IL-4 induces cathepsin protease activity in tumor-associated macrophages to promote cancer growth and invasion. Genes Dev. 2010;24:241-255. [PMID: 20080943 DOI: 10.1101/gad.1874010]

Cathepsin Inhibition Modulates Metabolism and Polarization of Tumor-Associated Macrophages

Simple Summary

Stroma-infiltrating tumor-associated macrophages (TAM) play an important role in regulating tumor progression and chemoresistance. Many tumor-infiltrating macrophage populations can be identified by preferential expression of distinct marker genes associated with an M2 phenotype and may execute tumor-promoting functions by enhancing tissue remodeling, facilitating angiogenesis, and suppressing immune responses. In this study, we aimed to characterize the impact of cathepsins in maintaining the TAM phenotype. For this purpose, we investigated the molecular effects of cathepsin inhibition on the viability and polarization of human primary macrophages as well as its metabolic consequences. Pharmacological inhibition of cathepsins B, L, and S using a novel inhibitor, GB111-NH₂, led to a polarization shift from M2- to M1 macrophages, associated with distinct alterations in lysosomal signaling and lipid metabolism. This could be therapeutically exploited in tumors with strong infiltration of M2-macrophages, thereby possibly reverting M2 polarization, overcoming drug resistance, and improving the prognosis of our patients.

Abstract

Stroma-infiltrating immune cells, such as tumor-associated macrophages (TAM), play an important role in regulating tumor progression and chemoresistance. These effects are mostly conveyed by secreted mediators, among them several cathepsin proteases. In addition, increasing evidence suggests that stroma-infiltrating immune cells are able to induce profound metabolic changes within the tumor microenvironment. In this study, we aimed to characterize the impact of cathepsins in maintaining the TAM phenotype in more detail. For this purpose, we investigated the molecular effects of pharmacological cathepsin inhibition on the viability and polarization of human primary macrophages as well as its metabolic consequences. Pharmacological inhibition of cathepsins B, L, and S using a novel inhibitor, GB111-NH₂, led to changes in cellular recycling processes characterized by an increased expression of autophagy- and lysosome-associated marker genes and reduced adenosine triphosphate (ATP) content. Decreased cathepsin activity in primary macrophages further led to distinct changes in fatty acid metabolites associated with increased expression of key modulators of fatty acid metabolism, such as fatty acid synthase (FASN) and acid ceramidase (ASAH1). The altered fatty acid profile was associated with an increased synthesis of the pro-inflammatory prostaglandin PGE₂, which correlated with the upregulation of numerous NF_kB-dependent pro-inflammatory mediators, including interleukin-1 (IL-1), interleukin-6 (IL-6), C-C motif chemokine ligand 2 (CCL2), and tumor necrosis factor-alpha (TNFα). Our data indicate a novel link between cathepsin activity and metabolic reprogramming in macrophages, demonstrated by a profound impact on autophagy and fatty acid metabolism, which facilitates a pro-inflammatory micromilieu generally associated with enhanced tumor elimination. These results provide a strong rationale for therapeutic cathepsin inhibition to overcome the tumor-promoting effects of the immune-evasive tumor micromilieu.

Novel Opportunities for Cathepsin S Inhibitors in Cancer Immunotherapy by Nanocarrier-Mediated Delivery

Cathepsin S (CatS) is a secreted cysteine protease that cleaves certain extracellular matrix proteins, regulates antigen presentation in antigen-presenting cells (APC), and promotes M2-type macrophage and dendritic cell polarization. CatS is overexpressed in many solid cancers, and overall, it appears to promote an immune-suppressive and tumor-promoting microenvironment. While most data suggest that CatS inhibition or knockdown promotes anti-cancer immunity, cell-specific inhibition, especially in myeloid cells, appears to be important for therapeutic efficacy. This makes the design of CatS selective inhibitors and their targeting to tumor-associated M2-type macrophages (TAM) and DC an attractive therapeutic strategy compared to the use of non-selective immunosuppressive compounds or untargeted approaches. The selective inhibition of CatS can be achieved through optimized small molecule inhibitors that show good pharmacokinetic profiles and are orally bioavailable. The targeting of these inhibitors to TAM is now more feasible using nanocarriers that are functionalized for a directed delivery. This review discusses the role of CatS in the immunological tumor microenvironment and upcoming possibilities for a nanocarrier-mediated delivery of potent and selective CatS inhibitors to TAM and related APC to promote anti-tumor immunity.

Genomic landscape of the immune microenvironments of brain metastases in breast cancer

Background

This study was intended to investigate the genomic landscape of the immune microenvironments of brain metastases in breast cancer.

Methods

Three gene expression profile datasets (GSE76714, GSE125989 and GSE43837) of breast cancer with brain metastases were downloaded from Gene Expression Omnibus (GEO) database. After differential expression analysis, the tumor immune microenvironment and immune cell infiltration were analyzed. Then immune-related genes were identified, followed by function analysis, transcription factor (TF)-miRNA–mRNA co-regulatory network analysis, and survival analysis of metastatic recurrence.

Results

The present results showed that the tumor immune microenvironment in brain metastases was immunosuppressed compared with primary caner. Compared with primary cancer samples, the infiltration ratio of plasma cells in brain metastases samples was significantly higher, while the infiltration ratio of macrophages M2 cells in brain metastases samples was significantly lower. Total 42 immune-related genes were identified, such as THY1 and NEU2. CD1B, THY1 and DOCK2 were found to be implicated in the metastatic recurrence of breast cancer.

Conclusions

Targeting macrophages or plasma cells may be new strategies for immunotherapy of breast cancer with brain metastases. THY1 and NEU2 may be potential therapeutic targets for breast cancer with brain metastases, and THY1, CD1B and DOCK2 may serve as potential prognostic markers for improvement of brain metastases survival.

Conditional Gene Targeting Reveals Cell Type-Specific Roles of the Lysosomal Protease Cathepsin L in Mammary Tumor Progression

Background: Cathepsin L (Ctsl) is a cysteine protease mainly located within the endosomal/lysosomal cell compartment. High expression of Ctsl indicates poor prognosis in human breast cancer. However, the cell type-specific Ctsl functions responsible for this association remain elusive. Methods: Because constitutive Ctsl-/- mice develop a complex phenotype, we developed a conditional model allowing for cell type-specific inactivation of Ctsl in mammary epithelium or myeloid cells in the transgenic mouse mammary tumor virus (MMTV)-polyoma middle T (PyMT) breast cancer model. Results: Ctsl ablation in mammary epithelial cells resulted in delayed initiation and end-stage of cancers. The latter displayed large dead cell areas. Inducible in vitro deletion of Ctsl in MMTV-PyMT-derived breast cancer cells revealed expansion of the acidic cell compartment, alteration of intracellular amino acid levels, and impaired mTOR signaling. In consequence, Ctsl-deficient cells exhibited slow growth rates and high apoptosis susceptibility. In contrast to Ctsl-deficient mammary epithelium, selective knockout of Ctsl in myeloid cells had no effects on primary tumors, but promoted lung metastasis formation. Conclusions: Our cell type-specific in vivo analysis provides strong evidence for a cancer cell-intrinsic, tumor-promoting role of Ctsl in primary breast cancer, whereas metastasis is negatively regulated by Ctsl expressed by bone marrow-derived cells.

M2b macrophage subset decrement as an indicator of cognitive function in Alzheimer's disease

AIM

Alzheimer's disease (AD) is a chronic neurodegenerative disease. Various inflammatory processes account for the pathology of AD, and macrophages in particular have a distinct polarization phenotype related to M1/M2 classification. We aimed to investigate macrophage polarization patterns as an indicator of cognitive function in AD.

METHODS

We recruited 54 non-demented individuals as control and 105 AD patients as experimental groups respectively. Percentages of macrophage (PM2K⁺ CD14⁺ and PM2K⁺ CD14^- ) and macrophage polarization subsets (M1, M2a, M2b, and M2c) were assessed using flow cytometry. All AD patients were classified by dementia severity using clinical Dementia Rating scale (CDR) as CDR 0.5, 1 and ≧2. AD patients had cognitive function evaluation using Mini-Mental State Examination (MMSE) and Cognitive Assessment Screening Instrument (CASI). We compared the macrophage polarization patterns between control and patient groups. Cognitive function was evaluated in association with macrophage polarization patterns in AD patients.

