Andrographolide suppresses the malignancy of triple-negative breast cancer by reducing THOC1-promoted cancer stem cell characteristics

Triple-negative breast cancers (TNBCs) are difficult to cure and currently lack of effective treatment strategies. Cancer stem cells (CSCs) are highly associated with the poor clinical outcome of TNBCs. Thoc1 is a core component of the THO complex (THOC) that regulates the elongation, processing and nuclear export of mRNA. The function of thoc1 in TNBC and whether Thoc1 serves as a drug target are poorly understood. In this study, we demonstrated that thoc1 expression is elevated in TNBC cell lines and human TNBC patient tissues. Knockdown of thoc1 decreased cancer stem cell populations, reduced mammosphere formation, impaired THOC function, and downregulated the expression of stemness-related proteins. Moreover, the thoc1-knockdown 4T1 cells showed less lung metastasis in an orthotopic breast cancer mouse model. Overexpression of Thoc1 promoted TNBC malignancy and the mRNA export of stemness-related genes. Furthermore, treatment of TNBC cells with the natural compound andrographolide reduced the expression of Thoc1 expression, impaired homeostasis of THOC, suppressed CSC properties, and delayed tumor growth in a 4T1-implanted orthotopic mouse model. Andrographolide also reduced the activity of NF-κB, an upstream transcriptional regulator of Thoc1. Notably, thoc1 overexpression attenuates andrographolide-suppressed cellular proliferation. Altogether, our results demonstrate that THOC1 promotes cancer stem cell characteristics of TNBC, and andrographolide is a potential natural compound for eliminating CSCs of TNBCs by downregulating the NF-κB-thoc1 axis.