Specific activation of the TLR1-TLR2 heterodimer by small-molecule agonists

Design and Synthesis of 3-(2H-Chromen-3-yl)-5-aryl-1,2,4-oxadiazole Derivatives as Novel Toll-like Receptor 2/1 Agonists That Inhibit Lung Cancer In Vitro and In Vivo

Toll-like receptor (TLR) 2 is a transmembrane receptor that participates in the innate immune response by forming a heterodimer with TLR1 or TLR6. TLR2 agonists play an important role in tumor therapy. Herein, we synthesized a series of 3-(2H-chromen-3-yl)-5-aryl-1,2,4-oxadiazole derivatives and identified WYJ-2 as a potent small and selective molecule agonist of TLR2/1, with an EC50 of 18.57 ± 0.98 nM in human TLR2 and TLR1 transient-cotransfected HEK 293T cells. WYJ-2 promoted the formation of TLR2/1 heterodimers and activated the nuclear factor kappa B (NF-κB) signaling pathway. Moreover, our study indicated that WYJ-2 could induce pyroptosis in cancer cells, mediated by activating the NOD-like receptor pyrin domain containing 3 (NLRP3) inflammasome. WYJ-2 exhibited effective anti-non-small cell lung cancer (NSCLC) activity in vitro and in vivo. The discovery that activating TLR2/1 induces pyroptosis in cancer cells may highlight the prospects of TLR2/1 agonists in cancer treatment in the future.

Immune Epitopes of SARS-CoV-2 Spike Protein and Considerations for Universal Vaccine Development

Despite the success of global vaccination programs in slowing the spread of COVID-19, these efforts have been hindered by the emergence of new SARS-CoV-2 strains capable of evading prior immunity. The mutation and evolution of SARS-CoV-2 have created a demand for persistent efforts in vaccine development. SARS-CoV-2 Spike protein has been the primary target for COVID-19 vaccine development, but it is also the hotspot of mutations directly involved in host susceptibility and virus immune evasion. Our ability to predict emerging mutants and select conserved epitopes is critical for the development of a broadly neutralizing therapy or a universal vaccine. In this article, we review the general paradigm of immune responses to COVID-19 vaccines, highlighting the immunological epitopes of Spike protein that are likely associated with eliciting protective immunity resulting from vaccination in humans. Specifically, we analyze the structural and evolutionary characteristics of the SARS-CoV-2 Spike protein related to immune activation and function via the TLRs, B cells, and T cells. We aim to provide a comprehensive analysis of immune epitopes of Spike protein, thereby contributing to the development of new strategies for broad neutralization or universal vaccination.

Seasonal influenza vaccines differentially activate and modulate toll-like receptor expression within the tumor microenvironment

Toll-like receptors (TLRs) are well-known for their role in cancer development as well as in directing anti-tumor immunity. Because TLRs have also been implicated in the innate recognition of the influenza virus, it was of great interest to investigate the potential TLRs' contribution to the reduction in tumor growth following intratumoral injection of an unadjuvanted influenza vaccine and the lack of antitumor response from an adjuvanted vaccine. In our previous publication, we showed that the unadjuvanted flu vaccine modulates TLR7 expression leading to anti-tumor response in a murine model of melanoma. Here, we show that the unadjuvanted and adjuvanted flu vaccines robustly stimulate different sets of TLRs, TLR3 and TLR7, and TLR4 and TLR9, respectively. In addition, the reduction in tumor growth and improved survival from intratumoral administration of the unadjuvanted vaccine was found to be diminished in TLR7-deficient mice. Finally, we observed that both vaccines have the capacity to modulate TLR expression on both innate and adaptive immune cells. Our findings add to the mechanistic understanding of the parameters that influence tumor outcomes in unadjuvanted and adjuvanted influenza vaccines.

Toll-like receptor signalling via IRAK4 affects epithelial integrity and tightness through regulation of junctional tension

Toll-like receptors (TLRs) in mammalian systems are well known for their role in innate immunity. In addition, TLRs also fulfil crucial functions outside immunity, including the dorsoventral patterning function of the original Toll receptor in Drosophila and neurogenesis in mice. Recent discoveries in flies suggested key roles for TLRs in epithelial cells in patterning of junctional cytoskeletal activity. Here, we address the function of TLRs and the downstream key signal transduction component IRAK4 in human epithelial cells. Using differentiated human Caco-2 cells as a model for the intestinal epithelium, we show that these cells exhibit baseline TLR signalling, as revealed by p-IRAK4, and that blocking IRAK4 function leads to a loss of epithelial tightness involving key changes at tight and adherens junctions, such as a loss of epithelial tension and changes in junctional actomyosin. Changes upon IRAK-4 inhibition are conserved in human bronchial epithelial cells. Knockdown of IRAK4 and certain TLRs phenocopies the inhibitor treatment. These data suggest a model whereby TLR receptors near epithelial junctions might be involved in a continuous sensing of the epithelial state to promote epithelial tightness and integrity.

Small molecule modulators of immune pattern recognition receptors

Pattern recognition receptors (PRRs) represent a re-emerging class of therapeutic targets for vaccine adjuvants, inflammatory diseases and cancer. In this review article, we summarize exciting developments in discovery and characterization of small molecule PRR modulators, focusing on Toll-like receptors (TLRs), NOD-like receptors (NLRs) and the cGAS-STING pathway. We also highlight PRRs that are currently lacking small molecule modulators and opportunities for chemical biology and therapeutic discovery.

Microbial sensing in the intestine

The gut microbiota plays a key role in host health and disease, particularly through their interactions with the immune system. Intestinal homeostasis is dependent on the symbiotic relationships between the host and the diverse gut microbiota, which is influenced by the highly co-evolved immune-microbiota interactions. The first step of the interaction between the host and the gut microbiota is the sensing of the gut microbes by the host immune system. In this review, we describe the cells of the host immune system and the proteins that sense the components and metabolites of the gut microbes. We further highlight the essential roles of pattern recognition receptors (PRRs), the G protein-coupled receptors (GPCRs), aryl hydrocarbon receptor (AHR) and the nuclear receptors expressed in the intestinal epithelial cells (IECs) and the intestine-resident immune cells. We also discuss the mechanisms by which the disruption of microbial sensing because of genetic or environmental factors causes human diseases such as the inflammatory bowel disease (IBD).

A novel missense compound heterozygous variant in TLR1 gene is associated with susceptibility to rheumatoid arthritis - structural perspective and functional annotations

INTRODUCTION

Besides human leukocyte antigen (HLA-DRB1) locus, more than 100 loci across the genome have been identified and linked with the onset, expression and/or progression of rheumatoid arthritis (RA). However, there are still grey areas in our understanding of the key genetic contributors of the disease, particularly in familial cases.

METHODS

In the present study, we have performed the whole exome sequencing (WES) of RA patients from two consanguineous families of Pakistan in a quest to identify novel, high-impact, RA-susceptibility genetic variants.

RESULTS

Through stepwise filtering, around 17,000 variants (common in the affected members) were recognized, out of which 2651 were predicted to be deleterious. Of these, 196 had direct relevance to RA. When selected for homozygous recessive mode of inheritance, two novel pathogenic variants (c.1324T>C, p.Cys442→Arg442; c.2036T>C, p.Ile679→Thr679) in the TLR1 gene displayed the role of compound heterozygosity in modulating the phenotypic expression and penetrance of RA. The structural and functional consequences of the TLR1 missense single nucleotide mutations (Cys442→Arg442; Ile679→Thr679) were evaluated through molecular dynamic simulation (MDS) studies. Analysis showed domain's rigidification, conferring stability to mutant TLR1-TIR/TIRAP-TIR complex with concomitant increase in molecular interactions with pro-inflammatory cytokines, compared to the wild-type conformation. Gene co-expression network analysis highlighted interlinked partnering genes along with interleukin-6 production of TLR1 (corrected p-value 2.98e-4) and acetylcholine receptor activity of CHRNG (corrected p-value 6.12e-2) as highly enriched associated functions.

