A study on metabolic inflexibility as a possible weakness in mammary tumours

Reprogramming of energy metabolism has emerged as one of the hallmarks of cancer, and there is now a strong conviction that processes of cancer cell metabolism may serve as new and promising therapeutic targets. Evidently, tumor metabolism is not uniform, and may involve both inherent and acquired metabolic properties. Furthermore, the metabolic changes observed in human cancers are tightly linked with alterations in common signaling pathways. Based on previous reports, there are reasons to believe that oncogenic mutations attenuate metabolic versatility. In this project, we therefore asked if metabolic reprogramming may narrow the capacity of metabolic flexibility in human cancer cells. If this is the case, the cancer cells would be more sensitive to certain types of metabolic stress compared to normal cells, which consequently might reveal new therapeutic targets. Therefore, this project aims to identify molecular mechanisms of metabolic reprogramming, in order to find new biomarkers of metabolic transformation; and to link these effects to established traits of aggressive cancers, including epithelial-to-mesenchymal transition (EMT) and metastasis. The main outcomes of the projects can be summarized as follows: 1) New methods: We established novel strategies to quantify changes in mitochondrial biomass and morphology in 3 dimensions (3D), based on fluorescence confocal microscopy (Nikolaisen et al, 2014, Plos ONE). In this regard, we also wrote a review article summarizing current aspects of mitochondrial regulation and quantification (Tronstad et al, 2014, Curr Pharm Design). Furthermore, we made a new live-cell reporter system to study physiological mechanisms involving changes in mitochondrial biogenesis and dynamics (Hodneland Nilsson et al, 2015, Sci Rep). These methods were utilized in subsequent studies of metabolic stress responses. 2) Mechanisms and importance of metabolic flexibility in relation to cellular stress: Together with our collaborators (M. Ziegler) we characterized metabolic stress effects due to changes in subcellular pools of NAD+ (VanLinden et al, 2015, JBC). In another study, we characterized metabolic remodeling in breast epithelial cells undergoing EMT, and in drug resistant breast cancer cells (submitted manuscript, Røsland et al). In the same study, corresponding features of metabolic reprogramming were also found in gene expression data from human breast and endometrial tumors. 3) New therapeutic targets and treatments: we studied the general effects of PPAR activation in an animal model to characterize physiological mechanisms related to modulation of energy metabolism (Hagland et al, 2013, BBRC). This treatment was found to induce mitochondrial biogenesis and respiration, probably via a pathway involving the mTOR protein, which also is known to regulate cancer cell metabolism. Subsequently, we identified respiratory complex I as a specific target for beta-sitosterol, a new agent that demonstrated potent antitumor effects in animal studies (submitted manuscript, Sundstrøm et al). In summary, the outcome of this project includes new methods, molecular mechanisms, potential therapeutic targets, and new candidate drugs. The results strengthen the hypothesis that metabolic inflexibility is a possible weakness in human tumor cells.

Reprogramming of energy metabolism has emerged as one of the hallmarks of cancer, and there is now a strong conviction that cancer cell metabolism encompasses new promising therapeutic targets. In extension of the classical Warburg theory explaining the h igh glucose demand in tumors, it is now clear that tumor metabolism not uniform and new inborn and acquired metabolic defects have recently been found. The metabolic changes observed in human cancers are tightly linked with alterations in common signaling pathways. Although it is evident that metabolic reprogramming promotes malignant development, there are strong indications that oncogenic mutations attenuate metabolic versatility. In this proposal, therefore, we hypothesize that metabolic reprogramming narrows the capacity of metabolic flexibility in human cancer cells, and that this lowers the threshold for induction of metabolic stress responses leading to antitumor effects and increased sensitivity for chemotherapy. To test this hypothesis, we will u se coordinated metabolic modulation as a strategy to induce stress (e.g. energetic stress, or oxidative stress) and cell death in mammary cancer cells and animal models. This will enable us to study the underlying mechanisms involving novel traits in mali gnancies. We will also use a global metabolic profiling approach to search for new biomarkers of metabolic transformation in breast cancer models, and link these effects to established traits of aggressive cancers, including epithelial-to-mesenchymal tran sition (EMT) and metastasis. The conclusions from human breast cancer cells in vitro will allow us to design in vivo experiments in animals, in order to test therapeutic strategies that may potentially be further exploited in future clinical studies. The collaborators in this project will bring together unique model systems and competence in experimental as well as clinical aspects of breast cancer, in addition to leading technology in the field of metabolomics.