Characterization of new multimeric erythropoietin receptor agonists

Structural Basis of Interleukin-5 Inhibition by the Small Cyclic Peptide AF17121

Interleukin-5 (IL-5) is a T-helper cell of subtype 2 cytokine involved in many aspects of eosinophil life. Eosinophilic granulocytes play a pathogenic role in the progression of atopic diseases, such as allergy, asthma and atopic dermatitis and hypereosinophilic syndromes. Here, eosinophils upon activation degranulate leading to the release of proinflammatory proteins and mediators stored in intracellular vesicles termed granula thereby causing local inflammation, which when persisting leads to tissue damage and organ failure. As a key regulator of eosinophil function, IL-5 therefore presents a major pharmaceutical target and approaches to interfere with IL-5 receptor activation are of great interest. Here we present the structure of the IL-5 inhibiting peptide AF17121 bound to the extracellular domain of the IL-5 receptor IL-5Rα. The small 18mer cyclic peptide snugly fits into the wrench-like cleft of the IL-5 receptor, thereby blocking access of key residues for IL-5 binding. While AF17121 and IL-5 seemingly bind to a similar epitope at IL-5Rα, functional studies show that recognition and binding of both ligands differ. Using the structure data, peptide variants with improved IL-5 inhibition have been generated, which might present valuable starting points for superior peptide-based IL-5 antagonists.

Aminooxylated Carbohydrates: Synthesis and Applications

Among other classes of biomolecules, carbohydrates and glycoconjugates are widely involved in numerous biological functions. In addition to addressing the related synthetic challenges, glycochemists have invested intense efforts in providing access to structures that can be used to study, activate, or inhibit these biological processes. Over the past few decades, aminooxylated carbohydrates have been found to be key building blocks for achieving these goals. This review provides the first in-depth overview covering several aspects related to the syntheses and applications of aminooxylated carbohydrates. After a brief introduction to oxime bonds and their relative stabilities compared to related C═N functions, synthetic aspects of oxime ligation and methodologies for introducing the aminooxy functionality onto both glycofuranosyls and glycopyranosyls are described. The subsequent section focuses on biological applications involving aminooxylated carbohydrates as components for the construcion of diverse architectures. Mimetics of natural structures represent useful tools for better understanding the features that drive carbohydrate-receptor interaction, their biological output and they also represent interesting structures with improved stability and tunable properties. In the next section, multivalent structures such as glycoclusters and glycodendrimers obtained through oxime ligation are described in terms of synthetic design and their biological applications such as immunomodulators. The second-to-last section discusses miscellaneous applications of oxime-based glycoconjugates, such as enantioselective catalysis and glycosylated oligonucleotides, and conclusions and perspectives are provided in the last section.

Mannose-Functionalized Hyperbranched Polyglycerol Loaded with Zinc Porphyrin: Investigation of the Multivalency Effect in Antibacterial Photodynamic Therapy

The antibacterial photodynamic activity of hyperbranched polyglycerol (hPG) loaded with zinc porphyrin photosensitizers and mannose units was investigated. hPG, with a M_W of 19.5 kDa, was functionalized with about 15 molecules of the photosensitizer {5,10,15-tris(3-hydroxyphenyl)-20-[4-(prop-2-yn-1-ylamino)tetrafluorophenyl]porphyrinato}-zinc(II) by using copper(I)-catalyzed 1,3-dipolar cycloaddition (CuAAC). These nanoparticle conjugates were functionalized systematically with increasing loadings of mannose in the range of approximately 20 to 110 groups. With higher mannose loadings (ca. 58-110 groups) the water-insoluble zinc porphyrin photosensitizer could thus be transferred into a water-soluble form. Targeting of the conjugates was proven in binding studies to the mannose-specific lectin concanavalin A (Con A) by using surface plasmon resonance (SPR). The antibacterial phototoxicity of the conjugates on Staphylococcus aureus (as a typical Gram-positive germ) was investigated in phosphate-buffered saline (PBS). It was shown that conjugates with approximately 70-110 mannose units exhibit significant antibacterial activity, whereas conjugates with approximately 20-60 units did not induce bacterial killing at all. These results give an insight into the multivalency effect in combination with photodynamic therapy (PDT). On addition of serum to the bacterial cultures, a quenching of this antibacterial phototoxicity was observed. In fluorescence studies with the conjugates in the presence of increasing bovine serum albumin (BSA) concentrations, protein-conjugate associations could be identified as a plausible cause for this quenching.

Oxime conjugation in protein chemistry: from carbonyl incorporation to nucleophilic catalysis

Use of oxime forming reactions has become a widely applied strategy for peptide and protein bioconjugation. The efficiency of the reaction and robust stability of the oxime product has led to the development of a growing list of methods to introduce the required ketone or aldehyde functionality site specifically into proteins. Early methods focused on site-specific oxidation of an N-terminal serine or threonine and more recently transamination methods have been developed to convert a broader set of N-terminal amino acids into a ketone or aldehyde. More recently, site-specific modification of protein has been attained through engineering enzymes involved in posttranslational modifications in order to accommodate aldehyde-containing substrates. Similarly, a growing list of unnatural amino acids can be introduced through development of selective amino-acyl tRNA synthetase/tRNA pairs combined with codon reassignment. In the case of glycoproteins, glycans can be selectively modified chemically or enzymatically to introduce aldehyde functional groups. Finally, the total chemical synthesis of proteins complements these biological and chemoenzymatic approaches. Once introduced, the oxime ligation of these aldehyde and ketone groups can be catalyzed by aniline or a variety of aniline derivatives to tune the activity, pH preference, stability and solubility of the catalyst. Copyright © 2016 European Peptide Society and John Wiley & Sons, Ltd.

