Project description:Medulloblastoma (MB) is the most common malignant pediatric brain tumor. Current treatments carry significant morbidity, and prognosis remains poor in subgroups with TP53 mutations or relapse, underscoring the need for new therapeutic strategies. Senescence is a tumor-suppressive program disrupted in MB. We hypothesized that restoring senescence through p53-independent mechanisms could be therapeutic. Here, we identify Protein Phosphatase 2A (PP2A) as a key regulator of senescence in MB. Genetic ablation of the PP2A catalytic subunit (PP2Ac) or knockdown of the regulatory subunit PP2A-B56α induces robust senescence in TP53-mutant MB models. Senescent PP2Ac-deficient cells show increased MHC-I expression and enhanced immunogenicity. In a syngeneic orthotopic model, PP2Ac loss prolongs survival in an immune- and CD8-dependent manner, indicating enhanced immune-mediated tumor clearance. Analysis of MB patient datasets links senescence signatures with improved survival, and integrative single-cell analysis reveals reduced PP2A activity in immunogenic senescent clusters. Although the PP2A inhibitor LB-100 is under clinical investigation, it fails to cross the blood-brain barrier. To overcome this, we developed a lipid nanoparticle (LNP) formulation delivering siRNA against PP2Ac. LNP-siPP2Ac efficiently silences PP2Ac in vitro and, when locally delivered in vivo, extends survival and increases tumor MHC-I expression. These findings establish PP2A as a central modulator of senescence and immunogenicity in MB and support a therapeutic strategy that induces tumor cell senescence and enhances anti-tumor immunity for treatment of MB.
Project description:Glioblastoma (GBM) is the deadliest type of brain cancer, exhibiting resistance not only to traditional treatments like radiation and chemotherapy but also to modern immunotherapy. GBM is classified as an immunologically cold tumor with an immunosuppressive microenvironment. Radio- and chemotherapy have been shown to alter the tumor microenvironment and trigger an anti-tumor immune response in various cancers, including breast, lung, and colorectal cancer, via the cGAS/STING and type I interferon (IFN-I) pathway. Additionally, STING agonists and inhibitors of DNA damage response and cell cycle checkpoints, which promote the accumulation of immunostimulatory cytoplasmic dsDNA, have been found to enhance the effects of radiation. Here we examined the immunogenic response of four different GBM cell lines (U251, T98G, GB-1, KALS-1) exposed to hypofractionated X-ray radiation (3x8 Gy) in combination with a STING agonist or with inhibitors targeting immune signaling (PARP7). We performed RNA-seq analysis of all four GBM cell lines treated with 3x8 Gy, PARP7i, diABZI alone or in combination with 3x8 Gy.
Project description:Glioblastoma (GBM) is an incurable cancer despite aggressive treatment paradigms. Current immunotherapies, such as CTLA-4 and/or PD-1 blockade, have yet to demonstrate benefits for GBM. A key barrier is the immunologically “cold” nature of GBM defined by insufficient tumor antigen presentation and lack of T cells infiltration. We previously demonstrated that pharmacologic inhibition of Protein Phosphatase-2A (PP2A), using a small molecule inhibitor, synergized with PD1 blockade in multiple preclinical tumor models including GBM. However, PP2A is ubiquitously expressed in many cell types and regulates many cellular pathways. The cell type or molecular mechanism responsible for PP2A-modulated tumor immunity is poorly understood. Here, we demonstrate that genetic ablation of PP2A in glioma cells sufficiently promotes tumor immunogenicity by enhancing 1) dsDNA production and thereby cGAS-Type I interferon (IFN) signaling, 2) MHC-I expression and 3) tumor mutational burden. PP2A deficient glioma enhances DC activation and cross presentation to promote clonal expansion of tumor antigen specific CD8 cells. PP2A deficiency also markedly sensitize tumors to immune checkpoint blockade and radiotherapy. Single cell analysis of murine glioma demonstrates that PP2A deficient tumors have 1) increased infiltration of CD8+ T cell, NK cell and cDC1 cells, 2) reduced infiltration of immunosuppressive tumor associated macrophages, 3) promotion of IFN signaling in both myeloid and tumor cells, and 4) reduced glioma-associated gene signature that predicts poor prognosis in glioma patients. This is the first study to establish a role for PP2A in regulating dsDNA-cGAS-STING signaling and collectively, our results suggest that PP2A is a promising novel target to enhance anti-tumor immunity for glioma.
Project description:Glioblastoma (GBM) is an incurable cancer despite aggressive treatment paradigms. Current immunotherapies, such as CTLA-4 and/or PD-1 blockade, have yet to demonstrate benefits for GBM. A key barrier is the immunologically “cold” nature of GBM defined by insufficient tumor antigen presentation and lack of T cells infiltration. We previously demonstrated that pharmacologic inhibition of Protein Phosphatase-2A (PP2A), using a small molecule inhibitor, synergized with PD1 blockade in multiple preclinical tumor models including GBM. However, PP2A is ubiquitously expressed in many cell types and regulates many cellular pathways. The cell type or molecular mechanism responsible for PP2A-modulated tumor immunity is poorly understood. Here, we demonstrate that genetic ablation of PP2A in glioma cells sufficiently promotes tumor immunogenicity by enhancing 1) dsDNA production and thereby cGAS-Type I interferon (IFN) signaling, 2) MHC-I expression and 3) tumor mutational burden. PP2A deficient glioma enhances DC activation and cross presentation to promote clonal expansion of tumor antigen specific CD8 cells. PP2A deficiency also markedly sensitize tumors to immune checkpoint blockade and radiotherapy. Single cell analysis of murine glioma demonstrates that PP2A deficient tumors have 1) increased infiltration of CD8+ T cell, NK cell and cDC1 cells, 2) reduced infiltration of immunosuppressive tumor associated macrophages, 3) promotion of IFN signaling in both myeloid and tumor cells, and 4) reduced glioma-associated gene signature that predicts poor prognosis in glioma patients. This is the first study to establish a role for PP2A in regulating dsDNA-cGAS-STING signaling and collectively, our results suggest that PP2A is a promising novel target to enhance anti-tumor immunity for glioma.
