GRM1 to induce M-CSF and CCL2 expression to lead to an upregulation of M2 macrophages in melanoma

• Published in: Journal of clinical oncology Vol. 35; no. 7_suppl; p. 122
• Main Authors: Li, Jiadong, Wen, Yu, Jeong, Byeong-Seon, Shah, Raj, Isola, Allison, Silk, Ann W., Chen, Suzie, Goydos, James Steven
• Format: Journal Article
• Language: English
• Published: 01-03-2017
• ISSN: 0732-183X; 1527-7755
• DOI: 10.1200/JCO.2017.35.7_suppl.122

Abstract only
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Background: GRM1 transgenic mice in an immune competent background (C57BL6) develope melanoma with 100% penetrance (TG-3 mice). Ectopic expression of GRM1 in immortalized mouse melanocytes (MelanA) produce cells (MASS20) that are tumorigenic in both SCID and immune competent C57BL6 mice. We have examined the downstream events of GRM1 signaling that allow transformed cells to evade immune destruction. Methods: Cytokine antibody arrays and Western blot were used to examine differences in cytokine expression between MASS20 cells and parental controls. Next, we cultured C57BL6 bone marrow cells in MASS20 conditioned medium for 24 and 48 hours and determined resultant M2 macrophage levels. Finally, we used oral weekly liposome clodronate (LC) treatment to deplete macrophages in murine models to determine the effect on tumor growth. Results: MASS20 cells produce higher levels of M-CSF and CCL2 as compared with control cells. These two cytokines recruit and induce the polarization of tumor associated macrophages (TAM) to increase the M2 fraction resulting in accelerated tumor progression. Culturing C57BL6 bone marrow cells in MASS20 conditioned medium increased expression of the M2 macrophage marker arginase1 at both time points. Weekly oral LC treatment to C57BL6 mice greatly inhibited the growth of MASS20 tumors as compared to growth in control animals. Single-cell suspensions of spleen and tumor cells from these animals were subjected to flow cytometry and showed that LC treatment depleted macrophages by 90% in the spleen, and increased the percentage of cd8+T and cd335+ NK cells in tumors from treated mice as compared to controls. Finally, we treated TG-3 transgenic mice with weekly oral LC and found that treated animals still developed tumors, but progression was greatly slowed, and survival greatly prolonged, compared to untreated animals. Within 1 week of stopping LC in the treated animals there was rapid growth of the tumors. These findings suggest a link between GRM1-signal transduction and TAM-induced suppression of tumor-immunity in melanoma. Conclusions: We conclude that GRM1-induced suppression of tumor immunity occurs through induction of M2 macrophages in the tumor microenvironment.