Targeting xCT with sulfasalazine suppresses triple-negative breast cancer growth via inducing autophagy and coordinating cell cycle and proliferation

There is a substantial unmet need for effective treatment strategies in triple-negative breast cancer (TNBC). Recently, renewed attention has been directed towards targeting glutamine (Gln) metabolism to enhance the efficacy of cancer treatment. Nonetheless, a comprehensive exploration into the mechanistic implications of targeting Gln metabolism in TNBC is lacking. In this study, our objective was to probe the sensitivity of TNBC to alterations in Gln metabolism, using representative TNBC cell lines: MDA-MB-231, MDA-MB-468, and 4T1. Through an integration of bioinformatics, in-vitro, and in-vivo investigations, we demonstrated that sulfasalazine (SAS), like erastin (a known xCT inhibitor), effectively suppressed the expression and transport function of xCT, resulting in a depletion of glutathione levels in MDA-MB-231 and MDA-MB-468 cells. Furthermore, both xCT knockdown and SAS treatment demonstrated the promotion of cellular autophagy. We unveiled a positive correlation between xCT and the autophagy-related molecule p62, their co-expression indicating poor survival outcomes in breast cancer patients. In addition, our research revealed the influence of SAS and xCT on the expression of proteins regulating cell cycle and proliferation. Treatment with SAS or xCT knockdown led to the inhibition of MYC, CDK1, and CD44 expression. Significantly, the combined administration of SAS and rapamycin exhibited a synergistic inhibitory effect on the growth of transplanted breast tumor in mouse models constructed from murine-derived 4T1 cells. Taken together, our findings suggested the potential and clinical relevance of the SAS and rapamycin combination in the treatment of TNBC.