SDZ MRL 953, a novel immunostimulatory monosaccharidic lipid A analog with an improved therapeutic window in experimental sepsis

Synthetic Glycolipids as Molecular Vaccine Adjuvants: Mechanism of Action in Human Cells and In Vivo Activity

Modern adjuvants for vaccine formulations are immunostimulating agents whose action is based on the activation of pattern recognition receptors (PRRs) by well-defined ligands to boost innate and adaptive immune responses. Monophosphoryl lipid A (MPLA), a detoxified analogue of lipid A, is a clinically approved adjuvant that stimulates toll-like receptor 4 (TLR4). The synthesis of MPLA poses manufacturing and quality assessment challenges. Bridging this gap, we report here the development and preclinical testing of chemically simplified TLR4 agonists that could sustainably be produced in high purity and on a large scale. Underpinned by computational and biological experiments, we show that synthetic monosaccharide-based molecules (FP compounds) bind to the TLR4/MD-2 dimer with submicromolar affinities stabilizing the active receptor conformation. This results in the activation of MyD88- and TRIF-dependent TLR4 signaling and the NLRP3 inflammasome. FP compounds lack in vivo toxicity and exhibit adjuvant activity by stimulating antibody responses with a potency comparable to MPLA.

Natural and synthetic carbohydrate-based vaccine adjuvants and their mechanisms of action

Modern subunit vaccines based on homogeneous antigens offer more precise targeting and improved safety compared with traditional whole-pathogen vaccines. However, they are also less immunogenic and require an adjuvant to increase the immunogenicity of the antigen and potentiate the immune response. Unfortunately, few adjuvants have sufficient potency and low enough toxicity for clinical use, highlighting the urgent need for new, potent and safe adjuvants. Notably, a number of natural and synthetic carbohydrate structures have been used as adjuvants in clinical trials, and two have recently been approved in human vaccines. However, naturally derived carbohydrate adjuvants are heterogeneous, difficult to obtain and, in some cases, unstable. In addition, their molecular mechanisms of action are generally not fully understood, partly owing to the lack of tools to elucidate their immune-potentiating effects, thus hampering the rational development of optimized adjuvants. To address these challenges, modification of the natural product structure using synthetic chemistry emerges as an attractive approach to develop well-defined, improved carbohydrate-containing adjuvants and chemical probes for mechanistic investigation. This Review describes selected examples of natural and synthetic carbohydrate-based adjuvants and their application in synthetic self-adjuvanting vaccines, while also discussing current understanding of their molecular mechanisms of action.

Modulatory effect of different doses of β-1,3/1,6-glucan on the expression of antioxidant, inflammatory, stress and immune-related genes of Oreochromis niloticus challenged with Streptococcus iniae

β-glucans are widely-known immunostimulants that are profusely used in aquaculture industry. The present study was conducted to evaluate the effect of different in-feed doses of β-1,3/1,6-glucans on the expression of antioxidant and stress-related genes (GST, HSP-70, Vtg), inflammation related genes (Il-8, TNFα, CXC-chemokine and CAS) and adaptive immune-related genes (MHC-IIβ, TLR-7, IgM-H, and Mx) of Oreochromis niloticus challenged and non-challenged with Streptococcus iniae. Six experimental groups were established: non-challenged control (non-supplemented diet), challenged control (non-supplemented diet), non-challenged supplemented with 0.1% β-glucan, challenged supplemented with 0.1% β-glucan, non-challenged supplemented with 0.2% β-glucan and challenged supplemented with 0.2% β-glucan. Fish were fed with β-glucan for 21 days prior challenge and then sampled after 1, 3 and 7 days post-challenge. In non-challenged group, variable effects of the two doses of β-Glucans on the expression of the studied genes were observed; 0.1% induced higher expression of HSP70, CXC chemokine, MHC-IIβ and MX genes. Meanwhile, 0.2% induced better effect on the expression of Vtg, TNF-α, CAS and IgM-H, and almost equal effects of both doses on GST and IL8. However, with the challenged group, 0.2% β-Glucans showed better effect than 0.1% at day one post challenge through significant up-regulation of GST, HSP, IL8, TNF-α, CXC, and MHC-IIβ, meanwhile, the effect of 0.1% was only on the expression of HSP70, MHC-IIβ, and TLR7 at day 3 post challenge. No stimulatory role for both doses of β-Glucans on the expression of almost all genes at day 7 post-challenge. We conclude that both doses of β-glucan can modulate the antioxidant, inflammation, stress and immune-related genes in Nile tilapia, moreover, 0.2% β-Glucans showed better protective effect with Streptococcus iniae challange.