CONCLUSION

The results, validated through case-control study subjects, suggested that the variants identified through WES and confirmed through Sanger sequencing and MDS are the novel disease variants and are likely to confer RA-susceptibility, independently and/or in a family-specific context. Key Points • Exploration of population based/ethno-specific big data is imperative to identify novel causal variants of RA. • Two new deleterious missense mutations in mutational hotspot exon 4 of TLR1 gene have been identified in Pakistani RA patients. • MD simulation data provides evidence for domain's rigidification, conferring stability to mutant TLR1-TIR/TIRAP-TIR complex, with concomitant increase in production of pro-inflammatory cytokines, thus adding to the onset/erosive outcome of RA.

Immune Epitopes of SARS-CoV-2 Spike Protein and Considerations for Universal Vaccine Development

Despite the success of global vaccination programs in slowing the spread of COVID-19, these efforts have been hindered by the emergence of new SARS-CoV-2 strains capable of evading prior immunity. The mutation and evolution of SARS-CoV-2 have created a demand for persistent efforts in vaccine development. SARS-CoV-2 Spike protein has been the primary target for COVID-19 vaccine development, but it is also the hotspot of mutations directly involved in host susceptibility and immune evasion. Our ability to predict emerging mutants and select conserved epitopes is critical for the development of a broadly neutralizing therapy or a universal vaccine. In this article, we review the general paradigm of immune responses to COVID-19 vaccines, highlighting the immunological epitopes of Spike protein that are likely associated with eliciting protective immunity resulting from vaccination. Specifically, we analyze the structural and evolutionary characteristics of the SARS-CoV-2 Spike protein related to immune activation and function via the toll-like receptors (TLRs), B cells, and T cells. We aim to provide a comprehensive analysis of immune epitopes of Spike protein, thereby contributing to the development of new strategies for broad neutralization or universal vaccination.

Identification of a Self-Assembling Small-Molecule Cancer Vaccine Adjuvant with an Improved Toxicity Profile

Protein or peptide cancer vaccines usually include immune potentiators, so-called adjuvants. However, it remains challenging to identify structurally simple, chemically accessible synthetic molecules that are effective and safe as vaccine adjuvant. Here, we present cholicamideβ (6), a self-assembling small-molecule vaccine adjuvant with an improved toxicity profile and proven efficacy in vivo. We demonstrate that cholicamideβ (6), which is less cytotoxic than its parent compound, forms virus-like particles to potently activate dendritic cells with the concomitant secretion of cytokines. When combined with a peptide antigen, cholicamideβ (6) potentiated the antigen presentation on dendritic cells to induce antigen-specific T cells. As a therapeutic cancer vaccine adjuvant in mice, a mixture of cholicamideβ (6) and a peptide antigen protected mice from the challenges of malignant cancer cells without overt toxicity. Cholicamideβ (6) may offer a translational opportunity as an unprecedented class of small-molecule cancer vaccine adjuvants.

Toll-like receptor-guided therapeutic intervention of human cancers: molecular and immunological perspectives

Toll-like receptors (TLRs) serve as the body's first line of defense, recognizing both pathogen-expressed molecules and host-derived molecules released from damaged or dying cells. The wide distribution of different cell types, ranging from epithelial to immune cells, highlights the crucial roles of TLRs in linking innate and adaptive immunity. Upon stimulation, TLRs binding mediates the expression of several adapter proteins and downstream kinases, that lead to the induction of several other signaling molecules such as key pro-inflammatory mediators. Indeed, extraordinary progress in immunobiological research has suggested that TLRs could represent promising targets for the therapeutic intervention of inflammation-associated diseases, autoimmune diseases, microbial infections as well as human cancers. So far, for the prevention and possible treatment of inflammatory diseases, various TLR antagonists/inhibitors have shown to be efficacious at several stages from pre-clinical evaluation to clinical trials. Therefore, the fascinating role of TLRs in modulating the human immune responses at innate as well as adaptive levels directed the scientists to opt for these immune sensor proteins as suitable targets for developing chemotherapeutics and immunotherapeutics against cancer. Hitherto, several TLR-targeting small molecules (e.g., Pam3CSK4, Poly (I:C), Poly (A:U)), chemical compounds, phytocompounds (e.g., Curcumin), peptides, and antibodies have been found to confer protection against several types of cancers. However, administration of inappropriate doses of such TLR-modulating therapeutics or a wrong infusion administration is reported to induce detrimental outcomes. This review summarizes the current findings on the molecular and structural biology of TLRs and gives an overview of the potency and promises of TLR-directed therapeutic strategies against cancers by discussing the findings from established and pipeline discoveries.

Discovery of novel aporphine alkaloid derivative as potent TLR2 antagonist reversing macrophage polarization and neutrophil infiltration against acute inflammation

Toll-like receptor 2 (TLR2) mediated macrophages regulate the protective immune response to infectious microorganisms, but the aberrant activation of macrophages often leads to pathological inflammation, including tissue damage. In this study, we identified antagonists of TLR2 by screening 2100 natural products and subsequently identified Taspine, an aporphine alkaloid, as an excellent candidate. Furthermore, analysis of the 10 steps chemical synthesis route and structural optimization yielded the Taspine derivative SMU-Y6, which has higher activity, better solubility, and improved drug-feasible property. Mechanistic studies and seq-RNA analysis revealed that SMU-Y6 inhibited TLR2 over other TLRs, hindered the formation of TLR2/MyD88 complex, and blocked the downstream NF-κB and MAPK signaling pathway, thus suppressing the release of inflammatory cytokines. SMU-Y6 could stabilize TLR2 and bind to TLR2 protein with a Kd of 0.18 μmol/L. Additionally, SMU-Y6 could efficiently reverse the M1 phenotype macrophage polarization, reduce the production of cytokines as well as infiltration of neutrophiles and alleviate the local inflammation in mice with acute paw edema and colitis. Collectively, we reported the first aporphine alkaloid derivative that selectively inhibits TLR2 with high binding affinity and superior drug-feasible property, thus providing an urgently-needed molecular probe and potential drug candidate for inflammatory and autoimmune disease therapy.

NHWD-1062 ameliorates inflammation and proliferation by the RIPK1/NF-κB/TLR1 axis in Psoriatic Keratinocytes

Psoriasis is a common chronic inflammatory skin disease. RIPK1 plays an important role in inflammatory diseases. At present, the clinical efficacy of the RIPK1 inhibitor is limited and the regulatory mechanism is unclear in the treatment of psoriasis. Therefore, our team developed a new RIPK1 inhibitor, NHWD-1062, which showed a slightly lower IC50 in U937 cells than that of GSK'772 (a RIPK1 inhibitor in clinical trials) (11 nM vs. 14 nM), indicating that the new RIPK1 inhibitor was no less inhibitory than GSK'772. In this study, we evaluated the therapeutic effects of NHWD-1062 using an IMQ-induced mouse model of psoriasis and explored the precise regulatory mechanism involved. We found that gavage of NHWD-1062 significantly ameliorated the inflammatory response and inhibited the abnormal proliferation of the epidermis in IMQ-induced psoriatic mice. We then elucidated the mechanism of NHWD-1062, which was that suppressed the proliferation and inflammation of keratinocytes in vitro and in vivo through the RIPK1/NF-κB/TLR1 axis. Dual-luciferase reporter assay indicated that P65 can directly target the TLR1 promoter region and activate TLR1 expression, leading to inflammation. In summary, our study demonstrates that NHWD-1062 alleviates psoriasis-like inflammation by inhibiting the activation of the RIPK1/NF-κB/TLR1 axis, which has not been previously reported and further provides evidence for the clinical translation of NHWD-1062 in the treatment of psoriasis.

