Discovery of a CXCR4 agonist pepducin that mobilizes bone marrow hematopoietic cells

Identifying and Assessing Putative Allosteric Sites and Modulators for CXCR4 Predicted through Network Modeling and Site Identification by Ligand Competitive Saturation

The chemokine receptor CXCR4 is a critical target for the treatment of several cancer types and HIV-1 infections. While orthosteric and allosteric modulators have been developed targeting its extracellular or transmembrane regions, the intramembrane region of CXCR4 may also include allosteric binding sites suitable for the development of allosteric drugs. To investigate this, we apply the Gaussian Network Model (GNM) to the monomeric and dimeric forms of CXCR4 to identify residues essential for its local and global motions located in the hinge regions of the protein. Residue interaction network (RIN) analysis suggests hub residues that participate in allosteric communication throughout the receptor. Mutual residues from the network models reside in regions with a high capacity to alter receptor dynamics upon ligand binding. We then investigate the druggability of these potential allosteric regions using the site identification by ligand competitive saturation (SILCS) approach, revealing two putative allosteric sites on the monomer and three on the homodimer. Two screening campaigns with Glide and SILCS-Monte Carlo docking using FDA-approved drugs suggest 20 putative hit compounds including antifungal drugs, anticancer agents, HIV protease inhibitors, and antimalarial drugs. In vitro assays considering mAB 12G5 and CXCL12 demonstrate both positive and negative allosteric activities of these compounds, supporting our computational approach. However, in vivo functional assays based on the recruitment of β-arrestin to CXCR4 do not show significant agonism and antagonism at a single compound concentration. The present computational pipeline brings a new perspective to computer-aided drug design by combining conformational dynamics based on network analysis and cosolvent analysis based on the SILCS technology to identify putative allosteric binding sites using CXCR4 as a showcase.

Triazolothiadiazine derivative positively modulates CXCR4 signaling and improves diabetic wound healing

Development of specific therapies that target and accelerate diabetic wound repair is an urgent need to alleviate pain and suffering and the huge socioeconomic burden of this debilitating disease. C-X-C Motif Chemokine Ligand 12 (CXCL12) also know an stromal cell-derived factor 1α (SDF-1α) is a chemokine that binds the CXC chemokine receptor type 4 (CXCR4) and activates downstream signaling resulting in recruitment of hematopoietic cells to locations of tissue injury and promotes tissue repair. In diabetes, low expression of CXCL12 correlates with impaired wound healing. Activation of CXCR4 receptor signaling with agonists or positive allosteric modulators (PAMs) provides a potential for small molecule therapeutic discovery and development. We recently reported high throughput screening and identification of the CXCR4 partial agonist UCUF-728, characterization of in vitro activity and reduced wound closure time in diabetic mice at 100 μM as a proof-of-concept study. We report here, the discovery of a second chemical scaffold demonstrating increased agonist potency and represented by thiadiazine derivative, UCUF-965. UCUF-965 is a potent partial agonist of β-arrestin recruitment in CXCR4 receptor overexpressing cell line. Furthermore, UCUF-965 potentiates the CXCL12 maximal response in cAMP signaling pathway, activates CXCL12 stimulated migration in lymphoblast cells and modulates the levels of specific microRNA involved in the complex wound repair process, specifically in mouse fibroblasts. Our results indicate that UCUF-965 acts as a PAM agonist of the CXCR4 receptor. Furthermore, UCUF-965 enhanced angiogenesis markers and reduced wound healing time by 36% at 10.0 μM in diabetic mice models compared to untreated control.

High-Dose Vitamin C Alleviates Pancreatic Necrosis by Inhibiting Platelet Activation Through the CXCL12/CXCR4 Pathway in Severe Acute Pancreatitis

Background

Platelet activation in the early stage of pancreatitis is the key step developing into pancreatic necrosis. Studies suggested that vitamin C (Vit C) can inhibit platelet activity by targeting CXCL12/CXCR4 pathway. High-dose Vit C were showed to reduce pancreatic necrosis in severe acute pancreatitis (SAP) but the mechanism remains unclear. Here we speculate high-dose Vit C reduce pancreatic necrosis by inhibiting platelet activation through downregulating CXCL12/CXCR4 pathway.

