Abstract GS6-06: Identifying metastatic drivers in patient-derived xenograft models of triple negative breast cancer

Metastases are responsible for the vast majority of deaths due to breast cancer. Triple negative breast cancer (TNBC) is an aggressive subtype of breast cancer characterized by high rates of metastasis and poor prognosis. We are employing patient derived xenograft (PDX) models of TNBC to identify drivers of metastasis. Tumor samples are obtained from the breast tumors of patients with TNBC and engrafted immediately into the humanized mammary fat pads of immune compromised mice. Lentiviral transduction was employed to express bioluminescent and fluorescent markers in two independent PDX models of TNBC. Using these models, we demonstrated that human breast tumors are capable of completing all stages of the metastatic cascade in mice, and metastatic lesions are observed in organs normally found in patients with metastatic breast cancer including lung, liver, bone, brain, and lymph nodes. Dynamic and reversible epithelial to mesenchymal transition (EMT) was observed as tumors metastasized to lung and were re-passaged to recipient mouse mammary glands. Lung metastases were isolated using bioluminescence imaging and lung metastasis gene expression signatures were generated. Metastasis signatures from two independent PDX models were compared to identify genes that were commonly de-regulated in lung metastases relative to corresponding mammary tumors. Comprehensive gain-of-function screens were then conducted in vivo to identify functional drivers of TNBC metastasis. Carcinoembryonic antigen-related cell adhesion molecule 5 (CEACAM5) was identified as a metastatic driver in this screen. CEACAM5 mRNA and protein levels were elevated in lung metastases relative to corresponding mammary gland tumors in mice. In addition, we demonstrated that CEACAM5 expression was upregulated in the lung metastases of breast cancer patients, and its expression inversely correlated with patient survival. Our data indicate that the metastatic function of CEACAM5 is to promote growth of breast tumors in the lung by inducing MET (mesenchymal to epithelial transition).

Citation Format: Powell E, Shao J, Picon HM, Ge Z, Echeverria GV, Peoples M, Bristow C, Cai S, Tu Y, McCoy AM, Piwnica-Worms D, Draetta G, Edwards JR, Moulder SL, Symmans WF, Heffernan TP, Liang H, Piwnica-Worms H. Identifying metastatic drivers in patient-derived xenograft models of triple negative breast cancer [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr GS6-06.