Amino-terminal dimerization of an erythropoietin mimetic peptide results in increased erythropoietic activity

Single-chain tandem macrocyclic peptides as a scaffold for growth factor and cytokine mimetics

Mimetics of growth factors and cytokines are promising tools for culturing large numbers of cells and manufacturing regenerative medicine products. In this study, we report single-chain tandem macrocyclic peptides (STaMPtides) as mimetics in a new multivalent peptide format. STaMPtides, which contain two or more macrocyclic peptides with a disulfide-closed backbone and peptide linkers, are successfully secreted into the supernatant by Corynebacterium glutamicum-based secretion technology. Without post-secretion modification steps, such as macrocyclization or enzymatic treatment, bacterially secreted STaMPtides form disulfide bonds, as designed; are biologically active; and show agonistic activities against respective target receptors. We also demonstrate, by cell-based assays, the potential of STaMPtides, which mimic growth factors and cytokines, in cell culture. The STaMPtide technology can be applied to the design, screening, and production of growth factor and cytokine mimetics.

Double Conjugation Using Mercapto-Acryloyl and Alkyne-Azide Reactions for the Synthesis of Branched Multiantigenic Vaccine Candidates

Chemical conjugation of peptide epitopes and lipids into a single branched lipopeptide is a promising strategy for the generation of multiantigenic vaccines. We developed a double conjugation strategy that utilizes a mercapto-acryloyl Michael addition reaction between two unprotected peptides, followed by a copper-catalyzed alkyne-azide 1,3-dipolar cycloaddition (CuAAC) click reaction. The technique proved capable of producing branched multiantigenic vaccine candidates with an overall yield of 78%.

One-Step Protein-Polymer Conjugates from Boronic-Acid-Functionalized Polymers

Polymer-protein conjugates are hybrid materials with interesting and useful properties. Methods to prepare diverse diblock materials of this sort often struggle to deal with the complexity and size of reagents, and so polymer-protein conjugation represents a stringent testing ground for nontraditional bioconjugation methods, such as metal-catalyzed arylation. This work demonstrates a simple Ni²⁺-promoted arylation of cysteine residues with end-functionalized polymer-boronic acid reagents, and explores some molecular and physical properties possible in these hybrid structures.

1,3-Dichloroacetone: A Robust Reagent for Preparing Bicyclic Peptides

The chemical synthesis of cyclic peptides is a well-established area of research. This has been further expanded by development of bio-orthogonal reactions that enable access to peptides of greater structural complexity. One approach utilizes 1,3-dichloroacetone to selectively link free cysteine side-chains with an acetone-like bridge via an S_N2 reaction. Here, we have used this reaction to dimerize cyclic peptide monomers to create novel bicyclic dimeric peptides. We investigated a range of reaction parameters to identify the optimal dimerization conditions for our model systems. One of the acetone-linked dimeric peptides was analyzed for proteolytic stability in human serum and was observed to still be fully intact after 48 h. This study provides valuable insights into the application of 1,3-dichloroacetone as a tool in the synthesis of complex, multicyclic peptides.

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.

A novel GLP-1 analog, a dimer of GLP-1 via covalent linkage by a lysine, prolongs the action of GLP-1 in the treatment of type 2 diabetes

GLP-1 is an incretin hormone that can effectively lower blood glucose, however, the short time of biological activity and the side effect limit its therapeutic application. Many methods have been tried to optimize GLP-1 to extend its in vivo half-time, reduce its side effect and enhance its activity. Here we have chosen the idea to dimerize GLP-1 with a C-terminal lysine to form a new GLP-1 analog, DLG3312. We have explored the structure and the biological property of DLG3312, and the results indicated that DLG3312 not only remained the ability to activate the GLP-1R, but also strongly stimulated Min6 cell to secrete insulin. The in vivo bioactivities have been tested on two kinds of animal models, the STZ induced T2DM mice and the db/db mice, respectively. DLG3312 showed potent anti-diabetic ability in glucose tolerance assay and single-dose administration of DLG3312 could lower blood glucose for at least 10 hours. Long-term treatment with DLG3312 can reduce fasted blood glucose, decrease water consumption and food intake and significantly reduce the HbA1c level by 1.80% and 2.37% on STZ induced T2DM mice and the db/db mice, respectively. We also compared DLG3312 with liraglutide to investigate its integrated control of the type 2 diabetes. The results indicated that DLG3312 almost has the same effect as liraglutide but with a much simpler preparation process. In conclusion, we, by using C-terminal lysine as a linker, have synthesized a novel GLP-1 analog, DLG3312. With simplified preparation and improved physiological characterizations, DLG3312 could be considered as a promising candidate for the type 2 diabetes therapy.

