Regulation of intrinsic and extrinsic metabolic pathways in tumour-associated macrophages.

Tumour-associated macrophages (TAMs) are highly plastic and are broadly grouped into two major functional states, namely the pro-inflammatory M1-type and the pro-tumoural M2-type. Conversion of the functional states of TAMs is regulated by various cytokines, chemokines growth factors and other secreted factors in the microenvironment. Dysregulated metabolism is a hallmark of cancer. Emerging evidence suggests that metabolism governs the TAM differentiation and functional conversation in support of tumour growth and metastasis. Aside from the altered metabolism reprogramming in TAMs, extracellular metabolites secreted by cancer, stromal and/or other cells within the tumour microenvironment have been found to regulate TAMs through passive competition for metabolite availability and direct regulation via receptor/transporter-mediated signalling reaction. In this review, we focus on the regulatory roles of different metabolites and metabolic pathways in TAM conversion and function. We also discuss if the dysregulated metabolism in TAMs can be exploited for the development of new therapeutic strategies against cancer.

Autophagy Drives Galectin-1 Secretion From Tumor-Associated Macrophages Facilitating Hepatocellular Carcinoma Progression.

Galectin-1 (Gal-1) is a secretory lectin with pro-tumor activities and is associated strongly with hepatocellular carcinoma (HCC) development. Although Gal-1 is a well-known soluble pro-tumor factor in the tumor microenvironment (TME), the secretion mode of Gal-1 is not clearly defined. On the other hand, in addition to cancer cells, Gal-1 is widely expressed in tumor stromal cells, including tumor-associated macrophages (TAMs). TAMs are a significant component of stromal cells in TME; however, their contributions in producing Gal-1 to TME are still not explored. Here we reveal that TAMs can actively secrete Gal-1 in response to stimuli of HCC cells. Gal-1 produced by TAMs leads to an increase of the systemic level of Gal-1 and HCC tumor growth in mice. Mechanistically, TLR2-dependent secretory autophagy is found to be responsible for Gal-1 secretion from TAMs. Gal-1 acts as a cargo of autophagosomes to fuse with multivesicular bodies via Rab11 and VAMP7-mediated vesicle trafficking before being secreted. This autophagy-regulated Gal-1 secretion in TAMs correlates to poor overall survival and progression-free survival rates of HCC patients. Our findings uncover the secretion mode of Gal-1 via secretory autophagy and highlight the pathological role of TAM-produced Gal-1 in HCC progression.

Hepatocellular carcinoma-derived high mobility group box 1 triggers M2 macrophage polarization via a TLR2/NOX2/autophagy axis.

In many human cancers, including hepatocellular carcinoma (HCC), high density of infiltrating tumor-associated macrophages (TAM) is associated with poor prognosis. Most TAMs express a M2 phenotype subsequently supporting tumor growth. How tumor cells polarize these TAMs to a pro-tumor M2 phenotype is still poorly understood. Our previous studies have revealed that a Toll-like receptor 2 (TLR2)-dependent autophagy triggered by hepatoma-derived factors down-regulates NF-κB p65 and drives M2 macrophage differentiation. However, the underlying mechanisms and potential hepatoma-derived TLR2 ligands are not clear. Here, we provide evidence to reveal that NADPH oxidase 2 (NOX2)-dependent reactive oxygen species (ROS) generation is crucial for HCC-induced autophagy, NF-κB p65 down-regulation and M2 phenotype polarization in primary macrophages. This NOX2-generated ROS production in abolished in TLR2-deficient macrophages. HCC-derived or recombinant high-mobility group box 1 (HMGB1) is able to trigger this TLR2-mediated M2 macrophage polarization. Blockage of HMGB1 and ROS by inhibitors, ethyl pyruvate and N-acetylcysteine amide, respectively, significantly reduces both M2 macrophage accumulation and liver nodule formation in HCC-bearing mice. Our findings uncover a HMGB1/TLR2/NOX2/autophagy axis to trigger M2 macrophage polarization in HCC that can be considered as a novel therapeutic target for treating HCC.

Galectin-1-Induced Autophagy Facilitates Cisplatin Resistance of Hepatocellular Carcinoma.

Hepatocellular carcinoma (HCC) is one of the most common cancers in Taiwan. Although chemotherapy is the primary treatment for HCC patients, drug resistance often leads to clinical failure. Galectin-1 is a beta-galactoside binding lectin which is up-regulated in HCC patients and promotes tumor growth by mediating cancer cell adhesion, migration and proliferation, but its role in chemoresistance of HCC is poorly understood. In this study we found that galectin-1 is able to lead to chemoresistance against cisplatin treatment, and subsequent inhibition has reversed the effect of cell death in HCC cells. Moreover, galectin-1 was found to induce autophagic flux in HCC cells. Inhibition of autophagy by inhibitors or knockdown of Atg5 cancels galectin-1-induced cisplatin resistance in HCC cells. Increase of mitophagy triggered by galectin-1 was found to reduce the mitochondrial potential loss and apoptosis induced by cisplatin treatment. Finally, using an in situ hepatoma mouse model, we clearly demonstrated that inhibition of galectin-1 by thiodigalactoside could significantly augment the anti-HCC effect of cisplatin. Taken together, our findings offer a new insight into the chemoresistance galectin-1 causes against cisplatin treatment, and points to a potential approach to improve the efficacy of cisplatin in the treatment of HCC patients.