Cyclooxygenase-2 inhibitor enhances the efficacy of a breast cancer vaccine: role of IDO

Facts and Hopes on Neutralization of Protumor Inflammatory Mediators in Cancer Immunotherapy

In cancer pathogenesis, soluble mediators are responsible for a type of inflammation that favors the progression of tumors. The mechanisms chiefly involve changes in the cellular composition of the tumor tissue stroma and in the functional modulation of myeloid and lymphoid leukocytes. Active immunosuppression, proangiogenesis, changes in leukocyte traffic, extracellular matrix remodeling, and alterations in tumor-antigen presentation are the main mechanisms linked to the inflammation that fosters tumor growth and metastasis. Soluble inflammatory mediators and their receptors are amenable to various types of inhibitors that can be combined with other immunotherapy approaches. The main proinflammatory targets which can be interfered with at present and which are under preclinical and clinical development are IL1β, IL6, the CXCR1/2 chemokine axis, TNFα, VEGF, leukemia inhibitory factor, CCL2, IL35, and prostaglandins. In many instances, the corresponding neutralizing agents are already clinically available and can be repurposed as a result of their use in other areas of medicine such as autoimmune diseases and chronic inflammatory conditions.

Amino acid metabolism reprogramming: shedding new light on T cell anti-tumor immunity

Metabolic reprogramming of amino acids has been increasingly recognized to initiate and fuel tumorigenesis and survival. Therefore, there is emerging interest in the application of amino acid metabolic strategies in antitumor therapy. Tremendous efforts have been made to develop amino acid metabolic node interventions such as amino acid antagonists and targeting amino acid transporters, key enzymes of amino acid metabolism, and common downstream pathways of amino acid metabolism. In addition to playing an essential role in sustaining tumor growth, new technologies and studies has revealed amino acid metabolic reprograming to have wide implications in the regulation of antitumor immune responses. Specifically, extensive crosstalk between amino acid metabolism and T cell immunity has been reported. Tumor cells can inhibit T cell immunity by depleting amino acids in the microenvironment through nutrient competition, and toxic metabolites of amino acids can also inhibit T cell function. In addition, amino acids can interfere with T cells by regulating glucose and lipid metabolism. This crucial crosstalk inspires the exploitation of novel strategies of immunotherapy enhancement and combination, owing to the unprecedented benefits of immunotherapy and the limited population it can benefit. Herein, we review recent findings related to the crosstalk between amino acid metabolism and T cell immunity. We also describe possible approaches to intervene in amino acid metabolic pathways by targeting various signaling nodes. Novel efforts to combine with and unleash potential immunotherapy are also discussed. Hopefully, some strategies that take the lead in the pipeline may soon be used for the common good.

Interactions of IDO and the Kynurenine Pathway with Cell Transduction Systems and Metabolism at the Inflammation-Cancer Interface

The mechanisms underlying a relationship between inflammation and cancer are unclear, but much emphasis has been placed on the role of tryptophan metabolism to kynurenine and downstream metabolites, as these make a substantial contribution to the regulation of immune tolerance and susceptibility to cancer. The proposed link is supported by the induction of tryptophan metabolism by indoleamine-2,3-dioxygenase (IDO) or tryptophan-2,3-dioxygenase (TDO), in response to injury, infection or stress. This review will summarize the kynurenine pathway and will then focus on the bi-directional interactions with other transduction pathways and cancer-related factors. The kynurenine pathway can interact with and modify activity in many other transduction systems, potentially generating an extended web of effects other than the direct effects of kynurenine and its metabolites. Conversely, the pharmacological targeting of those other systems could greatly enhance the efficacy of changes in the kynurenine pathway. Indeed, manipulating those interacting pathways could affect inflammatory status and tumor development indirectly via the kynurenine pathway, while pharmacological modulation of the kynurenine pathway could indirectly influence anti-cancer protection. While current efforts are progressing to account for the failure of selective IDO1 inhibitors to inhibit tumor growth and to devise means of circumventing the issue, it is clear that there are wider factors involving the relationship between kynurenines and cancer that merit detailed consideration as alternative drug targets.

Vaccination with celecoxib-treated dendritic cells improved cellular immune responses in an animal breast cancer model

PURPOSE

Prostaglandin E2 (PGE2), a product of cyclooxygenase (COX) pathway of arachidonic acid, exerts inhibitory impacts on dendritic cell (DC) activity to repress anti-tumor immune responses. Therefore, targeting COX during DC vaccine generation may enhance DC-mediated antitumor responses. We aimed to investigate the impacts of DC vaccine treated with celecoxib (CXB), a selective COX2 inhibitor, on some T cell-related parameters.

MATERIALS AND METHODS

Breast cancer (BC) was induced in BALB/c mice, and then they received DC vaccine treated with lipopolysaccharide (LPS-mDCs), LPS with a 5 ​μM dose of CXB (LPS/CXB5-mDCs) and LPS with a 10 ​μM dose of CXB (LPS/CXB10-mDCs). The frequency of splenic Th1 and Treg cells and amounts of IFN-γ, IL-12 and TGF-β production by splenocytes, as well as, the expression of Granzyme-B, T-bet and FOXP3 in tumors were determined using flow cytometry, ELISA, and real-time PCR, respectively.

RESULTS

Compared with untreated tumor group (T-control), treatment with LPS/CXB5-mDCs and LPS/CXB10-mDCs decreased tumor growth (P ​= ​0.009 and P ​< ​0.0001), escalated survival rate (P ​= ​0.002), increased the frequency of splenic Th1 cells (P ​= ​0.0872, and P ​= ​0.0155), increased the IFN-γ (P ​= ​0.0003 and P ​= ​0.0061) and IL-12 (P ​= ​0.001 and P ​= ​0.0009) production by splenocytes, upregulated T-bet (P ​= ​0.062 and P ​< ​0.0001) and Granzyme-B (P ​= ​0.0448 and P ​= ​0.4485), whereas decreased the number of Treg cells (P ​= ​0.0014, and P ​= ​0.0219), reduced the amounts of TGF-β production by splenocytes (P ​= ​0.0535 and P ​= ​0.0169), and reduced the expression of FOXP3 (P ​= ​0.0006 and P ​= ​0.0057) in comparison with T-control group.

CONCLUSIONS

Our findings show that LPS/CXB-treated DC vaccine potently modulated antitumor immune responses in a mouse BC model.

Liposomal celecoxib combined with dendritic cell therapy enhances antitumor efficacy in melanoma

Cancer vaccine efficacy is limited by the immunosuppressive nature of the tumor microenvironment created by inflammation, immune inhibitory factors, and regulatory T cells (Tregs). Inspired by the role of cyclooxygenase-2 (COX-2) in inflammation in the tumor site, we proposed that normalization of the tumor microenvironment by celecoxib as a COX-2 inhibitor might improve the efficacy of Dendritic Cell (DC) therapy in a melanoma model. In the present study, liposomal celecoxib (Lip-CLX) was combined with ex vivo generated DC vaccines pulsed with gp100 peptide (in liposomal and non-liposomal forms) for prophylactic and therapeutic evaluation in the B16F10 melanoma model. Tumor site analysis by flow cytometry demonstrated that intravenous administration of Lip-CLX at a dose of 1 mg/kg in four doses effectively normalized the tumor microenvironment by reducing Tregs and IL-10 production. Furthermore, in combination with DC vaccination (DC + Lip-peptide+Lip-CLX), it significantly increased tumor-infiltrating CD4⁺ and CD8⁺ T cells and secretion of IFN-γ. This combinatorial strategy produced an effective prophylactic and therapeutic antitumor response, which reduced tumor growth and prolonged the overall survival. In conclusion, our findings suggest that the liposomal celecoxib targets the inhibitory mechanisms of the tumor microenvironment and broadens the impact of DC therapy to improve the outcome of immunotherapy in solid tumors.