Methods

The pancreatic microcirculation of rats was observed by intravital microscopy. The platelet activity of SAP rats treated with or without high-dose Vit C was analyzed by platelet function test. Besides, the activity of platelets preincubated with high-dose Vit C or vehicle from SAP patients was also evaluated. Then, the TFA (CXCR4 agonist) and rCXCL12 were used to neutralize the effect of high-dose Vit C in SAP rats treated with high-dose Vit C. Meanwhile, the levels of enzymes and inflammatory cytokines in rat plasma, and rats' pancreatic histopathology and mortality were assessed.

Results

Platelets from animals and patients with SAP are more sensitive to agonists and are more easily activated. Administration of high-dose Vit C significantly ameliorated excessive activation of platelets in SAP rats, ultimately increasing the microvessel density and inducing microthrombus and blood stasis; these results were consistent with clinical sample analysis. Moreover, high-dose Vit C significantly inhibited the release of amylase, lipase, TNF-α, and IL-6 in SAP rat plasma, reducing pancreatic damage and the mortality of SAP rats. However, using TFA and rCXCL12 significantly reversed the effect of high-dose Vit C on excessive activation of platelets, aggravating microcirculation impairment and pancreatic damage.

Conclusion

The present study suggests that high-dose Vit C can ameliorate pancreatic necrosis by improving microcirculation disorders of SAP. For the first time, the underlying mechanism is related with inhibiting platelet activation through the CXCL12/CXCR4 pathway.

Lipidation of a bioactive cyclotide-based CXCR4 antagonist greatly improves its pharmacokinetic profile in vivo

The CXCR4 chemokine is a key molecular regulator of many biological functions controlling leukocyte functions during inflammation and immunity, and during embryonic development. Overexpression of CXCR4 is also associated with many types of cancer where its activation promotes angiogenesis, tumor growth/survival, and metastasis. In addition, CXCR4 is involved in HIV replication, working as a co-receptor for viral entry, making CXCR4 a very attractive target for developing novel therapeutic agents. Here we report the pharmacokinetic profile in rats of a potent CXCR4 antagonist cyclotide, MCo-CVX-5c, previously developed in our group that displayed a remarkable in vivo resistance to biological degradation in serum. This bioactive cyclotide, however, was rapidly eliminated through renal clearance. Several lipidated versions of cyclotide MCo-CVX-5c showed a significant increase in the half-life when compared to the unlipidated form. The palmitoylated version of cyclotide MCo-CVX-5c displayed similar CXCR4 antagonistic activity as the unlipidated cyclotide, while the cyclotide modified with octadecanedioic (18-oxo-octadecanoic) acid exhibited a remarkable decrease in its ability to antagonize CXCR4. Similar results were also obtained when tested for its ability to inhibit growth in two cancer cell lines and HIV infection in cells. These results show that the half-life of cyclotides can be improved by lipidation although it can also affect their biological activity depending on the lipid employed.

Allosteric Regulation of G-Protein-Coupled Receptors: From Diversity of Molecular Mechanisms to Multiple Allosteric Sites and Their Ligands

Allosteric regulation is critical for the functioning of G protein-coupled receptors (GPCRs) and their signaling pathways. Endogenous allosteric regulators of GPCRs are simple ions, various biomolecules, and protein components of GPCR signaling (G proteins and β-arrestins). The stability and functional activity of GPCR complexes is also due to multicenter allosteric interactions between protomers. The complexity of allosteric effects caused by numerous regulators differing in structure, availability, and mechanisms of action predetermines the multiplicity and different topology of allosteric sites in GPCRs. These sites can be localized in extracellular loops; inside the transmembrane tunnel and in its upper and lower vestibules; in cytoplasmic loops; and on the outer, membrane-contacting surface of the transmembrane domain. They are involved in the regulation of basal and orthosteric agonist-stimulated receptor activity, biased agonism, GPCR-complex formation, and endocytosis. They are targets for a large number of synthetic allosteric regulators and modulators, including those constructed using molecular docking. The review is devoted to the principles and mechanisms of GPCRs allosteric regulation, the multiplicity of allosteric sites and their topology, and the endogenous and synthetic allosteric regulators, including autoantibodies and pepducins. The allosteric regulation of chemokine receptors, proteinase-activated receptors, thyroid-stimulating and luteinizing hormone receptors, and beta-adrenergic receptors are described in more detail.

