Pancreatic cancer tumor microenvironment is a major therapeutic barrier and target

Pancreatic Ductal Adenocarcinoma (PDAC) is projected to become the 2nd leading cause of cancer-related deaths in the United States. Limitations in early detection and treatment barriers contribute to the lack of substantial success in the treatment of this challenging-to-treat malignancy. Desmoplasia is the hallmark of PDAC microenvironment that creates a physical and immunologic barrier. Stromal support cells and immunomodulatory cells face aberrant signaling by pancreatic cancer cells that shifts the complex balance of proper repair mechanisms into a state of dysregulation. The product of this dysregulation is the desmoplastic environment that encases the malignant cells leading to a dense, hypoxic environment that promotes further tumorigenesis, provides innate systemic resistance, and suppresses anti-tumor immune invasion. This desmoplastic environment combined with the immunoregulatory events that allow it to persist serve as the primary focus of this review. The physical barrier and immune counterbalance in the tumor microenvironment (TME) make PDAC an immunologically cold tumor. To convert PDAC into an immunologically hot tumor, tumor microenvironment could be considered alongside the tumor cells. We discuss the complex network of microenvironment molecular and cellular composition and explore how they can be targeted to overcome immuno-therapeutic challenges.

Tumor microenvironment, histone modifications, and myeloid-derived suppressor cells

Myeloid-derived suppressor cells (MDSCs) are important components of the tumor microenvironment (TME), which drive the tumor immune escape by inducing immunosuppression. The expansion and function of MDSCs are tightly associated with signaling pathways induced by molecules from tumor cells, stromal cells, and activated immune cells in the TME. Although these pathways have been well-characterized, the understanding of the epigenetic regulators involved is incomplete. Since histone modifications are the most studied epigenetic changes in MDSCs, we summarize current knowledge on the role of histone modifications in MDSCs within this review. We first discuss the influence of the TME on histone modifications in MDSCs, with an emphasis on histone modifications and modifiers that direct MDSC differentiation and function. Furthermore, we highlight current epigenetic interventions that can reverse MDSC-induced immunosuppression by modulating histone modifications and discuss future research directions to fully appreciate the role of histone modifications in MDSCs.

Methylation across the central dogma in health and diseases: new therapeutic strategies

The proper transfer of genetic information from DNA to RNA to protein is essential for cell-fate control, development, and health. Methylation of DNA, RNAs, histones, and non-histone proteins is a reversible post-synthesis modification that finetunes gene expression and function in diverse physiological processes. Aberrant methylation caused by genetic mutations or environmental stimuli promotes various diseases and accelerates aging, necessitating the development of therapies to correct the disease-driver methylation imbalance. In this Review, we summarize the operating system of methylation across the central dogma, which includes writers, erasers, readers, and reader-independent outputs. We then discuss how dysregulation of the system contributes to neurological disorders, cancer, and aging. Current small-molecule compounds that target the modifiers show modest success in certain cancers. The methylome-wide action and lack of specificity lead to undesirable biological effects and cytotoxicity, limiting their therapeutic application, especially for diseases with a monogenic cause or different directions of methylation changes. Emerging tools capable of site-specific methylation manipulation hold great promise to solve this dilemma. With the refinement of delivery vehicles, these new tools are well positioned to advance the basic research and clinical translation of the methylation field.

H3K4 trimethylation regulates cancer immunity: a promising therapeutic target in combination with immunotherapy

With the advances in cancer immunity regulation and immunotherapy, the effects of histone modifications on establishing antitumor immunological ability are constantly being uncovered. Developing combination therapies involving epigenetic drugs (epi-drugs) and immune checkpoint blockades or chimeric antigen receptor-T cell therapies are promising to improve the benefits of immunotherapy. Histone H3 lysine 4 trimethylation (H3K4me3) is a pivotal epigenetic modification in cancer immunity regulation, deeply involved in modulating tumor immunogenicity, reshaping tumor immune microenvironment, and regulating immune cell functions. However, how to integrate these theoretical foundations to create novel H3K4 trimethylation-based therapeutic strategies and optimize available therapies remains uncertain. In this review, we delineate the mechanisms by which H3K4me3 and its modifiers regulate antitumor immunity, and explore the therapeutic potential of the H3K4me3-related agents combined with immunotherapies. Understanding the role of H3K4me3 in cancer immunity will be instrumental in developing novel epigenetic therapies and advancing immunotherapy-based combination regimens.