Review: D-Galactosamine lethality model: scope and limitations

D-Galactosamine (D-galN) is well established as sensitizing mice and other animals to the lethal effects of TNF, specifically, and by several orders of magnitude. Protection by anti-TNF neutralizing antibody is complete, as is (metabolically-based) protection by uridine. Sensitization occurs regardless of the origin of the released TNF, whether it is released from macrophages and/or T-cells. The same is true for the challenging agent which leads to the release of TNF, whether it is endotoxin, a superantigen, lipoprotein, bacterial DNA, or bacteria, either killed or proliferating. Most studies have utilized endotoxin as the challenging agent, and more than 70 agents have been reported to confer protection against LPS and/or TNF challenge in the model. The model has provided new insight regarding modes of protection, including from dexamethasone, which protects against challenge from LPS but not from challenge by TNF. The D-galN lethality model has also been used to test for synergistic behavior between different bacterial components, and to test for lethality when only small amounts of the challenging agent are available (lipid A chemistry).

Small-Molecule Carbohydrate-Based Immunostimulants

In this review, we discuss small-molecule, carbohydrate-based immunostimulants that target Toll-like receptor 4 (TLR-4) and cluster of differentiation 1D (CD1d) receptors. The design and use of these molecules in immunotherapy as well as results from their use in clinical trials are described. How these molecules work and their utilization as vaccine adjuvants are also discussed. Future applications and extensions for the use of these analogues as therapeutic agents will be outlined.

Characterization of TRIF selectivity in the AGP class of lipid A mimetics: role of secondary lipid chains

TLR4 agonists that favor TRIF-dependent signaling and the induction of type 1 interferons may have potential as vaccine adjuvants with reduced toxicity. CRX-547 (4), a member of the aminoalkyl glucosaminide 4-phosphate (AGP) class of lipid A mimetics possessing three (R)-3-decanoyloxytetradecanoyl groups and d-relative configuration in the aglycon, selectively reduces MyD88-dependent signaling resulting in TRIF-selective signaling, whereas the corresponding secondary ether lipid 6a containing (R)-3-decyloxytetradecanoyl groups does not. In order to determine which secondary acyl groups are important for the reduction in MyD88-dependent signaling activity of 4, the six possible ester/ether hybrid derivatives of 4 and 6a were synthesized and evaluated for their ability to induce NF-κB in a HEK293 cell reporter assay. An (R)-3-decanoyloxytetradecanoyl group on the 3-position of the d-glucosamine unit was found to be indispensable for maintaining low NF-κB activity irrespective of the substitutions (decyl or decanoyl) on the other two secondary positions. These results suggest that the carbonyl group of the 3-secondary lipid chain may impede homodimerization and/or conformational changes in the TLR4-MD2 complex necessary for MyD88 binding and pro-inflammatory cytokine induction.

The Effects of β - Glucan on Fish Immunity

Administration of glucans through immersion, dietary inclusion or injection has been found to enhance many types of immune responses, resistance to bacterial and viral infections and to environmental stress in many fish species. Although the efficacy of the glucan varies with types and administration, glucan used as an immunomodulatory and mostly immunostimulatory additive has been found satisfactory in eliciting immunity in commercial aquaculture. Development of more efficient administration methods will facilitate the routine and prophylactic use of glucans as natural immunostimulants of fish. Using a PubMed search, this review has an extensive literature on glucan in fish immunity.

Lipid A-induced responses in vivo

The lipid A analogs used in preclinical studies and clinical trials are not naturally-occurring forms of lipid A; they are synthetic molecules produced to be less toxic than lipid A itself and they do not reproduce the effects of natural lipid A molecules especially in vivo. The responses induced by lipid A analogs are summarized in this chapter: their fate in the blood stream and their toxicity as well as the lipid A tolerance and the tumor immune responses they induce. Lipid A is not found in the mammalian organism under normal circumstances so its use in cancer therapy raises important questions as to its different effects in vivo and its toxicity, particularly in cancer patients. Lipid A has to be injected intravenously (i.v.) to study its effects. Injections of chemically synthesized lipid A in humans and in animals produce sepsis symptoms, such as tachycardia, tachypnea, hyper or hypothermia and leukocytosis or leukopenia. Similar manifestations are observed after injection of purified lipopolysaccharide (LPS), which is why lipid A is usually thought of as the active part of LPS. While lipid A injection is therefore expected to induce reactions similar to septic shock, the lipid A molecules used to treat cancer are not natural forms but analogs, produced by chemical synthesis or genetic engineering, specifically selected for their low toxicity. The in vivo effects of such low-toxicity lipid A analogs are summarized in this chapter.

