Immunopharmacological activities and clinical development of muramyl peptides with particular emphasis on murabutide

Anti-neoplastic and immunomodulatory potency of co-treatment based on bovine lactoferrin and/or muramyl dipeptide in tumor-bearing mice

The current study investigates anti-neoplastic and immunomodulatory activities of co-treatment based on bovine lactoferrin (bLF) and/or muramyl dipeptide (MDP) with or without cisplatin (Cis) in tumor-bearing mice. In the present study, bLF (100 mg/kg; orally) and MDP (0.5 mg/kg; subcutaneously) was administered alone or together. MDP or bLF was co-treated with Cis (1 mg/kg; intraperitoneally) in mice-bearing Ehrlich solid carcinoma. Tumor size, tumor mass proliferation, apoptosis using immunohistochemistry, the alteration in spleen cell proliferation, phenotype using flow cytometry and white blood cells total and differential counts were detected. Treatment with Cis or (bLF and MDP) significantly reduced tumor size, upregulated the pro-apoptotic p53 expression and downregulated the anti-apoptotic Bcl-2 and proliferative marker PCNA expression compared to non-treated tumor-bearing animals. Moreover, co-treatment of MDP and Cis significantly potentiated the reduction of the tumor size, downregulated the Bcl-2 and PCNA expression and upregulated the p53 expression compared to Cis-treated animals. While bLF and Cis co-treatment positively controlled PCNA and p53 expression compared to tumor-bearing animals, it significantly potentiated the reduction of the tumor size and downregulated the Bcl-2 expression compared to Cis-treated animals. Co-treatment of (bLF and MDP), (bLF and Cis) or (MDP and Cis) increased the spleen cell proliferation and altered the immunological profile of the CD3⁺CD4⁺, CD3⁺CD8⁺, CD3⁺CD4⁺CD69⁺, CD3⁺CD8⁺CD69⁺ and CD11b⁺Ly6G⁺ cells to achieve better immune response against tumor. In conclusion, co-treatments based on bLF and/or MDP are promising therapies against cancer, through their potency to control proliferation, enhance apoptosis and improve the immune status against tumor cells.

Harnessing the untapped potential of nucleotide-binding oligomerization domain ligands for cancer immunotherapy

In the last decade, cancer immunotherapy has emerged as an effective alternative to traditional therapies such as chemotherapy and radiation. In contrast to the latter, cancer immunotherapy has the potential to distinguish between cancer and healthy cells, and thus to avoid severe and intolerable side‐effects, since the cancer cells are effectively eliminated by stimulated immune cells. The cytosolic nucleotide‐binding oligomerization domains 1 and 2 receptors (NOD1 and NOD2) are important components of the innate immune system and constitute interesting targets in terms of strengthening the immune response against cancer cells. Many NOD ligands have been synthesized, in particular NOD2 agonists that exhibit favorable immunostimulatory and anticancer activity. Among them, mifamurtide has already been approved in Europe by the European Medicine Agency for treating patients with osteosarcoma in combination with chemotherapy after complete surgical removal of the primary tumor. This review is focused on NOD receptors as promising targets in cancer immunotherapy as well as summarizing current knowledge of the various NOD ligands exhibiting antitumor and even antimetastatic activity in vitro and in vivo.

NOD1 and NOD2: Molecular targets in prevention and treatment of infectious diseases

Nucleotide-binding oligomerization domain (NOD) 1 and NOD2 are pattern-recognition receptors responsible for sensing fragments of bacterial peptidoglycan known as muropeptides. Stimulation of innate immunity by systemic or local administration of NOD1 and NOD2 agonists is an attractive means to prevent and treat infectious diseases. In this review, we discuss novel data concerning structural features of selective and non-selective (dual) NOD1 and NOD2 agonists, main signaling pathways and biological effects induced by NOD1 and NOD2 stimulation, including induction of pro-inflammatory cytokines, type I interferons and antimicrobial peptides, induction of autophagy, alterations of metabolism. We also discuss interactions between NOD1/NOD2 and Toll-like receptor agonists in terms of synergy and cross-tolerance. Finally, we review available animal data on the role of NOD1 and NOD2 in protection against infections, and discuss how these data could be applied in human infectious diseases.

