Abstract B08: Astrocytes in the microenvironment influence breast cancer cell metastasis

Microenvironment plays a critical role in the metastasis and progression of tumor cells. Our laboratory has recently identified that cells in the brain microenvironment namely the astrocytes, play a critical role in breast cancer cell metastasis in vivo and in vitro. Previous data from our lab provide evidence that the both adult and neonatal rat astrocyte secretome influences the local matrix, thereby facilitating extravasation of cancer cells into brain parenchyma and other distant sites. In that study, we cultured and passaged breast cancer cells in the astrocyte culture media and the resultant astrocyte-conditioned breast cancer cells (ABCs) were injected via the intra-cardiac route into CB17/Severe Combined Immunodeficiency (SCID) mice. Now, we have injected the ABCs into the mammary fat pad and intravenous route, and find that irrespective of the route, these cells are highly metastatic in vivo with a few cells reaching the brain as well. ABCs also showed marked change in phenotype and became increasingly invasive, a phenotype that intriguingly was reversed when the ABCs were cultured in normal tumor media (NBCs) over subsequent passages. Based on this data, we hypothesized that solid tumors with propensity for brain metastasis respond to molecules secreted by astrocytes that induce genomic changes in cancer cells that creates a transitional state in these cells to facilitate metastasis. To investigate this hypothesis, the purpose of this study was to determine the genomic changes in ABCs, and in turn the underlying mechanisms governing ABCs metastasis. We performed microarray analysis on ABCs and NBCs and identified significant up regulation of pro-metastasis genes in ABCs with a concomitant down regulation of the same genes in NBCs thereby providing excellent correlation between genotype and phenotype. One of the genes Angiopoietin-like 4 (ANGPTL4) has been functionally implicated in breast cancer cell invasion in vitro, and knockdown of ANGPTL4 decreased migration, invasion and proliferation, as well as increased apoptosis of these cells. On a phenotypic level, we identified two different cellular morphologies in ABCs, one a small spindle like and a second large irregular cell, and FACS sorting of these two cell populations revealed that the invasive phenotype is associated with the larger irregular cell type. We also have evidence now that human astrocytes differentiated from fetal cortex also induce breast cancer cell invasion in vitro, and the ABCs invasion and metastasis phenomenon is broadly observed in other cancers including lung cancer albeit the genomic changes are not conserved suggesting a level of specificity to these changes. Collectively, these findings suggest a metastasis plan induced by astrocytes on solid tumors with a propensity to make these cells highly tumorigenic and metastatic thus providing novel avenues for intervention. Citation Format: Ling Wang, Michael Lepley, Allison Ebert, David R. Harder, Ramani Ramchandran. Astrocytes in the microenvironment influence breast cancer cell metastasis. [abstract]. In: Proceedings of the AACR Special Conference: Advances in Brain Cancer Research; May 27-30, 2015; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2015;75(23 Suppl):Abstract nr B08.