Myeloid-derived suppressor cell: A crucial player in autoimmune diseases

Myeloid-derived suppressor cells (MDSCs) are identified as a highly heterogeneous group of immature cells derived from bone marrow and play critical immunosuppressive functions in autoimmune diseases. Accumulating evidence indicates that the pathophysiology of autoimmune diseases was closely related to genetic mutations and epigenetic modifications, with the latter more common. Epigenetic modifications, which involve DNA methylation, covalent histone modification, and non-coding RNA-mediated regulation, refer to inheritable and potentially reversible changes in DNA and chromatin that regulate gene expression without altering the DNA sequence. Recently, numerous reports have shown that epigenetic modifications in MDSCs play important roles in the differentiation and development of MDSCs and their suppressive functions. The molecular mechanisms of differentiation and development of MDSCs and their regulatory roles in the initiation and progression of autoimmune diseases have been extensively studied, but the exact function of MDSCs remains controversial. Therefore, the biological and epigenetic regulation of MDSCs in autoimmune diseases still needs to be further characterized. This review provides a detailed summary of the current research on the regulatory roles of DNA methylation, histone modifications, and non-coding RNAs in the development and immunosuppressive activity of MDSCs, and further summarizes the distinct role of MDSCs in the pathogenesis of autoimmune diseases, in order to provide help for the diagnosis and treatment of diseases from the perspective of epigenetic regulation of MDSCs.

miR-aculous new avenues for cancer immunotherapy

The rising toll of cancer globally necessitates ingenuity in early detection and therapy. In the last decade, the utilization of immune signatures and immune-based therapies has made significant progress in the clinic; however, clinical standards leave many current and future patients without options. Non-coding RNAs, specifically microRNAs, have been explored in pre-clinical contexts with tremendous success. MicroRNAs play indispensable roles in programming the interactions between immune and cancer cells, many of which are current or potential immunotherapy targets. MicroRNAs mechanistically control a network of target genes that can alter immune and cancer cell biology. These insights provide us with opportunities and tools that may complement and improve immunotherapies. In this review, we discuss immune and cancer cell-derived miRNAs that regulate cancer immunity and examine miRNAs as an integral part of cancer diagnosis, classification, and therapy.

Interaction Between microRNAs and Myeloid-Derived Suppressor Cells in Tumor Microenvironment

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of cells generated during a series of pathologic conditions including cancer. MicroRNA (miRNA) has been considered as a regulator in different tumor microenvironments. Recent studies have begun to unravel the crosstalk between miRNAs and MDSCs. The knowledge of the effect of both miRNAs and MDSCs in tumor may improve our understanding of the tumor immune escape and metastasis. The miRNAs target cellular signal pathways to promote or inhibit the function of MDSCs. On the other hand, MDSCs transfer bioinformation through exosomes containing miRNAs. In this review, we summarized and discussed the bidirectional regulation between miRNAs and MDSCs in the tumor microenvironment.

