Abstract 5077: Metastasis suppressors regulate the tumor microenvironment by blocking recruitment of pro-metastatic TAMs

Abstract

Abstract Triple-negative breast cancer (TNBC) patients have the highest risk of recurrence and metastasis. Because they cannot be treated with targeted therapies, and many do not respond to chemotherapy, they represent a clinically underserved group. While physiological inhibitors of metastasis (metastasis suppressors) play key roles in regulating tumor growth, invasion and metastasis, their role in regulating the tumor microenvironment and immune system is unknown. We hypothesized that the metastasis suppressor Raf Kinase Inhibitory Protein (RKIP) regulates stromal cells, which then affect tumor invasiveness. Using species-specific RNAseq we determined that expression of RKIP in tumors markedly reduces the number and metastatic potential of infiltrating TAMs. While TAMs isolated from TNBC xenografts drive in vitro invasion, RKIP+ derived TAMs did not drive invasion and had decreased secretion of pro-metastatic factors including SLPI, OPN, MMP-12, Galectin-3, VEGF-A, VEGF-D, TNFR2, and PGRN. We determined that RKIP regulates TAM recruitment by blocking HMGA2, which activates CCL5 expression. CCL5 rescued TAM infiltration as well as tumor intravasation. We additionally showed that factors decreased in RKIP-derived TAMs were restored in CCL5-derived TAMs. Finally, we demonstrated the TAM secreted factor PGRN is both necessary and sufficient for TAM driven invasiveness. To determine the clinical utility of these TAM genes we combined their expression with RKIP signaling in the tumor to create a signature that strikingly separates TNBC patients based on outcome. Our results demonstrate for the first time that metastasis suppressors can regulate the microenvironment, regulating invasion through TAMs. Our results also suggest TNBC patients with decreased RKIP activity and increased TAM infiltration may respond to therapies targeting CCL5 or PGRN. Citation Format: Daniel C. Rabe, Casey Frankenberger, Russell Bainer, Devipriya Sankarasharma, Kiran Chada, Thomas Krausz, Yoav Gilad, Lev Becker, Marsha R. Rosner. Metastasis suppressors regulate the tumor microenvironment by blocking recruitment of pro-metastatic TAMs. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5077. doi:10.1158/1538-7445.AM2015-5077