RESULTS

The percentages of PM2K⁺ CD14⁺ and PM2K⁺ CD14^- macrophages were higher in AD patients than in controls. M2b macrophage subset decrement and M1 macrophage subset increment of PM2K⁺ CD14⁺ and PM2K⁺ CD14^- macrophages were observed in AD patients compared with controls. Although percentages of macrophage subsets were not consistent with CDR staging, PM2K⁺ CD14⁺ M2b macrophage subset decrement was correlated with worse cognitive functioning by MMSE and CASI in AD patients.

CONCLUSION

M2b macrophage subset decrement and M1 macrophage subset increment were noted in AD patients, while PM2K⁺ CD14⁺ M2b macrophage subset decrement indicated worse cognitive function in such patients.

Antisense oligonucleotide targeting of thrombopoietin represents a novel platelet depletion method to assess the immunomodulatory role of platelets

BACKGROUND

Platelets are effector cells of the innate and adaptive immune system; however, understanding their role during inflammation-driven pathologies can be challenging due to several drawbacks associated with current platelet depletion methods. The generation of antisense oligonucleotides (ASOs) directed to thrombopoietin (Tpo) mRNA represents a novel method to reduce circulating platelet count.

OBJECTIVE

To understand if Tpo-targeted ASO treatment represents a viable strategy to specifically reduce platelet count in mice.

METHODS

Female and male mice were treated with TPO-targeted ASOs and platelet count and function was assessed, in addition to circulating blood cell counts and hematopoietic stem and progenitor cells. The utility of the platelet-depletion strategy was assessed in a murine model of lower airway dysbiosis.

RESULTS AND CONCLUSIONS

Herein, we describe how in mice, ASO-mediated silencing of hepatic TPO expression reduces platelet, megakaryocyte, and megakaryocyte progenitor count, without altering platelet activity. TPO ASO-mediated platelet depletion can be achieved acutely and sustained chronically in the absence of adverse bleeding. TPO ASO-mediated platelet depletion allows for the reintroduction of new platelets, an advantage over commonly used antibody-mediated depletion strategies. Using a murine model of lung inflammation, we demonstrate that platelet depletion, induced by either TPO ASO or anti-CD42b treatment, reduces the accumulation of inflammatory immune cells, including monocytes and macrophages, in the lung. Altogether, we characterize a new platelet depletion method that can be sustained chronically and allows for the reintroduction of new platelets highlighting the utility of the TPO ASO method to understand the role of platelets during chronic immune-driven pathologies.

Serum markers improve current prediction of metastasis development in early-stage melanoma patients: a machine learning-based study

Metastasis development represents an important threat for melanoma patients, even when diagnosed at early stages and upon removal of the primary tumor. In this scenario, determination of prognostic biomarkers would be of great interest. Serum contains information about the general status of the organism and therefore represents a valuable source for biomarkers. Thus, we aimed to define serological biomarkers that could be used along with clinical and histopathological features of the disease to predict metastatic events on the early‐stage population of patients. We previously demonstrated that in stage II melanoma patients, serum levels of dermcidin (DCD) were associated with metastatic progression. Based on the relevance of the immune response on the cancer progression and the recent association of DCD with local and systemic immune response against cancer cells, serum DCD was analyzed in a new cohort of patients along with interleukin 4 (IL‐4), IL‐6, IL‐10, IL‐17A, interferon γ (IFN‐γ), transforming growth factor‐β (TGF‐ β), and granulocyte–macrophage colony‐stimulating factor (GM‐CSF). We initially recruited 448 melanoma patients, 323 of whom were diagnosed as stages I‐II according to AJCC. Levels of selected cytokines were determined by ELISA and Luminex, and obtained data were analyzed employing machine learning and Kaplan–Meier techniques to define an algorithm capable of accurately classifying early‐stage melanoma patients with a high and low risk of developing metastasis. The results show that in early‐stage melanoma patients, serum levels of the cytokines IL‐4, GM‐CSF, and DCD together with the Breslow thickness are those that best predict melanoma metastasis. Moreover, resulting algorithm represents a new tool to discriminate subjects with good prognosis from those with high risk for a future metastasis.

The effects of umbilical cord-derived macrophage exosomes loaded with cisplatin on the growth and drug resistance of ovarian cancer cells

Objective: To assess the feasibility of an exosome-based drug delivery platform for the potent chemotherapeutic agent cisplatin to treat ovarian cancer.Significance: Exosomes have recently been used as drug delivery vehicles because of their natural advantages. Platinum-resistant forms of ovarian cancer require novel drug delivery methods to improve patient outcomes.Methods: We developed and compared different methods of loading exosomes released by mononuclear M1 and M2 macrophages from umbilical cord blood with cisplatin. We characterized the morphology, drug capacity, method of cellular entry, and antitumor efficacy of the exosomes in vitro.Results: Disruption of the exosomal membrane by sonication facilitated a high loading efficiency. Importantly, incorporation of cisplatin into umbilical cord blood-derived M1 macrophage exosomes increased its cytotoxicity 3.3× in drug-resistant A2780/DDP cells and 1.4× in drug-sensitive A2780 cells over chemotherapy alone. Loading of cisplatin into M2 exosomes increased its cytotoxicity by nearly 1.7× in drug-resistant A2780/DDP cells and 1.4× in drug-sensitive A2780 cells.Conclusions: We conclude that cisplatin-loaded M1 exosomes are potentially powerful new tools for the delivery of chemotherapeutics to treat cancers regardless of drug resistance.

Leading the invasion: The role of Cathepsin S in the tumour microenvironment

Elevated expression of the cysteine protease Cathepsin S has been correlated with a number of different cancer types in recent years. As tools have been developed to enable more accurate examination of individual cathepsin species, our knowledge and appreciation of the role that this protease plays in facilitating cancer has increased exponentially. This review focuses on our current understanding of the role of Cathepsin S within tumours and the surrounding microenvironment. While various publications have shown that Cathepsin S can be derived from tumour cells themselves, a plethora of more recent studies have identified that Cathepsin S can also be derived from other cell types within the tumour microenvironment including endothelial cells, macrophages and T cells. Furthermore, specific proteolytic substrates cleaved by Cathepsin S have also been identified which have reinforced our hypothesis that this protease facilitates key steps within tumours leading to their invasion, angiogenesis and metastasis.

The Role of Tumor-Associated Myeloid Cells in Modulating Cancer Therapy

Myeloid cells include various cellular subtypes that are distinguished into mononuclear and polymorphonuclear cells, derived from either common myeloid progenitor cells (CMPs) or myeloid stem cells. They play pivotal roles in innate immunity since, following invasion by pathogens, myeloid cells are recruited and initiate phagocytosis and secretion of inflammatory cytokines into local tissues. Moreover, mounting evidence suggests that myeloid cells may also regulate cancer development by infiltrating the tumor to directly interact with cancer cells or by affecting the tumor microenvironment. Importantly, mononuclear phagocytes, including macrophages and dendritic cells (DCs), can have either a positive or negative impact on the efficacy of chemotherapy, radiotherapy as well as targeted anti-cancer therapies. Tumor-associated macrophages (TAMs), profusely found in the tumor stroma, can promote resistance to chemotherapeutic drugs, such as Taxol and Paclitaxel, whereas the suppression of TAMs can lead to an improved radiotherapy outcome. On the contrary, the presence of TAMs may be beneficial for targeted therapies as they can facilitate the accumulation of large quantities of nanoparticles carrying therapeutic compounds. Tumor infiltrating DCs, however, are generally thought to enhance cytotoxic therapies, including those using anthracyclines. This review focuses on the role of tumor-infiltrating and stroma myeloid cells in modulating tumor responses to various treatments. We herein report the impact of myeloid cells in a number of therapeutic approaches across a wide range of malignancies, as well as the efforts toward the elimination of myeloid cells or the exploitation of their presence for the enhancement of therapeutic efficacy against cancer.

