Novel TREM-1 Inhibitors Attenuate Tumor Growth and Prolong Survival in Experimental Pancreatic Cancer

[68Ga]Ga-NOTA-C-IPB-AIT: A novel radiotracer for in vivo detection of TREM-1 expression

Triggering receptor expressed on myeloid cells 1 (TREM-1) plays a critical role in the initiation and advancement of cancer. The noninvasive and rapid detection of TREM-1 expression provides a significant value for oncologic diagnosis, tumor evaluation and the guide of TREM-1-targeted therapy. In this study, we developed three peptide-based TREM-1 targeted radiotracers and evaluated their radiochemical and biological properties, in order to identify the candidate for the detection of TREM-1 expression on tumors. Among three radiotracers, [68Ga]Ga-NOTA-C-IPB-AIT showed a high radiochemical purity (> 98 %), excellent stability and hydrophilicity, favorable binding affinity, remarkable tumor uptake, ideal tumor-to-muscle ratio, and prolonged tumor retention, indicating that it is promising for potential use in TREM-1 expression detection.

Inhibiting triggering receptor expressed on myeloid cells 1 signaling to ameliorate skin fibrosis

Systemic sclerosis (SSc) is characterized by immune system failure, vascular insult, autoimmunity, and tissue fibrosis. TGF-β is a crucial mediator of persistent myofibroblast activation and aberrant extracellular matrix production in SSc. The factors responsible for this are unknown. By amplifying pattern recognition receptor signaling, triggering receptor expressed on myeloid cells 1 (TREM-1) is implicated in multiple inflammatory conditions. In this study, we used potentially novel ligand-independent TREM-1 inhibitors in preclinical models of fibrosis and explanted SSc skin fibroblasts in order to investigate the pathogenic role of TREM-1 in SSc. Selective pharmacological TREM-1 blockade prevented and reversed skin fibrosis induced by bleomycin in mice and mitigated constitutive collagen synthesis and myofibroblast features in SSc fibroblasts in vitro. Our results implicate aberrantly activated TREM-1 signaling in SSc pathogenesis, identify a unique approach to TREM-1 blockade, and suggest a potential therapeutic benefit for TREM-1 inhibition.

Stored RBC transfusions leads to the systemic inflammatory response syndrome in anemic murine neonates

OBJECTIVE

RBC transfusions (RBCT) are life-saving treatment for premature and critically ill infants. However, the procedure has been associated with the development of systemic inflammatory response syndrome (SIRS) and potentially multiple organ dysfunction syndrome (MODS) in neonates. The present study aimed to investigate the mechanisms of RBCT-related SIRS in severely anemic murine neonates.

METHODS

C57BL/6 (WT), TLR4-/- and myeloid-specific triggered myeloid receptor-1 (trem1)-/- mouse pups were studied in 4 groups (n = 6 each): (1) naïve controls, (2) transfused control, (3) anemic (hematocrit 20-24%) and (4) anemic with RBC transfused using our established murine model of phlebotomy-induced anemia (PIA) and RBC transfusion. Plasma was measured for quantifying inflammatory cytokines (IFN-γ, IL-1β, TNF-α, IL-6, MIP-1α, MIP-1β, MIP2 and LIX) using a Luminex assay. In vitro studies included (i) sensitization by exposing the cells to a low level of lipopolysaccharide (LPS; 500 ng/ml) and (ii) trem1-siRNA transfection with/without plasma supernatant from stored RBC to assess the acute inflammatory response through trem1 by qRT-PCR and immunoblotting.

RESULTS

Anemic murine pups developed cytokine storm within 2 h of receiving stored RBCs, which increased until 6 h post-transfusion, as compared to non-anemic mice receiving stored RBCTs ("transfusion controls"), in a TLR4-independent fashion. Nonetheless, severely anemic pups had elevated circulating endotoxin levels, thereby sensitizing circulating monocytes to presynthesize proinflammatory cytokines (IFN-γ, IL-1β, TNF-α, IL-6, MIP-1α, MIP-1β, MIP2, LIX) and express trem1. Silencing trem1 expression in Raw264.7 cells mitigated both endotoxin-associated presynthesis of proinflammatory cytokines and the RBCT-induced release of inflammatory cytokines. Indeed, myeloid-specific trem1-/- murine pups had significantly reduced evidence of SIRS following RBCTs.

CONCLUSION

Severe anemia-associated low-grade inflammation sensitizes monocytes to enhance the synthesis of proinflammatory cytokines and trem1. In this setting, RBCTs further activate these monocytes, thereby inducing SIRS. Inhibiting trem1 in myeloid cells, including monocytes, alleviates the inflammatory response associated with the combined effects of anemia and RBCTs in murine neonates.

Pharmacological Inhibition or Silencing of TREM1 Restrains HCC Cell Metastasis by Inactivating TLR/PI3K/AKT Signaling

Hepatocellular carcinoma (HCC), a widely prevalent malignancy strongly linked to inflammation, remains a significant public health concern. Triggering receptor expressed on myeloid cells 1 (TREM1), a modulator of inflammatory responses identified in recent years, has emerged as a crucial facilitator in cancer progression. Despite its significance, the precise regulatory mechanism of TREM1 in HCC metastasis remains unanswered. In the present investigation, we observed aberrant upregulation of TREM1 in HCC tissues, which was significantly linked to poorer overall survival. Inhibition of TREM1 expression resulted in a significant reduction in HCC Huh-7 and MHCC-97H cell proliferation, invasion, and epithelial-mesenchymal transition (EMT) process. Furthermore, inhibiting TREM1 decreased protein expressions of toll-like receptor 2/4 (TLR2/4) and major myeloid differentiation response gene 88 (MyD88), leading to the inactivation of phosphatidylinositol 3-kinase (PI3K) and protein kinase B (AKT) in HCC cells. Notably, these effects were reversed by treatment with TLR2-specific agonist (CU-T12-9), indicating a potential crosstalk between TREM1 and TLR2/4. Mechanistic studies revealed a direct interaction between TREM1 and both TLR2 and TLR4. In vivo studies demonstrated that inhibition of TREM1 suppressed the growth of HCC cells in the orthotopic implant model and its metastatic potential in the experimental lung metastasis model. Overall, our findings underscore the role of TREM1 inhibition in regulating EMT and metastasis of HCC cells by inactivating the TLR/PI3K/AKT signaling pathway, thereby providing deeper mechanistic insights into how TREM1 regulates metastasis during HCC progression.