Structure-function relationships of bacterial endotoxins. Contribution to microbial sepsis

A substantial body of knowledge has emerged over the past several decades concerning the primary and tertiary, and quaternary structure of endotoxic LPS and their contribution to the pathogenesis of gram-negative sepsis; however, important questions remain. Among them are the precise three-dimensional configuration of the LPS macromolecule and the contribution of the quaternary structure to the ability of these potent microbial factors to interact with host humoral and cellular inflammatory mediator systems. Also remaining to be sufficiently addressed is the relative contribution of endotoxin interactions with the host to the overall manifestation of disease and conditions under which such contributions serve as the pivotal event in determining outcome. The answers to these questions can be expected to provide valuable insights into potential novel therapeutic intervention strategies and approaches that will ultimately reduce both morbidity and mortality in infection from gram-negative microbes.

Downregulation of the Proinflammatory Cytokine Response to Endotoxin by Pretreatment With the Nontoxic Lipid A Analog SDZ MRL 953 in Cancer Patients

Interfering with the endotoxin-mediated cytokine cascade is thought to be a promising approach to prevent septic complications in gram-negative infections. The synthetic lipid A analog SDZ MRL 953 has been shown to be protective against endotoxic shock and bacterial infection in preclinical in vivo models. As part of a trial of unspecific immunostimulation in cancer patients, we conducted a double-blind, randomized, vehicle-controlled phase I trial of SDZ MRL 953 to investigate, first, its biologic effects and safety of administration in humans and, second, its influence on reactions to a subsequent challenge of endotoxin (Salmonella abortus equi). Twenty patients were treated intravenously with escalating doses of SDZ MRL 953 or vehicle control, followed by an intravenous application of endotoxin (2 ng/kg of body weight [BW]). Administration of SDZ MRL 953 was safe and well-tolerated. SDZ MRL 953 itself increased granulocyte counts and serum levels of granulocyte colony-stimulating factor (G-CSF ) and interleukin-6 (IL-6), but not of the proinflammatory cytokines tumor necrosis factor-α (TNF-α), IL-1β, and IL-8. Compared with vehicle control, pretreatment with SDZ MRL 953 markedly reduced the release of TNF-α, IL-1β, IL-8, IL-6, and G-CSF, but augmented the increase in granulocyte counts to endotoxin. Induction of tolerance to the endotoxin-mediated cascade of proinflammatory cytokines by pretreatment with SDZ MRL 953 in patients at risk may help to prevent complications of gram-negative sepsis.

Downregulation of the Proinflammatory Cytokine Response to Endotoxin by Pretreatment With the Nontoxic Lipid A Analog SDZ MRL 953 in Cancer Patients

Interfering with the endotoxin-mediated cytokine cascade is thought to be a promising approach to prevent septic complications in gram-negative infections. The synthetic lipid A analog SDZ MRL 953 has been shown to be protective against endotoxic shock and bacterial infection in preclinical in vivo models. As part of a trial of unspecific immunostimulation in cancer patients, we conducted a double-blind, randomized, vehicle-controlled phase I trial of SDZ MRL 953 to investigate, first, its biologic effects and safety of administration in humans and, second, its influence on reactions to a subsequent challenge of endotoxin (Salmonella abortus equi). Twenty patients were treated intravenously with escalating doses of SDZ MRL 953 or vehicle control, followed by an intravenous application of endotoxin (2 ng/kg of body weight [BW]). Administration of SDZ MRL 953 was safe and well-tolerated. SDZ MRL 953 itself increased granulocyte counts and serum levels of granulocyte colony-stimulating factor (G-CSF ) and interleukin-6 (IL-6), but not of the proinflammatory cytokines tumor necrosis factor-α (TNF-α), IL-1β, and IL-8. Compared with vehicle control, pretreatment with SDZ MRL 953 markedly reduced the release of TNF-α, IL-1β, IL-8, IL-6, and G-CSF, but augmented the increase in granulocyte counts to endotoxin. Induction of tolerance to the endotoxin-mediated cascade of proinflammatory cytokines by pretreatment with SDZ MRL 953 in patients at risk may help to prevent complications of gram-negative sepsis.

