Hypoxia-driven immunosuppression contributes to the pre-metastatic niche

Targeting Hypoxia and HIF1α in Triple-Negative Breast Cancer: New Insights from Gene Expression Profiling and Implications for Therapy

Breast cancer is a complex and multifaceted disease with diverse risk factors, types, and treatment options. Triple-negative breast cancer (TNBC), which lacks the expression of estrogen receptor, progesterone receptor, and human epidermal growth factor receptor 2 (HER2), is the most aggressive subtype. Hypoxia is a common feature of tumors and is associated with poor prognosis. Hypoxia can promote tumor growth, invasion, and metastasis by stimulating the production of growth factors, inducing angiogenesis, and suppressing antitumor immune responses. In this study, we used mRNA-seq technology to systematically investigate the gene expression profile of MDA-MB-231 cells under hypoxia. We found that the hypoxia-inducible factor (HIF) signaling pathway is the primary pathway involved in the cellular response to hypoxia. The genes in which expression levels were upregulated in response to hypoxia were regulated mainly by HIF1α. In addition, hypoxia upregulated various genes, including Nim1k, Rimkla, Cpne6, Tpbgl, Kiaa11755, Pla2g4d, and Ism2, suggesting that it regulates cellular processes beyond angiogenesis, metabolism, and known processes. We also found that HIF1α was hyperactivated in MDA-MB-231 cells under normoxia. A HIF1α inhibitor effectively inhibited the invasion, migration, proliferation, and metabolism of MDA-MB-231 cells. Our findings suggest that hypoxia and the HIF signaling pathway play more complex and multifaceted roles in TNBC than previously thought. These findings have important implications for the development of new therapeutic strategies for TNBC.

S100A10 promotes cancer metastasis via recruitment of MDSCs within the lungs

Tumor-derived exosomes bind to organ resident cells, activating S100 molecules during the remodeling of the local immune microenvironment. However, little is known regarding how organ resident cell S100A10 mediates cancer metastatic progression. Here, we provided evidence that S100A10 plays an important role in regulating the lung immune microenvironment and cancer metastasis. S100A10-deficient mice reduced cancer metastasis in the lung. Furthermore, the activation of S100A10 within lung fibroblasts via tumor-derived exosomes increased the expression of CXCL1 and CXCL8 chemokines, accompanied by the myeloid-derived suppressor cells (MDSCs) recruitment. S100A10 inhibitors such as 1-Substituted-4-Aroyl-3-hydroxy-5-Phenyl-1 H-5-pyrrol-2(5 H)-ones inhibit lung metastasis in vivo. Our findings highlight the crucial role of S100A10 in driving MDSC recruitment in order to remodel the lung immune microenvironment and provide potential therapeutic targets to block cancer metastasis to the lung.

A Hypoxia-Related miRNA-mRNA Signature for Predicting the Response and Prognosis of Transcatheter Arterial Chemoembolization in Hepatocellular Carcinoma

Purpose

Transcatheter arterial chemoembolization (TACE) is commonly used in the treatment of hepatocellular carcinoma (HCC). However, not all patients respond to this treatment. TACE typically leads to hypoxia in the tumor microenvironment. Therefore, we aimed to construct a prognostic model based on hypoxia-related differentially expressed microRNA (miRNAs) in hepatocellular carcinoma (HCC) and to investigate the potential target mRNAs for predicting TACE response.

Methods

The hypoxia-related miRNAs (HRMs) were identified in liver cancer cells, then global test was performed to further select the miRNAs which were associated with recurrence and vascular invasion. A prognostic model was constructed based on multivariate Cox regression analysis; qRT-PCR analysis was used to validate the differentially expressed miRNAs in HCC cell lines under hypoxic condition. We further identified the putative target genes of the miRNAs and investigate the relationship between the target genes and TACE response, immune cells infiltration.

Results

We established a HRMs prognostic model for HCC patients, containing two miRNAs (miR-638, miR-501-5p), the patients with high-HRMs score showed worse survival in discovery and validation cohort; qRT-PCR analysis confirmed that these two miRNAs are up-regulated in hepatoma cells under hypoxic condition. Furthermore, four putative target genes of these two miRNAs were identified (ADH1B, CTH, FTCD, RCL1), which were significantly associated with TACE response, immune score, immunosuppressive immune cells infiltration, PDCD1 and CTLA4.

Conclusion

The HCC-HRMs signature may be utilized as a promising prognostic factor and may have implications for guiding TACE and immune therapy.

Myeloid-derived suppressor cells in cancer and cancer therapy

Anticancer agents continue to dominate the list of newly approved drugs, approximately half of which are immunotherapies. This trend illustrates the considerable promise of cancer treatments that modulate the immune system. However, the immune system is complex and dynamic, and can have both tumour-suppressive and tumour-promoting effects. Understanding the full range of immune modulation in cancer is crucial to identifying more effective treatment strategies. Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of myeloid cells that develop in association with chronic inflammation, which is a hallmark of cancer. Indeed, MDSCs accumulate in the tumour microenvironment, where they strongly inhibit anticancer functions of T cells and natural killer cells and exert a variety of other tumour-promoting effects. Emerging evidence indicates that MDSCs also contribute to resistance to cancer treatments, particularly immunotherapies. Conversely, treatment approaches designed to eliminate cancer cells can have important additional effects on MDSC function, which can be either positive or negative. In this Review, we discuss the interplay between MDSCs and various other cell types found in tumours as well as the mechanisms by which MDSCs promote tumour progression. We also discuss the relevance and implications of MDSCs for cancer therapy.

Effects of extracellular vesicle-derived noncoding RNAs on pre-metastatic niche and tumor progression

A pre-metastatic niche (PMN) is a protective microenvironment that facilitates the colonization of disseminating tumor cells in future metastatic organs. Extracellular vesicles (EVs) play a role in intercellular communication by delivering cargoes, such as noncoding RNAs (ncRNAs). The pivotal role of extracellular vesicle-derived noncoding RNAs (EV-ncRNAs) in the PMN has attracted increasing attention. In this review, we summarized the effects of EV-ncRNAs on the PMN in terms of immunosuppression, vascular permeability and angiogenesis, inflammation, metabolic reprogramming, and fibroblast alterations. In particular, we provided a comprehensive overview of the effects of EV-ncRNAs on the PMN in different cancers. Finally, we discussed the promising clinical applications of EV-ncRNAs, including their potential as diagnostic and prognostic markers and therapeutic targets.

Cellular Context Dictates the Suppression or Augmentation of Triple-Negative Mammary Tumor Metastasis by NLRX1

Prior studies have defined multiple, but inconsistent, roles for the enigmatic pattern recognition receptor NLRX1 in regulating several cancer-associated biological functions. In this study, we explore the role of NLRX1 in the highly metastatic murine 4T1 mammary tumor model. We describe a functional dichotomy of NLRX1 between two different cellular contexts: expression in healthy host cells versus expression in the 4T1 tumor cells. Using Nlrx1-/- mice engrafted with 4T1 tumors, we demonstrate that NLRX1 functions as a tumor suppressor when expressed in the host cells. Specifically, NLRX1 in healthy host cells attenuates tumor growth and lung metastasis through suppressing characteristics of epithelial-mesenchymal transition and the lung metastatic niche. Conversely, we demonstrate that NLRX1 functions as a tumor promoter when expressed in 4T1 tumor cells using gain- and loss-of-function studies both in vitro and in vivo. Mechanistically, NLRX1 in the tumor cells augments 4T1 aggressiveness and metastasis through regulating epithelial-mesenchymal transition hallmarks, cell death, proliferation, migration, reactive oxygen species levels, and mitochondrial respiration. Collectively, we provide critical insight into NLRX1 function and establish a dichotomous role of NLRX1 in the 4T1 murine mammary carcinoma model that is dictated by cellular context.

Chronic psychological stress promotes breast cancer pre-metastatic niche formation by mobilizing splenic MDSCs via TAM/CXCL1 signaling

BACKGROUND

Emerging studies have identified chronic psychological stress as an independent risk factor influencing breast cancer growth and metastasis. However, the effects of chronic psychological stress on pre-metastatic niche (PMN) formation and the underlying immunological mechanisms remain largely unknown.