TREM1: Activation, signaling, cancer and therapy

Triggering receptor expressed on myeloid cells 1 (TREM1) is a cell surface receptor expressed on neutrophils, monocytes and some tissue macrophages, where it functions as an immunoregulator that controls myeloid cell responses. The activation of TREM1 is suggested to be an upregulation-based, ligands-induced and structural multimerization-mediated process, in which damage- and pathogen-associated molecular patterns play important roles. Activated TREM1 initiates an array of downstream signaling pathways that ultimately result in the production of pro-inflammatory cytokines and chemokines, whereby it functions as an amplifier of inflammation and is implicated in the pathogenesis of many inflammation-associated diseases. Over the past decade, there has been growing evidence for the involvement of TREM1 overactivation in tumor stroma inflammation and cancer progression. Indeed, it was shown that TREM1 promotes tumor progression, immunosuppression, and resistance to therapy by activating tumor-infiltrating myeloid cells. TREM1-deficiency or blockade provide protection against tumors and reverse the resistance to anti-PD-1/PD-L1 therapy and arginine-deprivation therapy in preclinical models. Here, we first review the structure, activation modes and signaling pathways of TREM1 and emphasize the role of soluble TREM1 as a biomarker of infection and cancer. We then focus on the role of TREM1 in cancer and systematically summarize its expression patterns, upregulation mechanisms and functions in tumor development and progression. Lastly, we discuss the therapeutic prospects of TREM1 inhibition, via effective pharmacological inhibitors, in treating cancer and other diseases.

Triggering receptor expressed in myeloid cells 1 (TREM1) as a potential prognostic biomarker and association with immune infiltration in oral squamous cell carcinoma

OBJECTIVE

The objective of this study is to investigate the significance and impact of Triggering Receptor Expression on Myeloid Cells-1 (TREM-1) in the context of oral squamous cell carcinoma (OSCC).

METHODS

This study involved 51 OSCC patients, 21 oral epithelial dysplasia patients (OED), and the TCGA-HNSCC dataset. TREM1 expression was analyzed using quantitative reverse transcription PCR (RT-qPCR), and Western blot. Furthermore, we assessed TREM1 expression for clinicopathological, prognosis, and immune infiltration correlations utilizing publicly available TCGA-HNSCC datasets through UALCAN, Protein Atlas, Kaplan-Meier plot, TIMER2.0, and TISIDB. We also conducted bioinformatic analyses for functional enrichment employing publicly accessible datasets.

RESULTS

TREM1 was significantly upregulated in OSCC and OED when compared to normal tissues, confirmed through multiple methods. Analysis of clinicopathological features showed associations with disease stage, grade, nodal metastasis, HPV status, and TP53 mutation. High TREM1 expression correlated with poorer patient survival. TREM1 was linked to immune cell infiltration and immune-related pathways.

CONCLUSION

TREM1 is significantly upregulated in OSCC and is associated with poor clinicopathological features and survival. It may hold promise as a therapeutic target and prognostic marker in OSCC. Further research is needed to understand its functional role in OSCC.

Clinically impactful metabolic subtypes of pancreatic ductal adenocarcinoma (PDAC)

Background: Pancreatic ductal adenocarcinoma (PDAC) is a lethal disease characterized by a diverse tumor microenvironment. The heterogeneous cellular composition of PDAC makes it challenging to study molecular features of tumor cells using extracts from bulk tumor. The metabolic features in tumor cells from clinical samples are poorly understood, and their impact on clinical outcomes are unknown. Our objective was to identify the metabolic features in the tumor compartment that are most clinically impactful. Methods: A computational deconvolution approach using the DeMixT algorithm was applied to bulk RNASeq data from The Cancer Genome Atlas to determine the proportion of each gene's expression that was attributable to the tumor compartment. A machine learning algorithm designed to identify features most closely associated with survival outcomes was used to identify the most clinically impactful metabolic genes. Results: Two metabolic subtypes (M1 and M2) were identified, based on the pattern of expression of the 26 most important metabolic genes. The M2 phenotype had a significantly worse survival, which was replicated in three external PDAC cohorts. This PDAC subtype was characterized by net glycogen catabolism, accelerated glycolysis, and increased proliferation and cellular migration. Single cell data demonstrated substantial intercellular heterogeneity in the metabolic features that typified this aggressive phenotype. Conclusion: By focusing on features within the tumor compartment, two novel and clinically impactful metabolic subtypes of PDAC were identified. Our study emphasizes the challenges of defining tumor phenotypes in the face of the significant intratumoral heterogeneity that typifies PDAC. Further studies are required to understand the microenvironmental factors that drive the appearance of the metabolic features characteristic of the aggressive M2 PDAC phenotype.