Binding behaviour of a 12-mer peptide and its tandem dimer to gymnospermae and angiospermae lignins

Analysis of conformational changes of lignin-binding dodecapeptide and its tandem dimer on addition of lignin by ATR-FTIR.

Designing a small molecule erythropoietin mimetic

Erythropoietin (EPO) is a protein made by the kidneys in response to low red blood cell count that is secreted into the bloodstream and binds to a receptor on hematopoietic stem cells in the bone marrow inducing them to become new red blood cells. EPO made with recombinant DNA technology was brought to market in the 1980s to treat anemia caused by kidney disease and cancer chemotherapy. Because EPO infusion was able to replace blood transfusions in many cases, it rapidly became a multibillion dollar per year drug and as the first biologic created with recombinant technology it launched the biotech industry. For many years intense research was focused on creating a small molecule orally available EPO mimetic. The Robert Wood Johnson (RWJ) group seemed to definitively establish that only large peptides with a minimum of 60 residues could replace EPO, as anything less was not a full agonist. An intense study of the published work led me to hypothesize that the size of the mimetic is not the real issue, but the symmetry making and breaking of the EPO receptor induced by the ligand is the key to activating the stem cells. This analysis meant that residues in the binding site of the receptor deemed absolutely essential for ligand binding and activation from mutagenesis experiments, were probably not really that important. My fundamental hypotheses were: (a) the symmetric state of the homodimeric receptor is the most stable state and thus must be the off-state, (b) a highly localized binding site exists at a pivot point where the two halves of the receptor meet, (c) small molecules can be created that have high potency for this site that will be competitive with EPO and thus can displace the protein-protein interaction, (d) small symmetric molecules will stabilize the symmetric off-state of the receptor, and (e) a key asymmetry in the small molecule will stabilize a mirror image asymmetry in the receptor resulting in the stabilization of the on-state and proliferation of the stem cells into red blood cells. Researchers at Amgen published a co-crystal structure of EPO bound to the EPO receptor, which has a beautiful twofold symmetry-it was argued that this is the active state of the receptor. Activating the EPO receptor with EPO induces an almost instantaneous shutdown mechanism to sharply curtail any proliferative signal transduction, and thus, my hypotheses lead to the conclusion that the Amgen co-crystal is actually the state after receptor downregulation and thus an off-state. To put these hypotheses to the test, my computational method of Simulated Annealing of Chemical Potential was run using the co-crystal created at RWJ, which is the receptor trapped in a partial agonist state. The simulations predicted a previously unknown high affinity binding site at the pivot point where the two halves of the dimeric receptor meet, and detailed analysis of the fragment patterns led to the prediction of a molecule less than 300 MW that is basically twofold symmetric with a chiral center on one side and not the other. Thus, to the degree that computer simulations can be taken seriously, these results support my hypotheses on small molecule receptor activation. When this small molecule was synthesized and tested it indeed induced human hematopoietic stems cells to become red blood cells. When the predicted chiral center of this molecule was removed eliminating its one asymmetric feature, the resulting molecule was an antagonist-it could potently displace hot EPO but could no longer induce stem cell proliferation and differentiation. These results provided strong support for my theories on how to create potent small molecule EPO agonists and were used to launch the new company Locus Pharmaceuticals. These molecules, however, required significant chemical changes in order to make them stable in other in vitro assays and to be in vivo active, but these alterations had to be done in a way that maintained the symmetry-asymmetry considerations that led to the creation of an in vitro active molecule. The combination of changing functional groups to enable good pharmacokinetics, while not changing the key intrinsic symmetry properties were never seriously pursued at Locus and the program died. Investigations into how red blood cells are created have occupied many prominent researchers for the entire twentieth century. In the second half of the century EPO was discovered and by the end of the century it became a blockbuster commercial product that launched the biotech revolution.

