Abstract 37: Pulmonary pre-metastatic modifications induced by breast cancer

Breast cancer can be highly curable at early stages, while the survival rate plummets with the occurrence of metastasis. Thus, studies of molecular mechanisms that allow cancer cells to leave the primary tumor and ultimately establish colonies at distant sites are of crucial importance. First proposed by Stephen Paget in 1889, the “seed and soil” hypothesis suggests that the secondary organ microenvironment undergoes constant modification induced by the primary tumor through circulating chemokines. This leads to the migration of activated bone marrow derived cells to secondary organs, increased matrix metalloproteases (MMPs), and extracellular matrix (ECM) modifications in the secondary organ, collectively termed the pre-metastatic niche, which provides desirable docking sites for cancer cells. Our previous studies have shown persistent changes in the collagenous stroma and proteoglycans in pre-metastatic lungs of mice growing metastatic breast tumors, whose extent directly correlated with the malignancy of the primary tumor [1]. Elevated proteolytic MMP activity was also detected in these pre-metastatic lungs [2]. Based on these findings, we have continued our pre-metastatic niche studies by building an appropriate cell culture model, which consists of lung fibroblasts that were exposed to cell culture media conditioned by differentially malignant human breast epithelial cells. Cell lines used for fibroblast conditioning were nonmalignant MCF-12A breast epithelial cells (control), non-metastatic MCF-7 breast cancer cells, and highly metastatic, triple-negative MDA-MB-231 breast cancer cells. We focused our studies on ECM- and MMP-related changes, which we analyzed using qRT-PCR and immunoblotting. qRT-PCR analysis revealed that metastatic MDA-MB-231 cells induced an increase in the ECM protein Col14A1 as well as MMP-2 and MMP-14 in lung fibroblast as compared to induction by MCF-12A control. Immunoblotting analyses of lung fibroblasts showed that breast cancer cells induced increases in MMP expression in lung fibroblasts. Even higher MMP levels in fibroblasts were induced by metastatic MDA-MB-231 cells as compared to non-metastatic MCF-7 cells. Breast cancer cells also induced decreased expression levels of secreted MMPs in lung fibroblasts, most likely due to an enhanced release of these MMPs. This decrease was most significantly induced by the metastatic cell line. In conclusion, we have observed elevated levels in ECM molecules and MMPs in lung fibroblasts upon exposure of conditioned media from breast cancer cells. Our findings point towards an important role of lung fibroblasts in the evolution of the pre-metastatic niche in modifying the ECM, and their ability to directly respond to factors released from primary breast cancer cells with which they are not in direct contact. [1] Paidi SK et al. Cancer Res. 2017; 77:247-56. [2] Rizwan et al. Npj Breast Cancer 2015; 1: 15017. Citation Format: Ruoqing Cai, Caitlin M. Tressler, Menglin Cheng, Kanchan Sonkar, Santosh K. Paidi, Ishan Barman, Kristine Glunde. Pulmonary pre-metastatic modifications induced by breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 37.