TLR-1, TLR-2, and TLR-6 MYD88-dependent signaling pathway: A potential factor in the interaction of high-DNA fragmentation human sperm with fallopian tube epithelial cells

OBJECTIVE

The DNA integrity of spermatozoa that attach to fallopian tube (FT) cells is higher than spermatozoa that do not attach. FT epithelial cells can distinguish normal and abnormal sperm chromatin. This study investigated the effects of sperm with a high-DNA fragmentation index (DFI) from men with unexplained repeated implantation failure (RIF) on the Toll-like receptor (TLR) signaling pathway in human FT cells in vitro.

METHODS

Ten men with a RIF history and high-DFI and 10 healthy donors with low-DFI comprised the high-DFI (>30%) and control (<30%) groups, respectively. After fresh semen preparation, sperm were co-cultured with a human FT epithelial cell line (OE-E6/E7) for 24 hours. RNA was extracted from the cell line and the human innate and adaptive immune responses were tested using an RT2 profiler polymerase chain reaction (PCR) array.

RESULTS

The PCR array data showed significantly higher TLR-1, TLR-2, TLR-3, TLR-6, interleukin 1α (IL-1α), IL-1β, IL-6, IL-12, interferon α (IFN-α), IFN-β, tumor necrosis factor α (TNF-α), CXCL8, GM-CSF, G-CSF, CD14, ELK1, IRAK1, IRAK2, IRAK4, IRF1, IRF3, LY96, MAP2K3, MAP2K4, MAP3K7, MAP4K4, MAPK8, MAPK8IP3, MYD88, NFKB1, NFKB2, REL, TIRAP, and TRAF6 expression in the high-DFI group than in the control group. These factors are all involved in the TLR-MyD88 signaling pathway.

CONCLUSION

The MyD88-dependent pathway through TLR-1, TLR-2, and TLR-6 activation may be one of the main inflammatory pathways activated by high-DFI sperm from men with RIF. Following activation of this pathway, epithelial cells produce inflammatory cytokines, resulting in neutrophil infiltration, activation, phagocytosis, neutrophil extracellular trap formation, and apoptosis.

Toll-like Receptors and Thrombopoiesis

Platelets are the second most abundant blood component after red blood cells and can participate in a variety of physiological and pathological functions. Beyond its traditional role in hemostasis and thrombosis, it also plays an indispensable role in inflammatory diseases. However, thrombocytopenia is a common hematologic problem in the clinic, and it presents a proportional relationship with the fatality of many diseases. Therefore, the prevention and treatment of thrombocytopenia is of great importance. The expression of Toll-like receptors (TLRs) is one of the most relevant characteristics of thrombopoiesis and the platelet inflammatory function. We know that the TLR family is found on the surface or inside almost all cells, where they perform many immune functions. Of those, TLR2 and TLR4 are the main stress-inducing members and play an integral role in inflammatory diseases and platelet production and function. Therefore, the aim of this review is to present and discuss the relationship between platelets, inflammation and the TLR family and extend recent research on the influence of the TLR2 and TLR4 pathways and the regulation of platelet production and function. Reviewing the interaction between TLRs and platelets in inflammation may be a research direction or program for the treatment of thrombocytopenia-related and inflammatory-related diseases.

Patterns of NFkB activation resulting from damage, reactive microglia, cytokines, and growth factors in the mouse retina

Müller glia are a cellular source for neuronal regeneration in vertebrate retinas. However, the capacity for retinal regeneration varies widely across species. Understanding the mechanisms that regulate the reprogramming of Müller glia into progenitor cells is key to reversing the loss of vision that occurs with retinal diseases. In the mammalian retina, NFkB signaling promotes glial reactivity and represses the reprogramming of Müller glia into progenitor cells. Here we investigate different cytokines, growth factors, cell signaling pathways, and damage paradigms that influence NFkB-signaling in the mouse retina. We find that exogenous TNF and IL1β potently activate NFkB-signaling in Müller glia in undamaged retinas, and this activation is independent of microglia. By comparison, TLR1/2 agonist indirectly activates NFkB-signaling in Müller glia, and this activation depends on the presence of microglia as Tlr2 is predominantly expressed by microglia, but not other types of retinal cells. Exogenous FGF2 did not activate NFkB-signaling, whereas CNTF, Osteopontin, WNT4, or inhibition of GSK3β activated NFkB in Müller glia in the absence of neuronal damage. By comparison, dexamethasone, a glucocorticoid agonist, suppressed NFkB-signaling in Müller glia in damaged retinas, in addition to reducing numbers of dying cells and the accumulation of reactive microglia. Although NMDA-induced retinal damage activated NFkB in Müller glia, optic nerve crush had no effect on NFkB activation within the retina, whereas glial cells within the optic nerve were responsive. We conclude that the NFkB pathway is activated in retinal Müller glia in response to many different cell signaling pathways, and activation often depends on signals produced by reactive microglia.

Unraveling the Tomaralimab Epitope on the Toll-like Receptor 2 via Molecular Dynamics and Deep Learning

Tomaralimab (OPN-305) is the first humanized immunoglobulin G4 monoclonal antibody against TLR2 and is designed to prevent inflammation that is driven by inappropriate or excessive activation of innate immune pathways. Here, we constructed a homology model of Tomaralimab and its complex with TLR2 at different mapped epitopes and unraveled their behavior at the atomistic level. Furthermore, we predicted a novel epitope (leucine-rich region 9-12) near the lipopeptide-binding site that can be targeted and studied for the utility of therapeutic antibodies. A geometric deep learning algorithm was used to envisage Tomaralimab binding affinity changes upon mutation. There was a significant difference in binding affinity for Tomaralimab following epitope-mutated alanine substitutions of Val266, Pro294, Arg295, Asn319, Pro326, and His372. Using deep learning-based ΔΔG prediction, we computationally contrasted human TLR2-TLR2, TLR2-TLR1, and TLR2-TLR6 dimerization. These results reveal the mechanism that underlies Tomaralimab binding to TLR2 and should help to design structure-based mimics or bispecific antibodies that can be used to inhibit both lipopeptide-binding and TLR2 dimerization.

Akkermansia muciniphila phospholipid induces homeostatic immune responses

Multiple studies have established associations between human gut bacteria and host physiology, but determining the molecular mechanisms underlying these associations has been challenging1-3. Akkermansia muciniphila has been robustly associated with positive systemic effects on host metabolism, favourable outcomes to checkpoint blockade in cancer immunotherapy and homeostatic immunity4-7. Here we report the identification of a lipid from A. muciniphila's cell membrane that recapitulates the immunomodulatory activity of A. muciniphila in cell-based assays8. The isolated immunogen, a diacyl phosphatidylethanolamine with two branched chains (a15:0-i15:0 PE), was characterized through both spectroscopic analysis and chemical synthesis. The immunogenic activity of a15:0-i15:0 PE has a highly restricted structure-activity relationship, and its immune signalling requires an unexpected toll-like receptor TLR2-TLR1 heterodimer9,10. Certain features of the phospholipid's activity are worth noting: it is significantly less potent than known natural and synthetic TLR2 agonists; it preferentially induces some inflammatory cytokines but not others; and, at low doses (1% of EC50) it resets activation thresholds and responses for immune signalling. Identifying both the molecule and an equipotent synthetic analogue, its non-canonical TLR2-TLR1 signalling pathway, its immunomodulatory selectivity and its low-dose immunoregulatory effects provide a molecular mechanism for a model of A. muciniphila's ability to set immunological tone and its varied roles in health and disease.

