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Glioblastoma (GBM) is the most common primary brain tumor with almost 100% recurrence rate after surgery and radiochemotherapy. Previously, Liu laboratory at DKFZ found that glycerol-3-phosphate dehydrogenase 1 (GPD1) was expressed specifically in GBM stem cells (GSCs), and that GPD1 expression drove tumor relapse after chemotherapy. So far the role of GPD1 expression in GBM receiving radiation therapy remains unclear. We therefore investigated the role of GPD1 expression in GBM receiving radiation therapy.

We built GPD1 overexpression model and GPD1 Crispr/cas 9 knockout (KO) model in vitro. Furthermore, we induced organoids with human induced pluripotent stem cells (iPSC), and accordingly conducted PTEN & P53 KO organoids (C1) and PTEN & P53 & GPD1 KO organoids (G1). The Cancer Genome Atlas (TCGA) database was queried for the impact of GPD1 gene expression on survival of GBM patients. R 4.0.3 was used to determine the optimal cutoff value of GPD1.

3D-clonogenic survival assay was conducted with GPD1 overexpression NCH601 cells, and showed that they became more resistant to radiation after GPD1 overexpression (P = 0.049). Meanwhile, 3D-clonogenic survival assay was also conducted with GPD1 KO NCH601 cells, and showed that they became more sensitive to radiation after KD GPD1 (P = 0.007). In addition, we co-stained GPD1 and SOX-2 (a common biomarker for GSCs) in C1 organoids with immunofluorescence (IF) staining, and found that almost all GPD1 cells were SOX-2 positive, and GPD1 cells located close to the hypoxic core. Meanwhile, we stained rH2AX in C1 and G1 organoids 1h and 24h after radiation, and determined that G1 organoids had much more rH2AX foci number per nuclei than C1 organoids 1h after radiation (11 vs. 6), and recovered worse 24h after radiation (P < 0.05). Using the TCGA database, we found that GPD1 was highly expressed in GBM tissues, compared with normal brain tissues. For 501 GBM patients both clinical and GPD1 gene expression data were available in the TCGA database. 275 of these patients underwent radiation therapy with or without chemotherapy. The cutoff value of GPD1 expression was 4.449 log2(affy RMA) (range, 3.973-8.612), 183 tumors showed high GPD1 expression and 92 low expression. Patients with high GPD1 expressing GMB had significantly inferior OS than those with low GPD1 expression (P = 0.012), with median survival times of 15.9 months vs. 20.9 months.

GPD1 expression in GSCs plays a (significant) role in radiation resistance of GBM in preclinical models in vitro and is associated with impaired overall survival of patients receiving radiation therapy with or without chemotherapy. Further preclinical research is currently ongoing to determine the mechanisms by which GPD1 expression confers radiation resistance.

Reference: Patricia Rusu, et al. GPD1 Specifically Marks Dormant Glioma Stem Cells with a Distinct Metabolic Profile. Cell Stem Cell. 2019;25(2):241-257.