Abstract 1531: Reactive astrocytes promote the growth of cancer stem-like cells of metastatic breast tumor by activating Notch signaling in brain

Metastatic diseases are responsible for the majority of deaths in breast cancer patients, and brain is one of the most common metastatic sites. The metastatic tumor in the brain profoundly affects the cognitive and sensory functions as well as morbidity of patients, and the one year survival rate among these patients remains less than 20%. However, little is known about the pathogenesis of brain metastasis, and therefore, it is of paramount importance to elucidate the molecular mechanism of metastatic process in order to define a specific therapeutic target. Our analysis of existing microarray database indicate that interleukin-1α (IL-1α) is highly expressed in MDA-MB231BrM2a (231BrM) cell line which is capable of preferentially metastasizing to the brain. IL-1α is known to have an ability of “activating” astrocytes that are often found in the metastatic niche, and therefore, it is speculated that the reactive astrocytes can promote growth and invasion of metastasized cells in the brain. To explore this possibility, we examined the effect of IL-1α and the conditioned medium of 231BrM cells on rat primary astrocytes in vitro. Our results of qRT-PCR and Western blot analysis indicate that IL-1α and the conditioned medium significantly up-regulated the Notch ligand, JAG1, in astrocytes, and that this up-regulation was abrogated by the NF-κB inhibitor, PDTC. We also found that the interaction between CSCs and astrocytes significantly enhances the self-renewal ability of CSCs. To further examine the interaction of astrocytes and tumor cells in the brain, we intracardially injected 231BrM cells in nude mice, and tumor growth was monitored by Xenogen bioimager. After 4 weeks, metastatic tumor growth was observed at multiple sites of the brain, and the results of immunohistochemical analysis indicated that astrocytes adjacent to the metastatic lesions strongly expressed JAG1 and the reactive astrocyte marker, GFAP (Glial fibrillary acidic protein). Finally, we found that a BBB-permeable Notch inhibitor was able to significantly suppress metastatic growth of breast cancer in the brain in our animal model. These results represent a novel paradigm for the understanding of how metastatic breast CSCs re-establish their niche for their self-renewal in a totally different microenvironment, which opens a new avenue to identify a novel and specific target for the brain metastatic disease. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1531. doi:1538-7445.AM2012-1531