Noncoding RNAs link metabolic reprogramming to immune microenvironment in cancers

Altered metabolic patterns in tumor cells not only meet their own growth requirements but also shape an immunosuppressive microenvironment through multiple mechanisms. Noncoding RNAs constitute approximately 60% of the transcriptional output of human cells and have been shown to regulate numerous cellular processes under developmental and pathological conditions. Given their extensive action mechanisms based on motif recognition patterns, noncoding RNAs may serve as hinges bridging metabolic activity and immune responses. Indeed, recent studies have shown that microRNAs, long noncoding RNAs and circRNAs are widely involved in tumor metabolic rewiring, immune cell infiltration and function. Hence, we summarized existing knowledge of the role of noncoding RNAs in the remodeling of tumor metabolism and the immune microenvironment, and notably, we established the TIMELnc manual, which is a free and public manual for researchers to identify pivotal lncRNAs that are simultaneously correlated with tumor metabolism and immune cell infiltration based on a bioinformatic approach.

Circulating CD15+ LOX-1+ PMN-MDSCs are a potential biomarker for the early diagnosis of non-small-cell lung cancer

AIMS

Non-small-cell lung cancer (NSCLC) is the most common clinical lung cancer. Polymorphonuclear-myeloid derived suppressor cells (PMN-MDSCs), which are the major population of MDSCs, are involved in NSCLC progression. Recently, it was found that lectin-type oxidized LDL receptor 1 (LOX-1) could identify human PMN-MDSCs. However, the role of CD15⁺ LOX-1⁺ PMN-MDSCs in NSCLC early diagnosis has not been revealed. Here, we tried to confirm the application of the newly identified CD15⁺ LOX-1⁺ PMN-MDSCs in the early diagnosis of NSCLC.

METHODS

Flow cytometry (FCM) was used to detect the proportion of CD15⁺ LOX-1⁺ PMN-MDSCs in the peripheral blood (PB) of healthy controls (HC) and NSCLC patients. The correlation of CD15⁺ LOX-1⁺ PMN-MDSC frequency with levels of cytokeratin 19-fragments (CYFRA21-1), carcinoembryonic antigen (CEA), and carbohydrate antigen 125 (CA125) was analysed. Receiver operating characteristic (ROC) curve was used to estimate the diagnostic efficacy of CD15⁺ LOX-1⁺ PMN-MDSCs for NSCLC. Additionally, the association of CD15⁺ LOX-1⁺ PMN-MDSC frequency with NSCLC prognosis/recurrence after surgery was explored.

RESULTS

The proportion of CD15⁺ LOX-1⁺ PMN-MDSCs increased in PB of NSCLC patients. CD15⁺ LOX-1⁺ PMN-MDSC proportion was positively correlated with levels of CEA, CA125 and CYFRA21-1. Detection of PMN-MDSC percentage in PB owed high sensitivity and specificity for NSCLC diagnosis. The proportion of CD15⁺ LOX-1⁺ PMN-MDSCs decreased in patients after surgery. The frequency of CD15⁺ LOX-1⁺ PMN-MDSCs was lower in NSCLC patients without recurrence compared to those with recurrence after surgery.

CONCLUSIONS

Circulating CD15⁺ LOX-1⁺ PMN-MDSCs are a potential diagnostic marker for NSCLC, and are associated with NSCLC prognosis and recurrence after surgery.

Identification and characterization of B220+/B220- subpopulations in murine Gr1+CD11b+ cells during tumorigenesis

