vulnerabilities resulting from this imbalance and focus on alternative metabolic pathways activated in the cancer cells to ensure growth and survival. The main focus of our work is a rather poorly characterized metabolic pathway, that we first described to be active in starved cancer cells, (partial) gluconeogenesis. In our project, we could unveal several novel aspects of cancer cell metabolic adaptation, that lead to a better understanding of critical cancer vulnerabilities: 1) a regulatory role of a gluconeogenesis enzyme on cellular respiration and resistance towards oxidative stress, 2) a dynamic interplay of gluconeogenesis and glycolysis to fuel the synthesis of an important amino acid, serine, and 3) an unexpected exchange of metabolites with the extracellular space under glucose shortage. The results of this project, which are all novel and already got published in acknowledged journals or are under consideration for publication. They contribute significantly to the understanding of cancer metabolism and might contribute to improved treatment options or the identification of biomarkers in the future.