Regression of tumors in guinea pigs after treatment with synthetic muramyl dipeptides and trehalose dimycolate

Uptake, recognition and responses to peptidoglycan in the mammalian host

Microbiota, and the plethora of signalling molecules that they generate, are a major driving force that underlies a striking range of inter-individual physioanatomic and behavioural consequences for the host organism. Among the bacterial effectors, one finds peptidoglycan, the major constituent of the bacterial cell surface. In the steady-state, fragments of peptidoglycan are constitutively liberated from bacterial members of the gut microbiota, cross the gut epithelial barrier and enter the host system. The fate of these peptidoglycan fragments, and the outcome for the host, depends on the molecular nature of the peptidoglycan, as well the cellular profile of the recipient tissue, mechanism of cell entry, the expression of specific processing and recognition mechanisms by the cell, and the local immune context. At the target level, physiological processes modulated by peptidoglycan are extremely diverse, ranging from immune activation to small molecule metabolism, autophagy and apoptosis. In this review, we bring together a fragmented body of literature on the kinetics and dynamics of peptidoglycan interactions with the mammalian host, explaining how peptidoglycan functions as a signalling molecule in the host under physiological conditions, how it disseminates within the host, and the cellular responses to peptidoglycan.

Translation of peptidoglycan metabolites into immunotherapeutics

The discovery of defined peptidoglycan metabolites that activate host immunity and their specific receptors has revealed fundamental insights into host-microbe recognition and afforded new opportunities for therapeutic development against infection and cancer. In this review, we summarise the discovery of two key peptidoglycan metabolites, γ-d-glutamyl-meso-diaminopimelic acid (iE-DAP) and muramyl dipeptide and their respective receptors, Nod1 and Nod2, and review progress towards translating these findings into therapeutic agents. Notably, synthetic derivatives of peptidoglycan metabolites have already yielded approved drugs for chemotherapy-induced leukopenia and paediatric osteosarcoma; however, the broad effects of peptidoglycan metabolites on host immunity suggest additional translational opportunities for new therapeutics towards other cancers, microbial infections and inflammatory diseases.

Muramyl dipeptide induces NOD2-dependent Ly6C(high) monocyte recruitment to the lungs and protects against influenza virus infection

Bacterial peptidoglycan-derived muramyl dipeptide (MDP) and derivatives have long-recognized antiviral properties but their mechanism of action remains unclear. In recent years, the pattern-recognition receptor NOD2 has been shown to mediate innate responses to MDP. Here, we show that MDP treatment of mice infected with Influenza A virus (IAV) significantly reduces mortality, viral load and pulmonary inflammation in a NOD2-dependent manner. Importantly, the induction of type I interferon (IFN) and CCL2 chemokine was markedly increased in the lungs following MDP treatment and correlated with a NOD2-dependent enhancement in circulating monocytes. Mechanistically, the protective effect of MDP could be explained by the NOD2-dependent transient increase in recruitment of Ly6C^high “inflammatory” monocytes and, to a lesser extent, neutrophils to the lungs. Indeed, impairment in both Ly6C^high monocyte recruitment and survival observed in infected Nod2-/- mice treated with MDP was recapitulated in mice deficient for the chemokine receptor CCR2 required for CCL2-mediated Ly6C^high monocyte migration from the bone marrow into the lungs. MDP-induced pulmonary monocyte recruitment occurred normally in IAV-infected and MDP-treated Ips-1-/- mice. However, IPS-1 was required for improved survival upon MDP treatment. Finally, mycobacterial N-glycolyl MDP was more potent than N-acetyl MDP expressed by most bacteria at reducing viral burden while both forms of MDP restored pulmonary function following IAV challenge. Overall, our work sheds light on the antiviral mechanism of a clinically relevant bacterial-derived compound and identifies the NOD2 pathway as a potential therapeutic target against IAV.