miR-301a Deficiency Attenuates the Macrophage Migration and Phagocytosis through YY1/CXCR4 Pathway

(1) Background: the miR-301a is well known involving the proliferation and migration of tumor cells. However, the role of miR-301a in the migration and phagocytosis of macrophages is still unclear. (2) Methods: sciatic nerve injury, liver injury models, as well as primary macrophage cultures were prepared from the miR-301a knockout (KO) and wild type (WT) mice to assess the macrophage's migration and phagocytosis capabilities. Targetscan database analysis, Western blotting, siRNA transfection, and CXCR4 inhibition or activation were performed to reveal miR301a's potential mechanism. (3) Results: the macrophage's migration and phagocytosis were significantly attenuated by the miR-301a KO both in vivo and in vitro. MiR-301a can target Yin-Yang 1 (YY1), and miR-301a KO resulted in YY1 up-regulation and CXCR4 (YY1's down-stream molecule) down-regulation. siYY1 increased the expression of CXCR4 and enhanced migration and phagocytosis in KO macrophages. Meanwhile, a CXCR4 inhibitor or agonist could attenuate or accelerate, respectively, the macrophage migration and phagocytosis. (4) Conclusions: current findings indicated that miR-301a plays important roles in a macrophage's capabilities of migration and phagocytosis through the YY1/CXCR4 pathway. Hence, miR-301a might be a promising therapeutic candidate for inflammatory diseases by adjusting macrophage bio-functions.

The CXCR4-CXCL12 axis promotes T cell reconstitution via efficient hematopoietic immigration

T cells play a critical role in immunity to protect against pathogens and malignant cells. T cell immunodeficiency is detrimental, especially when T cell perturbation occurs during severe infection, irradiation, chemotherapy, and age-related thymic atrophy. Therefore, strategies that enhance T cell reconstitution provide considerable benefit and warrant intensive investigation. Here, we report the construction of a T cell ablation model in Tg(coro1a:DenNTR) zebrafish via metronidazole administration. The nascent T cells are mainly derived from the hematopoietic cells migrated from the kidney, the functional homolog of bone marrow and the complete recovery time is 6.5 days post-treatment. The cxcr4b gene is upregulated in the responsive hematopoietic cells. Functional interference of CXCR4 via both genetic and chemical manipulations does not greatly affect T lymphopoiesis, but delays T cell regeneration by disrupting hematopoietic migration. In contrast, cxcr4b accelerates the replenishment of hematopoietic cells in the thymus. Consistently, Cxcl12b, a ligand of Cxcr4, is increased in the thymic epithelial cells of the injured animals. Decreased or increased expression of Cxcl12b results in compromised or accelerated T cell recovery, respectively, similar to those observed with Cxcr4b. Taken together, our study reveals a role of CXCR4-CXCL12 signaling in promoting T cell recovery and provides a promising target for the treatment of immunodeficiency due to T cell injury.

Pepducin-mediated G Protein-Coupled Receptor Signaling in the Cardiovascular System

ABSTRACT

Pepducins are small-lipidated peptides designed from the intracellular loops of G protein-coupled receptors (GPCRs) that act in an allosteric manner to modulate the activity of GPCRs. Over the past 2 decades, pepducins have progressed initially from pharmacologic tools used to manipulate GPCR activity in an orthosteric site-independent manner to compounds with therapeutic potential that have even been used safely in phase 1 and 2 clinical trials in human subjects. The effect of pepducins at their cognate receptors has been shown to vary between antagonist, partial agonist, and biased agonist outcomes in various primary and clonal cell systems, with even small changes in amino acid sequence altering these properties and their receptor selectivity. To date, pepducins designed from numerous GPCRs have been studied for their impact on pathologic conditions, including cardiovascular diseases such as thrombosis, myocardial infarction, and atherosclerosis. This review will focus in particular on pepducins designed from protease-activated receptors, C-X-C motif chemokine receptors, formyl peptide receptors, and the β2-adrenergic receptor. We will discuss the historic context of pepducin development for each receptor, as well as the structural, signaling, pathophysiologic consequences, and therapeutic potential for each pepducin class.