Immunotherapy and targeted therapy for lung cancer: Current status and future perspectives

Lung cancer has the highest incidence of morbidity and mortality throughout the globe. A large number of patients are diagnosed with lung cancer at the later stages of the disease. This eliminates surgery as an option and places complete dependence on radiotherapy or chemotherapy, and/or a combination of both, to halt disease progression by targeting the tumor cells. Unfortunately, these therapies have rarely proved to be effective, and this necessitates the search for alternative preventive approaches to reduce the mortality rate of lung cancer. One of the effective therapies against lung cancer comprises targeting the tumor microenvironment. Like any other cancer cells, lung cancer cells tend to use multiple pathways to maintain their survival and suppress different immune responses from the host's body. This review comprehensively covers the role and the mechanisms that involve the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) in lung adenocarcinoma and methods of treating it by altering the tumor microenvironment. It focuses on the insight and understanding of the lung cancer tumor microenvironment and chemokines, cytokines, and activating molecules that take part in angiogenesis and metastasis. The review paper accounts for the novel and current immunotherapy and targeted therapy available for lung cancer in clinical trials and in the research phases in depth. Special attention is being paid to mark out single or multiple genes that are required for malignancy and survival while developing targeted therapies for lung cancer treatment.

IDO/kynurenine pathway in cancer: possible therapeutic approaches

Cancer is one of the leading causes of death in both men and women worldwide. One of the main changes associated with cancer progression, metastasis, recurrence, and chemoresistance is the change in the tumor immune microenvironment, especially immunosuppression. Cancer immunosuppression appears in multiple forms, such as inhibition of immuno-stimulant cells with downregulation of immuno-stimulant mediators or through stimulation of immuno-suppressive cells with upregulation of immunosuppressive mediators. One of the most immunosuppressive mediators that approved potency in lung cancer progression is indoleamine 2,3-dioxygenase (IDO) and its metabolite kynurenine (Kyn). The current review tries to elucidate the role of IDO/Kyn on cancer proliferation, apoptosis, angiogenesis, oxidative stress, and cancer stemness. Besides, our review investigates the new therapeutic modalities that target IDO/Kyn pathway and thus as drug candidates for targeting lung cancer and drugs that potentiate IDO/Kyn pathway and thus can be cancer-promoting agents.

Inhibition of the Na+/K+-ATPase by cardiac glycosides suppresses expression of the IDO1 immune checkpoint in cancer cells by reducing STAT1 activation

Despite extensive basic and clinical research on immune checkpoint regulatory pathways, little is known about the effects of the ionic tumor microenvironment on immune checkpoint expression and function. Here we describe a mechanistic link between Na+/K+-ATPase (NKA) inhibition and activity of the immune checkpoint protein indoleamine-pyrrole 2',3'-dioxygenase 1 (IDO1). We found that IDO1 was necessary and sufficient for production of kynurenine, a downstream tryptophan metabolite, in cancer cells. We developed a spectrophotometric assay to screen a library of 31 model ion transport-targeting compounds for potential effects on IDO1 function in A549 lung and MDA-MB-231 breast cancer cells. This revealed that the cardiac glycosides ouabain and digoxin inhibited kynurenine production at concentrations that did not affect cell survival. NKA inhibition by ouabain and digoxin resulted in increased intracellular Na+ levels and downregulation of IDO1 mRNA and protein levels, which was consistent with the reduction in kynurenine levels. Knockdown of ATP1A1, the ɑ1 subunit of the NKA and target of cardiac glycosides, increased Na+ levels to a lesser extent than cardiac glycoside treatment and did not affect IDO1 expression. However, ATP1A1 knockdown significantly enhanced the effect of cardiac glycosides on IDO1 expression and kynurenine production. Mechanistically, we show that cardiac glycoside treatment resulted in curtailing the length of phosphorylation-mediated stabilization of STAT1, a transcriptional regulator of IDO1 expression, an effect enhanced by ATP1A1 knockdown. Our findings reveal cross talk between ionic modulation via cardiac glycosides and immune checkpoint protein expression in cancer cells with broad mechanistic and clinical implications.

Tryptophan Metabolism in Atherosclerosis and Diabetes

The essential amino acid tryptophan (Trp) undergoes catabolism through several pathways, producing biologically active metabolites that significantly impact physiological processes. The metabolic pathway responsible for the majority of Trp catabolism is the kynurenine synthesis pathway (KP). Serotonin and melatonin are among the most essential Trp pathways degradation products. It has emerged that a strong relationship exists between alterations in Trp metabolism and the onset and progression of atherosclerosis and diabetes. Atherosclerosis is a chronic inflammatory disease of the small and medium arteries wall caused by maladaptive local immune responses, which underpins several cardiovascular diseases (CVD). Systemic low-grade immune-mediated inflammation is implicated in atherosclerosis where pro-inflammatory cytokines, such as interferon-γ (IFN-γ), play a significant role. IFN-γ upregulates the enzyme indoleamine 2,3-dioxygenase (IDO), decreasing serum levels of the Trp and increasing metabolite levels of kynurenine. Increased IDO expression and activity could accelerate the atherosclerosis process. Therefore, activated IDO inhibition could offer possible treatment options regarding atherosclerosis management. Diabetes is a chronic metabolic disease characterized by hyperglycemia that, over time, leads to severe damage to the heart, blood vessels, eyes, kidneys, and peripheral nerves. Trp serum levels and lower activity of IDO were higher in future type 2 diabetes (T2DM) patients. This article reviews recent findings on the link between mammalian Trp metabolism and its role in atherosclerosis and diabetes and outlines the intervention strategies.

Targeting hippocampal phospholipid and tryptophan metabolism for antidepressant-like effects of albiflorin

BACKGROUND

Current antidepressant therapy remains unsatisfactory due to its delayed clinical onset of action and the heterogeneity of depression. Targeting disturbed neurometabolic pathways could provide a novel therapeutic approach for the treatment of depression. Albiflorin is a phytomedicine isolated from the root of Peony (Paeonia albiflora Pall) with excellent clinical tolerance. Until now, the antidepressant-like activities of albiflorin in different subtypes of depression and its effects on neurometabolism are unknown.

PURPOSE

The objective of this study was to investigate the rapid antidepressant-like effects of albiflorin in three common animal models of depression and elucidate the pharmaco-metabolic mechanisms of its action using a multi-omics approach.

RESULTS

We found that albiflorin produces rapid antidepressant-like effects in chronic unpredictable mild stress (CUMS), olfactory bulbectomy (OBX), and lipopolysaccharide (LPS)-induced murine models of depression. Using a system-wide approach combining metabolomics, lipidomics, and transcriptomics, we showed that the therapeutic effects of albiflorin are highly associated with the rapid restoration of a set of common metabolic abnormities in the hippocampus across all three depression models, including phospholipid and tryptophan metabolism. Further mechanistic analysis revealed that albiflorin normalized the metabolic dysregulation in phospholipid metabolism by suppressing hippocampal cytosolic phospholipases A2 (cPLA2). Additionally, inhibition of cPLA2 overexpression by albiflorin corrects abnormal kynurenine pathway of tryptophan metabolism via the cPLA2-protein kinase B (Akt1)-indoleamine 2,3-dioxygenase 1(IDO1) regulatory loop and directs tryptophan catabolism towards more hippocampal serotonin biosynthesis.

CONCLUSION

Our study contributed to a better understanding of the homogeneity in the metabolic mechanisms of depression and established a proof-of-concept for rapid treatment of depression through targeting dysregulated neurometabolic pathways.

Kynurenines as a Novel Target for the Treatment of Malignancies

Malignancies are unquestionably a significant public health problem. Their effective treatment is still a big challenge for modern medicine. Tumors have developed a wide range of mechanisms to evade an immune and therapeutic response. As a result, there is an unmet clinical need for research on solutions aimed at overcoming this problem. An accumulation of tryptophan metabolites belonging to the kynurenine pathway can enhance neoplastic progression because it causes the suppression of immune system response against cancer cells. They are also involved in the development of the mechanisms responsible for the resistance to antitumor therapy. Kynurenine belongs to the most potent immunosuppressive metabolites of this pathway and has a significant impact on the development of malignancies. This fact prompted researchers to assess whether targeting the enzymes responsible for its synthesis could be an effective therapeutic strategy for various cancers. To date, numerous studies, both preclinical and clinical, have been conducted on this topic, especially regarding the inhibition of indoleamine 2,3-dioxygenase activity and their results can be considered noteworthy. This review gathers and systematizes the knowledge about the role of the kynurenine pathway in neoplastic progression and the findings regarding the usefulness of modulating its activity in anticancer therapy.

