Design and synthesis of small semi-mimetic peptides with immunomodulatory activity based on myelin basic protein (MBP)

The Long Road of Immunotherapeutics against Multiple Sclerosis

This commentary highlights novel immunomodulation and vaccine-based research against multiple sclerosis (MS) and reveals the amazing story that triggered this cutting-edge MS research in Greece and worldwide. It further reveals the interest and solid support of some of the world's leading scientists, including sixteen Nobel Laureates who requested from European leadership to take action in supporting Greece and its universities in the biggest ever financial crisis the country has encountered in the last decades. This support endorsed vaccine-based research on MS, initiated in Greece and Australia, leading to a worldwide network aiming to treat or manage disease outcomes. Initiatives by bright and determined researchers can result in frontiers science. We shed light on a unique story behind great research on MS which is a step forward in our efforts to develop effective treatments for MS.

Mannosylated Linear and Cyclic Single Amino Acid Mutant Peptides Using a Small 10 Amino Acid Linker Constitute Promising Candidates Against Multiple Sclerosis

Multiple sclerosis (MS) is a serious autoimmune demyelinating disease leading to loss of neurological function. The design and synthesis of various altered peptide ligands of immunodominant epitopes of myelin proteins to alter the autoimmune response, is a promising therapeutic approach for MS. In this study, linear and cyclic peptide analogs based on the myelin basic protein 83–99 (MBP_83–99) immunodominant epitope conjugated to reduced mannan via the (KG)₅ and keyhole limpet hemocyanin (KLH) bridge, respectively, were evaluated for their biological/immunological profiles in SJL/J mice. Of all the peptide analogs tested, linear MBP_83–99(F⁹¹) and linear MBP_83–99(Y⁹¹) conjugated to reduced mannan via a (KG)₅ linker and cyclic MBP_83–99(F⁹¹) conjugated to reduce mannan via KLH linker, yielded the best immunological profile and constitute novel candidates for further immunotherapeutic studies against MS in animal models and in human clinical trials.

Structural analysis of the complex between calmodulin and full-length myelin basic protein, an intrinsically disordered molecule

Myelin basic protein (MBP) is present between the cytoplasmic leaflets of the compact myelin membrane in both the peripheral and central nervous systems, and characterized to be intrinsically disordered in solution. One of the best-characterized protein ligands for MBP is calmodulin (CaM), a highly acidic calcium sensor. We pulled down MBP from human brain white matter as the major calcium-dependent CaM-binding protein. We then used full-length brain MBP, and a peptide from rodent MBP, to structurally characterize the MBP-CaM complex in solution by small-angle X-ray scattering, NMR spectroscopy, synchrotron radiation circular dichroism spectroscopy, and size exclusion chromatography. We determined 3D structures for the full-length protein-protein complex at different stoichiometries and detect ligand-induced folding of MBP. We also obtained thermodynamic data for the two CaM-binding sites of MBP, indicating that CaM does not collapse upon binding to MBP, and show that CaM and MBP colocalize in myelin sheaths. In addition, we analyzed the post-translational modifications of rat brain MBP, identifying a novel MBP modification, glucosylation. Our results provide a detailed picture of the MBP-CaM interaction, including a 3D model of the complex between full-length proteins.

Solution NMR structure of an immunodominant epitope of myelin basic protein. Conformational dependence on environment of an intrinsically unstructured protein

Using solution NMR spectroscopy, three-dimensional structures have been obtained for an 18-residue synthetic polypeptide fragment of 18.5 kDa myelin basic protein (MBP, human residues Q81-T98) under three conditions emulating the protein's natural environment in the myelin membrane to varying degrees: (a) an aqueous solution (100 mM KCl pH 6.5), (b) a mixture of trifluoroethanol (TFE-d2) and water (30 : 70% v/v), and (c) a dispersion of 100 mM dodecylphosphocholine (DPC-d38, 1 : 100 protein/lipid molar ratio) micelles. This polypeptide sequence is highly conserved in MBP from mammals, amphibians, and birds, and comprises a major immunodominant epitope (human residues N83-T92) in the autoimmune disease multiple sclerosis. In the polypeptide fragment, this epitope forms a stable, amphipathic, alpha helix under organic and membrane-mimetic conditions, but has only a partially helical conformation in aqueous solution. These results are consistent with recent molecular dynamics simulations that showed this segment to have a propensity to form a transient alpha helix in aqueous solution, and with electron paramagnetic resonance (EPR) experiments that suggested a alpha-helical structure when bound to a membrane [I. R. Bates, J. B. Feix, J. M. Boggs & G. Harauz (2004) J Biol Chem, 279, 5757-5764]. The high sensitivity of the epitope structure to its environment is characteristic of intrinsically unstructured proteins, like MBP, and reflects its association with diverse ligands such as lipids and other proteins.