Probing GPCR Dimerization Using Peptides

G protein-coupled receptors (GPCRs) are the largest class of membrane proteins and the most common and extensively studied pharmacological target. Numerous studies over the last decade have confirmed that GPCRs do not only exist and function in their monomeric form but in fact, have the ability to form dimers or higher order oligomers with other GPCRs, as well as other classes of receptors. GPCR oligomers have become increasingly attractive to investigate as they have the ability to modulate the pharmacological responses of the receptors which in turn, could have important functional roles in diseases, such as cancer and several neurological & neuropsychiatric disorders. Despite the growing evidence in the field of GPCR oligomerisation, the lack of structural information, as well as targeting the 'undruggable' protein-protein interactions (PPIs) involved in these complexes, has presented difficulties. Outside the field of GPCRs, targeting PPIs has been widely studied, with a variety of techniques being investigated; from small-molecule inhibitors to disrupting peptides. In this review, we will demonstrate several physiologically relevant GPCR dimers and discuss an array of strategies and techniques that can be employed when targeting these complexes, as well as provide ideas for future development.

Wandering beyond small molecules: peptides as allosteric protein modulators

Recent years have seen the rise of allosteric modulation as an innovative approach for drug design and discovery, efforts which culminated in the development of several clinical candidates. Allosteric modulation of many drug targets, including mainly membrane-embedded receptors, have been vastly explored through small molecule screening campaigns, but much less attention has been paid to peptide-based allosteric modulators. However, peptides have a significant impact on the pharmaceutical industry due to the typically higher potency and selectivity for their targets, as compared with small molecule therapeutics. Therefore, peptides represent one of the most promising classes of molecules that can modulate key biological pathways. Here, we report on the allosteric modulation of proteins (ranging from G protein-coupled receptors to specific protein-protein interactions) by peptides for applications in drug discovery.

Allosteric Modulator Leads Hiding in Plain Site: Developing Peptide and Peptidomimetics as GPCR Allosteric Modulators

Allosteric modulators (AMs) of G-protein coupled receptors (GPCRs) are desirable drug targets because they can produce fewer on-target side effects, improved selectivity, and better biological specificity (e.g., biased signaling or probe dependence) than orthosteric drugs. An underappreciated source for identifying AM leads are peptides and proteins-many of which were evolutionarily selected as AMs-derived from endogenous protein-protein interactions (e.g., transducer/accessory proteins), intramolecular receptor contacts (e.g., pepducins or extracellular domains), endogenous peptides, and exogenous libraries (e.g., nanobodies or conotoxins). Peptides offer distinct advantages over small molecules, including high affinity, good tolerability, and good bioactivity, and specific disadvantages, including relatively poor metabolic stability and bioavailability. Peptidomimetics are molecules that combine the advantages of both peptides and small molecules by mimicking the peptide's chemical features responsible for bioactivity while improving its druggability. This review 1) discusses sources and strategies to identify peptide/peptidomimetic AMs, 2) overviews strategies to convert a peptide lead into more drug-like "peptidomimetic," and 3) critically analyzes the advantages, disadvantages, and future directions of peptidomimetic AMs. While small molecules will and should play a vital role in AM drug discovery, peptidomimetics can complement and even exceed the advantages of small molecules, depending on the target, site, lead, and associated factors.