The PorB porin from commensal Neisseria lactamica induces Th1 and Th2 immune responses to ovalbumin in mice and is a potential immune adjuvant

Porins from pathogenic Neisseriae are among several bacterial products with immune adjuvant activity. Neisseria meningitidis (Nme) PorB, has been shown to induce immune cells activation in a TLR2-dependent manner and acts as a vaccine immune adjuvant. The PorB porin from Neisseria lactamica (Nlac), a common nasopharyngeal commensal, shares significant structural and functional similarities with Nme PorB. In this work we ask whether the immune adjuvant ability of porins from pathogenic Neisserial strains is a characteristic shared with porins from non-pathogenic Neisserial species or whether it is unique for bacterial products derived from microorganisms capable of inducing inflammation and disease. We evaluated the potential immune adjuvant effect of Nlac PorB in mice using ovalbumin (OVA) as a prototype antigen. Immunization with Nlac PorB/OVA induced high OVA-specific IgG and IgM titers compared to OVA alone, similar to other adjuvants such as Nme PorB and alum. High titers of IgG1 and IgG2b were detected as well as production of IL-4, IL-10, IL-12 and INF-gamma in response to Nlac PorB, consistent with induction of both a Th1-type and a Th2-type immune response. OVA-specific proliferation was also determined in splenocytes from Nlac PorB/OVA-immunized mice. In addition, B cell activation in vitro and cytokine production in response to Nlac PorB was found to be mediated by TLR2, in a similar manner to Nme PorB.

Cancer relapse under chemotherapy: why TLR2/4 receptor agonists can help

Liver or lung metastases usually relapse under chemotherapy. Such life-threatening condition urgently needs new, systemic anticancer compounds, with original and efficient mechanisms of action. In B16 melanoma mice treated with cyclophosphamide, D'Agostini et al. [D'Agostini, C., Pica, F., Febbraro, G., Grelli, S., Chiavaroli, C., Garaci, E., 2005. Antitumour effect of OM-174 and Cyclophosphamide on murine B16 melanoma in different experimental conditions. Int. Immunopharmacol. 5, 1205-1212.] recently found that OM-174, a chemically defined Toll-like receptor(TLR)2/4 agonist, reduces tumor progression and prolongs survival. Here we review 149 articles concerning molecular mechanisms of TLR2/4 agonists, alone or in combination with chemotherapy. It appears that TLR2/4 agonists induce a well controlled tumor necrosis factor-alpha (TNF-alpha) secretion, at plasma levels known to permeabilize neoangiogenic tumor vessels to the passage of cytotoxic drugs. Moreover, TLR2/4 agonists induce inducible nitric oxide synthase (iNOS) expression, and nitric oxide is able to induce apoptosis of chemotherapy-resistant tumor cell clones. Finally, TLR2/4-stimulation activates dendritic cell traffic and its associated tumor-specific, cytotoxic T-cell responses. Therefore, parenteral TLR2/4 agonists seem promising molecules to prolong survival in cancer patients who relapse under chemotherapy.

Peptidoglycan and lipoteichoic acid in gram-positive bacterial sepsis: receptors, signal transduction, biological effects, and synergism

In sepsis and multiple organ dysfunction syndrome (MODS) caused by gram-negative bacteria, lipopolysaccharide (LPS) initiates the early signaling events leading to the deleterious inflammatory response. However, it has become clear that LPS can not reproduce all of the clinical features of sepsis, which emphasize the roles of other contributing factors. Gram-positive bacteria, which lack LPS, are today responsible for a substantial part of the incidents of sepsis with MODS. The major wall components of gram-positive bacteria, peptidoglycan and lipoteichoic acid, are thought to contribute to the development of sepsis and MODS. In this review, the literature underlying our current understanding of how peptidoglycan and lipoteichoic acid activate inflammatory responses will be presented, with a focus on recent advances in this field.

Synthesis of O-[2-acetamido-2-deoxy-6-O-stearoyl- and -6-O-(2-tetradecylhexadecanoyl)-beta-D-glucopyranosyl]-(1-->4)-N- acetylnormuramoyl-L-alpha-aminobutanoyl-D-isoglutamine, lipophilic disaccharide analogues of MDP

Silver triflate-promoted condensation of 3,4,6-tri-O-acetyl-2-deoxy-2- phthalimido-beta-D-glucopyranosyl bromide (1) with benzyl 2-acetamido-6-O-benzyl-2-deoxy-3-O- (methoxycarbonyl)methyl-alpha-D-glucopyranoside (4) afforded the key compound, benzyl 2-acetamido-6-O-benzyl-2-deoxy-3-O- (methoxy-carbonyl)methyl-4-O-(3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido-b eta-D- glucopyranosyl)-alpha-D-glucopyranoside (5), which after deprotection was transformed into acid 10. Condensation of 10 with the benzyl ester of L-alpha-aminobutanoyl-D-isoglutamine and deisopropylidenation of the product 11 afforded the benzyl ester of N-(2-O-[benzyl 2-acetamido-4-O-(2-acetamido-3-O-benzyloxymethyl-2- deoxy-beta-D-glucopyranosyl)-6-O-benzyl-2,3-dideoxy-alpha-D-glucopyra nosid-3- yl]glycoloyl)-L-alpha-aminobutanoyl-D-isoglutamine (12). Partial O-acylation of 12 and hydrogenolysis of protecting groups gave the 6-O-stearoyl- and 6-O-(2-tetradecylhexadecanoyl)-disaccharide-dipeptides 17 and 18, respectively. Pyrogenicity and adjuvant activity in cell-mediated immunity are reported.