Next-Generation Diprovocims with Potent Human and Murine TLR1/TLR2 Agonist Activity That Activate the Innate and Adaptive Immune Response

The diprovocims, a new class of toll-like receptor (TLR) agonists, bear no similarity to prior TLR agonists, act through a well-defined mechanism (TLR1/TLR2 agonist), exhibit exquisite structure-activity relationships, and display in vivo adjuvant activity. They possess potent and efficacious agonist activity toward human TLR1/TLR2 but modest agonism toward the murine receptor. A manner by which diprovocims can be functionalized without impacting hTLR1/TLR2 activity is detailed, permitting future linkage to antigenic, targeting, or delivery moieties. Improvements in both potency and its low efficacy in the murine system were also achieved, permitting more effective use in animal models while maintaining the hTLR1/TLR2 activity. The prototypical member diprovocim-X exhibits the excellent potency/efficacy of diprovocim-1 in human cells, displays substantially improved potency/efficacy in mouse macrophages, and serves as an adjuvant in mice when coadministered with a nonimmunogenic antigen, indicating stimulation of the adaptive as well as innate immune response.

SIX1 attenuates inflammation and rheumatoid arthritis by silencing MyD88-dependent TLR1/2 signaling

OBJECTIVES

Rheumatoid arthritis (RA) is a chronic autoimmune disease that severely affects the patients' quality of life. Sine oculis homeobox 1 (SIX1) has been reported as a key regulator of organogenesis and inflammation. This study aimed to explore the effects of SIX1 on RA.

METHODS

Wistar rats were immunized with type II collagen to induce an animal model of RA. RA synovial fibroblasts (RASFs) were isolated from the rats. SIX1 expression in RA rats and RASFs was detected by qRT-PCR and western blot. CCK-8, EdU, transwell, flow cytometer, and ELISA were conducted to assay the effects of SIX1 on RASFs. The effects of SIX1 on RA rats were studied by Safranin O staining, H&E staining, and ELISA. Besides, GSEA and KEGG analysis were used to predict the underlying signaling pathways.

RESULTS

SIX1 was low expressed in synovial tissue of RA rats and RASFs. SIX1 overexpression inhibited the proliferation, invasion, and levels of TNF-α, IL-6, and IL-8 in RASFs. However, SIX1 overexpression promoted the apoptosis of RASFs. SIX1 overexpression enhanced body weight, and attenuated the cartilage damage, pathological injury, and pro-inflammatory cytokine release of RA rat model. MyD88-dependent TLR1/2 might be a downstream signaling of SIX1. RelA acted as a transcription factor of TLR1/2, and SIX1 inhibited TLR1/2 signaling possibly via interaction with RelA. Adding with Pam₃CSK₄, a specific agonist of TLR1/2 signaling, attenuated the effects of SIX1 on RASFs.

CONCLUSION

SIX1 attenuated inflammation and RA by silencing MyD88-dependent TLR1/2 signaling. SIX1 may be a promising target for RA treatment.

Built-in adjuvants for use in vaccines

Vaccine refers to biological products that are produced using various pathogenic microorganisms for inoculation. The goal of vaccination is to induce a robust immune response against a specific antigen, thus preventing the organism from getting infected. In vaccines, adjuvants have been widely employed to enhance immunity against specific antigens. An ideal adjuvant should be stable, biodegradable, and low cost, not induce system rejection and promote an immune response. Various adjuvant components have been investigated across diverse applications. Typically, adjuvants are employed to meet the following objectives: (1) to improve the effectiveness of immunization with vaccines for specific populations, such as newborns and the elderly; (2) enhance the immunogenicity of highly purified or recombinant antigens; (3) allow immunization with a smaller dose of the vaccine, reducing drug dosage. In the present review, we primarily focus on chemically synthesized compounds that can be used as built-in adjuvants. We elaborate the classification of these compounds based on the induced immune activation mechanism and summarize their application in various vaccine types.

Targeting the Toll-like receptor pathway as a therapeutic strategy for neonatal infection

Toll-like receptors (TLRs) are crucial transmembrane receptors that form part of the innate immune response. They play a role in the recognition of various microorganisms and their elimination from the host. TLRs have been proposed as vital immunomodulators in the regulation of multiple neonatal stressors that extend beyond infection such as oxidative stress and pain. The immune system is immature at birth and takes some time to become fully established. As such, babies are especially vulnerable to sepsis at this early stage of life. Findings suggest a gestational age-dependent increase in TLR expression. TLRs engage with accessory and adaptor proteins to facilitate recognition of pathogens and their activation of the receptor. TLRs are generally upregulated during infection and promote the transcription and release of proinflammatory cytokines. Several studies report that TLRs are epigenetically modulated by chromatin changes and promoter methylation upon bacterial infection that have long-term influences on immune responses. TLR activation is reported to modulate cardiorespiratory responses during infection and may play a key role in driving homeostatic instability observed during sepsis. Although complex, TLR signaling and downstream pathways are potential therapeutic targets in the treatment of neonatal diseases. By reviewing the expression and function of key Toll-like receptors, we aim to provide an important framework to understand the functional role of these receptors in response to stress and infection in premature infants.

Microbe-Mediated Activation of Toll-like Receptor 2 Drives PDL1 Expression in HNSCC

Simple Summary

Tumors use immunosuppressive signals to evade detection by the immune system. While recurrent and metastatic head and neck squamous cell carcinoma has historically carried a poor prognosis, therapies targeting the immunosuppressive PD1:PDL1 axis have improved survival in certain patients. Defining mechanisms regulating PDL1 in various contexts may inform refinement of immunotherapy protocols. We identified a role for Toll-like Receptor 2 (TLR2) signaling in driving PDL1 expression. In antigen-presenting cells, TLR2 functions to initiate response to pathogens, and it is overexpressed or genetically altered in some tumors. We found that the synthetic TLR2 ligand Pam3CSK4, as well as whole bacteria, induced PDL1 expression in specific HNSCC cell line models, suggesting that TLR2 may contribute to immune evasion in chronically inflamed tissues.

Abstract

As immunotherapies targeting the PDL1 checkpoint have become a mainstay of treatment for a subset of head and neck squamous cell carcinoma (HNSCC) patients, a detailed understanding of the mechanisms underlying PDL1-mediated immune evasion is needed. To elucidate factors regulating expression of PDL1 in HNSCC cells, a genome-wide CRISPR profiling approach was implemented to identify genes and pathways conferring altered PDL1 expression in an HNSCC cell line model. Our screen nominated several candidate PDL1 drivers, including Toll-like Receptor 2 (TLR2). Depletion of TLR2 blocks interferon-γ-induced PDL1 expression, and stimulation of TLR2 with either Staphylococcus aureus or a bacterial lipopeptide mimetic, Pam3CSK4, enhanced PDL1 expression in multiple models. The data herein demonstrate a role for TLR2 in modulating the expression of PDL1 in HNSCC models and suggest that microbiota may directly modulate immunosuppression in cancer cells. Our study represents a step toward disentangling the diverse pathways and stimuli regulating PDL1 expression in HNSCC and underscores a need for future work to characterize the complex microbiome in HNSCC patients treated with immunotherapy.