Inhibitory effects of a selective prostaglandin E2 receptor antagonist RQ-15986 on inflammation-related colon tumorigenesis in APC-mutant rats

Prostaglandin E2 receptor EP4 is involved in inflammation and related tumorigenesis in the colorectum. This study aimed to investigate the chemopreventive ability of RQ-15986, a selective EP4 antagonist, in colitis-related colorectal tumorigenesis. Male Kyoto APC delta rats, which have APC mutations, were treated with azoxymethane and dextran sulfate sodium and subsequently administered RQ-15986 for eight weeks. At the end of the experiment, the development of colorectal tumor was significantly inhibited in the RQ-15986-treated group. The cell proliferation of the crypts and tumors in the colorectum was decreased following RQ-15986 treatment. RQ-15986 also suppressed the expression of pro-inflammatory cytokines, including tumor necrosis factor-α, interleukin-6, interleukin-18, and monocyte chemotactic protein-1, in the colon mucosa. In addition, the expression levels of indoleamine 2,3-dioxygenase, which is involved in immune tolerance, were decreased in the colorectal epithelium and tumors of the RQ-15986-treated group. These findings indicate that RQ-15986 inhibits colitis-associated colorectal tumorigenesis by attenuating inflammation, suppressing cell proliferation, and modulating the expression of indoleamine 2,3-dioxygenase. Targeting prostaglandin E2/EP4 signaling might be a useful strategy for chemoprevention of inflammation-related colorectal cancer.

Cytoguardin: A Tryptophan Metabolite against Cancer Growth and Metastasis

Cytoguardin was identified in the conditioned medium of fibroblasts as a tryptophan metabolite, 5-methoxytryptophan (5-MTP). It is synthesized via two enzymatic steps: tryptophan hydroxylase (TPH) and hydroxyindole O-methyltransferase (HIOMT). A truncated HIOMT isoform, HIOMT298, catalyzes 5-MTP synthesis. Cancer cells produce scarce 5-MTP due to defective HIOMT298 expression. 5-MTP inhibits cancer cell COX-2 expression and thereby reduces COX-2-mediated cell proliferation and migration. 5-MTP also inhibits MMP-9 expression and thereby reduces cancer cell invasion. 5-MTP exerts its anti-cancer effect by blocking p38 MAPK and p38-mediated NF-κB and p300 HAT activation. The stable transfection of A549 cells with HIOMT298 restores 5-MTP production which renders cancer cells less aggressive. The implantation of HIOMT-transfected A549 into subcutaneous tissues of a murine xenograft tumor model shows that HIOMT-transduced A549 cells form smaller tumors and generate fewer metastatic lung nodules than control A549 cells. HIOMT298 transfection suppresses aromatic amino acid decarboxylase (AADC) expression and serotonin production. Serotonin is a cancer-promoting factor. By restoring 5-MTP and suppressing serotonin production, HIOMT298 overexpression converts cancer cells into less malignant phenotypes. The analysis of HIOMT expression in a human cancer tissue array showed reduced HIOMT levels in a majority of colorectal, pancreatic, and breast cancer. HIOMT298 may be a biomarker of human cancer progression. Furthermore, 5-MTP has the potential to be a lead compound in the development of new therapy for the chemoprevention of certain cancers such as hepatocellular cancer.

The footprint of kynurenine pathway in every cancer: a new target for chemotherapy

Treatment of cancers has always been a challenge for physicians. Typically, several groups of anti-cancer medications are needed for effective management of an invasive and metastatic cancer. Recently, therapeutic potentiation of immune system markedly improved treatment of cancers. Kynurenine pathway has an interwoven correlation with immune system. Kynurenine promotes T Reg (regulatory) differentiation, which leads to increased production of anti-inflammatory cytokines and suppression of cytotoxic activity of T cells. Overactivation of kynurenine pathway in cancers provides an immunologically susceptible microenvironment for mutant cells to survive and invade surrounding tissues. Interestingly, kynurenine pathway vigorously interacts with other molecular pathways involved in tumorigenesis. For instance, kynurenine pathway interacts with phospoinosisitide-3 kinase (PI3K), extracellular signal-regulated kinase (ERK), Wnt/β-catenin, P53, bridging integrator 1 (BIN-1), cyclooxygenase 2 (COX-2), cyclin-dependent kinase (CDK) and collagen type XII α1 chain (COL12A1). Overactivation of kynurenine pathway, particularly overactivation of indoleamine 2,3-dioxygenase (IDO) predicts poor prognosis of several cancers such as gastrointestinal cancers, gynecological cancers, hematologic malignancies, breast cancer, lung cancer, glioma, melanoma, prostate cancer and pancreatic cancer. Furthermore, kynurenine increases the invasion, metastasis and chemoresistance of cancer cells. Recently, IDO inhibitors entered clinical trials and successfully passed their safety tests and showed promising therapeutic efficacy for cancers such as melanoma, brain cancer, renal cell carcinoma, prostate cancer and pancreatic cancer. However, a phase III trial of epacadostat, an IDO inhibitor, could not increase the efficacy of treatment with pembrolizumab for melanoma. In this review the expanding knowledge towards kynurenine pathway and its application in each cancer is discussed separately.

Role of tryptophan metabolism in cancers and therapeutic implications

Tryptophan (Trp) metabolism is associated with diverse biological processes, including nerve conduction, inflammation, and the immune response. The majority of free Trp is broken down through the kynurenine (Kyn) pathway (KP), in which indoleamine-2,3-dioxygenase (IDO) and tryptophan-2,3-dioxygenase (TDO) catalyze the rate-limiting step. Clinical studies have demonstrated that Trp metabolism promotes tumor progression due to modulation of the immunosuppressive microenvironment through multiple mechanisms. In this process, IDO-expressing dendritic cells (DCs) exhibit tolerogenic potential and orchestrate T cell immune responses. Various signaling molecules control IDO expression, initiating the immunoregulatory pathway of Trp catabolism. Based on these characteristics, KP enzymes and catabolites are emerging as significant prognostic indicators and potential therapeutic targets of cancer. The physiological and oncologic roles of Trp metabolism are briefly summarized here, along with great challenges for treatment strategies.

Tumor resistance mechanisms and their consequences on γδ T cell activation

Human γδ T lymphocytes are predominated by two major subsets, defined by the variable domain of the δ chain. Both, Vδ1 and Vδ2 T cells infiltrate in tumors and have been implicated in cancer immunosurveillance. Since the localization and distribution of tumor-infiltrating γδ T cell subsets and their impact on survival of cancer patients are not completely defined, this review summarizes the current knowledge about this issue. Different intrinsic tumor resistance mechanisms and immunosuppressive molecules of immune cells in the tumor microenvironment have been reported to negatively influence functional properties of γδ T cell subsets. Here, we focus on selected tumor resistance mechanisms including overexpression of cyclooxygenase (COX)-2 and indolamine-2,3-dioxygenase (IDO)-1/2, regulation by tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)/TRAIL-R4 pathway and the release of galectins. These inhibitory mechanisms play important roles in the cross-talk of γδ T cell subsets and tumor cells, thereby influencing cytotoxicity or proliferation of γδ T cells and limiting a successful γδ T cell-based immunotherapy. Possible future directions of a combined therapy of adoptively transferred γδ T cells together with γδ-targeting bispecific T cell engagers and COX-2 or IDO-1/2 inhibitors or targeting sialoglycan-Siglec pathways will be discussed and considered as attractive therapeutic options to overcome the immunosuppressive tumor microenvironment.

Influence of Indoleamine-2,3-Dioxygenase and Its Metabolite Kynurenine on γδ T Cell Cytotoxicity against Ductal Pancreatic Adenocarcinoma Cells

BACKGROUND

Pancreatic ductal adenocarcinoma (PDAC) is a malignant gastrointestinal disease. The enzyme indoleamine-2,3-dioxgenase (IDO) is often overexpressed in PDAC and its downstream metabolite kynurenine has been reported to inhibit T cell activation and proliferation. Since γδ T cells are of high interest for T cell-based immunotherapy against PDAC, we studied the impact of IDO and kynurenine on γδ T cell cytotoxicity against PDAC cells.

METHODS

IDO expression was determined in PDAC cells by flow cytometry and Western blot analysis. PDAC cells were cocultured with γδ T cells in medium or were stimulated with phosphorylated antigens or bispecific antibody in the presence or absence of IDO inhibitors. Additionally, γδ T cells were treated with recombinant kynurenine. Read-out assays included degranulation, cytotoxicity and cytokine measurement as well as cell cycle analysis.