Contribution of peptides to multiple sclerosis research

Multiple sclerosis (MS) is an autoimmune disease associated with chronic inflammatory demyelination of the central nervous system in genetically susceptible individuals. Because of the disease complexity and heterogeneity, its pathogenesis remains unknown despite extensive research efforts, and specific effective treatments have not yet been developed. Peptide-based research has been important in attempts to unravel particular aspects of this complex disease, including the characterization of the different molecular mechanisms of MS, with the goal of providing useful products for immune-mediated therapies. In fact, in the past decade, peptide-based research has been predominant in research aimed to identify and/or develop target antigens as synthetic probes for specific biomarkers as well as innovative immunomodulating therapies. This review presents an overview of the contributions of peptide science to MS research and discusses future directions of peptide-based investigations.

Design and synthesis of a novel potent myelin basic protein epitope 87-99 cyclic analogue: enhanced stability and biological properties of mimics render them a potentially new class of immunomodulators

A cyclic analogue, [cyclo(87-99)MBP(87)(-)(99)], of the human immunodominant MBP(87)(-)(99) epitope, was designed based on ROESY/NMR distance information and modeling data for linear epitope 87-99, taking into account T-cell (Phe(89), Lys(91), Pro(96)) and HLA (His(88), Phe(90), Ile(93)) contact side-chain information. The cyclic analogue was found to induce experimental allergic encephalomyelitis (EAE), to bind HLA-DR4, and to increase CD4 T-cell line proliferation, like that of the conformationally related linear MBP(87)(-)(99) epitope peptide. The mutant cyclic peptides, the cyclo(91-99)[Ala(96)]MBP(87)(-)(99) and the cyclo(87-99)[Arg(91)Ala(96)]MBP(87)(-)(99), reported previously for suppressing, to a varying degree, autoimmune encephalomyelitis in a rat animal model, were found in this study to possess the following immunomodulatory properties: (i) they suppressed the proliferation of a CD4 T-cell line raised from a multiple sclerosis patient, (ii) they scored the best in vitro TH2/TH1 cytokine ratio in peripheral blood mononuclear cell cultures derived from 13 multiple sclerosis patients, inducing IL-10 selectively, and (iii) they bound to HLA-DR4, first to be reported for cyclic MBP peptides. In addition, cyclic peptides were found to be more stable to lysosomal enzymes and Cathepsin B, D, and H, compared to their linear counterparts. Taken together, these data render cyclic mimics as putative drugs for treating multiple sclerosis and potentially other Th1-mediated autoimmune diseases.

Antagonistic effects of human cyclic MBP(87-99) altered peptide ligands in experimental allergic encephalomyelitis and human T-cell proliferation

The immunodominant myelin basic protein (MBP) peptide comprising residues 87-99 is a self-antigen in multiple sclerosis (MS). In Lewis rats this epitope induces experimental allergic encephalomyelitis (EAE), a demyelinating disease of the central nervous system, and is a model of MS. Structure-activity studies have shown that Lys(91) and Pro(96) residues are important for encephalitogenicity. Replacement of Lys and/or Pro residues with Arg and/or Ala, respectively, results in suppression of EAE. A potent linear altered peptide ligand of the immunodominant sequence MBP(83-99) has been selected for clinical trial (Nat. Med. 2000, 6, 1167, 1176). In the present report, two cyclic analogues, cyclo(91-99)[Ala(96)]MBP(87-99) and cyclo(87-99)[Arg(91), Ala(96)]MBP(87-99) were designed by NMR and molecular modeling data on human MBP(87-99) epitope (Val(87)-His-Phe-Phe-Lys-Asn-Ile-Val-Thr-Pro-Arg-Thr-Pro(99)) and its linear antagonist peptide analogue [Arg(91), Ala(96)]MBP(87-99). These analogues (altered peptide ligands) inhibited EAE in Lewis rats and decreased inflammation in the spinal cord. In addition, the analogue cyclo(87-99)[Arg(91), Ala(96)]MBP(87-99) induced proliferation of human peripheral blood T-cells. These cyclic MBP(87-99) peptide analogues may lead to the design of potent antagonist mimetics for treating MS.

Palmitoyl derivatives of GpMBP epitopes: T-cell response and peptidases susceptibility

We report for the first time the immunoadjuvant effects of lipoconjugation of peptide antigens in an in vitro system by using CD4+ T-cells. The lipopeptides obtained by conjugating a palmitoyl moiety at the N(alpha)-terminal of Gln(74) or at the epsilon-NH(2) of Lys(75) of GpMBP(74-85) induced increased T-cell responsiveness compared to the native nonlipidated peptide. On the other hand, lipoderivatives of GpMBP(82-98) did not increase the T-cell response, demonstrating that the superagonist inducing effect of lipoconjugation is epitope-specific. Digestion of the two native peptides with cathepsin D and L, both implicated in antigen processing, and with a complete lysosomal fraction of a EBV-transformed B cell line shows that GpMBP(74-85) is resistant to cellular proteases, while GpMBP(82-98) is easily digested by these enzymes. These results suggest that the first prerequisite for increasing the T-cell response by lipoconjugation is the stability of the native peptide to peptidases, providing an important insight into the understanding of the immunoadjuvant effect of lipoderivative antigens.

