Abstract 5062: The role of fibroblast MMP2 in breast to lung metastasis.
Authors: Bates Andreia , Fingleton Barbara 
Published: August 2014

Breast cancer is the second most common fatal malignancy of women in the United States. Matrix metalloproteinases (MMPs) have been implicated in virtually all stages of breast cancer. MMP2 was identified as part of a subset of genes upregulated in breast to lung metastases (Minn). These studies focused on epithelial derived MMP2, however, a host of other sources have emphasized the importance of stromal cell derived MMP2 in breast cancer growth. We have directed our studies to investigate the role of MMP2 from stromal cells in tumor outgrowth at the secondary site. We hypothesize that stromal MMP2 at the secondary site contributes to metastatic progression. Spontaneous metastasis models have shown that MMP2−/− mice demonstrate reduced lung metastatic lesions compared to wildtype (WT) animals. In an experimental metastasis model using luciferase labeled tumor cells, we have found that MMP2−/− mice have a significant reduction in lung tumor outgrowth compared to WT animals as measured by bioluminescent imaging. The reduction in growth only manifests approximately seven days post inoculation, suggesting that decreased tumor growth is due to defects in tumor outgrowth and not seeding ability or survival. Immunohistochemical staining of Ki67 revealed that MMP2 selectively facilitates the proliferation of tumor cells in the lung. MMP2 in our model is primarily localized to stromal cells surrounding lung tumor nodules. We determined by dual labeling for MMP2 and vimentin or αSMA positive areas that fibroblasts were the major cellular source of MMP2. Hematopoietic cells (CD45 positive areas) and endothelial cells (CD31 positive areas) showed minimal expression of MMP2 and were ruled out as a significant source. To determine if there is a direct role of MMP2 in tumor cell proliferation, we took an in vitro approach and analyzed tumor cell proliferation after treatment with recombinant protein or fibroblast conditioned media. There was no difference in two-dimensional (2D) proliferation after either treatment, suggesting that MMP2 plays an indirect role in the proliferation of tumor cells. In our present studies, we investigate the role of MMP2 in fibroblasts and the effect this has on the outgrowth of tumor cells in the lung. A knock down approach was used to assess the impact of MMP2 on 2D fibroblast proliferation by cell counting. Our results demonstrated no difference in 2D proliferation between control and MMP2 knockdown fibroblasts. We have developed a 3D co-culture system to evaluate the role of MMP2 in fibroblast promotion of tumor spheroid proliferation. Our present data suggests that MMP2 mediated recruitment and functionality of tumor associated fibroblasts promotes tumor outgrowth via proliferation. Results from these experiments will lead to new insights on the role of MMP2 in fibroblasts and how these cells then enable a permissive environment for tumor outgrowth at secondary sites.

Minn, AJ et al. Nature. 2005 Jul 28;436(7050):518-24

Citation Format: Andreia Bates, Barbara Fingleton. The role of fibroblast MMP2 in breast to lung metastasis. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5062. doi:10.1158/1538-7445.AM2013-5062