Abstract A28: Systematic identification of astrocyte-tumor crosstalk regulating brain metastatic tumors
Authors: Liu Haowen Nikola , Sheng Jianting , Zhao Hong , Wong Stephen 
Published: June 2020

Abstract
Twenty-four to 45% of all cancer patients develop brain metastasis (BM) with the majority from lung, breast, and melanoma primary cancers, but few patients with BM live longer than a year. Therefore, it is of paramount importance to obtain a deep understanding of mechanisms that promote BM growth, which could be specifically leveraged to develop novel therapeutic strategies. Astrocytes, the most common type of glial cells comprising ~50% of all human brain cells, are a well-characterized perilesional component of BM. Recent discoveries, including ours, provide compelling evidence that molecular crosstalk between astrocytes and cancer cells is integral to BM development. Although seminal findings indicate that interactions with astrocytes occur at both early and late stages of tumor colonization process, our understanding of the reciprocal astrocyte-cancer cell crosstalk is limited. In our studies, we employed the Cell-Cell Communication Explorer (CCCExplorer), a unique computational biology modeling tool, to systematically identify astrocyte-tumor crosstalk signaling in regulating BM. Syngeneic mouse models for BM from breast and lung cancer were injected with mouse cell lines 4T1 (breast cancer) into Balb/c mice and 393N1 (lung cancer) into C57BL/6 mice through internal carotid artery. Whole-brain astrocytes and tumor cells were purified at day 3 post tumor injection (early astrocyte activation) and were profiled by RNA-seq. Even at early stages of BM, transcriptional responses of astrocytes are dramatic, and different tumor origins can induce similar molecular responses in astrocytes. The RNA-seq data were input into the CCCExplorer software to identify four types of cell-cell interaction signaling, i.e., astrocyte→tumor paracrine signaling, astrocyte↔astrocyte autocrine signaling, tumor→astrocyte paracrine signaling, and tumor↔tumor autocrine signaling. For example, our preliminary results show that 30 receptors, 8 transcription factors, and 9 signaling pathways within the 4T1 breast tumor cells were activated by 27 potential ligands secreted by astrocytes. Pathways known to contribute to brain metastatic tumor growth, including TGF-β, PI3K-AKT, gap junction, and MAPK signaling, were reliably identified. Importantly, our unique approach was also able to discern potentially novel inducers of these pathways, such as PCDH7-EGFR, IHNBB-ACVR2A, IL6-IL6R, and CCL5-CCR5. Using in vitro astrocyte and tumor cell coculture assays and astrocyte-specific gene knockout using lenti-CRIPRv2, we demonstrated the significance of the astrocyte→tumor IL6-IL6R, CCL5-CCR5, and PCDH7-EGFR paracrine signaling in early BM. Given that more complicated paracrine signaling networks may evolve during different stages of BM development, we will continue to use CCCExplorer to identify both anti- and prometastatic stimuli from astrocytes to cancer cells and evaluate potential therapeutic targets through in vitro assays and in vivo animal studies.
Citation Format: Haowen Nikola Liu, Jianting Sheng, Hong Zhao, Stephen Wong. Systematic identification of astrocyte-tumor crosstalk regulating brain metastatic tumors [abstract]. In: Proceedings of the AACR Special Conference on the Evolving Landscape of Cancer Modeling; 2020 Mar 2-5; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2020;80(11 Suppl):Abstract nr A28.