Adjuvants--a balance between toxicity and adjuvanticity

Adjuvants have been used to augment the immune response in experimental immunology as well as in practical vaccination for more than 60 years. The chemical nature of adjuvants, their mode of action and the profile of their side effects are highly variable. Some of the side effects can be ascribed to an unintentional stimulation of different mechanisms of the immune system whereas others may reflect general adverse pharmacological reactions. The most common adjuvants for human use today are still aluminium hydroxide, aluminium phosphate and calcium phosphate although oil emulsions, products from bacteria and their synthetic derivatives as well as liposomes have also been tested or used in humans. In recent years monophosphoryl lipid A, ISCOMs with Quil-A and Syntex adjuvant formulation (SAF) containing the threonyl derivative of muramyl dipeptide have been under consideration for use as adjuvants in humans. At present the choice of adjuvants for human vaccination reflects a compromise between a requirement for adjuvanticity and an acceptable low level of side effects.

In vivo modulation of atypical mycobacterial infection: adjuvant therapy increases resistance to Mycobacterium avium by enhancing macrophage effector functions

Susceptible BALB/c mice were infected iv with a strain of Mycobacterium avium and infused with different biological response modifiers (BRM) in a gel delivery system so as to modify the progression of the infection in a beneficial fashion. Infusion of IL-2 or IL-4 in hydrophobic gels led to no significant enhancement of resistance. Infusion of muramyl dipeptide in hypromellose led to a significant enhancement of resistance against the M. avium, as seen by a significant reduction of colony-forming units (CFU) in the spleens of infected mice. Similarly, infusion of interleukin-1 beta in hypromellose in infected mice led to a significant reduction in CFU counts in the organs of mice. The mechanism(s) responsible for this enhanced resistance was studied further. It was found that infected mice developed profound immunosuppression, as judged by mitogenic and antigenic stimulation. Mice infused with MDP/hypromellose developed a similar immuno-suppression, suggesting that this adjuvant immunotherapy did not act by stimulating a T-cell response or by abrogating a putative suppressive phenomenon. Macrophages from mice infused with MDP alone were no more bacteriostatic for a virulent M. avium than control cells. However, macrophages from infected mice infused with MDP/hypromellose were more bacteriostatic for M. avium than cells from mice infected with M. avium and infused with the hydrophobic gel only. Overall, these results suggest that adjuvant immunotherapy is beneficial in M. avium infections.

Macrophage activation for antitumour function by muramyl dipeptide-protein conjugates

A muramyl dipeptide (MDP) has been conjugated directly with various proteins by means of a water-soluble carbodiimide. The enhancement of the antitumour activity of mouse peritoneal macrophages by the MDP-protein conjugates has been investigated to assess the ability of the proteins for targeting MDP to the macrophages. These were activated to inhibit the in-vitro growth of tumour cells much more effectively, when immunoglobulin (IgG), fibronectin (FN), and gelatin conjugates were used than when MDP was used alone. The minimum amount of MDP in both the MDP-gelatin and the MDP-IgG conjugates necessary for macrophage activation was approximately 2000 times lower than the amount of free MDP needed. The macrophages activated by the conjugates exhibited growth inhibitory activity against phenotypically diverse tumour cells. The activity induced by the MDP-gelatin conjugate was higher than that of the MDP-IgG conjugate over the range of MDP concentrations, regardless of the isoelectric point of the gelatin used. When MDP was conjugated with bovine serum albumin (BSA), the antitumour activity of macrophages was reduced as the amount of BSA conjugated increased. With both free MDP and MDP-protein conjugates, the macrophages were more strongly activated, the longer they were pretreated. However, less pretreatment time was needed to potentiate macrophage activation by the MDP-gelatin conjugate than by free MDP. Also, the macrophages pretreated with the MDP-gelatin conjugate could maintain their activated state for longer than those pretreated with free MDP. It is concluded that gelatin is an effective carrier protein for the targeting MDP to macrophages, resulting in their activation.