Design of growth factor sequestering biomaterials

Growth factors (GFs) are major regulatory proteins that can govern cell fate, migration, and organization. Numerous aspects of the cell milieu can modulate cell responses to GFs, and GF regulation is often achieved by the native extracellular matrix (ECM). For example, the ECM can sequester GFs and thereby control GF bioavailability. In addition, GFs can exert distinct effects depending on whether they are sequestered in solution, at two-dimensional interfaces, or within three-dimensional matrices. Understanding how the context of GF sequestering impacts cell function in the native ECM can instruct the design of soluble or insoluble GF sequestering moieties, which can then be used in a variety of bioengineering applications. This Feature Article provides an overview of the natural mechanisms of GF sequestering in the cell milieu, and reviews the recent bioengineering approaches that have sequestered GFs to modulate cell function. Results to date demonstrate that the cell response to GF sequestering depends on the affinity of the sequestering interaction, the spatial proximity of sequestering in relation to cells, the source of the GF (supplemented or endogenous), and the phase of the sequestering moiety (soluble or insoluble). We highlight the importance of context for the future design of biomaterials that can leverage endogenous molecules in the cell milieu and mitigate the need for supplemented factors.

Captides: rigid junctions between beta sheets and small molecules

An extensive series of covalently linked small molecule-peptide adducts based on a terminally capped-beta hairpin motif is reported. The constructs can be prepared by standard solid-phase Fmoc chemistry with one to four peptide chains linked to small molecule hubs bearing carboxylic acid moieties. The key feature of interest is the precise, buried environment of the small molecule, and its rigid orientation relative to one or more short but fully structured peptide chain(s). Most of this study employs a minimalist nine residue 'captide', a capped β-turn, but we illustrate general applicability to peptides which can terminate in a beta strand. The non-peptide portion of these adducts can include nearly any molecule bearing one or more carboxylic acid groups. Fold-dependent rigidity sets this strategy apart from the currently available bioconjugation methods, which typically engender significant flexibility between peptide and tag. Applications to catalyst enhancement, drug design, higher-order assembly, and FRET calibration rulers are discussed.

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.

OMICS-strategies and methods in the fight against doping

During the past decade OMICS-methods not only continued to have their impact on research strategies in life sciences and in particular molecular biology, but also started to be used for anti-doping control purposes. Research activities were mainly reasoned by the fact that several substances and methods, which were prohibited by the World Anti-Doping Agency (WADA), were or still are difficult to detect by direct methods. Transcriptomics, proteomics, and metabolomics in theory offer ideal platforms for the discovery of biomarkers for the indirect detection of the abuse of these substances and methods. Traditionally, the main focus of transcriptomics and proteomics projects has been on the prolonged detection of the misuse of human growth hormone (hGH), recombinant erythropoietin (rhEpo), and autologous blood transfusion. An additional benefit of the indirect or marker approach would also be that similarly acting substances might then be detected by a single method, without being forced to develop new direct detection methods for new but comparable prohibited substances (as has been the case, e.g. for the various forms of Epo analogs and biosimilars). While several non-OMICS-derived parameters for the indirect detection of doping are currently in use, for example the blood parameters of the hematological module of the athlete's biological passport, the outcome of most non-targeted OMICS-projects led to no direct application in routine doping control so far. The main reason is the inherent complexity of human transcriptomes, proteomes, and metabolomes and their inter-individual variability. The article reviews previous and recent research projects and their results and discusses future strategies for a more efficient application of OMICS-methods in doping control.

Supramolecular nanostructures that mimic VEGF as a strategy for ischemic tissue repair

There is great demand for the development of novel therapies for ischemic cardiovascular disease, a leading cause of morbidity and mortality worldwide. We report here on the development of a completely synthetic cell-free therapy based on peptide amphiphile nanostructures designed to mimic the activity of VEGF, one of the most potent angiogenic signaling proteins. Following self-assembly of peptide amphiphiles, nanoscale filaments form that display on their surfaces a VEGF-mimetic peptide at high density. The VEGF-mimetic filaments were found to induce phosphorylation of VEGF receptors and promote proangiogenic behavior in endothelial cells, indicated by an enhancement in proliferation, survival, and migration in vitro. In a chicken embryo assay, these nanostructures elicited an angiogenic response in the host vasculature. When evaluated in a mouse hind-limb ischemia model, the nanofibers increased tissue perfusion, functional recovery, limb salvage, and treadmill endurance compared to controls, which included the VEGF-mimetic peptide alone. Immunohistological evidence also demonstrated an increase in the density of microcirculation in the ischemic hind limb, suggesting the mechanism of efficacy of this promising potential therapy is linked to the enhanced microcirculatory angiogenesis that results from treatment with these polyvalent VEGF-mimetic nanofibers.