Differential regulation of surface receptor expression, proliferation, and apoptosis in HaCaT cells stimulated with interferon-γ, interleukin-4, tumor necrosis factor-α, or muramyl dipeptide

Keratinocytes are routinely subjected to both internal and external stimulation. This study investigates the effects of interferon gamma, interleukin-4, tumor necrosis factor alpha, and the synthetic immunomodulator muramyl dipeptide on the human keratinocyte cell line, HaCaT. Following HaCaT stimulation with cytokines or muramyl dipeptide for different time periods, changes in the expression of different cell surface receptors, cell proliferation, and cell apoptosis were evaluated by flow cytometry, tritiated thymidine uptake, and annexin-V staining, respectively. A significant decrease in the expression of CD49d was found upon treatment with interleukin-4. Interferon gamma and tumor necrosis factor alpha increased the expression of intercellular adhesion molecule 1 and major histocompatibility complex class I, whereas major histocompatibility complex class II and CD1b were only upregulated by interferon gamma. Interferon gamma and tumor necrosis factor alpha had opposite effects regarding CD119 expression, with the former downregulating, while the latter upregulating its expression. Of the stimuli tested, only interferon gamma and tumor necrosis factor alpha significantly inhibited proliferation of HaCaT cells, yet only interferon gamma played a significant role in inducing HaCaT cell apoptosis. Our data demonstrate differential effects of the three tested cytokines on keratinocytes and reveal that the absence of HaCaT cell responses to muramyl dipeptide is associated with undetectable levels of its cytoplasmic receptor, nucleotide-binding oligomerization domain-containing protein 2.

Advax-adjuvanted recombinant protective antigen provides protection against inhalational anthrax that is further enhanced by addition of murabutide adjuvant

Subunit vaccines against anthrax based on recombinant protective antigen (PA) potentially offer more consistent and less reactogenic anthrax vaccines but require adjuvants to achieve optimal immunogenicity. This study sought to determine in a murine model of pulmonary anthrax infection whether the polysaccharide adjuvant Advax or the innate immune adjuvant murabutide alone or together could enhance PA immunogenicity by comparison to an alum adjuvant. A single immunization with PA plus Advax adjuvant afforded significantly greater protection against aerosolized Bacillus anthracis Sterne strain 7702 than three immunizations with PA alone. Murabutide had a weaker adjuvant effect than Advax when used alone, but when murabutide was formulated together with Advax, an additive effect on immunogenicity and protection was observed, with complete protection after just two doses. The combined adjuvant formulation stimulated a robust, long-lasting B-cell memory response that protected mice against an aerosol challenge 18 months postimmunization with acceleration of the kinetics of the anamnestic IgG response to B. anthracis as reflected by ∼4-fold-higher anti-PA IgG titers by day 2 postchallenge versus mice that received PA with Alhydrogel. In addition, the combination of Advax plus murabutide induced approximately 3-fold-less inflammation than Alhydrogel as measured by in vivo imaging of cathepsin cleavage resulting from injection of ProSense 750. Thus, the combination of Advax and murabutide provided enhanced protection against inhalational anthrax with reduced localized inflammation, making this a promising next-generation anthrax vaccine adjuvanting strategy.

Intranasal vaccination with murabutide enhances humoral and mucosal immune responses to a virus-like particle vaccine

Murabutide (MB) is a synthetic immunomodulator recognized by the nucleotide-binding oligomerization domain-containing protein 2 (NOD2) receptor on mammalian cells. MB has previously been approved for testing in multiple human clinical trials to determine its value as an antiviral therapeutic, and as an adjuvant for injected vaccines. We have found a new use for this immunomodulator; it functions as a mucosal adjuvant that enhances immunogenicity of virus-like particles (VLP) administered intranasally. MB enhanced Norwalk virus (NV) VLP-specific IgG systemically and IgA production at distal mucosal sites following intranasal (IN) vaccination. A dose escalation study identified 100 µg as the optimal MB dosage in mice, based on the magnitude of VLP-specific IgG, IgG1, IgG2a and IgA production in serum and VLP-specific IgA production at distal mucosal sites. IN vaccination using VLP with MB was compared to IN delivery VLP with cholera toxin (CT) or gardiquimod (GARD) and to parenteral VLP delivery with alum; the MB groups were equivalent to CT and GARD and superior to alum in inducing mucosal immune responses and stimulated equivalent systemic VLP-specific antibodies. These data support the further testing of MB as a potent mucosal adjuvant for inducing robust and durable antibody responses to non-replicating subunit vaccines.

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.

Muramyl dipeptide and its derivatives: peptide adjuvant in immunological disorders and cancer therapy

Muramyl dipeptide (MDP) is a synthetic immunoreactive peptide consisting of N-acetyl muramic acid attached to a short amino acid chain of L-Ala-D-isoGln. It was first identified in bacterial cell wall peptidoglycan as an active component in Freund's complete adjuvant. In the cell, MDP is detected by NOD2, a cytoplasmic receptor belonging to the human innate immune system. NOD2 mutations are frequently observed in patients with Crohn's disease, an autoimmune disorder, suggesting the significance of the MDP-NOD2 pathway in activating immunity. For this reason, structural modifications of MDP and its derivatives have been extensively studied in an attempt to increase adjuvant activity and boost the immune response effectively for clinical use in the treatment of cancer and other diseases. This review summarizes the synthetic chemistry of MDP and its derivatives and discusses their pharmacological action and stereoselective synthesis.