Although all murine MDSCs are defined as Gr1⁺CD11b⁺, their true immunophenotype remains elusive. In this study, we found murine Gr1⁺CD11b⁺ cells can be divided into two subsets: Gr1⁺CD11b⁺B220^- and Gr1⁺CD11b⁺B220⁺, especially in the spleen tissues. Unlike the dominant B220^- subset, the B220⁺ subpopulation was not induced by tumor in vivo. Moreover, Gr1⁺CD11b⁺B220⁺ cells from tumor-bearing mice spleens were unable to induce arginase 1 and inducible nitric oxide synthase expression, inhibit T cell proliferation, or promote tumor growth in primary tumor site. Nevertheless, these cells suppressed tumor metastasis in vivo and reduced cancer cell motility in vitro, while Gr1⁺CD11b⁺B220^- cells from tumor-bearing mice spleens promoted tumor metastasis and enhanced cancer cell motility. Furthermore, both the polymorphonuclear (PMN-MDSCs) and monocytic MDSCs (Mo-MDSCs) could be further divided into B220^- and B220⁺ subsets; interestingly, tumor only induced the expansion of B220^- PMN-MDSCs and B220^- Mo-MDSCs, but not the B220⁺ counterparts. Compared with B220^- PMN-MDSCs and B220^- Mo-MDSCs, the Ly6G⁺Ly6C^-CD11b⁺B220⁺ and Ly6G^-Ly6C⁺CD11b⁺B220⁺ cells from tumor-bearing mice spleens exhibited a more mature phenotype without immunosuppressive activity. Additionally, IL-6 deficiency attenuated the tumor-induced accumulation of MDSCs, B220^- MDSCs and B220^- PMN-MDSCs but increased the percentages of Gr1⁺CD11b⁺B220⁺, Ly6G⁺Ly6C^-CD11b⁺B220⁺, and Ly6G^-Ly6C⁺CD11b⁺B220⁺ cells, indicating the opposing roles of the IL-6 signaling pathway in the expansion of B220^- MDSCs and their B220⁺ counterparts. Taken together, our findings indicate that the B220⁺ subset is a distinct subset of Gr1⁺CD11b⁺ cells functionally different from the B220^- subpopulation during tumorigenesis and induction of MDSCs to B220⁺ cells may be helpful for cancer therapy.

ASH2L drives proliferation and sensitivity to bleomycin and other genotoxins in Hodgkin's lymphoma and testicular cancer cells

It is of clinical importance to identify biomarkers predicting the efficacy of DNA damaging drugs (genotoxins) so that nonresponders are not unduly exposed to the deleterious effects of otherwise inefficient drugs. Here, we initially focused on the bleomycin genotoxin because of the limited information about the genes implicated in the sensitivity or resistance to this compound. Using a whole-genome CRISPR/Cas9 gene knockout approach, we identified ASH2L, a core component of the H3K4 methyl transferase complex, as a protein required for bleomycin sensitivity in L1236 Hodgkin lymphoma. Knocking down ASH2L in these cells and in the NT2D1 testicular cancer cell line rendered them resistant to bleomycin, etoposide, and cisplatin but did not affect their sensitivity toward ATM or ATR inhibitors. ASH2L knockdown decreased cell proliferation and facilitated DNA repair via homologous recombination and nonhomologous end-joining mechanisms. Data from the Tumor Cancer Genome Atlas indicate that patients with testicular cancer carrying alterations in the ASH2L gene are more likely to relapse than patients with unaltered ASH2L genes. The cell models we have used are derived from cancers currently treated either partially (Hodgkin’s lymphoma), or entirely (testicular cancer) with genotoxins. For such cancers, ASH2L levels could be used as a biomarker to predict the response to genotoxins. In situations where tumors are expressing low levels of ASH2L, which may allow them to resist genotoxic treatment, the use of ATR or ATM inhibitors may be more efficacious as our data indicate that ASH2L knockdown does not affect sensitivity to these inhibitors.

MicroRNAs and lncRNAs-A New Layer of Myeloid-Derived Suppressor Cells Regulation

Myeloid-derived suppressor cells (MDSCs) constitute an important component in regulating immune responses in several abnormal physiological conditions such as cancer. Recently, novel regulatory tumor MDSC biology modulating mechanisms, including differentiation, expansion and function, were defined. There is growing evidence that miRNAs and long non-coding RNAs (lncRNA) are involved in modulating transcriptional factors to become complex regulatory networks that regulate the MDSCs in the tumor microenvironment. It is possible that aberrant expression of miRNAs and lncRNA contributes to MDSC biological characteristics under pathophysiological conditions. This review provides an overview on miRNAs and lncRNAs epiregulation of MDSCs development and immunosuppressive functions in cancer.