Recent developments in doping testing for erythropoietin

The constant development of new erythropoiesis-stimulating agents (ESAs), since the first introduction of recombinant erythropoietin (rhEpo) for clinical use, has also necessitated constant development of methods for detecting the abuse of these substances. Doping with ESAs is prohibited according to the World Anti-Doping Code and its prohibited list of substances and methods. Since the first publication of a direct and urine-based detection method in 2000, which uses changes in the Epo isoform profile as detected by isoelectric focusing in polyacrylamide slab gels (IEF-PAGE), the method has been constantly adapted to the appearance of new ESAs (e.g., Dynepo, Mircera). Blood had to be introduced as an additional matrix, because Mircera (a PEGylated Epo) is best confirmed in serum or plasma after immunoaffinity purification. A Mircera ELISA was developed for fast screening of sera. With the appearance of Dynepo and copy epoetins, the additional application of sodium dodecylsulfate polyacrylamide gel electrophoresis (SDS-PAGE or equivalent) became necessary. The haematological module of the Athlete Biological Passport is the latest development in multivariable indirect testing for ESA doping. The article summarizes the main strategies currently used in Epo anti-doping testing with special focus on new developments made between 2009 and 2010.

Directed evolution of a three-finger neurotoxin by using cDNA display yields antagonists as well as agonists of interleukin-6 receptor signaling

Background

Directed evolution of biomolecules such as DNA, RNA and proteins containing high diversity has emerged as an effective method to obtain molecules for various purposes. In the recent past, proteins from non-immunoglobulins have attracted attention as they mimic antibodies with respect to binding potential and provide further potential advantages. In this regard, we have attempted to explore a three-finger neurotoxin protein (3F). 3F proteins are small (~7 kDa), structurally well defined, thermally stable and resistant to proteolysis that presents them as promising candidates for directed evolution.

Results

We have engineered a snake α-neurotoxin that belongs to the 3F family by randomizing the residues in the loops involved in binding with acetylcholine receptors and employing cDNA display to obtain modulators of interleukin-6 receptor (IL-6R). Selected candidates were highly specific for IL-6R with dissociation constants and IC50s in the nanomolar range. Antagonists as well as agonists were identified in an IL-6 dependent cell proliferation assay. Size minimization yielded peptides of about one-third the molecular mass of the original proteins, without significant loss of activities and, additionally, lead to the identification of the loops responsible for function.

Conclusions

This study shows 3F protein is amenable to introduce amino acid changes in the loops that enable preparation of a high diversity library that can be utilized to obtain ligands against macromolecules. We believe this is the first report of protein engineering to convert a neurotoxin to receptor ligands other than the parent receptor, the identification of an agonist from non-immunoglobulin proteins, the construction of peptide mimic of IL-6, and the successful size reduction of a single-chain protein.

Erythropoietin receptor response circuits

PURPOSE OF REVIEW

In 1985-1989, erythropoietin (EPO), its receptor (EPOR), and janus kinase 2 were cloned; established to be essential for definitive erythropoiesis; and initially intensely studied. Recently, new impetus, tools, and model systems have emerged to re-examine EPO/EPOR actions, and are addressed in this review. Impetus includes indications that EPO affects significantly more than standard erythroblast survival pathways, the development of novel erythropoiesis-stimulating agents, increasing evidence for EPO/EPOR cytoprotection of ischemically injured tissues, and potential EPO-mediated worsening of tumorigenesis.

RECENT FINDINGS

New findings are reviewed in four functional contexts: (pro)erythroblast survival mechanisms, new candidate EPO/EPOR effects on erythroid cell development and new EPOR responses, EPOR downmodulation and trafficking, and novel erythropoiesis-stimulating agents.

