Verbascoside suppresses malignant phenotypes and induces senescence-associated changes in glioblastoma cells associated with Skp2 downregulation

Περίληψη

Glioblastoma (GBM) is characterized by aggressive growth, diffuse invasion, cellular plasticity, and glioblastoma stem-like cell-associated therapeutic resistance. Verbascoside (VB), a naturally occurring phenylethanoid glycoside, has previously been reported to exert anti-GBM effects; however, whether VB modulates Skp2-associated EMT-like/mesenchymal transition-related plasticity, stem-like properties, and senescence-associated changes remains incompletely understood. In this study, the effects of VB on GBM cell viability, clonogenic growth, migration, invasion, EMT-like/mesenchymal transition-associated markers, glioblastoma stem-like cell properties, and senescence-associated changes were examined in U87, U251, and glioblastoma stem-like cells. Skp2 mRNA and protein expression were assessed by RT-qPCR and western blotting, respectively, and ectopic Skp2 overexpression was used to evaluate the functional contribution of Skp2 to VB-mediated effects. The in vivo activity of VB was further examined in an intracranial xenograft model. VB reduced GBM cell viability, clonogenic growth, migration, and invasion, and decreased the expression of EMT-like/mesenchymal transition-associated markers, including Vimentin and Snail. VB also impaired sphere-forming capacity and reduced stemness-associated marker expression in glioblastoma stem-like cells. In addition, VB induced senescence-associated changes, as indicated by increased SA-β-gal positivity and increased expression of p21 and p16^INK4A, together with reduced EdU incorporation. VB treatment significantly reduced Skp2 mRNA levels in U87 and U251 cells, accompanied by dose-dependent downregulation of Skp2 protein expression. Ectopic Skp2 overexpression partially attenuated VB-mediated suppression of malignant phenotypes and stem-like properties, as well as VB-induced senescence-associated changes, including p16^INK4A induction and increased SA-β-gal positivity. In vivo , VB treatment reduced intracranial tumor growth, prolonged survival, and was associated with decreased Skp2 expression in tumor tissues. These findings suggest that VB suppresses multiple malignant phenotypes and induces senescence-associated changes in GBM cells, at least in part in association with Skp2 downregulation. The observed reduction in Skp2 mRNA suggests that VB-associated Skp2 downregulation occurs, at least partially, at the mRNA abundance level. However, Skp2 should be interpreted as a VB-associated and partially contributing mechanism rather than a direct molecular target or fully required mediator of VB activity.