Emerging concepts and approaches for chemokine-receptor drug discovery

Engineering broad-spectrum inhibitors of inflammatory chemokines from subclass A3 tick evasins

Chemokines are key regulators of leukocyte trafficking and attractive targets for anti-inflammatory therapy. Evasins are chemokine-binding proteins from tick saliva, whose application as anti-inflammatory therapeutics will require manipulation of their chemokine target selectivity. Here we describe subclass A3 evasins, which are unique to the tick genus Amblyomma and distinguished from "classical" class A1 evasins by an additional disulfide bond near the chemokine recognition interface. The A3 evasin EVA-AAM1001 (EVA-A) bound to CC chemokines and inhibited their receptor activation. Unlike A1 evasins, EVA-A was not highly dependent on N- and C-terminal regions to differentiate chemokine targets. Structures of chemokine-bound EVA-A revealed a deep hydrophobic pocket, unique to A3 evasins, that interacts with the residue immediately following the CC motif of the chemokine. Mutations to this pocket altered the chemokine selectivity of EVA-A. Thus, class A3 evasins provide a suitable platform for engineering proteins with applications in research, diagnosis or anti-inflammatory therapy.

Co-receptor signaling in the pathogenesis of neuroHIV

The HIV co-receptors, CCR5 and CXCR4, are necessary for HIV entry into target cells, interacting with the HIV envelope protein, gp120, to initiate several signaling cascades thought to be important to the entry process. Co-receptor signaling may also promote the development of neuroHIV by contributing to both persistent neuroinflammation and indirect neurotoxicity. But despite the critical importance of CXCR4 and CCR5 signaling to HIV pathogenesis, there is only one therapeutic (the CCR5 inhibitor Maraviroc) that targets these receptors. Moreover, our understanding of co-receptor signaling in the specific context of neuroHIV is relatively poor. Research into co-receptor signaling has largely stalled in the past decade, possibly owing to the complexity of the signaling cascades and functions mediated by these receptors. Examining the many signaling pathways triggered by co-receptor activation has been challenging due to the lack of specific molecular tools targeting many of the proteins involved in these pathways and the wide array of model systems used across these experiments. Studies examining the impact of co-receptor signaling on HIV neuropathogenesis often show activation of multiple overlapping pathways by similar stimuli, leading to contradictory data on the effects of co-receptor activation. To address this, we will broadly review HIV infection and neuropathogenesis, examine different co-receptor mediated signaling pathways and functions, then discuss the HIV mediated signaling and the differences between activation induced by HIV and cognate ligands. We will assess the specific effects of co-receptor activation on neuropathogenesis, focusing on neuroinflammation. We will also explore how the use of substances of abuse, which are highly prevalent in people living with HIV, can exacerbate the neuropathogenic effects of co-receptor signaling. Finally, we will discuss the current state of therapeutics targeting co-receptors, highlighting challenges the field has faced and areas in which research into co-receptor signaling would yield the most therapeutic benefit in the context of HIV infection. This discussion will provide a comprehensive overview of what is known and what remains to be explored in regard to co-receptor signaling and HIV infection, and will emphasize the potential value of HIV co-receptors as a target for future therapeutic development.

Targeting Chemokines and Chemokine Receptors in Multiple Sclerosis and Experimental Autoimmune Encephalomyelitis

Multiple sclerosis (MS) is an immune-mediated and neurodegenerative disorder that results in inflammation and demyelination of the central nervous system (CNS). MS symptoms include walking difficulties, visual weakening, as well as learning and memory impairment, thus affecting the quality of the patient's life. Chemokines and chemokine receptors are expressed on the immune cells as well as the CNS resident cells. Several sets of chemokine receptors and their ligands tend to be pathogenic players in MS, including CCL2, CCL3, CCL4, CCL5, CCL7, CCL8, CCL11, CCL17, CCL19, CCL21, CCL22, CXCL1, CXCL8, CXCL9, CXCL10, CXCL11, and CXCL16. Furthermore, current modulatory drugs that are used in the treatment of MS and its animal model, the experimental autoimmune encephalomyelitis (EAE), affect the expression of several chemokine and chemokine receptors. In this review, we highlight the pathogenic roles of chemokines and their receptors as well as utilizing them as potential therapeutic targets through selective agents, such as specific antibodies and receptor blockers, or indirectly through MS or EAE immunomodulatory drugs.