The biology of TREM receptors

Triggering receptors expressed on myeloid cells (TREMs) encompass a family of cell-surface receptors chiefly expressed by granulocytes, monocytes and tissue macrophages. These receptors have been implicated in inflammation, neurodegenerative diseases, bone remodelling, metabolic syndrome, atherosclerosis and cancer. Here, I review the structure, ligands, signalling modes and functions of TREMs in humans and mice and discuss the challenges that remain in understanding TREM biology.

High Expression of Triggering Receptor Expressed on Myeloid Cells 1 Predicts Poor Prognosis in Glioblastoma

Background

Glioblastoma (GBM) is a highly malignant tumor with poor prognosis, and new treatment strategies are urgently needed. Currently, the role of triggering receptor expressed on myeloid cells 1 (TREM-1) in tumors has been studied, but the role of TREM-1 in GBM remains unclear.

Methods

Immunohistochemical staining for TREM-1 was performed in 91 patients diagnosed with GBM. Clinicopathological characteristics and survival times were recorded. TREM-1 expression and its effect on prognosis were analyzed using online Gene Expression Profiling Interactive Analysis (GEPIA), The Cancer Genome Atlas (TCGA), and Chinese Glioma Genome Atlas (CGGA) databases. The expression profile of TCGA-GBM cohort was used to perform functional enrichment analysis. The CIBERSORT method and Tumor Immune Estimation Resource (TIMER) database were used to estimate the tumor-infiltrating immune cells (TIICs). The ESTIMATE algorithm was used to estimate the immune-stromal scores. Finally, the relationships of TREM-1 with TIICs, immune-stromal score, and immune checkpoint genes (ICGs) were analyzed.

Results

The expression of TREM-1 was upregulated in GBM, and high TREM-1 expression predicted a poor prognosis. TREM-1, surgical resection, postoperative radiotherapy, and temozolomide (TMZ) chemotherapy were associated with the survival time of patients with GBM, but only surgical resection and TREM-1 expression were independent prognostic factors. GBM with high TREM-1 expression exhibited increased neutrophil and macrophage infiltration. TREM-1 was positively associated with the immune-stromal score and multiple ICGs, and most of which were involved in immunosuppressive responses.

Conclusion

The present study revealed that high expression of TREM-1 in GBM is an independent poor prognosis factor and that TREM-1 is associated with the immunosuppressive microenvironment. Thus, blocking TREM-1 may be a strategy for enhancing the GBM immune response.

Inhibition of TREM-2 Markedly Suppresses Joint Inflammation and Damage in Experimental Arthritis

The triggering receptors expressed on myeloid cells (TREMs) are a family of activating immune receptors that regulate the inflammatory response. TREM-1, which is expressed on monocytes and/or macrophages and neutrophils, functions as an inflammation amplifier and plays a role in the pathogenesis of rheumatoid arthritis (RA). Unlike TREM-1, the role in RA of TREM-2, which is expressed on macrophages, immature monocyte-derived dendritic cells, osteoclasts, and microglia, remains unclear and controversial. TREM-2 ligands are still unknown, adding further uncertainty to our understanding of TREM-2 function. Previously, we demonstrated that TREM-1 blockade, using a ligand-independent TREM-1 inhibitory peptide sequence GF9 rationally designed by our signaling chain homooligomerization (SCHOOL) model of cell signaling, ameliorates collagen-induced arthritis (CIA) severity in mice. Here, we designed a TREM-2 inhibitory peptide sequence IA9 and tested it in the therapeutic CIA model, either as a free 9-mer peptide IA9, or as a part of a 31-mer peptide IA31 incorporated into lipopeptide complexes (IA31-LPC), for targeted delivery. We demonstrated that administration of IA9, but not a control peptide, after induction of arthritis diminished release of proinflammatory cytokines and dramatically suppressed joint inflammation and damage, suggesting that targeting TREM-2 may be a promising approach for the treatment of RA.

Triggering Receptors Expressed on Myeloid Cells 1 : Our New Partner in Human Oncology?

Inflammation is recognized as one of the hallmarks of cancer. Indeed, strong evidence indicates that chronic inflammation plays a major role in oncogenesis, promoting genome instability, epigenetic alterations, proliferation and dissemination of cancer cells. Mononuclear phagocytes (MPs) have been identified as key contributors of the inflammatory infiltrate in several solid human neoplasia, promoting angiogenesis and cancer progression. One of the most described amplifiers of MPs pro-inflammatory innate immune response is the triggering receptors expressed on myeloid cells 1 (TREM-1). Growing evidence suggests TREM-1 involvement in oncogenesis through cancer related inflammation and the surrounding tumor microenvironment. In human oncology, high levels of TREM-1 and/or its soluble form have been associated with poorer survival data in several solid malignancies, especially in hepatocellular carcinoma and lung cancer. TREM-1 should be considered as a potential biomarker in human oncology and could be used as a new therapeutic target of interest in human oncology (TREM-1 inhibitors, TREM-1 agonists). More clinical studies are urgently needed to confirm TREM-1 (and TREM family) roles in the prognosis and the treatment of human solid cancers.

An Inflammatory Response Related Gene Signature Associated with Survival Outcome and Gemcitabine Response in Patients with Pancreatic Ductal Adenocarcinoma

Background: Pancreatic ductal adenocarcinoma (PDAC) is one of the most aggressive tumors with an extremely low 5-year survival rate. Accumulating evidence has unveiled that inflammatory response promotes tumor progression, enhances angiogenesis, and causes local immunosuppression. Herein, we aim to develop an inflammatory related prognostic signature, and found it could be used to predict gemcitabine response in PDAC.