RESULTS

Since IDO overexpression was variable in PDAC, IDO inhibitors improved γδ T cell cytotoxicity only against some but not all PDAC cells. γδ T cell degranulation and cytotoxicity were significantly decreased after their treatment with recombinant kynurenine.

CONCLUSIONS

Bispecific antibody drastically enhanced γδ T cell cytotoxicity against all PDAC cells, which can be further enhanced by IDO inhibitors against several PDAC cells, suggesting a striking heterogeneity in PDAC escape mechanisms towards γδ T cell-mediated anti-tumor response.

Nanoparticle mediated cancer immunotherapy

The versatility and nanoscale size have helped nanoparticles (NPs) improve the efficacy of conventional cancer immunotherapy and opened up exciting approaches to combat cancer. This review first outlines the tumor immune evasion and the defensive tumor microenvironment (TME) that hinders the activity of host immune system against tumor. Then, a detailed description on how the NP based strategies have helped improve the efficacy of conventional cancer vaccines and overcome the obstacles led by TME. Sustained and controlled drug delivery, enhanced cross presentation by immune cells, co-encapsulation of adjuvants, inhibition of immune checkpoints and intrinsic adjuvant like properties have aided NPs to improve the therapeutic efficacy of cancer vaccines. Also, NPs have been efficient modulators of TME. In this context, NPs facilitate better penetration of the chemotherapeutic drug by dissolution of the inhibitory meshwork formed by tumor associated cells, blood vessels, soluble mediators and extra cellular matrix in TME. NPs achieve this by suppression, modulation, or reprogramming of the immune cells and other mediators localised in TME. This review further summarizes the applications of NPs used to enhance the efficacy of cancer vaccines and modulate the TME to improve cancer immunotherapy. Finally, the hurdles faced in commercialization and translation to clinic have been discussed and intriguingly, NPs owe great potential to emerge as clinical formulations for cancer immunotherapy in near future.

Indomethacin enhances anti-tumor efficacy of a MUC1 peptide vaccine against breast cancer in MUC1 transgenic mice

In recent years, vaccines against tumor antigens have shown potential for combating invasive cancers, including primary tumors and metastatic lesions. This is particularly pertinent for breast cancer, which is the second-leading cause of cancer-related death in women. MUC1 is a glycoprotein that is normally expressed on glandular epithelium, but is overexpressed and under-glycosylated in most human cancers, including the majority of breast cancers. This under-glycosylation exposes the MUC1 protein core on the tumor-associated form of the protein. We have previously shown that a vaccine consisting of MUC1 core peptides stimulates a tumor-specific immune response. However, this immune response is dampened by the immunosuppressive microenvironment within breast tumors. Thus, in the present study, we investigated the effectiveness of MUC1 vaccination in combination with four different drugs that inhibit different components of the COX pathway: indomethacin (COX-1 and COX-2 inhibitor), celecoxib (COX-2 inhibitor), 1-methyl tryptophan (indoleamine 2,3 dioxygenase inhibitor), and AH6809 (prostaglandin E₂ receptor antagonist). These treatment regimens were explored for the treatment of orthotopic MUC1-expressing breast tumors in mice transgenic for human MUC1. We found that the combination of vaccine and indomethacin resulted in a significant reduction in tumor burden. Indomethacin did not increase tumor-specific immune responses over vaccine alone, but rather appeared to reduce the proliferation and increase apoptosis of tumor cells, thus rendering them susceptible to immune cell killing.

Novel immunotherapy strategies for hepatobiliary cancers

Despite recent advancements in therapeutic options for advanced hepatobiliary cancers, there remains an unmet need for innovative systemic treatments. Immunotherapy has shown an ability to provide prolonged clinical benefit, but this benefit remains limited to a small subset of patients. Numerous ongoing endeavors are investigating novel immunotherapy concepts. Immunotherapies that have demonstrated clinical efficacy in hepatobiliary cancers include PD-1 inhibitor therapy and CTLA-4 inhibitor therapy. Novel immunotherapy concepts include targeting emerging checkpoint proteins, bispecific T-cell engagers, combinatorial trials with checkpoint inhibitors, oncolytic virotherapy and chimeric antigen receptor T cells. The goal for these new treatment strategies is to achieve a meaningful expansion of patients deriving prolonged clinical benefit from immunotherapy.

Significance of Cyclooxygenase-2 in Oncogenesis

The cyclooxygenase-2 (COX-2) enzyme catalyses the first stage of biosynthesis of prostanoids, proteins that are implicated in various physiological and pathological processes in humans and animals. The expression of COX-2 increases significantly during pathological processes accompanied by inflammation, pain and fever. Overexpression of COX-2 was determined in tumour tissues, which suggests that this enzyme participates in oncogenesis. In this paper the topics discussed are mechanisms regulating COX-2 expression, COX isoforms, their role in the body and the oncogenic mechanisms triggered by the overexpression of COX-2, including inhibition of apoptosis, intensification of neoangiogenesis, increased metastatic capacity, and weakening of the immune system. The significance of and the mechanisms by which COX-2 participates in oncogenesis have been studied intensively in recent years. The results are highly promising, and they expand our understanding of the complex processes and changes at the molecular, cellular and tissue level that promote oncogenesis and cancer progression. Notwithstanding the knowledge already gleaned, many processes and mechanisms have not yet been elucidated in human medicine and, in particular, in veterinary medicine. Further research is required to develop effective tumour diagnostic methods and treatment procedures for humans and animals.

Control of the Antitumor Immune Response by Cancer Metabolism

The metabolic reprogramming of tumor cells and immune escape are two major hallmarks of cancer cells. The metabolic changes that occur during tumorigenesis, enabling survival and proliferation, are described for both solid and hematological malignancies. Concurrently, tumor cells have deployed mechanisms to escape immune cell recognition and destruction. Additionally, therapeutic blocking of tumor-mediated immunosuppression has proven to have an unprecedented positive impact in clinical oncology. Increased evidence suggests that cancer metabolism not only plays a crucial role in cancer signaling for sustaining tumorigenesis and survival, but also has wider implications in the regulation of antitumor immune signaling through both the release of signaling molecules and the expression of immune membrane ligands. Here, we review these molecular events to highlight the contribution of cancer cell metabolic reprogramming on the shaping of the antitumor immune response.

Vaccine Strategies to Improve Anti-cancer Cellular Immune Responses

More than many other fields in medicine, cancer vaccine development has been plagued by a wide gap between the massive amounts of highly encouraging preclinical data on one hand, and the disappointing clinical results on the other. It is clear now that traditional approaches from the infectious diseases' vaccine field cannot be borrowed as such to treat cancer. This review highlights some of the strategies developed to improve vaccine formulations for oncology, including research into more powerful or “smarter” adjuvants to elicit anti-tumoral cellular immune responses. As an illustration of the difficulties in translating smart preclinical strategies into real benefit for the cancer patient, the difficult road of vaccine development in lung cancer is given as example. Finally, an outline is provided of the combinatorial strategies that leverage the increasing knowledge on tumor-associated immune suppressive networks. Indeed, combining with drugs that target the dominant immunosuppressive pathway in a given tumor promises to unlock the true power of cancer vaccines and potentially offer long-term protection from disease relapse.

Influence of Cyclooxygenase-2 Inhibitors on Kynurenic Acid Production in Rat Brain in Vitro

Significant body of evidence suggests that abnormal kynurenic acid (KYNA) level is involved in the pathophysiology of central nervous system disorders. In the brain, KYNA is synthesized from kynurenine (KYN) by kynurenine aminotransferases (KATs), predominantly by KAT II isoenzyme. Blockage of ionotropic glutamate (GLU) receptors is a main cellular effect of KYNA. High KYNA levels have been linked with psychotic symptoms and cognitive dysfunction in animals and humans. As immunological imbalance and impaired glutamatergic neurotransmission are one of the crucial processes in neurological pathologies, we aimed to analyze the effect of anti-inflammatory agents, inhibitors of cyclooxygenase-2 (COX-2): celecoxib, niflumic acid, and parecoxib, on KYNA synthesis and KAT II activity in rat brain in vitro. The influence of COX-2 inhibitors was examined in rat brain cortical slices and on isolated KAT II enzyme. Niflumic acid and parecoxib decreased in a dose-dependent manner KYNA production and KAT II activity in rat brain cortex in vitro, whereas celecoxib was ineffective. Molecular docking results suggested that niflumic acid and parecoxib interact with an active site of KAT II. In conclusion, niflumic acid and parecoxib are dual COX-2 and KAT II inhibitors.

