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Abstract
The estrogen receptor (ER) is implicated in breast cancer progression and is a target of environmental chemicals and breast cancer therapies. Previous studies have shown that ER is regulated by multiple components of the mammary microenvironment, but most in vitro models only include the breast cancer cell. I hypothesized that the microenvironment regulates responses to chemicals that target the ER signaling pathway, and that chemical responses are missed when evaluated in traditional in vitro platforms. I developed the adverse outcome pathway (AOP) for ER+ breast cancer to identify readouts and culture conditions important to modeling ER-driven responses in breast cancer cells. Using the AOP as my guide, I optimized a microfluidic organotypic model of the breast consisting of a ductal structure lined with ER+ breast cancer cells surrounded by stromal cells in a collagen matrix. I used the organotypic model to show that mammary stromal cells modulate ER protein, and speed estradiol-induced hyperplasia by reducing apoptosis. I also demonstrated that mammary stromal cells indirectly regulate ER-driven responses by producing aromatase, the enzyme responsible for estrogen production. To assess if the organotypic model was more predictive than a traditional co-culture platform, I evaluated the aromatase inhibitor anastrazole when breast cancer cells were co-cultured with mammary adipose stromal cells derived from lean or obese women in a 2D co-culture or the organotypic co-culture platform. Breast cancer cells co-cultured with obese stromal cells in the organotypic model exhibited increased anastrazole resistance. In contrast, the 2D co-culture platform did not segregate the anastrazole responses of lean and obese patients. Next, I hypothesized that environmental chemicals differently affect breast cancer cells when cultured as a 2D monoculture, compared to when co-cultured with adipose stromal cells in 2D or in the organotypic model. MCF7 cells differed in response to tributyltin chloride when cultured alone compared to when co-cultured with adipose stromal cells. Altogether, these studies add to existing information that implicate the mammary microenvironment as a regulator of ER driven responses and suggest that in vitro platforms that consider only the breast cancer cell provide an incomplete picture of chemical responses.