Multivalent Interactions: Synthesis and Evaluation of Melanotropin Multimers - Tools for Melanoma Targeting

In order to develop agents for early detection and selective treatment of melanomas, high affinity and high specificity molecular tools are required. Enhanced specificity may be obtained by simultaneously binding to multiple cell surface targets via the use of multimeric analogs of naturally occurring ligands. Trimers targeting overexpressed melanocortin receptors have been found to be potential candidates for this purpose. In the present letter, we describe the synthesis and study of multimers based on a dendrimer-like scaffold. The binding affinity and activity results revealed that dendrimers promote multivalent interactions via statistical and/or cooperative effects on binding. Moreover, viability studies showed no significant toxicity at micromolar concentrations, which will allow these molecular complexes to be used in vivo. Finally, imaging studies showed effective internalization for all the molecules confirming their potential as delivery agents.

Understanding cytokine and growth factor receptor activation mechanisms

Our understanding of the detailed mechanism of action of cytokine and growth factor receptors - and particularly our quantitative understanding of the link between structure, mechanism and function - lags significantly behind our knowledge of comparable functional protein classes such as enzymes, G protein-coupled receptors, and ion channels. In particular, it remains controversial whether such receptors are activated by a mechanism of ligand-induced oligomerization, versus a mechanism in which the ligand binds to a pre-associated receptor dimer or oligomer that becomes activated through subsequent conformational rearrangement. A major limitation to progress has been the relative paucity of methods for performing quantitative mechanistic experiments on unmodified receptors expressed at endogenous levels on live cells. In this article, we review the current state of knowledge on the activation mechanisms of cytokine and growth factor receptors, critically evaluate the evidence for and against the different proposed mechanisms, and highlight other key questions that remain unanswered. New approaches and techniques have led to rapid recent progress in this area, and the field is poised for major advances in the coming years which promise to revolutionize our understanding of this large and biologically and medically important class of receptors.

Design, synthesis, and biological studies of efficient multivalent melanotropin ligands: tools toward melanoma diagnosis and treatment

To achieve early detection and specific cancer treatment, we propose the use of multivalent interactions in which a series of binding events leads to increased affinity and consequently to selectivity. Using melanotropin (MSH) ligands, our aim is to target melanoma cells which overexpress melanocortin receptors. In this study, we report the design and efficient synthesis of new trivalent ligands bearing MSH ligands. Evaluation of these multimers on a cell model engineered to overexpress melanocortin 4 receptors (MC4R) showed up to a 350-fold increase in binding compared to the monomer, resulting in a trivalent construct with nanomolar affinity starting from a micromolar affinity ligand. Cyclic adenosine monophosphate (cAMP) production was also investigated, leading to more insights into the effects of multivalent compounds on transduction mechanisms.

Maleimido-functionalized NOTA derivatives as bifunctional chelators for site-specific radiolabeling

Two basic and simple synthetic routes for mono- and bis-maleimide bearing 1,4,7-triazacyclononane-N,N’,N’’-triacetic acid (NOTA) chelators as new bifunctional chelators are described. The syntheses are characterized by their simplicity and short reaction times, as well as practical purification methods and acceptable to very good chemical yields. The usefulness of these two synthetic pathways is demonstrated by the preparation of a set of mono- and bis-maleimide functionalized NOTA derivatives. In conclusion, these two methods can easily be expanded to the syntheses of further tailored maleimide-NOTA chelators for diverse applications.

Synthesis and structure-activity relationships of dimeric peptide antagonists of the human immunoglobulin G-human neonatal Fc receptor (IgG-FcRn) interaction

The neonatal Fc receptor, FcRn, regulates the half-life of IgG in vivo and may be a target in the treatment of autoimmune disease. Monomeric peptide antagonists of the human IgG-human FcRn interaction were dimerized using three different synthetic methodologies: thiol/alkyl halide coupling of unprotected peptides, reductive alkylation of unprotected peptides, and on-resin amide bond formation with protected peptides. It was found that dimerization of monomeric peptides increased the in vitro activity of the peptide monomers more than 200-fold. Human IgG catabolism experiments in human FcRn transgenic mice were used to assess the in vivo activity of peptide dimers that possessed different linkers, cyclizations, and affinities for FcRn. Overall, it was found that the linker joining two monomeric peptides had only a minor effect on the in vitro potency but that in vitro potency was predictive of in vivo activity.

Use of agents stimulating erythropoiesis in digestive diseases

Anemia is the most common complication of inflammatory bowel disease (IBD). Control and inadequate treatment leads to a worse quality of life and increased morbidity and hospitalization. Blood loss, and to a lesser extent, malabsorption of iron are the main causes of iron deficiency in IBD. There is also a variable component of anemia related to chronic inflammation. The anemia of chronic renal failure has been treated for many years with recombinant human erythropoietin (rHuEPO), which significantly improves quality of life and survival. Subsequently, rHuEPO has been used progressively in other conditions that occur with anemia of chronic processes such as cancer, rheumatoid arthritis or IBD, and anemia associated with the treatment of hepatitis C virus. Erythropoietic agents complete the range of available therapeutic options for treatment of anemia associated with IBD, which begins by treating the basis of the inflammatory disease, along with intravenous iron therapy as first choice. In cases of resistance to treatment with iron, combined therapy with erythropoietic agents aims to achieve near-normal levels of hemoglobin/hematocrit (11-12 g/dL). New formulations of intravenous iron (iron carboxymaltose) and the new generation of erythropoietic agents (darbepoetin and continuous erythropoietin receptor activator) will allow better dosing with the same efficacy and safety.