Background/Objectives: The toxic side effects and resistance-associated limitations of conventional chemotherapeutic agents necessitate the development of more effective and selective combination strategies incorporating naturally derived compounds. In this study, the cytotoxic, apoptotic, oxidative stress-associated, and immunomodulatory effects of thymoquinone (TQ), a bioactive compound derived from Nigella sativa, and docetaxel (Dos), a taxane-based chemotherapeutic agent, were investigated alone and in combination in OVCAR3 ovarian cancer cells using integrated two-dimensional (2D) and three-dimensional (3D) experimental models. Materials and Methods: Cell viability was evaluated following treatment with TQ (10–500 µM), Dos (1–500 nM), and the TQ + Dos combination, and synergistic interactions were assessed by IC50− and combination index-based analyses. Apoptosis and cell cycle distribution were analyzed by flow cytometry. Cytokine levels were determined using ELISA, whereas apoptosis- and cell cycle-associated gene expression profiles were evaluated by RT-qPCR. Active caspase-3 expression was assessed by immunocytochemistry. Intracellular reactive oxygen species (ROS) accumulation was examined using DCFH-DA-based fluorescence imaging and antioxidant rescue experiments using N-acetyl-L-cysteine (NAC). In addition, the antitumor activity of the combination was further evaluated in OVCAR3-derived 3D tumor spheroid models using spheroid morphology, ATP-based viability, and live/dead fluorescence imaging analyses. Results: The TQ + Dos combination demonstrated enhanced cytotoxic and apoptotic activity in OVCAR3 cells compared with single-agent treatments and induced marked G2/M cell cycle arrest. Combination treatment increased pro-apoptotic gene expression and was associated with reduced expression of anti-apoptotic markers and modulated inflammatory cytokine profiles. Fluorescence-based analyses demonstrated marked intracellular ROS accumulation following TQ + Dos treatment, whereas NAC pretreatment partially attenuated oxidative stress and restored viability, suggesting partial involvement of ROS-associated mechanisms in treatment-induced cytotoxicity. Importantly, the combination maintained stronger cytotoxic and growth-inhibitory effects than either monotherapy in 3D ovarian cancer spheroids, where combination treatment induced pronounced spheroid shrinkage, viability loss, and structural disruption. Relatively lower toxicity observed in HaCaT cells suggested partial selectivity toward cancer cells. Conclusions: Collectively, these in vitro findings suggest that the TQ + Dos combination produces greater cytotoxic, apoptotic, and growth-inhibitory effects than either agent alone in ovarian cancer models and is associated with alterations in apoptosis-, cell cycle-, and oxidative stress-related responses. The observation of these effects in 3D spheroid models supports further investigation of this combination in more advanced preclinical systems.
Orhaner et al. (Sat,) studied this question.