Muramyl-dipeptide-induced mitochondrial proton leak in macrophages is associated with upregulation of uncoupling protein 2 and the production of reactive oxygen and reactive nitrogen species

The synthetic immunomodulator muramyl dipeptide (MDP) has been shown to induce, in vivo, mitochondrial proton leak. In the present work, we extended these findings to the cellular level and confirmed the effects of MDP in vitro on murine macrophages. The macrophage system was then used to analyse the mechanism of the MDP-induced mitochondrial proton leak. Our results demonstrate that the cellular levels of superoxide anion and nitric oxide were significantly elevated in response to MDP. Moreover, isolated mitochondria from cells treated with MDP presented a significant decrease in respiratory control ratio, an effect that was absent following treatment with a non-toxic analogue such as murabutide. Stimulation of cells with MDP, but not with murabutide, rapidly upregulates the expression of the mitochondrial protein uncoupling protein 2 (UCP2), and pretreatment with vitamin E attenuates upregulation of UCP2. These findings suggest that the MDP-induced reactive species upregulate UCP2 expression in order to counteract the effects of MDP on mitochondrial respiratory efficiency.

[A protein interaction network and cell signaling pathways activated by muramyl peptides]

Review is devoted to studying the interaction muramyl peptides with protein components of immune system cells. Systems analysis of published results may be useful to select not only the strategy to further explore the function of this class of glycopeptides, but their use in clinical practice.

Effect of muramyl peptides on mitochondrial respiration

Muramyl peptides have been shown to exert several biological activities including potentiation of humoral and cell-mediated immunity and stimulation of natural resistance. The mode of action of muramyl peptides has not been elucidated fully and the immunological activities of some derivatives have been associated with toxic effects, including pyrogenicity and inflammatory reactions. Nevertheless, the impact of muramyl peptides on mitochondrial respiration has never been addressed. In this study, the in vitro effects of muramyl peptides on rat liver mitochondria were examined. Toxic muramyl peptides induced a significant decrease in respiratory control ratio versus non-toxic analogues. These results were confirmed by in vivo studies in mice and were extended to mitochondria isolated from spleens. Our data address, for the first time, the effect of muramyl peptides on mitochondrial bioenergetics. Further studies are required to reveal the mechanism of mitochondrial toxicity in relation to the damaging effects of toxic muramyl peptides.

Exosomes as Potent Cell-Free Peptide-Based Vaccine. II. Exosomes in CpG Adjuvants Efficiently Prime Naive Tc1 Lymphocytes Leading to Tumor Rejection

Ideal vaccines should be stable, safe, molecularly defined, and out-of-shelf reagents efficient at triggering effector and memory Ag-specific T cell-based immune responses. Dendritic cell-derived exosomes could be considered as novel peptide-based vaccines because exosomes harbor a discrete set of proteins, bear functional MHC class I and II molecules that can be loaded with synthetic peptides of choice, and are stable reagents that were safely used in pioneering phase I studies. However, we showed in part I that exosomes are efficient to promote primary MHC class I-restricted effector CD8(+) T cell responses only when transferred onto mature DC in vivo. In this work, we bring evidence that among the clinically available reagents, Toll-like receptor 3 and 9 ligands are elective adjuvants capable of triggering efficient MHC-restricted CD8(+) T cell responses when combined to exosomes. Exosome immunogenicity across species allowed to verify the efficacy of good manufactory procedures-manufactured human exosomes admixed with CpG oligonucleotides in prophylactic and therapeutic settings of melanoma in HLA-A2 transgenic mice. CpG adjuvants appear to be ideal adjuvants for exosome-based cancer vaccines.