Cell-Based Therapies for Trabecular Meshwork Regeneration to Treat Glaucoma

Glaucoma is clinically characterized by elevated intraocular pressure (IOP) that leads to retinal ganglion cell (RGC) and optic nerve damage, and eventually blindness if left untreated. Even in normal pressure glaucoma patients, a reduction of IOP is currently the only effective way to prevent blindness, by either increasing aqueous humor outflow or decreasing aqueous humor production. The trabecular meshwork (TM) and the adjacent Schlemm’s canal inner wall play a key role in regulating IOP by providing resistance when aqueous humor drains through the tissue. TM dysfunction seen in glaucoma, through reduced cellularity, abnormal extracellular matrix accumulation, and increased stiffness, contributes to elevated IOP, but current therapies do not target the TM tissue. Stem cell transplantation for regeneration and re-functionalization of damaged TM has shown promise in providing a more direct and effective therapy for glaucoma. In this review, we describe the use of different types of stem cells for TM regeneration in glaucoma models, the mechanisms of regeneration, and the potential for glaucoma treatment using autologous stem cell transplantation.

New Insight Into Neutrophils: A Potential Therapeutic Target for Cerebral Ischemia

Ischemic stroke is one of the main issues threatening human health worldwide, and it is also the main cause of permanent disability in adults. Energy consumption and hypoxia after ischemic stroke leads to the death of nerve cells, activate resident glial cells, and promote the infiltration of peripheral immune cells into the brain, resulting in various immune-mediated effects and even contradictory effects. Immune cell infiltration can mediate neuronal apoptosis and aggravate ischemic injury, but it can also promote neuronal repair, differentiation and regeneration. The central nervous system (CNS), which is one of the most important immune privileged parts of the human body, is separated from the peripheral immune system by the blood-brain barrier (BBB). Under physiological conditions, the infiltration of peripheral immune cells into the CNS is controlled by the BBB and regulated by the interaction between immune cells and vascular endothelial cells. As the immune response plays a key role in regulating the development of ischemic injury, neutrophils have been proven to be involved in many inflammatory diseases, especially acute ischemic stroke (AIS). However, neutrophils may play a dual role in the CNS. Neutrophils are the first group of immune cells to enter the brain from the periphery after ischemic stroke, and their exact role in cerebral ischemia remains to be further explored. Elucidating the characteristics of immune cells and their role in the regulation of the inflammatory response may lead to the identification of new potential therapeutic strategies. Thus, this review will specifically discuss the role of neutrophils in ischemic stroke from production to functional differentiation, emphasizing promising targeted interventions, which may promote the development of ischemic stroke treatments in the future.

Role of CXCR4 in the progression and therapy of acute leukaemia

CXCR4 is expressed on leukaemia cells and haematopoietic stem cells (HSCs), and its ligand stromal-derived factor 1 (SDF-1) is produced abundantly by stromal cells in the bone marrow (BM). The SDF-1/CXCR4 axis plays important roles in homing to and retention in the protective BM microenvironment of malignant leukaemia cells and normal HSCs. CXCR4 expression is regulated by multiple mechanisms and the level of CXCR4 expression on leukaemia cells has prognostic indications in patients with acute leukaemia. CXCR4 antagonists can mobilize leukaemia cells from BM to circulation, which render them effectively eradicated by chemotherapeutic agents, small molecular inhibitors or hypomethylating agents. Therefore, such combinational therapies have been tested in clinical trials. However, new evidence emerged that drug-resistant leukaemia cells were not affected by CXCR4 antagonists, and the migration of certain leukaemia cells to the leukaemia niche was independent of SDF-1/CXCR4 axis. In this review, we summarize the role of CXCR4 in progression and treatment of acute leukaemia, with a focus on the potential of CXCR4 as a therapeutic target for acute leukaemia. We also discuss the potential value of using CXCR4 antagonists as chemosensitizer for conditioning regimens and immunosensitizer for graft-vs-leukaemia effects of allogeneic haematopoietic stem cell transplantation.

Comparison of the efficacy of hematopoietic stem cell mobilization regimens: a systematic review and network meta-analysis of preclinical studies

BACKGROUND

Mobilization failure may occur when the conventional hematopoietic stem cells (HSCs) mobilization agent granulocyte colony-stimulating factor (G-CSF) is used alone, new regimens were developed to improve mobilization efficacy. Multiple studies have been performed to investigate the efficacy of these regimens via animal models, but the results are inconsistent. We aim to compare the efficacy of different HSC mobilization regimens and identify new promising regimens with a network meta-analysis of preclinical studies.