SUMMARY

As Current Opinion, this monograph seeks to summarize, and provoke, new EPO/EPOR action concepts. Specific problems addressed include: beyond (and before) BCL-XL, what key survival factors are deployed in early-stage proerythroblasts? Are distinct EPO/EPOR signals transduced in stage-selective fashions? Is erythroblast proliferation also modulated by EPO/EPOR signals? What functions are subserved by new noncanonical EPO/EPOR response factors (e.g. podocalyxin like-1, tribbles 3, reactive oxygen species, and nuclear factor kappa B)? What key regulators mediate EPOR inhibition and trafficking? And for emerging erythropoiesis-stimulating agents, to what extent do activities parallel EPOs (or differ in advantageous, potentially complicating ways, or both)?

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.

Erythropoietin after a century of research: younger than ever

In the light of the enthusiasm regarding the use of recombinant human erythropoietin (Epo) and its analogues for treatment of the anaemias of chronic renal failure and malignancies it is worth remembering that today's success has been based on a century of laborious research. The concept of the humoral regulation of haematopoiesis was first formulated in 1906. The term 'erythropoietin' for the erythropoiesis-stimulating hormone was introduced in 1948. Native human Epo was isolated in 1977 and its gene cloned in 1985. During the last 15 yr, major progress has been made in identifying the molecules controlling Epo gene expression, primarily the hypoxia-inducible transcription factors (HIF) that are regulated by specific O2 and oxoglutarate requiring Fe2+-containing dioxygenases. With respect to the action of Epo, its dimeric receptor (Epo-R) has been characterised and shown to signal through protein kinases, anti-apoptotic proteins and transcription factors. The demonstration of Epo-R in non-haematopoietic tissues indicates that Epo is a pleiotropic viability and growth factor. The neuroprotective and cardioprotective potentials of Epo are reviewed with a focus on clinical research. In addition, studies utilising the Epo derivatives with prolonged half-life, peptidic and non-peptidic Epo mimetics, orally active drugs stimulating endogenous Epo production and Epo gene transfer are reviewed.

Multivalency—a way to enhance binding avidities and bioactivity—preliminary applications to EPO

Multivalency has advantages over monovalency for binding interactions and even for activity. In particular, avidity is higher since the off-rate of a multivalent species is much slower than that of a monomer. This is particularly profitable for ligand-binding receptors that require dimerization for activity, such as the receptor of erythropoietin (EPOR). Peptides that mimic the action of erythropoietin (EPO) have been described with no sequence similarity with the human hormone: erythropoietin mimetic peptide (EMP) and EPO receptor peptide (ERP). These two peptides have similar activity but interact through different sites on the EPOR. Here, we describe the construction of several new synthetic homo- and hetero-dimers based on EMP-ERP sequences. To link the monomeric molecules together, several monodisperse polyamide linkers of different lengths were synthesized with dialdehyde functionalities. Chemoselective oxime chemistry was used to obtain homogeneous constructs. Certain chemical incompatibilities were dealt with via a protection approach. The oximes are stable under normal conditions and so lend themselves to biological testing.

Comparison of epoetin alfa and darbepoetin alfa biological activity under different administration schedules in normal mice

The unit of erythropoietic activity has long been the standard by which erythropoietic agents are judged, but the development of long-acting agents such as darbepoetin alfa has highlighted the shortcomings of this approach. To this point, we compared the in vivo activity of Epoetin alfa and darbepoetin alfa per microgram of protein core. Using the established mass-to-unit conversion for Epoetin alfa (1 microg congruent with 200 U), we then calculated darbepoetin alfa activity in units. Activity varied with treatment regimen (1 microg darbepoetin alfa congruent with 800 U for 3 times weekly dosing to 8,000 U for a single injection). This analysis reveals the inadequacy of evaluating darbepoetin alfa activity in terms of standard erythropoietic units. We therefore propose that for molecules with heightened biological activity, a more legitimate basis for comparison is the protein mass.

