Copper-Potentiated Disulfiram Cytotoxicity in HCT116 and SW480 Colorectal Cancer Cells: Redox Imbalance and Telomerase Suppression Without Direct Enzyme Inhibition

Abstract Background Disulfiram (DSF) is being repurposed as a copper-dependent anticancer agent, but whether its activity involves telomerase, and by what route, remains undefined. Methods HCT116 and SW480 colorectal cancer cells were exposed for 48 h to copper sulfate, DSF, or DSF plus 0.1 µM copper, and viability was measured by MTT. Telomerase activity (telomeric repeat amplification protocol), reduced glutathione (GSH), and reactive oxygen species (ROS) were assessed after 24 h in intact cells, and telomerase was also assayed in cell-free lysates, over six independent biological replicates. Results DSF IC 50 values were 2.04 µM (HCT116) and 1.73 µM (SW480); 0.1 µM copper reduced them to 0.39 and 0.56 µM. DSF lowered telomerase activity in HCT116 ( P < 0.005), and DSF/copper lowered it in both lines ( P < 0.001) while depleting GSH and raising ROS. In cell-free lysates, copper-containing conditions instead increased telomerase activity slightly ( P < 0.05). GSH correlated with telomerase activity (ρ = 0.75) and inversely with ROS (ρ = −0.85), and ROS inversely with telomerase activity (ρ = −0.80). Conclusions Sub-toxic copper potentiates DSF cytotoxicity alongside redox imbalance and telomerase suppression. The opposite cell-free response argues against direct enzyme inhibition and supports an indirect, redox-linked mechanism.