Abstract 1043: CSF-1R inhibitor prevented pre-metastatic lung niches in metastatic mammary tumor
Authors: Borin Thaiz F. , Angara Kartik , Rashid Mohammad , Shankar Adarsh , Iskander Asm , Ara Roxan , Jain Meenu , Achyut Bhagelu R. , Arbab Ali S. 
Published: July 2017

Abstract
Exosomes are small vesicle cellular products originating from the endocytic pathway abundantly secreted by tumor cells. These exosomes have the ability to alter their immediate microenvironment (ME) through cell-cell interaction by fusion with plasma membrane and subsequent endocytosis or release of their cargo. Exosomes are critical modulators of pre-metastatic niche creation by increasing the recruitment of inflammatory cells. In breast cancer, tumor-derived exosomes recruit myeloid derived suppressor cells in the creation of an immunosuppressive pro-tumorigenic lung niches. Colony stimulating factor 1-receptor (CSF1R), which is a key regulator of myeloid cell proliferation, survival, and differentiation can be blocked by a selective inhibitor GW2580. Overexpression of CSF-1 has been implicated in the creation of increased number of metastatic niches in numerous cancers. In our study, we have demonstrated that the exosomes secreted under hypoxic conditions can initiate early pre-metastatic niche creation in lungs in a metastatic breast cancer model compared to normoxia-secreted exosomes. Exosomes were injected intravenously into Balb/c female mice three days after the implantation of 4T1 breast tumor and continued for a week with injections on alternated days. The animals were pre-treated with GW2580 the day before tumor implantation and continued for a week concomitantly with exosomes on alternate days. Lungs, bone marrow, spleen and brain tissues were collected and analyzed by flow cytometer to detect myeloid and angiogenic cells populations. GW2580 was able to prevent myeloid cell infiltration in lungs and bone marrow. Further, we observed significant increase in anti-tumorigenic M1-macrophage population in the lungs of exosome treated animals pre-treated with GW2580. However, these findings were not observed in the bone marrows of the same group. Vasculogenic leukocyte and angiogenic myeloid cell populations were significantly decreased in the lung of exosome treated animals pre-treated with GW2580. A similar decrease in these populations of cells was not seen in the lungs of animals pre-treated with GW2580 only. These surprising results have led us to hypothesize that GW2580 treatment can prevent the effects of exosomes, which causes infiltration of myeloid cells in the lung to create metastatic niche. These observations indicate a role of CSF1R inhibitor in preventing the distant metastatic niche formation.
Citation Format: Thaiz F. Borin, Kartik Angara, Mohammad Rashid, Adarsh Shankar, Asm Iskander, Roxan Ara, Meenu Jain, Bhagelu R. Achyut, Ali S. Arbab. CSF-1R inhibitor prevented pre-metastatic lung niches in metastatic mammary tumor [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1043. doi:10.1158/1538-7445.AM2017-1043