Differentially expressed genes in HIV-1-infected macrophages following treatment with the virus-suppressive immunomodulator murabutide

The synthetic immunomodulator murabutide has been found to suppress human immunodeficiency virus type-1 (HIV-1) replication, in macrophages, through a regulated expression of cellular factors needed at different steps in the virus replication cycle. To identify cellular genes implicated in the murabutide-induced virus inhibition, we have carried out a differential display analysis on HIV-1-infected macrophages that were treated, or not, with murabutide. Sequencing of the differentially regulated cDNA bands and verification of the reproducibility of the murabutide effects, by reverse transcription-polymerase chain reaction or by Northern blotting, revealed an up-regulated expression of 21 genes and a down-regulation of seven others. The murabutide-regulated genes encoded proteins implicated in DNA binding, regulation of transcription, oxidative stress, metal binding, and other physiological functions. Six of the genes corresponded to unassigned/expressed sequence tags with yet unknown function. Among the genes which were up-regulated by murabutide and with established effects on inhibiting virus transcription, was the octamer binding factor 1 (Oct-1). We demonstrate the ability of murabutide to induce enhanced Oct-1 protein expression and DNA-binding activity in macrophages. Furthermore, our findings suggest the potential implication of additional transcription factors and metal-binding proteins in mediating the inhibitory effect of murabutide on virus transcription.

A novel cellular RNA helicase, RH116, differentially regulates cell growth, programmed cell death and human immunodeficiency virus type 1 replication

In an effort to define novel cellular factors regulating human immunodeficiency virus type 1 (HIV-1) replication, a differential display analysis has been performed on endogenously infected cells stimulated with the HIV-suppressive immunomodulator Murabutide. In this study, the cloning and identification of a Murabutide-downregulated gene, named RH116, bearing classical motifs that are characteristic of the DExH family of RNA helicases, are reported. The 116 kDa encoded protein shares 99·9 % similarity with MDA-5, an inducible RNA helicase described recently. Ectopic expression of RH116 in HeLa-CD4 cells inhibited cell growth and cell proliferation but had no measurable effect on programmed cell death. RH116 presented steady state cytoplasmic localization and could translocate to the nucleus following HIV-1 infection. Moreover, the endogenous expression of RH116, at both the transcript and protein levels, was found to be considerably upregulated after infection. Overexpression of RH116 in HIV-1-infected HeLa-CD4 cells also resulted in a dramatic increase in the level of secreted viral p24 protein. This enhancement in virus replication did not stem from upregulated proviral DNA levels but correlated with increased unspliced and singly spliced viral mRNA transcripts. These findings implicate RH116 in the regulation of HIV-1 replication and point to an apoptosis-independent role for this novel helicase in inducing cell growth arrest.

Clinical tolerance and immunologic effects after single or repeated administrations of the synthetic immunomodulator murabutide in HIV-1-infected patients

Correction of the virus-induced deficits in innate immunity of HIV-infected subjects could well contribute to enhanced immune recovery and efficacious control of viral replication. The safe synthetic immunomodulator Murabutide (ISTAC Biotechnology, Lille, France) has been found to regulate the function of antigen-presenting cells and to selectively activate CD4 lymphocytes leading to dramatic suppression of HIV replication, in vitro. Therefore, as a first step toward the evaluation of the immunotherapeutic potential of Murabutide in HIV disease, we have conducted two phase 1/2 clinical trials to address the safety and the immunologic effects of Murabutide administration into HIV-infected subjects receiving antiretroviral therapy. The first study revealed that single administration of 5, 7, or 9 mg of Murabutide, to 6 patients per dose, was well tolerated. This was accompanied by a selective induction of cytokines and chemokines detectable in the serum, and the levels appeared to plateau at the 7-mg dose. The second study then evaluated the safety and biological effects of repeated administrations of 7 mg Murabutide, on 5 consecutive days, in 12 HIV-1-infected patients. A good clinical tolerance was noted throughout the study. Moreover, changes in several immune parameters, including downregulation of coreceptor expression on lymphocytes and improved lymphoproliferative responses, were detected during or/and up to 3 weeks after Murabutide administration. These encouraging results warrant further evaluation of longer periods or cycles of immunotherapy with Murabutide in HIV-infected subjects.

The transcriptional response of human macrophages to murabutide reflects a spectrum of biological effects for the synthetic immunomodulator

The synthetic immunomodulator murabutide (MB) presents multiple biological activities with minimal toxicity in animals and in man. Although MB is known to target cells of the reticuloendothelial system and to regulate cytokine synthesis, the molecular mechanisms underlying several of its biological effects are still largely unknown. In an effort to define cellular factors implicated in the immunomodulatory and HIV-suppressive activities of MB, we have undertaken profiling the regulated expression of genes in human monocyte-derived macrophages (MDM) following a 6-h stimulation with this synthetic glycopeptide. Oligonucleotide microarray analysis was performed on RNA samples of differentiated MDM from four separate donors, using probe sets corresponding to 1081 genes. We have identified, in a reproducible fashion, the enhanced expression of 40 genes and the inhibition of 16 others in MB-treated MDM. These regulated genes belonged to different families of immune mediators or their receptors, transcription factors and kinases, matrix proteins and their inhibitors, ion channels and transporters, and proteins involved in cell metabolic pathways. Additional verification of the regulated expression of selected genes was carried out using Northern blots or the quantification of released proteins in MDM cultures. The profile of MB-regulated genes in MDM provides a molecular basis for some of its previously reported biological activities, and reveals new set of genes targeted by the immunomodulator suggesting potential application in novel therapeutic indications.