Pro-tumorigenic functions of macrophages at the primary, invasive and metastatic tumor site

The tumor microenvironment (TME) not only facilitates cancer progression from the early formation to distant metastasis, but also it differs itself from time to time alongside the tumor evolution. Tumor-associated macrophages (TAMs), whether as pre-existing tissue-resident macrophages or recruited monocytes, are an inseparable part of this microenvironment. As their parents are broadly classified into a dichotomic, simplistic M1 and M2 subtypes, TAMs also exert paradoxical and diverse phenotypes as they are settled in different regions of TME and receive different microenvironmental signals. Briefly, M1 macrophages induce an inflammatory precancerous niche and flame the early oncogenic mutations, whereas their M2 counterparts are reprogrammed to release various growth factors and providing an immunosuppressive state in TME as long as abetting hypoxic cancer cells to set up a new vasculature. Further, they mediate stromal micro-invasion and co-migrate with invasive cancer cells to invade the vascular wall and neural sheath, while another subtype of TAMs prepares suitable niches much earlier than metastatic cells arrive at the target tissues. Accordingly, at the neoplastic transformation, during the benign-to-malignant transition and through the metastatic cascade, macrophages are involved in shaping the primary, micro-invasive and pre-metastatic TMEs. Whether their behavioral plasticity is derived from distinct genotypes or is fueled by microenvironmental cues, it could define these cells as remarkably interesting therapeutic targets.

Myeloid deletion of phosphoinositide-dependent kinase-1 enhances NK cell-mediated antitumor immunity by mediating macrophage polarization

A large number of heterogeneous macrophages can be observed in solid tumor lesions. Classically activated M1 macrophages are a powerful killer of cancer cells. In contrast, tumor-associated macrophages (TAMs) are often referred to as M2 phenotype and usually impair tumor immunity mediated by cytotoxic lymphocytes, natural killer (NK) cells and CD8⁺ T cells. Therefore, orchestrating M2 to M1 reprogramming will provide a promising approach to tumor immunotherapy. Here we used a PyMT-induced spontaneous breast cancer model in which M2-polarized macrophages were abundant. This M2 phenotype was closely related to tumor progression and immune dysfunction of NK cells and CD8⁺ T cells. We then found that these TAMs showed increased energy expenditure and over-activation of two kinases, Akt and mammalian target of rapamycin (mTOR). Myeloid inactivation of phosphoinositide-dependent kinase-1 (PDK1), the upstream regulator for Akt and mTOR signaling, significantly reduced excessive metabolic activation of macrophages. Notably, the loss of PDK1 significantly led to regression of breast cancer and prevented lung metastasis. Mechanistically, PDK1 deficiency mainly inhibited the activation of mTOR complex 1 (mTORC1), transforming TAMs into M1 phenotype, thereby reversing tumor-related dysfunction of T cells and NK cells. Therefore, targeting PDK1 may be a new approach for M2 macrophage-enriched solid tumor immunotherapy.

Molecular Aspects and Future Perspectives of Cytokine-Based Anti-cancer Immunotherapy

Cytokine-based immunotherapy is a promising field in the cancer treatment, since cytokines, as proteins of the immune system, are able to modulate the host immune response toward cancer cell, as well as directly induce tumor cell death. Since a low dose monotherapy with some cytokines has no significant therapeutic results and a high dose treatment leads to a number of side effects caused by the pleiotropic effect of cytokines, the problem of understanding the influence of cytokines on the immune cells involved in the pro- and anti-tumor immune response remains a pressing one. Immune system cells carry CD makers on their surface which can be used to identify various populations of cells of the immune system that play different roles in pro- and anti-tumor immune responses. This review discusses the functions and specific CD markers of various immune cell populations which are reported to participate in the regulation of the immune response against the tumor. The results of research studies and clinical trials investigating the effect of cytokine therapy on the regulation of immune cell populations and their surface markers are also discussed. Current trends in the development of cancer immunotherapy, as well as the role of cytokines in combination with other therapeutic agents, are also discussed.

Carcinogenesis of Pancreatic Ductal Adenocarcinoma

Although the estimated time for development of pancreatic ductal adenocarcinoma (PDA) is more than 20 years, PDAs are usually detected at late, metastatic stages. PDAs develop from duct-like cells through a multistep carcinogenesis process, from low-grade dysplastic lesions to carcinoma in situ and eventually to metastatic disease. This process involves gradual acquisition of mutations in oncogenes and tumor suppressor genes, as well as changes in the pancreatic environment from a pro-inflammatory microenvironment that favors the development of early lesions, to a desmoplastic tumor microenvironment that is highly fibrotic and immune suppressive. This review discusses our current understanding of how PDA originates.

Blood and Cancer: Cancer Stem Cells as Origin of Hematopoietic Cells in Solid Tumor Microenvironments

The concepts of hematopoiesis and the generation of blood and immune cells from hematopoietic stem cells are some steady concepts in the field of hematology. However, the knowledge of hematopoietic cells arising from solid tumor cancer stem cells is novel. In the solid tumor microenvironment, hematopoietic cells play pivotal roles in tumor growth and progression. Recent studies have reported that solid tumor cancer cells or cancer stem cells could differentiate into hematopoietic cells. Here, we discuss efforts and research that focused on the presence of hematopoietic cells in tumor microenvironments. We also discuss hematopoiesis from solid tumor cancer stem cells and clarify the notion of differentiation of solid tumor cancer stem cells into non-cancer hematopoietic stem cells.

The malignancy of liver cancer cells is increased by IL-4/ERK/AKT signaling axis activity triggered by irradiated endothelial cells

The malignant traits involved in tumor relapse, metastasis and the expansion of cancer stem-like cells are acquired via the epithelial-mesenchymal transition (EMT) process in the tumor microenvironment. In addition, the tumor microenvironment strongly supports the survival and growth of malignant tumor cells and further contributes to the reduced efficacy of anticancer therapy. Ionizing radiation can influence the tumor microenvironment, because it alters the biological functions of endothelial cells composing tumor vascular systems. However, to date, studies on the pivotal role of these endothelial cells in mediating the malignancy of cancer cells in the irradiated tumor microenvironment are rare. We previously evaluated the effects of irradiated endothelial cells on the malignant traits of human liver cancer cells and reported that endothelial cells irradiated with 2 Gy reinforce the malignant properties of these cancer cells. In this study, we investigated the signaling mechanisms underlying these events. We revealed that the increased expression level of IL-4 in endothelial cells irradiated with 2 Gy eventually led to enhanced migration and invasion of cancer cells and further expansion of cancer stem-like cells. In addition, this increased level of IL-4 activated the ERK and AKT signaling pathways to reinforce these events in cancer cells. Taken together, our data indicate that ionizing radiation may indirectly modulate malignancy by affecting endothelial cells in the tumor microenvironment. Importantly, these indirect effects on malignancy are thought to offer valuable clues or targets for overcoming the tumor recurrence after radiotherapy.

The secreted inhibitor of invasive cell growth CREG1 is negatively regulated by cathepsin proteases

Previous clinical and experimental evidence strongly supports a breast cancer-promoting function of the lysosomal protease cathepsin B. However, the cathepsin B-dependent molecular pathways are not completely understood. Here, we studied the cathepsin-mediated secretome changes in the context of the MMTV-PyMT breast cancer mouse model. Employing the cell-conditioned media from tumor-macrophage co-cultures, as well as tumor interstitial fluid obtained by a novel strategy from PyMT mice with differential cathepsin B expression, we identified an important proteolytic and lysosomal signature, highlighting the importance of this organelle and these enzymes in the tumor micro-environment. The Cellular Repressor of E1A Stimulated Genes 1 (CREG1), a secreted endolysosomal glycoprotein, displayed reduced abundance upon over-expression of cathepsin B as well as increased abundance upon cathepsin B deletion or inhibition. Moreover, it was cleaved by cathepsin B in vitro. CREG1 reportedly could act as tumor suppressor. We show that treatment of PyMT tumor cells with recombinant CREG1 reduced proliferation, migration, and invasion; whereas, the opposite was observed with reduced CREG1 expression. This was further validated in vivo by orthotopic transplantation. Our study highlights CREG1 as a key player in tumor–stroma interaction and suggests that cathepsin B sustains malignant cell behavior by reducing the levels of the growth suppressor CREG1 in the tumor microenvironment.