Alteration of aliphatic lipid proton NMR linewidths by malignant tumors in guinea pigs

Water-suppressed proton nuclear magnetic resonance spectroscopy was used to observe plasma lipoprotein lipid methyl and methylene resonances from guinea pigs which had been injected with viable or heat-killed line 1 or line 10 tumor cells or sterile oil. It was shown that the widths of these resonances became significantly sharper as the number of tumor cells grew. Plasma from tumor-free control animals showed no change in the NMR linewidths. It is concluded that the changes observed reflect a specific host response to viable tumor cells, and in these models there is a reciprocal relationship between the number of viable tumor cells and the linewidths of plasma lipoprotein methyl and methylene resonances.

Chemical combination of 6-deoxy-6-mycoloylamino-alpha,alpha-trehalose and N-acetyl-6-O-(aminoacyl)muramoyl dipeptide

6-Deoxy-6-mycoloylamino-alpha,alpha-trehalose, a biologically active derivative of 6,6'-di-O-mycoloyl-alpha,alpha-trehalose (TDM), and N-acetyl-6-O-(aminoacyl)-muramoyl dipeptide (MDP) were joined chemically by a succinic acid unit. The compounds synthesized showed activities that are characteristics of both TDM and MDP.

Lethal toxicity and adjuvant activities of synthetic TDM and its related compounds in mice

Trehalose-6,6'-dimycolate (TDM) and its monosaccharide-type analogues were synthesized, and their lethal and adjuvant activities were examined in mice. All the monosaccharide-type analogues with a glucose or N-acetylglucosamine moiety were devoid of lethal toxicity to mice; in particular, D-GlcNAcM(1-deoxy) and D-GlcNM did not cause any loss of body weight at an early stage after intravenous administration as a 9% oil-in-water emulsion. Intraperitoneal administration of D-GlcNAcM(1-deoxy) in aqueous suspension, as well as TDM, could activate macrophages to become tumoricidal against tumour cells, whereas D-GlcNAcM(1-deoxy) in oil emulsion, unlike TDM, caused no granulomatous formation in the lung after intravenous injection. Squalane-treated D-GlcNAcM(1-deoxy) showed significant inhibition of spontaneous lung metastases by B16-BL6 melanoma cells when it was administered twice intratumorally. The non-toxic monosaccharide-type analogue of TDM [D-GlcNAcM(1-deoxy)] was a beneficial adjuvant for the activation of macrophages and the prevention of cancer metastasis.

Regression of line-10 hepatocellular carcinoma by a less toxic cord factor analogue combined with L18-MDP or synthetic lipid A analogues

A transplantable hepatocarcinoma of strain 2 guinea pigs was used as an experimental model for immunotherapy of cancer. 6,6'-Dideoxy-6,6'-bis-mycoloylamino-alpha,alpha- trehalose (TDNM) was found to be more effective in producing regression of transplantable line-10 tumours than 6,6'-di-O-mycoloyl-alpha,alpha-trehalose (TDM) when combined with 6-O-stearoyl muramyldipeptide (L18-MDP). TDNM showed potent antitumour activity in combination with synthetic lipid A of Escherichia coli (compound 506), but not with the lipid A analogues (GLA-59 and 60). As with the combination of MDP derivative and lipid A analogue, MDP derivatives conjugated with GLA-60 (GMD compounds) showed no tumour regression activity of line-10 cells in guinea-pigs.

Biomedical applications of chromatographic fraction containing trehalose dimycolate in squalane emulsion

Trehalose dimycolate extracted from mycobacteria is a potent immunomodulator. Incorporation of trehalose dimycolate in a squalane-in-water emulsion leads predominantly to the formation of vesicular structures, which are observable by electron microscopy. The interaction between vesicles of trehalose dimycolate and the immunocompetent cells results in an enhancement of the host defence mechanisms and induction of non-specific resistance against viral, parasitic, and bacterial pathogens and certain tumors. A brief review of the pertinent observations is presented.

