Anti-Notch plus endocrine therapy in ER+ breast cancer inhibits cancer stem cells by increasing DAXX

Resistance to endocrine therapy (ET) in ER + breast cancer is mediated by Notch signaling, but the clinical application of anti-Notch therapy has been limited by the lack of predictive biomarkers. To identify Notch-regulated biomarkers, we conducted a pre-surgical window study evaluating ET combined with the γ-secretase inhibitor (GSI) MK-0752. RNA expressions in tumors were measured using an Affymetrix array and by real-time PCR. ET plus GSI showed more genes were decreased than ET alone. Specifically, DAXX , NOXA , and LFNG RNAs were increased, while fifteen additional transcripts were decreased. Mechanistically, GSI reduced Notch1 occupancy at CSL-binding elements within HES1 , HEY2 , HEYL , CCND1 , MKI67 , and DAXX genes, and inhibited cancer stem cells (CSCs) by 90% to 100%. This anti-CSC effect required DAXX, while GSI treatment or Notch1/4 knockdown increased DAXX expression, suggesting transcriptional repression by Notch. Using mouse tumor xenograft studies, ET plus MK-0752 resulted in complete regression of MCF-7 tumors, with DAXX-high tumors showing greater treatment sensitivity. Clinically, high DAXX expression was associated with improved recurrence-free and overall survival. This study found that anti-Notch plus ET in ER + breast cancer inhibits cancer stem cells by increasing DAXX, a promising predictive biomarker. These findings support clinical evaluation of therapies that increase DAXX expression.