Selective cytotoxicity of solamargine via oxidative stress and caspase-independent mechanisms in human glioblastoma cells

IDH-wild-type glioblastoma (IDH-wildtype GB) is an aggressive and genetically heterogeneous tumor characterized by intrinsic resistance to radiotherapy and chemotherapy, while surgical resection remains inherently limited by its diffuse infiltrative growth, leading to poor clinical outcomes. Natural products such as solamargine (SM), a steroidal glycoalkaloid with cytotoxic and antitumor properties, have emerged as potential adjuvant strategies. Here, we investigated the effects of SM on proliferation, clonogenic survival, morphology and migration of IDH-wildtype GB cell lines (U-87MG, U-251MG and T98-G) and non-tumoral astrocytes under normoxic and hypoxic conditions, as well as its interaction with temozolomide (TMZ). Under normoxia, SM reduced cell viability in a dose- and time-dependent manner, with IC₅₀ values between 5.04 and 9.53 μM and showed enhanced cytotoxicity under hypoxia. TMZ alone displayed modest activity, and its combination with SM produced predominantly antagonistic effects. Clonogenic assays confirmed the antiproliferative potential of SM, with significant inhibition of colony formation at 2.5 μM. SM induced marked morphological alterations but did not significantly impair migration in wound-healing assays. In U-87MG cells, SM triggered G₂/M cell-cycle arrest, increased intracellular reactive oxygen species generation, and elevated γH2AX protein expression, indicating oxidative stress-associated DNA damage. However, cleaved caspase-3 and p53 were not detected, suggesting a predominantly non-apoptotic mode of cell death. Together, these findings support SM as a promising candidate for IDH-wildtype GB therapy and underscore the need for further studies to clarify its mechanisms of action and optimize its therapeutic use.