Disruption of redox balance in glutaminolytic triple negative breast cancer by inhibition of glutaminase and glutamate export

Resistance to chemotherapy is an important challenge in the clinical management of triple-negative breast cancer (TNBC). Utilization of the amino acid glutamine as a key nutrient is a metabolic signature of TNBC featuring high glutaminase (GLS) activity and a large pool of cellular glutamate, which mediates intracellular enrichment of cystine via xCT (SLC7A11) antiporter activity. To overcome chemo-resistant TNBC, we identified a strategy of dual metabolic inhibition of GLS and xCT to sensitize resistant TNBC cells to chemotherapy. We successfully tested this strategy in a human TNBC line and its chemoresistant variant in vitro and their xenograft models in vivo. Key findings of our study include: 1. Dual metabolic inhibition induced pronounced reductions of cellular glutathione accompanying significant increases of cellular superoxide level in both parent and resistant TNBC cells. While GLS and xCT inhibition did not directly kill cells via apoptosis, they potentiated doxorubicin (DOX) and cisplatin (CIS) to induce remarkably higher levels of apoptosis than DOX or CIS alone. 2. Although the resistant TNBC cells exhibited higher capacity to mitigate oxidative stress than the parent cells, their resistance was overcome by dual metabolic inhibition combined with DOX or CIS. 3. In vivo efficacy and safety of the triple combination (GLS and xCT inhibition plus DOX or CIS) were demonstrated in both chemo sensitive and resistant TNBC tumors in mice. In conclusion, GLS and xCT inhibition resulted in unmitigated oxidative stress due to depletion of glutathione, representing a promising strategy to overcome chemoresistance in glutamine-dependent TNBC.