Effects of pretreatment with SDZ MRL 953, a novel immunostimulatory lipid A analog, on endotoxin-induced acute lung injury in guinea pigs

SDZ MRL 953 (SDZ), a novel immunostimulatory lipid A analog, has been reported to have immunopharmacological activities similar to those of lipopolysaccharide (LPS) but to have little of the toxicity of LPS. We investigated the effects of pretreatment with SDZ on Escherichia coli endotoxin-induced acute lung injury in guinea pigs. Four experimental groups consisted of saline control (n = 16), SDZ (-12 h) plus LPS (2 mg/kg of SDZ per kg of body weight injected intravenously 12 h before intravenous injection of 2 mg of LPS per kg; n = 15), SDZ (-10 min) plus LPS (SDZ injected 10 min before LPS injection; n = 10), and LPS alone (n = 16). The animals were sacrificed, and lung tissue was sampled 4 h after LPS or saline infusion. Lung injury was assessed by measuring the wet weight-to-dry weight ratio and the level of 125I-labeled albumin accumulation in bronchoalveolar lavage fluid relative to that in plasma. In the SDZ (-12 h) plus LPS group, these two parameters of acute lung injury were decreased compared with those in the LPS alone group. However, they were not decreased in the SDZ (-10 min) plus LPS group. We conclude that SDZ attenuates endotoxin-induced acute lung injury when it is administered 12 h before LPS injection. The attenuating effects of SDZ are speculated to be due to down regulation of the response to endotoxin rather than to receptor blocking.

Expression of endotoxic activities by synthetic monosaccharide lipid A analogs with alkyl-branched acyl substituents

Synthetic monosaccharide lipid A analogs with alkyl-branched acyl substituents instead of the usual ester-branched acyl substituents were investigated for their biological activities. The activities were compared with those of a representative synthetic monosaccharide lipid A analog with an ester branch (GLA-60) and synthetic complete lipid A (506) to estimate the role of the attaching mode of the branched side chains for expression of endotoxic activities. Among the analogs with alkyl branches, GLA-146 and GLA-147, which have C12 and C14 alkyl side chains, respectively, showed strong endotoxic activities. These analogs exhibited comparable or stronger activities than those of GLA-60 in murine macrophage activation activities to induce mediators such as tumor necrosis factors, interleukin 6, and nitric oxide and in mitogenic activity towards murine spleen cells; however, these activities were weaker than the respective activities of 506. With respect to lethal toxicity to galactosamine-sensitized mice, the analogs showed stronger activity than that of GLA-60 and activity closer to that of 506. With respect to adjuvant activity, no significant activity was observed in the analogs, while the activities of GLA-60 and 506 were strong. When lipopolysaccharide-resistant C3H/HeJ mice were used, the activities described above were not observed either for the analogs under investigation nor for GLA-60 and 506. These findings indicate that the ester type of branch in lipid A and its analogs does not play an indispensable role in the expression of various endotoxic activities. However, it may play some role in the expression of adjuvant activity and in lowering the level of toxicity.

Molecular adjuvants and immunomodulators: new approaches to immunization

Epitopes on microbial antigens responsible for protective immunity have begun to be identified and isolated, and their chemical structures have been determined. Ensuing knowledge of their weak immunizing capacity per se has led to an appreciation of the need for adjuvants to increase the immunogenicity of these low-molecular-weight synthetic structures. As such, a recent surge in adjuvant research has emerged. Accordingly, this review will highlight a number of those adjuvant substances whose activity in animals indicates a potential use in human vaccines. In addition, the potential of several well-defined substances, termed immunomodulators, which nonspecifically stimulate resistance of animals to multiple 50% lethal doses of microbial challenge is described. Among the most extensively characterized adjuvants of microbial origin discussed in detail are (i) the lipopolysaccharides isolated from gram-negative bacteria and their nontoxic analogs, (ii) the synthetic muramyl dipeptides and their multiple analogs, and (iii) the synthetic polyribonucleotide complexes, mimicking the interferon-inducing capacity of viruses. Discussed also are the heat-labile enterotoxin of Escherichia coli, the nonionic block copolymers, the saponins, a quinolamine derivative, and the hormone dihydroepiandrosterone.

Induction of early gene expression in murine macrophages by synthetic lipid A analogs with differing endotoxic potentials