The roles of tumor-associated macrophages in tumor angiogenesis and metastasis

Tumor associated macrophages (TAMs) are the most frequent immune cells within tumor microenvironment (TME). There is growing evidence that TAMs are involved in tumor progression via multiple mechanisms. TAMs create an immunosuppressive TME by producing growth factors, chemokines, and cytokines which modulate recruitment of immune cells and inhibit anti-tumor responses. They also serve as angiogenesis promoting cells by production of pro-angiogenic factors and matrix metalloproteinases (MMPs) and vascular constructing which guarantee supplying oxygen and nutrients to solid tumor cells. Furthermore, TAMs play important functions in tumor metastasis through contributing to invasion, extravasation, survival, intravasation, and colonization of tumor cells. In this review, we summarized macrophage classification, TAMs polarization, and mechanisms underlying TAM-promoting angiogenesis and metastasis.

Myeloid Cells in Metastasis

Metastatic disease is the leading cause of death in patients with solid cancers. The progression to metastasis is a multistep process that involves detachment of tumor cells from their constraining basement membrane at the primary site, migration and intravasation into the circulation, survival in the circulation, extravasation into the secondary organ, and survival and growth at the secondary site. During these steps, tumor and immune cells interact and influence each other both within the tumor microenvironment and systemically. In particular, myeloid cells such as monocytes, macrophages, neutrophils, and myeloid-derived suppressor cells (myeloid regulatory cells) have been shown to play important roles in the metastatic process. These interactions open new avenues for targeting cancer metastasis, especially given the increasing interest in development of cancer immunotherapies. In this review, we describe the currently reported pathways and mechanisms involved in myeloid cell enhancement of the metastatic cascade.

Contribution of Macrophages and T Cells in Skeletal Metastasis

Bone is a common site for metastases with a local microenvironment that is highly conducive for tumor establishment and growth. The bone marrow is replete with myeloid and lymphoid linage cells that provide a fertile niche for metastatic cancer cells promoting their survival and growth. Here, we discuss the role of macrophages and T cells in pro- and anti-tumoral mechanisms, their interaction to support cancer cell growth, and their contribution to the development of skeletal metastases. Importantly, immunotherapeutic strategies targeting macrophages and T cells in cancer are also discussed in this review as they represent a great promise for patients suffering from incurable bone metastases.

Low expression of RGL4 is associated with a poor prognosis and immune infiltration in lung adenocarcinoma patients

Lung adenocarcinoma (LUAD) is a frequently diagnosed histologic subtype with increasing morbidity and mortality. RalGDS-Like 4 (RGL4) has not been reported to be associated with cancer risk, prognosis, immunotherapy or any other treatments. We perform a bioinformatics analysis on data downloaded from the Cancer Genome Atlas (TCGA)-LUAD, and we find that low expression of RGL4 is accompanied by worse outcomes and prognosis in LUAD patients. As a promising predictor, the potential influence and mechanisms of RGL4 on overall survival are worth exploring. Moreover, RGL4 expression is significantly associated with a variety of tumor-infiltrating immune cells (TIICs), particularly memory B cells, CD8⁺T cells and neutrophils. Subsequently, we evaluated the most notable KEGG pathways, including glycolysis gluconeogenesis, the P53 signaling pathway, RNA degradation, and the B cell receptor signaling pathway, among others. Our findings provide evidence that the decreased expression of RGL4 is significantly associated with poor prognosis and immune cell infiltration in patients with LUAD and highlight the use of RGL4 as a novel predictive biomarker for the prognosis of LUAD and other cancers. RGL4 may also be used in combination with immune checkpoints to identify the benefits of immunotherapy. Subjects: Bioinformatics, Genomics, Oncology, Thoracic surgery.

Tumor cell- and microenvironment-specific roles of cysteine cathepsins in mouse models of human cancers

The human genome encodes for 11 papain-like endolysosomal cysteine peptidases, collectively known as the cysteine cathepsins. Based on their biochemical properties and with the help of experiments in cell culture, the cysteine cathepsins have acquired a reputation as promotors of progression and metastasis of various cancer entities. However, tumors are known to be complex tissues in which non-cancerous cells are also critical for tumorigenesis. Here we discuss the results of the intense investigation of cathepsins in mouse models of human cancers. We focus on models in immunocompetent mice, because only such models allow for analysis of cathepsins in a fully functional tumor microenvironment. An important outcome of those studies was the identification of cancer-promoting cathepsins in tumor-associated macrophages. Another interesting outcome of these animal studies was the identification of a homeostatic tumor-suppressive role for cathepsin L in skin and intestinal cancers. Taken together, these in vivo findings provide a basis for the use of cysteine cathepsins as therapeutic targets, prodrug activators, or as proteases for imaging tumors.

The Immune Microenvironment and Cancer Metastasis

The dynamic interplay between neoplastic cells and the immune microenvironment regulates every step of the metastatic process. Immune cells contribute to invasion by secreting a cornucopia of inflammatory factors that promote epithelial-to-mesenchymal transition and remodeling of the stroma. Cancer cells then intravasate to the circulatory system assisted by macrophages and use several pathways to avoid recognition by cytotoxtic lymphocytes and phagocytes. Circulating tumor cells that manage to adhere to the vasculature and encounter premetastic niches are able to use the associated myeloid cells to extravasate into ectopic organs and establish a dormant microscopic colony. If successful at avoiding repetitive immune attack, dormant cells can subsequently grow into overt, clinically detectable metastatic lesions, which ultimately account to most cancer-related deaths. Understanding how disseminated tumor cells evade and corrupt the immune system during the final stages of metastasis will be pivotal in developing new therapeutic modalities that combat metastasis.

Plasma proteomic signature of the risk of developing mobility disability: A 9-year follow-up

INTRODUCTION

Mobility disability is a powerful indicator of poor health in older adults. The biological and pathophysiological mechanism underlying the development of mobility disability remains unknown. This study conducted a data-driven discovery phase investigation to identify plasma proteins that predict the incidence of mobility disability in community-dwelling older adults without mobility disability at baseline.

METHODS

We investigated 660 women and men, aged 71.9 ± 6.0 (60-94) years, who participated in the Invecchiare in Chianti, "Aging in the Chianti Area" study and completed the 400-m walk at fast pace (400-m walk) at enrollment. Median follow-up time was 8.57 [interquartile, 3.20-9.08] years. SOMAscan technology was used to measure 1,301 plasma proteins at enrollment. The incident of mobility disability was defined as inability to complete the 400-m walk. Protein-specific Cox proportional hazard model was adjusted for sex, age, and other important covariates.

RESULTS

Plasma levels of 75 proteins predicted mobility disability (p < .05). Significant proteins were enriched for the KEGG "PI3K-Akt signaling," "phagosomes," and "cytokine-cytokine receptor interaction" pathways. After multiple comparison adjustment, plasma cathepsin S (CTSS; hazard ratio [HR] 1.33, 95% CI: 1.17, 1.51, q = 0.007), growth/differentiation factor 15 (GDF15; HR: 1.45, 95% CI: 1.23, 1.72, q = 0.007), and thrombospondin-2 (THBS2; HR: 1.44, 95% CI: 1.22, 1.69, q = 0.007) remained significantly associated with high risk of losing mobility.

CONCLUSION

CTSS, GDF15, and THBS2 are novel blood biomarkers associated with new mobility disability in community-dwelling individuals. Overall, our analysis suggests that cellular senescence and inflammation should be targeted for prevention of mobility disability.

