Abstract 2250: COX2-MMP1 pathway promotes brain metastasis by tampering with blood-brain barrier and supporting tumor initiating cells in the brain microenvironment

Brain is one of the major sites of metastasis in breast cancer; however, the pathological mechanism of brain metastasis is yet poorly understood. Metastatic tumor cells must first breach the blood-brain barrier (BBB) which acts as a selective interface between the peripheral circulation and the central nervous system. We analyzed clinical significance of 23 metalloproteinases on brain metastasis-free survival of breast cancer patients followed by verification in brain metastatic cell lines and found that only MMP1 among all metalloproteinses was significantly correlated with brain metastasis. We then performed the transmigration assay to study the role of MMP1 in transmigrating ability of breast cancer cells across the blood-brain barrier. This assay simulates the BBB structure as we seeded the brain endothelial cells on the luminal side of a polyester membrane with 3.0μm pore size inside a 24-well cell culture insert and we seeded the astrocytes on the abluminal side. We have shown that MMP1 was highly expressed in brain metastatic cells and it was positively correlated to the transmigrating ability of breast cancer cells. By Western blot and immunocytochemistry analyses, we found that MMP1 was capable of degrading Occludin and Claudin but not Zo-1 that are three key components of blood brain barrier. These results indicated that Occludin and Claudin are the targets of MMP1, and degradation of these proteins contributes to the increased permeability of BBB. Importantly, knockdown of MMP1 in brain metastatic cells significantly blocked their ability of brain metastasis in vitro as well as in our animal model, while ectopic expression of MMP1 significantly increased the brain metastatic ability of the cells. We also found that Cox2 was highly up-regulated in brain metastatic cells and that prostaglandin was directly able to promote the expression of MMP1 at both transcriptional and translational levels leading to augmentation of brain metastasis. Furthermore, we found that Cox2 and prostaglandin were able to activate astrocytes to release CCL7, which in turn promoted self-renewal of tumor initiating cells in the brain while knockdown of Cox2 as well as treatment with Cox2 inhibitor significantly reduced the brain metastatic ability of tumor cells both in vitro and in vivo. Our results warrant further investigation on the Cox2-PGE-MMP1 pathway as a novel therapeutic target for brain metastasis despite the past failure of MMP inhibitors for the treatment of metastatic disease, possibly by developing more specific drug to MMP1 and stratifying the target patient population. Citation Format: Kerui Wu, Koji Fukuda, Fei Xing, Yingyu Zhang, Sambad Sharma, Yin Liu, Kounosuke Watabe. COX2-MMP1 pathway promotes brain metastasis by tampering with blood-brain barrier and supporting tumor initiating cells in the brain microenvironment. [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 2250. doi:10.1158/1538-7445.AM2015-2250