TAMI-06. TUMOR CELL-DERIVED CYTOKINE EXPRESSION CHANGES ASSOCIATED WITH BRAIN METASTASIS IN A SYNGENEIC MOUSE MODEL OF BREAST CANCER

Breast cancer is the most common malignancy in women in the United States, and brain metastases occur in almost a third of patients with metastatic dissemination. Immunoediting is a critical component of metastatic tumor cell elimination, and tumor clones that develop immune-escape mechanisms are associated with progression and metastatic dissemination. We hypothesized that breast cancer brain metastatic cells harbor immunomodulatory cytokine expression changes that promote an immunosuppressive environment to avoid immune cell-mediated elimination. To study this, a syngeneic mouse model of metastatic breast cancer was used. A brain metastatic line derived from the 4T1 breast cancer parental cell line was created by serially selecting brain metastatic populations of cells after intracardiac injection (4T1 BrM). A gene-expression analysis using an 800-gene cancer immunology-specific microarray panel was performed comparing the 4T1 parental and 4T1 BrM lines. 4T1 BrM cells demonstrate gene expression changes promoting immunosuppression including significant upregulation of IL18 and Lgals9 (Galectin-9) and downregulation of CD40, IL2rg, CCL2, and EOMES. When compared to 4T1 parental lines, the 4T1 BrM line demonstrated decreased expression of CCL2 and increased expression of GM-CSF on a cytokine array, corresponding to results obtained from gene expression analysis. These results suggest tumor-intrinsic cytokine expression changes that may mediate an immunosuppressive environment.