DDDR-41. Targeting the Rho GTPase Pathway to Chemosensitize TMZ/Cisplatin-Resistant GBM via p53-Dependent Mechanisms

Abstract Glioblastoma multiforme (GBM) is the most frequent and aggressive brain tumor, routinely treated with ionizing radiation (IR). However, therapy resistance inevitably recurs. The actin cytoskeleton of GBM contributes to its high invasive capacity, but whether Rho GTPases modulate DNA damage repair and therapeutic sensitivity remains unclear. We hypothesized that the Rho GTPase pathway plays a role in GBM chemoresistance to temozolomide (TMZ) and cisplatin by regulating DNA repair mechanisms, representing a potential vulnerability in GBM chemotherapy. Our results demonstrate that prolonged cisplatin exposure upregulates Rho GTPase regulatory genes in U87-MG cells. Immunoblotting confirmed this observation, showing increased activity in both Rho and p53 pathways following cisplatin treatment. tractRho inhibition reduced the IC50 for TMZ and cisplatin, as well as impaired survival and proliferation—but only in p53 wild-type (WT) cells. Additionally, Rho inhibition diminished DNA repair capacity for both TMZ- and cisplatin-induced lesions. p53 knockdown abolished Rho inhibition-induced chemosensitivity and DNA repair impairment. Repeated DNA damage exposure led to enhanced p53 phosphorylation, nuclear localization, and F-actin polymerization and dynamics. TMZ-resistant cells exhibited a significantly higher TMZ IC50, while Rho inhibition reduced IC50 in both resistant and parental clones, effectively reversing acquired resistance. These findings strongly suggest that Rho GTPases play a critical role in DNA repair and acquire TMZ resistance, indicating that the Rho pathway may be a therapeutic target to enhance the efficacy of conventional therapies. Notably, this effect is strictly dependent on p53 transcriptional activity.