WNT Signaling in Cancer Immunosurveillance

Deregulated WNT signaling has been shown to favor malignant transformation, tumor progression, and resistance to conventional cancer therapy in a variety of preclinical and clinical settings. Accumulating evidence suggests that aberrant WNT signaling may also subvert cancer immunosurveillance, hence promoting immunoevasion and resistance to multiple immunotherapeutics, including immune checkpoint blockers. Here, we discuss the molecular and cellular mechanisms through which WNT signaling influences cancer immunosurveillance and present potential therapeutic avenues to harness currently available WNT modulators for cancer immunotherapy.

Celecoxib in breast cancer prevention and therapy

Breast cancer has a high incidence worldwide. The results of substantial studis reveal that inflammation plays an important role in the initiation, development, and aggressiveness of many malignancies. The use of celecoxib, a novel NSAID, is repetitively associated with the reduced risk of the occurrence and progression of a number of types of cancer, particularly breast cancer. This observation is also substantiated by various meta-analyses. Clinical trials have been implemented on integration treatment of celecoxib and shown encouraging results. Celecoxib could be treated as a potential candidate for antitumor agent. There are, nonetheless, some unaddressed questions concerning the precise mechanism underlying the anticancer effect of celecoxib as well as its activity against different types of cancer. In this review, we discuss different mechanisms of anticancer effect of celecoxib as well as preclinical/clinical results signifying this beneficial effect.

Indoleamine 2, 3-dioxygenase inhibitors in immunochemotherapy of breast cancer: challenges and opportunities

Trafficking of macromolecular immunotherapy agent into the tumor microenvironment (TME) is a challenging issue. In the TME, cancer cells exploit indoleamine 2, 3-dioxygenase (IDO), as a cytosolic enzyme that catalyzes the L-tryptophan (Trp) through the kynurenine (Kyn) pathway, which could negatively regulate the activity of T cells. Thus, Trp/Kyn pathway, can be targeted with novel treatment modalities such as IDO1 inhibitor to benefit patients with aggressive solid tumors.

Delivery Strategies for Immune Checkpoint Blockade

Immune checkpoint blockade, which blocks the regulatory pathways that express on immune cells to improve antitumor immunological responses, is becoming one of the most promising approaches for antitumor therapy. This therapy has achieved important clinical advancement and provided a new opportunity against a variety of cancers. However, limitations of checkpoint inhibitors application, including the risk of autoimmune disease, low objective response rates, and high cost, still largely affect their broad applications in patients. Therefore, it is desirable to seek effective delivery methods to further enhance the therapeutic efficacy and reduce drawbacks of immune checkpoint blockade. This brief review summarizes strategies to increase the antitumor immunity, including the local and targeted delivery of checkpoint inhibitors, and a combination of different checkpoint inhibitors or with other therapeutic treatments.

Indoximod: An Immunometabolic Adjuvant That Empowers T Cell Activity in Cancer

Exploding interest in immunometabolism as a source of new cancer therapeutics has been driven in large part by studies of tryptophan catabolism mediated by IDO/TDO enzymes. A chief focus in the field is IDO1, a pro-inflammatory modifier that is widely overexpressed in cancers where it blunts immunosurveillance and enables neovascularization and metastasis. The simple racemic compound 1-methyl-D,L-tryptophan (1MT) is an extensively used probe of IDO/TDO pathways that exerts a variety of complex inhibitory effects. The L isomer of 1MT is a weak substrate for IDO1 and is ascribed the weak inhibitory activity of the racemate on the enzyme. In contrast, the D isomer neither binds nor inhibits the purified IDO1 enzyme. However, clinical development focused on D-1MT (now termed indoximod) due to preclinical cues of its greater anticancer activity and its distinct mechanisms of action. In contrast to direct enzymatic inhibitors of IDO1, indoximod acts downstream of IDO1 to stimulate mTORC1, a convergent effector signaling molecule for all IDO/TDO enzymes, thus possibly lowering risks of drug resistance by IDO1 bypass. In this review, we survey the unique biological and mechanistic features of indoximod as an IDO/TDO pathway inhibitor, including recent clinical findings of its ability to safely enhance various types of cancer therapy, including chemotherapy, chemo-radiotherapy, vaccines, and immune checkpoint therapy. We also review the potential advantages indoximod offers compared to selective IDO1-specific blockade, which preclinical studies and the clinical study ECHO-301 suggest may be bypassed readily by tumors. Indoximod lies at a leading edge of broad-spectrum immunometabolic agents that may act to improve responses to many anticancer modalities, in a manner analogous to vaccine adjuvants that act to boost immunity in settings of infectious disease.

Importance of kynurenine 3-monooxygenase for spontaneous firing and pharmacological responses of midbrain dopamine neurons: Relevance for schizophrenia

Kynurenine 3-monooxygenase (KMO) is an essential enzyme of the kynurenine pathway, converting kynurenine into 3-hydroxykynurenine. Inhibition of KMO increases kynurenine, resulting in elevated levels of kynurenic acid (KYNA), an endogenous N-methyl-d-aspartate and α*7-nicotinic receptor antagonist. The concentration of KYNA is elevated in the brain of patients with schizophrenia, possibly as a result of a reduced KMO activity. In the present study, using in vivo single cell recording techniques, we investigated the electrophysiological characteristics of ventral tegmental area dopamine (VTA DA) neurons and their response to antipsychotic drugs in a KMO knock-out (K/O) mouse model. KMO K/O mice exhibited a marked increase in spontaneous VTA DA neuron activity as compared to wild-type (WT) mice. Furthermore, VTA DA neurons showed clear-cut, yet qualitatively opposite, responses to the antipsychotic drugs haloperidol and clozapine in the two genotypes. The anti-inflammatory drug parecoxib successfully lowered the firing activity of VTA DA neurons in KMO K/O, but not in WT mice. Minocycline, an antibiotic and anti-inflammatory drug, produced no effect in this regard. Taken together, the present data further support the usefulness of KMO K/O mice for studying distinct aspects of the pathophysiology and pharmacological treatment of psychiatric disorders such as schizophrenia.

Immune System Modulation in Patients with Malignant and Benign Breast Disorders: Tryptophan Degradation and Serum Neopterin

Tryptophan degradation metabolites are known to suppress T-cell function, which is a mechanism of resistance of tumor cells against immune surveillance. The aim of this study was to evaluate tryptophan degradation along with serum neopterin levels in benign and malignant breast disease. Serum tryptophan and kynurenine levels and neopterin concentrations of 30 patients with malignant and 27 patients with benign breast disease were determined by HPLC and ELISA, respectively. The slight increase in tryptophan degradation in a subgroup of cancer patients with higher grade tumors was not statistically significant, but the increased degradation was correlated with higher neopterin concentrations. Neopterin levels in patients with malignant breast disease were significantly higher than in the benign group (p<0.05). Tryptophan degradation positively correlates with the aggressiveness of the tumor because it changes with tumor grade rather than disease stage.

Inflammatory Reprogramming with IDO1 Inhibitors: Turning Immunologically Unresponsive 'Cold' Tumors 'Hot'

We discuss how small-molecule inhibitors of the tryptophan (Trp) catabolic enzyme indoleamine 2,3-dioxygenase (IDO) represent a vanguard of new immunometabolic adjuvants to safely enhance the efficacy of cancer immunotherapy, radiotherapy, or 'immunogenic' chemotherapy by leveraging responses to tumor neoantigens. IDO inhibitors re-program inflammatory processes to help clear tumors by blunting tumor neovascularization and restoring immunosurveillance. Studies of regulatory and effector pathways illuminate IDO as an inflammatory modifier. Recent work suggests that coordinate targeting of the Trp catabolic enzymes tryptophan 2,3-dioxygenase (TDO) and IDO2 may also safely broaden efficacy. Understanding IDO inhibitors as adjuvants to turn immunologically 'cold' tumors 'hot' can seed new concepts in how to improve the efficacy of cancer therapy while limiting collateral damage.

