Amphiphilic Guanidinocalixarenes Inhibit Lipopolysaccharide (LPS)- and Lectin-Stimulated Toll-like Receptor 4 (TLR4) Signaling

TAK-242 inhibits glioblastoma invasion, migration, and proneural-mesenchymal transition by inhibiting TLR4 signaling

Resatorvid (TAK-242), a small-molecule inhibitor of Toll-like receptor 4 (TLR4), has the ability to cross the blood-brain barrier (BBB). In this study, we explored the role of TAK-242 on glioblastoma (GBM) invasion, migration, and proneural-mesenchymal transition (PMT). RNA sequencing (RNA-Seq) data and full clinical information of glioma patients were downloaded from the Chinese Glioma Genome Atlas (CGGA) and the Cancer Genome Atlas (TCGA) cohorts and then analyzed using R language; patients were grouped based on proneural (PN) and mesenchymal (MES) subtypes. Bioinformatics analysis was used to detect the difference in survival and TLR4-pathway expression between these groups. Cell viability assay, wound-healing test, and transwell assay, as well as an intracranial xenotransplantation mice model, were used to assess the functional role of TAK-242 in GBM in vitro and in vivo. RNA-Seq, Western blot, and immunofluorescence were employed to investigate the possible mechanism. TLR4 expression in GBM was significantly higher than in normal brain tissue and upregulated the expression of MES marker genes. Moreover, TAK-242 inhibited GBM progression in vitro and in vivo via linking with PMT, which could be a novel treatment strategy for inhibiting GBM recurrence.

Discovery of the Diphenyl 6-Oxo-1,6-dihydropyridazine-3-carboxylate/carboxamide Analogue J27 for the Treatment of Acute Lung Injury and Sepsis by Targeting JNK2 and Inhibiting the JNK2-NF-κB/MAPK Pathway

Acute lung injury (ALI) and sepsis are both serious and complex conditions associated with high mortality, yet there are no effective treatments. Herein, we designed and synthesized a series of diphenyl 6-oxo-1,6-dihydropyridazine-3-carboxylate/carboxamide analogues exhibiting anti-inflammatory activity. The optimal compound J27 decreased the release of TNF-α and IL-6 in mouse and human cells J774A.1 and THP-1 (IL-6 IC50 = 0.22 μM) through the NF-κB/MAPK pathway. J27 demonstrated remarkable protection against ALI and sepsis in vivo and exhibited good safety in subacute toxicity experiments. Pharmacokinetic study indicated that J27 had good bioavailability (30.74%). To our surprise, J27 could target JNK2 with a totally new molecular skeleton compared with the only few JNK2 inhibitors reported. Moreover, there is no report that JNK2 inhibitors could apply for ALI and sepsis. Therefore, this work provides a new lead structure for the study of JNK2 inhibitors and a new target of JNK2 to treat ALI and sepsis.

New Glucosamine-Based TLR4 Agonists: Design, Synthesis, Mechanism of Action, and In Vivo Activity as Vaccine Adjuvants

We disclose here a panel of small-molecule TLR4 agonists (the FP20 series) whose structure is derived from previously developed TLR4 ligands (FP18 series). The new molecules have increased chemical stability and a shorter, more efficient, and scalable synthesis. The FP20 series showed selective activity as TLR4 agonists with a potency similar to FP18. Interestingly, despite the chemical similarity with the FP18 series, FP20 showed a different mechanism of action and immunofluorescence microscopy showed no NF-κB nor p-IRF-3 nuclear translocation but rather MAPK and NLRP3-dependent inflammasome activation. The computational studies related a 3D shape of FP20 series with agonist binding properties inside the MD-2 pocket. FP20 displayed a CMC value lower than 5 μM in water, and small unilamellar vesicle (SUV) formation was observed in the biological activity concentration range. FP20 showed no toxicity in mouse vaccination experiments with OVA antigen and induced IgG production, thus indicating a promising adjuvant activity.