METHODS

We searched Medline and Embase databases for the eligible animal studies that compared the efficacy of different HSC mobilization regimens. Primary outcome is the number of total colony-forming cells (CFCs) in per milliliter of peripheral blood (/ml PB), and the secondary outcome is the number of Lin^- Sca1⁺ Kit⁺ (LSK) cells/ml PB. Bayesian network meta-analyses were performed following the guidelines of the National Institute for Health and Care Excellence Decision Support Unit (NICE DSU) with WinBUGS version 1.4.3. G-CSF-based regimens were classified into the SD (standard dose, 200-250 μg/kg/day) group and the LD (low dose, 100-150 μg/kg/day) group based on doses, and were classified into the short-term (2-3 days) group and the long-term (4-5 days) group based on administration duration. Long-term SD G-CSF was chosen as the reference treatment. Results are presented as the mean differences (MD) with the associated 95% credibility interval (95% CrI) for each regimen.

RESULTS

We included 95 eligible studies and reviewed the efficacy of 94 mobilization agents. Then 21 studies using the poor mobilizer mice model (C57BL/6 mice) to investigate the efficacy of different mobilization regimens were included for network meta-analysis. Network meta-analyses indicated that compared with long-term SD G-CSF alone, 14 regimens including long-term SD G-CSF + Me6, long-term SD G-CSF + AMD3100 + EP80031, long-term SD G-CSF + AMD3100 + FG-4497, long-term SD G-CSF + ML141, long-term SD G-CSF + desipramine, AMD3100 + meloxicam, long-term SD G-CSF + reboxetine, AMD3100 + VPC01091, long-term SD G-CSF + FG-4497, Me6, long-term SD G-CSF + EP80031, POL5551, long-term SD G-CSF + AMD3100, AMD1300 + EP80031 and long-term LD G-CSF + meloxicam significantly increased the collections of total CFCs. G-CSF + Me6 ranked first among these regimens in consideration of the number of harvested CFCs/ml PB (MD 2168.0, 95% CrI 2062.0-2272.0). In addition, 7 regimens including long-term SD G-CSF + AMD3100, AMD3100 + EP80031, long-term SD G-CSF + EP80031, short-term SD G-CSF + AMD3100 + IL-33, long-term SD G-CSF + ML141, short-term LD G-CSF + ARL67156, and long-term LD G-CSF + meloxicam significantly increased the collections of LSK cells compared with G-CSF alone. Long-term SD G-CSF + AMD3100 ranked first among these regimens in consideration of the number of harvested LSK cells/ml PB (MD 2577.0, 95% CrI 2422.0-2733.0).

CONCLUSIONS

Considering the number of CFC and LSK cells in PB as outcomes, G-CSF plus AMD3100, Me6, EP80031, ML141, FG-4497, IL-33, ARL67156, meloxicam, desipramine, and reboxetine are all promising mobilizing regimens for future investigation.

Biased agonism at chemokine receptors

In the human chemokine system, interactions between the approximately 50 known endogenous chemokine ligands and 20 known chemokine receptors (CKRs) regulate a wide range of cellular functions and biological processes including immune cell activation and homeostasis, development, angiogenesis, and neuromodulation. CKRs are a family of G protein-coupled receptors (GPCR), which represent the most common and versatile class of receptors in the human genome and the targets of approximately one third of all Food and Drug Administration-approved drugs. Chemokines and CKRs bind with significant promiscuity, as most CKRs can be activated by multiple chemokines and most chemokines can activate multiple CKRs. While these ligand-receptor interactions were previously regarded as redundant, it is now appreciated that many chemokine:CKR interactions display biased agonism, the phenomenon in which different ligands binding to the same receptor signal through different pathways with different efficacies, leading to distinct biological effects. Notably, these biased responses can be modulated through changes in ligand, receptor, and or the specific cellular context (system). In this review, we explore the biochemical mechanisms, functional consequences, and therapeutic potential of biased agonism in the chemokine system. An enhanced understanding of biased agonism in the chemokine system may prove transformative in the understanding of the mechanisms and consequences of biased signaling across all GPCR subtypes and aid in the development of biased pharmaceuticals with increased therapeutic efficacy and safer side effect profiles.