Pattern recognition receptors in health and diseases

Pattern recognition receptors (PRRs) are a class of receptors that can directly recognize the specific molecular structures on the surface of pathogens, apoptotic host cells, and damaged senescent cells. PRRs bridge nonspecific immunity and specific immunity. Through the recognition and binding of ligands, PRRs can produce nonspecific anti-infection, antitumor, and other immunoprotective effects. Most PRRs in the innate immune system of vertebrates can be classified into the following five types based on protein domain homology: Toll-like receptors (TLRs), nucleotide oligomerization domain (NOD)-like receptors (NLRs), retinoic acid-inducible gene-I (RIG-I)-like receptors (RLRs), C-type lectin receptors (CLRs), and absent in melanoma-2 (AIM2)-like receptors (ALRs). PRRs are basically composed of ligand recognition domains, intermediate domains, and effector domains. PRRs recognize and bind their respective ligands and recruit adaptor molecules with the same structure through their effector domains, initiating downstream signaling pathways to exert effects. In recent years, the increased researches on the recognition and binding of PRRs and their ligands have greatly promoted the understanding of different PRRs signaling pathways and provided ideas for the treatment of immune-related diseases and even tumors. This review describes in detail the history, the structural characteristics, ligand recognition mechanism, the signaling pathway, the related disease, new drugs in clinical trials and clinical therapy of different types of PRRs, and discusses the significance of the research on pattern recognition mechanism for the treatment of PRR-related diseases.

Design, Synthesis, and Structure-Activity Relationship of N-Aryl-N'-(thiophen-2-yl)thiourea Derivatives as Novel and Specific Human TLR1/2 Agonists for Potential Cancer Immunotherapy

The previous virtual screening of ten million compounds yielded two novel nonlipopeptide-like chemotypes as TLR2 agonists. Herein, we present the chemical optimization of our initial hit, 1-phenyl-3-(thiophen-2-yl)urea, which resulted in the identification of SMU-C80 (EC₅₀ = 31.02 ± 1.01 nM) as a TLR2-specific agonist with a 370-fold improvement in bioactivity. Mechanistic studies revealed that SMU-C80, through TLR1/2, recruits the adaptor protein MyD88 and triggers the NF-κB pathway to release cytokines such as TNF-α and IL-1β from human, but not murine, cells. To the best of our knowledge, it is the first species-specific TLR1/2 agonist reported until now. Moreover, SMU-C80 increased the percentage of T, B, and NK cells ex vivo and activated the immune cells, which suppressed cancer cell growth in vitro. In summary, we obtained a highly efficient and specific human TLR1/2 agonist that acts through the MyD88 and NF-κB pathway, facilitating cytokine release and the simultaneous activation of immune cells that in turn affects the apoptosis of cancer cells.

TLR2 Agonistic Small Molecules: Detailed Structure-Activity Relationship, Applications, and Future Prospects

Toll-like receptors (TLRs) are the pattern recognition receptors (PRRs) that recognize pathogen-associated molecular patterns (PAMPs) in microbial species. Among the various TLRs, TLR2 has a special place due to its ability to sense the widest repertoire of PAMPs owing to its heterodimerization with either TLR1 or TLR6, broadening its ligand diversity against pathogens. Various scaffolds are reported to activate TLR2, which include naturally occurring lipoproteins, synthetic lipopeptides, and small heterocyclic molecules. We described a detailed SAR in TLR2 agonistic scaffolds and also covered the design and chemistry for the conjugation of TLR2 agonists to antigens, carbohydrates, polymers, and fluorophores. The approaches involved in delivery of TLR2 agonists such as lipidation of antigen, conjugation to polymers, phosphonic acids, and other linkers to achieve surface adsorption, liposomal formulation, and encapsulating nanoparticles are elaborated. The crystal structure analysis and computational modeling are also included with the structural features that facilitate TLR2 activation.

Modulation of the Innate Immune Response by Targeting Toll-like Receptors: A Perspective on Their Agonists and Antagonists

Toll-like receptors (TLRs) are a class of proteins that recognize pathogen-associated molecular patterns (PAMPs) and damaged-associated molecular patterns (DAMPs), and they are involved in the regulation of innate immune system. These transmembrane receptors, localized at the cellular or endosomal membrane, trigger inflammatory processes through either myeloid differentiation primary response 88 (MyD88) or TIR-domain-containing adapter-inducing interferon-β (TRIF) signaling pathways. In the last decades, extensive research has been performed on TLR modulators and their therapeutic implication under several pathological conditions, spanning from infections to cancer, from metabolic disorders to neurodegeneration and autoimmune diseases. This Perspective will highlight the recent discoveries in this field, emphasizing the role of TLRs in different diseases and the therapeutic effect of their natural and synthetic modulators, and it will discuss insights for the future exploitation of TLR modulators in human health.

Chemical Strategies to Boost Cancer Vaccines

Personalized cancer vaccines (PCVs) are reinvigorating vaccine strategies in cancer immunotherapy. In contrast to adoptive T-cell therapy and checkpoint blockade, the PCV strategy modulates the innate and adaptive immune systems with broader activation to redeploy antitumor immunity with individualized tumor-specific antigens (neoantigens). Following a sequential scheme of tumor biopsy, mutation analysis, and epitope prediction, the administration of neoantigens with synthetic long peptide (SLP) or mRNA formulations dramatically improves the population and activity of antigen-specific CD4+ and CD8+ T cells. Despite the promising prospect of PCVs, there is still great potential for optimizing prevaccination procedures and vaccine potency. In particular, the arduous development of tumor-associated antigen (TAA)-based vaccines provides valuable experience and rational principles for augmenting vaccine potency which is expected to advance PCV through the design of adjuvants, delivery systems, and immunosuppressive tumor microenvironment (TME) reversion since current personalized vaccination simply admixes antigens with adjuvants. Considering the broader application of TAA-based vaccine design, these two strategies complement each other and can lead to both personalized and universal therapeutic methods. Chemical strategies provide vast opportunities for (1) exploring novel adjuvants, including synthetic molecules and materials with optimizable activity, (2) constructing efficient and precise delivery systems to avoid systemic diffusion, improve biosafety, target secondary lymphoid organs, and enhance antigen presentation, and (3) combining bioengineering methods to innovate improvements in conventional vaccination, "smartly" re-educate the TME, and modulate antitumor immunity. As chemical strategies have proven versatility, reliability, and universality in the design of T cell- and B cell-based antitumor vaccines, the union of such numerous chemical methods in vaccine construction is expected to provide new vigor and vitality in cancer treatment.

Emerging Adjuvants for Cancer Immunotherapy

Cancer is a life-threatening disease, and immunotherapies have been developed as a novel, potent treatment for cancer. Adjuvants, used alone or in combination with other agents, play crucial roles in immune activation. This is necessary for cancer immunotherapy, particularly in the construction of therapeutic cancer vaccines. Adjuvants activate antigen-presenting cells and promote the presentation of antigen epitopes on major histocompatibility complex molecules, further enhancing adaptive immune responses, including cytotoxic T lymphocytes, to elicit cancer-cell death. However, the applications of adjuvants are limited by their poor efficacy or insufficient safety. In recent studies, researchers attempted to develop safe, efficacious adjuvants for cancer immunotherapy, and many compounds (including inorganic compounds, organic molecules, polymers, and colloids) have been identified and optimized as agonists of various pathways. In this review, we focus on the discovery and structural design of emerging adjuvants and discuss how these findings benefit healthcare.

