PROJECT SUMMARY Glioblastoma (GBM) is the most prevalent primary malignant brain tumor and is highly lethal with a median survival of approximately 20 months. GBM is incurable despite aggressive standard treatment with radiation, surgical resection and chemotherapy. The resistance of GBM to therapy is due to multiple factors, including tumor heterogeneity, diffuse tumor growth, and a highly immunosuppressive environment. Naturally occurring polyamines (PAs) have been found in increased levels in GBM patients. PAs have been identified as a potential therapeutic target in several other types of cancers but have yet to be studied in the context of GBM. Under normal conditions, PAs contribute to cell growth and proliferation as well as maintain cell health through autophagy. Further studies are needed to understand methods of action of PA contribution in GBM. Additionally, PAs are also consumed in diet and produced by several bacterial strains present in the gut microbiota. The gut microbiome has surfaced as a prominent influence on immune system responses to disease. Cytokines and metabolites produced by gut bacteria can enter the bloodstream and interact with peripheral immune cells as well as the tumor microenvironment. PAs specifically affect cytokine production, altering the immune response and providing an immune link between the gut microbiota and cancer. Gut dysbiosis reduces the efficacy of immunotherapies such as immune checkpoint inhibitors in lung cancer. The mechanisms through which PAs drive GBM progression need to be investigated and whether this pathway can be harnessed for therapy. PAs are of particular interest as they can be produced both by tumor cells as well as by the microbiome and it is unclear how each source may contribute to GBM growth. Preliminary data I have obtained provides evidence that PAs decrease survival in mouse GBM models and in vitro analysis revealed PAs inhibit several immune cell populations. Based on these observations, I hypothesize that PAs drive GBM growth via intrinsic cellular mechanisms as well as the gut-brain-microbiome axis. This hypothesis will be tested in two experimental aims. Aim 1 will test the hypothesis that tumor-derived PAs drive GBM growth by promoting an immunosuppressive environment and will focus on the tumor cell intrinsic response to PA. Aim 2 will test the hypothesis that PAs absorbed from diet or produced by gut microbes drive GBM progression and decrease survival and will focus on the tumor cell extrinsic/systemic response to PA. These aims will be accomplished through a series of in vivo experiments in immune competent and germ-free GBM mouse models, as well as an in vitro investigation of molecular mechanisms. The short-term impact of this project is the elucidation of gut microbiome effects on GBM, using the function of PA as a paradigm. The long-term impact of this project is the development of therapies that target gut-brain-microbiome axis pathways in order to more effective...