Characterizing ER+ Breast Cancer Cell Responses to Dormancy-Inducing Culture Conditions

• Max Andrews, Chemical Engineering, University of Delaware

• April Kloxin, Chemical Engineering, University of Delaware

Breast cancer is the most common type of cancer affecting women worldwide. T47D cells are an estrogen receptor-positive (ER+) human breast cancer cell line representative of Luminal A breast cancer, the most prevalent type, accounting for 50-60% of all cases. Although Luminal A breast cancer has a five-year survival rate of ~95%, patients remain at risk for late metastatic relapse, making the study of cellular dormancy clinically relevant. T47D cells are widely used to study hormone-responsive breast cancer biology and therapeutic response, particularly associated with dormancy. This project aims to evaluate how different microenvironmental conditions influence T47D cell behavior using both two- and three-dimensional (2D and 3D) in vitro models. Two-dimensional cultures were selected first because they provide a high-throughput, cost-effective platform for preliminary analysis before more complex 3D and coculture models. T47D cells were cultured with serum-deprived, exhausted conditioned media, or TNF-α media, where serum deprivation and cytokine application have been reported to influence cellular dormancy. Cellular responses were monitored over multiple time points using Alamar Blue assays to assess metabolic activity and Ki67 immunostaining to evaluate proliferation. Routine cell counting was also performed to compare counting methods and quantify changes in cell viability and number throughout the experiments. Preliminary findings indicate that serum deprivation results in minimal cell growth and significantly reduced cell viability and number compared with a positive growth control, suggesting that this condition may not support long-term cell survival. These findings contribute to a better understanding of these conditioned environments affecting T47D cells and provide a foundation for future studies using more relevant 3D culture systems, as well as, coculture models, and additional assays to further investigate breast cancer cell dormancy.