DDDR-68. HDAC inhibition–induced neuronal-like state creates cytoskeletal vulnerabilities in glioblastoma

Abstract Glioblastoma (GBM) remains universally fatal due to adaptive resistance mechanisms that enable tumor persistence despite initial treatment response. Quisinostat (QST), a brain-penetrant histone deacetylase inhibitor (HDACi), significantly prolongs survival when combined with radiation in patient-derived GBM models. However, tumor progression eventually occurs, suggesting surviving cells undergo adaptive phenotypic reprogramming rather than complete elimination. Here, we demonstrate that QST treatment drives glioma cells toward a neuronal-like differentiated state characterized by robust upregulation of neuronal signaling components and extensive cytoskeletal remodeling. Transcriptomic analysis revealed enhanced expression of neuronal signaling genes following QST treatment, validated at the protein level through immunohistochemistry and immunofluorescence. Treated tumors showed markedly increased expression of neuronal receptors (GABRA2, GRIK2, GluA4, CACNA1), structural proteins (TUBB3, acetylated α-tubulin), and tumor microtube associated markers (GAP43) particularly at the invasive tumor edge where therapy-resistant populations reside. To determine whether this represents treatment adaptation, we developed QST-tolerant cell lines that maintained high neuronal marker expression and demonstrated enhanced resistance to subsequent QST treatment compared to naïve cells. Importantly, these reprogrammed cells exhibited extensive microtubule-rich projections and cytoskeletal reorganization, suggesting structural vulnerabilities. We hypothesized that while cytoskeletal remodeling supports neuronal-like survival, it simultaneously creates therapeutic dependencies. Indeed, QST-surviving cells showed increased sensitivity to microtubule-targeting agents (MTAs), with combination treatment significantly enhancing cytotoxicity compared to single agents. These findings reveal that HDACi treatment paradoxically promotes survival through a reprogrammed neuronal-like state while creating exploitable structural vulnerabilities. This work provides mechanistic insight into GBM’s adaptive resistance strategies and identifies cytoskeletal targeting as a rational combination approach to overcome HDACi resistance.