Modulation of natural killer cytotoxicity by muramyl dipeptide and trehalose dimycolate incorporated in squalane droplets

The effect on natural killer (NK) cytotoxicity of splenic cells from BALB/c mice pretreated i.v. with squalane-in-water preparations of muramyl dipeptide (MDP), trehalose dimycolate (TDM), or the combination of MDP-plus-TDM was investigated. MDP or TDM augmented the NK cytotoxicity which peaked 48 h after the pretreatment whereas the combination of MDP and TDM induced an inhibition of the NK activity. Infection with influenza virus, a potent stimulator of NK cells, after the pretreatment with biological response modifiers resulted in a markedly enhanced NK activity on day 2 in MDP and control groups. Mice pretreated with TDM or the combination of MDP and TDM showed only moderate NK activity which peaked on day 3 after influenza infection. The NK activity was susceptible to asialo GM1 and complement treatment. The cytotoxicity of MDP-plus-TDM cells could be significantly enhanced after treatment with anti-macrophage monoclonal antibody and complement. NK activity induced by MDP or TDM was reduced by mixing MDP-plus-TDM cells. Addition of adherent cell-depleted MDP-plus-TDM suspension to MDP or TDM cells had a NK restorative effect. Splenic cells from mice pretreated 2 days earlier with MDP or TDM, but not MDP-plus-TDM, generated enhanced levels of luminol-dependent chemiluminescence.

Stimulatory effects of muramyl dipeptide and its butyl ester derivative on the proliferation and activation of macrophages in vitro

Muramyl dipeptide (MDP) and the butyl ester derivative, N-acetylmuramyl-L-alanyl-D-glutamine-alpha-n-butyl ester (MDP[Gln]OnBu), were shown to induce the in vitro proliferation of oil-induced guinea pig peritoneal exudate cells (PEC). Both agents induced 10-20 fold increases in tritiated thymidine incorporation in PEC cultures. The maximal effects occurred in 72 h cultures stimulated with either 0.1 microgram MDP or 10 micrograms MDP[Gln]OnBu. The mitogenic effects of MDP appeared to be mediated by a macrophage product detected in the supernatants of MDP-stimulated cultures. Supernatants of MDP- or MDP[Gln]OnBu-stimulated PEC cultures were also inhibitory to normal fibroblast growth and cytotoxic to L929 tumor cells. These results indicated that these agents may stimulate macrophages by modulating secretory functions. In addition, either peptidoglycan was capable of activating bactericidal activity in in vitro macrophage cultures. Initial studies of possible mechanisms of action revealed an early increase in the level of cyclic GMP. The possible role of cyclic GMP in mediating the stimulation of macrophage secretory processes is discussed.

Trehalose dimycolate from various mycobacterial species induces differing anti-infectious activities in combination with muramyl dipeptide

Significant resistance against influenza virus and Mycobacterium tuberculosis infections was induced when trehalose dimycolate from M. tuberculosis or M. bovis but not M. avium was combined with muramyl dipeptide. Trehalose dimycolate from M. tuberculosis, in contrast to that from M. avium, could confer resistance against Toxoplasma gondii infections.

Prevention of oncogenic viral infections in mice with CGP 11637, a synthetic muramyl dipeptide analog

The efficacy of N-acetyl-nor-muramyl-L-alanyl-D-isoglutamine (nor-MDP) in controlling viral oncogenesis in mice was investigated. The tumors studied were blood cell malignancies induced by Friend leukemia virus in SJL/J mice, spontaneous mammary neoplasms in RIII/Imr and C3H/OuJ mice, and spontaneous lymphocytic leukemia in AKR/J mice. A transplantable tumor, Lewis lung carcinoma, in C57BL/6J mice was used as a nonvirally induced control model. The nor-MDP was dissolved in saline and made into an emulsion with an equal volume of squalene-Arlacel A and injected subcutaneously at 1- to 2-month intervals. Test and control mice were challenged with exogenous virus or tumor transplant 2 weeks after a second injection of nor-MDP. Administration was started at around 2 months of age in mice that develop spontaneous neoplasms. Electron microscopy studies were done on neoplastic tissues of selected test and control mice. This administration of nor-MDP prevented erythroleukemia in SJL/J mice caused by low doses of Friend leukemia virus (although erythroleukemia survivors were not protected from a late-developing lymphoma) and also delayed (possibly prevented) the development of a spontaneous mammary neoplasm in RIII/Imr mice. No antitumor effects were observed on the spontaneous neoplasms of C3H/OuJ and AKR/J mice or on the Lewis lung carcinoma implanted into C57BL/6J mice. Electron microscopic examinations of the various neoplastic tissues indicated that nor-MDP administration eliminated or reduced extracellular viruses. The results suggested that under the experimental conditions used nor-MDP appears to effect the viruses and not the malignant cells per se.