CXCR4-targeting nanobodies differentially inhibit CXCR4 function and HIV entry

The chemokine receptor CXCR4 and its ligand CXCL12 contribute to a variety of human diseases, such as cancer. CXCR4 is also a major co-receptor facilitating HIV entry. Accordingly, CXCR4 is considered as an attractive therapeutic target. Drug side effects and poor pharmacokinetic properties have been major hurdles that have prevented the implementation of CXCR4-directed inhibitors in treatment regimes. We evaluated the activity of a new and promising class of biologics, namely CXCR4-targeting nanobodies, with the purpose of identifying nanobodies that would preferentially inhibit HIV infection, while minimally disturbing other CXCR4-related functions. All CXCR4-interacting nanobodies inhibited CXCL12 binding and receptor-mediated calcium mobilization with comparable relative potencies. Importantly, the anti-HIV-1 activity of the nanobodies did not always correlate with their ability to modulate CXCR4 signaling and function, indicating that the anti-HIV and anti-CXCR4 activity are not entirely overlapping and may be functionally separated. Three nanobodies with divergent activity profiles (VUN400, VUN401 and VUN402) were selected for in depth biological evaluation. While all three nanobodies demonstrated inhibitory activity against a wide range of HIV (X4) strains, VUN402 poorly blocked CXCL12-induced CXCR4 internalization, chemotaxis and changes in cell morphology. Each of these nanobodies recognized distinct, although partially overlapping epitopes on CXCR4, which might underlie their distinct activity profiles. Our results demonstrate the potential of CXCR4-targeting nanobody VUN402 as a novel lead and starting point for the development of a more potent and selective anti-HIV agent.

High levels of cerebrospinal fluid chemokines point to the presence of neuroinflammation in peripheral neuropathic pain: a cross-sectional study of 2 cohorts of patients compared with healthy controls

According to animal models, neuroinflammation is a major feature of neuropathic pain. The present findings confirm that this hypothesis is of relevance to humans.

Animal models suggest that chemokines are important mediators in the pathophysiology of neuropathic pain. Indeed, these substances have been called “gliotransmitters,” a term that illustrates the close interplay between glial cells and neurons in the context of neuroinflammation and pain. However, evidence in humans is scarce. The aim of the study was to determine a comprehensive cerebrospinal fluid (CSF) inflammatory profile of patients with neuropathic pain. Our hypothesis was that we would thereby find indications of a postulated on-going process of central neuroinflammation. Samples of CSF were collected from 2 cohorts of patients with neuropathic pain (n = 11 and n = 16, respectively) and healthy control subjects (n = 11). The samples were analyzed with a multiplex proximity extension assay in which 92 inflammation-related proteins were measured simultaneously (Proseek Multiplex Inflammation I; Olink Bioscience, Uppsala, Sweden). Univariate testing with control of false discovery rate, as well as orthogonal partial least squares discriminant analysis, were used for statistical analyses. Levels of chemokines CXCL6, CXCL10, CCL8, CCL11, CCL23 in CSF, as well as protein LAPTGF-beta-1, were significantly higher in both neuropathic pain cohorts compared with healthy controls, pointing to neuroinflammation in patients. These 6 proteins were also major results in a recent similar study in patients with fibromyalgia. The findings need to be confirmed in larger cohorts, and the question of causality remains to be settled. Because it has been suggested that prevalent comorbidities to chronic pain (eg, depression, anxiety, poor sleep, and tiredness) also are associated with neuroinflammation, it will be important to determine whether neuroinflammation is a common mediator.

Chemokines from a Structural Perspective

Chemokines are a family of small, highly conserved cytokines that mediate various biological processes, including chemotaxis, hematopoiesis, and angiogenesis, and that function by interacting with cell surface G-Protein Coupled Receptors (GPCRs). Because of their significant involvement in various biological functions and pathologies, chemokines and their receptors have been the focus of therapeutic discovery for clinical intervention. There are several sub-families of chemokines (e.g., CXC, CC, C, and CX3C) defined by the positions of sequentially conserved cysteine residues. Even though all chemokines also have a highly conserved, three-stranded β-sheet/α-helix tertiary structural fold, their quarternary structures vary significantly with their sub-family. Moreover, their conserved tertiary structures allow for subunit swapping within and between sub-family members, thus promoting the concept of a “chemokine interactome”. This review is focused on structural aspects of CXC and CC chemokines, their functional synergy and ability to form heterodimers within the chemokine interactome, and some recent developments in structure-based chemokine-targeted drug discovery.