Strategies to Improve Vaccine Efficacy against Tuberculosis by Targeting Innate Immunity

The global tuberculosis epidemic is the most common cause of death after infectious disease worldwide. Increasing numbers of infections with multi- and extensively drug-resistant variants of the Mycobacterium tuberculosis complex, resistant even to newly discovered and last resort antibiotics, highlight the urgent need for an efficient vaccine. The protective efficacy to pulmonary tuberculosis in adults of the only currently available vaccine, M. bovis BCG, is unsatisfactory and geographically diverse. More importantly, recent clinical studies on new vaccine candidates did not prove to be better than BCG, yet. Here, we propose and discuss novel strategies to improve efficacy of existing anti-tuberculosis vaccines. Modulation of innate immune responses upon vaccination already provided promising results in animal models of tuberculosis. For instance, neutrophils have been shown to influence vaccine efficacy, both, positively and negatively, and stimulate specific antibody secretion. Modulating immune regulatory properties after vaccination such as induction of different types of innate immune cell death, myeloid-derived suppressor or regulatory T cells, production of anti-inflammatory cytokines such as IL-10 may have beneficial effects on protection efficacy. Incorporation of lipid antigens presented via CD1 molecules to T cells have been discussed as a way to enhance vaccine efficacy. Finally, concepts of dendritic cell-based immunotherapies or training the innate immune memory may be exploitable for future vaccination strategies against tuberculosis. In this review, we put a spotlight on host immune networks as potential targets to boost protection by old and new tuberculosis vaccines.

Indoleamine 2,3-dioxygenase: As a potential prognostic marker and immunotherapeutic target for hepatocellular carcinoma

Tumor cells induce an immunosuppressive microenvironment which leads towards tumor immune escape. Understanding the intricacy of immunomodulation by tumor cells is essential for immunotherapy. Indoleamine 2,3-dioxygenase (IDO) is an immunosuppressive enzyme which mediates tumor immune escape in various cancers including hepatocellular carcinoma (HCC). IDO up-regulation in HCC may lead to recruitment of regulatory T-cells into tumor microenvironment and therefore inhibit local immune responses and promote metastasis. HCC associated fibroblasts stimulate natural killer cells dysfunction through prostaglandin E2 and subsequently IDO promotes favorable condition for tumor metastasis. IDO up-regulation induces immunosuppression and may enhance the risk of hepatitis C virus and hepatitis B virus induced HCC. Therefore, IDO inhibitors as adjuvant therapeutic agents may have clinical implications in HCC. This review proposes future prospects of IDO not only as a therapeutic target but also as a prognostic marker for HCC.

The innate and adaptive infiltrating immune systems as targets for breast cancer immunotherapy

A cancer cell-centric view has long dominated the field of cancer biology. Research efforts have focussed on aberrant cancer cell signalling pathways and on changes to cancer cell DNA. Mounting evidence demonstrates that many cancer-associated cell types within the tumour stroma co-evolve and support tumour growth and development, greatly modifying cancer cell behaviour, facilitating invasion and metastasis and controlling dormancy and sensitivity to drug therapy. Thus, these stromal cells represent potential targets for cancer therapy. Among these cell types, immune cells have emerged as a promising target for therapy. The adaptive and the innate immune system play an important role in normal mammary development and breast cancer. The number of infiltrating adaptive immune system cells with tumour-rejecting capacity, primarily, T lymphocytes, is lower in breast cancer compared with other cancer types, but infiltration occurs in a large proportion of cases. There is strong evidence demonstrating the importance of the immunosuppressive role of the innate immune system during breast cancer progression. A consideration of components of both the innate and the adaptive immune system is essential for the design and development of immunotherapies in breast cancer. In this review, we focus on the importance of immunosuppressive myeloid-derived suppressor cells (MDSCs) as potential targets for breast cancer therapy.

Nanomedicine and cancer immunotherapy: focus on indoleamine 2,3-dioxygenase inhibitors

Nanomedicine application in cancer immunotherapy is currently one of the most challenging areas in cancer therapeutic intervention. Innovative solutions have been provided by nanotechnology to deliver cytotoxic agents to the cancer cells partially affecting the healthy cells of the body during the process. Nanoparticle-based drug delivery is an emerging approach to stimulate the immune responses against cancer. The inhibition of indoleamine 2,3-dioxygenase (IDO) is a pivotal area of research in cancer immunotherapy. IDO is a heme-containing immunosuppressive enzyme, which is responsible for the degradation of tryptophan while increasing the concentration of kynurenine metabolites. Various preclinical studies showed that IDO inhibition in certain diseases may result in significant therapeutic effects. Here, we provide a review of the natural and synthetic inhibitors of IDO. These inhibitors are classified according to their source, inhibitory concentrations, the chemical structure, and the mechanism of action. Tumor-targeted chemotherapy is an advanced technique and has more advantages as compared to the conventional chemotherapy. Search for more efficient and less toxic nanoparticles in conjunction with compounds to inhibit IDO is still an area of interest for several research groups worldwide, especially revealing to be an extensive and a promising area in cancer therapeutic innovations.

Modulation of cancer-specific immune responses by amino acid degrading enzymes

To evade immune destruction, tumors exploit a wide range of immune escape mechanisms, including the induction of an immunosuppressive tumor microenvironment. This is mediated, in part, by amino acid degrading enzymes indoleamine 2,3-dioxygenase, tryptophan 2,3-dioxygenase, arginase 1 and arginase 2, which have emerged as key players in the regulation of tumor-induced immune tolerance. Here we describe how the expression of tryptophan- and arginine-degrading enzymes by tumor and tumor-infiltrating cells can hamper cancer-specific immune responses, and discuss how this knowledge is being exploited to develop new strategies for cancer immunotherapy.

Tryptophan Catabolism and Cancer Immunotherapy Targeting IDO Mediated Immune Suppression

Over the last decade, tryptophan catabolism has been firmly established as a powerful mechanism of innate and adaptive immune tolerance. The catabolism of tryptophan is a central pathway maintaining homeostasis by preventing autoimmunity or immunopathology that would result from uncontrolled and overreacting immune responses. This is driven by the key and rate-limiting enzymes indoleamine-2,3-dioxygenase 1 (IDO1) and tryptophan-2,3-dioxygenase 2 (TDO), resulting in local depletion of tryptophan, while tryptophan catabolites accumulate, including kynurenine and its derivatives, depending on the presence of downstream enzymes in the kynurenine pathway. These metabolic modifications result in a local microenvironment that is profoundly immunosuppressive, as a result of various mechanisms whose respective role remains incompletely characterized. Drugs targeting this pathway, specifically IDO1, are already in clinical trials with the aim at reverting cancer-induced immunosuppression. Recent studies have demonstrated favorable pharmacokinetics profiles for first-generation (Indoximod NLG8189) and second-generation IDO1 inhibitors (INCB024360 and NLG919). Targeting tryptophan catabolism in combination with additional methods of therapy may improve efficacy of cancer immunotherapy. These methods include, but are not limited to vaccination, adoptive cellular therapy, checkpoint inhibitor blockade, and cyclooxygenase-2 (COX2) inhibition. Over the last decade, there has been a considerable increase in our understanding of the regulation and downstream mediators of tryptophan metabolism. This detailed understanding will expand opportunities to interfere with the pathway therapeutically on multiple levels. The object of this chapter is to highlight current and past key findings that implicate tryptophan catabolism as an important mediator of cancer immunity and discuss the development of multiple therapeutic targets.

Blockade of high mobility group box 1 augments antitumor T-cell response induced by peptide vaccination as a co-adjuvant

High mobility group box 1 (HMGB1) is a member of the family of damage-associated molecular patterns, which cause inflammation and trigger innate immunity through Toll-like receptors 2/4 and the receptor for advanced glycation end products. We examined the effect of glycyrrhizin, a selective inhibitor of HMGB1, on the induction of CTLs in mice. B6 mice, either OT-1 spleen cell-transferred or untransferred, were immunized with an s.c. injection of OVA_257-264 peptide with topical imiquimod, and glycyrrhizin was mixed with the antigen peptide. Proliferation of OT-1 cells after immunization was enhanced by glycyrrhizin. The effect of glycyrrhizin was confirmed in other adjuvant systems, such as CpG oligonucleotide and monophosphoryl lipid A, but glycyrrhizin was not effective in Freund's incomplete adjuvant system. The augmenting effects of glycyrrhizin were also observed in other synthetic HMGB1 inhibitors, gabexate mesilate, nafamostat, and sivelestat. Thus, the effects are common to the HMGB1 inhibitors. Induction of CTLs detected by γ-interferon enzyme-linked immunospot assay was similarly augmented by glycyrrhizin. In a therapeutic vaccine model, glycyrrhizin inhibited the growth of s.c. transplanted EG.7 tumors. Expression of inflammatory cytokines in the skin inoculation site was downregulated by glycyrrhizin. These results suggest that HMGB1 inhibitors might be useful as a co-adjuvant for peptide vaccination with an innate immunity receptor-related adjuvant.