Full-Atom Model of the Agonist LPS-Bound Toll-like Receptor 4 Dimer in a Membrane Environment

The Toll-like receptor 4 (TLR4)/myeloid differentiation factor 2 (MD-2) innate immunity system is a membrane receptor of paramount importance as therapeutic target. Its assembly, upon binding of Gram-negative bacteria lipopolysaccharide (LPS), and also dependent on the membrane composition, finally triggers the immune response cascade. We have combined ab-initio calculations, molecular docking, all-atom molecular dynamics simulations, and thermodynamics calculations to provide the most realistic and complete 3D models of the active full TLR4 complex embedded into a realistic membrane to date. Our studies give functional and structural insights into the transmembrane domain behavior in different membrane environments, the ectodomain bouncing movement, and the dimerization patterns of the intracellular Toll/Interleukin-1 receptor domain. Our work provides TLR4 models as reasonable 3D structures for the (TLR4/MD-2/LPS)2 architecture accounting for the active (agonist) state of the TLR4, and pointing to a signal transduction mechanism across cell membrane. These observations unveil relevant molecular aspects involved in the TLR4 innate immune pathways and will promote the discovery of new TLR4 modulators.

Fighting Against Bacterial Lipopolysaccharide-Caused Infections through Molecular Dynamics Simulations: A Review

Lipopolysaccharide (LPS) is the primary component of the outer leaflet of Gram-negative bacterial outer membranes. LPS elicits an overwhelming immune response during infection, which can lead to life-threatening sepsis or septic shock for which no suitable treatment is available so far. As a result of the worldwide expanding multidrug-resistant bacteria, the occurrence and frequency of sepsis are expected to increase; thus, there is an urge to develop novel strategies for treating bacterial infections. In this regard, gaining an in-depth understanding about the ability of LPS to both stimulate the host immune system and interact with several molecules is crucial for fighting against LPS-caused infections and allowing for the rational design of novel antisepsis drugs, vaccines and LPS sequestration and detection methods. Molecular dynamics (MD) simulations, which are understood as being a computational microscope, have proven to be of significant value to understand LPS-related phenomena, driving and optimizing experimental research studies. In this work, a comprehensive review on the methods that can be combined with MD simulations, recently applied in LPS research, is provided. We focus especially on both enhanced sampling methods, which enable the exploration of more complex systems and access to larger time scales, and free energy calculation approaches. Thereby, apart from outlining several strategies for surmounting LPS-caused infections, this work reports the current state-of-the-art of the methods applied with MD simulations for moving a step forward in the development of such strategies.

TLR4 as a therapeutic target for respiratory and neurological complications of SARS-CoV-2

Introduction: The COVID-19 pandemic remains aglobal challenge. While there are mRNA agents on the horizon as apotential prevention, adefinitive drug therapy is an unmet medical need. The hyperinflammatory response, known as the 'cytokine storm', is chiefly responsible for complications and deaths. The binding of spike-glycoprotein of SARS-CoV-2 to TLR4 receptors has been documented in several studies and has been found to play arole in hyperinflammation; hence, there is an interest in TLR4 as apotential drug target.Areas covered: This review discusses the neurological and respiratory complications of SARS-CoV-2 infection and progresses to examine the role of the 'cytokine storm' and the involvement of TLR4 receptors in these complications. The possibility of using TLR4 modulators to curb the complications are considered and finally, ashort perspective on future potential drug treatments is offered. Various databases were searched including Pub-Med, Google Scholar, and Medline. The search mainly included research articles, meta-analysis, retrospective studies, reports, and systematic reviews.Expert opinion: TLR4 modulators are being investigated in clinical trials for COVID-19. Challenges in terms of structural diversity of the agents, their natural origin, and efficacy demand extensive research.

Synthesis of calix[4]azacrown substituted sulphonamides with antioxidant, acetylcholinesterase, butyrylcholinesterase, tyrosinase and carbonic anhydrase inhibitory action

A series of novel calix[4]azacrown substituted sulphonamide Schiff bases was synthesised by the reaction of calix[4]azacrown aldehydes with different substituted primary and secondary sulphonamides. The obtained novel compounds were investigated as inhibitors of six human (h) isoforms of carbonic anhydrases (CA, EC 4.2.1.1). Their antioxidant profile was assayed by various bioanalytical methods. The calix[4]azacrown substituted sulphonamide Schiff bases were also investigated as inhibitors of acetylcholinesterase (AChE), butyrylcholinesterase (BChE) and tyrosinase enzymes, associated with several diseases such as Alzheimer, Parkinson, and pigmentation disorders. The new sulphonamides showed low to moderate inhibition against hCAs, AChE, BChE, and tyrosinase enzymes. However, some of them possessed relevant antioxidant activity, comparable with standard antioxidants used in the study.

