Phenotypic functional activities of monocyte change during crosstalk with breast cancer cell and enhancing effect of metformin of IFN-γ-associated antitumor cytokine production

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 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 (ifCa2+), 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 ifCa2+ 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 ifCa2+, as well as cytotoxicity during breast cancer cell-MO crosstalk. Novel Highlights include