Blockade of AP-1 Potentiates Endocrine Therapy and Overcomes Resistance

Area of Science:

• Oncology
• Molecular Biology
• Endocrinology

Background:

• Estrogen receptor (ER) signaling is crucial in breast cancer, but resistance to endocrine therapies like tamoxifen is a major clinical challenge.
• The transcription factor AP-1 (activator protein 1) is implicated in growth factor receptor and stress kinase pathways, which are linked to endocrine resistance.

Purpose of the Study:

• To provide direct evidence for the role of AP-1 in mediating breast cancer endocrine resistance.
• To investigate AP-1 as a potential therapeutic target to overcome endocrine resistance.

Main Methods:

• Comparative analysis of gene expression profiles in tamoxifen-resistant breast cancer and growth factor-induced ER cistromes.
• Inhibition of AP-1 using a dominant-negative cJun (DN-cJun) in MCF7 cells (in vitro) and xenograft models (in vivo).

Main Results:

• Genes modulated in tamoxifen resistance significantly overlapped with genes regulated by growth factor-induced ER, enriched for AP-1 binding motifs.
• AP-1 blockade enhanced endocrine treatment efficacy, accelerated tumor response, promoted regression, and delayed tamoxifen resistance onset.
• DN-cJun induction in established tamoxifen-resistant tumors caused significant shrinkage, reduced proliferation, and increased apoptosis.

Conclusions:

• AP-1 is a key determinant of endocrine resistance in breast cancer.
• AP-1 blockade is a promising strategy to overcome endocrine resistance and enhance therapeutic outcomes.