Methods: PDAC cohorts with mRNA expression profiles and clinical information were systematically collected from the four public databases. An inflammatory response related genes (IRRGs) prognostic signature was constructed by LASSO regression analysis. Kaplan–Meier survival analysis, receiver operating characteristic analysis, principal component analysis, and univariate and multivariate Cox analyses were carried out to evaluate effectiveness, and reliability of the signature. The correlation between gemcitabine response and risk score was evaluated in the TCGA-PAAD cohort. The GDSC database, pRRophetic algorithm, and connectivity map analysis were used to predict gemcitabine sensitivity and identify potential drugs for the treatment of PDAC. Finally, we analyzed differences in frequencies of gene mutations, infiltration of immune cells, as well as biological functions between different subgroups divided by the prognostic signature.

Results: We established a seven IRRGs (ADM, DCBLD2, EREG, ITGA5, MIF, TREM1, and BTG2) signature which divided the PDAC patients into low- and high-risk groups. Prognostic value of the signature was validated in 11 PDAC cohorts consisting of 1337 PDAC patients from 6 countries. A nomogram that integrated the IRRGs signature and clinicopathologic factors of PDAC patients was constructed. The risk score showed positive correlation with gemcitabine resistance. Two drugs (BMS-536924 and dasatinib) might have potential therapeutic implications in high-risk PDAC patients. We found that the high-risk group had higher frequencies of KRAS, TP53, and CDKN2A mutations, increased infiltration of macrophages M0, neutrophils, and macrophages M2 cells, as well as upregulated hypoxia and glycolysis pathways, while the low-risk group had increased infiltration of CD8⁺ T, naïve B, and plasma and macrophages M1 cells.

Conclusion: We constructed and validated an IRRGs signature that could be used to predict the prognosis and gemcitabine response of patients with PDAC, as well as two drugs (BMS-536924 and dasatinib) may contribute to PDAC treatment.

C1QTNF6 promotes oral squamous cell carcinoma by enhancing proliferation and inhibiting apoptosis

BACKGROUND

C1QTNF6 (CTRP6), a member of the CTRP family, has recently been implied to play a role in the tumorigenesis of for a variety of cancer types. However, the role of C1QTNF6 in oral squamous cell carcinoma (OSCC) and its potential molecular remains unclear.

METHODS

C1QTNF6 expression was detected by qRT-PCR and western blot analysis. Lentiviral vectors were constructed to knockdown C1QTNF6 in CaL27 and SCC-9 human OSCC cell lines. Cell viability, cell cycle and cell apoptosis analyses were performed by MTT assay, PI/Annexin V staining, and flow cytometry. The effect of C1QTNF6 knockdown on in vivo tumorigenicity of OSCC cells in vivo was evaluated using nude mouse xenograft tumor model. Downstream signaling mechanisms were identified by microarray and Ingenuity Pathway Analysis.

RESULTS

Immunohistochemistry of OSCC tissue and data from TCGA demonstrate that C1QTNF6 was overexpressed in OSCC tissues, and that cellular proliferation was significantly decreased after C1QTNF6 was knockdown in CaL27 and SCC-9 cell lines. Knockdown of C1QTNF6 also resulted in cell cycle arrest at the G2/M phase and enhanced cell apoptosis in in CaL27 and SCC-9 cell lines. Furthermore, knockdown of C1QTNF6 in Cal-27 cells inhibited tumor growth of OSCC in vivo. Microarray analysis revealed that C1QTNF6 silencing resulted in significant alterations of gene expression, with the Acute Phase Response signaling pathway significantly activated following C1QTNF6 silencing.

CONCLUSIONS

These results suggest that C1QTNF6 plays an important role in promoting OSCC tumorigenesis, which indicates that C1QTNF6 may comprise a promising therapeutic target for OSCC treatment.

Bulk and Single-Cell Profiling of Breast Tumors Identifies TREM-1 as a Dominant Immune Suppressive Marker Associated With Poor Outcomes

Background

Triggering receptor expressed on myeloid cells (TREM)-1 is a key mediator of innate immunity previously associated with the severity of inflammatory disorders, and more recently, the inferior survival of lung and liver cancer patients. Here, we investigated the prognostic impact and immunological correlates of TREM1 expression in breast tumors.

Methods

Breast tumor microarray and RNAseq expression profiles (n=4,364 tumors) were analyzed for associations between gene expression, tumor immune subtypes, distant metastasis-free survival (DMFS) and clinical response to neoadjuvant chemotherapy (NAC). Single-cell (sc)RNAseq was performed using the 10X Genomics platform. Statistical associations were assessed by logistic regression, Cox regression, Kaplan-Meier analysis, Spearman correlation, Student’s t-test and Chi-square test.

Results

In pre-treatment biopsies, TREM1 and known TREM-1 inducible cytokines (IL1B, IL8) were discovered by a statistical ranking procedure as top genes for which high expression was associated with reduced response to NAC, but only in the context of immunologically “hot” tumors otherwise associated with a high NAC response rate. In surgical specimens, TREM1 expression varied among tumor molecular subtypes, with highest expression in the more aggressive subtypes (Basal-like, HER2-E). High TREM1 significantly and reproducibly associated with inferior distant metastasis-free survival (DMFS), independent of conventional prognostic markers. Notably, the association between high TREM1 and inferior DMFS was most prominent in the subset of immunogenic tumors that exhibited the immunologically hot phenotype and otherwise associated with superior DMFS. Further observations from bulk and single-cell RNAseq analyses indicated that TREM1 expression was significantly enriched in polymorphonuclear myeloid-derived suppressor cells (PMN-MDSCs) and M2-like macrophages, and correlated with downstream transcriptional targets of TREM-1 (IL8, IL-1B, IL6, MCP-1, SPP1, IL1RN, INHBA) which have been previously associated with pro-tumorigenic and immunosuppressive functions.

