Synergistic Antitumor Effects of Etoposide and Curcumin in Ovarian Cancer Cells

Background: Overcoming therapeutic resistance and tumor microenvironment-mediated survival remains a major challenge in ovarian cancer treatment. This study investigated the individual and combined antitumor effects of etoposide and curcumin in human ovarian cancer models, with emphasis on synergistic interactions, apoptosis induction, tumor microenvironment modulation, and oxidative stress-associated mechanisms. We hypothesized that the combination of etoposide and curcumin exerts enhanced antitumor activity through an integrated mechanism involving DNA damage-associated apoptotic signaling, tumor microenvironment modulation, and ROS-associated cellular stress, rather than through a single dominant pathway. Methods: Cell viability was assessed using the MTT assay, and drug-drug interactions were quantitatively evaluated using the Chou-Talalay and Bliss independence models. Apoptosis was analyzed by Annexin V/propidium iodide flow cytometry, caspase-8/9 activity assays, and cell cycle analysis. Transcriptional regulation of apoptosis- and microenvironment-related genes was examined by quantitative real-time PCR. Inflammatory and angiogenic cytokines were measured by ELISA. Therapeutic efficacy was further validated in three-dimensional (3D) tumor spheroid models using morphological assessment and adenosine triphosphate (ATP)-based viability assays. The contribution of reactive oxygen species (ROS) was evaluated using antioxidant pretreatment. Results: The etoposide-curcumin combination demonstrated significantly enhanced antiproliferative and pro-apoptotic effects compared with either agent alone, with consistent synergism observed across quantitative interaction models. Combination treatment increased apoptotic cell death, activated both intrinsic and extrinsic apoptotic pathways, and induced G2/M cell cycle arrest. In parallel, inflammatory and angiogenic signaling was markedly suppressed at both transcriptional and protein levels. These effects were preserved and amplified in 3D tumor spheroid models, where combination therapy induced pronounced spheroid shrinkage and reduced viability. Antioxidant pretreatment partially attenuated ROS generation and cytotoxicity, indicating that oxidative stress contributes to, but does not fully account for, the observed antitumor effects. Conclusions: The combination of etoposide and curcumin exerts synergistic and multi-layered antitumor effects in ovarian cancer models by integrating apoptosis induction, tumor microenvironment modulation, and ROS-associated mechanisms. These findings support further preclinical evaluation of this combination as a rational therapeutic strategy for ovarian cancer.