Abstract 3023: Dissecting mechanisms of breast cancer metastasis through patient-derived circulating tumor cells
Authors: Klotz Remi , Thomas Amal , Restrepo-Vassalli Sara , Iriondo Oihana , Han Jane , Teng Teng , MacKay Matthew , Wang Alan , Izadian Negeen , Moon Byoung-San , Bardia Aditya , Hicks James , Smith Andrew , Yu Min 
Published: August 2018

Abstract
During tumor progression, tumor cells invade the primary tumor microenvironment and intravasate into blood vessels, where they are referred to as circulating tumor cells (CTCs). These CTCs disseminate to other organs, and a subset of these cells will form metastasis. The growing interest for CTCs is confronted with the difficulty associated with their isolation and scarcity of material. To address this challenge, our established CTC lines from breast cancer patients offered a unique opportunity to investigate the signal pathways involved in the metastatic cascade. We assessed the metastatic potential of breast cancer patient-derived CTC lines by injecting them directly into the left ventricle of the heart in NSG mice. CTC lines are capable of generating metastases in most organs that are listed as common sites of metastases from breast cancer, such as the brain, lungs, bones and ovaries. Two patient-derived CTC lines harbored a high metastatic potential (over 80% of mice had metastases after 3 months) with generation of simultaneous metastases in the bones, lungs and ovaries. These mice remained brain-metastases free for up to 8 months. However, in 2 patient-derived CTC lines we demonstrated the brain as the preferential site of metastasis despite their low metastatic potential. Interestingly, in our mouse model, CTC lines recapitulated human cancer metastatic progression, as shown by the clinical data collected from patients where CTC lines were generated. We further investigated genetic and epigenetic determinants that regulate the organotropism of CTCs. To address this we isolated metastatic variants with a preferential tropism for the brain, lungs and bones. Investigating the gene expression signatures of metastatic variants lead us to identify the semaphorin 4D as a possible regulator of the brain metastasis. High SEMA4D expression at the primary site correlated with decreased brain metastasis-free survival in the breast cancer patients. Amplification of the chromosome 9 where the SEMA4D gene resides was also found in CTC-derived brain metastases. The SEMA4D overexpression promoted the ability of CTCs to transmigrate the blood-brain-barrier in vitro. We simultaneously investigated expression changes in stromal cells in organ-specific metastases, and among the pathways with the highest enrichment scores we found TNF and IFN signaling in the brain metastatic microenvironment. Next we used ATAC-seq to assay chromatin accessibility and identified potential regulatory factors mediating the brain metastasis formation. These data provides the evidence for the promising role of CTCs as an early prognostic factor for metastasis. Additionally, we expect to develop novel organ tropism associated markers, which can be considered for potential therapeutic targets in breast cancer.
Citation Format: Remi Klotz, Amal Thomas, Sara Restrepo-Vassalli, Oihana Iriondo, Jane Han, Teng Teng, Matthew MacKay, Alan Wang, Negeen Izadian, Byoung-San Moon, Aditya Bardia, James Hicks, Andrew Smith, Min Yu. Dissecting mechanisms of breast cancer metastasis through patient-derived circulating tumor cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3023.