METHODS

The effects and molecular mechanisms of chronic unpredictable mild stress (CUMS) on modulating tumor-associated macrophages (TAMs) and PMN formation were clarified by multiplex immunofluorescence technique, cytokine array, chromatin immunoprecipitation, the dual-luciferase reporter assay, and breast cancer xenografts. Transwell and CD8⁺ T cytotoxicity detection were used to analyze the mobilization and function of myeloid-derived suppressor cells (MDSCs). mCherry-labeled tracing strategy and bone marrow transplantation were applied to explore the crucial role of splenic CXCR2^+/+ MDSCs facilitating PMN formation under CUMS.

RESULTS

CUMS significantly promoted breast cancer growth and metastasis, accompanied by TAMs accumulation in the microenvironment. CXCL1 was identified as a crucial chemokine in TAMs facilitating PMN formation in a glucocorticoid receptor (GR)-dependent manner. Interestingly, the spleen index was significantly reduced under CUMS, and splenic MDSCs were validated as a key factor mediating CXCL1-induced PMN formation. The molecular mechanism study revealed that TAM-derived CXCL1 enhanced the proliferation, migration, and anti-CD8⁺ T cell functions of MDSCs via CXCR2. Moreover, CXCR2 knockout and CXCR2^-/-MDSCs transplantation significantly impaired CUMS-mediated MDSC elevation, PMN formation, and breast cancer metastasis.

CONCLUSION

Our findings shed new light on the association between chronic psychological stress and splenic MDSC mobilization, and suggest that stress-related glucocorticoid elevation can enhance TAM/CXCL1 signaling and subsequently recruit splenic MDSCs to promote PMN formation via CXCR2.

Physio-metabolic and clinical consequences of wearing face masks—Systematic review with meta-analysis and comprehensive evaluation

Background

As face masks became mandatory in most countries during the COVID-19 pandemic, adverse effects require substantiated investigation.

Methods

A systematic review of 2,168 studies on adverse medical mask effects yielded 54 publications for synthesis and 37 studies for meta-analysis (on n = 8,641, m = 2,482, f = 6,159, age = 34.8 ± 12.5). The median trial duration was only 18 min (IQR = 50) for our comprehensive evaluation of mask induced physio-metabolic and clinical outcomes.

Results

We found significant effects in both medical surgical and N95 masks, with a greater impact of the second. These effects included decreased SpO2 (overall Standard Mean Difference, SMD = −0.24, 95% CI = −0.38 to −0.11, p < 0.001) and minute ventilation (SMD = −0.72, 95% CI = −0.99 to −0.46, p < 0.001), simultaneous increased in blood-CO2 (SMD = +0.64, 95% CI = 0.31–0.96, p < 0.001), heart rate (N95: SMD = +0.22, 95% CI = 0.03–0.41, p = 0.02), systolic blood pressure (surgical: SMD = +0.21, 95% CI = 0.03–0.39, p = 0.02), skin temperature (overall SMD = +0.80 95% CI = 0.23–1.38, p = 0.006) and humidity (SMD +2.24, 95% CI = 1.32–3.17, p < 0.001). Effects on exertion (overall SMD = +0.9, surgical = +0.63, N95 = +1.19), discomfort (SMD = +1.16), dyspnoea (SMD = +1.46), heat (SMD = +0.70), and humidity (SMD = +0.9) were significant in n = 373 with a robust relationship to mask wearing (p < 0.006 to p < 0.001). Pooled symptom prevalence (n = 8,128) was significant for: headache (62%, p < 0.001), acne (38%, p < 0.001), skin irritation (36%, p < 0.001), dyspnoea (33%, p < 0.001), heat (26%, p < 0.001), itching (26%, p < 0.001), voice disorder (23%, p < 0.03), and dizziness (5%, p = 0.01).

Discussion

Masks interfered with O2-uptake and CO2-release and compromised respiratory compensation. Though evaluated wearing durations are shorter than daily/prolonged use, outcomes independently validate mask-induced exhaustion-syndrome (MIES) and down-stream physio-metabolic disfunctions. MIES can have long-term clinical consequences, especially for vulnerable groups. So far, several mask related symptoms may have been misinterpreted as long COVID-19 symptoms. In any case, the possible MIES contrasts with the WHO definition of health.

Conclusion

Face mask side-effects must be assessed (risk-benefit) against the available evidence of their effectiveness against viral transmissions. In the absence of strong empirical evidence of effectiveness, mask wearing should not be mandated let alone enforced by law.

Systematic review registration

https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42021256694, identifier: PROSPERO 2021 CRD42021256694.

The Combination of Immune Checkpoint Blockade with Tumor Vessel Normalization as a Promising Therapeutic Strategy for Breast Cancer: An Overview of Preclinical and Clinical Studies

Immune checkpoint inhibitors (ICIs) have a modest clinical activity when administered as monotherapy against breast cancer (BC), the most common malignancy in women. Novel combinatorial strategies are currently being investigated to overcome resistance to ICIs and promote antitumor immune responses in a greater proportion of BC patients. Recent studies have shown that the BC abnormal vasculature is associated with immune suppression in patients, and hampers both drug delivery and immune effector cell trafficking to tumor nests. Thus, strategies directed at normalizing (i.e., at remodeling and stabilizing) the immature, abnormal tumor vessels are receiving much attention. In particular, the combination of ICIs with tumor vessel normalizing agents is thought to hold great promise for the treatment of BC patients. Indeed, a compelling body of evidence indicates that the addition of low doses of antiangiogenic drugs to ICIs substantially improves antitumor immunity. In this review, we outline the impact that the reciprocal interactions occurring between tumor angiogenesis and immune cells have on the immune evasion and clinical progression of BC. In addition, we overview preclinical and clinical studies that are presently evaluating the therapeutic effectiveness of combining ICIs with antiangiogenic drugs in BC patients.

Pre-metastatic niche: from revealing the molecular and cellular mechanisms to the clinical applications in breast cancer metastasis

Breast cancer (BC) is one of the most commonly diagnosed cancers and the leading cause of cancer-related deaths in women worldwide. Metastasis is a major contributor to high cancer mortality and is usually the endpoint of a series of sequential and dynamic events. One of the critical events is forming a pre-metastatic niche (PMN) that occurs before macroscopic tumor cell invasion and provides a suitable environment for tumor cells to colonize and progress into metastases. Due to the unique characteristics of PMN in cancer metastasis, developing therapies to target PMN may bring new advantages in preventing cancer metastasis at an early stage. Various biological molecules, cells, and signaling pathways are altered in BC, regulating the functions of distinctive immune cells and stromal remodeling, inducing angiogenesis, and effect metabolic reprogramming and organotropism to promote PMN formation. In this review, we elucidate the multifaceted mechanisms contributing to the development of PMN in BC, discuss the characteristics of PMN, and highlight the significance of PMN in providing potential diagnostic and therapeutic strategies for BC metastasis, which may bring promising insights and foundations for future studies.

Saga of monokines in shaping tumour-immune microenvironment: Origin to execution

Cellular communication mediated by cytokines is an important mechanism dictating immune responses, their cross talk and final immune output. Cytokines play a major role in dictating the immune outcome to cancer by regulating the events of development, differentiation and activation of innate immune cells. Cytokines are pleiotropic in nature, hence understanding their role individually or as member of network cytokines is critical to delineate their role in tumour immunity. Tumour systemically manipulates the immune system to evade and escape immune recognition for their uncontrollable growth and metastasis. The developing tumour comprise a large and diverse set of myeloid cells which are vulnerable to manipulation by the tumour-microenvironment. The innate immune cells of the monocytic lineage skew the fate of the adaptive immune cells and thus dictating cancer elimination or progression. Targeting cells at tumour cite is preposterous owing to their tight network, poor reach and abundance of immunosuppressive mechanisms. Monocytic lineage-derived cytokines (monokines) play crucial role in tumour regression or progression by either directly killing the tumour cells with TNFα or promoting its growth by TGFβ. In addition, the monokines like IL-12, IL-1β, IL-6, IL-10 and TGFβ direct the adaptive immune cells to secrete anti-tumour cytokines, TNFα, IFNγ, perforin and granzyme or pro-tumour cytokines, IL-10 and TGFβ. In this review, we elucidate the roles of monokines in dictating the fate of tumour by regulating responses at various stages of generation, differentiation and activation of immune cells along with the extensive cross talk. We have attempted to delineate the synergy and antagonism of major monokines among themselves or with tumour-derived or adaptive immune cytokines. The review provides an update on the possibilities of placing monokines to potential practical use as cytokine therapy against cancer.

