The majority of breast cancer related deaths are not due to the primary tumor, but rather to the dissemination of metastatic tumor cells from it to distant sites. Our lab has previously identified the tumor microenvironment of metastasis (TMEM) in mouse and human mammary tumors, sites where transendothelial migration, intravasation and dissemination occur. The constituent cells of TMEM are an endothelial cell, a perivascular TIE2-expressing macrophage (TEM) and an invasive Mena-over expressing tumor cell in direct contact. TMEM are present in human invasive breast tumors and the density of TMEM is positively associated with the risk of developing metastases.

Using invasive ductal carcinoma cells of the breast obtained from patients by fine needle aspiration (FNA), we demonstrated that intravasation-directed transendothelial migration (iTEM) of these cancer cells requires macrophages and, depending on clinical subtype, involves either paracrine (macrophage CSF1-R; tumor cell EGFR), or both paracrine and autocrine (tumor cell EGFR + CSF1-R) signaling. Compared to the total population of primary breast cancer cells assayed, cells capable of transendothelial migration expressed relatively high MenaINV and low Mena11a levels, independently of clinical subtype. MenaINV and Mena11a are functionally distinct isoforms of Mena, a key regulator of motility and invasion. Depletion of MenaINV using siRNA showed that MenaINV is required for efficient macrophage-dependent iTEM of tumor cells. Furthermore, relative MenaINV expression correlated with the density of TMEM, which were previously shown to correlate with risk of metastasis in patients. From these observations we have identified the signaling pathways involved in macrophage-dependent tumor cell iTEM. Two novel small molecule inhibitors, Rebastinib (Tie2 inhibitor) and Altiratinib (c-MET inhibitor), have been identified that show great promise in preventing key steps in iTEM.

Our data reveal targetable signaling events required for transendothelial migration of human breast cancer cells, and indicate that relative MenaINV levels and TMEM frequency are correlated prognostic markers of metastasis and therapeutic targets for most human breast cancers.

Citation Format: Jeanine Pignatelli, Joan Jones, Xiaoming Chen, Bryan Smith, Daniel Flynn, John Condeelis, Maja Oktay. Mechanisms of transendothelial migration by invasive breast carcinoma cells from patients. [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 4112. doi:10.1158/1538-7445.AM2015-4112