Clinical tolerance and profile of cytokine induction in healthy volunteers following the simultaneous administration of ifn-alpha and the synthetic immunomodulator murabutide

As the therapeutic use of interferon-alpha (IFN-alpha) is limited by a dose-dependent toxicity and variable efficacy, ways of improving the therapeutic index of the cytokine are being sought. Murabutide (N-acetyl muramyl-L-alanyl-D-glutamine-O-n-butyl-ester) (ISTAC Biotechnology, Lille, France) is a safe synthetic and clinically acceptable immunomodulator that enhances the biologic activities of IFN-alpha in different experimental models. We evaluated in healthy human volunteers tolerance of the coadministration of Murabutide with increasing doses of IFN-alpha. The simultaneous administration of the two drugs was well tolerated without any increased or prohibiting toxicity, and all recipients experienced side effects that were similar to those observed after the administration of IFN-alpha alone. We also profiled the serum levels of cytokines induced following coinjection of the two drugs. We mostly detected an induction of anti-inflammatory cytokines and of human immunodeficiency virus type 1 (HIV-1)-suppressive beta-chemokines, in the absence of release of key proinflammatory cytokines. Therefore, the simultaneous administration of Murabutide and IFN-alpha is well tolerated and does not lead to increased toxicity. In addition, the selectivity in the profile of cytokines and chemokines induced following the coadministration of Murabutide and IFN-alpha points to the potential use of this combination in the treatment of inflammatory diseases and chronic viral infections.

Enhanced maturation and functional capacity of monocyte-derived immature dendritic cells by the synthetic immunomodulator Murabutide

Murabutide is a safe synthetic immunomodulator derived from muramyl dipeptide, the smallest bioactive unit of bacterial peptidoglycan. Although it is well known that muramyl peptides modulate the functions of monocytes/macrophages, their activity on dendritic cells is poorly documented. We thus investigated the effects of Murabutide on immunophenotype, endocytosis, T-cell stimulatory capacity, and cytokine secretion of human monocyte-derived immature dendritic cells (iDCs). We found that Murabutide triggers immunophenotypic changes as upon treatment, iDCs up-regulate the surface expression of the major histocompatibility complex type II molecule human leucocyte antigen-DR, the co-stimulatory molecules CD80, CD86 and CD40 and the differentiation marker CD83, and down-regulate the expression of the mannose receptor. These phenotypic changes are also mirrored by changes in their biological activity. Subsequent to treatment with the synthetic immunomodulator, DC have a decreased endocytic capacity but exhibit enhanced stimulatory capacity for both allogeneic and autologous T cells. In addition, Murabutide-stimulated iDCs have a greater cytostatic activity toward the tumour cell line THP-1. Furthermore, in the presence of Murabutide, DCs transiently increased the release of macrophage inhibitory protein-1 beta, tumour necrosis factor-alpha and interleukin-10, whereas the enhanced production of macrophage-colony stimulating factor was sustained over the 3-day period analysed. In addition, Murabutide triggers the phosphorylation of the three classes of mitogen-activated protein kinases in iDCs. Altogether our results demonstrate that Murabutide triggers the maturation and activation of monocyte-derived iDCs. As this immunomodulator is approved for administration in humans, it could be a useful adjunct to boost the efficacy of DC-based vaccines designed against tumours or virus-infected cells.

Selective regulation of human immunodeficiency virus-infected CD4(+) lymphocytes by a synthetic immunomodulator leads to potent virus suppression in vitro and in hu-PBL-SCID mice