Mechanistic diversity of cytokine receptor signaling across cell membranes

Circulating cytokines bind to specific receptors on the cell outer surface to evoke responses inside the cell. Binding of cytokines alters the association between receptor molecules that often cross the membrane only once in a single alpha-helical segment. As a consequence, association of protein domains on the inside of the membrane are also altered. Increasing evidence suggests that an initial "off-state" of associated receptors is perturbed, and brought to an activated state that leads to intracellular signaling and eventually effects a change in DNA transcription. The initial detection event that transduces the change in receptor association is sensitive to both proximity and orientation of the receptors, and probably also to the time that the activated state or receptor association is maintained. Ultimately, a cascade of phosphorylation events is triggered. The initial kinases are sometimes part of the intracellular domains of the receptors. The kinases can also be separate proteins that may be pre-associated with intracellular domains of the receptors, or can be recruited after the intracellular association of the activated receptors. We focus here on each of the cases for which structures of the activated cytokine-receptor complexes are known, in a search for underlying mechanisms. The variations in modes of association, stoichiometries of receptors and cytokines, and orientations before and after activation of these receptors are almost as great as the number of complexes themselves. The principles uncovered nevertheless illustrate the basis for high specificity and fidelity in cytokine-mediated signaling.

Drugs for increasing oxygen and their potential use in doping: a review

Blood oxygenation is a fundamental factor in optimising muscular activity. Enhancement of oxygen delivery to tissues is associated with a substantial improvement in athletic performance, particularly in endurance sports. Progress in medical research has led to the identification of new chemicals for the treatment of severe anaemia. Effective and promising molecules have been created and sometimes used for doping purposes. The aim of this review is to present methods, and drugs, known to be (or that might be) used by athletes to increase oxygen transport in an attempt to improve endurance capacity. These methods and drugs include: (i) blood transfusion; (ii) endogenous stimulation of red blood cell production at altitude, or using hypoxic rooms, erythropoietins (EPOs), EPO gene therapy or EPO mimetics; (iii) allosteric effectors of haemoglobin; and (iv) blood substitutes such as modified haemoglobin solutions and perfluorochemicals. Often, new chemicals are used before safety tests have been completed and athletes are taking great health risks. Such new chemicals have also created the need for new instrumental strategies in doping control laboratories, but not all of these chemicals are detectable. Further progress in analytical research is necessary.

Structural biology of insulin and IGF1 receptors: implications for drug design

Type 2 diabetes mellitus -- in which the body produces insufficient amounts of insulin or the insulin that is produced does not function properly to control blood glucose -- is an increasingly common disorder. Prospective clinical studies have proven the benefits of tighter glucose control in reducing the frequency and severity of complications of the disease, leading to the advocation of earlier and more aggressive use of insulin therapy. Given the reluctance of patients with type 2 diabetes to inject themselves with insulin, orally active insulin mimetics would be a major therapeutic advance. Here, we discuss recent progress in understanding the structure-function relationships of the insulin and insulin-like growth factor 1 (IGF1) receptors, their mechanism of activation and their implications for the design of insulin-receptor agonists for diabetes therapy and IGF1-receptor antagonists for cancer therapy.

Dimeric erythropoietin fusion protein with enhanced erythropoietic activity in vitro and in vivo

High doses of recombinant human erythropoietin (rhEpo) are required for the treatment of chronic anemia. Thus, it is clear that therapy for chronic anemia would greatly benefit from an erythropoietin derivative with increased erythropoietic activity rather than the native endogenous hormone. In this report, the activity of a human Epo-Epo dimer protein, obtained by recombinant technology, is described and compared with its Epo monomer counterpart produced under identical conditions. Although monomer Epo and dimer Epo-Epo had similar pharmacokinetics in normal mice, the increase in hematocrit value was greater with the dimer than with the monomer. Moreover, in clonogenic assays using CD34(+) human hematopoietic cells, the human dimer induced a 3- to 4-fold-greater proliferation of erythroid cells than the monomer. Controlled secretion of dimeric erythropoietin was achieved in beta-thalassemic mice by in vivo intramuscular electrotransfer of a mouse Epo-Epo plasmid containing the tetO element and of a plasmid encoding the tetracycline controlled transactivator tTA. Administration of tetracycline completely inhibited the expression of the mEpo dimer. On tetracycline withdrawal, expression of the Epo-Epo dimer resumed, thereby resulting in a large and sustained hematocrit increase in beta-thalassemic mice. No immunologic response against the dimer was apparent in mice because the duration of the hematocrit increase was similar to that observed with the monomeric form of mouse erythropoietin. (Blood. 2001;97:3776-3782)

Sorting polyclonal antibodies into functionally distinct fractions using peptide phage display: 'a library on top of a library'

