Title:

Establishing a Clinically Relevant Mouse Model to Study Necrosis as a Primary Variable in Glioblastoma

Abstract:

All glioblastoma (GBM) molecular subsets share the common trait of accelerated progression following necrosis which cannot be adequately explained by cellular proliferation arising from accumulated genetic alterations. We suggest that development of necrosis is much more than a passive phenomenon related to rapid growth but rather is a driving force behind tumor microenvironment (TME) restructuring responsible for sustaining accelerated expansion. However, mechanisms related to TME restructuring and biologic progression, including glioma stem cell (GSC) enrichment and the influx and polarization of tumor-associated macrophages (TAMs), remain poorly understood due to a lack of animal models to study necrosis as a primary variable. To reveal spatio-temporal changes following the development of hypoxia and necrosis, we developed an immunocompetent RCAS/tv-a model that can be used to study TME restructuring in a precise and reproducible manner. We generate diffuse high-grade gliomas that lack necrosis by introducing RCAS-PDGFB and RCAS-Cre in a Nestin-tv-a TP53^flox/flox, PTEN ^flox/flox background mouse. We then photoactivate Rose Bengal with specific, targeted blood vessels in the glioma to induce thrombosis, hypoxia and necrosis. We are then able to visualize TME restructure and its impact on glioma growth in real time using multiphoton microscope. TAMs increase dramatically with the onset of necrosis, with preferential localization to the hypoxic zone in the peri-necrotic niche, which supports their survival. Flow cytometry on digested pre- and post-necrotic GBMs, show increased TAM influx and GSC enrichment as necrosis emerges. Our immunofluorescence staining along with in silico analysis of Ivy GAP data suggests podoplanin (PDPN) expression by GBM cells within the peri-necrotic niche causes polarization of TAMs by activating CLEC5A on TAMs to cause an immunosuppressive phenotypic switch. Collectively, this model captures glioma growth dynamics, GSC enrichment and TAM influx, and will facilitate the development of therapies that antagonize these mechanisms to improve outcomes.

Biography:

My name is Jiabo Li, I am a Postdoctoral Scholar at Department of Pathology, Northwestern University Feinberg School of Medicine. I come from China and received my B.S in Clinical Medicine from Shanxi Medical University in 2017 and obtained my M.D. and Ph.D. degrees in Neurosurgery (Neuro-Oncology) from Tianjin Medical University in 2022. My long-term research interests involve understanding the complex mechanisms of how the tumor microenvironment (TME) that contribute to tumor progression, therapeutic resistance and disease recurrence of glioblastoma (GBM), including contributions from genetic alterations, necrosis, tumor-associated macrophages/microglia (TAMs) and glioma stem cells (GSCs). As a graduate student at Tianjin Medical University, I focused on disrupting crosstalk between GSCs and immunosuppressive components within GBM TME using a novel multi-targeted agent – ACT001. This agent is derived from an ancient anti-inflammatory drug and has been identified to cross the blood-brain barrier preclinically. As a neurosurgeon specialized in neuro-oncology, my academic training and clinical experience have enabled me to possess a professional knowledge for diagnosis and treatment of GBM. For my postdoctoral training, I will continue to investigate the unique necrosis-related immune dysregulation in GBM to uncover potential prognostic biomarkers for immunosuppression and unravel necrosis-driven mechanisms that influence GSC and TAM behavior in the peri-necrotic niche. To reveal spatio-temporal changes following the development of hypoxia and necrosis, we developed an immunocompetent RCAS/tv-a model that can be used to study TME restructuring in a precise and reproducible manner.