Conclusions

Together, these findings indicate that increased TREM1 expression is prognostic of inferior breast cancer outcomes and may contribute to myeloid-mediated breast cancer progression and immune suppression.

Trem1 mediates neuronal apoptosis via interaction with SYK after spinal cord ischemia-reperfusion injury

OBJECTIVE

This research aimed to study the impact and regulatory mechanism of Trem1 in spinal cord ischemia-reperfusion injury (SCIRI).

METHOD

Temporary aortic cross clamp followed by reperfusion was used to establish SCIRI mice model. Mice motion function was estimated by Basso, Beattie, Bresnahan (BBB) score. Spinal cord infract zone was analyzed by HE and TUNEL staining. High throughput sequencing was performed to explore potential target for SCIRI. N2a cells were used to simulate the pathophysiological process of SCIRI in vitro with oxygen-glucose-serum deprivation/restoration (OGSD/R). RT-PCR and Western blot were token to determine mRNA and protein expression levels. Knockdown of Trem1 was performed with siRNA transfection in vitro and shRNA adenovirus injection in vivo. The relationship between Trem1 and SYK was analyzed by immunoprecipitation and immunofluorescence.

RESULT

We observed that neuronal apoptosis of spinal cord was aggravated after SCIRI. Trem1 expression was dramatically upregulated as shown by high throughput sequencing, RT-PCR and Western blot results. Furthermore, Trem1 triggered apoptosis of N2a cells induced by OGSD/R, and knockdown of Trem1 by siRNAs blocked apoptosis via PI3K/AKT and NF-κB signaling pathway by interacting with SYK. In addition, we found that intrathecal injection of adenovirus with Trem1 shRNA could downregulate SYK and inhibit neuron apoptosis caused by SCIRI in vivo.

CONCLUSION

Trem1 interacts with SYK and mediates neuronal apoptosis via the PI3K/AKT and NF-κB signaling pathway. Trem1 may be a therapeutic candidate for patients with SCIRI.

Pancreatic cancer is marked by complement-high blood monocytes and tumor-associated macrophages

Pancreatic ductal adenocarcinoma (PDA) is accompanied by reprogramming of the local microenvironment, but changes at distal sites are poorly understood. We implanted biomaterial scaffolds, which act as an artificial premetastatic niche, into immunocompetent tumor-bearing and control mice, and identified a unique tumor-specific gene expression signature that includes high expression of C1qa, C1qb, Trem2, and Chil3 Single-cell RNA sequencing mapped these genes to two distinct macrophage populations in the scaffolds, one marked by elevated C1qa, C1qb, and Trem2, the other with high Chil3, Ly6c2 and Plac8 In mice, expression of these genes in the corresponding populations was elevated in tumor-associated macrophages compared with macrophages in the normal pancreas. We then analyzed single-cell RNA sequencing from patient samples, and determined expression of C1QA, C1QB, and TREM2 is elevated in human macrophages in primary tumors and liver metastases. Single-cell sequencing analysis of patient blood revealed a substantial enrichment of the same gene signature in monocytes. Taken together, our study identifies two distinct tumor-associated macrophage and monocyte populations that reflects systemic immune changes in pancreatic ductal adenocarcinoma patients.

Activation of TREM-1 induces endoplasmic reticulum stress through IRE-1α/XBP-1s pathway in murine macrophages

Increasing evidence suggests that endoplasmic reticulum (ER) stress activates several pro-inflammatory signaling pathways in many diseases, including acute lung injury (ALI). We have reported that blocking triggering receptor expressed on myeloid cells 1 (TREM-1) protects against ALI by suppressing pulmonary inflammation in mice with ALI induced by lipopolysaccharides (LPS). However, the molecular mechanism underlying the TREM-1-induced pro-inflammatory microenvironment in macrophages remains unclearly. Herein, we aimed to determine whether TREM-1 regulates the inflammatory responses induced by LPS associated with ER stress activation. We found that the activation of TREM-1 by a monoclonal agonist antibody (anti-TREM-1) increased the mRNA and protein levels of IL-1β, TNF-α, and IL-6 in primary macrophages. Treatment of the anti-TREM-1 antibody increased the expression of ER stress markers (ATF6, PERK, IRE-1α, and XBP-1s) in primary macrophages. While pretreatment with 4-PBA, an inhibitor of ER stress, significantly inhibited the expression of ER stress markers and pro-inflammatory cytokines and reduced LDH release. Furthermore, inhibiting the activity of the IRE-1α/XBP-1s pathway by STF-083010 significantly mitigated the increased levels of IL-1β, TNF-α, and IL-6 in macrophages treated by the anti-TREM-1 antibody. XBP-1 silencing attenuated pro-inflammatory microenvironment evoked by activation of TREM-1. Besides, we found that blockade of TREM-1 with LR12 ameliorated ER stress induced by LPS in vitro and in vivo. In conclusion, we conclude that TREM-1 activation induces ER stress through the IRE-1α/XBP-1s pathway in macrophages, contributing to the pro-inflammatory microenvironment.

Novel ligands and modulators of triggering receptor expressed on myeloid cells receptor family: 2015-2020 updates

Introduction: Triggering receptors expressed on myeloid cells (TREMs) are inflammatory amplifiers with defined pathophysiological role in various infectious diseases, acute and chronic aseptic inflammations, and a variety of cancers, depicting TREMs as prominent therapeutic targets.Areas covered: Herein, updates from 2015 to 2020 are discussed to divulge the TREM ligands, as well as their peptide blockers, claimed to modulate their expression. The article also presents different strategies employed during the last five years to block interactions between TREMs and their ligands to treat various disease conditions by modulating their expression and activity.Expert opinion: There has been significant progress in the discovery of novel ligands and modulators of TREMs in the last five years that mainly revolved around the function of TREM molecules. A few peptides showed encouraging results to modulate the expression and activity of TREMs in preclinical studies, and these peptides are currently under clinical investigation. Based on the findings so far in several careful studies, we expect novel therapeutics in the near future which could have the ability to treat various disease conditions associated with TREM expression.

