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Nogo receptor type 1 (NgR1) is known to inhibit neuronal regeneration in the CNS. Previously, we have shown that lateral olfactory tract usher substance (LOTUS) interacts with NgR1 and inhibits its function by blocking its ligand binding. Therefore, LOTUS is expected to have therapeutic potential for the promotion of neuronal regeneration. However, it remains unknown whether the soluble form of LOTUS (s-LOTUS) also has an inhibitory action on NgR1 function as a candidate for therapeutic agents. Here, we show that s-LOTUS inhibits NgR1-mediated signaling by inhibiting the molecular interaction between NgR1 and its coreceptor, p75 neurotrophin receptor (p75NTR). In contrast to the membrane-bound form of LOTUS, s-LOTUS did not block ligand binding to NgR1. However, we identified p75NTR as a novel LOTUS binding partner and found that s-LOTUS suppressed the interaction between p75NTR and NgR1. s-LOTUS inhibited myelin-associated inhibitor (MAI)-induced RhoA activation in murine cortical neurons. Functional analyses revealed that s-LOTUS inhibited MAI-induced growth cone collapse and neurite outgrowth inhibition in chick DRG neurons. In addition, whereas olfactory bulb neurons of lotus-KO mice are sensitive to MAI due to a lack of LOTUS expression, treatment with s-LOTUS inhibited MAI-induced growth cone collapse in these neurons. Finally, we observed that s-LOTUS promoted axonal regeneration in optic nerve crush injury of mice (either sex). These findings suggest that s-LOTUS inhibits NgR1-mediated signaling, possibly by interfering with the interaction between NgR1 and p75NTR Therefore, s-LOTUS may have potential as a therapeutic agent for neuronal regeneration in the damaged CNS.SIGNIFICANCE STATEMENT Nogo receptor type 1 (NgR1) is a receptor well known to inhibit neuronal regeneration in the CNS. Because the membrane-bound form of lateral olfactory tract usher substance (LOTUS) antagonizes NgR1 through a cis-type molecular interaction between LOTUS and NgR1, the soluble form of LOTUS (s-LOTUS) is expected to be a therapeutic agent for neuronal regeneration. In our present study, we show that s-LOTUS inhibits the interaction between NgR1 and p75NTR, NgR1 ligand-induced RhoA activation, growth cone collapse, and neurite outgrowth inhibition and promotes axonal regeneration. Our results indicate that s-LOTUS inhibits NgR1-mediated signaling through a trans-type molecular interaction between LOTUS and NgR1 and, therefore, s-LOTUS may have therapeutic potential for neuronal regeneration.

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BACKGROUND AND PURPOSE: One class of poststroke restorative therapy focuses on promoting axon outgrowth by blocking myelin-based inhibitory proteins such as myelin-associated glycoprotein. The purpose of the current study was to extend preclinical and clinical findings of GSK249320, a humanized monoclonal antibody to myelin-associated glycoprotein with disabled Fc region, to explore effects on motor outcomes poststroke. METHODS: In this phase IIb double-blind, randomized, placebo-controlled study, patients at 30 centers with ischemic stroke 24 to 72 hours prior and gait deficits were randomized to 2 IV infusions of GSK249320 or placebo. Primary outcome measure was change in gait velocity from baseline to day 90. RESULTS: A total of 134 subjects were randomized between May 2013 and July 2014. The 2 groups were overall well matched at baseline. The study was stopped at the prespecified interim analysis because the treatment difference met the predefined futility criteria cutoff; change in gait velocity to day 90 was 0.55±0.46 (mean±SD) in the GSK249320 group and 0.56±0.50 for placebo. Secondary end points including upper extremity function were concordant. The 2 IV infusions of GSK249320 were well tolerated. No neutralizing antibodies to GSK249320 were detected. CONCLUSIONS: GSK249320, within 72 hours of stroke, demonstrated no improvement on gait velocity compared with placebo. Possible reasons include challenges translating findings into humans and no direct evidence that the therapy reached the biological target. The antibody was well tolerated and showed low immunogenicity, findings potentially useful to future studies aiming to use a monoclonal antibody to modify activity in specific biological pathways to improve recovery from stroke. CLINICAL TRIAL REGISTRATION: URL: http://www.clinicaltrials.gov. Unique identifier: NCT01808261.

