TMIC-99. Exploring influence of oxygen tension on glioblastoma phenotypes: Erk/Pi3K/Akt Signaling and epithelial to mesenchymal transition

Abstract Glioblastoma (GBM) is an aggressive brain tumor with a median survival 15–20 months, despite maximal treatment including surgery, chemotherapy, radiation, and tumor-treating fields. Recurrence is nearly inevitable, and long-term survival remains low. GBM often contains necrotic regions with decreased perfusion and oxygen delivery. Our goal is to better understand how chronic hypoxia affects GBM signaling and cancer phenotypes. Normoxia(~21% O₂) reflects ambient air; physioxia(~5% O₂) more closely resembles physiological oxygen levels in brain tissue. We hypothesized that chronic physioxia alters GBM phenotypes, metabolism, and treatment responses through modulation of key signaling pathways, including ERK. ERK signaling, a key regulator of tumor survival and therapy resistance, is influenced by oxygen levels. Under normoxia, ERK is activated by receptor tyrosine kinases and the PI3K/AKT pathway. Physioxia modulates ERK activity, potentially enhancing resistance via signaling crosstalk. Most GBM studies use short-term hypoxia(<48 hours), but in situ hypoxia is chronic. Here, GBM cells were maintained under physioxia for two passages(> 10 days) prior to experiments for improved clinical relevance. We investigated patient-derived GBM lines (GB10 and GB43) under normoxia and physioxia. Cell proliferation decreased under physioxia, with significantly reduced doubling times in GB10(p=0.0013) and GB43(p=0.0124). Physioxia also decreased cell migration in GB43(p=0.0123, transwell assay). We examined markers of EMT, with RT-PCR showing increased Slug (p=0.0228 at d3) and decreased IGFBP1(p<0.0001 at d7) transcripts in GB43 cells maintained in physioxia. Physioxia also increased phosphorylation of ERK(GB43), PDGFRβ, and AKT (GB10, Western Blot). Physioxia increased chemoresistance to temozolomide in GB10(p<0.001, BrdU). Thus chronic exposure to physioxia alters cell proliferation, migration, and therapeutic responsiveness with correlation to cell signaling via ERK/AKT signaling pathways. Future work will explore how corticosteroids like dexamethasone affect cancer phenotypes and signaling under both oxygen conditions, contributing to a better understanding of cancer cell phenotypes in clinically relevant conditions in GBM.