Effect of CSF1R inhibition in tumor macrophages on gene expression in metastatic epithelial cells

Metastasis is the primary cause of mortality in breast cancer patients. Tumor associated macrophages (TAMs) are active collaborators in mediating several steps of the tumor metastatic cascade, but the molecular details governing this collaboration remain ill-defined. Colony Stimulating Factor 1 (CSF1), a factor critical for macrophage differentiation and survival, functions to recruit TAMs to the primary tumor site, and anti-CSF1 therapies are in clinical trials.In this study, we tested the effect of inhibiting CSF1 signaling in macrophages on gene expression in metastatic tumor cells in mouse models of breast cancer metastasis. Tumor cells were sorted from lung metastases from control and CSF1R inhibitor treated mice. Several pro-tumor processes were significantly affected by CSF1R inhibitor treatment, including angiogenesis and tumor cell proliferation. In addition, a 29 gene signature derived from this data could retrospectively predict survival in a cohort of luminal B breast cancer patients. Collectievly, our results highlight the utility of employing CSF1R inhibitors for the treatment of metastatic breast cancer. GFP tagged MVT1 metastatic mammary tumor cells were injected intravenously into FVB/N mice. Mice were gavaged with the CSF1R inhibitor GW2580 or vehicle starting one week post injection. GFP tagged tumor cells were sorted from metastatic tumor bearing lungs 1 and 2 weeks post injection from 2 vehicle treated mice for each. These are denoted 1_week_WT and 2_week_WT respectively. GFP tagged tumor cells were simultaneously sorted from mice gavaged with GW2580. These samples are denoted 2_week_GW. RNA was extracted and gene expression profiling was performed using the Affymetrix Mouse Genome 430 2.0 Array platform.