The role of tumor-associated macrophages in gastric cancer development and their potential as a therapeutic target

Gastric cancer (GC) represents the fifth cause of cancer-related death worldwide. Molecular biology has become a central area of research in GC and there are currently at least three major classifications available to elucidate the mechanisms that drive GC oncogenesis. Further, tumor microenvironment seems to play a crucial role, and tumor-associated macrophages (TAMs) are emerging as key players in GC development. TAMs are cells derived from circulating chemokine- receptor-type 2 (CCR2) inflammatory monocytes in blood and can be divided into two main types, M1 and M2 TAMs. M2 TAMs play an important role in tumor progression, promoting a pro-angiogenic and immunosuppressive signal in the tumor. The diffuse GC subtype, in particular, seems to be strongly characterized by an immuno-suppressive and pro-angiogenic phenotype. No molecular targets in this subgroup have yet been identified. There is an urgent need to understand the molecular pathways and tumor microenvironment features in the GC molecular subtypes. The role of anti-angiogenics and checkpoint inhibitors has recently been clinically validated in GC. Both ramucirumab, a fully humanized IgG1 monoclonal anti-vascular endothelial growth factor receptor 2 (VEGFR2) antibody, and checkpoint inhibitors in Epstein Bar Virus (EBV) and Microsatellite Instable (MSI) subtypes, have proved beneficial in advanced GC. Nevertheless, there is a need to identify predictive markers of response to anti-angiogenics and immunotherapy in clinical practice for a personalized treatment approach. The importance of M2 TAMs in development of solid tumors is currently gaining increasing interest. In this literature review we analyze immune microenvironment composition and signaling related to M1 and M2 TAMs in GC as well as its potential role as a therapeutic target.

Modeling chemical effects on breast cancer: the importance of the microenvironment in vitro

Accumulating evidence suggests that our ability to predict chemical effects on breast cancer is limited by a lack of physiologically relevant in vitro models; the typical in vitro breast cancer model consists of the cancer cell and excludes the mammary microenvironment. As the effects of the microenvironment on cancer cell behavior becomes more understood, researchers have called for the integration of the microenvironment into in vitro chemical testing systems. However, given the complexity of the microenvironment and the variety of platforms to choose from, identifying the essential parameters to include in a chemical testing platform is challenging. This review discusses the need for more complex in vitro breast cancer models and outlines different approaches used to model breast cancer in vitro. We provide examples of the microenvironment modulating breast cancer cell responses to chemicals and discuss strategies to help pinpoint what components should be included in a model.

A Protease-Activated Fluorescent Probe Allows Rapid Visualization of Keratinocyte Carcinoma during Excision

Keratinocyte carcinomas, including basal and squamous cell carcinomas, are the most common human cancers worldwide. While 75% of all keratinocyte carcinoma (4 million annual cases in the United States) are treated with conventional excision, this surgical modality has much lower cure rates than Mohs micrographic surgery, likely due to the bread-loaf histopathologic assessment that visualizes <1% of the tissue margins. A quenched protease-activated fluorescent probe 6qcNIR, which produces a signal only in the protease-rich tumor microenvironment, was topically applied to 90 specimens ex vivo immediately following excision. "Puzzle-fit" analysis was used to correlate the fluorescent images with histology. Probe-dependent fluorescent images correlated with cancer determined by conventional histology. Point-of-care fluorescent detection of skin cancer had a clinically relevant sensitivity of 0.73 and corresponding specificity of 0.88. Importantly, clinicians were effectively trained to read fluorescent images within 15 minutes with reliability and confidence, resulting in sensitivities of 62%-78% and specificities of 92%-97%. Fluorescent imaging using 6qcNIR allows 100% tumor margin assessment by generating en face images that correlate with histology and may be used to overcome the limitations of conventional bread-loaf histology. The utility of 6qcNIR was validated in a busy real-world clinical setting, and clinicians were trained to effectively read fluorescent margins with a short guided instruction, highlighting clinical adaptability. When used in conventional excision, this approach may result in higher cure rates at a lower cost by allowing same-day reexcision when needed, reducing patient anxiety and improving compliance by expediting postsurgical specimen assessment. SIGNIFICANCE: A fluorescent-probe-tumor-visualization platform was developed and validated in human keratinocyte carcinoma excision specimens that may provide simple, rapid, and global assessment of margins during skin cancer excision, allowing same-day reexcision when needed.

Astragalus membranaceus-Derived Anti-Programmed Death-1 Monoclonal Antibodies with Immunomodulatory Therapeutic Effects against Tumors

Astragalus membranaceus polysaccharide (APS) components are main ingredients of TCM and have proven efficacy to activate T cells and B cells, enhancing immunity in humans. In this study, elevated cytokine and anti-PD-1 antibody titers were found in mice after immunization with APS. Therefore, phage-display technology was utilized to isolate specific anti-programmed death-1 (PD-1) antibodies from mice stimulated by APS and to confirm whether the isolated anti-PD-1 antibody could inhibit the interaction of PD-1 with the programmed death-ligand 1 (PD-L1), resulting in tumor growth inhibition. The isolated single-chain fragment variable (scFv) S12 exhibited the highest binding affinity of 20 nM to PD-1, completed the interaction between PD-1 and PD-L1, and blocked the effect of PD-L1-induced T cell exhaustion in peripheral blood mononuclear cells in vitro. In the animal model, the tumor growth inhibition effect after scFv S12 treatment was approximately 48%. However, meaningful synergistic effects were not observed when scFv S12 was used as a cotreatment with ixabepilone. Moreover, this treatment caused a reduction in the number of tumor-associated macrophages in the tumor tissue. These experimental results indirectly indicate the ability of APS to induce specific antibodies associated with the immune checkpoint system and the potential benefits for improving immunity in humans.

Paracrine and cell autonomous signalling in pancreatic cancer progression and metastasis

Pancreatic ductal adenocarcinoma (PDAC) shows remarkable propensity to metastasize. This predilection to escape from the primary tumor is driven by paracrine and autocrine mechanisms that guide cancer cells through a multi-step process concluding with colonization in distant tissues. Although cell-intrinsic features support the metastatic ability of cancer cells, permissive microenvironments within the primary organ and at sites of distant metastasis may be rate-limiting. Identification of cancer cell-extrinsic factors that regulate formation of these environments lend new therapeutic targets for intervening on the metastatic cascade. In addition, the bipolar, yet fundamental, role of the immune system in the metastatic process presents therapeutic opportunities. Herein, we review the current knowledge of the metastatic cascade in PDAC, and propose that genomically stable determinants of metastasis (e.g. the pro-metastatic niche and immune system) are actionable targets for preventing, containing, and treating metastasis in PDAC.

Adhesion, motility and matrix-degrading gene expression changes in CSF-1-induced mouse macrophage differentiation

Migratory macrophages play critical roles in tissue development, homeostasis and disease, so it is important to understand how their migration machinery is regulated. Whole-transcriptome sequencing revealed that CSF-1-stimulated differentiation of bone marrow-derived precursors into mature macrophages is accompanied by widespread, profound changes in the expression of genes regulating adhesion, actin cytoskeletal remodeling and extracellular matrix degradation. Significantly altered expression of almost 40% of adhesion genes, 60-86% of Rho family GTPases, their regulators and effectors and over 70% of extracellular proteases occurred. The gene expression changes were mirrored by changes in macrophage adhesion associated with increases in motility and matrix-degrading capacity. IL-4 further increased motility and matrix-degrading capacity in mature macrophages, with additional changes in migration machinery gene expression. Finally, siRNA-induced reductions in the expression of the core adhesion proteins paxillin and leupaxin decreased macrophage spreading and the number of adhesions, with distinct effects on adhesion and their distribution, and on matrix degradation. Together, the datasets provide an important resource to increase our understanding of the regulation of migration in macrophages and to develop therapies targeting disease-enhancing macrophages.

Characterization of Gut Microbiota, Bile Acid Metabolism, and Cytokines in Intrahepatic Cholangiocarcinoma

Intrahepatic cholangiocarcinoma (ICC), a type of bile duct cancer, has a high mortality rate. Gut microbiota, bile acid (BA) metabolism, and cytokines have not been characterized in patients with ICC, and better noninvasive diagnostic approaches for ICC are essential to be established. Therefore, in this study we aimed to improve our understanding of changes in gut microbiota, BA metabolism, and cytokines in patients with ICC. We found that the α-diversities and β-diversities of ICC were highest and that the abundances of four genera (Lactobacillus, Actinomyces, Peptostreptococcaceae, and Alloscardovia) were increased in patients with ICC compared with those in patients with hepatocellular carcinoma or liver cirrhosis and in healthy individuals. The glycoursodeoxycholic acid and tauroursodeoxycholic acid (TUDCA) plasma-stool ratios were obviously increased in patients with ICC. Furthermore, the genera Lactobacillus and Alloscardovia that were positively correlated with TUDCA plasma-stool ratios were combined to discriminate ICC from the other three diseases. Vascular invasion (VI) frequently led to a poor prognosis in patients with ICC. Compared with patients with ICC without VI, patients with VI had a greater abundance of the family Ruminococcaceae, increased levels of plasma interleukin (IL)-4 and six conjugated BAs, and decreased levels of plasma IL-6 and chenodeoxycholic acid. A positive correlation between plasma taurocholic acid and IL-4 was observed in patients with ICC. Plasma TUDCA was negatively correlated with the abundance of the genus Pseudoramibacter and the survival time of patients with ICC, but had no effect on tumor size, as determined in two murine tumor models. Conclusion: In this study, we identified some biomarkers, including gut microbiota, BAs and inflammatory cytokines, for the diagnosis of ICC and prediction of VI in patients with ICC.