Multifunctional nanoassemblies target bacterial lipopolysaccharides for enhanced antimicrobial DNA delivery

The development of new therapeutic strategies against multidrug resistant Gram-negative bacteria is a major challenge for pharmaceutical research. In this respect, it is increasingly recognized that an efficient treatment for resistant bacterial infections should combine antimicrobial and anti-inflammatory effects. Here, we explore the multifunctional therapeutic potential of nanostructured self-assemblies from a cationic bolaamphiphile, which target bacterial lipopolysaccharides (LPSs) and associates with an anti-bacterial nucleic acid to form nanoplexes with therapeutic efficacy against Gram-negative bacteria. To understand the mechanistic details of these multifunctional antimicrobial-anti-inflammatory properties, we performed a fundamental study, comparing the interaction of these nanostructured therapeutics with synthetic biomimetic bacterial membranes and live bacterial cells. Combining a wide range of experimental techniques (Confocal Microscopy, Fluorescence Correlation Spectroscopy, Microfluidics, NMR, LPS binding assays), we demonstrate that the LPS targeting capacity of the bolaamphiphile self-assemblies, comparable to that exerted by Polymixin B, is a key feature of these nanoplexes and one that permits entry of therapeutic nucleic acids in Gram-negative bacteria. These findings enable a new approach to the design of efficient multifunctional therapeutics with combined antimicrobial and anti-inflammatory effects and have therefore the potential to broadly impact fundamental and applied research on self-assembled nano-sized antibacterials for antibiotic resistant infections.

Increasing the Chemical Variety of Small-Molecule-Based TLR4 Modulators: An Overview

Toll-Like Receptor 4 (TLR4) is one of the receptors of innate immunity. It is activated by Pathogen- and Damage-Associated Molecular Patterns (PAMPs and DAMPs) and triggers pro-inflammatory responses that belong to the repertoire of innate immune responses, consequently protecting against infectious challenges and boosting adaptive immunity. Mild TLR4 stimulation by non-toxic molecules resembling its natural agonist (lipid A) provided efficient vaccine adjuvants. The non-toxic TLR4 agonist monophosphoryl lipid A (MPLA) has been approved for clinical use. This suggests the development of other TLR4 agonists as adjuvants or drugs for cancer immunotherapy. TLR4 excessive activation by a Gram-negative bacteria lipopolysaccharide (LPS) leads to sepsis, while TLR4 stimulation by DAMPs is a common mechanism in several inflammatory and autoimmune diseases. TLR4 inhibition by small molecules and antibodies could therefore provide access to innovative therapeutics targeting sepsis as well as acute and chronic inflammations. The potential use of TLR4 antagonists as anti-inflammatory drugs with unique selectivity and a new mechanism of action compared to corticosteroids or other non-steroid anti-inflammatory drugs fueled the search for compounds of natural or synthetic origin able to block or inhibit TLR4 activation and signaling. The wide spectrum of clinical settings to which TLR4 inhibitors can be applied include autoimmune diseases (rheumatoid arthritis, inflammatory bowel diseases), vascular inflammation, neuroinflammations, and neurodegenerative diseases. The last advances (from 2017) in TLR4 activation or inhibition by small molecules (molecular weight <2 kDa) are reviewed here. Studies on pre-clinical validation of new chemical entities (drug hits) on cellular or animal models as well as new clinical studies on previously developed TLR4 modulators are reported. Innovative TLR4 modulators discovered by computer-assisted drug design and an artificial intelligence approach are described. Some "old" TLR4 agonists or antagonists such as MPLA or Eritoran are under study for repositioning in different pharmacological contexts. The mechanism of action of the molecules and the level of TLR4 involvement in their biological activity are critically discussed.

Calix[4]API-s: fully functionalized calix[4]arene-based facial active pharmaceutical ingredients

This mini-review covers 25 fully functionalized facial calix[4]arene-based symmetrical and conical cyclic tetramers with significant (comparable to established therapeutic agents) anticancer and anti-infective activities. The main role of the calixarene scaffold in these calix[4]arene-based active pharmaceutical ingredients (calix[4]API-s) is to replicate embedded phenolic units in the cyclic tetramers. So, probably owing to the multivalency, facial, conical structures of calix[4]API-s and synergistic effect of their four replicated units, they can be considered as effective bioactive agents.