Tryptophan-2,3-dioxygenase is regulated by prostaglandin E2 in malignant glioma via a positive signaling loop involving prostaglandin E receptor-4

Malignant gliomas and other types of tumors generate a local immunosuppressive microenvironment, which prohibits an effective anti-tumor immune response and promotes tumor growth. Along with others, we have recently demonstrated that catabolism of the essential amino acid tryptophan via tryptophan-2,3-dioxygenase (TDO) is an important mechanism mediating tumor-associated immunosuppression particularly in gliomas. The pathways regulating TDO in tumors, however, are poorly understood. Here, we show that prostaglandins enhance TDO expression and enzymatic activity in malignant gliomas via activation of prostaglandin E receptor-4 (EP4). Stimulation with prostaglandin E₂ (PGE₂ ) up-regulated TDO-mediated kynurenine release in human glioma cell lines, whereas knockdown of the PGE₂ receptor EP4 inhibited TDO expression and activity. In human malignant glioma tissue expression of the PGE₂ -producing enzyme cyclooxygenase-2 (COX2) and its receptor EP4 were associated with TDO expression both on transcript and protein level. High expression of EP4 correlated with poor survival in malignant glioma patients WHO III-IV. Importantly, treatment of glioma cells with an EP4 inhibitor decreased TDO expression and activity. Moreover, TDO-over-expressing murine gliomas showed increased COX2 and EP4 expression suggesting a positive feedback mechanism in vivo. In summary, targeting EP4 may inhibit - in addition to immunosuppressive COX2 signaling - tryptophan degradation as another important immunosuppressive pathway and thus, could provide a dual clinically relevant immunotherapeutic avenue for the treatment of malignant gliomas. We proposed that in malignant gliomas prostaglandin E₂ (PGE₂ ) produced by cyclooxygenases (COX) up-regulates tryptophan-2,3-dioxygenase (TDO) expression and enzyme activity through binding to its Gs-coupled receptor EP4 and therefore may mediate tumor immune escape in part through aryl hydrocarbon receptor (AHR) activation. Moreover, TDO activity itself seems to induce intratumoral PGE₂ metabolism suggesting an immunosuppressive loop involving COX/EP4/TDO.

The Role of Indoleamine 2,3-Dioxygenase in Diethylnitrosamine-Induced Liver Carcinogenesis

Indoleamine 2,3-dioxygenase (IDO), a tryptophan-catabolizing intracellular enzyme of the L-kynurenine pathway, causes preneoplastic cells and tumor cells to escape the immune system by inducing immune tolerance; this mechanism might be associated with the development and progression of human malignancies. In the present study, we investigated the role of IDO in diethylnitrosamine (DEN)-induced hepatocarcinogenesis by using IDO-knockout (KO) mice. To induce hepatocellular carcinoma (HCC), hepatic adenoma, and preneoplastic hepatocellular lesions termed foci of cellular alteration (FCA), male IDO-wild-type (WT) and IDO-KO mice with a C57BL/6J background received a single intraperitoneal injection of DEN at 2 weeks of age. The mice were sacrificed to evaluate the development of FCA and hepatocellular neoplasms. HCC overexpressed IDO and L-kynurenine compared to surrounding normal tissue in the DEN-treated IDO-WT mice. The number and cell proliferative activity of FCAs, and the incidence and multiplicity of HCC were significantly greater in the IDO-WT than in the IDO-KO mice. The expression levels of the IDO protein, of L-kynurenine, and of IFN-γ, COX-2, TNF-α, and Foxp3 mRNA were also significantly increased in the DEN-induced hepatic tumors that developed in the IDO-WT mice. The mRNA expression levels of CD8, perforin and granzyme B were markedly increased in hepatic tumors developed in IDO-KO mice. Moreover, Foxp3-positive inflammatory cells had infiltrated into the livers of DEN-treated IDO-WT mice, whereas fewer cells had infiltrated into the livers of IDO-KO mice. Induction of IDO and elevation of L-kynurenine might play a critical role in both the early and late phase of liver carcinogenesis. Our findings suggest that inhibition of IDO might offer a promising strategy for the prevention of liver cancer.

Cancer prevention and therapy through the modulation of the tumor microenvironment

Cancer arises in the context of an in vivo tumor microenvironment. This microenvironment is both a cause and consequence of tumorigenesis. Tumor and host cells co-evolve dynamically through indirect and direct cellular interactions, eliciting multiscale effects on many biological programs, including cellular proliferation, growth, and metabolism, as well as angiogenesis and hypoxia and innate and adaptive immunity. Here we highlight specific biological processes that could be exploited as targets for the prevention and therapy of cancer. Specifically, we describe how inhibition of targets such as cholesterol synthesis and metabolites, reactive oxygen species and hypoxia, macrophage activation and conversion, indoleamine 2,3-dioxygenase regulation of dendritic cells, vascular endothelial growth factor regulation of angiogenesis, fibrosis inhibition, endoglin, and Janus kinase signaling emerge as examples of important potential nexuses in the regulation of tumorigenesis and the tumor microenvironment that can be targeted. We have also identified therapeutic agents as approaches, in particular natural products such as berberine, resveratrol, onionin A, epigallocatechin gallate, genistein, curcumin, naringenin, desoxyrhapontigenin, piperine, and zerumbone, that may warrant further investigation to target the tumor microenvironment for the treatment and/or prevention of cancer.

Vaccines versus immunotherapy: overview of approaches in deciding between options

This review compares the optimal use of vaccines vs. other forms of immunotherapy, which includes cytokines, such as IL-2, monoclonal antibodies, such as the 'checkpoint inhibitors', against CTLA-4 and PD-1. The review includes both prophylactic and therapeutic vaccines using a variety of technologies. It is already established that vaccines can be enhanced by other immunotherapies, such as cytokines (IL-2) and there is scope for combining both of these with the 'checkpoint' antibodies. Moreover, both can be enhanced with other modalities, such as radiotherapy, ablative therapy and both high and low dose chemotherapies.

Interferon-alpha treatment induces depression-like behaviour accompanied by elevated hippocampal quinolinic acid levels in rats

Immunotherapy with the cytokine interferon-alpha (IFN-α) can induce symptoms of depression, and it is likely that the tryptophan-kynurenine pathway may be involved in this regard. In this study we investigated the effects of IFN-α on depression-like behaviour and central metabolites of the tryptophan-kynurenine pathway in rats. Secondly, we explored the modulating effects of an antidepressant (imipramine) and anti-inflammatory drug (celecoxib) on IFN-α-induced behavioural and pathophysiological changes in the brain. The following treatment groups were used: Control (saline), IFN-α (6×10(4)IU/kg s.c.), IFN-α+imipramine or IFN-α+celecoxib. Drugs were administered daily for 1 week. IFN-α treatment induced depression-like behaviour by increasing immobility in the forced swim test (FST), and decreased tryptophan levels in the brain. There was a trend for an increased kynurenine/tryptophan ratio, indicative of indoleamine 2,3-dioxygenase (IDO) activation, and increased quinolinic acid in the hippocampus. Imipramine decreased immobility in the FST, but did not reverse the IFN-α-induced changes in the tryptophan-kynurenine pathway. There was a trend for celecoxib to decrease immobility and to reverse the IFN-α-induced increase in the kynurenine/tryptophan ratio. Thus, our study provides further evidence for IFN-α-induced depression-like behaviour through central changes of the tryptophan-kynurenine pathway.