Immunopotentiating conjugates

Current interest in the development of sub-cellular vaccines and in cancer immunotherapy has rekindled interest in immunopotentiating agents. In addition, peptide sequences of protective antigens are being synthesized or genetically engineered and it is likely that these peptides will have a small relative molecular mass and be non-immunogenic by themselves. A variety of experimental studies have shown that such protective antigens could be included in conjugated vaccines with carrier protein and/or immunopotentiator. The insertion of peptides with hydrophobic sequences into artificial lipid bilayers (liposomes) offers another mode of presentation of antigen to the immune system.

Inhibition of tumor growth in mice treated with synthetic muramyl dipeptide

Treatment with synthetic MDP inhibited growth of transplantable, chemically induced tumors in syngeneic mice. The tumor-inhibitory effect was dependent on the schedule of MDP administration. Growth of SC transplants of a nonmetastasizing, MC-induced fibrosarcoma, MC11, was inhibited by local treatment with 200 micrograms and 1,000 micrograms MDP given SC 5-7 weeks before challenge. Treatment with lower (10 micrograms and 100 micrograms) doses of MDP and shorter (1-4 weeks) time intervals was not effective. Single doses of MDP (10-1,000 micrograms) 1-3 weeks after challenge had no effect. Growth of IV-inoculated, metastasizing AAT-induced hepatoma A was inhibited by IV injections of 20 micrograms MDP given 1 and 2 days prior to the challenge. Significant increases in the survival of hepatoma-bearing mice were observed only after injections of MDP incorporated in multilamellar liposomes.

Selective macrophage activation by muramyldipeptide bound to monoclonal antibodies specific for mouse tumor cells

IgM monoclonal antibodies directed against tumor cells which do not mediate antibody-dependent macrophage cytotoxicity (ADMC) even when they are cytotoxic in the presence of complement, have been shown to render macrophages tumoricidal when they carry an immunomodulating agent, i.e., muramyldipeptide (MDP). This statement is based on experiments using two IgM monoclonal antibodies selected for their ability to bind L1210 leukemia cells (F2-10-23-IgM) and 3LL Lewis lung carcinoma cells (6B6-IgM) specifically, as shown by flow cytofluorometry analysis. The MDP-IgM conjugates, containing 45 MDP molecules per IgM molecule, were prepared by allowing MDP-hydroxy-succinimide ester to react with IgM monoclonal antibodies. The MDP-IgM conjugates are shown to bind to relevant tumor cells and to induce the activation of thioglycolate-elicited peritoneal mouse macrophages leading to 80% growth inhibition of target cells at optimum concentrations of bound MDP. These concentrations of bound MDP were 10 times lower than the concentration of free MDP, giving a maximum activation that is limited to 20% growth inhibition. No macrophage activation was evidenced when tumor cells were incubated in the presence of irrelevant MDP-IgM conjugates and macrophages or when macrophages were preincubated in the presence of MDP-IgM conjugates and then incubated in the presence of relevant or irrelevant tumor cells but in the absence of the MDP-IgM conjugates. The reported results are discussed with reference to the mechanism of activation of macrophage by muramyldipeptide and to the usefulness of such MDP-IgM conjugates as potential antitumor agents in cancer therapy.

Stimulation of chemiluminescence and resistance against aerogenic influenza virus infection by synthetic muramyl dipeptide combined with trehalose dimycolate

The effect on respiratory burst of splenic cells from mice pretreated with oil-in-water emulsions of muramyl dipeptide (MDP), trehalose dimycolate (TDM), or the combination of MDP with TDM was studied by luminol-dependent chemiluminescence in response to stimulation by zymosan. Spleen cells from mice pretreated with TDM, but not those of mice treated with MDP, generated increased chemiluminescence. Spleen cells from animals pretreated with the combination of MDP and TDM exhibited markedly enhanced chemiluminescence activity. The effect of enhanced activity of preparations containing MDP combined with TDM was further examined in vivo by an aerosol infection of pretreated mice with a mouse-pathogenic influenza virus. Pretreatment with 6-O-acyl analogs and one ubiquinone derivative of MDP alone did not induce any resistance against influenza virus. Significant protection was conferred only when MDP and certain analogs were combined with TDM. The enhancement of nonspecific resistance to influenza virus infection was related to the chemical structure of the synthetic immunostimulant. A greater degree of protection was induced by the combination of TDM with the lipophilic derivatives like B 30-MDP and L-18 MDP.