Circulating chemokine ligand levels before and after successful kidney transplantation

BACKGROUND

Chemokine ligands (CCLs) play a pivotal role in tissue injury before and after kidney transplantation. Meanwhile, transplantation improves patient's survival and diminishes morbidity. It is hypothesized, then, that kidney transplantation diminishes pre-transplant (pre-TX) levels of circulating inflammatory CCLs. This retrospective study compared circulating levels and profiles of CCLs before transplantation (pre-TX) and after transplantation (post-TX).

METHODS

Nineteen CCLs (1, 2, 3, 4, 5, 8, 11, 13, 15, 17, 21, 24, 26, 27, CXCL 5, 8, 10, 12 and 13) were measured in 47 stable post-TX recipients, and their stored pre-TX plasma was analyzed by multiplexed fluorescent bead-based immunoassay. Twenty normal controls were included for comparisons. Normalized data was presented as mean ± SD and non-normalized data as median (5-95 % CI). Significance was measured at p < 0.01. Arbitrary upper and lower margins for each CCL at the 95 % CI or 2SD levels in each group were chosen to calculate the percentile of patients in the other group who exceeded these limits. Significant CCL levels present in more than 75 % of patients in a group that exceeded the arbitrary upper or lower set margins in the other two groups were labeled as preferentially characteristic for the respective group.

RESULTS

More than 75 % of pre- and post-TX patients had levels that exceeded the upper control for CCL1, 11, 15 and CCL15, CCL26 and CXCL13 levels, respectively. More than 75 % of pre- and post-TX patients exceeded the lower control for CCL3, 21, and CCL5 limits, respectively. More than 75 % of post-TX patients demonstrated elevated levels of CCL2, 3, 21, 26 and CXCL13 above the upper pre-TX cut offs. Meanwhile, more than 75 % of post-TX patients exceeded the lower pre-TX levels for CCL1, 4, 5, 8, 13, 15, 17, 24 and CXCL8 and10. Pre-TX was preferentially characterized by elevated CCL1 and 15 and diminished CCL3 and 21. Post-TX was preferentially characterized by elevated CCL26 and CXCL13 and diminished CCL4 and 5.

CONCLUSION

End stage kidney disease is associated with enhanced circulating inflammatory chemokine levels. Stable kidney transplantation is associated with 1) lowered burden of circulating inflammatory chemokine levels and, 2) elevation in the pro T-helper2 chemokine, CCL26 and the homeostatic CXCL13.

Synthesis of polymers and nanoparticles bearing polystyrene sulfonate brushes for chemokine binding

This paper describes the synthesis of polymers and silica nanoparticles, both bearing polystyrene sulfonate brushes, and the measurement of their binding affinity for the chemokine monocyte chemoattractant protein-1 (MCP-1) in monomeric and dimeric form.

Elucidation of the CCR1- and CCR5-binding modes of MIP-1α by application of an NMR spectra reconstruction method to the transferred cross-saturation experiments

C-C chemokine receptor 1 (CCR1) and CCR5 are involved in various inflammation and immune responses, and regulate the progression of the autoimmune diseases differently. However, the number of residues identified at the binding interface was not sufficient to clarify the differences in the CCR1- and CCR5-binding modes to MIP-1α, because the NMR measurement time for CCR1 and CCR5 samples was limited to 24 h, due to their low stability. Here we applied a recently developed NMR spectra reconstruction method, Conservation of experimental data in ANAlysis of FOuRier, to the amide-directed transferred cross-saturation experiments of chemokine receptors, CCR1 and CCR5, embedded in lipid bilayers of the reconstituted high density lipoprotein, and MIP-1α. Our experiments revealed that the residues on the N-loop and β-sheets of MIP-1α are close to both CCR1 and CCR5, and those in the C-terminal helix region are close to CCR5. These results suggest that the genetic influence of the single nucleotide polymorphisms of MIP-1α that accompany substitution of residues in the C-terminal helix region, E57 and V63, would provide clues toward elucidating how the CCR5-MIP-1α interaction affects the progress of autoimmune diseases.