We have previously observed that the synthetic immunomodulator Murabutide inhibits human immunodeficiency virus type 1 (HIV-1) replication at multiple levels in macrophages and dendritic cells. The present study was designed to profile the activity of Murabutide on CD8-depleted phytohemagglutinin-activated lymphocytes from HIV-1-infected subjects and on the outcome of HIV-1 infection in severe combined immunodeficiency mice reconstituted with human peripheral blood leukocytes (hu-PBL-SCID mice). Maintaining cultures of CD8-depleted blasts from 36 patients in the presence of Murabutide produced dramatically reduced levels of viral p24 protein in the supernatants. This activity correlated with reduced viral transcripts and proviral DNA, was evident in cultures harboring R5, X4-R5, or X4 HIV-1 isolates, was not linked to inhibition of cellular DNA synthesis, and did not correlate with beta-chemokine release. Moreover, c-myc mRNA expression was down-regulated in Murabutide-treated cells, suggesting potential interference of the immunomodulator with the nuclear transport of viral preintegration complexes. On the other hand, daily treatment of HIV-1-infected hu-PBL-SCID mice with Murabutide significantly reduced the viral loads in plasma and the proviral DNA content in human peritoneal cells. These results are the first to demonstrate that a clinically acceptable synthetic immunomodulator with an ability to enhance the host's nonspecific immune defense mechanisms against infections can directly regulate cellular factors in infected lymphocytes, leading to controlled HIV-1 replication.

Macrophage stimulation with Murabutide, an HIV-suppressive muramyl peptide derivative, selectively activates extracellular signal-regulated kinases 1 and 2, C/EBPbeta and STAT1: role of CD14 and Toll-like receptors 2 and 4

The smallest unit of bacterial peptidoglycans known to be endowed with biological activities is muramyl dipeptide (MDP). A clinically acceptable synthetic derivative of MDP, namely murabutide (MB), has been found to present interesting pharmacological properties and to suppress HIV-1 replication in monocyte-derived macrophages (MDM). We have addressed the signaling events activated in MDM following stimulation with either MB or the potent immunostimulant LPS. We also examined whether signaling by muramyl peptides involves the use of cell surface receptors, including CD14 and Toll-like receptor 2 (TLR2) or TLR4 that are known to be signal-transducing receptors for other bacterial cell wall components. We demonstrate that, unlike LPS, the safe immunomodulator MB selectively activates extracellular signal-regulated kinases (Erk) 1/2, in the absence of detectable Jun N-terminal kinase (JNK) or p38 mitogen-activated kinase activation. Furthermore, STAT1 activation but weak or no activation of STAT3 or STAT5 respectively, could be detected in MB-stimulated MDM. Using MonoMac6 cells, we observed high C/EBPbeta and AP-1 but weaker and transient NF-kappaB activation by MB.Moreover, the truncated form of C/EBPbeta, known to repress HIV-1 transcription, was detected in extracts from MB-treated THP-1 cells. Surprisingly, neither MB nor MDP were able to transduce signals via CD14 and TLR2 or 4. These findings present major differences in the early cell activation process between LPS and muramyl peptides, and strongly argue for the implication of co-receptors other than TLR2 and TLR4 in mediating the signaling events induced by defined subunits of bacterial peptidoglycans.

The synthetic immunomodulator murabutide controls human immunodeficiency virus type 1 replication at multiple levels in macrophages and dendritic cells

Macrophages and dendritic cells are known to play an important role in the establishment and persistence of human immunodeficiency virus (HIV) infection. Besides antiretroviral therapy, several immune-based interventions are being evaluated with the aim of achieving better control of virus replication in reservoir cells. Murabutide is a safe synthetic immunomodulator presenting a capacity to enhance nonspecific resistance against viral infections and to target cells of the reticuloendothelial system. In this study, we have examined the ability of Murabutide to control HIV type 1 (HIV-1) replication in acutely infected monocyte-derived macrophages (MDMs) and dendritic cells (MDDCs). Highly significant suppression of viral replication was consistently observed in Murabutide-treated cultures of both cell types. Murabutide did not affect virus entry, reverse transcriptase activity, or early proviral DNA formation in the cytoplasm of infected cells. However, treated MDMs and MDDCs showed a dramatic reduction in nuclear viral two-long terminal repeat circular form and viral mRNA transcripts. This HIV-1-suppressive activity was not mediated by inhibiting cellular DNA synthesis or by activating p38 mitogen-activated protein kinase. Furthermore, Murabutide-stimulated cells expressed reduced CD4 and CCR5 receptors and secreted high levels of beta-chemokines, although neutralization of the released chemokines did not alter the HIV-1-suppressive activity of Murabutide. These results provide evidence that a clinically acceptable immunomodulator can activate multiple effector pathways in macrophages and in dendritic cells, rendering them nonpermissive for HIV-1 replication.

Solid-phase synthesis of muramyl dipeptide (MDP) derivatives using a multipin method

Solid-phase synthetic method of muramyl dipeptide derivatives is reported. A diverse library of muramyl dipeptides could be potentially synthesized by acylation, reductive alkylation, sulfonamide formation, urea formation, N-alkylation, amine addition, or component Ugi reactions based on this method for drug screening.