Tumor-Associated Macrophages in Pancreatic Ductal Adenocarcinoma: Origin, Polarization, Function, and Reprogramming

Pancreatic ductal adenocarcinoma (PDAC) is a highly lethal malignancy. PDAC is only cured by surgical resection in its early stage, but there remains a relatively high possibility of recurrence. The development of PDAC is closely associated with the tumor microenvironment. Tumor-associated macrophages (TAMs) are one of the most abundant immune cell populations in the pancreatic tumor stroma. TAMs are inclined to M2 deviation in the tumor microenvironment, which promotes and supports tumor behaviors, including tumorigenesis, immune escape, metastasis, and chemotherapeutic resistance. Herein, we comprehensively reviewed the latest researches on the origin, polarization, functions, and reprogramming of TAMs in PDAC.

Androgen receptor signalling in macrophages promotes TREM-1-mediated prostate cancer cell line migration and invasion

The androgen receptor (AR) is the master regulator of prostate cancer (PCa) development, and inhibition of AR signalling is the most effective PCa treatment. AR is expressed in PCa cells and also in the PCa-associated stroma, including infiltrating macrophages. Macrophages have a decisive function in PCa initiation and progression, but the role of AR in macrophages remains largely unexplored. Here, we show that AR signalling in the macrophage-like THP-1 cell line supports PCa cell line migration and invasion in culture via increased Triggering Receptor Expressed on Myeloid cells-1 (TREM-1) signalling and expression of its downstream cytokines. Moreover, AR signalling in THP-1 and monocyte-derived macrophages upregulates IL-10 and markers of tissue residency. In conclusion, our data suggest that AR signalling in macrophages may support PCa invasiveness, and blocking this process may constitute one mechanism of anti-androgen therapy.

Anti-androgen therapy inhibits prostate cancer (PC) progression, and is thought to act directly on cancer cells. Here the authors show that androgen receptor is expressed on normal and PC-associated macrophages, and its stimulation alters macrophage secretome to promote migration of cultured PC cell lines.

SCHOOL of nature: ligand-independent immunomodulatory peptides

Groundbreaking studies in protein biophysics have identified the mechanisms of transmembrane signaling at the level of druggable protein-protein interactions (PPIs). This resulted in the development of the signaling chain homooligomerization (SCHOOL) strategy to modulate cell responses using receptor-specific peptides. Inspired by nature, these short peptides use ligand-independent mechanisms of receptor inhibition and demonstrate potent efficacy in vitro and in vivo. The SCHOOL strategy is especially important when receptor ligands are unknown. An example is the triggering receptor expressed on myeloid cells-1 (TREM-1) receptor, an emerging therapeutic target involved in the pathogenesis of most inflammatory diseases. Here, I discuss advances in the field with a focus on TREM-1 inhibitory SCHOOL peptides that offer new hope for a 'magic bullet' cure for cancer, arthritis, sepsis, retinopathy, and other medical challenges.

Targeting Mononuclear Phagocyte Receptors in Cancer Immunotherapy: New Perspectives of the Triggering Receptor Expressed on Myeloid Cells (TREM-1)

Inflammatory cells are major players in the onset of cancer. The degree of inflammation and type of inflammatory cells in the tumor microenvironment (TME) are responsible for tilting the balance between tumor progression and regression. Cancer-related inflammation has also been shown to influence the efficacy of conventional therapy. Mononuclear phagocytes (MPs) represent a major component of the inflammatory circuit that promotes tumor progression. Despite their potential to activate immunosurveillance and exert anti-tumor responses, MPs are subverted by the tumor to support its growth, immune evasion, and spread. MP responses in the TME are dictated by a network of stimuli integrated through the cross-talk between activatory and inhibitory receptors. Alterations in receptor expression/signaling can create excessive inflammation and, when chronic, promote tumorigenesis. Research advances have led to the development of new therapeutic strategies aimed at receptor targeting to induce a tumor-infiltrating MP switch from a cancer-supportive toward an anti-tumor phenotype, demonstrating efficacy in different human cancers. This review provides an overview of the role of MP receptors in inflammation-mediated carcinogenesis and discusses the most recent updates regarding their targeting for immunotherapeutic purposes. We focus in particular on the TREM-1 receptor, a major amplifier of MP inflammatory responses, highlighting its relevance in the development and progression of several types of inflammation-associated malignancies and the promises of its inhibition for cancer immunotherapy.

Triggering Receptor Expressed on Myeloid Cells-1 Inhibitor Targeted to Endothelium Decreases Cell Activation

TREM-1 (Triggering Receptor Expressed on Myeloid cells-1) is an immunoreceptor expressed on neutrophils, monocytes/macrophages, and endothelial cells. It amplifies the inflammatory response driven by Toll-Like Receptors (TLR) engagement. The pharmacological inhibition of TREM-1 confers protection in several pre-clinical models of acute inflammation. In this study, we aimed to investigate the role of TREM-1 in endothelial cells using a sneaking ligand construct (SLC) inhibiting TREM-1 in the endothelium. The SLC was made of 3 modules: an E-selectin targeting domain, a Pseudomonas aeruginosa exotoxin a translocation domain, and a 7 aa peptide (LSKSLVF) that contains the interaction site between TREM-1 and its adaptor protein DAP-12. SLC peptide was effectively picked up by endothelial cells following LPS stimulation. It decreased LPS induced TREM-1 up-regulation and cell activation, neutrophils extravasation, and improved median survival time during experimental peritonitis in mice. We reported that a targeted endothelial TREM-1 inhibition is able to dampen cell activation and to confer protection during septic shock in mice. The use of such cell-specific, ligand- independent TREM-1 inhibitors deserve further investigations during acute or chronic inflammatory disorders.