Activation of Host-NLRP3 Inflammasome in Myeloid Cells Dictates Response to Anti-PD-1 Therapy in Metastatic Breast Cancers

Tumor-associated inflammation leads to dysregulated cytokine production that promotes tumor immune evasion and anti-tumor immunity dysfunction. In advanced stage breast cancer, the proinflammatory cytokine IL-1β is overexpressed due to large proportions of activated myeloid cells in the tumor microenvironment (TME). Here, we demonstrate the role of the host nucleotide-binding domain, leucine-rich containing family, pyrin domain-containing 3 (NLRP3) inflammasome in metastatic breast cancer. In vitro, we show that stimulation of THP-1 cells with conditioned media collected from MDA-MB-468 cells induced NLRP3 activation and increased Pdcd1l1 expression. In vivo, mice deficient in NLRP3 orthotopically implanted with metastatic breast cancer cell line (E0771) showed significant reduction in tumor growth (p < 0.05) and increased survival (p < 0.01). Inhibition of NLRP3 with the small molecule OLT1177® reduced expression of Pdcd1l1 (p < 0.001), Casp1 (p < 0.01) and Il1b (p < 0.01) in primary tumors. Furthermore, tumor-bearing mice receiving OLT1177® showed reduced infiltration of myeloid-derived suppressor cells (MDSCs) (p < 0.001) and increased CD8+ T cells (p < 0.05) and NK cells (p < 0.05) in the TME. NLRP3 inhibition in addition to anti-PD-1 treatment significantly reduced tumor growth from the monotherapies (p < 0.05). These data define NLRP3 activation as a key driver of immune suppression in metastatic breast cancers. Furthermore, this study suggests NLRP3 as a valid target to increase efficacy of immunotherapy with checkpoint inhibitor in metastatic breast cancers.

Myeloid-Derived Suppressor Cells: A Multifaceted Accomplice in Tumor Progression

Myeloid-derived suppressor cell (MDSC) is a heterogeneous population of immature myeloid cells, has a pivotal role in negatively regulating immune response, promoting tumor progression, creating pre-metastases niche, and weakening immunotherapy efficacy. The underlying mechanisms are complex and diverse, including immunosuppressive functions (such as inhibition of cytotoxic T cells and recruitment of regulatory T cells) and non-immunological functions (mediating stemness and promoting angiogenesis). Moreover, MDSC may predict therapeutic response as a poor prognosis biomarker among multiple tumors. Accumulating evidence indicates targeting MDSC can reverse immunosuppressive tumor microenvironment, and improve therapeutic response either single or combination with immunotherapy. This review summarizes the phenotype and definite mechanisms of MDSCs in tumor progression, and provide new insights of targeting strategies regarding to their clinical applications.

Cancer-cell-intrinsic mechanisms regulate MDSCs through cytokine networks

Immunotherapy has shifted the paradigm of cancer treatment. However, the majority of cancer patients display de novo or acquired resistance to immunotherapy. One of the main mechanisms of immunotherapy resistance is the immunosuppressive microenvironment dominated by the myeloid-derived suppressor cells (MDSCs). Emerging evidence demonstrates that genetic or epigenetic aberrations in cancer cells shape the accumulation and activation of MDSCs. Understanding this genotype-immunophenotype relationship is critical to the rational design of combination immunotherapy. Here, we review the mechanisms of how molecular changes in cancer cells induce recruitment and reprogram the function of tumor-infiltrating myeloid cells, particularly MDSCs. Tumor-infiltrating MDSCs elicit various pro-tumor functions to promote tumor cell fitness, immune evasion, angiogenesis, tissue remodeling, and metastasis. Through understanding the genotype-immunophenotype relationship between neoplastic cells and MDSCs, new approaches can be developed to tailor current immunotherapy strategies to improve cancer patient outcomes.

Selectively targeting myeloid-derived suppressor cells through TRAIL receptor 2 to enhance the efficacy of CAR T cell therapy for treatment of breast cancer

BACKGROUND

Successful targeting of solid tumors such as breast cancer (BC) using chimeric antigen receptor (CAR) T cells has proven challenging, largely attributed to the immunosuppressive tumor microenvironment (TME). Myeloid-derived suppressor cells (MDSCs) inhibit CAR T cell function and persistence within the breast TME. To overcome this challenge, we have developed CAR T cells targeting tumor-associated mucin 1 (MUC1) with a novel chimeric costimulatory receptor that targets tumor necrosis factor-related apoptosis-inducing ligand receptor 2 (TR2) expressed on MDSCs.

METHODS

The function of the TR2.41BB costimulatory receptor was assessed by exposing non-transduced (NT) and TR2.41BB transduced T cells to recombinant TR2, after which nuclear translocation of NFκB was measured by ELISA and western blot. The cytolytic activity of CAR.MUC1/TR2.41BB T cells was measured in a 5-hour cytotoxicity assay using MUC1+ tumor cells as targets in the presence or absence of MDSCs. In vivo antitumor activity was assessed using MDSC-enriched tumor-bearing mice treated with CAR T cells with or without TR2.41BB.

RESULTS

Nuclear translocation of NFκB in response to recombinant TR2 was detected only in TR2.41BB T cells. The presence of MDSCs diminished the cytotoxic potential of CAR.MUC1 T cells against MUC1+ BC cell lines by 25%. However, TR2.41BB expression on CAR.MUC1 T cells induced MDSC apoptosis, thereby restoring the cytotoxic activity of CAR.MUC1 T cells against MUC1+ BC lines. The presence of MDSCs resulted in an approximately twofold increase in tumor growth due to enhanced angiogenesis and fibroblast accumulation compared with mice with tumor alone. Treatment of these MDSC-enriched tumors with CAR.MUC1.TR2.41BB T cells led to superior tumor cell killing and significant reduction in tumor growth (24.54±8.55 mm³) compared with CAR.MUC1 (469.79±81.46 mm³) or TR2.41BB (434.86±64.25 mm³) T cells alone. CAR.MUC1.TR2.41BB T cells also demonstrated improved T cell proliferation and persistence at the tumor site, thereby preventing metastases. We observed similar results using CAR.HER2.TR2.41BB T cells in a HER2+ BC model.

CONCLUSIONS

Our findings demonstrate that CAR T cells that coexpress the TR2.4-1BB receptor exhibit superior antitumor potential against breast tumors containing immunosuppressive and tumor promoting MDSCs, resulting in TME remodeling and improved T cell proliferation at the tumor site.

Cross-Talk between Oxidative Stress and m6A RNA Methylation in Cancer

Oxidative stress is a state of imbalance between oxidation and antioxidation. Excessive ROS levels are an important factor in tumor development. Damage stimulation and excessive activation of oncogenes cause elevated ROS production in cancer, accompanied by an increase in the antioxidant capacity to retain redox homeostasis in tumor cells at an increased level. Although moderate concentrations of ROS produced in cancer cells contribute to maintaining cell survival and cancer progression, massive ROS accumulation can exert toxicity, leading to cancer cell death. RNA modification is a posttranscriptional control mechanism that regulates gene expression and RNA metabolism, and m⁶A RNA methylation is the most common type of RNA modification in eukaryotes. m⁶A modifications can modulate cellular ROS levels through different mechanisms. It is worth noting that ROS signaling also plays a regulatory role in m⁶A modifications. In this review, we concluded the effects of m⁶A modification and oxidative stress on tumor biological functions. In particular, we discuss the interplay between oxidative stress and m⁶A modifications.