Treatment of experimental allergic encephalomyelitis (EAE) by a rationally designed cyclic analogue of myelin basic protein (MBP) epitope 72-85

In this report the rational design, synthesis and pharmacological properties of an amide-linked cyclic antagonist analogue of the guinea pig myelin basic protein epitope MBP(72-85) are described. Design of the potent cyclic analogue was based on 2D NOESY nuclear magnetic resonance and molecular dynamics studies carried out in the linear antagonist Ala81MBP(72-85). The cyclic antagonist completely prevented the induction of experimental allergic/autoimmune encephalomyelitis when coinjected with linear and cyclic agonist analogues MBP(72-85) and cyclo(2-9)MBP(72-85).

Treatment of experimental allergic encephalomyelitis (EAE) induced by guinea pig myelin basic protein epitope 72-85 with a human MBP(87-99) analogue and effects of cyclic peptides

Experimental autoimmune encephalomyelitis (EAE) is an inflammatory and demyelinating disease of the central nervous system and is an animal model of multiple sclerosis (MS). In the present report, a linear analogue and a series of cyclic semi-mimetic peptides were designed and synthesized based on the human myelin basic protein (MBP(87-99)) epitope (Val87-His-Phe-Phe-Lys-Asn-Ile-Val-Thr-Pro-Arg-Thr-Pro90) and on Copolymer I (a mixture of random polymers of Ala, Gln, Lys and Tyr used to treat MS). These analogues were designed looking for suppressors of EAE induced by guinea pig MBP(72-85) epitope (Gln-Lys-Ser-Gln-Arg-Ser-Gln-Asp-Glu-Asn-Pro-Val) in Lewis rats. The linear analogue [Arg91,Ala96]MBP(87-99), in which Arg substitutes Lys91 and Ala substitutes Pro96, was found to be a strong inhibitor which when administered to Lewis rats together with the encephalitogenic agonist MBP(72-85) completely prevented the induction of EAE. In contrast, three N- and C-termini amide-linked cyclic semi-mimetic peptides, [cyclo-Phe-Arg-Asn-Ile-Val-Thr-Ala-Acp (1), cyclo-Phe-Ala-Arg-Gln-Acp (2), cyclo-Tyr-Ala-Lys-Gln-Acp (3)] as well as a Lys side chain and C-terminous cyclic semi mimetic peptide cyclo(Lys, Acp)-Phe-Lys-Asn-Ile-Val-Thr-Ala-Acp (4) which contain segments of MBP(87-99) or are constituted from immunophoric residues of copolymer 1, were ineffective in inducing or inhibiting EAE in Lewis rats. However co-injection of cyclic analogues with MBP(72-85) delayed the onset of EAE indicating a modulatory effect on the EAE activity of MBP(72-85). These findings suggest that molecule length, size of cyclic moiety and backbone conformation are important elements for immunogenic activity. Moreover blockade of MBP(72-85) induced EAE by the unrelated peptide [Arg91,Ala56]MBP(87-99) could indicate that the mechanism of inhibition is not due to binding competition but rather due to the delivery of a negative signal by the antagonist which overcomes the agonist response possibly through the activation of antigen specific regulatory T cells.

Design and synthesis of a potent cyclic analogue of the myelin basic protein epitope MBP72-85: importance of the Ala81 carboxyl group and of a cyclic conformation for induction of experimental allergic encephalomyelitis

Experimental allergic encephalomyelitis (EAE) is induced in susceptible animals by immunodominant determinants of myelin basic protein (MBP), such as guinea pig sequence MBP72-85. Two linear and one cyclic analogues based on MBP72-85 have been synthesized and evaluated for EAE induction in Lewis rats. The linear peptide Gln1-Lys2-Ser3-Gln4-Arg5-Ser6-Gln7-+ ++Asp8-Glu9-Asn10-Pro11-Val12 (1) was found to induce EAE, while substitution of the Asp residue at position 8 with Ala resulted in an analogue (2) which suppressed the induction of EAE by its parent peptide. Nuclear magnetic resonance studies of analogue 1 in dimethyl sulfoxide (DMSO) using TOCSY/ROESY techniques revealed a head-to-tail intramolecular interaction (ROE connectivity between betaVal12-gammaGln1), indicating a pseudocyclic conformation for the immunogenic peptide 1. A conformational model was developed using NMR constraints and molecular dynamics. Based on this model, a novel amide-linked cyclic analogue has been designed and synthesized by connecting the side-chain amino and carboxyl groups of Lys and Glu at positions 2 and 9, respectively, of linear analogue 1. The cyclic analogue (3) had similar activity to the linear peptide 1, and the EAE effects induced by cyclic analogue 3 were completely suppressed by co-injection with the Ala81-substituted analogue 2 in Lewis rats. The similar potencies of analogues 1 and 3 support the proposed cyclic comformation suggested for analogue 1 from NMR studies and computer modeling and provides the basis for designing more potent molecules with improved properties such as increased resistance to degradation.15 The present findings suggest that a cyclic conformation for the MBP72-85 epitope positions the carboxyl group of Asp81 correctly and presumably other side groups of the peptide such as Arg78 in a manner which enables functional binding of the trimolecular complex MHC-peptide-T cell receptor resulting in EAE.