Therapeutic Effect of Modulating TREM-1 via Anti-inflammation and Autophagy in Parkinson's Disease

Parkinson’s disease (PD) is one of the most common age-related neurodegenerative diseases, and neuroinflammation has been identified as one of its key pathological characteristics. Triggering receptors expressed on myeloid cells-1 (TREM-1) amplify the inflammatory response and play a role in sepsis and cancer. Recent studies have demonstrated that the attenuation of TREM-1 activity produces cytoprotective and anti-inflammatory effects in macrophages. However, no study has examined the role of TREM-1 in neurodegeneration. We showed that LP17, a synthetic peptide blocker of TREM-1, significantly inhibited the lipopolysaccharide (LPS)-induced upregulation of proinflammatory cascades of inducible nitric oxide synthase (iNOS), cyclooxygenase-2, and nuclear factor-kappa B. Moreover, LP17 enhanced the LPS-induced upregulation of autophagy-related proteins such as light chain-3 and histone deacetylase-6. We also knocked down TREM-1 expression in a BV2 cell model to further confirm the role of TREM-1. LP17 inhibited 6-hydroxydopamine-induced locomotor deficit and iNOS messenger RNA expression in zebrafish. We also observed therapeutic effects of LP17 administration in 6-hydroxydopamine-induced PD syndrome using a rat model. These data suggest that the attenuation of TREM-1 could ameliorate neuroinflammatory responses in PD and that this neuroprotective effect might occur via the activation of autophagy and anti-inflammatory pathways.

Blocking Triggering Receptor Expressed on Myeloid Cells-1-Positive Tumor-Associated Macrophages Induced by Hypoxia Reverses Immunosuppression and Anti-Programmed Cell Death Ligand 1 Resistance in Liver Cancer

Tumor-associated macrophages (TAMs) are recognized as antitumor suppressors, but how TAMs behave in the hypoxic environment of hepatocellular carcinoma (HCC) remains unclear. Here, we demonstrated that hypoxia inducible factor 1α induced increased expression of triggering receptor expressed on myeloid cells-1 (TREM-1) in TAMs, resulting in immunosuppression. Specifically, TREM-1-positive (TREM-1⁺ ) TAMs abundant at advanced stages of HCC progression indirectly impaired the cytotoxic functions of CD8⁺ T cells and induced CD8⁺ T-cells apoptosis. Biological and functional assays showed that TREM-1⁺ TAMs had higher expression of programmed cell death ligand 1 (PD-L1) under hypoxic environment. However, TREM-1⁺ TAMs could abrogate spontaneous and PD-L1-blockade-mediated antitumor effects in vivo, suggesting that TREM-1⁺ TAM-induced immunosuppression was dependent on a pathway separate from PD-L1/programmed cell death 1 axis. Moreover, TREM-1⁺ TAM-associated regulatory T cells (Tregs) were crucial for HCC resistance to anti-PD-L1 therapy. Mechanistically, TREM-1⁺ TAMs elevated chemokine (C-C motif) ligand 20 expression through the extracellular signal-regulated kinase/NF-κβ pathway in response to hypoxia and tumor metabolites leading to CCR6⁺ Foxp3⁺ Treg accumulation. Blocking the TREM-1 pathway could significantly inhibit tumor progression, reduce CCR6⁺ Foxp3⁺ Treg recruitment, and improve the therapeutic efficacy of PD-L1 blockade. Thus, these data demonstrated that CCR6⁺ Foxp3⁺ Treg recruitment was crucial for TREM-1⁺ TAM-mediated anti-PD-L1 resistance and immunosuppression in hypoxic tumor environment. Conclusion: This study highlighted that the hypoxic environment initiated the onset of tumor immunosuppression through TREM-1⁺ TAMs attracting CCR6⁺ Foxp3⁺ Tregs, and TREM-1⁺ TAMs endowed HCC with anti-PD-L1 therapy resistance.

Pedf derived peptides affect colorectal cancer cell lines resistance and tumour re-growth capacity

Relapse after chemotherapy treatment depends on the cancer initiating cells (CICs). PEDF (Pigmented Epithelium Derived Factor) is an anti-angiogenic, neurotrophic and self-renewal regulator molecule, also involved in CICs biology. Acute and chronic exposition of colon cancer cell lines to CT/CTE PEDF-derived peptides decreased drug-resistance to conventional colorectal cancer treatments, such as oxaliplatin or irinotecan. We confirmed a reduction in the irinotecan and oxaliplatin IC50 doses for all tested tumour cell lines. After xenograft transplantation, CT/CTE treatments also produced a reduction in resistance to conventional chemotherapy treatments as in culture-assays. Metastatic capacity of these treated cell lines was also depleted. The PEDF signaling pathway could be a future therapeutic tool for use as an adjuvant therapy that decreases IC50 dosis, adverse effects and treatment costs. This pathway could also be involved in an increase of the time relapse in patients, decreased tumourigenicity, and decreased capacity to produce metastasis.