Opposite effects of the synthetic immunomodulator, muramyl dipeptide, on rejection of mouse skin allografts

The influence of muramyl dipeptide (N-acetylmuramyl-L-alanyl-D-isoglutamine) on the rejection of mouse skin allografts was investigated. While the 0.1-mg dose administered on days 7, 6, 5 prior to transplantation caused significant prolongation of the graft survival, the 0.5-mg dose administered on days 3, 2, 1 prior to transplantation resulted in remarkable augmentation of the graft rejection. The present results support the view that muramyl dipeptide can induce both stimulatory and suppressive immune mechanisms, depending on the treatment regimen.

Immunotherapy of B-16 melanoma with peptidoglycan monomer

B-16 melanoma-bearing mice received intravenously or intratumorally one or multiple injections of peptidoglycan monomer (PGM) derived from Brevibacterium divaricatum cell wall. Multiple injections of this non-toxic, water-soluble, low-molecular-weight peptidoglycan reduced the growth rate of tumor nodule on the leg, but did not significantly prolong the survival of tumor-bearing mice. One milligram of PGM administered 3 or 7 days after tumor inoculation inhibited formation of pulmonary metastases, induced either by intravenous injection of malignant cells or seeded spontaneously from tumor nodules in the legs before amputation. The inhibition reached about 50% of control values in saline-treated mice. Addition of PGM to in vitro cultures of B-16 melanoma cells did not change their growth rate. The phagocytic activity in the lungs, but not in the spleen and liver, was significantly augmented 3 and 7 days after treatment with PGM. These data indicate that the antimetastatic potency of PGM is probably due to activation of local (pulmonary) macrophages and not due to direct cytotoxic effects on B-16 melanoma cells or to activation of systemic antineoplastic defence.

Enhanced superoxide anion release from phagocytes by muramyl dipeptide or lipopolysaccharide

Muramyl dipeptide (MDP) and lipopolysaccharide (LPS) from Escherichia coli were tested for the ability to influence superoxide anion (O2-) release from guinea pig phagocytes. Both MDP and LPS alone did not, by themselves, stimulate O2- release by macrophages and polymorphonuclear leukocytes. However, the preincubation of macrophages with MDP or LPS primed the macrophages to release an enhanced amount of O2- when stimulated by cytochalasin E and wheat germ agglutinin. When polymorphonuclear leukocytes were treated in the same way, only LPS showed an enhancing effect. MDP enhanced NADPH oxidase activity of macrophages, which is probably the reason for enhanced O2- release by MDP.

Muramyl dipeptides: prospect for cancer treatments and immunostimulation

The immunopharmacological activities of bacterial cell walls and muramyl peptides were collected in table form with a comprehensive literature. The past and present studies emphasizing the host-defense enhancing activities of muramyl peptides for antitumor immunotherapy were surveyed along three possible approaches: 1) the nonspecific enhancement of natural defense ability of host against tumor cells themselves; 2) the enhancement of nonspecific resistance of host to microbial infections which are frequently encountered and difficult to treat in the advanced stage of tumor patients; and 3) the stimulation of immunity against tumor-specific or tumor-associated immunogens. Finally, the prospects of successful antitumor immunotherapy with muramyl peptides and their derivatives was discussed.

Synthesis of carbohydrate analogs (positional, configurational, and optical) of n-acetylmuramoyl-L-alanyl-D-isoglutamine, and their immunoadjuvant activities

2-Acetamido-2-deoxy-4- and -6-O-(D-2-propanoyl-L-alanyl-D-isoglutamine)-D-glucopyranose, 2-acetamido-2-deoxy-3-O-(D-2-propanoyl-L-alanyl-D-isoglutamine)-D-allopyranose, -D-gulopyranose, -D-galactopyranose, -D-mannopyranose, and -L-idopyranose, and 3-O-(D-2-propanoyl-L-alanyl-D-isoglutamine)-D- and -L-glucopyranose were synthesized, in order to clarify the structural requirements for the immunoadjuvant activity of the carbohydrate moiety in N-acetylmuramoyl-L-alanyl-D-isoglutamine. Immunoadjuvant activity of the N-acetylmuramoyl-dipeptide analogs was examined in guinea-pigs.

