IMMU-51. SINGLE-CELL ANALYSIS OF TUMOR-ASSOCIATED MICROGLIA AND MACROPHAGES FROM HUMAN GLIOBLASTOMA

Patients with glioblastoma, the most frequent and malignant primary brain tumor type, have a poor prognosis with a median survival of 14 months. A major therapeutic problem is chemoresistance. In surgically removed glioblastoma tissue, tumor-associated microglia and macrophages (TAMs) constitute up to 30 % of the total cells. TAMs are capable of secreting cytokines, chemokines and growth factors, thereby influencing the tumor microenvironment. However, the existence of different TAM subtypes and their role in glioblastoma is not fully comprehended and rarely considered therapeutically. This could explain why many glioblastoma clinical trials fail despite of promising preclinical results. This project aims to interrogate the existence and characteristics of different TAM subtypes in human glioblastoma biopsies in order to identify novel subpopulations and therapeutic targets. To study the heterogeneity in TAMs, CD11b+ cells were isolated from glioblastoma patient′s tissue, and single-cell RNA sequencing was performed using the 10X Genomics Chromium platform for single-cell generation and an Illumina NovaSeq6000 system for sequencing. We have sequenced TAMs from three glioblastomas and CD11b+ cells from brain tissue adjacent to two brain metastases samples. In the filtered data set of almost 71,000 CD11b+ cells, we were able to identify recently described TAM populations, such as an interferon-induced, a phagocytic, a hypoxic and a proliferating subset. Interestingly, we also discovered potential novel TAM subsets, such as a pro-angiogenic subset. We have detected a TAM population which is more complex than the established M1 and M2 phenotypes, constituting novel TAM subsets. We are currently investigating these findings to validate specific markers associated with these subpopulations, and for the identification of novel clinically relevant targets.

Suppression of mitochondrial ROS by prohibitin drives glioblastoma progression and therapeutic resistance

Low levels of reactive oxygen species (ROS) are crucial for maintaining cancer stem cells (CSCs) and their ability to resist therapy, but the ROS regulatory mechanisms in CSCs remains to be explored. Here, we discover that prohibitin (PHB) specifically regulates mitochondrial ROS production in glioma stem-like cells (GSCs) and facilitates GSC radiotherapeutic resistance. We find that PHB is upregulated in GSCs and is associated with malignant gliomas progression and poor prognosis. PHB binds to peroxiredoxin3 (PRDX3), a mitochondrion-specific peroxidase, and stabilizes PRDX3 protein through the ubiquitin-proteasome pathway. Knockout of PHB dramatically elevates ROS levels, thereby inhibiting GSC self-renewal. Importantly, deletion or pharmacological inhibition of PHB potently slows tumor growth and sensitizes tumors to radiotherapy, thus providing significant survival benefits in GSC-derived orthotopic tumors and glioblastoma patient-derived xenografts. These results reveal a selective role of PHB in mitochondrial ROS regulation in GSCs and suggest that targeting PHB improves radiotherapeutic efficacy in glioblastoma.

Visualizing reactive astrogliosis extends survival in glioblastoma patients

ABSTRACTGlioblastoma is a devastating brain tumor with dismal prognosis of only 15-month survival regardless of surgical resection with few alternatives. Here, we report a reactive astrogliosis-targeted neuroimaging technique using the fusion of 11C-acetate PET and MRI (AcePET) extended the overall survival of patients by 5.25 months compared to conventional MRI-guided surgery. Targeted biopsy of 11C-acetate uptake-increased regions showed the signs of reactive astrogliosis with cancer stem cells at the boundary of high-grade gliomas. The appearance of marginal reactive astrogliosis and MCT1-dependent 11C-acetate uptake was recapitulated in U87MG-orthotophic models. U87MG-derived excessive glutamate caused reactive astrogliosis and aberrant astrocytic GABA-release, which subsequently reduced neuronal glucose uptake through glucose transporter-3 (GLUT3). We propose AcePET-guided surgery, visualizing reactive astrogliosis, as an advanced surgical strategy to improve glioblastoma patient survival.One-Sentence SummaryAcePET-guided surgery extends patient survival by visualizing reactive astrogliosis at the tumor margin

Nivolumab with radiation therapy in a glioblastoma patient with Lynch syndrome

Lynch syndrome is an autosomal dominant disorder leading to cancer predisposition caused by mutations in mismatch repair genes. There is minimal published experience treating glioblastoma in patients with Lynch syndrome. We report a patient with Lynch syndrome who was initially diagnosed with a left occipital isocitrate dehydrogenase (IDH) wild-type glioblastoma. After resection, she was treated with chemoradiation, followed by tumour treating fields. Three years after diagnosis, recurrence was resected. After refusing cytotoxic chemotherapy, decision was made to treat with off-label nivolumab concurrently with radiation. She has been maintained on nivolumab without recurrence of her glioblastoma now over 5 years out from her initial diagnosis. This case provides the first report of glioblastoma in a patient with Lynch syndrome responding to nivolumab and concurrent radiation. In patients with Lynch syndrome and glioblastoma, immunotherapy in the form of nivolumab may be an alternative option to standard cytotoxic chemotherapy.