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Anti-PD-L1 antibody direct activation of macrophages contributes to an abscopal response in murine brain tumors

ABSTRACT: Immunotherapy approaches for glioblastoma multiforme have been thus far largely unsuccessful, suggesting unappreciated complexity in glioma biology and immunology. The intra-tumoral heterogeneity of these intrinsic brain tumors results in therapies killing only a subset of the tumor cells; therefore, therapeutic success will require achieving and optimizing an “abscopal effect” where tumor cells not specifically targeted are recognized and attacked as bystanders by the immune system. We have modified an immune-competent, genetically-driven mouse glioma model where a portion of the tumor burden is treated and another untreated portion is used as a readout of therapeutic efficacy. We find that following radiation of one lesion, anti-PD-L1 therapy enhances the abscopal response (macrophages and T-cells) to the un-irradiated lesion. In gliomas with few baseline T-cells, the anti-PD-L1-enhanced abscopal response occurs as an anti-PD-L1-driven, macrophage-mediated, and ERK-dependent increase in phagocytosis of tumor cells. Our results indicate that combined radiation and anti-PD-L1 therapy for gliomas results in peripherally-derived macrophages being responders in tumors with few baseline T-cells in the microenvironment.

ORGANISM(S): Mus musculus

PROVIDER: GSE111806 | GEO | 2019/10/01

REPOSITORIES: GEO

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Project description:PD-L1 Inhibitor Regulates the miR-33a-5p/PTEN Signaling Pathway and Can Be Targeted to Sensitize Glioblastomas to Radiation. Glioblastoma (GBM) is the most common and lethal brain tumor in adults. Ionizing radiation (IR) is a standard treatment for GBM patients and results in DNA damage. However, the clinical efficacy of IR is limited due to therapeutic resistance. The programmed death ligand 1 (PD-L1) blockade has a shown the potential to increase the efficacy of radiotherapy by inhibiting DNA damage and repair responses. The miR-33a-5p is an essential microRNA that promotes GBM growth and self-renewal. In this study, we investigated whether a PD-L1 inhibitor (a small molecule inhibitor) exerted radio-sensitive effects to impart an anti-tumor function in GBM cells by modulating miR-33a-5p. U87 MG cells and U251 cells were pretreated with PD-L1 inhibitor. The PD-L1 inhibitor-induced radio-sensitivity in these cells was assessed by assaying cellular apoptosis, clonogenic survival assays, and migration. TargetScan and luciferase assay showed that miR-33a-5p targeted the phosphatase and tensin homolog (PTEN) 3' untranslated region. The expression level of PTEN was measured by western blotting, and was also silenced using small interfering RNAs. The levels of DNA damage following radiation was measured by the presence of γ-H2AX foci, cell cycle, and the mRNA of the DNA damage-related genes, BRCA1, NBS1, RAD50, and MRE11. Our results demonstrated that the PD-L1 inhibitor significantly decreased the expression of the target gene, miR-33a-5p. In addition, pretreatment of U87 MG and U251 cells with the PD-L1 inhibitor increased radio-sensitivity, as indicated by increased apoptosis, while decreased survival and migration of GBM cells. Mir-33a-5p overexpression or silencing PTEN in U87 MG and U251 cells significantly attenuated PD-L1 radiosensitive effect. Additionally, PD-L1 inhibitor treatment suppressed the expression of the DNA damage response-related genes, BRCA1, NBS1, RAD50, and MRE11. Our results demonstrated a novel role for the PD-L1 inhibitor in inducing radio- sensitivity in GBM cells, where inhibiting miR-33a-5p, leading to PTEN activated, and inducing DNA damage was crucial for antitumor immunotherapies to treat GBM.

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Anti-PD-L1 antibody direct activation of macrophages contributes to an abscopal response in murine brain tumors

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