Improving vaccine performance with adjuvants

New vaccines are presently under development and in testing for the control of infectious diseases, including human immunodeficiency virus (HIV) and tuberculosis. Several of these vaccines are composed of synthetic, recombinant, or highly purified subunit antigens. Subunit vaccines are designed to include only the antigens required for protective immunization and to be safer than whole-inactivated or live-attenuated vaccines. However, the purity of the subunit antigens and the absence of the self-adjuvanting immunomodulatory components associated with attenuated or killed vaccines often result in weaker immunogenicity. Immunologic adjuvants are agents that enhance specific immune responses to vaccines. Formulation of vaccines with potent adjuvants is an attractive approach for improving the performance of vaccines composed of subunit antigens. Adjuvants have diverse mechanisms of action and should be selected for use on the basis of the route of administration and the type of immune response (antibody, cell-mediated, or mucosal immunity) that is desired for a particular vaccine.

Role of butyric acid and its derivatives in the treatment of colorectal cancer and hemoglobinopathies

Butyric acid, a short chain fatty acid (SCFA), is a natural component of the animal metabolism. Physiological concentrations induce multiple and reversible biological effects. They concern regulatory mechanisms of gene expression conducing to promote markers of cell differentiation, apoptosis and cell growth control. The described hyperacetylation of histones and the induction of several immune or non-immune cell-activating mediators are consistent with the pleiotropic stimulatory effect of the agent. Butyric acid is considered as a biological response modifier (BRM) and is an interesting tool for biological studies. The history of butyric acid as a putative medication in human health is spanning since 60 years and is confusing in part because of conflicting data between exciting experimental results and clinical trials. In light of minimal impact of systemic therapy and the short half-life of the saline molecule used, it is evident that continuous infusions of butyrate are required to improve the efficacy of the treatment. Butyric acid has been viewed with skepticism because of less convenient for long-term chronic therapy. New experimental data from several studies conduced within the past decade with butyric derivatives, delivery systems, and long-acting prodrugs, have demonstrated the practical value of the therapeutic concept. To support issues regarding clinical development, it was of interest to evaluate the recent information, showing butyric acid currently considered as therapeutic purposes in the treatment of colorectal cancer and hemoglobinopathies.

(+/-)-3-[4-(2-dimethylamino-1-methylethoxy)-phenyl]-1H-pyrazolo[3,4- B]pyridine-1-acetic acid (Y-25510) stimulates production of IL-1 beta and IL-6 at the level of messenger RNA expression in cultured human monocytes

(+/-)-3-[4-(2-Dimethylamino-1-methylethoxy)phenyl]-1H-pyrazolo[3, 4-b]pyridine-1-acetic acid (Y-25510) stimulated the mRNA expression for interleukin-1 beta (IL-1 beta), and enhanced the expression induced by lipopolysaccharide (LPS) in cultured human peripheral blood mononuclear cells (PBMC) and THP-1 cells, a cell-line derived from human monocytic leukemia. Y-25510 also stimulated the mRNA expression for IL-6 in both types of the cells, however, the stimulation required the presence of LPS. In THP-1 cells, the stimulation of IL-1 beta mRNA expression by Y-25510 was suppressed by cycloheximide, an inhibitor of protein synthesis. This phenomenon indicates that the stimulation requires de norv protein synthesis. In contrast, the stimulation of mRNA expression for IL-6 by Y-25510 was not suppressed by cycloheximide but suppressed by N alpha-p-tosyl-L-phenylalanine chloromethyl ketone (TPCK), an inhibitor of nuclear transcription factor-kappa B (NF-kappa B) activation, in the presence of LPS, suggesting that the stimulation requires NF-kappa activation. These results demonstrate that Y-25510 stimulates the mRNA expression for IL-1 beta and IL-6 by different mechanisms. Dexamethasone suppressed the LPS-induced expression of mRNA for IL-1 beta and IL-6 in THP-1 cells, whereas the drug never suppressed the mRNA expression for these cytokines in the presence of Y-25510. The result indicates that Y-25510 stimulates the mRNA expression for IL-1 beta and IL-6 by different mechanisms from those of LPS.

Immunostimulating agents: what next? A review of their present and potential medical applications

Many chemical entities, either from natural sources or prepared by synthesis, are known to exert stimulating activities on various functions of the immune system, such as antibody production, resistance to infections, rejection of malignant cells, etc. In this review, the origin, chemical structures and main activities of several immunostimulants are described, with special emphasis on their present or potential medical usefulness. An attempt is made to envisage the future of this type of pharmacological agents, excluding however from the presentation the endogenous modulators of the immune system (cytokines), the production and activities of which are influenced by the immunostimulants themselves.