Reversing Hypoxia with PLGA-Encapsulated Manganese Dioxide Nanoparticles Improves Natural Killer Cell Response to Tumor Spheroids

The adoptive transfer of natural killer (NK) cells, which can recognize and obliterate cancer cells, provides a practical alternative to current treatment modalities to improve cancer patients' survival. However, translating NK cell therapies to treat solid tumors has proven challenging due to the tumor microenvironment (TME). Hypoxia in the TME induces immunosuppression that inhibits the cytotoxic function of NK cells. Thus, reversing hypoxia-induced immunosuppression is critical for effective adoptive NK cell immunotherapy. In this study, we use manganese dioxide nanoparticles (MnO₂ NPs) to catalyze the degradation of tumor-produced hydrogen peroxide, thereby generating oxygen. For improved biocompatibility and modulation of oxygen production, the MnO₂ NPs were encapsulated into poly(lactic-co-glycolic) to produce particles that are 116 nm in size and with a ζ-potential of +17 mV (PLGA-MnO₂ NPs). The PLGA-MnO₂ NPs showed first-order oxygen production and sustained high oxygen tension compared to equivalent amounts of bare MnO₂ NPs in the presence of H₂O₂. The PLGA-MnO₂ NPs were biocompatible, reduced hypoxia after penetration into the core of cancer spheroids, and decreased hypoxia-induced factor 1 α expression. Reducing hypoxia in the spheroid resulted in a decrease in the potent immunosuppressors, adenosine, and lactate, which was confirmed by electrospray ionization mass spectroscopy (ESI-MS). ESI-MS also showed a change in the metabolism of the amino acids aspartate, glutamine, and glutamate after hypoxia reduction in the cancer cells. Notably, the spheroids' microenvironment changes enhanced NK cells' cytotoxicity, which obliterated the spheroids. These results demonstrate that reducing hypoxia-induced immunosuppression in tumors is a potent strategy to increase the potency of cytotoxic immune cells in the TME. The developed NPs are promising new tools to improve adoptive NK cell therapy.

MDSCs interactions with other immune cells and their role in maternal-fetal tolerance

MDSCs (myeloid-derived suppressor cells) are a population of immature and heterogeneous bone marrow cells with immunosuppressive functions, and they are mainly divided into two subgroups: granulocytic MDSCs (G-MDSCs) and monocytic MDSCs (M-MDSCs). Immunosuppression is the main and most important function of MDSCs, and they mainly exert an inhibitory effect through endoplasmic reticulum stress and some enzymes related to inhibitors, as well as some cytokines and other factors. In addition, MDSCs also interact with other immune cells, especially NK cells, DCs and Tregs, to participate in immune regulation. A large number of MDSCs are found during normal pregnancy. Combined with their immunosuppressive effects, these results suggest that MDSCs are likely to be closely related to maternal-fetal immune tolerance. This review mainly shows the interaction of MDSCs with other immune cells and the important role of MDSCs in maternal-fetal tolerance. The current research shows that MDSCs are mainly mediated by STAT3, HLA-G, CXCR2, Arg-1 and HIF1-α in immune regulation during pregnancy. Interpreting maternal-fetal tolerance from the perspective of MDSCs provides a special perspective for research on immune regulation and maternal-fetal tolerance of MDSCs to obtain a more comprehensive understanding of immune regulation and immune tolerance.

Pharmacological inhibition of MDA-9/Syntenin blocks breast cancer metastasis through suppression of IL-1β

Melanoma differentiation associated gene-9 (MDA-9), Syntenin-1, or syndecan binding protein is a differentially regulated prometastatic gene with elevated expression in advanced stages of melanoma. MDA-9/Syntenin expression positively associates with advanced disease stage in multiple histologically distinct cancers and negatively correlates with patient survival and response to chemotherapy. MDA-9/Syntenin is a highly conserved PDZ-domain scaffold protein, robustly expressed in a spectrum of diverse cancer cell lines and clinical samples. PDZ domains interact with a number of proteins, many of which are critical regulators of signaling cascades in cancer. Knockdown of MDA-9/Syntenin decreases cancer cell metastasis, sensitizing these cells to radiation. Genetic silencing of MDA-9/Syntenin or treatment with a pharmacological inhibitor of the PDZ1 domain, PDZ1i, also activates the immune system to kill cancer cells. Additionally, suppression of MDA-9/Syntenin deregulates myeloid-derived suppressor cell differentiation via the STAT3/interleukin (IL)-1β pathway, which concomitantly promotes activation of cytotoxic T lymphocytes. Biologically, PDZ1i treatment decreases metastatic nodule formation in the lungs, resulting in significantly fewer invasive cancer cells. In summary, our observations indicate that MDA-9/Syntenin provides a direct therapeutic target for mitigating aggressive breast cancer and a small-molecule inhibitor, PDZ1i, provides a promising reagent for inhibiting advanced breast cancer pathogenesis.

The role of myeloid-derived suppressor cells in gastrointestinal cancer

Gastrointestinal (GI) cancer encompasses a range of malignancies that originate in the digestive system, which together represent the most common form of cancer diagnosed worldwide. However, despite numerous advances in both diagnostics and treatment, the incidence and mortality rate of GI cancer are on the rise. Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of immature myeloid cells that increase in number under certain pathological conditions, such as infection and inflammation, and this expansion is of particular relevance to cancer. MDSCs are heavily involved in the regulation of the immune system and act to dampen its response to tumors, favoring the escape of tumor cells from immunosurveillance and increasing both metastasis and recurrence. Several recent studies have supported the use of MDSCs as a prognostic and predictive biomarker in patients with cancer, and potentially as a novel treatment target. In the present review, the mechanisms underlying the immunosuppressive functions of MDSCs are described, and recent researches concerning the involvement of MDSCs in the progression, prognosis, and therapies of GI cancer are reviewed. The aim of this work was to present the development of novel treatments targeting MDSCs in GI cancer in the hope of improving outcomes for patients with this condition.

Asah2 Represses the p53-Hmox1 Axis to Protect Myeloid-Derived Suppressor Cells from Ferroptosis

Myeloid-derived suppressor cells (MDSCs) are immune suppressive cells that massively accumulate under pathological conditions to suppress T cell immune response. Dysregulated cell death contributes to MDSC accumulation, but the molecular mechanism underlying this cell death dysregulation is not fully understood. In this study, we report that neutral ceramidase (N-acylsphingosine amidohydrolase [ASAH2]) is highly expressed in tumor-infiltrating MDSCs in colon carcinoma and acts as an MDSC survival factor. To target ASAH2, we performed molecular docking based on human ASAH2 protein structure. Enzymatic inhibition analysis of identified hits determined NC06 as an ASAH2 inhibitor. Chemical and nuclear magnetic resonance analysis determined NC06 as 7-chloro-2-(3-chloroanilino)pyrano[3,4-e][1,3]oxazine-4,5-dione. NC06 inhibits ceramidase activity with an IC₅₀ of 10.16-25.91 μM for human ASAH2 and 18.6-30.2 μM for mouse Asah2 proteins. NC06 induces MDSC death in a dose-dependent manner, and inhibition of ferroptosis decreased NC06-induced MDSC death. NC06 increases glutathione synthesis and decreases lipid reactive oxygen species to suppress ferroptosis in MDSCs. Gene expression profiling identified the p53 pathway as the Asah2 target in MDSCs. Inhibition of Asah2 increased p53 protein stability to upregulate Hmox1 expression to suppress lipid reactive oxygen species production to suppress ferroptosis in MDSCs. NC06 therapy increases MDSC death and reduces MDSC accumulation in tumor-bearing mice, resulting in increased activation of tumor-infiltrating CTLs and suppression of tumor growth in vivo. Our data indicate that ASAH2 protects MDSCs from ferroptosis through destabilizing p53 protein to suppress the p53 pathway in MDSCs in the tumor microenvironment. Targeting ASAH2 with NC06 to induce MDSC ferroptosis is potentially an effective therapy to suppress MDSC accumulation in cancer immunotherapy.