Immunotherapy of experimental cancer with a mixture of synthetic muramyl dipeptide and trehalose dimycolate

The antitumor activity of a mixture of synthetic N-acetylmuramyl-L-alanyl-D-isoglutamine (MDP) and trehalose-6,6'-dimycolate (TDM) (MDP+TDM) in emulsified form was studied in guinea pigs, each with a syngeneic dermal tumor and microscopically detectable metastases in regional lymph nodes. A single intralesional administration of an ultrasonically prepared emulsion containing MDP+TDM in squalane or in mineral oil caused tumor regression and elimination of lymph node metastases. Similar emulsions of MDP+TDM made with squalene or hexadecane were immunotherapeutically inactive.

Eradication of spontaneous metastases and activation of alveolar macrophages by intravenous injection of liposomes containing muramyl dipeptide

The multiple systemic administration of multilamellar liposomes composed of phosphatidylserine and phosphatidylcholine (molar ratio 3:7) that contained water-soluble muramyl dipeptide (MDP) activated alveolar macrophages to become tumoricidal and eradicated established spontaneous pulmonary and lymph node metastases. Spontaneously metastasizing melanoma cells were injected into the footpads of mice. After 4-5 weeks, the tumors were resected by a midfemoral amputation; 3 days later, twice-weekly injections of liposomes were initiated and continued for 4 weeks. In some experiments the mice were killed 2 weeks after the final treatment. Seventy-four percent of animals injected with liposomes containing MDP were free of visible metastases. In a separate life-span experiment, 60% of mice treated with liposome-encapsulated MDP were tumor-free 120 days after the last liposome treatment or 110 days after all control mice treated with free MDP or control liposome preparations had died of disseminated cancer. These data suggest that the systemic administration of liposomes containing MDP, or similar compounds that produce macrophage activation, may provide an additional useful approach to the therapeutic regimens currently used to eradicate cancer metastases.

Activation of macrophages for enhanced release of superoxide anion and greater killing of Candida albicans by injection of muramyl dipeptide

The adjuvant muramyl dipeptide (MDP) has been shown to affect a number of macrophage functions in vitro. We studied the effect of subcutaneous injection of MDP into mice. Cultured peritoneal macrophages from treated mice displayed increased spreading, total cell protein, and specific activity of beta-glucosaminidase a constituent of macrophage lysosomes, and of lactate dehydrogenase. Generation of superoxide anion (O2-) by MDP-treated macrophages stimulated by contact with phorbol myristate acetate was enhanced by over fivefold to levels achieved by macrophages from bacillus Calmette-Guérin-infected mice. The enhancement in stimulated O2- release was noted by 1 h after injection of MDP, peaked by 3 h, and remained high for at least 48 h. Priming for enhancement of O2- release by MDP was similar in athymic nude mice and in normal littermates, suggesting that mature T lymphocytes are not involved in this MDP effect. Priming for enhanced stimulated O2- release, and morphologic and enzymic changes, were not achieved by injection of the D-D stereoisomer of MDP. Phagocytosis of Candida albicans was only slightly greater by macrophages from mice give MDP, but MDP-stimulated cells killed two times more C. albicans in vitro than did cells from untreated animals. When MDP was given 18 h before, simultaneously with, or 24 h after lethal infectious challenge with C. albicans, treated mice were protected compared with controls. These results suggest that injection of MDP effectively and rapidly activates macrophages in the recipient animal. This agent should serve as an important probe of macrophage physiology and, perhaps ultimately, as a means of enhancing host defense in humans.

Comparison of muramyl dipeptide, trehalose dimycolate, and dimethyl dioctadecyl ammonium bromide as adjuvants in Brucella abortus 45/20 vaccines

The capacity of trehalose dimycolate (TDM), muramyl dipeptide (MDP), and dimethyl dioctadecyl ammonium bromide (DDA)--alone or in combination--to potentiate the immunogenicity of killed Brucella abortus 45/20 bacteria was studied in guinea pigs. Bacterins that contained TDM in oil droplet emulsion were as effective in the prevention of brucellosis as those emulsified in Freund complete adjuvant, wereas bacterins that contained a combination of TDM and MDP were most effective. Vaccinal emulsions of bacteria and MDP were ineffective in the prevention of splenic infections. Likewise, DDA was unable to potentiate acquired resistance to Brucella. Addition of DDA to 1% oil emulsions of bacteria, TDM, and MDP eliminated protection. Adjuvants without bacteria were not able to nonspecifically protect animals from infection, although TDM was able to significantly reduce the numbers of splenic Brucella. A positive correlation (P < 0.0001) between splenic infection and splenic weight was found.