Enhancement in vivo of the antiinflammatory and antitumor activities of type I interferon by association with the synthetic immunomodulator murabutide

The therapeutic efficacy of type I interferon (IFN) has been reported to vary considerably in different indications. The use of the cytokine as adjuvant therapy has been suggested to enhance its efficacy and reduce the toxicity frequently associated with long-term and high-dose administration. In this study, we have assessed the activity of type I IFN in the protection against and treatment of acute hepatitis induced in mice by the administration of concanavalin-A (ConA). At the same time, we have evaluated the efficacy of the synthetic immunomodulator murabutide when administered alone or in combination with type I IFN to protect against ConA hepatitis and in the treatment of tumors in MethA sarcoma-bearing mice. Our results demonstrate a prophylactic effect as well therapeutic effects of type I IFN and of murabutide in the inflammation-mediated model of liver damage. The use of combination therapy presented enhanced efficacy in inhibiting the ConA-induced elevation of plasma transaminases. Both compounds were found to suppress IFN-gamma mRNA accumulation in the livers of ConA treated mice. This activity is discussed with respect to the mechanism of action of the two immunomodulators. In addition, the combination of murabutide with type I IFN exhibited synergistic antitumor activity that was clearly seen in the significant regression of MethA tumors and resulted in almost 50 percent tumor-free mice. The potential clinical application of combination therapies using a cytokine and a safe immunomodulator is analyzed in terms of enhancing the cytokine efficacy and extending its use to new indications.

Enhancement by muramyl peptides of the protective response of interferon-alpha/beta against encephalomyocarditis virus infection

The use of interferon-alpha (IFN-alpha) in the treatment of infectious diseases has shown limited efficacy and dose-limiting toxicity. We have selected safe immunomodulators of the muramyl peptide family with the potential of enhancing the efficacy of IFN-alpha without resulting in increased toxicity. One of these synthetic muramyl dipeptide (MDP) derivatives, namely murabutide which is in a clinical stage of development, has been recently found to synergize with IFN-alpha 2a in the selective induction of anti-inflammatory mediators and to enhance the biological activities of the therapeutic cytokine. The present study was performed to assess the antiviral activity of such muramyl peptides and a possible potentiation of the antiviral activity of IFN-alpha/beta by associated therapy using the classical assay of Encephalomyocarditis virus (EMCV) infection. In vitro, pretreatment of Moloney Sarcoma virus (MSV)-transformed cell line with MDP derivatives followed by treatment with IFN-alpha/beta showed a synergistic protection against the cytopathogenic effect of a subsequent EMCV infection. None of the MSV cultures could be protected by stimulation with muramyl peptides alone. In vivo, all of the muramyl peptide derivatives tested were found to be more potent than the parent molecule MDP in inducing protection against death or in the prolongation of the mean survival time of infected mice. Sequential administration of suboptimal doses of exogenous IFN-alpha/beta and muramyl peptides established a strong antiviral state and considerably improved the protective effect of the cytokine, frequently leading to an abortive infection. Our findings suggest that combination therapy with safe muramyl peptides and IFN-alpha/beta could constitute a highly effective and new regimen for the treatment of viral infections in humans.

Synergistic effects between recombinant interleukin-2 and the synthetic immunomodulator murabutide: selective enhancement of cytokine release and potentiation of antitumor activity

The use of interleukin-2 (IL-2) in the treatment of cancer has shown limited efficacy and dose-limiting toxicity. Combination therapy with other cytokines and/or chemotherapeutic agents has been attempted to enhance the antitumor activity and to reduce the effective therapeutic dose of IL-2. We recently showed, in vitro and in vivo, a synergistic activity between the synthetic immunomodulator murabutide, which is in clinical stage of development, and another therapeutic cytokine, interferon-alpha (IFN-alpha). The present study was performed to assess a possible potentiation of the biologic activities of IL-2 by its association with murabutide. Human PBMC stimulated in vitro with IL-2 and murabutide showed synergistic levels of induced mRNA accumulation and protein secretion for IFN-gamma, IL-12, and colony-stimulating factors (CSFs). No such effects were obtained on the induction of most inflammatory cytokines, including IL-6, IL-8, and tumor necrosis factor alpha (TNF-alpha). Furthermore, the combined administration of murabutide with IL-2 into Meth-A sarcoma-bearing mice resulted in a very significant tumor inhibition as well as in complete tumor regression in nearly 70% of the treated mice. Under the same conditions, treatment with either compound separately had little or no antitumor effect. These preclinical findings will be pursued by the evaluation of the clinical tolerance and biologic activity of the murabutide/IL-2 combination therapy in cancer patients.