Abstract 516: Metformin inhibits monocyte differentiation to tumor associated macrophage (TAM) and may restore anti-tumor immunity

Abstract

Abstract Background: Tumor-associated macrophages (TAMs) play pivotal roles to regulate tumor cell behavior in tumor microenvironment and a high density of TAMs is associated with poor prognosis in various cancers. Recent studies have demonstrated that metformin, the first-line medication for the treatment of type 2 diabetes, have suppressive effects on tumor growth. Here, in this study, we investigated the effect of metformin on monocyte differentiation to TAMs. Methods: Peripheral blood mononuclear cells (PBMCs) were obtained from healthy volunteers and CD14+ peripheral blood monocytes(PBMo) were purified by positive selection using the magnetic cell separation system. The PBMo were co-cultured with Panc-1, a human pancreas cancer cell, with metformin (10μM~10mM) using double chamber inserts of 0.4-μm sized pores at 37°C in 5% CO2 conditions for 5 days. Separately, PBMo were cultured with M-CSF for 5 days and then with IL-10 (20ng/ml)+TGF-β(20ng/ml) for addition 2 days with or without metformin. The differentiation to TAM were evaluated by the expression of M1/M2 markers as well as PD-L1/L2 by flowcytometry. The macrophages were co-cultured with autologous T cells stimulated with anti-CD3 and anti-CD3 and anti-CD28 microbeads and the effect on T cell proliferation was evaluated with CFSE dilution assay. Results: PBMo co-cultured with Panc-1 showed significantly enhanced expression of CD163, CD206, as well as markedly increased side scatter, suggesting the differentiation to M2-type macrophages. The macrophage also highly expressed PD-L1 and strongly inhibited the proliferation of autologous T cells. However, the expression of these antigens and inhibition of T cell growth were significantly suppressed by the presence of metformin with dose dependent manner. Metformin was effective at 100μM and almost nullified the effects of Panc-1 at 1mM. Metformin did not affect the antigen expression pattern during the treatment by M-CSF, but did downregulate the expression of CD206 and PD-L1 if added together with IL-10 +TGF-β. Conclusion: During the co-culture with tumor cells, metformin suppresses the monocyte differentiation to TAM at relatively late stage. Metformin can restore T cell mediated-tumor immunity in tumor microenvironment, at least partly, through the effects on TAM, that may result in tumor inhibition. Citation Format: Akira Saito, Hideyuki Ohzawa, Mineyuki Tojo, Yuko Kumagai, Rihito Kanamaru, Hidenori Tsukui, Satomi Shiba, Homare Ito, Naohiro Sata, Joji Kitayama. Metformin inhibits monocyte differentiation to tumor associated macrophage (TAM) and may restore anti-tumor immunity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 516.