Pancreatic Cancer Cells Isolated from Muc1-Null Tumors Favor the Generation of a Mature Less Suppressive MDSC Population

Circadian rhythms of macrophages are altered by the acidic tumor microenvironment

Tumor-associated macrophages (TAMs) are prime therapeutic targets due to their pro-tumorigenic functions, but varying efficacy of macrophage-targeting therapies highlights our incomplete understanding of how macrophages are regulated within the tumor microenvironment (TME). The circadian clock is a key regulator of macrophage function, but how circadian rhythms of macrophages are influenced by the TME remains unknown. Here, we show that conditions associated with the TME such as polarizing stimuli, acidic pH, and lactate can alter circadian rhythms in macrophages. While cyclic AMP (cAMP) has been reported to play a role in macrophage response to acidic pH, our results indicate pH-driven changes in circadian rhythms are not mediated solely by cAMP signaling. Remarkably, circadian disorder of TAMs was revealed by clock correlation distance analysis. Our data suggest that heterogeneity in circadian rhythms within the TAM population level may underlie this circadian disorder. Finally, we report that circadian regulation of macrophages suppresses tumor growth in a murine model of pancreatic cancer. Our work demonstrates a novel mechanism by which the TME influences macrophage biology through modulation of circadian rhythms.

Platelet-activating factor (PAF) promotes immunosuppressive neutrophil differentiation within tumors

Chronic inflammatory milieu in the tumor microenvironment (TME) leads to the recruitment and differentiation of myeloid-derived suppressor cells (MDSCs). Polymorphonuclear (PMN)-MDSCs, which are phenotypically and morphologically defined as a subset of neutrophils, cause major immune suppression in the TME, posing a significant challenge in the development of effective immunotherapies. Despite recent advances in our understanding of PMN-MDSC functions, the mechanism that gives rise to immunosuppressive neutrophils within the TME remains elusive. Both in vivo and in vitro, newly recruited neutrophils into the tumor sites remained activated and highly motile for several days and developed immunosuppressive phenotypes, as indicated by increased arginase 1 (Arg1) and dcTrail-R1 expression and suppressed anticancer CD8 T cell cytotoxicity. The strong suppressive function was successfully recapitulated by incubating naive neutrophils with cancer cell culture supernatant in vitro. Cancer metabolite secretome analyses of the culture supernatant revealed that both murine and human cancers released lipid mediators to induce the differentiation of immunosuppressive neutrophils. Liquid chromatography-mass spectrometry (LC-MS) lipidomic analysis identified platelet-activation factor (PAF; 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine) as a common tumor-derived lipid mediator that induces neutrophil differentiation. Lysophosphatidylcholine acyltransferase 2 (LPCAT2), the PAF biosynthetic enzyme, is up-regulated in human pancreatic ductal adenocarcinoma (PDAC) and shows an unfavorable correlation with patient survival across multiple cancer types. Our study identifies PAF as a lipid-driven mechanism of MDSC differentiation in the TME, providing a potential target for cancer immunotherapy.

Pharmacological modulation of myeloid-derived suppressor cells to dampen inflammation

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous cell population with potent suppressive and regulative properties. MDSCs’ strong immunosuppressive potential creates new possibilities to treat chronic inflammation and autoimmune diseases or induce tolerance towards transplantation. Here, we summarize and critically discuss different pharmacological approaches which modulate the generation, activation, and recruitment of MDSCs in vitro and in vivo, and their potential role in future immunosuppressive therapy.

Repression of MUC1 Promotes Expansion and Suppressive Function of Myeloid-Derived Suppressor Cells in Pancreatic and Breast Cancer Murine Models

Myeloid-derived suppressor cells (MDSCs) are immature myeloid cells that are responsible for immunosuppression in tumor microenvironment. Here we report the impact of mucin 1 (MUC1), a transmembrane glycoprotein, on proliferation and functional activity of MDSCs. To determine the role of MUC1 in MDSC phenotype, we analyzed MDSCs derived from wild type (WT) and MUC1-knockout (MUC1KO) mice bearing syngeneic pancreatic (KCKO) or breast (C57MG) tumors. We observed enhanced tumor growth of pancreatic and breast tumors in the MUC1KO mice compared to the WT mice. Enhanced tumor growth in the MUC1KO mice was associated with increased numbers of suppressive MDSCs and T regulatory (Tregs) cells in the tumor microenvironment. Compared to the WT host, MUC1KO host showed higher levels of iNOS, ARG1, and TGF-β, thus promoting proliferation of MDSCs with an immature and immune suppressive phenotype. When co-cultured with effector T cells, MDSCs from MUC1KO mice led to higher repression of IL-2 and IFN-γ production by T cells as compared to MDSCs from WT mice. Lastly, MDSCs from MUC1KO mice showed higher levels of c-Myc and activated pSTAT3 as compared to MDSCs from WT mice, suggesting increased survival, proliferation, and prevention of maturation of MDSCs in the MUC1KO host. We report diminished T cell function in the KO versus WT mice. In summary, the data suggest that MUC1 may regulate signaling pathways that are critical to maintain the immunosuppressive properties of MDSCs.

