Accumulated evidence suggests that M2-like polarized tumor associated macrophages (TAMs) plays an important role in cancer progression and metastasis, establishing TAMs, especially M2-like TAMs as an appealing target for therapy intervention. Here we found that metformin significantly suppressed IL-13 induced M2-like polarization of macrophages, as illustrated by reduced expression of CD206, down-regulation of M2 marker mRNAs, and inhibition of M2-like macrophages promoted migration of cancer cells and endothelial cells. Metformin triggered AMPKα1 activation in macrophage and silencing of AMPKα1 partially abrogated the inhibitory effect of metformin in IL-13 induced M2-like polarization. Administration of AICAR, another activator of AMPK, also blocked the M2-like polarization of macrophages. Metformin greatly reduced the number of metastases of Lewis lung cancer without affecting tumor growth. In tumor tissues, the percentage of M2-like macrophage was decreased and the area of pericyte-coated vessels was increased. Further, the anti-metastatic effect of metformin was abolished when the animals were treated with macrophages eliminating agent clodronate liposome. These findings suggest that metformin is able to block the M2-like polarization of macrophages partially through AMPKα1, which plays an important role in metformin inhibited metastasis of Lewis lung cancer.

Tumor-associated macrophages (TAMs) are the most abundant inflammatory cells and orchestrate different stages of breast cancer development. TAMs participate in the tumor angiogenesis, matrix remodeling, invasion, immunosuppression, metastasis, and chemoresistance in breast cancer. Several clinical studies indicate the association between the high influx of TAMs in tumor with poor prognosis in hepatocellular, ovarian, cervical, and breast cancer. Previously developed hypotheses have proposed that TAMs participate in antitumor responses of the body, while recently many clinical and experimental studies have revealed that TAMs in tumor microenvironment predominantly resemble with M2-like polarized macrophages and produce a high amount of anti-inflammatory factors which are directly responsible for the development of tumor. Various studies have shown that TAMs in tumor either enhance or antagonize the anti-tumor efficacy of cytotoxic agents, antibodies-targeting cancer cells, and therapeutic agents depending on the nature of treatment. Thereby, multiple roles of TAMs suggests that it is very important to develop novel therapeutic strategies to target TAMs in breast tumor. In this review, we have discussed the functional role of TAMs in breast cancer and summarized available recent advances potential therapeutic strategies that effectively target to TAMs cells. J. Cell. Biochem. 118: 2484-2501, 2017. © 2017 Wiley Periodicals, Inc.

Studies have pointed to a role of PARP1 in regulating gene expression through poly(ADP-ribosyl)ating, sequence-specific, DNA-binding transcription factors. However, few examples exist that link this role of PARP1 to the immunogenicity of cancer cells. Here, we report that PARP1 poly(ADP-ribosyl)ates STAT3 and subsequently promotes STAT3 dephosphorylation, resulting in reduced transcriptional activity of STAT3 and expression of PD-L1. In this study, we showed that PARP1 silencing or pharmacologic inhibition enhanced the transcription of PD-L1 in cancer cells, which was accompanied by the upregulation of PD-L1 protein expression, both in the cytoplasm and on the cell surface. This induction of PD-L1 was attenuated in the absence of the transcription factor STAT3.Cell-based studies indicated that PARP1 interacted directly with STAT3 and caused STAT3 poly(ADP-ribosyl)ation. STAT3's activation of PD-L1 transcription was abolished by the overexpression of wild-type PARP1 but not mutant PARP1, which lacks catalytic activity. PARP1 downregulation or catalytic inhibition enhanced the phosphorylation of STAT3, which was reversed by the ectopic expression of wild-type PARP1 but not by mutated PARP1. An inverse correlation between PARP1 and PD-L1 was also observed in clinical ovarian cancer samples. Overall, our study revealed PARP1-mediated poly (ADP-ribosyl)ation of STAT3 as a key step in inhibiting the transcription of PD-L1, and this mechanism exists in a variety of cancer cells.

M2-like polarized tumor-associated macrophages (TAMs) play a pivotal role in promoting cancer cell growth, invasion, metastasis and angiogenesis. The identification of M2-like TAMs during tumor progression is an attractive approach for cancer therapy. In this study, we investigated the relevance of macrophage polarization and the antitumor effect of gefitinib in Lewis Lung cancer (LLC) in vitro and in vivo. Gefitinib at a concentration below 2.5 μmol/L did not cause significant growth inhibition on LLC and RAW 264.7 cell lines and bone marrow-derived macrophage (BMDMs). However, a small concentration of gefitinib (0.62 μmol/L) significantly inhibited IL-13-induced M2-like polarization of macrophages, evidenced by the decreased expression of the M2 surface markers CD206 and CD163, down-regulation of specific M2-marker genes (Mrc1, Ym1, Fizz1, Arg1, IL-10 and CCL2) as well as inhibition of M2-like macrophage-mediated invasion and migration of LLC cells. In RAW 264.7 cells, gefitinib inhibits IL-13-induced phosphorylation of STAT6, which was a crucial signaling pathway in macrophage M2-like polarization. In LLC mice metastasis model, oral administration of gefitinib (75 mg·kg·d, for 21 d) significantly reduced the number of lung metastasis nodules, down-regulated the expression of M2 marker genes and the percentages CD206 and CD68 macrophages in tumor tissues. These results demonstrated that gefitinib effectively inhibits M2-like polarization both in vitro and in vivo, revealing a novel potential mechanism for the chemopreventative effect of gefitinib.

Although M2-like tumor-associated macrophages (TAMs) have been considered as a vital therapeutic target in cancer therapy due to their role in promoting tumor progression and metastasis, very few compounds have been identified to inhibit M2-like polarization of TAMs. Here, we showed that Imatinib significantly prevented macrophage M2-like polarization induced by IL-13 or IL-4 in vitro, as illustrated by reduced expression of cell surface marker CD206 and M2-like genes, including Arg1, Mgl2, Mrc1, CDH1, and CCL2. Further, the migration of lung cancer cells promoted by the conditioned medium from M2-like macrophages could be restrained by Imatinib. Mechanistically, Imatinib inhibited STAT6 phosphorylation and nuclear translocation, resulting in the macrophage M2-like polarization arrest. Furthermore, Imatinib reduced the number of metastasis of Lewis lung cancer without affecting tumor growth. Both in tumor and lung tissues, the percentage of M2-like macrophages decreased after the administration of Imatinib for one week. Taken together, these data suggest that Imatinib is able to inhibit macrophage M2-like polarization, which plays a vital role in Imatinib suppressed metastasis of Lewis lung cancer.