Probing Biased Signaling in Chemokine Receptors

The chemokine system mediates leukocyte migration during homeostatic and inflammatory processes. Traditionally, it is described as redundant and promiscuous, with a single chemokine ligand binding to different receptors and a single receptor having several ligands. Signaling of chemokine receptors occurs via two major routes, G protein- and β-arrestin-dependent, which can be preferentially modulated depending on the ligands or receptors involved, as well as the cell types or tissues in which the signaling event occurs. The preferential activation of a certain signaling pathway to the detriment of others has been termed signaling bias and can accordingly be grouped into ligand bias, receptor bias, and tissue bias. Bias has so far been broadly overlooked in the process of drug development. The low number of currently approved drugs targeting the chemokine system, as well as the broad range of failed clinical trials, reflects the need for a better understanding of the chemokine system. Thus, understanding the character, direction, and consequence of biased signaling in the chemokine system may aid the development of new therapeutics. This review describes experiments to assess G protein-dependent and -independent signaling in order to quantify chemokine system bias.

Production of Recombinant Chemokines and Validation of Refolding

The diverse roles of chemokines in normal immune function and many human diseases have motivated numerous investigations into the structure and function of this family of proteins. Recombinant chemokines are often used to study how chemokines coordinate the trafficking of immune cells in various biological contexts. A reliable source of biologically active protein is vital for any in vitro or in vivo functional analysis. In this chapter, we describe a general method for the production of recombinant chemokines and robust techniques for efficient refolding that ensure consistently high biological activity. Considerations for initiating development of protocols consistent with Current Good Manufacturing Practices (cGMPs) to produce biologically active chemokines suitable for use in clinical trials are also discussed.

Chemokine receptor expression on monocytes from healthy individuals

Chronic immune mediated inflammation is characterized by continuous chemokine mediated recruitment and activation of pro-inflammatory cells, monocytes in particular. We believe that an evaluation of the recruitment profile of monocytes during healthy condition is essential for the understanding of cellular response in disease. For this, we have established normal reference values and 95% confidence intervals for receptor expression of 20 chemokine receptors on monocyte subsets; classical (CD14+ CD16−), non-classical (CD14+ CD16+) and HLA-DRhi monocytes from 20 healthy controls using flow cytometry. We demonstrate significant differences in the chemokine receptor expression profiles and high correlation between fraction of cells and level of expression. This is the first global approach to provide a platform for comparable evaluation of cell recruitment during normal and under inflammatory conditions. This will be useful when exploring chemokine–chemokine receptor interactions, inhibition of chemokine signaling and selective removal of migrating cells, which are new treatment strategies in immune mediated diseases.

Grapefruit-Derived Nanovectors Use an Activated Leukocyte Trafficking Pathway to Deliver Therapeutic Agents to Inflammatory Tumor Sites

Inflammation is a hallmark of cancer. Activated immune cells are intrinsically capable of homing to inflammatory sites. Using three inflammatory-driven disease mouse models, we show that grapefruit-derived nanovectors (GNV) coated with inflammatory-related receptor enriched membranes of activated leukocytes (IGNVs) are enhanced for homing to inflammatory tumor tissues. Blocking LFA-1 or CXCR1 and CXCR2 on the IGNVs significantly inhibits IGNV homing to the inflammatory tissue. The therapeutic potential of IGNVs was further demonstrated by enhancing the chemotherapeutic effect as shown by inhibition of tumor growth in two tumor models and inhibiting the inflammatory effects of dextran sulfate sodium-induced mouse colitis. The fact that IGNVs are capable of homing to inflammatory tissue and that chemokines are overexpressed in diseased human tissue provides the rationale for using IGNVs to more directly deliver therapeutic agents to inflammatory tumor sites and the rationale for the use of IGNVs as treatment for certain cancers in personalized medicine.