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BACKGROUND AND PURPOSE: New insights into the brain's ability to reorganize after injury are beginning to suggest novel restorative therapy targets. Potential therapies include pharmacological agents designed to promote axonal growth. The purpose of this study was to test the efficacy of one such drug, GSK249320, a monoclonal antibody that blocks the axon outgrowth inhibition molecule, myelin-associated glycoprotein, to facilitate recovery of motor skills in a nonhuman primate model of ischemic cortical damage. METHODS: Using a between-groups repeated-measures design, squirrel monkeys were randomized to 1 of 2 groups: an experimental group received intravenous GSK249320 beginning 24 hours after an ischemic infarct in motor cortex with repeated dosages given at 1-week intervals for 6 weeks and a control group received only the vehicle at matched time periods. The primary end point was a motor performance index based on a distal forelimb reach-and-retrieval task. Neurophysiological mapping techniques were used to determine changes in spared motor representations. RESULTS: All monkeys recovered to baseline motor performance levels by postinfarct day 16. Functional recovery in the experimental group was significantly facilitated on the primary end point, albeit using slower movements. At 7 weeks post infarct, motor maps in the spared ventral premotor cortex in the experimental group decreased in area compared with the control group. CONCLUSIONS: GSK249320, initiated 24 hours after a focal cortical ischemic infarct, facilitated functional recovery. Together with the neurophysiological data, these results suggest that GSK249320 has a substantial biological effect on spared cortical tissue. However, its mechanisms of action may be widespread and not strictly limited to peri-infarct cortex and nearby premotor areas.

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Siglec-4, also known as myelin-associated glycoprotein (MAG), is a member of the siglec (sialic acid-binding immunoglobulin-like lectins) family. MAG binds with high preference to sialic acids α(2-3)-linked to D-galactose. Although the involvement and relevance of its sialic acid binding activity is still controversial, it could be demonstrated that interactions of MAG with sialylated gangliosides play an important role in axon stability and regeneration. In this article we describe in detail our current understanding of the biological role and the carbohydrate specificity of siglec-4. Furthermore, this review compiles the intensive research efforts leading from the identification of the minimal oligosaccharide binding epitope in gangliosides via micromolar oligosaccharide mimics to the development of small molecular weight and more drug-like sialic acid derivatives binding with low nanomolar affinities. Such compounds will be useful to elucidate MAG's biological functions, which are currently not fully understood.

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BACKGROUND AND PURPOSE: Restorative therapies have the potential to improve function and reduce disability after stroke with a wide therapeutic window. The current study evaluated GSK249320, a monoclonal antibody that blocks the axon outgrowth inhibition molecule myelin-associated glycoprotein and also protects oligodendrocytes. METHODS: Patients with mild-moderate stroke were randomized to intravenous GSK249320 (1, 5, or 15 mg/kg per infusion, in escalating cohorts of 8-9 subjects) versus placebo (n=17). Infusion 1 was 24 to 72 hours after stroke; infusion 2 was 9 ± 1 days later. The primary objective evaluated safety and tolerability, and the secondary objectives evaluated immunogenicity, pharmacokinetics, biomarkers, neurophysiology, and motor function. RESULTS: Baseline (n=42) characteristics were similar across treatment groups. No safety concerns were found based on adverse events, examination, vital signs, ECG, nerve conduction tests, brain imaging, motor function testing, and laboratory studies. Two of the 25 subjects dosed with GSK249320 developed transient antidrug antibodies after infusion 1. The pharmacokinetics profile was as expected for an IgG1 type monoclonal antibody. Serum levels of the biomarker S100ß did not differ between groups. Global outcome measures were similar across groups. Modality-specific end points could be consistently measured in the first few days after stroke, and one of these, gait velocity, demonstrated a trend toward improvement with GSK249320 compared with placebo. CONCLUSIONS: GSK249320 was generally well tolerated. No major safety issues were identified in this first study of a monoclonal antibody to modulate the neurobiology of brain repair after stroke. Future studies might explore the efficacy of GSK249320 as a restorative therapy for stroke. Clinical Trial Registration- URL: http://www.clinicaltrials.gov. Unique Identifier: NCT00833989.