Interleukin-4 Signaling Plays a Major Role in Urogenital Schistosomiasis-Associated Bladder Pathogenesis

Interleukin-4 (IL-4) is crucial in many helminth infections, but its role in urogenital schistosomiasis, infection with Schistosoma haematobium worms, remains poorly understood due to a historical lack of animal models. The bladder pathology of urogenital schistosomiasis is caused by immune responses to eggs deposited in the bladder wall. A range of pathology occurs, including urothelial hyperplasia and cancer, but associated mechanisms and links to IL-4 are largely unknown. We modeled urogenital schistosomiasis by injecting the bladder walls of IL-4 receptor-alpha knockout (Il4ra-/- ) and wild-type mice with S. haematobium eggs. Readouts included bladder histology and ex vivo assessments of urothelial proliferation, cell cycle, and ploidy status. We also quantified the effects of exogenous IL-4 on urothelial cell proliferation in vitro, including cell cycle status and phosphorylation patterns of major downstream regulators in the IL-4 signaling pathway. There was a significant decrease in the intensity of granulomatous responses to bladder-wall-injected S. haematobium eggs in Il4ra-/- versus wild-type mice. S. haematobium egg injection triggered significant urothelial proliferation, including evidence of urothelial hyper-diploidy and cell cycle skewing in wild-type but not Il4ra-/- mice. Urothelial exposure to IL-4 in vitro led to cell cycle polarization and increased phosphorylation of AKT. Our results show that IL-4 signaling is required for key pathogenic features of urogenital schistosomiasis and that particular aspects of this signaling pathway may exert these effects directly on the urothelium. These findings point to potential mechanisms by which urogenital schistosomiasis promotes bladder carcinogenesis.

Models for Monocytic Cells in the Tumor Microenvironment

Monocytes (Mos) are immune cells that critically regulate cancer, enabling tumor growth and modulating metastasis. Mos can give rise to tumor-associated macrophages (TAMs) and Mo-derived dendritic cells (moDCs), all of which shape the tumor microenvironment (TME). Thus, understanding their roles in the TME is key for improved immunotherapy. Concurrently, various biological and mechanical factors including changes in local cytokines, extracellular matrix production, and metabolic changes in the TME affect the roles of monocytic cells. As such, relevant TME models are critical to achieve meaningful insight on the precise functions, mechanisms, and effects of monocytic cells. Notably, murine models have yielded significant insight into human Mo biology. However, many of these results have yet to be confirmed in humans, reinforcing the need for improved in vitro human TME models for the development of cancer interventions. Thus, this chapter (1) summarizes current insight on the tumor biology of Mos, TAMs, and moDCs, (2) highlights key therapeutic applications relevant to these cells, and (3) discusses various TME models to study their TME-related activity. We conclude with a perspective on the future research trajectory of this topic.

Cancer Stem Cell Marker DCLK1 Correlates with Tumorigenic Immune Infiltrates in the Colon and Gastric Adenocarcinoma Microenvironments

Immunotherapy that has proven efficacy in several solid cancers plays a partial role in improving clinical outcomes of advanced gastrointestinal (GI) cancers. There is an unmet need to find new immune-related therapeutic targets. Doublecortin-like kinase 1 (DCLK1) marks tuft cells which are recognized as cancer-initiating cells and regulators of the type II immune response, and has been studied for its role in many cancers including colon and gastric cancers, but its role in tumor immunity remains unexplored. In the current study, we analyzed colon and gastric cancer RNA sequencing data from 283 and 415 patients, respectively, from The Cancer Genome Atlas (TCGA). High DCLK1 expression predicted the worse clinical outcomes in colon and gastric cancer patients and correlated with increased immune and stromal components. Further analysis indicated that DCLK1 was strongly linked to infiltration of multiple immune cell types, especially TAMs and Treg, and strongly correlated with increased CD8+ T cell inhibitors TGFB1 and CXCL12 and their receptors, suggesting it may contribute to TAM-mediated inhibition of CD8+ T cells. Interestingly, we found that DCLK1 was a prognostic biomarker in left-sided colon cancer, which has worse outcomes and demonstrates a reduced response to existing immunotherapies. In conclusion, our results demonstrate that DCLK1 is linked with functional regulation of the tumor microenvironment and may have potential as a prognostic biomarker and adjuvant target to promote immunotherapy sensitivity in colon and gastric cancer patients.

Monocytes and Macrophages in Cancer: Unsuspected Roles

The behavior of cancer is undoubtedly affected by stroma. Macrophages belong to this microenvironment and their presence correlates with reduced survival in most cancers. After a tumor-induced "immunoediting", these monocytes/macrophages, originally the first line of defense against tumor cells, undergo a phenotypic switch and become tumor-supportive and immunosuppressive.The influence of these tumor-associated macrophages (TAMs) on cancer is present in all traits of carcinogenesis. These cells participate in tumor initiation and growth, migration, vascularization, invasion and metastasis. Although metastasis is extremely clinically relevant, this step is always reliant on the angiogenic ability of tumors. Therefore, the formation of new blood vessels in tumors assumes particular importance as a limiting step for disease progression.Herein, the once unsuspected roles of macrophages in cancer will be discussed and their importance as a promising strategy to treat this group of diseases will be reminded.

Cysteine Cathepsins: Potential Applications in Diagnostics and Therapy of Malignant Tumors

Cysteine cathepsins are proteolytic enzymes involved in protein degradation in lysosomes and endosomes. Cysteine cathepsins have been also found in the tumor microenvironment during carcinogenesis, where they are implicated in proliferation, invasion and metastasis of tumor cells through the degradation of extracellular matrix, suppression of cell-cell interactions, and promotion of angiogenesis. In this regard, cathepsins can have a diagnostic value and represent promising targets for antitumor drugs aimed at inhibition of these proteases. Moreover, cysteine cathepsins can be used as activators of novel targeted therapeutic agents. This review summarizes recent discovered roles of cysteine cathepsins in carcinogenesis and discusses new trends in cancer therapy and diagnostics using cysteine cathepsins as markers, targets, or activators.

Prognostic and therapeutic relevance of cathepsin B in pediatric acute myeloid leukemia

AML, the second most common childhood leukemia is also one of the deadliest cancers. High mortality rate in AML is due to high incidence of relapse after complete remission with chemotherapy and inadequate prognostic assessment of patients. Moreover, there is dearth of therapeutic targets for treatment of this malignancy. Previous pilot study (n = 24) by our group revealed strong association between cathepsin B (CTSB) overexpression in peripheral blood mononuclear cells (PBMCs) and poor survival outcome in pediatric AML patients. To further explore the clinical utility and role of this protease in pediatric AML, we measured its enzymatic activity and mRNA expression in PBMCs as well as bone marrow mononuclear cells (BMMCs) of patients (n = 101) and PBMCs of healthy controls. Our results revealed elevated CTSB activity (P < 0.01) and overexpression of its mRNA (P < 0.01) in AML patients. Interestingly CTSB in BMMCs of patients emerged as an independent prognostic marker when compared with other known risk factors. Moreover, chemical inhibition of CTSB activity compromised survival, and induced apoptosis in an AML cell line THP-1. We further demonstrate the inhibition of CTSB activity by chemotherapeutic agent doxorubicin in these cells. Docking and simulation studies suggested the binding of doxorubicin to CTSB with higher affinity than its known specific inhibitor CA-074 Me, thereby indicating that cell death induced by this drug may at least partly be mediated by CTSB inhibition. CTSB, therefore, may serve as a prognostic marker and an attractive chemotherapeutic target in pediatric AML.