Functionally biased signalling properties of 7TM receptors - opportunities for drug development for the ghrelin receptor

The ghrelin receptor is a 7 transmembrane (7TM) receptor involved in a variety of physiological functions including growth hormone secretion, increased food intake and fat accumulation as well as modulation of reward and cognitive functions. Because of its important role in metabolism and energy expenditure, the ghrelin receptor has become an important therapeutic target for drug design and the development of anti-obesity compounds. However, none of the compounds developed so far have been approved for commercial use. Interestingly, the ghrelin receptor is able to signal through several different signalling pathways including Gαq , Gαi/o , Gα12/13 and arrestin recruitment. These multiple signalling pathways allow for functionally biased signalling, where one signalling pathway may be favoured over another either by selective ligands or through mutations in the receptor. In the present review, we have described how ligands and mutations in the 7TM receptor may bias the receptors to favour either one G-protein over another or to promote G-protein independent signalling pathways rather than G-protein-dependent pathways. For the ghrelin receptor, both agonist and inverse agonists have been demonstrated to signal more strongly through the Gαq -coupled pathway than the Gα12/13 -coupled pathway. Similarly a ligand that promotes Gαq coupling over Gαi coupling has been described and it has been suggested that several different active conformations of the receptor may exist dependent on the properties of the agonist. Importantly, ligands with such biased signalling properties may allow the development of drugs that selectively modulate only the therapeutically relevant physiological functions, thereby decreasing the risk of side effects.

LINKED ARTICLES

This article is part of a themed section on Neuropeptides. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2013.170.issue-7.

The role of chemokines in Guillain-Barré syndrome

INTRODUCTION

Chemokines and their receptors are important mediators of inflammation. Guillain-Barré syndrome (GBS) is the most common cause of acute paralysis worldwide. Despite current treatments, outcomes are suboptimal. Specific chemokine receptor antagonists have the potential to be efficacious against pathogenic leukocyte trafficking in GBS.

METHODS

A 36-year literature review was performed to summarize available data on chemokine expression in GBS and its representative animal model, experimental autoimmune neuritis (EAN).

RESULTS

Although there were a few observational human and animal studies demonstrating chemokine ligand/receptor expression in GBS and EAN, in vitro and in vivo functional studies using gene knockouts, neutralizing antibodies, or small molecular antagonists were limited. CCL2-CCR2, CCL5-CCR5, and CXCL10-CXCR3 have been most strongly implicated in EAN and GBS pathogenesis, providing targets for molecular blockade.

CONCLUSIONS

Preclinical human in vitro and in vivo EAN studies are needed to evaluate the potential efficacy of chemokine signaling inhibition in GBS.

Biased and constitutive signaling in the CC-chemokine receptor CCR5 by manipulating the interface between transmembrane helices 6 and 7

The equilibrium state of CCR5 is manipulated here toward either activation or inactivation by introduction of single amino acid substitutions in the transmembrane domains (TMs) 6 and 7. Insertion of a steric hindrance mutation in the center of TM7 (G286F in position VII:09/7.42) resulted in biased signaling. Thus, β-arrestin recruitment was eliminated, whereas constitutive activity was observed in Gαi-mediated signaling. Furthermore, the CCR5 antagonist aplaviroc was converted to a full agonist (a so-called efficacy switch). Computational modeling revealed that the position of the 7TM receptor-conserved Trp in TM6 (Trp-248 in position VI:13/6.48, part of the CWXP motif) was influenced by the G286F mutation, causing Trp-248 to change orientation away from TM7. The essential role of Trp-248 in CCR5 activation was supported by complete inactivity of W248A-CCR5 despite maintaining chemokine binding. Furthermore, replacing Trp-248 with a smaller aromatic amino acid (Tyr/Phe) impaired the β-arrestin recruitment, yet with maintained G protein activity (biased signaling); also, here aplaviroc switched to a full agonist. Thus, the altered positioning of Trp-248, induced by G286F, led to a constraint of G protein active, but β-arrestin inactive and thus biased, CCR5 conformation. These results provide important information on the molecular interplay and impact of TM6 and TM7 for CCR5 activity, which may be extrapolated to other chemokine receptors and possibly to other 7TM receptors.

