Enhancing 5-Fluorouracil Efficacy in Colorectal Cancer by Inhibiting Glutathione Antioxidant Mechanisms with an xCT Inhibitor

Abstract

Colorectal cancer is a leading cause of cancer-related mortality, and chemotherapy resistance remains a major challenge. We investigated whether inhibiting glutathione could enhance the efficacy of 5-fluorouracil (5-FU) in colorectal cancer. Three small-molecule inhibitors targeting glutathione metabolism were tested in HCT-116 cells: CB-839 (glutaminase inhibitor), IKE (xCT transporter inhibitor), and Polydatin (glucose-6-phosphate dehydrogenase inhibitor). Their effects on glutathione levels, ROS accumulation, and cell viability were first evaluated. CB-839 decreased cell viability, Polydatin had no effect, and IKE reduced cystine uptake and increased ROS, although none of the inhibitors alone induced marked cell death. We next examined whether they could enhance 5-FU activity. Although CB-839 and Polydatin did not improve 5-FU efficacy, IKE increased ROS levels and reduced viability when combined with 5-FU. In an in ovo model, the combination of IKE and 5-FU reduced tumor growth, whereas each agent alone had a limited effect. These findings suggest that targeting xCT-mediated cystine uptake may enhance chemotherapy response and could be a promising approach for treating colorectal cancer.