Novel carboxylate-based glycolipids: TLR4 antagonism, MD-2 binding and self-assembly properties

New monosaccharide-based lipid A analogues were rationally designed through MD-2 docking studies. A panel of compounds with two carboxylate groups as phosphates bioisosteres, was synthesized with the same glucosamine-bis-succinyl core linked to different unsaturated and saturated fatty acid chains. The binding of the synthetic compounds to purified, functional recombinant human MD-2 was studied by four independent methods. All compounds bound to MD-2 with similar affinities and inhibited in a concentration-dependent manner the LPS-stimulated TLR4 signaling in human and murine cells, while being inactive as TLR4 agonists when provided alone. A compound of the panel was tested in vivo and was not able to inhibit the production of proinflammatory cytokines in animals. This lack of activity is probably due to strong binding to serum albumin, as suggested by cell experiments in the presence of the serum. The interesting self-assembly property in solution of this type of compounds was investigated by computational methods and microscopy, and formation of large vesicles was observed by cryo-TEM microscopy.

The synthesis and characterization of giant Calixarenes

Calixarenes are cyclic oligomers obtained by condensation of suitable p-functionalised phenols with formaldehyde, usually allowing for the synthesis of the well known small calixarenes (including up to eight phenolic subunits). We report here the discovery of much larger members of this family, exhibiting sizes up to 90 phenolic subunits: the giant calixarenes. These macrocycles are obtained according to simple, easily scalable processes, in yields up to 65%. We show that the formation of these giant macrocycles is favored by an oxygen-containing-group at the para-position of the starting phenol, high concentrations of heavy alkaline bases (rubidium or cesium hydroxides) and long reaction times. A mechanism is proposed to rationalize these observations. These giant macrocycles can also be obtained in the quasi-solid state, opening interesting perspectives in the field of calixarenes chemistry. Along with their intrinsic fundamental interest, these objects are also opening interesting applicative potentialities.

Mechanistic Evaluation of Lipopolysaccharide-Alexidine Interaction Using Spectroscopic and in Silico Approaches

The increasing problem of multidrug resistance (MDR) in bacteria calls for discovery of new molecules and diagnostic methodologies that are effective against a wide range of microbial pathogens. We have studied the role of alexidine dihydrochloride (alex) as a bioaffinity ligand against lipopolysaccharide (LPS), a pathogen-associated surface marker universally present on all Gram-negative bacteria. While the activity of alex against bacteria is biologically known, little information exists on its mechanism of action or binding stoichiometry. We have used nuclear magnetic resonance (NMR), fluorescence, and surface plasmon resonance (SPR) spectroscopies to probe the binding characteristics of alex and LPS molecules. Our results indicate that LPS:alex stoichiometry lies between 1:2 and 1:4 and has a dissociation constant ( K_D) of 38 μM that is mediated through electrostatic interactions between the negatively charged phosphate groups present on LPS and the positively charged guanidinium groups present in alex. Further, molecular dynamics (MD) simulations performed to determine the conformational interaction between the two molecules show good agreement with the experimental results, which substantiate the potential of alex molecule for LPS neutralization and hence, development of efficient in vitro diagnostic assays.

Bradyrhizobium Lipid A: Immunological Properties and Molecular Basis of Its Binding to the Myeloid Differentiation Protein-2/Toll-Like Receptor 4 Complex

Lipopolysaccharides (LPS) are potent activator of the innate immune response through the binding to the myeloid differentiation protein-2 (MD-2)/toll-like receptor 4 (TLR4) receptor complexes. Although a variety of LPSs have been characterized so far, a detailed molecular description of the structure–activity relationship of the lipid A part has yet to be clarified. Photosynthetic Bradyrhizobium strains, symbiont of Aeschynomene legumes, express distinctive LPSs bearing very long-chain fatty acids with a hopanoid moiety covalently linked to the lipid A region. Here, we investigated the immunological properties of LPSs isolated from Bradyrhizobium strains on both murine and human immune systems. We found that they exhibit a weak agonistic activity and, more interestingly, a potent inhibitory effect on MD-2/TLR4 activation exerted by toxic enterobacterial LPSs. By applying computational modeling techniques, we also furnished a plausible explanation for the Bradyrhizobium LPS inhibitory activity at atomic level, revealing that its uncommon lipid A chemical features could impair the proper formation of the receptorial complex, and/or has a destabilizing effect on the pre-assembled complex itself.

