Abstract 5611: Unraveling the role of F-actin in resistant GBM: Insights into DNA repair, GSC phenotype, and therapeutic implications
Authors: Magalhães Yuli Thamires , Forti Fábio Luís 
Published: March 2024

Abstract
Glioblastoma (GBM), a highly aggressive brain cancer, poses a formidable challenge marked by its resistance to conventional therapies. F-actin, a crucial cytoskeletal protein, influences DNA repair and impacts genomic stability. F-actin dynamics also shape the glioma stem cell (GSC) phenotype, affecting self-renewal and migration. Altered F-actin organization contributes to GBM resistance to conventional therapies. Understanding F-actin's multifaceted role is vital for developing targeted strategies to overcome treatment resistance and enhance outcomes for GBM patients. This study goes deeper into the intricate interplay between the F-actin cytoskeleton and the acquisition of resistance in GBM cells. Our primary goal was to explore the effects of pharmacological or genetic F-actin depolymerization on the reversal of acquired resistance to ionizing radiation (IR) and temozolomide (TMZ) in GBM cells, particularly focusing on the underlying mechanisms involving DNA repair, the glioma stem cell (GSC) phenotype, and therapeutic implications. To establish resistant sublines, GBM U87-MG cells underwent cycles of IR and TMZ exposure, revealing a significant increase in IC50 values for TMZ and ID50 values for IR through viability assays. Subsequent characterization of these sublines growth was in both adherent and spheroid cultures uncovering a distinct sphere-forming capacity. Notably, alterations in DNA repair and the Rho GTPase pathway were observed, with evident disorganized F-actin polymerization in resistant cells, especially at the periphery of spheroids. Elevated expression of stemness markers (Nestin, CD133, and CD44) highlighted a GSC-like profile in the resistant cells, a characteristic further accentuated in spheroid cultures. To assess the relevance of the actin cytoskeleton in maintaining the resistant phenotype, cells were treated with Rho-GTPase inhibitor (C3) or actin polymerization inhibitor (Cytochalasin D). Both treatments resulted in reduced TMZ IC50 and IR ID50 values, partially attributed to the negative modulation of DNA repair capacity - observed by alkaline comet and host-cell reactivation assays. Additionally, F-actin disassembly was found to impact the expression of stemness markers, further reinforcing the connection between cytoskeletal dynamics and the GSC phenotype. Overall, our data strongly suggest that F-actin cytoskeleton dynamics plays a pivotal role in the development and maintenance of resistance in GBM. Targeting these cytoskeletal components sees a promising pharmacological strategy for resensitizing recurrent and resistant GBM tumors, not only by diminishing DNA repair capabilities but also by influencing the GSC-like phenotype, thus opening new avenues for therapeutic interventions.
Citation Format: Yuli Thamires Magalhães, Fábio Luís Forti. Unraveling the role of F-actin in resistant GBM: Insights into DNA repair, GSC phenotype, and therapeutic implications [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(6_Suppl):Abstract nr 5611.