Recurrent triple-negative breast cancer from cysteine deprivation loses tumorigenicity via downregulation of the CST4 signaling

Abstract

Triple-negative breast cancer (TNBC) is an aggressive type of breast cancer with a high risk of recurrence following therapeutic treatments. Targeted cysteine therapy via inhibition of cysteine uptake by erastin effectively induces mesenchymal TNBC cells to ferroptosis. However, a small residual population of cancer cells exhibited the erastin-resistance and survived after the erastin treatment. This phenomenon is likely analogous to the event of tumor recurrence in patients after therapy. To characterize this resistance, we established the erastin-resistant/recurrent TNBC cell models in vitro by multi-cycles of erastin challenge. By an epigenetic compound library screen, the erastin-resistance be abolished by adjuvant epigenetic compounds. Intriguingly, the erastin-recurrent TNBC cells failed to grow in anchorage-independent conditions, implying a loss of tumorigenicity. By transcriptomic profiling analysis, the recurrent cells displayed many gene expression alterations and attenuated signaling processes, including K-Ras signaling. Three members of the cystatin gene family, including CST4, were significantly downregulated in recurrent cells. Knocking out of CST4 by CRISPR/Cas9 significantly suppressed the tumorigenic potential and K-Ras signaling. Our findings suggested that targeted cysteine therapy could be a valid treatment for mesenchymal TNBC with a low probability of tumor recurrence.