Glioblastoma multiforme (GBM) is a common and highly aggressive form of brain cancer in adults with a dismal prognosis and limited therapeutic options. A critical component of GBM malignancy derives from the distinct population of glioma stem cells (GSCs) that function to promote and maintain malignancy through their capacity for self-renewal, cellular adaptation and multipotency. These stem-like cells engage in a synergistic relationship with the surrounding microenvironment to promote tumor progression and are key drivers of intratumoral heterogeneity, immune-suppression, and therapy resistance. Targeting GSCs and mechanisms that drive the stem-like phenotype presents a promising avenue for targeted therapeutics. The broad goal of this proposal is to understand the cell-intrinsic mechanisms driving maintenance of a unique, immunosuppressive GSC subset, identify cellular vulnerabilities associated with immunosuppressive GBM cells, and develop preclinical therapeutics to target these cells. We will achieve this goal by utilizing our validated GSC cell models, state-of-the art single-cell sequencing technology, and cutting-edge spatially resolved omics platforms applied to clinical GBM specimens, and advanced molecular in vitro techniques to define immunosuppressive tumor cell populations and determine the transcriptomic and metabolic changes associated with these cell populations that are amenable to therapeutic targeting. Our preliminary findings demonstrate that TGF-beta type II receptor (TGFBR2) signaling induces a TGFBR2high subset of GSCs that co-opt certain immunosuppressive mechanisms associated with and utilized by regulatory T cells (Tregs) to exert immunosuppressive behavior. In the F99 phase, we will investigate the potential for boosting the anti-tumor immune response by targeting this specific subset of TGFBR2-induced immunosuppressive GSCs endowed with Treg-like capabilities. To do so, we will utilize inducible shRNA constructs and a clinically translatable small-molecule drug to inhibit TGFBR2 in orthotopic tumor allografts in immune-competent mice and analyze the effects on tumor growth, immune cell infiltration and function, and cooperativity with check point inhibitor therapy. In the K00 phase, we will conduct spatially resolved transcriptomics and metabolomics on patient GBM tissue specimens to identify potential metabolic vulnerabilities in immunosuppressive GBM cells. Metabolic inhibitors will be utilized to exploit candidate vulnerabilities in an attempt to attenuate the transcriptomic and functional immune-suppressive characteristics of these cells. Subsequently, validated metabolic vulnerabilities will be targeted in vivo to assess the effects on tumor growth and the anti-tumor immune response. Our proposed methods of pharmacological TGFBR2 inhibition and metabolic exploitation will inform the development of novel strategies to reprogram the GBM microenvironment and enhance anti-tumor immune responses when combined with current emerging immunotherapeutics (e.g. checkpoint inhibitors, CAR-T cell technology, vaccines).

Glioblastoma multiforme, a common and highly aggressive form of brain cancer with a universally fatal outcome, is characterized by a vast degree of heterogeneity and an immune-suppressive tumor microenvironment driven by cancer stem cells. Our preliminary results show that glioma cancer stem cells activate cell-intrinsic mechanisms to drive and maintain a unique, immunosuppressive cell phenotype and suggest that targeting immunosuppressive GBM cells will boost the anti-tumor immune response. Favorable results from this proposal will provide a rationale for combining therapeutics directed at immunosuppressive GBM cells with other immunotherapies (e.g. checkpoint inhibitors, CAR-T cells, vaccines) to treat brain tumors.