Hypoxic exosomes orchestrate tumorigenesis: molecular mechanisms and therapeutic implications

The solid tumor microenvironment possesses a hypoxic condition, which promotes aggressiveness and resistance to therapies. Hypoxic tumor cells undergo broadly metabolic and molecular adaptations and communicate with surrounding cells to provide conditions promising for their homeostasis and metastasis. Extracellular vesicles such as exosomes originating from the endosomal pathway carry different types of biomolecules such as nucleic acids, proteins, and lipids; participate in cell-to-cell communication. The exposure of cancer cells to hypoxic conditions, not only, increases exosomes biogenesis and secretion but also alters exosomes cargo. Under the hypoxic condition, different signaling pathways such as HIFs, Rab-GTPases, NF-κB, and tetraspanin are involved in the exosomes biogenesis. Hypoxic tumor cells release exosomes that induce tumorigenesis through promoting metastasis, angiogenesis, and modulating immune responses. Exosomes from hypoxic tumor cells hold great potential for clinical application and cancer diagnosis. Besides, targeting the biogenesis of these exosomes may be a therapeutic opportunity for reducing tumorigenesis. Exosomes can serve as a drug delivery system transferring therapeutic compounds to cancer cells. Understanding the detailed mechanisms involved in biogenesis and functions of exosomes under hypoxic conditions may help to develop effective therapies against cancer.

Reductive Stress, Bioactive Compounds, Redox-Active Metals, and Dormant Tumor Cell Biology to Develop Redox-Based Tools for the Treatment of Cancer

Significance: Cancer is related to redox biology from many points of view, such as initiation and promotion, metabolism and growth, invasion and metastasis, vascularization, or through the interaction with the immune system. In addition, this extremely complex relationship depends on the redox homeostasis of each cellular compartment, which might be used to fight cancer. Recent Advances: New ways of modulating specific and little explored aspects of redox biology have been revealed, as well as new delivery methods or uses of previously known treatments against cancer. Here, we review the latest experimental evidence regarding redox biology in cancer treatment and analyze its potential impact in the development of improved and more effective antineoplastic therapies. Critical Issues: A critical issue that deserves particular attention is the understanding that both extremes of redox biology (i.e., oxidative stress [OS] and reductive stress) might be useful or harmful in relation to cancer prevention and treatment. Future Directions: Additional research is needed to understand how to selectively induce reductive or OS adequately to avoid cancer proliferation or to induce cancer cell death.

The Roles of ceRNAs-Mediated Autophagy in Cancer Chemoresistance and Metastasis

Simple Summary

Chemoresistance and metastasis are the main causes of treatment failure in cancers. Autophagy contribute to the survival and metastasis of cancer cells. Competing endogenous RNA (ceRNA), particularly long non-coding RNAs and circular RNA (circRNA), can bridge the interplay between autophagy and chemoresistance or metastasis in cancers via sponging miRNAs. This review aims to discuss on the function of ceRNA-mediated autophagy in the process of metastasis and chemoresistance in cancers. ceRNA network can sequester the targeted miRNA expression to indirectly upregulate the expression of autophagy-related genes, and thereof participate in autophagy-mediated chemoresistance and metastasis. Our clarification of the mechanism of autophagy regulation in metastasis and chemoresistance may greatly improve the efficacy of chemotherapy and survival in cancer patients. The combination of the tissue-specific miRNA delivery and selective autophagy inhibitors, such as hydroxychloroquine, is attractive to treat cancer patients in the future.

Abstract

Chemoresistance and metastasis are the main causes of treatment failure and unfavorable outcome in cancers. There is a pressing need to reveal their mechanisms and to discover novel therapy targets. Autophagy is composed of a cascade of steps controlled by different autophagy-related genes (ATGs). Accumulating evidence suggests that dysregulated autophagy contributes to chemoresistance and metastasis via competing endogenous RNA (ceRNA) networks including lncRNAs and circRNAs. ceRNAs sequester the targeted miRNA expression to indirectly upregulate ATGs expression, and thereof participate in autophagy-mediated chemoresistance and metastasis. Here, we attempt to summarize the roles of ceRNAs in cancer chemoresistance and metastasis through autophagy regulation.

Suppressive myeloid cells are expanded by biliary tract cancer-derived cytokines in vitro and associate with aggressive disease

Background

BTC is an aggressive disease exacerbated by inflammation and immune suppression. Expansion of immunosuppressive cells occurs in biliary tract cancer (BTC), yet the role of BTC-derived cytokines in this process is unclear.

Methods

Activated signalling pathways and cytokine production were evaluated in a panel of human BTC cell lines. Human peripheral blood mononuclear cells (PBMCs) were cultured with BTC supernatants, with and without cytokine neutralising antibodies, and analysed by flow cytometry or immunoblot. A human BTC tissue microarray (TMA, n = 69) was stained for IL-6, GM-CSF, and CD33⁺S100a9⁺ cells and correlated with clinical outcomes.

Results

Immunomodulatory factors (IL-6, GM-CSF, MCP-1) were present in BTC supernatants. BTC supernatants expanded CD33^dimCD11b⁺HLA-DR^low/− myeloid-derived suppressor cells (MDSCs) from human PBMCs. Neutralisation of IL-6 and GM-CSF in BTC supernatants inhibited activation of STAT3/5, respectively, in PBMCs, with heterogeneous effects on MDSC expansion in vitro. Staining of a BTC TMA revealed a positive correlation between IL-6 and GM-CSF, with each cytokine and more CD33⁺S100a9⁺ cells. Increased CD33⁺S100a9⁺ staining positively correlated with higher tumour grade, differentiation and the presence of satellite lesions.

Conclusion

BTC-derived factors promote suppressive myeloid cell expansion, and higher numbers of CD33⁺S100a9⁺ cells in resectable BTC tumours correlates with more aggressive disease.

Role of Tumor-Associated Myeloid Cells in Breast Cancer

Stromal immune cells constitute the tumor microenvironment. These immune cell subsets include myeloid cells, the so-called tumor-associated myeloid cells (TAMCs), which are of two types: tumor-associated macrophages (TAMs) and myeloid-derived suppressor cells (MDSCs). Breast tumors, particularly those in human epidermal growth factor receptor 2 (HER-2)-positive breast cancer and triple-negative breast cancer, are solid tumors containing immune cell stroma. TAMCs drive breast cancer progression via immune mediated, nonimmune-mediated, and metabolic interactions, thus serving as a potential therapeutic target for breast cancer. TAMC-associated breast cancer treatment approaches potentially involve the inhibition of TAM recruitment, modulation of TAM polarization/differentiation, reduction of TAM products, elimination of MDSCs, and reduction of MDSC products. Furthermore, TAMCs can enhance or restore immune responses during cancer immunotherapy. This review describes the role of TAMs and MDSCs in breast cancer and elucidates the clinical implications of TAMs and MDSCs as potential targets for breast cancer treatment.

The Engagement Between MDSCs and Metastases: Partners in Crime

Tumor metastases represent the major cause of cancer-related mortality, confirming the urgent need to identify key molecular pathways and cell-associated networks during the early phases of the metastatic process to develop new strategies to either prevent or control distal cancer spread. Several data revealed the ability of cancer cells to establish a favorable microenvironment, before their arrival in distant organs, by manipulating the cell composition and function of the new host tissue where cancer cells can survive and outgrow. This predetermined environment is termed “pre-metastatic niche” (pMN). pMN development requires that tumor-derived soluble factors, like cytokines, growth-factors and extracellular vesicles, genetically and epigenetically re-program not only resident cells (i.e., fibroblasts) but also non-resident cells such as bone marrow-derived cells. Indeed, by promoting an “emergency” myelopoiesis, cancer cells switch the steady state production of blood cells toward the generation of pro-tumor circulating myeloid cells defined as myeloid-derived suppressor cells (MDSCs) able to sustain tumor growth and dissemination. MDSCs are a heterogeneous subset of myeloid cells with immunosuppressive properties that sustain metastatic process. In this review, we discuss current understandings of how MDSCs shape and promote metastatic dissemination acting in each fundamental steps of cancer progression from primary tumor to metastatic disease.

