Seco-Duocarmycin SA Augments the Impact of Proton Radiation on Human Glioblastoma Cells

Glioblastoma multiforme (GBM) is an aggressive brain tumor with limited treatment options and poor survival outcomes. This study evaluated the anticancer potential of seco-duocarmycin SA (seco-DSA), a potent DNA-alkylating agent, alone and in combination with proton radiation in human GBM cell lines. Human glioblastoma cell lines T98G and LN18 were treated with varying concentrations of seco-DSA, proton radiation doses (2, 4, or 8 Gy), or both. Proton irradiation was delivered with a 250-MeV beam. Clonogenic survival, cell proliferation, and cell cycle distribution were analyzed using colony formation and flow cytometry assays. Proteomic analysis of LN18 cells was performed by LC-MS/MS followed by bioinformatic pathway analysis. Statistical significance was determined using a two-tailed unpaired t-test (p ≤ 0.05), and Bliss synergy scores were calculated to assess treatment interactions. Combination therapy produced additive and synergistic inhibition of colony formation and enhanced G2/M phase arrest compared with either treatment alone. Apoptosis and necrosis increased modestly but did not fully account for observed cytotoxicity. Proteomic profiling revealed differential expression of proteins involved in DNA repair, apoptosis, and senescence, indicating that seco-DSA broadened radiation-induced stress responses. Seco-DSA potentiates the cytotoxic effects of proton radiation in GBM cells through enhanced clonogenic inhibition and modulation of cell cycle and DNA repair pathways. These findings support seco-DSA as a promising radiosensitizer for further preclinical evaluation.