Anti-proliferative and Apoptosis Inducing Effect of Thymoquinone in Human Teratocarcinomal (NTERA-2) Cancer Stem-Like Cells

Cancer stem cells (CSCs) are key drivers of tumor progression, therapeutic resistance and recurrence. Nigella sativa, a medicinal plant widely used in traditional medicine, has gained significant importance due to its diverse pharmacological properties. Thymoquinone (TQ), a biologically known active compound isolated from N.sativa, has demonstrated anticancer properties in various cancers. However, its effect on CSC-like cells has not been fully elucidated. In the present study, the anti-proliferative and apoptosis inducing properties of TQ was evaluated on human embryonal carcinoma cells (NTERA-2, cancer stem cell like model) and human peripheral blood mononuclear cells (PBMCs) in vitro. Antiproliferative effects of TQ on NTERA-2 cells and PBMCs were evaluated using the Sulforhodamine B (SRB) and WST-1 assays, respectively. The effect of TQ was further evaluated using colony formation assay, cell migration assay, fluorescence microscopy and quantification of caspase 3/7 activities. Oxidative stress markers (reactive oxygen species [ROS]) were also determined in NTERA-2 cells treated with TQ. Thymoquinone revealed promising dose- and time-dependent antiproliferative effects (half-maximal inhibitory concentration [IC50] 1.282, 1.167, and 0.984 g/mL at 24, 48, and 72 h post-treatment) in NTERA-2 cells while exerting a minimal cytotoxic effect in PBMCs. Apoptosis related morphological changes, and increased Caspase 3/7 activities confirmed the pro-apoptotic effects of TQ. Further, NTERA-2 cells treated with TQ expressed a significant increase (P < 0.001) in intracellular ROS activity. Overall results confirm that TQ exerts anti-proliferative and apoptotic effects in a dose- and time-dependent manner. Therefore, TQ can be considered as a potent drug lead for chemotherapy and radiotherapy resistant cancer stem cells.