BMP9 signaling promotes the normalization of tumor blood vessels

The presence of an immature tumor vascular network contributes to cancer dissemination and the development of resistance to therapies. Strategies to normalize the tumor vasculature are therefore of significant therapeutic interest for cancer treatments. VEGF inhibitors are used clinically to normalize tumor blood vessels. However, the time frame and dosage of these inhibitors required to achieve normalization is rather narrow, and there is a need to identify additional signaling targets to attain vascular normalization. In addition to VEGF, the endothelial-specific receptor Alk1 plays a critical role in vascular development and promotes vascular remodeling and maturation. Therefore, we sought to evaluate the effects of the Alk1 ligand BMP9 on tumor vascular formation. BMP9 overexpression in Lewis Lung Carcinoma (LLC) tumors significantly delayed tumor growth. Blood vessels in BMP9-overexpressing LLC tumors displayed markers of vascular maturation and were characterized by increased perivascular cell coverage. Tumor vasculature normalization was associated with decreased permeability and increased perfusion. These changes in vascular function in BMP9-overexpressing LLC tumors resulted in significant alterations of the tumor microenvironment, characterized by a decrease in hypoxia and an increase in immune infiltration. In conclusion, we show that BMP9 promotes vascular normalization in LLC tumors that leads to changes in the microenvironment.

Comparative gene expression analysis in melanocytes driven by tumor cell-derived exosomes

Abundant with organelle-like membranous structures, the tumor microenvironment is composed of cancer cells that secrete exosomes. Studies have shown that these secreted exosomes transport RNA and active molecules to other cells to reshape the tumor microenvironment and promote tumor growth. In fact, we found that exosomes derived from melanoma cells drive pre-malignant transition in primary melanocytes. However, there is little available in the scientific literature on how exosomes modulate melanocytes in the microenvironment to optimize conditions for tumor progression and metastasis. We therefore focused this current study on identifying these conditions genetically. Through RNA sequencing, we analyzed gene expression levels of melanocytes driven by exosomes derived from melanoma and lung cancer cells compared with those without exosome controls. Significant differences were found in gene expression patterns of melanocytes driven by exosomes derived from melanoma and lung cancer cells. In the melanocytes responding to exosomes derived from melanoma cells, genes of lipopolysaccharide and regulation of leukocyte chemotaxis were predominant. In the melanocytes responding to exosomes derived from lung cancer cells, genes of DNA replication and mitotic nuclear division played an important role. These results provide further mechanistic understanding of tumor progression promoted by tumor-derived exosomes. This will also help identify potential therapeutic targets for melanoma progression.

Role of tumor-derived exosomes in bone metastasis

Tight coupling between bone resorption and formation is essential for bone remodeling. Disruption of this equilibrium can lead to skeletal disorders. Osseous metastatic disease is a severe consequence of tumor cell dissemination from numerous primary cancer sites, including the prostate, lungs and breasts. Metastatic disease is one of the most common causes of mortality in patients with cancer. Rapid advances in the therapeutic options for bone disease, including the use of bisphosphonates, have achieved effective clinical effects. However, the overall survival time of patients with bone metastatic has not significantly improved. Exosomes, which originate from tumor tissue and preferentially the bone, provide a reasonable way to understand the mechanism of neoplastic bone metastasis. Recently, several studies have indicated that tumor-derived exosomes are involved in cancer progression. However, the potential role that exosomes serve in the pathological communication between tumor and bone cells within the skeletal microenvironment remains an emerging field. The present review reports some recent findings on the detrimental roles of exosomes in bone metastasis. In addition, since exosomes are involved in metabolic organ cross-talk, this review highlights the involvement of cancer-derived exosomes in the regulation of skeletal metastatic diseases. Lastly, the potential promising clinical applications and emerging therapeutic opportunities targeting exosomes are discussed as novel strategies for cancer therapy.

Elevated level of mitochondrial reactive oxygen species via fatty acid β-oxidation in cancer stem cells promotes cancer metastasis by inducing epithelial-mesenchymal transition

Background

Cancer stem cells (CSCs) play a critical role in tumor development and progression and are involved in cancer metastasis. The role of reactive oxygen species (ROS) in CSCs and cancer metastasis remains controversial. The aim of the present study was to investigate the correlation between ROS level of CSCs and cancer metastasis and to explore the possible underlying molecular mechanisms.

Methods

Four different cell lines were used to isolate tumor spheres and to analyze intrinsic properties of tumor sphere cells including proliferation, self-renewal potential, differentiation, drug-resistance and cancer metastasis in vitro and in vivo. ROS assays were used to detect the intracellular ROS level of tumor spheres cells. Gene expression analysis and western blot were used to investigate the underlying mechanisms of ROS in regulating cancer metastasis.

Results

Tumor spheres possessed the characteristic features of CSCs, and ROS-high tumor spheres (RH-TS) displayed elevated mitochondrial ROS level exclusively drove metastasis formation. The gene expression analysis showed elevated fatty acid β-oxidation, downregulation of epithelial marker upregulation of mesenchymal markers, and the activation of MAP kinase cascades. Furthermore, 14 up-regulated genes in RH-TS cells were associated with reduced overall survival of different cancer patients.

Conclusions

Our findings demonstrate that CSCs characterized by elevated mitochondrial ROS level potentiate cancer metastasis. Mechanistically, elevated mitochondrial ROS via fatty acid β-oxidation, activates the MAPK cascades, resulting in the epithelial-mesenchymal transition (EMT) process of RH-TS cells, thereby potentiating caner invasion and metastasis. Therefore, targeting mitochondrial ROS might provide a promising approach to prevent and alleviate cancer metastasis induced by RH-TS cells.

Electronic supplementary material

The online version of this article (10.1186/s13287-019-1265-2) contains supplementary material, which is available to authorized users.

Epithelial-Mesenchymal Plasticity in Organotropism Metastasis and Tumor Immune Escape

Most cancer deaths are due to metastasis, and almost all cancers have their preferential metastatic organs, known as “organotropism metastasis”. Epithelial-mesenchymal plasticity has been described as heterogeneous and dynamic cellular differentiation states, supported by emerging experimental evidence from both molecular and morphological levels. Many molecular factors regulating epithelial-mesenchymal plasticity have tissue-specific and non-redundant properties. Reciprocally, cellular epithelial-mesenchymal plasticity contributes to shaping organ-specific pre-metastatic niche (PMN) including distinct local immune landscapes, mainly through secreted bioactive molecular factors. Here, we summarize recent progress on the involvement of tumor epithelial-mesenchymal plasticity in driving organotropic metastasis and regulating the function of different immune cells in organ-specific metastasis.

Reactive oxygen species: a volatile driver of field cancerization and metastasis

Field cancerization and metastasis are the leading causes for cancer recurrence and mortality in cancer patients. The formation of primary, secondary tumors or metastasis is greatly influenced by multifaceted tumor-stroma interactions, in which stromal components of the tumor microenvironment (TME) can affect the behavior of the cancer cells. Many studies have identified cytokines and growth factors as cell signaling molecules that aid cell to cell communication. However, the functional contribution of reactive oxygen species (ROS), a family of volatile chemicals, as communication molecules are less understood. Cancer cells and various tumor-associated stromal cells produce and secrete a copious amount of ROS into the TME. Intracellular ROS modulate cell signaling cascades that aid in the acquisition of several hallmarks of cancers. Extracellular ROS help to propagate, amplify, and effectively create a mutagenic and oncogenic field which facilitate the formation of multifoci tumors and act as a springboard for metastatic tumor cells. In this review, we summarize our current knowledge of ROS as atypical paracrine signaling molecules for field cancerization and metastasis. Field cancerization and metastasis are often discussed separately; we offer a model that placed these events with ROS as the focal instigating agent in a broader "seed-soil" hypothesis.

