(68e) In Vitro 3D Modeling of ER+ Breast Cancer and Primary Adipose Derived Stem Cell Demonstrates Alterations in Endocrine Therapy Response Due to Patient Characteristics.

Endocrine therapy (ET) has been shown to be an effective treatment against estrogen receptor positive (ER+) breast cancer (BC); however, ~40% of diagnosed patients present de novo or acquired resistance to this therapy. While the precise mechanism of resistance is unknown, it may be attributed to the complexity of the tumor microenvironment (TME), a heterogeneous system in which not only cancer cells can be found but also stromal cells and immune cells. One cell type of interest in the TME is adipose-derived stem cells (ASCs), an adipocyte precursor and major stem cell of the breast, which have been demonstrated to have the ability to repair, maintain, and enhance surrounding tissue via paracrine signaling which has the potential to affect cancer drug efficacy. It is strongly believed that the genomic and non-genomic crosstalk between the ER and growth factors (GF) plays a crucial feature in this path as well as the activation/overexpression of growth factor receptors (GFR). Moreover, it is well documented that cancer can develop intratumor and intertumor heterogeneity which causes diverse single cell behavior inside the same tumor and across different patients. There are several studies on the patient response to different therapies that show diverse behavior under the same therapy conditions in patients with different attributes including age and BMI. To date, most of the in vitro studies addressing patient response rely on 2D approaches which do not properly replicate the behavior and characteristics of a real tumor. Because of this, spheroids have become a promising approach since they are able to mimic tumor pathophysiology and tumor structure. In this study ER⁺ cancer cells and ASCs were co-culture in a 3D environment by implementing a microfluidic droplet trapping array coupled with a degradable thiol-acrylate (TA) hydrogel scaffold capable of performing high-throughput single cell analysis coupled with data clustering as a tool to elucidate distinct subpopulations based on enhanced or diminished proliferation after being exposed to endocrine therapy. It was found that ASCs co-cultured with two ER+ breast cancer cell lines resulted in enhanced basal proliferation and induced some degree of resistance when they were exposed to the established endocrine therapy Fulvestrant. Moreover, the single spheroid response was found to depend on patient attributes in 3D co-cultured spheroids with ASCs from obese or older patients exhibiting enhanced resistance to Fulvestrant when compared to lean or younger patients. Results from this study confirm that ASCs are a major driving force for endocrine resistance in the breast TME and that specific patient attributes are a factor of de novo or developed endocrine resistance.