IDO1 Silencing Enhances Cisplatin Sensitivity in Gastric Cancer Cells via Modulation of Apoptosis and Oxidative Stress

Gastric cancer remains a leading cause of cancer-related mortality worldwide, largely due to resistance to platinum-based chemotherapy. Indoleamine 2,3-dioxygenase 1 (IDO1) has been implicated in tumor progression and immune evasion; however, its cell-intrinsic role in chemoresistance remains incompletely understood. This study demonstrates that IDO1 functions as a critical regulator of cisplatin sensitivity in gastric cancer cells through a ROS-mediated mechanism. IDO1 expression was suppressed using siRNA in two gastric cancer cell lines, AGS and MKN45, followed by cisplatin treatment. Cell viability, oxidative stress levels, apoptosis-related gene expression, and caspase-3/7 activity were assessed to evaluate the functional consequences of IDO1 knockdown. IDO1 silencing significantly enhanced cisplatin-induced cytotoxicity in both cell lines, accompanied by increased intracellular reactive oxygen species (ROS) levels and a marked transcriptional shift toward a pro-apoptotic gene expression profile characterized by upregulation of Bax and p53 and downregulation of anti-apoptotic Bcl-2. Critically, functional apoptosis analysis revealed that combined IDO1 silencing and cisplatin treatment markedly increased caspase-3/7 activity, confirming activation of the execution phase of apoptosis. These findings establish that IDO1 limits apoptotic susceptibility in a cell-intrinsic manner and contributes to cisplatin sensitivity in gastric cancer cells. The mechanistic basis involves IDO1’s ROS-scavenging function: by suppressing IDO1, cells lose their capacity to neutralize ROS, leading to excessive ROS accumulation that triggers mitochondrial dysfunction and activates p53-dependent apoptotic pathways. In conclusion, this study identifies IDO1 as a key regulator of oxidative stress-associated, caspase-dependent apoptosis in gastric cancer and suggests that targeting IDO1 in combination with platinum-based chemotherapy represents a promising strategy to enhance the efficacy of gastric cancer treatment. These findings provide a rationale for clinical translation and provide a foundation for future preclinical and clinical studies.