Tumor angiogenesis: causes, consequences, challenges and opportunities

Tumor vascularization occurs through several distinct biological processes, which not only vary between tumor type and anatomic location, but also occur simultaneously within the same cancer tissue. These processes are orchestrated by a range of secreted factors and signaling pathways and can involve participation of non-endothelial cells, such as progenitors or cancer stem cells. Anti-angiogenic therapies using either antibodies or tyrosine kinase inhibitors have been approved to treat several types of cancer. However, the benefit of treatment has so far been modest, some patients not responding at all and others acquiring resistance. It is becoming increasingly clear that blocking tumors from accessing the circulation is not an easy task to accomplish. Tumor vessel functionality and gene expression often differ vastly when comparing different cancer subtypes, and vessel phenotype can be markedly heterogeneous within a single tumor. Here, we summarize the current understanding of cellular and molecular mechanisms involved in tumor angiogenesis and discuss challenges and opportunities associated with vascular targeting.

Tumor-Infiltrating Immunosuppressive Cells in Cancer-Cell Plasticity, Tumor Progression and Therapy Response

In most tumors, cancer cells show the ability to dynamically transit from a non-cancer stem-like cell to a cancer stem-like cell (CSC) state and vice versa. This cell plasticity has been associated with the epithelial-to-mesenchymal transition program (EMT) and can be regulated by tumor cell-intrinsic mechanisms and complex interactions with various tumor microenvironment (TME) components. These interactions favor the generation of a specific "CSC niche" that helps maintain the main properties, phenotypic plasticity and metastatic potential of this subset of tumor cells. For this reason, TME has been recognized as an important promoter of tumor progression and therapy resistance. Tumors have evolved a network of immunosuppressive mechanisms that limits the cytotoxic T cell response to cancer cells. Some key players in this network are tumor-associated macrophages, myeloid-derived suppressor cells and regulatory T cells, which not only favor a pro-tumoral and immunosuppressive environment that supports tumor growth and immune evasion, but also negatively influences immunotherapy. Here, we review the relevance of cytokines and growth factors provided by immunosuppressive immune cells in regulating cancer-cell plasticity. We also discuss how cancer cells remodel their own niche to promote proliferation, stemness and EMT, and escape immune surveillance. A better understanding of CSC-TME crosstalk signaling will enable the development of effective targeted or immune therapies that block tumor growth and metastasis.

Recruitment of monocytes and epigenetic silencing of intratumoral CYP7B1 primarily contribute to the accumulation of 27-hydroxycholesterol in breast cancer

Previous studies showed that intratumoral 27-Hydroxycholesterol (27-HC), a metabolite of cholesterol, promotes growth, invasion and migration of breast cancer cells and that tumor-associated macrophages (TAMs) in breast cancers are closely related to tumor growth and metastatic progression. However, the relationship between 27-HC and TAMs in breast cancer remains unclear. In the present study, we observed that CYP27A1, the 27-HC synthesizing enzyme, was expressed in a much higher level in THP1 monocytes and THP1-derived macrophages than in breast cancer cells, and the promoter of CYP7B1, the degrading enzyme for 27-HC, was highly methylated in breast tumor cells. In addition, THP-1 monocytes and murine bone marrow cells were differentiated toward M2 type macrophages after being co-cultured with breast cancer cells or being exposed to exosomes derived from breast cancer cells. M2 type macrophages produced higher amounts of 27-HC than M0 and M1 type macrophages. 27-HC not only stimulated ER+ cancer cell proliferation as reported, but also promoted the recruitment of CCR2- and CCR5-expressing monocytes by inducing macrophages to express multiple chemokines including CCL2, CCL3 and CCL4. Taken together, our data demonstrate that the hypermethylation of CYP7B1 and recruitment of monocytes likely contribute to the accumulation of 27-Hydroxycholesterol in breast cancer and that the interaction of 27-HC with macrophages further promote the development of breast cancer.

Astragalus polysaccharides (PG2) Enhances the M1 Polarization of Macrophages, Functional Maturation of Dendritic Cells, and T Cell-Mediated Anticancer Immune Responses in Patients with Lung Cancer

Background: Recently, we demonstrated that Astragalus polysaccharide (PG2), the active ingredient in dried roots of astragalus membranaceus, ameliorates cancer symptom clusters and improves quality of life (QoL) in patients with metastatic disease by modulating inflammatory cascade against the background roles of inflammatory cells, including macrophages, dendritic cells (DCs), and cytotoxic T lymphocytes (CTLs) in tumor initiation, metastasis, and progression. Nevertheless, the role of PG2 in the modulation of anticancer immunogenicity and therapeutic response remains relatively underexplored and unclear. Purpose: The present study investigates how and to what extent PG2 modulates cellular and biochemical components of the inflammatory cascade and enhances anticancer immunity, as well as the therapeutic implication of these bio-events in patients with lung cancer. Methods and Results: Herein, we demonstrated that PG2 significantly increased the M1/M2 macrophage polarization ratio in non-small cell carcinoma (NSCLC) H441 and H1299 cells. This PG2-induced preferential pharmacologic up-regulation of tumoral M1 population in vitro positively correlated with the downregulation of tumor-promoting IL-6 and IL-10 expression in NSCLC cell-conditioned medium, with concomitant marked inhibition of cell proliferation, clonogenicity, and tumorsphere formation. Our ex vivo results, using clinical sample from our NSCLC cohort, demonstrated that PG2 also promoted the functional maturation of DCs with consequent enhancement of T cell-mediated anticancer immune responses. Consistent with the in vitro and ex vivo results, our in vivo studies showed that treatment with PG2 elicited significant time-dependent depletion of the tumor-associated M2 population, synergistically enhanced the anti-M2-based anticancer effect of cisplatin, and inhibited xenograft tumor growth in the NSCLC mice models. Moreover, in the presence of PG2, cisplatin-associated dyscrasia and weight-loss was markedly suppressed. Conclusion: These results do indicate a therapeutically-relevant role for PG2 in modulating the M1/M2 macrophage pool, facilitating DC maturation and synergistically enhancing the anticancer effect of conventional chemotherapeutic agent, cisplatin, thus laying the foundation for further exploration of the curative relevance of PG2 as surrogate immunotherapy and/or clinical feasibility of its use for maintenance therapy in patients with lung cancer.

Cathepsin L secretion by host and neoplastic cells potentiates invasion

The presence of macrophages within breast tumors correlates with metastatic potential. These tumor-associated macrophages often take on a pro-tumorigenic (M2-like) phenotype resulting in the secretion of growth factors and proteases, including the lysosomal protease cathepsin L. Since cathepsin L also is frequently secreted by breast cancer cells and contributes to tumor invasion, metastasis, and angiogenesis, we hypothesized that secretion of cathepsin L by both tumor-associated macrophages and neoplastic cells would facilitate the metastatic phenotype. Our results showed that the novel cathepsin L/K inhibitors KGP94 and KGP207 could inhibit in vitro M2 macrophage invasion and reduce the macrophage-stimulated invasion of 4T1 murine breast cancer cells. KGP94 and KGP207 treatment also reduced the expression of several M2-associated markers, suggesting that cathepsin L activity may be important for IL-4-driven M0 to M2 differentiation. In addition, cathepsin L shRNA knockdown studies revealed that cathepsin L from both the tumor cell and the macrophage population is important for tumor cell invasion. Thus our data suggest that tumor cells and macrophages may both contribute to the cathepsin L-driven metastatic phenotype of breast cancer. Taken together, these studies highlight the importance of cathepsin L in macrophage functions and suggest that cathepsin inhibition strategies may be therapeutically beneficial by impairing the progression of tumors with high infiltration of M2 macrophages.

