Metabolic interplay between exogenous cystine and glutamine dependence in triple-negative breast cancer.

Triple-negative breast cancer (TNBC) is an aggressive breast cancer subtype characterized by high recurrence rates and limited treatment options due to the absence of hormone receptors. Despite advancements in breast cancer research, effective therapies for TNBC remain inadequate, highlighting the need to elucidate subtype-specific metabolic vulnerabilities. TNBC cells exhibit a strong dependence on the exogenous amino acids cystine and glutamine, yet the interplay between these metabolic dependencies remains poorly understood. Here, we demonstrate that TNBC cells exhibit sensitivity to individual nutrient deprivation but can survive dual cystine and glutamine deprivation via distinct mechanisms. Exogenous glutamine primarily fuels glutamine anaplerosis, supporting TNBC cell proliferation. Notably, when exogenous glutamine is absent, restricted cystine uptake restores intracellular glutamate levels, fulfilling metabolic demands and sustaining TNBC cell growth. Under cystine deprivation, inhibition of glutaminolysis rescues TNBC cells by mitigating lipid peroxidation and reducing ROS production, whereas supplementation with the TCA cycle intermediates ɑ-ketoglutarate (ɑ-KG) and succinate induces profound cell death in both TNBC and luminal breast cancer cells under glutaminolysis blockade. Collectively, these findings highlight the metabolic interdependence of glutamine and cystine in TNBC, providing mechanistic insights into potential metabolic-targeted and dietary interventions for TNBC therapy.