SUMMARY: PROJECT 1: TARGETING GLIOMA TISSUE STATES Glioblastoma (GBM) displays extensive cellular heterogeneity which represents a major obstacle for effective treatment. This cellular heterogeneity not only consists of multiple tumor cell mutation factors that drive distinct tumor cell behavior, but also impacts various non-tumor cells, contributing to tumor initiation, progression, and treatment response. In fact, GBM’s microenvironment is multifaceted and consists of soluble factors, extracellular matrix components, tissue-resident cells (neuron, astrocytes, endothelial cells, pericytes, etc.) and resident (e.g. microglia) or recruited (e.g. bone-marrow derived macrophages) immune cells. Importantly, changes in the cellular composition and cellular phenotypes can alter GBM tissue states to drive tumor growth and therapeutic resistance. Thus, identifying the unique cellular composition and deciphering the multifaceted bidirectional network between tumor cells and tumor microenvironment signals in various GBM tissue states can lead to identification of novel therapeutic strategies. Our preliminary studies using single nucleus RNAseq of pre- and post-treatment GBM has identified 3 tissue states, corresponding to patterns of cohabitation of tumor and non-tumoral cell subpopulations. These correspond to infiltrated brain, highly cellular proliferating tumor, and astrocytic / inflamed reactive tissue, which is observed in the post-treatment samples and enriched in specific populations of myeloid cells and mesenchymal glioma cells. Co-habitation of specific non-tumor cellular phenotypes in the glioma microenvironment may influence glioma states signatures (astrocyte-like/mesenchymal, progenitor, proliferative) that associate with tumor progression and therapeutic response. The goal of this project is to define the patterns of cellular cohabitation associated with the tissue states and the cross-talk signals that influence local tissue state, phenotypic expression, transitions and disease progression. Because of its known role in cross-talk between specific populations in GBM, we will initially test the effects of targeting TWEAK-Fn14 signaling to drive changes in tissue state. We hypothesize that targeting this as well as other key cross-talk signaling pathways will induce tissue state transitions with corresponding alterations in cellular populations that will render tumors more sensitive to therapeutic vulnerabilities and can be leveraged to slow tumor growth/progression. To investigate the potential impact of such key states and their cross-talk, we propose three aims. Aim 1 focuses on refining our understanding of glioma tissue states in both the pre- and post- treatment setting. Aim 2 investigates cross talk between the glioma cells and their microenvironment and how it may influence progression. Aim 3 looks more locally at how cross-talk perturbations may impact tissue state transition.