Targeting of G-protein coupled receptors in sepsis

The Third International Consensus Definitions (Sepsis-3) define sepsis as life-threatening multi-organ dysfunction caused by a dysregulated host response to infection. Sepsis can progress to septic shock-an even more lethal condition associated with profound circulatory, cellular and metabolic abnormalities. Septic shock remains a leading cause of death in intensive care units and carries a mortality of almost 25%. Despite significant advances in our understanding of the pathobiology of sepsis, therapeutic interventions have not translated into tangible differences in the overall outcome for patients. Clinical trials of antagonists of various pro-inflammatory mediators in sepsis have been largely unsuccessful in the past. Given the diverse physiologic roles played by G-protein coupled receptors (GPCR), modulation of GPCR signaling for the treatment of sepsis has also been explored. Traditional pharmacologic approaches have mainly focused on ligands targeting the extracellular domains of GPCR. However, novel techniques aimed at modulating GPCR intracellularly through aptamers, pepducins and intrabodies have opened a fresh avenue of therapeutic possibilities. In this review, we summarize the diverse roles played by various subfamilies of GPCR in the pathogenesis of sepsis and identify potential targets for pharmacotherapy through these novel approaches.

Adipose-derived stem cells integrate into trabecular meshwork with glaucoma treatment potential

The trabecular meshwork (TM) is an ocular tissue that maintains intraocular pressure (IOP) within a physiologic range. Glaucoma patients have reduced TM cellularity and, frequently, elevated IOP. To establish a stem cell-based approach to restoring TM function and normalizing IOP, human adipose-derived stem cells (ADSCs) were induced to differentiate to TM cells in vitro. These ADSC-TM cells displayed a TM cell-like genotypic profile, became phagocytic, and responded to dexamethasone stimulation, characteristic of TM cells. After transplantation into naive mouse eyes, ADSCs and ADSC-TM cells integrated into the TM tissue, expressed TM cell markers, and maintained normal IOP, outflow facility, and extracellular matrix. Cell migration and affinity results indicated that the chemokine pair CXCR4/SDF1 may play an important role in ADSC-TM cell homing. Our study demonstrates the possibility of applying autologous or allogeneic ADSCs and ADSC-TM cells as a potential treatment to restore TM structure and function in glaucoma.

Cell-penetrating pepducins targeting the neurotensin receptor type 1 relieve pain

Pepducins are cell-penetrating, membrane-tethered lipopeptides designed to target the intracellular region of a G protein-coupled receptor (GPCR) in order to allosterically modulate the receptor's signaling output. In this proof-of-concept study, we explored the pain-relief potential of a pepducin series derived from the first intracellular loop of neurotensin receptor type 1 (NTS1), a class A GPCR that mediates many of the effects of the neurotensin (NT) tridecapeptide, including hypothermia, hypotension and analgesia. We used BRET-based biosensors to determine the pepducins' ability to engage G protein signaling pathways associated with NTS1 activation. We observed partial Gα_q and Gα₁₃ activation at a 10 μM concentration, indicating that these pepducins may act as allosteric agonists of NTS1. Additionally, we used surface plasmon resonance (SPR) as a label-free assay to monitor pepducin-induced responses in CHO-K1 cells stably expressing hNTS1. This whole-cell integrated assay enabled us to subdivide our pepducin series into three profile response groups. In order to determine the pepducins' antinociceptive potential, we then screened the series in an acute pain model (tail-flick test) by measuring tail withdrawal latencies to a thermal nociceptive stimulus, following intrathecal (i.t.) pepducin administration (275 nmol/kg). We further evaluated promising pepducins in a tonic pain model (formalin test), as well as in neuropathic (Chronic Constriction Injury) and inflammatory (Complete Freund's Adjuvant) chronic pain models. We report one pepducin, PP-001, that consistently reduced rat nociceptive behaviors, even in chronic pain paradigms. Finally, we designed a TAMRA-tagged version of PP-001 and found by confocal microscopy that the pepducin reached the rat dorsal root ganglia post i.t. injection, thus potentially modulating the activity of NTS1 at this location to produce its analgesic effect. Altogether, these results suggest that NTS1-derived pepducins may represent a promising strategy in pain-relief.