Role of indoleamine 2,3-dioxygenase in health and disease

IDO1 (indoleamine 2,3-dioxygenase 1) is a member of a unique class of mammalian haem dioxygenases that catalyse the oxidative catabolism of the least-abundant essential amino acid, L-Trp (L-tryptophan), along the kynurenine pathway. Significant increases in knowledge have been recently gained with respect to understanding the fundamental biochemistry of IDO1 including its catalytic reaction mechanism, the scope of enzyme reactions it catalyses, the biochemical mechanisms controlling IDO1 expression and enzyme activity, and the discovery of enzyme inhibitors. Major advances in understanding the roles of IDO1 in physiology and disease have also been realised. IDO1 is recognised as a prominent immune regulatory enzyme capable of modulating immune cell activation status and phenotype via several molecular mechanisms including enzyme-dependent deprivation of L-Trp and its conversion into the aryl hydrocarbon receptor ligand kynurenine and other bioactive kynurenine pathway metabolites, or non-enzymatic cell signalling actions involving tyrosine phosphorylation of IDO1. Through these different modes of biochemical signalling, IDO1 regulates certain physiological functions (e.g. pregnancy) and modulates the pathogenesis and severity of diverse conditions including chronic inflammation, infectious disease, allergic and autoimmune disorders, transplantation, neuropathology and cancer. In the present review, we detail the current understanding of IDO1’s catalytic actions and the biochemical mechanisms regulating IDO1 expression and activity. We also discuss the biological functions of IDO1 with a focus on the enzyme's immune-modulatory function, its medical implications in diverse pathological settings and its utility as a therapeutic target.

Nanoparticle-based immunotherapy for cancer

The design of nanovaccines capable of triggering effective antitumor immunity requires an understanding of how the immune system senses and responds to threats, including pathogens and tumors. Equally important is an understanding of the mechanisms employed by tumor cells to evade immunity and an appreciation of the deleterious effects that antitumor immune responses can have on tumor growth, such as by skewing tumor cell composition toward immunologically silent tumor cell variants. The immune system and tumors engage in a tug-of-war driven by competition where promoting antitumor immunity or tumor cell death alone may be therapeutically insufficient. Nanotechnology affords a unique opportunity to develop therapeutic compounds than can simultaneously tackle both aspects, favoring tumor eradication. Here, we review the current status of nanoparticle-based immunotherapeutic strategies for the treatment of cancer, ranging from antigen/adjuvant delivery vehicles (to professional antigen-presenting cell types of the immune system) to direct tumor antigen-specific T-lymphocyte-targeting compounds and their combinations thereof.

FoxP3 and indoleamine 2,3-dioxygenase immunoreactivity in sentinel nodes from melanoma patients

OBJECTIVE

1) Assess FoxP3/indoleamine 2,3-dioxygenase immunoreactivity in head and neck melanoma sentinel lymph nodes and 2) correlate FoxP3/indoleamine 2,3-dioxygenase with sentinel lymph node metastasis and clinical recurrence.

STUDY DESIGN

Retrospective cohort study.

METHODS

Patients with sentinel lymph node biopsy for head and neck melanoma between 2004 and 2011 were identified. FoxP3/indoleamine 2,3-dioxygenase prevalence and intensity were determined from the nodes. Poor outcome was defined as local, regional or distant recurrence. The overall immunoreactivity score was correlated with clinical recurrence and sentinel lymph node metastasis using the chi-square test for trend.

RESULTS

Fifty-six sentinel lymph nodes were reviewed, with 47 negative and 9 positive for melanoma. Patients with poor outcomes had a statistically significant trend for higher immunoreactivity scores (p=0.03). Positive nodes compared to negative nodes also had a statistically significant trend for higher immunoreactivity scores (p=0.03). Among the negative nodes, there was a statistically significant trend for a poor outcome with higher immunoreactivity scores (p=0.02).

CONCLUSION

FoxP3/indoleamine 2,3-dioxygenase immunoreactivity correlates with sentinel lymph node positivity and poor outcome. Even in negative nodes, higher immunoreactivity correlated with poor outcome. Therefore higher immunoreactivity may portend a worse prognosis even without metastasis in the sentinel lymph node. This could identify a subset of patients that may benefit from future trials and treatment for melanoma through Treg and IDO suppression.

A prostaglandin E (PGE) receptor EP4 antagonist protects natural killer cells from PGE2-mediated immunosuppression and inhibits breast cancer metastasis

Cyclooxygenase-2 is frequently upregulated in epithelial tumors and contributes to poor outcomes in multiple malignancies. The COX-2 product prostaglandin E₂ (PGE₂) promotes tumor growth and metastasis by acting on a family of four G protein-coupled receptors (EP1-4). Using a novel small molecule EP4 antagonist (RQ-15986) and a syngeneic murine model of metastatic breast cancer, we determined the effect of EP4 blockade on innate immunity and tumor biology. Natural killer (NK)-cell functions are markedly depressed in mice bearing murine mammary tumor 66.1 or 410.4 cells owing to the actions of PGE₂ on NK cell EP4 receptors. The EP4 agonist PGE₁-OH inhibits NK functions in vitro, and this negative regulation is blocked by RQ-15986. Likewise, the treatment of tumor-bearing mice with RQ-15986 completely protected NK cells from the immunosuppressive effects of the tumor microenvironment in vivo. RQ-15986 also has direct effects on EP4 expressed by tumor cells, inhibiting the PGE₂-mediated activation of adenylate cyclase and blocking PGE₂-induced tumor cell migration. The pretreatment of tumor cells with a non-cytotoxic concentration of RQ-15986 inhibited lung colonization, a beneficial effect that was lost in mice depleted of NK cells. The oral administration of RQ-15986 inhibited the growth of tumor cells implanted into mammary glands and their spontaneous metastatic colonization to the lungs, resulting in improved survival. Our findings reveal that EP4 antagonism prevents tumor-mediated NK-cell immunosuppression and demonstrates the anti-metastatic activity of a novel EP4 antagonist. These observations support the investigation of EP4 antagonists in clinical trials.

Early Carcinogenesis Involves the Establishment of Immune Privilege via Intrinsic and Extrinsic Regulation of Indoleamine 2,3-dioxygenase-1: Translational Implications in Cancer Immunotherapy

Although prolonged genetic pressure has been conjectured to be necessary for the eventual development of tumor immune evasion mechanisms, recent work is demonstrating that early genetic mutations are capable of moonlighting as both intrinsic and extrinsic modulators of the tumor immune microenvironment. The indoleamine 2,3-dioxygenase-1 (IDO) immunoregulatory enzyme is emerging as a key player in tumor-mediated immune tolerance. While loss of the tumor suppressor, BIN-1, and the over-expression of cyclooxygenase-2 have been implicated in intrinsic regulation of IDO, recent findings have demonstrated the loss of TβRIII and the upregulation of Wnt5a by developing cancers to play a role in the extrinsic control of IDO activity by local dendritic cell populations residing within tumor and tumor-draining lymph node tissues. Together, these genetic changes are capable of modulating paracrine signaling pathways in the early stages of carcinogenesis to establish a site of immune privilege by promoting the differentiation and activation of local regulatory T cells. Additional investigation of these immune evasion pathways promises to provide opportunities for the development of novel strategies to synergistically enhance the efficacy of the evolving class of T cell-targeted "checkpoint" inhibitors.

Therapeutic cancer vaccines and combination immunotherapies involving vaccination

Recent US Food and Drug Administration approvals of Provenge(®) (sipuleucel-T) as the first cell-based cancer therapeutic factor and ipilimumab (Yervoy(®)/anticytotoxic T-lymphocyte antigen-4) as the first "checkpoint blocker" highlight recent advances in cancer immunotherapy. Positive results of the clinical trials evaluating additional checkpoint blocking agents (blockade of programmed death [PD]-1, and its ligands, PD-1 ligand 1 and 2) and of several types of cancer vaccines suggest that cancer immunotherapy may soon enter the center stage of comprehensive cancer care, supplementing surgery, radiation, and chemotherapy. This review discusses the current status of the clinical evaluation of different classes of therapeutic cancer vaccines and possible avenues for future development, focusing on enhancing the magnitude and quality of cancer-specific immunity by either the functional reprogramming of patients' endogenous dendritic cells or the use of ex vivo-manipulated dendritic cells as autologous cellular transplants. This review further discusses the available strategies aimed at promoting the entry of vaccination-induced T-cells into tumor tissues and prolonging their local antitumor activity. Finally, the recent improvements to the above three modalities for cancer immunotherapy (inducing tumor-specific T-cells, prolonging their persistence and functionality, and enhancing tumor homing of effector T-cells) and rationale for their combined application in order to achieve clinically effective anticancer responses are addressed.