Mammary adipose stromal cells derived from obese women reduce sensitivity to the aromatase inhibitor anastrazole in an organotypic breast model

ABSTRACT Aromatase inhibitors are the preferred treatment for certain women with estrogen receptor (ER)‐positive breast cancer, but evidence suggests that women with obesity experience aromatase inhibitor resistance at higher rates. To compare how stromal cells derived from women who are lean or obese influence response to the aromatase inhibitor (anastrazole), we incorporated patient‐derived stroma in a previously characterized MCF7‐derived in vitro duct model. Coculture with adipose stromal cells enabled the metabolism of testosterone (T) to E 2 , which induced estrogen response element activity, epithelial proliferation, and hyperplasia in MCF7 cells. The effects of T were inhibited by the ER antagonist tamoxifen and aromatase inhibitor anastrazole and were increased by the aromatase inducer dexamethasone. Primary mammary adipose stromal cells derived from women with obesity displayed increased aromatase mRNA compared with lean controls. MCF7‐derived ducts cocultured with obese stromal cells exhibited higher maximal aromatization‐induced ER transactivation and reduced anastrazole sensitivity, a difference not seen in 2‐dimensional coculture. Finally, tamoxifen was more effective than anastrazole at reducing aromatization‐induced ER transactivation and proliferation. These findings suggest that patient‐specific responses to hormone therapies can be modeled and studied organotypically in vitro and add to evidence advocating obesity as a parameter to consider when identifying treatments for patients with ER‐positive breast cancer.—Morgan, M. M., Arendt, L. M., Alarid, E. T., Beebe, D. J., Johnson, B. P. Mammary adipose stromal cells derived from obese women reduce sensitivity to the aromatase inhibitor anastrazole in an organotypic breast model. FASEB J. 33, 8623–8633 (2019). www.fasebj.org