Epithelial-mesenchymal plasticity determines estrogen receptor positive breast cancer dormancy and epithelial reconversion drives recurrence

More than 70% of human breast cancers (BCs) are estrogen receptor α-positive (ER+). A clinical challenge of ER+ BC is that they can recur decades after initial treatments. Mechanisms governing latent disease remain elusive due to lack of adequate in vivo models. We compare intraductal xenografts of ER+ and triple-negative (TN) BC cells and demonstrate that disseminated TNBC cells proliferate similarly as TNBC cells at the primary site whereas disseminated ER+ BC cells proliferate slower, they decrease CDH1 and increase ZEB1,2 expressions, and exhibit characteristics of epithelial-mesenchymal plasticity (EMP) and dormancy. Forced E-cadherin expression overcomes ER+ BC dormancy. Cytokine signalings are enriched in more active versus inactive disseminated tumour cells, suggesting microenvironmental triggers for awakening. We conclude that intraductal xenografts model ER + BC dormancy and reveal that EMP is essential for the generation of a dormant cell state and that targeting exit from EMP has therapeutic potential.

Intraductal xenografts model estrogen receptor-positive (ER+) breast cancer dormancy and reveal a critical role for epithelial-mesenchymal transition (EMT) in its establishment

Patrik Aouad

Compared to estrogen receptor-negative (ER-) breast cancer (BC), ER+ BC often manifests with a latent disease that recurs decades after initial diagnosis. The mechanisms governing dormancy and distant recurrence of ER+ tumors remain elusive due to the lack of preclinical models. Here, we compared the tumor progression of ER+ and triple negative (TN; ER-, progesterone receptor and human epidermal growth factor receptor 2-negative) BCs by grafting cell lines- and patient-derived tumor cells into the milk ducts of immunocompromised mice. In the intraductal model, both ER+ and TN BC cells disseminate already during the in situ stage. TN disseminated tumor cells (DTCs) proliferate and form macro-metastases, while DTCs from ER+ BC xenografts have low proliferative indices, are arrested in the G0/G1 phase of the cell cycle, and express the dormancy marker p27. Dormant DTCs display mesenchymal and niche-specific characteristics, as revealed by three-dimensional single cell resolution imaging, and show molecular features of Epithelial-Mesenchymal Transition (EMT) with decreased CDH1, and in-creased ZEB1, ZEB2, and VIM expression levels. Surprisingly, EMT is neither detected in primary tumor cells, nor required for their invasion or dissemination, but is acquired upon their establishment in distant sites. In ex vivo cultures, dormant lung and brain DTCs, revert back to a proliferative state within 3 weeks through a Mesenchymal-Epithelial Transition (MET). In vivo, CDH1 restoration in dormant DTCs overcomes dormancy and increases the growth and proliferation of lung metastases, while decreasing the expression of EMT-transcription factors (MET). We conclude that the intraductal model provides exciting new experimental opportunities to study ER+ BC metastasis dormancy, and reveals that EMT could be exploited therapeutically to promote dormancy and prevent distant recurrence.

EPFL2021

Intraductal xenografts model estrogen receptor-positive (ER+) breast cancer dormancy and reveal a critical role for epithelial-mesenchymal transition (EMT) in its establishment

Patrik Aouad

EPFL2021