Biological Characterization, Mechanistic Investigation and Structure-Activity Relationships of Chemically Stable TLR2 Antagonists

Toll-like receptors (TLRs) build the first barrier in the innate immune response and therefore represent promising targets for the modulation of inflammatory processes. Recently, the pyrogallol-containing TLR2 antagonists CU-CPT22 and MMG-11 were reported; however, their 1,2,3-triphenol motif renders them highly susceptible to oxidation and excludes them from use in extended experiments under aerobic conditions. Therefore, we have developed a set of novel TLR2 antagonists (1-9) based on the systematic variation of substructures, linker elements, and the hydrogen-bonding pattern of the pyrogallol precursors by using chemically robust building blocks. The novel series of chemically stable and synthetically accessible TLR2 antagonists (1-9) was pharmacologically characterized, and the potential binding modes of the active compounds were evaluated structurally. Our results provide new insights into structure-activity relationships and allow rationalization of structural binding characteristics. Moreover, they support the hypothesis that this class of TLR ligands bind solely to TLR2 and do not directly interact with TLR1 or TLR6 of the functional heterodimer. The most active compound from this series (6), is chemically stable, nontoxic, TLR2-selective, and shows a similar activity with regard to the pyrogallol starting points, thus indicating the variability of the hydrogen bonding pattern.

Nanomedicine-mediated alteration of the pharmacokinetic profile of small molecule cancer immunotherapeutics

The advent of immunotherapy is a game changer in cancer therapy with monoclonal antibody- and T cell-based therapeutics being the current flagships. Small molecule immunotherapeutics might offer advantages over the biological drugs in terms of complexity, tissue penetration, manufacturing cost, stability, and shelf life. However, small molecule drugs are prone to rapid systemic distribution, which might induce severe off-target side effects. Nanotechnology could aid in the formulation of the drug molecules to improve their delivery to specific immune cell subsets. In this review we summarize the current efforts in changing the pharmacokinetic profile of small molecule immunotherapeutics with a strong focus on Toll-like receptor agonists. In addition, we give our vision on limitations and future pathways in the route of nanomedicine to the clinical practice.

Small-Molecule Modulators of Toll-like Receptors

Toll-like receptors (TLRs) are the "gatekeepers" of the immune system in humans and other animals to protect the host from invading bacteria, viruses, and other microorganisms. Since TLR4 was discovered as the receptor for endotoxin in the late 1990s, significant progress has been made in exploiting an understanding of the function of TLRs. The TLR-signaling pathway is crucial for the induction and progression of various diseases. Dysregulation of TLR signaling contributes to numerous pathological conditions, including chronic inflammation, sepsis, cancers, asthma, neuropathic pain, drug addiction, and autoimmune diseases. Therefore, manipulation of TLR signaling is promising to halt their activity in inflammatory diseases, to enhance their signaling to fight cancers, to modulate their role in autoimmune diseases, and to suppress them to treat drug addiction. TLR agonists have demonstrated great potential as antimicrobial agents and vaccine adjuvants, whereas TLR antagonists are being developed as reagents and drugs to dampen immune responses. Because of their pivotal potential therapeutic applications, fruitful small-molecule compounds and peptide fragments have been discovered, and many of them have advanced to various stages of clinical trials (though only two have been approved by the Food and Drug Administration (FDA): MPLA as a TLR4 agonist and imiquimod as a TLR7 agonist).In this Account, we focus on the progress in developing TLR signaling pathway modulators (mainly focused on the Yin and Wang laboratories) over the past decade and highlight the accomplishments and currently existing challenges in the development of TLR modulators. First, we briefly describe the members of the human TLR family along with their natural modulators. Second, we illustrate our endeavors to discover TLR-targeted agents using comprehensive approaches. Specifically, a discussion of identification and characterization of new chemical entities, determination of modes of action, and further applications is presented. For instance, the TLR3 antagonist was first discovered through in silico screening, and the inhibitory activity was confirmed in murine cells. Considering the glycosylation on TLR3, a new direction for TLR3 modulator design was pointed out to target asparagine glycosylation. We have particularly focused on the discovery of TLR4 antagonists and have assessed their great potential in the clinical treatment of drug addiction and alcohol use disorders. In addition, we discuss multiple other popular and robust techniques for modulator discovery. Not only small organic modulators but also stapled peptides and peptidomimetics will attract more and more attention in the future. Finally, current challenges, opportunities, and future perspectives for TLR-targeted agents are also discussed.

TLR2 agonists and their structure–activity relationships

We review the structure–activity relationships and synthetic studies of TLR2 agonists – important chemical targets in immunotherapy.

Targeting Cellular and Tissue HIV Reservoirs With Toll-Like Receptor Agonists

The elimination of both cellular and tissue latent reservoirs is a challenge toward a successful HIV cure. "Shock and Kill" are among the therapeutic strategies that have been more extensively studied to target these reservoirs. These strategies are aimed toward the reactivation of the latent reservoir using a latency-reversal agent (LRA) with the subsequent killing of the reactivated cell either by the cytotoxic arm of the immune system, including NK and CD8 T cells, or by viral cytopathic mechanisms. Numerous LRAs are currently being investigated in vitro, ex vivo as well as in vivo for their ability to reactivate and reduce latent reservoirs. Among those, several toll-like receptor (TLR) agonists have been shown to reactivate latent HIV. In humans, there are 10 TLRs that recognize different pathogen-associated molecular patterns. TLRs are present in several cell types, including CD4 T cells, the cell compartment that harbors the majority of the latent reservoir. Besides their ability to reactivate latent HIV, TLR agonists also increase immune activation and promote an antiviral response. These combined properties make TLR agonists unique among the different LRAs characterized to date. Additionally, some of these agonists have shown promise toward finding an HIV cure in animal models. When in combination with broadly neutralizing antibodies, TLR-7 agonists have shown to impact the SIV latent reservoir and delay viral rebound. Moreover, there are FDA-approved TLR agonists that are currently being investigated for cancer therapy and other diseases. All these has prompted clinical trials using TLR agonists either alone or in combination toward HIV eradication approaches. In this review, we provide an extensive characterization of the state-of-the-art of the use of TLR agonists toward HIV eradication strategies and the mechanism behind how TLR agonists target both cellular and tissue HIV reservoirs.

Screening for new macrophage therapeutics

Myeloid derived macrophages play a key role in many human diseases, and their therapeutic modulation via pharmacological means is receiving considerable attention. Of particular interest is the fact that these cells are i) dynamic phenotypes well suited to therapeutic manipulation and ii) phagocytic, allowing them to be efficiently targeted with nanoformulations. However, it is important to consider that macrophages represent heterogeneous populations of subtypes with often competing biological behaviors and functions. In order to develop next generation therapeutics, it is therefore essential to screen for biological effects through a combination of in vitro and in vivo assays. Here, we review the state-of-the-art techniques, including both cell based screens and in vivo imaging tools that have been developed for assessment of macrophage phenotype. We conclude with a forward-looking perspective on the growing need for noninvasive macrophage assessment and laboratory assays to be put into clinical practice and the potential broader impact of myeloid-targeted therapeutics.

Extracellular vesicles derived from ODN-stimulated macrophages transfer and activate Cdc42 in recipient cells and thereby increase cellular permissiveness to EV uptake

Endosomal Toll-like receptors (TLRs) mediate intracellular innate immunity via the recognition of DNA and RNA sequences. Recent work has reported a role for extracellular vesicles (EVs), known to transfer various nucleic acids, in uptake of TLR-activating molecules, raising speculation about possible roles of EVs in innate immune surveillance. Whether EV-mediated uptake is a general mechanism, however, was unresolved; and the molecular machinery that might be involved was unknown. We show that, when macrophages are stimulated with the TLR9 agonist CpG oligodeoxynucleotides (ODN), the secreted EVs transport ODN into naïve macrophages and induce the release of chemokine TNF-α. In addition, these EVs transfer Cdc42 into recipient cells, resulting in further enhancement of their cellular uptake. Transport of ODN and Cdc42 from TLR9-activated macrophages to naïve cells via EVs exerts synergetic effects in propagation of the intracellular immune response, suggesting a general mechanism of EV-mediated uptake of pathogen-associated molecular patterns.

