Abstract P4-04-15: Hierarchy of breast cancer associated fibroblasts communicate with cancer cells via microRNAs to drive breast cancer progression

Background: Increasing evidence has demonstrated that stromal cells play a pivotal role to promote breast cancer progression and metastasis. Breast cancer stroma is comprised mainly of Cancer Associated Fibroblasts (CAFs). Upon interaction with tumor cells, CAFs promote tumor progression by providing paracrine oncogenic signals mediated by activation of various pathways including developmental pathways, integrin signaling, and the MAPK pathway in tumor cells. CAFs have also been shown to promote the survival of CTCs and help them in metastasis at distant sites. Using breast cancer patient tumor datasets, we have previously identified a microRNA signature reflective of hyperactive MAPK signaling and that is significantly associated with reduced recurrence-free and overall survival. We have established 3 primary breast CAF lines, one from a Luminal A breast cancer, one from an ER-/Her2 amplified cancer, and one from a triple negative cancer, along with several primary tumor-derived dissociated tumor (DT) culture models that are tumorigenic in vivo and vary in metastatic ability. The CAFs express several hMAPK-microRNAs preferentially compared to the DTs. In addition to the paracrine interaction of stromal and tumor cells mediated by chemokines or hormones, miRNA cross talk between stromal and tumor cells can also occur. Results: To further investigate the connection between our miRNA signature and stroma, we analyzed the TCGA and METABRIC breast cancer datasets and found that the hMAPK-miRNA identifies tumors that with signficant stromal cell infiltrate. To investigate the role of specific expression of hMAPK-miRNAs in the CAFs, CM was isolated from CAFs from "aggressive" tumors, from the "indolent" tumor, and from normal human mammary fibroblasts (HMFs) and analyzed for exosome and microRNA secretion. CAFs from the aggressive tumors secrete more exosomes and more hMAPK-microRNAs into the CM than do HMFs or CAFs from the indolent tumor. Importantly, conditioned media (CM) from the "aggressive" CAFs activate MAPK and repress ER protein, mRNA and ER 3’UTR-reporter activity in ER+ MCF-7 breast cancer cells, while HMFs and "indolent" CAFs did not. Exosomes from the "aggressive" CAFs were responsible for the ER repression. To determine if the secreted miRNA differences exhibited by the CAFs could be seen in patients, serum from breast cancer patients with metastatic breast cancer and patients without metastases was analyzed for microRNA expression. Differentially expressed circulating hMAPK-miRNAs were identified in serum from metastatic breast cancer patients compared with patients without metastatses. Further analyses of the serum for CTCs and CAFs show that serum samples from metastatic patients had a significantly higher number of CTCs with CAFs compared to serum from patients without metastases. Conclusions: Collectively these data suggest that different CAF populations have distinct abilities to influence the phenotype and behavior of associated cancer cells and that CAF secreted hMAPK-miRNAs may play important roles in breast cancer progression. They further suggest that these CAF secreted miRNAs can be found in patient serum along with circulating CAFs. Citation Format: Sanket H Shah, Phil Miller, Zheng Ao, Emilio Issa, Katherine Drews Elger, Ram Datar, Marc Lippman, Dorraya El-Ashry. Hierarchy of breast cancer associated fibroblasts communicate with cancer cells via microRNAs to drive breast cancer progression [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P4-04-15.