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GSK249320, a monoclonal antibody directed against myelin-associated glycoprotein (MAG), is being developed for the enhancement of recovery of function poststroke. Potential safety concerns of adverse effects on myelin led to the inclusion of pharmacodynamic measures of peripheral and central neuronal function in this first-time-in-human (FTIH) study. The study also evaluated general safety, pharmacokinetics, and immunogenicity of GSK249320. Single intravenous infusions of GSK249320 (0.04, 0.4, 1.2, 3.5, 10, and 25 mg/kg) or placebo were administered to 47 healthy subjects aged 18-60 years. GSK249320 was well tolerated at all doses. No clinically significant abnormalities were observed in neurological examinations, nerve conduction tests (NCTs), quantitative sensory tests (QSTs), clinical laboratory tests, or electrocardiograms. There were no severe or serious adverse events. GSK249320 had a half-life (HL) of 21 days and a volume of distribution at steady state of 45.8 ml/kg, with AUC showing dose linearity. GSK249320 did not induce antidrug antibodies.

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Monoclonal antibodies are found in approximately 10% of patients with peripheral neuropathy (PN) of unknown etiology. Several autoantibodies, including anti-MAG (myelin-associated glycoprotein) antibodies, have been reported to induce neuropathy. It has been suggested that over 50% of patients with PN and IgM monoclonal gammopathy (MG) have anti-MAG IgM antibodies in their sera. This work aimed at studying the frequency and characteristics of PN in a group of Egyptian patients with MGs and to estimate the serum level of anti-MAG antibodies and its relationship to peripheral nerve dysfunction. Forty patients with MGs were enrolled in the study. Their mean age was 56.65 ± 8.55 years. There were 17 males and 23 females. Patients were subjected to complete general and neurological examination, laboratory investigations including serum LDH, ß2 microglobulin, serum protein electrophoresis, urinary Bence-Jones protein, bone marrow aspiration and/or trephine biopsy, quantitative estimation of serum IgM and IgG by nephelometry, detection of anti-MAG antibodies by indirect immunofluorescence, radiological assessment and nerve conduction study of both upper and lower limbs. Clinical and electrophysiological evidences of PN were found in 32 (80%) out of the 40 patients with MG. Twenty-five patients (62.5%) had distal symmetrical polyneuropathy and seven (17.5%) had mononeuritis or mononeuritis multiplex. The majority of patients (65%) had sensory or predominantly sensorimotor polyneuropathy. The neuropathy was mainly demyelinating in 22 patients (55%) and axonal in the other 10 (25%) patients. Anti-MAG antibodies were positive in nine patients (22.5%) and six of them (66.6%) had PN. The latter was predominantly demyelinating motor neuropathy in 4 and axonal in the remaining 2. However, the relationship between the presence of anti-MAG antibodies and the development and type of PN was not statistically significant. Anti-MAG showed significant association with IgM level (P = 0.003**) and the MG subtypes: Waldenström's macroglobulinemia (WM) and monoclonal gammopathy of undetermined significance (MGUS) (P = 0.004**). The present study showed high frequency (>60%) of distal symmetrical polyneuropathy in Egyptian patients with MG. The neuropathy was predominantly sensory and demyelinating. Anti-MAG antibodies were detected only in 22.5% of the patients, especially those with WM and MGUS and were associated with more motor and demyelinating neuropathy. We recommend that patients with chronic polyneuropathies should be evaluated for underlying plasma cell dyscrasia.