A review on the role of M2 macrophages in bladder cancer; pathophysiology and targeting

Tumor-associated macrophages (TAMs) which are often referred to as immunosuppressive cells (M2 macrophage), constitute a subset of tumor microenvironment cells and affect tumor progression in solid tumors. Recently, these cells have gained remarkable importance as therapeutic candidates for solid tumors. In bladder cancer, major studies have focused on evaluating TAMs in response to Bacillus Calmette-Guerin (BCG) therapy. M2 macrophages may directly impact the BCG-induced immune responses against tumor in bladder cancer. They are the main inhibitors of the tumor microenvironment that promotes growth and metastasis of the tumor. However, the clinical significance of M2 macrophages in bladder cancer is controversial. In this review, we will discuss the clinical significance of M2 macrophages in prognosis of bladder cancer as well as worth of their potential targeting in bladder cancer treatment. In the following, we will introduce important factors resulting in M2 macrophage promotion and also experimental therapeutic agents that may cause the inhibition of bladder cancer tumor growth.

Regulatory T Cells Control the Switch From in situ to Invasive Breast Cancer

Ductal carcinoma in situ (DCIS) is a non-obligate precursor of breast cancer, and it only progresses to invasive breast cancer in around 40% of patients. While immune infiltrates have been observed in these early cancer lesions, their potential prognostic value is still unclear. Regulatory T (Treg) cells accumulate in advanced breast cancers, and predict poor outcome. We have shown before that ablation of Treg cells in established tumors leads to significant decrease in primary and metastatic tumor burden. In this work, we sought to investigate Treg cell function in the progression from non-invasive to invasive breast cancer lesions. To this end, we used the murine mammary tumor virus polyoma middle T (MMTV-PyMT) murine model of spontaneous, stage-wise breast carcinogenesis crossed to Foxp3 DTR knock in mice, allowing Treg cell ablation by administration of diphtheria toxin. Transient targeting of Treg cells at the in situ carcinoma stage resulted in a significant increase in the number of tumor-bearing mammary glands and size of growing tumors compared with control mice. Whole mammary gland mounts and histological examination confirmed larger emergent tumor area in Treg cell-ablated mice, and revealed that these tumors were characterized by a more advanced tumor staging, with presence of early invasion, increased desmoplasia and collagen deposition. Furthermore, Treg cell ablation increased the percentage of cancer stem/progenitor cells in the mammary compartment. Interestingly, Treg cell ablation resulted in increased inflammatory cytokines IL-4 and IL-5 with a concomitant reduction in classically activated tumor associated macrophages. This TH2-biased immune regulatory mammary inflammation was consistent with the enhancement in tumor promotion that we observed. Overall, our study demonstrates that Treg cells oppose breast cancer progression at early stages, raising a cautionary note regarding the consideration of immune intervention targeted at boosting immune responses for DCIS.

Cysteine Cathepsins in Tumor-Associated Immune Cells

Cysteine cathepsins are key regulators of the innate and adaptive arms of the immune system. Their expression, activity, and subcellular localization are associated with the distinct development and differentiation stages of immune cells. They promote the activation of innate myeloid immune cells since they contribute to toll-like receptor signaling and to cytokine secretion. Furthermore, they control lysosomal biogenesis and autophagic flux, thus affecting innate immune cell survival and polarization. They also regulate bidirectional communication between the cell exterior and the cytoskeleton, thus influencing cell interactions, morphology, and motility. Importantly, cysteine cathepsins contribute to the priming of adaptive immune cells by controlling antigen presentation and are involved in cytotoxic granule mediated killing in cytotoxic T lymphocytes and natural killer cells. Cathepins'aberrant activity can be prevented by their endogenous inhibitors, cystatins. However, dysregulated proteolysis contributes significantly to tumor progression also by modulation of the antitumor immune response. Especially tumor-associated myeloid cells, such as tumor-associated macrophages and myeloid-derived suppressor cells, which are known for their tumor promoting and immunosuppressive functions, constitute the major source of excessive cysteine cathepsin activity in cancer. Since they are enriched in the tumor microenvironment, cysteine cathepsins represent exciting targets for development of new diagnostic and therapeutic moieties.

Prognostic significance of cathepsin V (CTSV/CTSL2) in breast ductal carcinoma in situ

AIMS

Cathepsin V (CTSV/CTSL2) is a lysosomal cysteine proteinase and plays a role in extracellular matrix degradation. It is associated with poor prognosis in invasive breast cancer (IBC), but its role in breast ductal carcinoma in situ (DCIS) remains unclear. In this study, we aimed to evaluate the prognostic significance of CTSV in DCIS.

METHODS

CTSV protein expression was immunohistochemically assessed in a well-characterised and annotated cohort of DCIS comprising pure DCIS (n=776) and DCIS coexisting with IBC (n=239). CTSV expression was analysed in tumour cells and surrounding stroma, including its association with clinicopathological parameters and outcome.

RESULTS

In pure DCIS, high CTSV expression was observed in 29% of epithelial tumour cells and 20% of surrounding stroma. High expression in both components was associated with features of poor prognosis including higher nuclear grade, hormone receptor negativity and HER2 positivity. In addition, stromal CTSV expression was associated with larger DCIS size, comedo-type necrosis and high proliferation index. DCIS associated with IBC showed higher CTSV expression than pure DCIS either within the epithelial tumour cells or surrounding stroma (p<0.0001 and p=0.001, respectively). In DCIS/IBC, CTSV expression was higher in the invasive component than DCIS component either in tumour cells or surrounding stroma (both p<0.0001). CTSV stromal expression was associated with invasive recurrence independent of other prognostic factors in patients treated with breast conserving surgery (HR=3.0, p=0.005).

CONCLUSION

High expression of CTSV is associated with poor outcome in DCIS and is a potential marker to predict DCIS progression to invasive disease.

Fisetin Suppresses the Proliferation and Metastasis of Renal Cell Carcinoma through Upregulation of MEK/ERK-Targeting CTSS and ADAM9

Fisetin, a natural flavonoid, is known to have anticarcinogenic effects against several cancers, but its role in mediating renal cell carcinoma (RCC) progression has not been delineated. Cell viability, cytotoxicity, and cell cycle distribution were measured using the 3-(4,5-cimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay and propidium iodide staining with flow cytometry. The in vitro migration and invasion assay was used to examine in vivo cell migration and invasion. Human protease antibody array analysis was conducted with cell migration/invasion-related proteins. Western blotting and quantitative reverse transcription polymerase chain reaction were used for assessing protein expression related to the cell cycle, cell invasion, and mitogen-activated protein kinase (MAPK) signaling pathway. We found that fisetin significantly inhibited cell viability through cell cycle arrest in the G2/M phase, in addition to downregulating cyclin D1 and upregulating p21/p27. Fisetin inhibited the migration and invasion of human RCC cells through the downregulation of CTSS and a disintegrin and metalloproteinase 9 (ADAM9). Fisetin also upregulated ERK phosphorylation in 786-O and Caki-1 cells. Furthermore, treatment with a MEK inhibitor (UO126) reduced the inhibitory effects of fisetin on the metastasis of RCC cells through the ERK/CTSS/ADAM9 pathway. Fisetin inhibits proliferation and metastasis of RCC cells by downregulating CTSS and ADAM9 through the MEK/ERK signaling pathway. These findings indicate that fisetin is a promising antitumor agent against RCC.

Tumorigenic Interplay Between Macrophages and Collagenous Matrix in the Tumor Microenvironment

The tumor microenvironment is a heterogeneous tissue that in addition to tumor cells, contain tumor-associated cell types such as immune cells, fibroblasts, and endothelial cells. Considerably important in the tumor microenvironment is its noncellular component, namely, the extracellular matrix (ECM). In particular, the collagenous matrix is subjected to significant alterations in its composition and structure that create a permissive environment for tumor growth, invasion, and dissemination. Among tumor-infiltrating immune cells, tumor-associated macrophages (TAMs) are numerous in the tumor stroma and are locally educated to mediate important biological functions that profoundly affect tumor initiation, growth, and dissemination. While the influence of TAMs and mechanical properties of the collagenous matrix on tumor invasion and progression have been comprehensively investigated individually, their interaction within the complex tumor microenvironment was overlooked. This review summarizes accumulating evidence that indicate the existence of an intricate tumorigenic crosstalk between TAMs and collagenous matrix. A better mechanistic comprehension of this reciprocal interplay may open a novel arena for cancer therapeutics.