Abstract 2959: Signatures of therapy-induced senescence in glioblastoma-derived extracellular vesicles

Abstract The recalcitrant nature of glioblastoma (GBM) may be due, in part, to the promotion of therapy-induced senescence (TIS) by standard of care treatments. TIS is a prolonged growth arrest associated with epigenetic, metabolic, and biochemical alterations, as well as a robust secretory phenotype. Despite an initial period of tumor stasis due to the loss of cell proliferation, TIS is associated with the development of stemness, increased drug resistance, and immune suppression. Our preliminary data demonstrate the prominent induction of TIS in GBM tumor cells and astrocytes following standard of care therapies for GBM in vitro. However, studies of TIS in GBM patients have been limited due to i) the impracticality of receiving multiple GBM biopsies post-treatment but prior to recurrence and ii) the lack of robust detection methods for TIS even with appropriate biopsy. These challenges argue the need for novel methods to survey TIS in patients. Extracellular vesicles (EVs) are small membrane-bound particles that readily cross the blood brain barrier, and convey information about originating cell identity and cell state through their cargo content. We hypothesize that TIS in host and tumor cells drives the elaboration of senescence-associated EVs (senEVs) with quantifiable senescence protein cargo signatures, and consequently, that EVs can serve as a liquid biopsy for senescence in patients. In a preliminary experiment, two patient derived xenografts grown as short-term in vitro cultures were exposed to 6GY irradiation, with supernatant collected prior to radiation (D0), at peak senescence (D7), and at late senescence (D10). EVs were isolated and subjected to unbiased mass spectrometry. Following unsupervised clustering, EVs were grouped by treatment rather than by cell line. Approximately 6000 proteins were identified across the entire data set, with 105 proteins unique to D7 samples, 162 proteins unique to D10 samples, and 688 proteins exclusive to D7 and D10 samples. Further, proteins from two established senescence gene sets were identified as unique to the D7 and/or D10 conditions. Current work to more robustly identify enrichment of senescence gene sets in EV cargo post-irradiation is underway. We have also established shRNA knockdown cell lines with abrogated TIS to equip validation studies of the TIS-EV cargo relationship. We anticipate that these studies will aid in the development of EVs as a novel reporter of senescence in the clinic. Citation Format: Valerie DeLuca, Priya Digumarti, Krystine Garcia-Mansfield, Patrick Pirrotte, Michael E. Berens. Signatures of therapy-induced senescence in glioblastoma-derived extracellular vesicles abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 2959.