P10.20.b postoperative ischemia caused by microsurgical resection promotes proneural-to-mesenchymal transition in glioblastoma

Abstract BACKGROUND Four glioblastoma (GB) cellular states drive the intratumoral heterogeneity of this lethal primary brain tumor and are influenced by genetics, the tumor microenvironment (TME), and response to treatment. The impact of microsurgical resection on the TME and plasticity of GB cells is unknown. Postoperative cerebral ischemic events have been described after these surgical resections, altering the proper distribution of subsequent chemo-radiotherapy treatment. Despite the aggressive standard of care, 90% of patients experience recurrence a few months after treatment and it usually begins with the regrowth of highly invasive cells that spread from the peritumoral brain resection zone. Therefore, the objective of this study was to perform morphological and transcriptomic phenotyping of residual tumor cells and TME after microsurgical resection. MATERIAL AND METHODS The GFP-transduced syngeneic GB IDH-wildtype cell lines CT2A and GL261 were orthotopically implanted in C57Bl6j mice brains. We developed a refined microsurgical resection protocol for GB in a size-matched study by carefully following the same surgical steps performed in patients. Mice were randomly divided into four groups: control (prior to surgery) and 1, 3, and 7 days post-surgery. Tumor tissues were harvested for time-resolved bulk and single-cell RNA sequencing as well as immunohistochemistry (IHC) studies. RESULTS According to our time-resolved transcriptomic and IHC analyses, microsurgical resection induced pronounced proneural-to-mesenchymal transition (PMT), chromatin remodeling, and stimulation of hypoxia-driven pathways in residual GB cells after surgery. Moreover, single-cell RNA-seq of post-resection tumors allowed us to observe significant changes in the TME relative to the immune response and vascular function in line with ischemia exposure. CONCLUSION The impact of microsurgical resection has important consequences on the phenotypic landscape of GB tumor cells and TME, which is characterized by a transient ischemic TME that induces PMT in GB cells. In addition, we developed a refined microsurgical resection model that can be useful in a wide variety of preclinical studies. Support/Disclosure: This study was supported by the Institut National du Cancer (INCa; 1154 INCa-2020-1-PLBIO-01-ICR-1) and by the Marie Skłodowska-Curie Postdoctoral Fellowship under the European Union’s programme Horizon2020 (HORIZON-MSCA-2021-PF-01, GlioSurg, Grant agreement ID: 101061921).