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Siglec-2, also known as CD22, is involved in the regulation and survival of B-cells and has been successfully targeted in cell depletion therapies with antibody-based approaches. Sialic acid derivatives, already known to bind with high affinity to myelin-associated glycoprotein (MAG, Siglec-4), were screened for their binding affinity for CD22 by surface plasmon resonance. The best compound identified was further modified with various hydrophobic substituents at the 2-, 5-, and 9-positions of the sialic acid scaffold, leading to nanomolar derivatives, of which ligand 17 b shows the most promising pharmacodynamic and pharmacokinetic profiles. Isothermal titration calorimetry measurements demonstrate that the binding is enthalpy driven. Interestingly, the thermodynamic fingerprints reveal an excellent correlation between gains in enthalpy and compensation by increased entropy costs. Moreover, 17 b exhibits a residence time in the range of a few seconds, clearly prolonged relative to residence times typically observed for carbohydrate-lectin interactions. Finally, initial tests regarding drug-like properties of 17 b demonstrate the required high plasma protein binding yet a lack of oral availability, although its distribution coefficient (log D) is in the required range.

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In earlier studies, we identified the C-9 amido derivative 1 (9-(4'-hydroxy-4-biphenyl)acetamido-9-deoxy-Neu5Gcα2-6GalOMP) and the C-9 amino derivative 2 (9-(4'-hydroxy-4-biphenyl)methylamino-9-deoxy-Neu5Gcα2-6GalOMP) have the most promising affinity for mouse CD22 and human CD22, respectively. Replacing the subterminal galactose residue (2-6Gal-OMP) of 1 with benzyl (5) or biphenylmethyl (6) as aglycone led to even higher potency for mCD22. In this study, both compounds showed improved potency and selectivity for CD22 (IC(50) 70 nM) and 712-fold more selective for CD22 than for MAG. The corresponding derivatives of 2, compounds 8 and 9, showed comparable activity to 2 but lower potency and selectivity than 5 and 6. Although compounds 5-9 are simple and small molecular weight antagonists, they showed much high potency and selectivity than the corresponding compounds having α 2-6Gal linkage. Both biological and computational docking simulation studies suggest that the 2-6Gal-OMP residues of 1 and 2 are not critical for binding process and could be replaced with hydrophobic non-carbohydrate moieties. The data presented herein has significant implications for the design and discovery of next-generation CD22-antagonists.

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The tetrasaccharide 4, a substructure of ganglioside GQ1balpha, shows a remarkable affinity for the myelin-associated glycoprotein (MAG) and was therefore selected as starting point for a lead optimization program. In our search for structurally simplified and pharmacokinetically improved mimics of 4, antagonists with modifications of the core disaccharide Galbeta(1-3)GalNAc, as well as the terminal alpha(2-3)- and the internal alpha(2-6)-linked neuraminic acid were synthesized and tested in target-based binding assays. Compared to the reference tetrasaccharide 4, the most potent antagonist 17 exhibits a 360-fold improved affinity. Furthermore, pharmacokinetic parameters such as stability in the cerebrospinal fluid, logD and permeation through the BBB indicate the drug-like properties of antagonist 17.

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Broad modifications of various positions of the minimal natural epitope recognized by the myelin-associated glycoprotein (MAG), a blocker of regeneration of neurite injuries, produced sialosides with nanomolar affinities. However, important pharmacokinetic issues, for example, the metabolic stability of these sialosides, remain to be addressed. For this reason, the novel non-carbohydrate mimic 3 was designed and synthesized from (-)-quinic acid. For the design of 3, previously identified beneficial modifications of side chains of Neu5Ac were combined with the replacement of the ring oxygen by a methylene group and the substitution of the C(4)-OH by an acetamide. Although docking experiments to a homology model of MAG revealed that mimic 3 forms all but one of the essential hydrogen bonds identified for the earlier reported lead 2, its affinity was substantially reduced. Extensive molecular-dynamics simulation disclosed that the missing hydrogen bond of the former C(8)-OH leads to a change of the orientation of the side chain. As a consequence, an important hydrophobic contact is compromised leading to a loss of affinity.

