Abstract P5-06-08: Triple-negative breast cancer CAFs induce a metastatic phenotype in MCF-7 cells via the SDF-1/CXCR4 axis
Authors: Sharma Utsav , Sun Jun , Medina-Saenz Kelsie , Bare Susan , Miller Philip , Picon-Ruiz Manuel , Slingerland Joyce , El-Ashry Dorraya , Lippman Marc 
Published: March 2022

Abstract
Background: Metastatic disease is the foremost cause of breast cancer (BC) related mortality in women. One of the crucial challenges in reducing metastasis-related mortality is in identifying and understanding why certain BCs metastasize and recur. Although cancer cell-intrinsic factors are a key determinant in BC metastasis, host-intrinsic factors like the cells of the tumor microenvironment (TME), such as cancer-associated fibroblasts (CAFs) are what might be driving certain BCs to metastasize and recur. We recently showed that CAFs from the primary (TME) enter into circulation as cCAFs, form heterotypic clusters with tumor cells, and arrive at metastatic sites. This interaction between CAFs and tumor cells is crucial in furthering the metastatic cascade. However, the functional heterogeneity of the different CAF phenotypes and how that impacts BC metastasis is unknown. Stromal derived factor-1 (SDF-1/CXCL12) is an important chemokine that is known to be involved in promoting tumor cell invasion and metastasis. In this study, we examine the functional differences between CAF isolated from different molecular subtypes of BC. Furthermore, we elucidate the role of CAF secreted SDF-1 as being one of the mechanisms by which a subset of CAF cells permanently reprograms poorly-metastatic MCF-7 cells to augment EMT-driven genes and become metastatic in vivo. Methods: We used primary CAF cell lines derived from BCs of different molecular subtypes and examined their global gene expression profiles using RNAseq. We used NSG mice xenografted with MCF-7 BC cells and primary CAF cells to evaluate the contribution of two different CAF phenotypes in promoting BC progression and metastasis. We developed dissociated tumor cell lines from CAF co-injected MCF-7 xenografts to determine the molecular changes that CAFs impart to MCF-7 cells in vivo. Using limiting dilution tumor xenograft assays and gene expression profiles we examined the molecular pathways, BC stemness markers, and tumor-initiating capacity of the dissociated tumor cell lines. By long-term SDF-1 treatment of MCF-7 cells in vitro and using these cells in various RNASeq, in vitro, and in vivo assays we determined the role of SDF-1 in altering the phenotype of MCF-7 cells. Results: We found that CAFs from different molecular subtypes have a differential effect on tumor initiation, progression, and metastasis in xenograft assays. We also found that a subset of CAFs has the ability to make the poorly-metastatic MCF-7 cells metastatic in vivo. We also found that this subset of CAF cells has a higher expression of SDF-1 and the tumors formed with the co-injection of MCF-7 cells with this subset of CAF cells are enriched in cancer stem cell-like metastasis initiating cells. We also found that upon serial transplant, the tumors formed by CAF-reprogramed MCF-7 cells have a gene expression profile that shows enrichment for EMT-driven genes and these tumors are robustly metastatic. Furthermore, we found that the SDF-1/CXCR4 axis is one of the critical mechanisms by which this subset of CAF cells permanently reprograms the phenotype of the MCF-7 cells. Conclusions: CAFs are a highly heterogeneous population of cells in the breast TME. This study examines the contribution of the functional heterogeneity of the CAF cells in BC metastasis. We have found that a unique subset of CAF cells has the ability to reprogram a poorly metastatic BC cell to not only become metastatic but induce a permanent EMT-driven phenotypic shift in the BC cells. SDF-1 may be one of the mechanisms that drive this CAF-induced change and understanding the CAF functional landscape and its role in BC metastasis might be crucial to developing new therapeutic modalities to abrogate BC metastasis.
Citation Format: Utsav Sharma, Jun Sun, Kelsie Medina-Saenz, Susan Bare, Philip Miller, Manuel Picon-Ruiz, Joyce Slingerland, Dorraya El-Ashry, Marc Lippman. Triple-negative breast cancer CAFs induce a metastatic phenotype in MCF-7 cells via the SDF-1/CXCR4 axis [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 P5-06-08.