Rationale for Combining Radiotherapy and Immune Checkpoint Inhibition for Patients With Hypoxic Tumors

In order to compensate for the increased oxygen consumption in growing tumors, tumors need angiogenesis and vasculogenesis to increase the supply. Insufficiency in this process or in the microcirculation leads to hypoxic tumor areas with a significantly reduced pO2, which in turn leads to alterations in the biology of cancer cells as well as in the tumor microenvironment. Cancer cells develop more aggressive phenotypes, stem cell features and are more prone to metastasis formation and migration. In addition, intratumoral hypoxia confers therapy resistance, specifically radioresistance. Reactive oxygen species are crucial in fixing DNA breaks after ionizing radiation. Thus, hypoxic tumor cells show a two- to threefold increase in radioresistance. The microenvironment is enriched with chemokines (e.g., SDF-1) and growth factors (e.g., TGFβ) additionally reducing radiosensitivity. During recent years hypoxia has also been identified as a major factor for immune suppression in the tumor microenvironment. Hypoxic tumors show increased numbers of myeloid derived suppressor cells (MDSCs) as well as regulatory T cells (Tregs) and decreased infiltration and activation of cytotoxic T cells. The combination of radiotherapy with immune checkpoint inhibition is on the rise in the treatment of metastatic cancer patients, but is also tested in multiple curative treatment settings. There is a strong rationale for synergistic effects, such as increased T cell infiltration in irradiated tumors and mitigation of radiation-induced immunosuppressive mechanisms such as PD-L1 upregulation by immune checkpoint inhibition. Given the worse prognosis of patients with hypoxic tumors due to local therapy resistance but also increased rate of distant metastases and the strong immune suppression induced by hypoxia, we hypothesize that the subgroup of patients with hypoxic tumors might be of special interest for combining immune checkpoint inhibition with radiotherapy.

CXCL17-derived CD11b+Gr-1+ myeloid-derived suppressor cells contribute to lung metastasis of breast cancer through platelet-derived growth factor-BB

Background

Metastasis is the major cause of death from breast cancer. Colonization and adaption of metastatic cells in distant organs is a rate-limiting step of the cancer spreading. The underlying mechanisms responsible for the colonization of breast cancer to lung metastatic niches are not fully understood.

Methods

Specific gene contributions to lung metastasis were identified by comparing gene profiles of 4T1 tumors metastasizing to various organs via microarray. The oncogenic properties CXCL17 were examined by in vivo spontaneous metastasis mouse model. The chemotactic activity of CXCL17 on CD11b⁺Gr-1⁺ myeloid-derived suppressor cells (MDSCs) was examined by both in vitro and in vivo models. The therapeutic effects of MDSC depletion and platelet-derived growth factor-BB (PDGF-BB) inhibition were examined by orthotic models.

Results

Here, we demonstrate that breast cancer cells secrete CXCL17, which increases the accumulation of CD11b⁺Gr-1⁺ MDSCs in the lungs. Metastatic lung-infiltrating CD11b⁺Gr-1⁺ MDSCs induce angiogenesis in the lungs and facilitate cancer extravasation and survival that ultimately promote lung metastases. CXCL17 increases CD11b⁺Gr-1⁺ MDSCs to express PDGF-BB, which not only contributes to CD11b⁺Gr-1⁺ MDSC-mediated angiogenesis in the lung metastatic niche, but is also involved in the colonization of breast cancer. Consequently, both CD11b⁺Gr-1⁺ MDSC depletion and PDGF receptor inhibitor effectively prevents CXCL17-driven lung metastasis in breast cancer. More importantly, patients with high levels of CXCL17 have shorter distant metastasis-free and overall survival rates, indicators of poor prognosis.

Conclusion

Our study reveals that MDSCs derived by CXCL17 contribute to the establishment of a lung metastatic niche by PDGF-BB secretion and provide a rationale for development of CXCL17 or PDGF-BB antagonists to inhibit or prevent lung metastasis in cases of breast cancer.

Electronic supplementary material

The online version of this article (10.1186/s13058-019-1114-3) contains supplementary material, which is available to authorized users.

MDSCs: Key Criminals of Tumor Pre-metastatic Niche Formation

The emergence of disseminated metastases remains the primary cause of mortality in cancer patients. Formation of the pre-metastatic niche (PMN), which precedes the establishment of tumor lesions, is critical for metastases. Bone marrow-derived myeloid cells (BMDCs) are indispensable for PMN formation. Myeloid-derived suppressor cells (MDSCs) are a population of immature myeloid cells that accumulate in patients with cancer and appear in the early PMN. The mechanisms by which MDSCs establish the pre-metastatic microenvironment in distant organs are largely unknown, although MDSCs play an essential role in metastasis. Here, we summarize the key factors associated with the recruitment and activation of MDSCs in the PMN and review the mechanisms by which MDSCs regulate PMN formation and evolution. Finally, we predict the potential value of MDSCs in PMN detection and therapy.

A Review of Exosomes and their Role in The Tumor Microenvironment and Host-Tumor "Macroenvironment"

Tumor-derived exosomes (TEX) are important intercellular messengers that contribute to tumorigenesis and metastasis through a variety of mechanisms such as immunosuppression and metabolic reprogramming that generate a pre-metastatic niche favorable to tumor progression. Our lab has contributed further to the understanding of the miRNA payloads in TEX by demonstrating that human melanoma-derived exosome (HMEX) associated miRNAs contribute to the metabolic reprogramming of normal stroma. This mini-review highlights the role of TEX in the tumor microenvironment (TME) and the hypothesis that exosomes may also generate a host-tumor "macroenvironment" beyond the TME through their miRNA and protein payloads, so to speak "fertilizing the soil for cancer seeding."

Hypoxia-Induced Resistance to Chemotherapy in Cancer

A major barrier to the successful management of cancer is the development of resistance to therapy. Chemotherapy resistance can either be an intrinsic property of malignant cells developed prior to therapy, or acquired following exposure to anti-cancer drugs. Given the impact of drug resistance to the overall poor survival of cancer patients, there is an urgent need to better understand the molecular pathways regulating this malignant phenotype. In this chapter we describe some of the molecular pathways that contribute to drug resistance in cancer, the role of a microenvironment deficient in oxygen (hypoxia) in malignant progression, and how hypoxia can be a significant factor in the development of drug resistance. We conclude by proposing potential therapeutic approaches that take advantage of a hypoxic microenvironment to chemosensitize therapy-resistant tumours.

Immune regulation of metastasis: mechanistic insights and therapeutic opportunities

Metastatic disease is the leading cause of death in cancer patients. Metastasis formation involves a cascade of events for which the underlying mechanisms are still poorly understood. During the metastatic cascade, cancer cells tightly interact with the immune system and they influence each other, both in the tumor microenvironment and systemically. The crosstalk between cancer and immune cells adds another layer of complexity to our understanding of metastasis formation, but at the same time opens new therapeutic opportunities for cancer patients. The intensifying development of immunotherapeutic strategies calls for a better understanding of immune regulation of metastasis in order to maximize the therapeutic benefit for patients with metastatic disease. In this Review and accompanying poster, we describe the main mechanisms of immune regulation of metastasis that have been reported to date, and present promising immunotherapeutic options that are currently available, or may become so in the near future, to tackle metastasis.

Role of hypoxia-induced exosomes in tumor biology

Purpose

Hypoxia is a major regulator of angiogenesis and always influences the release of exosomes in various types of tumors. The present review aimed to assess the role of hypoxia-induced exosomes in the tumor biology.

Methods

The relevant publications were retrieved from PubMed using keywords such as hypoxia, exosome, extracellular vesicles, tumor, cancer, and other similar terms.

Results

Recent studies have shown that cancer cells produce more exosomes under hypoxic conditions than do parental cells under normoxic conditions. The secretion and function of exosomes could be influenced by hypoxia in various types of cancer. Hypoxia-induced exosomes play critical roles in tumor angiogenesis, invasion, metastasis, and the immune system.

Conclusions

These findings provide new insights into the complex networks underlying cellular and genomic regulation in response to hypoxia and might provide novel and specific targets for future therapies.

