Targeting breast cancer stem cells by novel HDAC3-selective inhibitors.

Although histone deacetylase (HDAC) inhibitors have been known to suppress the cancer stem cell (CSC) population in multiple types of cancer cells, it remains unclear which HDAC isoforms and corresponding mechanisms contribute to this anti-CSC activity. Pursuant to our previous finding that HDAC8 regulates CSCs in triple-negative breast cancer (TNBC) cells by targeting Notch1 stability, we investigated related pathways and found HDAC3 to be mechanistically linked to CSC homeostasis by increasing β-catenin expression through the Akt/GSK3β pathway. Accordingly, we used a pan-HDAC inhibitor, AR-42 (1), as a scaffold to develop HDAC3-selective inhibitors, obtaining the proof-of-concept with 18 and 28. These two derivatives exhibited high potency and isoform selectivity in HDAC3 inhibition. Equally important, they showed in vitro and/or in vivo efficacy in suppressing the CSC subpopulation of TNBC cells via the downregulation of β-catenin.