TLR1/2 Specific Small-Molecule Agonist Suppresses Leukemia Cancer Cell Growth by Stimulating Cytotoxic T Lymphocytes

Toll-like receptor 2 (TLR2) expressed on antigen presenting cells evokes a series of critical cytokines, which favor the development of tumor-specific cytotoxic T lymphocytes (CTLs). Therefore, TLR2 represents an attractive cancer immunotherapeutic target. Here, a synthetic library of 14 000 compounds together with a series of newly developed compounds for NF-κB activation using HEK-Blue hTLR2 cells is initially screened. Following further screening in a variety of cells including HEK-Blue hTLRs reporter cells, murine, and human macrophage cell lines, a potent small molecule agonist 23 (SMU-Z1) is identified, which specifically activates TLR2 through its association with TLR1, with a EC50 of 4.88 ± 0.79 × 10-9 m. Toxicology studies, proinflammatory cytokines (e.g., TNF-α, IL-1β, IL-6, and nitric oxide) and target-protein based biophysical assays demonstrate the pharmacologically relevant characteristics of SMU-Z1. In addition, SMU-Z1 promotes murine splenocyte proliferation and upregulates the expression of CD8+ T cells, NK cells and DCs, which results in a significant antitumor effect in a murine leukemia model. Finally, the induced tumors in three out of seven mice disappear after administration of SMU-Z1. Our studies thus identify a novel and potent TLR1/2 small molecule agonist, which displays promising immune adjuvant properties and antitumor immunity.

Identification and immunological evaluation of novel TLR2 agonists through structure optimization of Pam3CSK4

Toll-like receptor 2 (TLR2) is a bridge between innate immunity and adaptive immunity. TLR2 agonists have been exploited as potential vaccine adjuvants and antitumor agents. However, no TLR2 agonists have been approved by FDA up to now. To discover drug-like TLR2 selective agonists, a novel series of Pam₃CSK₄ derivatives were designed based on the crystal structure of hTLR2-hTLR1-Pam₃CSK₄ complex, synthesized and evaluated for their immune-stimulatory activities. Among them, 35c was identified as a murine-specific TLR2 agonist, while 35f was a human-specific TLR2 agonist. Besides, 35d (human and murine TLR2 agonist) showed TLR2 agonistic activity comparable to Pam₃CSK₄, which included: elevated IL-6 expression level (EC₅₀ = 83.08 ± 5.94 nM), up-regulated TNF-α and IL-6 mRNA expression and promoted maturation of DCs through activating the NF-κB signaling pathway. TLRs antibodies test showed that 35a and 35d were TLR2/1 agonists, while 35f was a TLR2/6 agonist.

Structural Basis of TLR2/TLR1 Activation by the Synthetic Agonist Diprovocim

Diprovocim is a recently discovered exceptionally potent, synthetic small molecule agonist of TLR2/TLR1 and has shown significant adjuvant activity in anticancer vaccination against murine melanoma. Since Diprovocim bears no structural similarity to the canonical lipopeptide ligands of TLR2/TLR1, we investigated how Diprovocim interacts with TLR2/TLR1 through in vitro biophysical, structural, and computational approaches. We found that Diprovocim induced the formation of TLR2/TLR1 heterodimers as well as TLR2 homodimers in vitro. We determined the crystal structure of Diprovocim in a complex with a TLR2 ectodomain, which revealed, unexpectedly, two Diprovocim molecules bound to the ligand binding pocket formed between two TLR2 ectodomains. Extensive hydrophobic interactions and a hydrogen-bonding network between the protein and Diprovocim molecules are observed within the defined ligand binding pocket and likely underlie the high potency of Diprovocim. Our work shed first light into the activation mechanism of TLR2/TLR1 by a noncanonical agonist. The structural information obtained here may be exploited to manipulate TLR2/TLR1-dependent signaling.

Diprovocims: A New and Exceptionally Potent Class of Toll-like Receptor Agonists

A screen conducted with nearly 100000 compounds and a surrogate functional assay for stimulation of an immune response that measured the release of TNF-α from treated human THP-1 myeloid cells differentiated along the macrophage line led to the discovery of the diprovocims. Unique to these efforts and of special interest, the screening leads for this new class of activators of an immune response came from a compound library designed to promote cell-surface receptor dimerization. Subsequent comprehensive structure-activity relationship studies improved the potency 800-fold over that of the screening leads, providing diprovocim-1 and diprovocim-2. The diprovocims act by inducing cell-surface toll-like receptor (TLR)-2 dimerization and activation with TLR1 (TLR1/TLR2 agonist), bear no structural similarity to any known natural or synthetic TLR agonist, and are easy to prepare and synthetically modify, and selected members are active in both human and murine systems. The most potent diprovocim (3, diprovocim-1) elicits full agonist activity at extraordinarily low concentrations (EC₅₀ = 110 pM) in human THP-1 cells, being more potent than the naturally derived TLR1/TLR2 agonist Pam3CSK4 or any other known small molecule TLR agonist.

Glycyrrhizin Attenuates Salmonella enterica Serovar Typhimurium Infection: New Insights Into Its Protective Mechanism

Glycyrrhizin (GL), a triterpenoid glycoside, serves important functions in various biological activities, including antiviral and antitumor immune responses. However, the anti-inflammatory effects of GL on Salmonella enterica serovar Typhimurium (ST)-induced injury in mice and the mechanisms underlying the protection of GL are poorly understood. Here, we investigated the effects of GL on host immune responses against ST infection in mice. A phenotypic analysis using hematoxylin and eosin (H&E) staining and transmission electron microscopy showed that GL relieved ST-induced weight loss and intestinal mucosal injury. A colonization assay showed that GL significantly reduced ST colonization in the ileum and colon and translocation to the liver and spleen. An antibacterial activity assay and real-time PCR revealed that GL had no direct inhibitory impact on ST growth or virulence gene expression. ELISA showed that GL pretreatment significantly decreased proinflammatory cytokine (IFN-γ, TNF-α, IL-6) secretion and increased anti-inflammatory cytokine (IL-10) secretion in the ileum, colon and serum of ST-infected mice. Moreover, flora analysis showed that GL reduced Akkermansia, Sutterella, Prevotella and Coprococcus but enriched Parabacteroides and Anaerotruncus in the cecum of ST-infected mice. These results suggest that GL promotes the secretion of immune factors and modulates intestinal flora to prevent further ST infection. We also analyzed the effect of GL on immunocytes and found that GL promoted the phenotypic and functional maturation of murine bone marrow-derived dendritic cells (BMDCs). Flow cytometry and western blotting demonstrated that NF-κB, ERK, and p38 MAPK were required for GL-induced BMDC maturation. The above findings indicate that GL attenuates ST infection by modulating immune function and intestinal flora. This study enriches our current knowledge of GL-mediated immunological function and provides a new perspective on the prevention of Salmonella infection in animals and humans.

