Abstract PO3-24-09: May ESR1 mutant breast cancer cells influence fibroblast phenotype?

Abstract For almost 50 years, it has been postulated that carcinogenesis relies on the intrinsic genetic abnormalities of tumor cells, but in the last decades, it has been reported that their functional interactions with the tumor microenvironment (TME) might affect therapy response and contribute to the disease progression. Based on these observations, the aim of the present study was to investigate the functional interactions between one of the essential components of TME, the fibroblasts, and breast cancer (BC) cells, expressing mutations in the hormone-binding domain (HBD) of the gene encoding for the estrogen receptor alpha (ESR1). Thus, we employed estrogen receptor-positive MCF-7 BC cells CRISPR engineered to express the Y537S-HBD mutation. Y537S is the most commonly detected mutation harbored in HBD-ESR1 and is a major contributor to endocrine therapy resistance and poor clinical outcome in BC. We collected conditioned media (CM) from BC cells and fibroblasts isolated from primary human tissues (normal fibroblasts, NFs, and cancer-associated fibroblasts, CAFs) in order to assess in vitro co-culture systems that can mimic the complex in vivo TME. It was interesting to observe that CAFs displayed a significant increase in their proliferation and migration when exposed to CM of mutant BC cells with respect to the parental ones. These latter findings fit with the immunofluorescence analysis showing a more evident formation of actin stress fibers. However, proteomic analysis demonstrated, in the same circumstances, more significant changes in NFs than in CAFs. Among the up-regulated proteins revealed by NFs upon Y537S-CM exposure, most of them overlap the up-regulated proteins featuring the intrinsic phenotype of CAFs, mainly involved in the cellular ultrastructural organization (i.e. cytoskeleton, focal adhesion, vesicle, and organelle) as evidenced by Metacore functional analysis. On the other side, we demonstrated that mutant clones showed more aggressive behavior in terms of proliferation, growth, migration, and invasion, compared to the parental counterpart upon exposure to the CM-derived from NFs and CAFs. This led us to further investigate the intrinsic properties of the mutated clones through their genomic and proteomic profiles that evidenced, by using Metacore software, an enrichment of insulin-like growth factor 1 receptor (IGF1R) pathway. The relevance of the latter datum was confirmed by the higher content of the IGF-1 ligand found in the secretome of mutant cells. Thus, the short autocrine loop maintaining IGF1/IGF1R signaling activation in mutant clones might reasonably play an important role in mediating the autocrine and paracrine effects between mutant cells and fibroblasts. For instance, the pharmacological blockade of IGF1R signaling interfered with the reciprocal interactions between fibroblasts and BC cells that sustained tumor growth and progression as evidenced in both “in vitro” and “in vivo” experiments. In conclusion, our study addressed the IGF1R pathway as a potential druggable target helpful to disconnect mutant breast cancer cell-fibroblast crosstalk that potentiates breast tumor growth and progression. Citation Format: Luca Gelsomino, Amanda Caruso, Rocco Malivindi, Adel Elisabetta Leonetti, Emine Tasan, Salvatore Panza, Giuseppina Daniela Naimo, Ines Barone, Cinzia Giordano, Daniela Bonofiglio, Loredana Mauro, Guowei Gu, Suzanne Fuqua, Stefania Catalano, Sebastiano Andò. May ESR1 mutant breast cancer cells influence fibroblast phenotype? abstract. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO3-24-09.