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Successful axonal regeneration is a complex process determined by both axonal environment and endogenous neural capability of the regenerating axons in the central and the peripheral nervous systems. Numerous external inhibitory factors inhibit axonal regeneration after injury. In response, neurons express various regeneration-associated genes to overcome this inhibition and increase the intrinsic growth capacity. In the present study, we show that the brain-expressed X-linked (Bex1) protein was over-expressed as a result of peripheral axonal damage. Bex1 antagonized the axon outgrowth inhibitory effect of myelin-associated glycoprotein. The involvement of Bex1 in axon regeneration was further confirmed in vivo. We have demonstrated that Bex1 knock-out mice showed lower capability for regeneration after peripheral nerve injury than wild-type animals. Wild-type mice could recover from sciatic nerve injury much faster than Bex1 knock-out mice. Our findings suggest that Bex1 could be considered as regeneration-associated gene.

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Paraplegia is caused by injuries of the central nervous system (CNS) and especially young people suffer from these severe consequences as, for example, the loss of motor functions. The lack of repair of the injured nerve strands originates from the inhibitory environment for axon regeneration in the CNS. Specific inhibitory proteins block the regrowth of nerve roots. One of these neurite outgrowth inhibitors is the myelin-associated glycoprotein (MAG), which is a member of the Siglec family (sialic acid-binding immunoglobulin-like lectin). In previous studies, we identified potent small molecule MAG antagonists. In this communication, we report new neuraminic acid derivatives modified in the 4- and 5-position, and the influence of various structural modifications on their kinetic and thermodynamic binding properties.

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One of the major barriers to successful axon regeneration in the adult CNS is the presence of inhibitory molecules that originate from the myelin sheath and glial scar. So far, only a small number of pharmacological compounds have exhibited functional activity against CNS inhibitors in promoting axon regeneration after injury. To search for novel compounds that enhance neurite outgrowth in vitro, we initiated a screen of a collection of natural products. We identified four compounds with the potential to promote growth over a myelin substrate. Of these, Amphotericin B (AmB) was shown to enhance neurite outgrowth and antagonize activities of major myelin associated inhibitors and glial-scar-derived chondroitin sulfate proteoglycans. AmB was found to activate Akt and thereby suppress the activity of glycogen synthase kinase 3 beta. Also, a cell permeable peptide that inhibits Akt activity was shown to block the effect of AmB in promoting axonal growth, while another peptide that increases Akt activity stimulated axonal growth in the presence of the myelin associated inhibitors. Our results suggest that AmB can promote neurite outgrowth over a wide range of inhibitory substrates via a mechanism that involves activation of Akt.

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The injured adult mammalian central nervous system is an inhibitory environment for axon regeneration due to specific inhibitors, among them the myelin-associated glycoprotein (MAG), a member of the Siglec family (sialic-acid binding immunoglobulin-like lectin). In earlier studies, we identified the lead structure 5, which shows a 250-fold improved in vitro affinity for MAG compared to the tetrasaccharide binding epitope of GQ1balpha (1), the best physiological MAG ligand described so far. By modifying the 2- and 5-position, the affinity of 5 could be further improved to the nanomolar range (-->19a). Docking studies to a homology model of MAG allowed the rationalization of the experimental binding properties. Finally, pharmacokinetic parameters (stability in the cerebrospinal fluid, logD and permeation through the BBB) indicate the drug-like properties of the high-affinity antagonist 19a.

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The tetrasaccharide 1, a substructure of ganglioside GQ1b alpha, shows a remarkable affinity for the myelin-associated glycoprotein (MAG) and was therefore selected as starting point for a lead optimization program. In our search for structurally simplified and pharmacokinetically improved mimics of 1, modifications of the core disaccharide, the alpha(2-->3)- and the alpha(2-->6)-linked sialic acid were synthesized. Biphenylmethyl and (S)-lactate were identified as suitable replacements for the alpha(2-->6)-linked sialic acid. Combined with a core modification and the earlier found aryl amide substituent in the 9-position of the alpha(2-->3)-linked sialic acid, high affinity MAG antagonists were identified. All mimics were tested in a competitive target-based binding assay, providing relative inhibitory potencies (rIP). Compared to the reference tetrasaccharide 1, the rIPs of the most potent antagonists 59 and 60 are enhanced nearly 400-fold. Their K(D)s determined in surface plasmon resonance experiments are in the low micromolar range. These results are in semiquantitative agreement with molecular modeling studies. This new class of glycomimetics will allow to validate the role of MAG in the axon regeneration process.

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