Adjuvant effect of the novel TLR1/TLR2 agonist Diprovocim synergizes with anti-PD-L1 to eliminate melanoma in mice

Successful cancer immunotherapy entails activation of innate immune receptors to promote dendritic cell (DC) maturation, antigen presentation, up-regulation of costimulatory molecules, and cytokine secretion, leading to activation of tumor antigen-specific cytotoxic T lymphocytes (CTLs). Here we screened a synthetic library of 100,000 compounds for innate immune activators using TNF production by THP-1 cells as a readout. We identified and optimized a potent human and mouse Toll-like receptor (TLR)1/TLR2 agonist, Diprovocim, which exhibited an EC₅₀ of 110 pM in human THP-1 cells and 1.3 nM in primary mouse peritoneal macrophages. In mice, Diprovocim-adjuvanted ovalbumin immunization promoted antigen-specific humoral and CTL responses and synergized with anti-PD-L1 treatment to inhibit tumor growth, generating long-term antitumor memory, curing or prolonging survival of mice engrafted with the murine melanoma B16-OVA. Diprovocim induced greater frequencies of tumor-infiltrating leukocytes than alum, of which CD8 T cells were necessary for the antitumor effect of immunization plus anti-PD-L1 treatment.

Siegesbeckia pubescens Makino inhibits Pam3CSK4-induced inflammation in RAW 264.7 macrophages through suppressing TLR1/TLR2-mediated NF-κB activation

Background

Siegesbeckia pubescens Makino (SP) is one of the important plant origins for the anti-inflammatory Chinese herbal medicine of Siegesbeckiae Herba. The current investigations indicated that the anti-inflammatory effects of SP were associated with the toll-like receptors (TLRs)-mediated nuclear factor-κB (NF-κB) and the mitogen-activated protein kinase (MAPK) signaling pathways.

Methods

Raw 264.7 macrophages were pretreated with the 50% ethanol extract of SP (SPE, 50–200 µg/mL) and then co-treated with Pam₃CSK₄ (200 ng/mL) for another 12 h. The inhibitory effect of SPE on Pam₃CSK₄-stimulated NO release and post-inflammatory cytokines secretions were determined using Griess reagent and Elisa kits, respectively. The influence of SPE on NF-κB and MAPKs signaling relevant proteins was measured by Western blotting analysis, while the intracellular nitric oxide (NO) generation and NF-κB/p65 nuclear translocation were determined using Leica TCS SP8 laser scanning confocal microscope. Moreover, the effect of SPE on luciferase reporter gene in NF-κB-luc DNA transfected raw 264.7 cells was determined using the Dual-Glo luciferase assay system kit.

Results

SPE dose-dependently (50–200 µg/mL) attenuated Pam₃CSK₄-induced NO release, post-inflammatory cytokines (IL-6, TNF-α and MCP-1) secretions and intracellular NO generation in raw 264.7 cells. Biologically, SPE suppressed Pam₃CSK₄-induced expressions of cyclooxygenase-2 (COX-2), inducible nitric oxide synthase (iNOS), phosphorylation of NF-κB/p65 and IκBα, but did not significantly show effect on the proteins involved in MAPKs signaling (p38, ERK and JNK). The results were further confirmed by NF-κB-luc reporter gene assay and p65 nuclear translocation assay.

Conclusions

In conclusion, SPE ameliorated Pam₃CSK₄-induced inflammation in raw 264.7 cells through suppressing TLR 1/2-mediated NF-κB activation.

Electronic supplementary material

The online version of this article (10.1186/s13020-018-0193-x) contains supplementary material, which is available to authorized users.

Synthesis, structure-activity relationships and preliminary mechanism study of N-benzylideneaniline derivatives as potential TLR2 inhibitors

Toll-like receptor 2 (TLR2) can recognize pathogen-associated molecular patterns to defense against invading organisms and has been represents an attractive therapeutic target. Until today, none TLR2 small molecule antagonist have been developed in clinical trial. Herein, we designed and synthesized 50 N-benzylideneaniline compounds with the help of CADD. And subsequent in vitro studies leading to the optimized compound SMU-A0B13 with most potent inhibitory activity to TLR2 (IC₅₀=18.21 ± 0.87 μM). Preliminary mechanism studies indicated that this TLR2 inhibitor can work through the NF-κB signaling pathway with high specificity and low toxicity, and can also efficiently downregulate inflammatory cytokines, such as SEAP, TNF-α and NO in HEK-Blue hTLR2, human PBMC and Raw 264.7 cell lines. Additionally, the docking situation also indicate SMU-A0B13 can well bind to the TLR2-TIR (PDB: 1FYW) active domain, which probably explains the bioactivity.

The phosphatase PPM1A controls monocyte-to-macrophage differentiation

Differentiation of circulating monocytes into tissue-bound or tissue-resident macrophages is a critical regulatory process affecting host defense and inflammation. However, the regulatory signaling pathways that control the differentiation of monocytes into specific and distinct functional macrophage subsets are poorly understood. Herein, we demonstrate that monocyte-to-macrophage differentiation is controlled by the Protein Phosphatase, Mg²⁺/Mn²⁺-dependent 1A (PPM1A). Genetic manipulation experiments demonstrated that overexpression of PPM1A attenuated the macrophage differentiation program, while knockdown of PPM1A expression accelerated the ability of monocytes to differentiate into macrophages. We identify imiquimod and Pam3CSK4 as two Toll-like receptor agonists that induce PPM1A expression, and show that increased expression of PPM1A at the onset of differentiation impairs cellular adherence, reduces expression of inflammatory (M1) macrophage-specific markers, and inhibits the production of inflammatory cytokines. Our findings reveal PPM1A as a negative threshold regulator of M1-type monocyte-to-macrophage differentiation, establishing it as a key phosphatase that orchestrates this program.

Structure-based discovery of a specific TLR1–TLR2 small molecule agonist from the ZINC drug library database

We report herein the identification of urea structure-like small molecules TLR1/2 agonists by structure-based virtual screening of 10.5 million compounds.

TLR2 agonism reverses chemotherapy-induced neutropenia in Macaca fascicularis

Neutropenia is a common consequence of radiation and chemotherapy in cancer patients. The resulting immunocompromised patients become highly susceptible to potentially life-threatening infections. Granulocyte colony-stimulating factor (G-CSF) is known to stimulate neutrophil production and is widely used as a treatment of chemotherapy-induced neutropenia. A small-molecule G-CSF secretagogue without a requirement for refrigerated supply chain would offer a more convenient and cost-effective treatment of chemotherapy-induced neutropenia. Bacterial lipopeptides activate innate immune responses through Toll-like receptor 2 (TLR2) and induce the release of cytokines, including G-CSF, from macrophages, monocytes, and endothelial. Pam₂CSK₄ is a synthetic lipopeptide that effectively mimics bacterial lipoproteins known to activate TLR2 receptor signaling through the TLR2/6 heterodimer. Substrate-based drug design led to the discovery of GSK3277329, which stimulated the release of G-CSF in activated THP-1 cells, peripheral blood mononuclear cells, and human umbilical vein endothelial cells. When administered subcutaneously to cynomolgus monkeys (Macaca fascicularis), GSK3277329 caused systemic elevation of G-CSF and interleukin-6 (IL-6), but not IL-1β or tumor necrosis factor α, indicating a selective cytokine-stimulation profile. Repeat daily injections of GSK3277329 in healthy monkeys also raised circulating neutrophils above the normal range over a 1-week treatment period. More importantly, repeated daily injections of GSK3277329 over a 2-week period restored neutrophil loss in monkeys given chemotherapy treatment (cyclophosphamide, Cytoxan). These data demonstrate preclinical in vivo proof of concept that TLR2 agonism can drive both G-CSF induction and subsequent neutrophil elevation in the cynomolgus monkey and could be a therapeutic strategy for the treatment of chemotherapy-induced neutropenia.