Abstract 1005: Ecological interactions in breast cancer: Cell cooperation within heterogeneous populations promotes growth and survival under drug pressure
Authors: Emond Rena , Griffiths Jason , Grolmusz Vince K. , Sousa Rachel , Chen Jinfeng , Castaneda Eric M. , Bild Andrea H. , Adler Frederick R. 
Published: June 2022

Abstract
The interplay of positive and negative interactions between drug sensitive and resistant cells determines the efficacy of treatment in heterogeneous cancer cell populations. While competition between different cell lineages within tumors has been considered in cancer evolution and progression, cooperative interactions receive far less study. We have developed in vitro ER+ breast cancer model systems to investigate cell-cell communication in heterogeneous cancer populations under selective drug pressure and probe for differences in growth, resistance, and interactions, such as cooperation, between cell types. Using cells resistant and sensitive to ribociclib (CDK 4/6 inhibitor), we have compared cell population growth in monoculture and coculture under different treatments. Furthermore, with the application of mathematical models, we have unraveled the contributions of proliferation rates, treatment effects, competition, and cooperation. Under ribociclib treatment, resistant cells confer an increased survival benefit to sensitive cells when cocultured together. Treatment-conditioned media taken from monocultured resistant cells and used to supplement sensitive cells reproduces this advantage, suggesting that secretion of some factor from resistant cells manifest the effect. Resistant cells may promote this growth by supplying estradiol as LC-MS/MS assays detected increased estradiol levels in coculture media compared with monoculture media under ribociclib pressure. This suggests estrogen-dependent sensitive cells benefit from the increase in local estradiol from resistant cells under treatment in coculture, resulting in cooperation. scRNA sequencing data between populations also revealed broad dysregulation of cell cycle pathways in resistant cells with cocultured sensitive cells shifting toward this resistant phenotype. Western blot detection in conjunction with scRNAseq data also supports an increased expression of estradiol conversion enzyme, HSD17β1, in resistant cells and increased expression of estradiol inactivating enzyme, HSD17β8, in sensitive cells shedding mechanistic insight into the estrogen-induced survival benefit provided by resistant cells. Proliferation of drug sensitive cells by resistant cells in co-culture is also enhanced through addition of estradiol, and blocked by small molecule inhibitors targeting the estrogen signaling pathway. These studies show that cooperation imparts drug resistance to normally sensitive cells and promotes survival, which highlights how interactions within heterogenous cell populations can shape the dynamics of growth and resistance. From a therapeutic standpoint, uncovering the mechanisms and consequences of cooperative cell-cell interactions may lead to strategic advancements for promoting drug response by targeting these influential interactions.
Citation Format: Rena Emond, Jason Griffiths, Vince K. Grolmusz, Rachel Sousa, Jinfeng Chen, Eric M. Castaneda, Andrea H. Bild, Frederick R. Adler. Ecological interactions in breast cancer: Cell cooperation within heterogeneous populations promotes growth and survival under drug pressure [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1005.