Checkpoint Kinase 2 Inhibition Can Reverse Tamoxifen Resistance in ER-Positive Breast Cancer

Area of Science:

• Oncology
• Molecular Biology
• Genetics

Background:

• Breast cancer is a heterogeneous disease often treated with tamoxifen.
• Tamoxifen resistance is a significant clinical challenge, particularly in ER-positive breast cancer.
• A novel NCOR2 splice variant, BQ323636.1 (BQ), has been identified as a mediator of tamoxifen resistance.

Purpose of the Study:

• To elucidate the upstream mechanisms regulating BQ expression and its role in tamoxifen resistance.
• To investigate the signaling pathways involved in tamoxifen-induced BQ modulation.
• To evaluate the therapeutic potential of targeting these pathways to overcome tamoxifen resistance.

Main Methods:

• Investigated the effect of tamoxifen on DNA damage and BQ expression.
• Analyzed the activation of ATM/CHK2 and ATR/CHK1 signaling cascades.
• Utilized siRNA and small molecule inhibitors targeting CHK2 to assess BQ phosphorylation and stability.
• Evaluated the efficacy of CHK2 inhibition in reversing tamoxifen resistance in vitro and in vivo models.
• Correlated CHK2 and BQ expression with clinical outcomes in patient samples.

Main Results:

• Tamoxifen treatment induces DNA damage, which enhances BQ expression.
• The ATM/CHK2 signaling pathway is activated by DNA damage and enhances BQ protein stability.
• Inhibition of CHK2 reduces BQ phosphorylation and increases its poly-ubiquitination, leading to decreased BQ expression.
• Targeting CHK2 with CCT241533 reversed tamoxifen resistance in vitro and in vivo.
• High p-CHK2 and nuclear BQ expression in clinical samples correlated with tamoxifen resistance and poorer survival.

Conclusions:

• Tamoxifen treatment enhances BQ expression in ER-positive breast cancer via the ATM/CHK2 axis.
• CHK2 plays a critical role in stabilizing BQ and mediating tamoxifen resistance.
• Targeting CHK2 represents a promising therapeutic strategy to overcome tamoxifen resistance in ER-positive breast cancer.