Numerous lipid A analogs have been synthesized in an attempt to dissociate endotoxic activities from beneficial immunomodulatory activities. In the present study, we have evaluated select lipid A analogs in macrophages for their ability to induce a panel of lipopolysaccharide (LPS)-inducible genes to gain insights into the molecular mechanisms which underlie endotoxicity. We evaluated three monosaccharide lipid A analogs: SDZ MRL 953, an agonist with an improved therapeutic margin over endotoxin; SDZ 281.288, a more toxic analog; and SDZ 880.431, an analog with proven LPS-inhibitory activity. In addition, three disaccharide lipid A analogs (i.e., lipid IVA, SDZ 880.611, and SDZ 880.924) that differ in acylation and phosphorylation patterns were also examined and compared with synthetic lipid A. With the exception of SDZ 880.431, each of these structurally diverse analogs was able to induce the complete panel of LPS-inducible genes, specifically genes which encode tumor necrosis factor alpha (TNF-alpha), interleukin-1 beta, 75-kDa type 2 TNF receptor (D7), IP-10, D3, and D8. These results underscore that macrophage stimulation by lipid A analogs is permissive to considerable structural diversity. Structures with favorable therapeutic indices (SDZ MRL 953, SDZ 880.611, and SDZ 880.924) were not different from structures with poor therapeutic indices (lipid A, lipid IVA, and SDZ 281.288) with regard to gene induction. Nonetheless, the nontoxic SDZ MRL 953 was approximately 1,000-fold less potent than synthetic lipid A at inducing TNF-alpha secretion, and perhaps this contributes to the lack of toxicity exhibited by this compound. The ability of compound SDZ 880.431 to inhibit TNF-alpha secretion induced by both SDZ MRL 953 and smooth LPS suggests that the monosaccharide and smooth LPS share a receptor or a portion thereof. A pattern of protein tyrosine phosphorylation similar to that induced by LPS was stimulated by the monosaccharide SDZ MRL 953 and SDZ 281.288 and disaccharides lipid IVA, SDZ 880.924, and SDZ 880.611, providing evidence for a common signalling pathway.

Selection of a muramyl peptide based on its lack of activation of nuclear factor-kappa B as a potential adjuvant for AIDS vaccines

Activation of the cellular transcription factor nuclear factor-kappa B (NF-kappa B) by cytokines and other immunostimulants has been tightly linked with enhanced replication of human immunodeficiency virus-type 1 (HIV-1) in infected cells. Various immunomodulators are currently being examined in animal and human trials for their suitability as adjuvants in potential vaccines against acquired immunodeficiency syndrome (AIDS). It may prove to be beneficial to select adjuvants that do not induce NF-kappa B activation and particularly if the vaccines are to be aimed at seropositive individuals. We have examined a battery of synthetic immunostimulants of the muramyl peptide family for their ability to activate NF-kappa B in human and mouse cell lines. In this report, we demonstrate selective activation of NF-kappa B in different cell lines and by different muramyl peptides possessing immunostimulatory activities. The mechanism of such activation is apparently via production of reactive oxygen intermediates (ROI) since pretreatment of cells with antioxidants blocked subsequent activation of NF-kappa B. However, among all the molecules tested only one lipophilic, non-pyrogenic adjuvant active muramyl peptide showed a complete lack of NF-kappa B activation in all cell lines tested. This molecule could well become the adjuvant of choice in future AIDS vaccines.

Function of lipopolysaccharide (LPS)-binding protein (LBP) and CD14, the receptor for LPS/LBP complexes: a short review

With the recent discovery and cloning of the lipopolysaccharide-binding protein (LBP), the "adapter-molecule" for LPS-binding to the cell surface receptor CD14 was found. The ligand-receptor pair LPS/LBP-CD14 seems to be one important element in LPS-mediated activation of monocytic cells and possibly granulocytes and B cells. Here, some of the known functions of the proteins involved, LBP and CD14, are reviewed in the context of other endotoxin recognition studies, and the outlook for ongoing and future investigations is described.

Effect of SDZ MRL 953 on the survival of mice with advanced sepsis that cannot be cured by antibiotics alone

Stimulation of nonspecific immunity as an additional modality for therapy of sepsis that cannot be cured by antibiotics alone was investigated. SDZ MRL 953, a novel monosaccharidic lipid A analog as a prototype immunostimulant, and cefotaxime or gentamicin were administered to normal or myelosuppressed mice in a state of advanced sepsis caused by Escherichia coli or Staphylococcus aureus. In this novel model, antibiotic therapy was initiated when the infected mice appeared moribund. At this stage, neither pretreatment with the immunostimulant nor therapy with high doses of cefotaxime or gentamicin was effective in protecting the animals from fatal sepsis. However, pretreatment with a single dose of SDZ MRL 953 1 day prior to microbial inoculation dramatically improved the curative effects of the antibiotics. Hence, long-term survival was significantly enhanced with increasing doses of the immunostimulant in the combined therapy. Peritoneal macrophages from SDZ MRL 953-pretreated animals were primed for enhanced production of microbicidal reactive oxygen metabolites in vitro. In conclusion, the results of the present study indicate that SDZ MRL 953 is a potential candidate for use in a clinical setting as an adjunct to antimicrobial therapy for infections that cannot be treated successfully with appropriate antibiotics alone.