BackgroundCisplatin-based chemotherapy is frequently used to treat advanced gastric cancer (GC). However, the resistance often occurs with the mechanisms being not well understood. Recently, emerging evidence indicates that tumor-associated macrophages (TAMs) play an important role in chemoresistance of cancer. As the important mediators in intercellular communications, exosomes secreted by host cells mediate the exchange of genetic materials and proteins to be involved in tumor aggressiveness. The aim of the study was to investigate whether exosomes derived from TAMs mediate cisplatin resistance in gastric cancer.MethodsM2 polarized macrophages were obtained from mouse bone marrow or human PBMCs stimulated with IL-4 and IL-13. Exosomes isolated from M2 macrophages culture medium were characterized, and miRNA expression profiles of M2 derived exosomes (M2-exos) were analyzed using miRNA microarray. In vitro cell coculture was further conducted to investigate M2-exos mediated crosstalk between TAMs and tumor cells. Moreover, the in vivo experiments were performed using a subcutaneous transplantation tumor model in athymic nude mice.ResultsIn this study, we showed that M2 polarized macrophages promoted cisplatin (DDP) resistance in gastric cancer cells and exosomes derived from M2 macrophages (M2-exos) are involved in mediating the resistance to DDP. Using miRNA profiles assay, we identify significantly higher levels of microRNA-21 (miR21) isomiRNAs in exosomes and cell lysate isolated from M2 polarized macrophage. Functional studies revealed that exosomal miR-21 can be directly transferred from macrophages to the gastric cancer cells, where it suppresses cell apoptosis and enhances activation of PI3K/AKT signaling pathway by down-regulation of PTEN.ConclusionsOur findings suggest that exosomal transfer of tumor-associated macrophages derived miR-21 confer DDP resistance in gastric cancer, and targeting exosome communication may be a promising new therapeutic strategy for gastric cancer patients.Electronic supplementary materialThe online version of this article (doi:10.1186/s13046-017-0528-y) contains supplementary material, which is available to authorized users.

Tumor-associated macrophages (TAMs) are a major component of the tumor microenvironment and have been shown to contribute to tumor aggressiveness. However, the detailed mechanisms underlying the pro-metastatic effect of TAMs on gastric cancer are not clearly defined. Here, we show that TAMs are enriched in gastric cancer. TAMs are characterized by M2-polarized phenotype and promote migration of gastric cancer cells in vitro and in vivo. Furthermore, we find that M2-derived exosomes determine the TAMs-mediated pro-migratory activity. Using mass spectrometry, we identify that apolipoprotein E (ApoE) is highly specific and effective protein in M2 macrophages-derived exosomes. Moreover, TAMs are uniquely immune cells population expressed ApoE in gastric cancer microenvironment. However, exosomes derived from M2 macrophages of Apoe−/− mice have no significant effect on the migration of gastric cancer cells in vitro and in vivo. Mechanistically, M2 macrophage-derived exosomes mediate an intercellular transfer of ApoE-activating PI3K-Akt signaling pathway in recipient gastric cancer cells to remodel the cytoskeleton-supporting migration. Collectively, our findings signify that the exosome-mediated transfer of functional ApoE protein from TAMs to the tumor cells promotes the migration of gastric cancer cells.

ObjectiveIn the tumour microenvironment, critical drivers of immune escape include the oncogenic activity of the tumour cell-intrinsic osteopontin (OPN), the expression of programmed death ligand 1 (PD-L1) and the expansion of tumour-associated macrophages (TAMs). We investigated the feasibility of targeting these pathways as a therapeutic option in hepatocellular carcinoma (HCC) mouse models.DesignWe analysed the number of tumour-infiltrating immune cells and the inflammatory immune profiles in chemically induced liver tumour isolated from wild-type and OPNknockout (KO) mice. In vitro cell cocultures were further conducted to investigate the crosstalk between TAMs and HCC cells mediated by OPN, colony stimulating factor-1 (CSF1) and CSF1 receptor (CSF1R). The in vivo efficacy of anti-PD-L1 and CSF1/CSF1R inhibition was evaluated in OPN overexpressing subcutaneous or orthotopic mouse model of HCC.ResultsThe numbers of TAMs, as well as the expression levels of M2 macrophage markers and PD-L1 were significantly decreased, but the levels of cytokines produced by T-helper 1 (Th1) cells were upregulated in tumour tissues from OPN KO mice compared with that from the controls. In addition, we observed a positive association between the OPN and PD-L1 expression, and OPN expression and TAM infiltration in tumour tissues from patients with HCC. We further demonstrated that OPN facilitates chemotactic migration, and alternative activation of macrophages, and promotes the PD-L1 expression in HCC via activation of the CSF1-CSF1R pathway in macrophages. Combining anti-PD-L1 and CSF1R inhibition elicited potent antitumour activity and prolonged survival of OPNhigh tumour-bearing mice. Histological, flow cytometric and ELISA revealed increased CD8+ T cell infiltration, reduced TAMs and enhanced Th1/Th2 cytokine balance in multiple mouse models of HCC.ConclusionsOPN/CSF1/CSF1R axis plays a critical role in the immunosuppressive nature of the HCC microenvironment. Blocking CSF1/CSF1R prevents TAM trafficking and thereby enhances the efficacy of immune checkpoint inhibitors for the treatment of HCC.