A general approach for sorting antibodies (Abs) to a restricted protein domain was developed using phage-displayed peptide libraries. The method is demonstrated by fractionating polyclonal antibodies (pAbs), raised against a short peptide derived from the extracellular, juxtamembrane region of fibroblast growth factor receptor 1 (FGFR1) into fractions with distinct chemical and biological characteristics. Screening two combinatorial peptide libraries, with the pAb, several sequences, homologous to different regions within the original peptide, were identified. Four of the corresponding peptides were synthesized and used as peptide-conjugated affinity columns for the fractionation of the pAbs. The fractions obtained were unique in their recognition patterns and in their capacity to immunoprecipitate and immunoblot, as well as to modulate the activity of FGFR1. This technique is, therefore, highly sufficient in separating pAbs to monospecific fractions and may also be used for fine mapping of different, even overlapping, sequences within a restricted peptide or protein domain.

The structure, organization, activation and plasticity of the erythropoietin receptor

Dimerization of the erythropoietin receptor has long been accepted as the singular step in its mechanism of activation. Recent studies have revealed a regulator process for activation that is dependent on the actual configuration of the receptor-ligand dimer assembly. This aspect of the receptor subunit assembly appears to extend to the unliganded receptor, which can dimerize on the cell surface and diminish any spontaneous background signaling in the absence of ligand. This self-recognition, as well as the multiple ligand binding capabilities of the receptor binding site, is consistent with an emerging theme of plasticity in protein-protein and ligand-receptor interactions.

Macromolecular docking of a three-body system: the recognition of human growth hormone by its receptor

Human growth hormone (hGH) binds to its receptor (hGHr) in a three-body interaction: one molecule of the hormone and two identical monomers of the receptor form a trimer. Curiously, the hormone-receptor interactions in the trimer are not equivalent and the formation of the complex occurs in a specific kinetic order (Cunningham BC, Ultsch M, De Vos AM, Mulkerrin MG, Clauser KR, Wells JA, 1991, Science 254:821-825). In this paper, we model the recognition of hGH to the hGHr using shape complementarity of the three-dimensional structures and macromolecular docking to explore possible binding modes between the receptor and hormone. The method, reported previously (Hendrix DK, Kuntz ID, 1998, Pacific symposium on biocomputing 1998, pp 1234-1244), is based upon matching complementary-shaped strategic sites on the molecular surface. We modify the procedure to examine three-body systems. We find that the order of binding seen experimentally is also essential to our model. We explore the use of mutational data available for hGH to guide our model. In addition to docking hGH to the hGHr, we further test our methodology by successfully reproducing 16 macromolecular complexes from X-ray crystal structures, including enzyme-inhibitor, antibody-antigen, protein dimer, and protein-DNA complexes.

An antagonist peptide-EPO receptor complex suggests that receptor dimerization is not sufficient for activation

Dimerization of the erythropoietin (EPO) receptor (EPOR), in the presence of either natural (EPO) or synthetic (EPO-mimetic peptides, EMPs) ligands is the principal extracellular event that leads to receptor activation. The crystal structure of the extracellular domain of EPOR bound to an inactive (antagonist) peptide at 2.7 A resolution has unexpectedly revealed that dimerization still occurs, but the orientation between receptor molecules is altered relative to active (agonist) peptide complexes. Comparison of the biological properties of agonist and antagonist EMPs with EPO suggests that the extracellular domain orientation is tightly coupled to the cytoplasmic signaling events and, hence, provides valuable new insights into the design of synthetic ligands for EPOR and other cytokine receptors.

Higher order iminodiacetic acid libraries for probing protein-protein interactions

Higher order iminodiacetic acid diamide trimer (560 compounds) and tetramer libraries (1260 compounds) are described and were assembled in a convergent multistep solution-phase synthesis for use in studying protein-protein interactions.

Targeting growth factor and cytokine receptors with recombinant peptide libraries

The single-transmembrane-spanning receptors of cytokines and growth factors have historically proven resistant to the small-molecule screening efforts of the pharmaceutical industry. Advances in combinatorial library approaches to ligand discovery have begun to show success with these targets. There are several recent reports of peptides, derived from randomly assembled collections of L-peptides expressed in recombinant display vectors, that are high-affinity antagonists and even agonists of these receptors. These results indicate that molecules much smaller than the natural protein factors can interact effectively with these receptors, and this may lead the way to the discovery of even smaller nonpeptidic agents.