Abstract P5-12-06: Msc engulfing by triple negative breast cancer cells induces a hybrid cell population with senescence
Authors: Paolì Alessandro , Gonzalez Maria Elena , Mauro Loredana , Andò Sebastiano , Kleer Celina Graciela 
Published: March 2022

Abstract
Introduction: Triple negative breast cancer (TNBC) represents ~15% of all breast cancers. The TNBC subtype is characterized by the absence of estrogen and progesterone receptors and of ErbB2. Biologically, it is well recognized that TNBC has a more aggressive phenotype compared to other subtypes, offering limited treatment options and a worse clinical outcome. Tumor cells, through production of paracrine and endocrine molecules, can recruit mesenchymal stem/stromal cells (MSCs) from the bone marrow and adipose tissue to the tumor microenvironment. MSCs, reside mainly in the bone marrow and in adipose tissue. MSCs may exert a crucial role in tumor development and progression, by increasing stemness of tumor cells and promoting extracellular matrix remodeling, cell migration and invasion, neo-angiogenesis, and drug resistance. We have shown that breast cancer cells (BCCs) can engulf MSCs and induce an aggressive phenotype and increased metastasis. The mechanisms through which MSC engulfment occurs and the generated phenotypes need to be investigated. In this study, we tested the hypothesis that MSC engulfment by BCC cells may result in a hybrid tumor cell population with features of cell senescence, a well-recognized mechanism of tumor progression and recurrence. Methods: We employed MDA-MB-231 TNBC cells and patient-derived MSCs developed and validated in our lab. MDA-MB-231 were labeled with DsRED (231- DsRED) and MSCs were not labeled. Single culture of MDA-MB-231, MSCs, and MDA-MB-231/MSC co-cultures (1:1 ratio) were subjected to SA-β-galactosidase activity assay, flow cytometry, and immunofluorescence to detect and quantify the percentage of hybrid and senescence cells. SA-β-galactosidase activity assay was assessed using Senescence-associated β-galactosidase Staining Kit. For each sample of the single cultures and co-cultures, 10 randomly chosen fields were photographed using a camera-equipped bright field microscope (Olympus). Data was plotted as the percentage of cells with β-galactosidase activity (blue cells). We performed flow cytometry to detect β-galactosidase activity in MSCs and in DsRED-231 in single cultures or co-cultures. Immunofluorescence assay was performed to evaluate β-galactosidase activity in the same conditions previously described. Results: Our studies identified the emergence of a hybrid cell population in the co-cultures of MDA-MB-231 and MSCs cells. The hybrid population contained a significantly higher percentage of senenscent cells compared to 231 and MSCs (44%, 10.23%, and 14%, respectively, t test 0.001). These results were confirmed by immunofluorescence analysis for β-galactosidase, DsRed and DAPI in situ. Conclusion: These results highlight that MSCs engulfment by TNBC cells induces the formation of senescent hybrid breast cancer cells, which may explain their survival advantage. Studies are under way to investigate if the senescent phenotype of hybrid cells is influenced by EMT-MET states and its role in TNBC chemoresistance.
Citation Format: Alessandro Paolì, Maria Elena Gonzalez, Loredana Mauro, Sebastiano Andò, Celina Graciela Kleer. Msc engulfing by triple negative breast cancer cells induces a hybrid cell population with senescence [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P5-12-06.