Sequential staining improves detection of CCR2 and CX3CR1 on monocytes when simultaneously evaluating CCR5 by multicolor flow cytometry

Chemokines and their receptors play an essential role within the immune system by dictating cellular migration. In vivo, receptor-ligand interactions rarely occur in isolation as cellular recruitment and migration are complex and highly coordinated processes often involving networks of multiple chemokines and multiple receptors. Simultaneous detection of multiple chemokine receptors on the single cell level is necessary to allow immunophenotyping studies that will help understand the intricacies of these networks. Chemokine receptors undergo a basal level of ongoing internalization, intracellular trafficking, and recycling back to the cell surface, even in the absence of the ligand. In the presence of ligand, receptor-ligand interactions enhance receptor internalization, reducing the cell surface receptor concentration, making precise determination of intrinsic levels challenging. Using multicolor flow cytometry, we sought to evaluate and optimize the simultaneous detection of cell surface expression levels of CCR2, CX3CR1, and CCR5 in primary human monocytes using a single antibody panel. We observed that staining for CCR2 alone or for CX3CR1 alone showed greater expression levels than when the cells were stained with the full panel of antibodies. Fluorescent-minus-one (FMO) controls revealed that ligation of the CCR5 monoclonal antibody to the receptor interfered with detection of CX3CR1 and CCR2. Sequential addition of antibodies during the staining procedure was sufficient to restore the detection levels, suggesting close proximity and possible functional interactions between CCR2/CCR5 and CX3CR1/CCR5 in monocytes. This study highlights the importance of optimizing staining procedures and using proper controls when simultaneously evaluating expression levels of multiple chemokine receptors by flow cytometry. Concurrent assessment of multiple receptors will provide insight and greater understanding of the complex interactions involved in cellular migration.

Nematode asparaginyl-tRNA synthetase resolves intestinal inflammation in mice with T-cell transfer colitis

The therapeutic effects of a controlled parasitic nematode infection on the course of inflammatory bowel disease (IBD) have been demonstrated in both animal and human models. However, the inability of individual well-characterized nematode proteins to recreate these beneficial effects has limited the application of component immunotherapy to human disease. The nematodes that cause chronic human lymphatic filariasis, Brugia malayi and Wuchereria bancrofti, are among the parasites that induce immune suppression. Filarial lymphatic pathology has been shown to involve NF-κB pathway-dependent production of vascular endothelial growth factor (VEGF), and stimulation of VEGF expression has also been reported by interleukin 8 (IL-8) via NF-κB pathways. Previously, we have shown that the filarial asparaginyl-tRNA synthetase (rBmAsnRS) interacts with IL-8 receptors using a combination of extracellular loops that differ from those bound by IL-8. To test the hypothesis that rBmAsnRS might induce an anti-inflammatory effect in vivo, we studied the effects of rBmAsnRS in an established murine colitis model using T-cell transfer mice. T-cell transfer colitis mice treated intraperitoneally with 100 μg of rBmAsnRS four times over 2 weeks showed resolution of cellular infiltration in the colonic mucosa, along with induction of a CD8(+) cellular response. In addition, rBmAsnRS induced a rise in IL-10 production from CD3(+) and lipopolysaccharide (LPS)- and cytosine phosphate guanosine (CPG)-stimulated splenic cells. In summary, this work demonstrates a novel anti-inflammatory nematode protein, supports the hygiene hypothesis, and supports continued refinement of alternative immunotherapies for treatment of IBD.

Potent CXCR4 antagonists containing amidine type Peptide bond isosteres

A series of FC131 [cyclo(-d-Tyr-Arg-Arg-Nal-Gly-)] analogues containing amidine type peptide bond isosteres were synthesized as selective CXC chemokine receptor type 4 (CXCR4) antagonists. An isosteric amidine substructure was constructed by a macrocyclization process using nitrile oxide-mediated C-N bond formation. All of the amidine-containing FC131 analogues exhibited potent SDF-1 binding inhibition to CXCR4. The Nal-Gly-substituted analogue was characterized as one of the most potent cyclic pentapeptide-based CXCR4 antagonists reported to date. The improved activity against human immunodeficiency virus (HIV) type-1 X4 strains suggested that addition of another basic amidine group to the peptide backbone effectively increases the selective binding of the peptides to CXCR4 receptor.