P12.20.A CELLULAR SENESCENCE AFFECTS NEOPLASTIC AND MICROENVIRONMENTAL CELLS IN PRIMARY GLIOBLASTOMA

Abstract BACKGROUND Cellular senescence is a complex stress response characterized by permanent cell cycle arrest and secretion of pro-inflammatory factors (SASP). In glioblastoma, senescent cells may arise due to intrinsic oncogenic cell stress and/or in response to therapy-induced damage. They are supposed to contribute to tumor recurrence. Yet, their frequency, spatial distribution and impact on survival remain incompletely understood, especially in relation to patient age and related comorbidities such as Alzheimer’s disease neuropathological change (ADNC). Herein, we aimed at characterizing senescent tumor and microenvironmental cells in a representative cohort of glioblastoma-patients. MATERIAL AND METHODS We analyzed 364 FFPE primary, pre-treatment glioblastoma samples of 163 patients using single- and multiplex immunohistochemistry (IHC). Since senescence is a complex, hard-to-measure cell state, we used two key markers (p16, p21) in addition to cell-type specific markers covering neurons, microglia and endothelial cells (NeuN, Iba1, CD34) and ADNC comorbidity (β-A4, tau-AT8). Stainings were scanned at the Vectra Polaris platform, and quantified by HALO software and R. RESULTS Upon single-plex IHCs, p16 was expressed in either sparse (67%), moderate (21%), and abundant (12%) cell fractions. In contrast to p21, whose expression was less variable and less abundant (range: 0.02% to 54%, median: 3.5%). They did not correlate with each other (R=0.08). Upon multiplex IHC p16+p21+ senescent cells comprised 1.8% of all detected cells, being enriched for microglia (16.8%) and endothelial cells (17.3%). Senescence was reported in 0-4% of tumor cells (median: 1.1%). No significant differences in the extent of senescence were observed between the tumor core and the tumor-infiltrated cortex (p-value=0.86). Senescent endothelial cells increased with age (p-value=0.0023). Notably, a higher fraction of senescent endothelial and neuronal cells was found in the presence of ADNC, with 89.5% of neurofibrillary tangles being in senescent neurons. CONCLUSION In primary glioblastoma tumors, 1.8% of cells show p16+p21+ double labeling as putative marker for senescence, which involves neoplastic and microenvironmental cells alike, prominently including microglial, endothelial and neuronal cells. Senescent cells increase with age and presence of Alzheimer-type comorbidity.