Myeloid-Derived Suppressor Cells Hinder the Anti-Cancer Activity of Immune Checkpoint Inhibitors

Immune checkpoint inhibitors (ICI) used for cancer immunotherapy were shown to boost the existing anti-tumor immune response by preventing the inhibition of T cells by tumor cells. Antibodies targeting two negative immune checkpoint pathways, namely cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), programmed cell death protein 1 (PD-1), and programmed cell death-ligand 1 (PD-L1), have been approved first for patients with melanoma, squamous non-small cell lung cancer (NSCLC), and renal cell carcinoma. Clinical trials are ongoing to verify the efficiency of these antibodies for other cancer types and to evaluate strategies to block other checkpoint molecules. However, a number of patients do not respond to this treatment possibly due to profound immunosuppression, which is mediated partly by myeloid-derived suppressor cells (MDSC). This heterogeneous population of immature myeloid cells can strongly inhibit anti-tumor activities of T and NK cells and stimulate regulatory T cells (Treg), leading to tumor progression. Moreover, MDSC can contribute to patient resistance to immune checkpoint inhibition. Accumulating evidence demonstrates that the frequency and immunosuppressive function of MDSC in cancer patients can be used as a predictive marker for therapy response. This review focuses on the role of MDSC in immune checkpoint inhibition and provides an analysis of combination strategies for MDSC targeting together with ICI to improve their therapeutic efficiency in cancer patients.

The role of hypoxia in shaping the recruitment of proangiogenic and immunosuppressive cells in the tumor microenvironment

Hypoxia characterizes growing tumors and contributes significantly to their aggressiveness. Hypoxia-inducible factors (HIFs 1 and 2) are stabilized and act differentially as transcription factors on tumor growth and are responsible for important cancer hallmarks such as pathologic angiogenesis, cellular proliferation, apoptosis, differentiation and genetic instability as well as affecting tumor metabolism, tumor immune responses, invasion and metastasis. Taking into account the tumor tissue as a whole and considering the interplay of the various partners which react with hypoxia in the tumor site lead to reconsideration of the treatment strategies. Key limitations of treatment success result from the adaptation to the hypoxic milieu sustained by tumor anarchic angiogenesis. This raises immune tolerance by influencing the recruitment of immunosuppressive cells as bone marrow derived suppressor cells (MDSC) or by impairing the infiltration and killing of tumor cells by cytotoxic cells at the level of the endothelial cell wall of the hypoxic tumor vessels, as summarized in the schematic abstract.

Targeting Myeloid-Derived Suppressor Cells to Bypass Tumor-Induced Immunosuppression

The immune system has many sophisticated mechanisms to balance an extensive immune response. Distinct immunosuppressive cells could protect from excessive tissue damage and autoimmune disorders. Tumor cells take an advantage of those immunosuppressive mechanisms and establish a strongly immunosuppressive tumor microenvironment (TME), which inhibits antitumor immune responses, supporting the disease progression. Myeloid-derived suppressor cells (MDSC) play a crucial role in this immunosuppressive TME. Those cells represent a heterogeneous population of immature myeloid cells with a strong immunosuppressive potential. They inhibit an antitumor reactivity of T cells and NK cells. Furthermore, they promote angiogenesis, establish pre-metastatic niches, and recruit other immunosuppressive cells such as regulatory T cells. Accumulating evidences demonstrated that the enrichment and activation of MDSC correlated with tumor progression, recurrence, and negative clinical outcome. In the last few years, various preclinical studies and clinical trials targeting MDSC showed promising results. In this review, we discuss different therapeutic approaches on MDSC targeting to overcome immunosuppressive TME and enhance the efficiency of current tumor immunotherapies.

Suppressive role of myeloid-derived suppressor cells (MDSCs) in the microenvironment of breast cancer and targeted immunotherapies

Myeloid-derived suppressor cells (MDSCs) play a pivotal role in promoting tumor growth and metastasis and can even decrease the efficacy of immunotherapy. In breast cancer, MDSCs are recruited mainly by breast cancer cells to form a tumor-favoring microenvironment to suppress the anti-tumor immune response. In addition, MDSCs can react directly with breast cancer cells. In this paper, we describe several ways to recruit MDSCs in breast cancer, including breast cancer cell-derived cytokines and chemokines. The intracellular pathways in MDSCs during recruitment are classified as the STAT3-NF-κB-IDO pathway, the STAT3/IRF-8 pathway and the PTEN/Akt pathway. MDSCs act on T cells and NK cells to suppress the body's immunity, and via IL-6 trans-signaling, promote breast cancer directly. We further describe MDSC-targeted immune therapies for breast cancer, which are classified as: preventing the formation of MDSCs, eliminating MDSDCs, and reducing the products of MDSCs. Furthermore, MDSC-targeted immunotherapy potentiates the effect of the other immunotherapies. Based on the facts that MSDCs have significant roles in breast cancer malignant behaviors and can be suppressed by various strategies, we do believe MDSC-targeted immunotherapy presents a broad prospect in the future.

Chronic psychological stress promotes lung metastatic colonization of circulating breast cancer cells by decorating a pre-metastatic niche through activating β-adrenergic signaling

Numerous studies have indicated that primary tumors induce the formation of a pre-metastatic niche in distant organs by secreting tumor-derived factors. The present study shows that pre-exposure to chronic stress enhanced lung colonization efficiency by circulating tumor cells, suggesting that chronic stress critically influences pre-metastatic lungs before the arrival of disseminated tumor cells. Ablation of the sympathetic nerve function by 6-OHDA or blockage of the β-adrenergic signaling by propranolol remarkably suppressed stress-induced lung metastasis. Depletion of circulating monocytes or lung macrophages strongly abolished stress-induced lung seeding by tumor cells, whereas treatment of mice with the β-adrenergic agonist isoproterenol (ISO) during the pre-metastatic phase promoted the infiltration of macrophages to the lung. Meanwhile, the numbers of monocytes in peripheral blood, spleen, and bone marrow were remarkably increased in response to ISO stimulation. These data indicate that the β-adrenergic signaling promotes lung metastatic colonization by tumor cells through increased output of monocytes in the pre-metastatic phase and infiltration of macrophages into the pre-metastatic lung. Mechanistic studies revealed that ISO stimulation upregulated the expression of CCL2 in pulmonary stromal cells and CCR2 in monocytes/macrophages, leading to the recruitment and infiltration of macrophages into the pre-metastatic lung. By inducing a response of monocytes/macrophages driven by the CCL2/CCR2 axis, stress-related catecholamine may act as a crucial factor in regulating the pre-metastatic niche for and lung colonization by tumor cells. Our data demonstrate that disturbance of host macro-environmental homeostasis has an influence on future metastatic organs. Copyright © 2017 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

The immune system in cancer metastasis: friend or foe?

Metastatic disease is the leading cause of death among cancer patients and involves a complex and inefficient process. Every step of the metastatic process can be rate limiting and is influenced by non-malignant host cells interacting with the tumor cell. Over a century ago, experiments first indicated a link between the immune system and metastasis. This phenomenon, called concomitant immunity, indicates that the primary tumor induces an immune response, which may not be sufficient to destroy the primary tumor, but prevents the growth of a secondary tumor or metastases. Since that time, many different immune cells have been shown to play a role in both inhibiting and promoting metastatic disease. Here we review classic and new observations, describing the links between the immune system and metastasis that inform the development of cancer therapies.

KLF4-dependent perivascular cell plasticity mediates pre-metastatic niche formation and metastasis

A deeper understanding of the metastatic process is required for the development of new therapies that improve patient survival. Metastatic tumor cell growth and survival in distant organs is facilitated by the formation of a pre-metastatic niche composed of hematopoietic cells, stromal cells, and extracellular matrix (ECM). Perivascular cells, including vascular smooth muscle cells (vSMCs) and pericytes, are involved in new vessel formation and in promoting stem cell maintenance and proliferation. Given the well-described plasticity of perivascular cells, we hypothesize that perivascular cells similarly regulate tumor cell fate at metastatic sites. Using perivascular cell-specific and pericyte-specific lineage-tracing models, we trace the fate of perivascular cells in the pre-metastatic and metastatic microenvironments. We show that perivascular cells lose the expression of traditional vSMC/pericyte markers in response to tumor-secreted factors and exhibit increased proliferation, migration, and ECM synthesis. Increased expression of the pluripotency gene Klf4 in these phenotypically-switched perivascular cells promotes a less differentiated state characterized by enhanced ECM production that establishes a pro-metastatic fibronectin-rich environment. Genetic inactivation of Klf4 in perivascular cells decreases pre-metastatic niche formation and metastasis. Our data reveal a previously unidentified role for perivascular cells in pre-metastatic niche formation and uncover novel strategies for limiting metastasis.