Curcumin inhibits the growth of liver cancer by impairing myeloid-derived suppressor cells in murine tumor tissues

Curcumin, one of the active ingredients of Curcuma longa (Jianghuang), has been reported to exert multiple bioactivities, including pro-apoptotic and anti-inflammatory activities. In recent years, curcumin has been extensively studied, and it has been revealed that curcumin inhibits the growth of numerous types of cancer. However, to the best of our knowledge, the inhibitory effects of curcumin on the activation or expansion of myeloid-derived suppressor cells (MDSCs) in liver cancer and the underlying mechanism have not yet been determined. Therefore, the present study aimed to investigate the inhibitory effect of curcumin on MDSC activity and the associated anti-neoplastic mechanism in a HepG2 ×enograft mouse model. The effect of curcumin on the viability of Huh-7, MHCC-97H and HepG2 cells in vitro was analyzed using a Cell Counting Kit-8 assay. The effects of curcumin on tumor growth, numbers of MDSCs, expression levels of proteins involved in the toll-like receptor 4 (TLR4)/NF-κB signaling pathway, levels of related inflammatory factors and angiogenesis were determined in HepG2 ×enograft model mice, which were given different doses of curcumin via intragastrical administration. The results of the present study revealed that curcumin inhibited the viability of Huh-7, MHCC-97H and HepG2 cells and the growth of HepG2 ×enograft tumors in mice. Flow cytometric analysis indicated that curcumin reduced the number of MDSCs in mouse xenograft tumors. In addition, the results demonstrated that curcumin inhibited the TLR4/NF-κB signaling pathway and the expression of inflammatory factors, including IL-6, IL-1β, prostaglandin E2 and cyclooxygenase-2, in mouse xenograft tumors. Furthermore, curcumin suppressed the secretion of granulocyte-macrophage colony-stimulating factor (GM-CSF) and granulocyte-colony stimulating factor (G-CSF), which are essential factors for MDSCs modulation, in tumor tissues. Additionally, curcumin was revealed to inhibit angiogenesis, which was demonstrated by the downregulation of the expression levels of vascular endothelial growth factor, CD31 and α-smooth muscle actin in western blotting, immunohistochemistry and immunofluorescence experiments. In conclusion, the findings of the present study identified a novel mechanism via which curcumin may suppress the growth of liver cancer by reducing the numbers of MDSCs and subsequently disrupting the process of angiogenesis. These conclusions were supported by the observed inactivation of the TLR4/NF-κB signaling pathway-mediated inflammatory response and the downregulation of GM-CSF and G-CSF secretion in xenograft tissues.

Cross-talk between myeloid-derived suppressor cells and Mucin1 in breast cancer vaccination: On the verge of a breakthrough

Although breast cancer is one of the leading troublesome cancers, the available therapeutic options have not fulfilled the desired outcomes. Immune-based therapy has gained special attention for breast cancer treatment. Although this approach is highly tolerable, its low response rate has rendered it as an undesirable approach. This review aims to describe the essential oncogenic pathways involved in breast cancer, elucidate the immunosuppression and oncogenic effect of Mucin1, and introduce myeloid-derived suppressor cells, which are the main culprits of anti-tumoral immune response attenuation. The various auto-inductive loops between Mucin1 and myeloid-derived suppressor cells are focal in the suppression of anti-tumoral immune responses in patients with breast cancer. These cross-talks between the Mucin1 and myeloid-derived suppressor cells can be the underlying causes of immunotherapy's impotence for patients with breast cancer. This approach can pave the road for the development of a potent vaccine for patients with breast cancer and is translated into clinical settings.

Clinical significance of SQSTM1/P62 and nuclear factor-κB expression in pancreatic carcinoma

BACKGROUND

Overexpression of SQSTM1 (sequestosome 1, P62) and nuclear factor-κB (NF-κB) plays an important role in the invasion and metastasis of a variety of malignant tumors.

AIM

To explore the expression of P62 and NF-κB in pancreatic cancer and their relationship with clinicopathological features.

METHODS

The expression levels of P62 and NF-κB were analyzed by immunohistochemistry with a tissue chip containing 40 cases of human pancreatic carcinoma. Then we analyzed the correlation among P62 expression, phospho-P65 expression, and clinicopathological features of pancreatic carcinoma samples.

RESULTS

P62 expression was mainly observed in the cytoplasm of pancreatic carcinoma cells. Phosphorylated P65 (phospho-P65) was mainly expressed in the nucleus and cytoplasm of pancreatic carcinoma cells. There was a significant difference in P62 expression among T stages. And a significant difference in phosphor-P65 expression among pathology types was noted. In the cases with strongly positive P62 expression, significant differences were found in age. And there were significant differences in T stage and tumor-node-metastasis stage in the cases with strongly positive phosphor-P65 expression.

CONCLUSION

In pancreatic carcinoma, P62 expression is significantly correlated with T stage. It may be a valuable malignant indicator for human pancreatic carcinoma.