Structure-Activity Relationship in Monosaccharide-Based Toll-Like Receptor 4 (TLR4) Antagonists

The structure-activity relationship was investigated in a series of synthetic TLR4 antagonists formed by a glucosamine core linked to two phosphate esters and two linear carbon chains. Molecular modeling showed that the compounds with 10, 12, and 14 carbons chains are associated with higher stabilization of the MD-2/TLR4 antagonist conformation than in the case of the C16 variant. Binding experiments with human MD-2 showed that the C12 and C14 variants have higher affinity than C10, while the C16 variant did not interact with the protein. The molecules, with the exception of the C16 variant, inhibited the LPS-stimulated TLR4 signal in human and murine cells, and the antagonist potency mirrored the MD-2 affinity calculated from in vitro binding experiments. Fourier-transform infrared, nuclear magnetic resonance, and small angle X-ray scattering measurements suggested that the aggregation state in aqueous solution depends on fatty acid chain lengths and that this property can influence TLR4 activity in this series of compounds.

Recent progress in the discovery of myeloid differentiation 2 (MD2) modulators for inflammatory diseases

Myeloid differentiation protein 2 (MD2), together with Toll-like receptor 4 (TLR4), binds lipopolysaccharide (LPS) with high affinity, inducing the formation of the activated homodimer LPS-MD2-TLR4. MD2 directly recognizes the Lipid A domain of LPS, leading to the activation of downstream signaling of cytokine and chemokine production, and initiation of inflammatory and immune responses. However, excessive activation and potent host responses generate severe inflammatory syndromes such as acute sepsis and septic shock. MD2 is increasingly being considered as an attractive pharmacological target for the development of potent anti-inflammatory agents. In this Keynote review, we provide a comprehensive overview of the recent advances in the structure and biology of MD2, and present MD2 modulators as promising agents for anti-inflammatory intervention.

Effects of Tim-3 silencing on the viability of fibroblast-like synoviocytes and lipopolysaccharide-induced inflammatory reactions

The objective of the present study was to investigate the effects of Tim-3 silencing on cell viability and lipopolysaccharide (LPS)-induced inflammatory reactions in fibroblast-like synoviocytes (FLS). T-cell immunoglobulin mucin domain molecule (Tim)-3 expression in FLS obtained from patients with rheumatoid arthritis (RA) and normal controls were detected by western blot analysis and reverse transcription-polymerase chain reaction (RT-PCR). Small interfering (si)RNA was transfected using Lipofectamine^® 2000 to decrease Tim-3 expression. Following transfection, FLS were stimulated by LPS. An MTT assay, RT-PCR and western blot analysis were performed to measure cell viability, Toll-like receptor 4 (TLR4) signaling pathway-related protein expression and inflammatory cytokine release, respectively. The results of the present study indicated that Tim-3 expression was increased in FLS from patients with RA compared with FLS from healthy controls. Transfection of Tim-3 siRNA significantly decreased Tim-3 expression in FLS from patients with RA. Notably, Tim-3 silencing decreased FLS cell viability. Following stimulation with LPS, cell viability and the expression of TLR4, myeloid differentiation protein gene 88 (MyD88) and nuclear factor-κB (NF-κB) p65 were enhanced in FLS. By contrast, Tim-3 silencing attenuated LPS-induced cell proliferation and the expression of TLR4, MyD88 and NF-κB p65. In addition, LPS significantly increased levels of cytokines in the supernatant, including tumor necrosis factor-α, interferon-γ and interleukin-6 (P<0.01). By contrast, Tim-3 silencing significantly decreased LPS-induced cytokine release (P<0.01). However, Tim-3 silencing did not affect TLR4, MyD88 and NF-κB p65 expression and the release of cytokines in cells that did not undergo treatment with LPS. Therefore, the results of the present study indicate that Tim-3 silencing decreases the viability of FLS in RA and attenuates the LPS-induced inflammatory reaction.