20(S)-protopanaxadiol enhances temozolomide responsiveness in MGMT-expressing glioblastoma: Wnt/β-catenin attenuation and MGMT downregulation

Background Glioblastoma is a highly aggressive primary brain malignancy, and O 6 -methylguanine-DNA methyltransferase (MGMT)-mediated DNA repair contributes to reduced temozolomide (TMZ) responsiveness. This study investigated whether 20(S)-protopanaxadiol (20(S)-PPD) enhances TMZ responsiveness in MGMT-expressing glioblastoma models and explored a potential mechanism. Methods U87, U251, LN18, and T98G glioblastoma cells were studied, with combination and mechanistic analyses focused on MGMT-expressing LN18 and T98G cells. Network pharmacology was used to prioritize candidate targets and pathways, followed by experimental evaluation using cell viability, apoptosis, migration, invasion, comet assays, western blotting, and immunofluorescence assays. Preclinical in vivo activity was assessed in an intracranial zebrafish xenograft model and an LN18 subcutaneous xenograft model in BALB/c nude mice. Results 20(S)-PPD reduced viability in all four cell lines and promoted apoptosis while decreasing migration- and invasion-related phenotypes in LN18 and T98G cells. Combined treatment produced greater inhibitory effects than either monotherapy and enhanced TMZ-induced DNA damage. Network pharmacology prioritized Wnt signaling as a candidate pathway. Subsequent cellular and in vivo analyses showed attenuated Wnt/β-catenin signaling and reduced MGMT expression after 20(S)-PPD treatment. β-Catenin or MGMT overexpression partially attenuated the TMZ-sensitizing effect of 20(S)-PPD. The combination treatment markedly inhibited tumor growth in both xenograft models. Conclusion 20(S)-PPD enhanced TMZ responsiveness in MGMT-expressing glioblastoma models, and this effect was associated with attenuated Wnt/β-catenin signaling and reduced MGMT expression. Acquired TMZ-resistant derivatives and patient-derived resistant models were not examined; therefore, the conclusions are limited to the models evaluated here. These findings provide preclinical evidence supporting further evaluation of 20(S)-PPD as a potential TMZ chemosensitizer.