MUC1 Story: Great Expectations, Disappointments and the Renaissance

In the course of studying human mucin MUC1, the attitude towards this molecule has been changing time and again. Initially, the list of presumable functions of MUC1 was restricted to protecting and lubricating epithelium. To date, it is assumed to play an important role in cell signaling as well as in all stages of oncogenesis, from malignant cell transformation to tumor dissemination. The story of MUC1 is full of hopes and disappointments. However, the scientific interest to MUC1 has never waned, and the more profoundly it has been investigated, the clearer its hidden potential turned to be disclosed. The therapeutic potential of mucin MUC1 has already been noted by various scientific groups at the early stages of research. Over forty years ago, the first insights into MUC1 functions became a strong ground for considering this molecule as potential target for anticancer therapy. Therefore, this direction of research has always been of particular interest and practical importance. More than 200 papers on MUC1 were published in 2016; the majority of them are dedicated to MUC1-related anticancer diagnostics and therapeutics. Here we review the history of MUC1 studies from the very first attempts to reveal its functions to the ongoing renaissance.

Optimized construction of MUC1-VNTRn DNA vaccine and its anti-pancreatic cancer efficacy

Considering mucin 1-variable number tandem repeat (MUC1-VNTR_n) as a novel target for pancreatic cancer immunotherapy, the present study aimed to screen and identify the pVAX1-MUC1-VNTR_n DNA vaccine with the strongest immunogenicity. Following construction of a pVAX1-MUC1-VNTR_n plasmid, immature dendritic cells (DCs) were subjected to transfection, and mature DCs were then co-cultured with autologous T-cells. The numbers of cytotoxic T lymphocytes (CTLs) secreting interferon (IFN)-γ were determined using an enzyme-linked immunospot assay, and CytoTox^® was also used to examine the MUC1-VNTR_n-specific Lethal effect of CTLs on Capan2 cells. Additional in vivo experiments in mice were performed to confirm the antitumor effect of the DNA vaccine candidate. The present study successfully constructed the pVAX1-MUC1-VNTR_n plasmid, which expresses the target protein in eukaryotic cells. Additionally, upon uptake of the pVAX1-MUC1-VNTR_n plasmid, the immature DCs differentiated into mature DCs. The levels of the DC surface molecules cluster of differentiation (CD) 80, CD86, human leukocyte antigen-antigen D related, interleukin (IL)-12, IL-17 and IFN-γ were significantly higher, while the levels of IL-10 and IL-14 were lower, in mature DCs of the stimulated groups compared with the immature DCs of the non-stimulated groups (all P<0.01). In addition, the MUC1-VNTR₆ and MUC1-VNTR₉ groups, in which DCs were capable of activating autologous T-cells, showed increased IFN-γ-producing T-cells compared with the other groups (strong MUC1-VNTR₁, weak VNTR₁, VNTR₃, VNTR₄ and MUC1-cDNA groups; all P<0.001). In addition, the Lethal effect of CTLs on Capan2 cells in these two groups was stronger compared with the other groups (all P<0.001). Furthermore, the induced protective and therapeutic immune responses in mouse experiments showed that the pVAX1-MUC1-VNTR₆DNA vaccine likely possessed the strongest immunogenicity, and its ability to inhibit panc02-MUC1 tumor growth was superior to other DNA vaccines (P<0.01). The present study provides compelling evidence that pVAX1-MUC1-VNTR_n has the potential to express the target protein in eukaryotic cells, and thatpVAX1-MUC1-VNTR₆ was characterized by the strongest Lethal effect in both in vivo and in vitro experiments.

IL1 Receptor Antagonist Inhibits Pancreatic Cancer Growth by Abrogating NF-κB Activation

PURPOSE

Constitutive NF-κB activation is identified in about 70% of pancreatic ductal adenocarcinoma (PDAC) cases and is required for oncogenic KRAS-induced PDAC development in mouse models. We sought to determine whether targeting IL-1α pathway would inhibit NF-κB activity and thus suppress PDAC cell growth.

EXPERIMENTAL DESIGN

We determined whether anakinra, a human IL-1 receptor (rhIL-1R) antagonist, inhibited NF-κB activation. Assays for cell proliferation, migration, and invasion were performed with rhIL-1R antagonist using the human PDAC cell lines AsPc1, Colo357, MiaPaCa-2, and HPNE/K-ras(G12V)/p16sh. In vivo NF-κB activation-dependent tumorigenesis was assayed using an orthotopic nude mouse model (n = 20, 5 per group) treated with a combination of gemcitabine and rhIL-1RA.

RESULTS

rhIL-1R antagonist treatment led to a significant decrease in NF-κB activity. PDAC cells treated with rhIL-1R antagonist plus gemcitabine reduced proliferation, migration, and invasion as compared with single gemcitabine treatment. In nude mice, rhIL-1R antagonist plus gemcitabine significantly reduced the tumor burden (gemcitabine plus rhIL-1RA vs. control, P = 0.014).

CONCLUSIONS

We found that anakinra, an FDA-approved drug that inhibits IL-1 receptor (IL-1R), when given with or without gemcitabine, can reduce tumor growth by inhibiting IL1α-induced NF-κB activity; this result suggests that it is a useful therapeutic approach for PDAC.