Background Immune activities of monocytes (MOs) can be altered within the microenvironment of solid malignancies, including breast cancer. Metformin (1,1-dimethylbiguanide hydrochloride, MET), has been shown to decrease tumor cell proliferation, but its effects have yet to be explored with respect to MOs (monocytes) activity during their crosstalk with breast cancer cells. Here, we investigated the effects of MET on overall phenotypic functional activities, including cellular immunometabolism and protective redox signaling based-biomarkers, intracellular free calcium ions ( if Ca 2+ ), phagocytosis and co-operative cytokines (IFN-γ and IL-10) of autologous MOs before and during their interplay with primary ER - /PR - /HER2 + breast cancer cells. Methods Human primary breast cancer cells were either cultured alone or co-cultured with autologous MOs before treatment with MET. Results MET downregulated breast cancer cell proliferation and phagocytosis, while having no significant effect on the ratio of phosphorylated Akt (p-Akt) to total Akt. Additionally, we observed that, in the absence of MET treatment, the levels of lactate dehydrogenase (LDH)-based cytotoxicity, catalase, if Ca 2+ , IL-10 and arginase activity were significantly reduced in co-cultures compared to levels in MOs cultured alone whereas levels of inducible nitric oxide synthase (iNOS) activity were significantly increased. In contrast, MET treatment reduced the effects measured in co-culture on the levels of LDH-based cytotoxicity, arginase activity, catalase, if Ca 2+ , and IFN-γ. MET also induced upregulation of both iNOS and arginase in MO cells, although the increase did not reach significant difference for iNOS activity. Moreover, MET induced a robust increase of superoxide dismutase (SOD) activity in MOs, but not in MOs co-cultured with breast cancer cells. Furthermore, MET markedly upregulated the levels of IFN-γ production and downregulated those of IL-10 in isolated MOs, while inducing a slight opposing up-regulation of IL-10 production in co-cultures. Conclusions Our results show that the biomarkers of phenotypic functional activities of MOs are modified after co-culturing with primary human breast cancer cells. Treatment of co-cultures with MET resulted in increased release of antitumor cytokine IFN-γ and if Ca 2+ , and increased cell necrosis during breast cancer cells-MOs crosstalk.

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Background: Immune activities of monocytes (MOs) can be altered within the microenvironment of solid malignancies, including breast cancer. Metformin (1,1dimethylbiguanide hydrochloride, MET), has been shown to decrease tumor cell proliferation, but its effects have yet to be explored with respect to the crosstalk between monocytes and breast cancer cells. Here, we investigated the effects of MET on overall phenotypic functional activities of autologous MOs during the interplay with primary breast cancer cells. Methods:Human primary breast cancer cells were either cultured alone or co-cultured with autologous MOs before treatment with MET.Results: MET downregulated both breast cancer cell proliferation and the ratio of phosphorylated Akt (p-Akt)-to-Akt in breast cancer cells. Additionally, we observed that, in the absence of MET treatment, the levels of LDH-based cytotoxicity, catalase, intracellular free calcium ions (i fCa 2+ ), IL-10 and arginase activity were significantly reduced in co-cultures compared to those of MOs cultivated alone whereas levels of iNOS were significantly increased (for all comparisons, p < 0.05). In contrast, MET upregulated breast cancer cell LDH-based cytotoxicity levels when co-cultured with MO. MET also induced upregulation of both the inducible enzymatic activity of nitric oxide synthase (iNOS) and arginase activity in MO cells and co-culture systems, although these differences did not reach significant levels for iNOS activity (p > 0.05). MET greatly decreased phagocytic activity in isolated MOs while inducing a robust increase of catalase activity in co-culture systems and of superoxide dismutase (SOD) activity in MOs, but not in MOs co-cultured with breast cancer cells. MET strongly upregulated the levels of ifCa 2+ in co-culture systems and IFN-γ production in both isolated MOs and co-culture systems. Moreover, MET treatment markedly downregulated IL-10 production in MOs, while inducing a slight increase in co-cultures (p > 0.05). Conclusions: Our results show that the phenotypic functional activities of MOs change when co-cultured with primary human breast cancer cells. Furthermore, treatment with MET induced enhancing effects on the production of antitumor cytokine IFN-γ and ifCa 2+ , as well as cytotoxicity during breast cancer cell-MO crosstalk. Keywords: Akt activation; metformin; monocyte/primary human breast cancer cell crosstalk; monocyte phenotypic functional activity changes; primary breast cancer cell proliferation and viability; MO IFN-γ-associated anti-tumor activity