STEM-03. TARGETING F-ACTIN DYNAMICS OF GLIOBLASTOMAS TO OVERCOME THERAPY RESISTANCE: IMPACTS ON DNA REPAIR AND GLIOMA STEM CELL PHENOTYPE

Abstract Glioblastoma (GBM) is a highly aggressive brain tumor with high recurrence and resistance to therapies. The F-actin cytoskeleton in GBM is related to cell invasion and the glioma stem cell (GSC) phenotype, affecting self-renewal and migration. Our research identifies a novel role for the F-actin pathway in DNA repair, impacting genomic stability and contributing to therapy resistance. Understanding F-actin’s role is crucial for developing targeted strategies to improve GBM treatment outcomes. This study examines the effects of pharmacological F-actin depolymerization on reversing resistance to ionizing radiation (IR) and temozolomide (TMZ) in GBM spheroids. We established resistant sublines of GBM U87-MG cells through IR and TMZ cycles, observing significant resistance increases via MTT assays. Also, resistant cells had enhanced spheroid formation capacity, with higher size and proliferation. Alterations in DNA repair and F-actin pathway were observed, with intensified and disorganized F-actin polymerization and efficient repair in resistant cells. Elevated expression of stemness markers (Nestin, CD133, and CD44) indicated a GSC-like phenotype in resistant cells, corroborated by increased tumorigenicity and de novo spheroid formation. These markers were further enhanced by DNA damage. Treating cells with actin polymerization inhibitors reduced resistance to TMZ and IR, partly due to impaired DNA repair capacity. Additionally, F-actin disassembly affected stemness marker expression, reinforcing the link between cytoskeletal dynamics and the GSC phenotype. Our findings suggest that F-actin dynamic is crucial for resistance in GBM. Targeting F-actin could resensitize recurrent GBM tumours by diminishing DNA repair capabilities and affecting the GSC-like phenotype, offering new therapeutic avenues.