repression by pluripotency factors and consequent chemoresistance in breast cancer stem-like cells is reversed by aspirin.

The high abundance of drug efflux pumps in cancer stem cells (CSCs) contributes to chemotherapy resistance. The transcriptional regulator SMAR1 suppresses CSC expansion in colorectal cancer, and increased abundance of SMAR1 is associated with better prognosis. Here, we found in breast tumors that the expression of was decreased in CSCs through the cooperative interaction of the pluripotency factors Oct4 and Sox2 with the histone deacetylase HDAC1. Overexpressing SMAR1 sensitized CSCs to chemotherapy through SMAR1-dependent recruitment of HDAC2 to the promoter of the gene encoding the drug efflux pump ABCG2. Treating cultured CSCs or 4T1 tumor-bearing mice with the nonsteroidal anti-inflammatory drug aspirin restored expression and repression and enhanced tumor sensitivity to doxorubicin. Our findings reveal transcriptional mechanisms regulating that also regulate cancer stemness and chemoresistance and suggest that, by restoring expression, aspirin might enhance chemotherapeutic efficacy in patients with stem-like tumors.