Inhibition of Triggering Receptor Expressed on Myeloid Cells 1 Ameliorates Inflammation and Macrophage and Neutrophil Activation in Alcoholic Liver Disease in Mice

Alcoholic liver disease (ALD) is characterized by macrophage and neutrophil leukocyte recruitment and activation in the liver. Damage‐ and pathogen‐associated molecular patterns contribute to a self‐perpetuating proinflammatory state in ALD. Triggering receptor expressed on myeloid cells 1 (TREM‐1) is a surface receptor that amplifies inflammation induced by toll‐like receptors (TLRs) and is expressed on neutrophils and monocytes/macrophages. We hypothesized that TREM‐1 signaling contributes to proinflammatory pathway activation in ALD. Using an in vivo ALD model in mice, we tested the effects of ligand‐independent TREM‐1 inhibitory peptides that were formulated into human high‐density lipoprotein (HDL)‐mimicking complexes GF9‐HDL and GA/E31‐HDL. As revealed in vitro, macrophages endocytosed these rationally designed complexes through scavenger receptors. A 5‐week alcohol feeding with the Lieber‐DeCarli diet in mice resulted in increased serum alanine aminotransferase (ALT), liver steatosis, and increased proinflammatory cytokines in the liver. TREM‐1 messenger RNA (mRNA) expression was significantly increased in alcohol‐fed mice, and TREM‐1 inhibitors significantly reduced this increase. TREM‐1 inhibition significantly attenuated alcohol‐induced spleen tyrosine kinase (SYK) activation, an early event in both TLR4 and TREM‐1 signaling. The TREM‐1 inhibitors significantly inhibited macrophage (epidermal growth factor‐like module‐containing mucin‐like hormone receptor‐like 1 [F4/80], clusters of differentiation [CD]68) and neutrophil (lymphocyte antigen 6 complex, locus G [Ly6G] and myeloperoxidase [MPO]) markers and proinflammatory cytokines (monocyte chemoattractant protein 1 [MCP‐1], tumor necrosis factor α [TNF‐α], interleukin‐1β [IL‐1β], macrophage inflammatory protein 1α [MIP‐1α]) at the mRNA level compared to the HDL vehicle. Administration of TREM‐1 inhibitors ameliorated liver steatosis and early fibrosis markers (α‐smooth muscle actin [αSMA] and procollagen1α [Pro‐Col1α]) at the mRNA level in alcohol‐fed mice. However, the HDL vehicle also reduced serum ALT and some cytokine protein levels in alcohol‐fed mice, indicating HDL‐related effects. Conclusion: HDL‐delivered novel TREM‐1 peptide inhibitors ameliorate early phases of inflammation and neutrophil and macrophage recruitment and activation in the liver and attenuate hepatocyte damage and liver steatosis. TREM‐1 inhibition represents a promising therapeutic approach for further investigations in ALD.

TREM-1; Is It a Pivotal Target for Cardiovascular Diseases?

Cardiovascular diseases (CVDs) are as menacing as ever and still continue to kill adults worldwide, notwithstanding tremendous efforts to decrease their consequent mortality and morbidity. Lately, a growing body of research indicated that inflammation plays a pivotal role in the pathogenesis and complications of CVDs. A receptor of the immunoglobulin superfamily, triggering receptors expressed on myeloid cells-1 (TREM-1) was shown to induce and amplify the inflammation in both acute and chronic disease’ pathogenesis and progression, which hence makes it one of the most important complication factors of CVDs. Thus, studies endeavored to investigate the role played by TREM-1 in CVDs with respect to their etiologies, complications, and possible therapeutics. We examined here, for the first time, the most relevant studies regarding TREM-1 involvement in CVDs. We critically analyzed and summarized our findings and made some suggestions for furtherance of the investigations with the aim to utilize TREM-1 and its pathways for diagnostic, management, and prognosis of CVDs. Overall, TREM-1 was found to be involved in the pathogenesis of acute and chronic cardiovascular conditions, such as acute myocardial infarction (AMI) and atherosclerosis. Although most therapeutic approaches are yet to be elucidated, our present research outcome displays a promising future to utilizing the TREM-1 pathway as a potential target for understanding and managing CVDs.

Blockade of TREM-1 prevents vitreoretinal neovascularization in mice with oxygen-induced retinopathy

In pathological retinal neovascularization (RNV) disorders, the retina is infiltrated by activated leukocytes and macrophages. Triggering receptor expressed on myeloid cells 1 (TREM-1), an inflammation amplifier, activates monocytes and macrophages and plays an important role in cancer, autoimmune and other inflammation-associated disorders. Hypoxia-inducible TREM-1 is involved in cancer angiogenesis but its role in RNV remains unclear. Here, to close this gap, we evaluated the role of TREM-1 in RNV using a mouse model of oxygen-induced retinopathy (OIR). We found that hypoxia induced overexpression of TREM-1 in the OIR retinas compared to that of the room air group. TREM-1 was observed specifically in areas of pathological RNV, largely colocalizing with macrophage colony-stimulating factor (M-CSF) and CD45- and Iba-1-positive cells. TREM-1 blockade using systemically administered first-in-class ligand-independent TREM-1 inhibitory peptides rationally designed using the signaling chain homooligomerization (SCHOOL) strategy significantly (up to 95%) reduced vitreoretinal neovascularization. The peptides were well-tolerated when formulated into lipopeptide complexes for peptide half-life extension and targeted delivery. TREM-1 inhibition substantially downregulated retinal protein levels of TREM-1 and M-CSF suggesting that TREM-1-dependent suppression of pathological angiogenesis involves M-CSF. Targeting TREM-1 using TREM-1-specific SCHOOL peptide inhibitors represents a novel strategy to treat retinal diseases that are accompanied by neovascularization including retinopathy of prematurity.