Curcumin Enhances Gemcitabine Sensitivity in Breast Cancer Cells Through ROS-Associated Mitochondrial Apoptosis and Transcriptional Reprogramming

Breast cancer is a leading cause of cancer-related mortality in women, necessitating new treatment strategies. Curcumin (Cur), a natural polyphenol, and gemcitabine (Gem), a standard chemotherapeutic, were investigated for their combined anticancer effects. We hypothesized that Cur sensitizes breast cancer cells to Gem via reactive oxygen species (ROS)-mediated apoptosis, and that this effect is associated with selective oxidative vulnerability in malignant cells compared to normal breast epithelial cells. MCF-7 (hormone receptor-positive) and MDA-MB-231 (triple-negative) cells were treated with Cur and Gem alone or in combination. Normal breast epithelial MCF-10A cells were included to evaluate therapeutic selectivity. Cell viability (MTT), apoptosis (Annexin V/PI), oxidative stress (TOS/TAS), intracellular ROS generation (DCFH-DA assay), mitochondrial membrane potential (ΔΨm) (JC-1 staining), caspase activation, synergy (Bliss/HSA/Chou-Talalay), VEGF secretion (ELISA), and transcriptomic changes (RNA-Seq) were assessed. Cur and Gem showed dose-dependent cytotoxicity. Combination treatment demonstrated strong synergistic activity, significantly enhancing apoptosis, oxidative stress, and caspase activation. Direct quantification of intracellular ROS revealed marked ROS accumulation in MCF-7 and MDA-MB-231 cells following combination treatment, whereas MCF-10A cells exhibited only modest oxidative changes. JC-1 analysis demonstrated substantial mitochondrial depolarization in breast cancer cells, which was largely reversible by ROS scavenging and minimal in MCF-10A cells. VEGF secretion was markedly suppressed. Transcriptomic analysis revealed profound alterations in apoptosis, cell cycle, and angiogenesis-related pathways, with more pronounced transcriptional reprogramming observed in the triple-negative subtype. Cur synergistically enhances Gem's efficacy in breast cancer cells through ROS-mediated apoptosis and anti-angiogenic effects, characterized by cancer-selective ROS amplification and mitochondrial membrane depolarization, supporting its potential as a combination therapy, particularly for triple-negative breast cancer.