Abstract B19: Role of cell-cell communication in endocrine therapy-resistant breast cancer

Abstract Endocrine therapy is the mainstay for the treatment of estrogen-receptor positive (ER+) breast cancer. However, frequent emergence of endocrine resistance is a major clinical challenge. Cell-cell cooperation in the tumor microenvironment plays a vital role in acquiring resistance, but its role is poorly understood. We studied the interactions among endocrine-resistant (R) and -sensitive (S) breast cancer cells in the presence and absence of ER-targeted endocrine therapy. We measured changes in admixed cell population remodeling by dual fluorescent labeling of LCC1 (S) with eGFP (green fluorescent protein) and their derived resistant variant (selected against the antiestrogen fulvestrant) LCC9 (R) with mCherry (red fluorescent protein), respectively. Thus, unlike most prior studies, these are genetically related cells, rather than ER+ and ER- cell lines obtained from different patients. Our results revealed that “S”cells (LCC1) acquired the phenotype of “R” cells when cultured in a mixed population. A ratio of 5:1 of S:R cells in mixed population was sufficient to confer resistance to fulvestrant to the S cells within a six-day period. Furthermore, we show that acquirement of this resistant phenotype for the S cells was partially blocked by inhibition of either gap junctions or exosome secretion, suggesting a role of cell-cell contact as well as extracellular vesicles. Global proteomic analysis of pure and admixed S and R cell populations showed that R and S can alter key molecular features of each other when present in mixed cell populations. We used a Bayesian approach to fit single culture cell populations to infer density-dependent growth parameters (growth rate, carrying capacity) and a generalized Lotka-Volterra model to understand how S and R coculture populations may be depressing or supporting growth of the other. Our results identify a net mutualistic interaction between the susceptible and resistant cancer strains, demonstrating that there are ecological dynamics to cancer resistance. In some tumors, ecological dynamics may be more mechanistically relevant than simple Darwinian-based clonal selection in driving tumor heterogeneity and determining response to treatment. Our study strongly indicates that different tumor cell types that may exist in tumors are able to influence each other, which leads to alteration of phenotype. Note: This abstract was not presented at the conference. Citation Format: Surojeet Sengupta, Rong Hu, Zachary Susswein, Adeola Fagunloye, Shweta Bansal, Robert Clarke. Role of cell-cell communication in endocrine therapy-resistant breast cancer [abstract]. In: Proceedings of the AACR Special Conference on the Evolving Landscape of Cancer Modeling; 2020 Mar 2-5; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2020;80(11 Suppl):Abstract nr B19.