Small molecule and peptide-based CXCR4 modulators as therapeutic agents. A patent review for the period from 2010 to 2018

Introduction: The chemokine receptor CXCR4 has been under intense study due to the central role it plays in immune system regulation and the pathology of many human diseases. The FDA approval of the first CXCR4 antagonist drug Plerixafor (i.e. AMD3100, Mozobil®) ushered in an increase in patent activity covering CXCR4 based therapeutic agents over the past decade.Areas covered: This article describes patent documents published during the period of 2010 through 2018 for both small molecules and peptide-based CXCR4 modulators as therapeutic agents. There is an expansion of intellectual property (IP) around existing and new small molecules of clinical interest, including new chemotypes featuring aromatic and aliphatic heterocycles. There is also significant IP covering peptide-based therapeutics, although about half as many in number as those covering small molecules.Expert opinion: In the last decade there has been significant interest in modulators of the CXCR4 receptor, as gauged by the number of patent filings and clinical investigations targeting this receptor for human disease intervention. Seven of the many CXCR4 modulators described herein, that are currently in human clinical trials, are likely to spur the creation of other FDA approved therapeutics in the near future, most likely as immune and oncology drugs.

Design and biological assessment of membrane-tethering neuroprotective peptides derived from the pituitary adenylate cyclase-activating polypeptide type 1 receptor

BACKGROUND

The pituitary adenylate cyclase-activating polypeptide (PACAP) type 1 receptor (PAC1), a class B G protein-coupled receptor (GPCR), has emerged as a promising target for treating neurodegenerative conditions. Unfortunately, despite years of research, no PAC1-specific agonist has been discovered, as activity on two other GPCRs, VPAC1 and VPAC2, is retained with current analogs. Cell signaling is related to structural modifications in the intracellular loops (ICLs) of GPCRs. Thus, we hypothesized that peptides derived from the ICLs (called pepducins) of PAC1 might initiate, as allosteric ligands, signaling cascades after recognition of the parent receptor and modulation of its conformational landscape.

METHODS

Three pepducins were synthesized and evaluated for their ability to 1) promote cell survival; 2) stimulate various signaling pathways associated with PAC1 activation; 3) modulate selectively PAC1, VPAC1 or VPAC2 activation; and 4) sustain mobility and prevent death of dopaminergic neurons in a zebrafish model of neurodegeneration.

RESULTS

Assays demonstrated that these molecules promote SH-SY5Y cell survival, a human neuroblastoma cell line expressing PAC1, and activate signaling via Gα_s and Gα_q, with distinct potencies and efficacies. Also, PAC1-Pep1 and PAC1-Pep2 activated selectively PAC1-mediated Gα_s stimulation. Finally, experiments, using a zebrafish neurodegeneration model, showed a neuroprotective action with all three pepducins and in particular, revealed the ability of PAC1-Pep1 and PAC1-Pep3 to preserve fish mobility and tyrosine hydroxylase expression in the brain.

CONCLUSION

We have developed the first neuroprotective pepducins derived from PAC1, a class B GPCR.

GENERAL SIGNIFICANCE

PAC1-derived pepducins represent attractive templates for the development of innovative neuroprotecting molecules.

Trabecular Meshwork Regeneration - A Potential Treatment for Glaucoma

Purpose

In this review, we overview the pathophysiology of primary open-angle glaucoma as it relates to the trabecular meshwork (TM), exploring modes of TM dysfunction and regeneration via stem cell therapies.

Recent Findings

Stem cells from a variety of sources, including trabecular meshwork, mesenchymal, adipose and induced pluripotent stem cells, have shown the potential to differentiate into TM cells in vitro or in vivo and to regenerate the TM in vivo, lowering intraocular pressure (IOP) and reducing glaucomatous retinal ganglion cell damage.

Summary

Stem cell therapies for TM regeneration provide a robust and promising suite of treatments for eventual lowering of IOP and prevention of glaucomatous vision loss in humans in the future. Further investigation into stem cell homing mechanisms and the safety of introducing these cells into human anterior chamber, for instance, are required before clinical applications in treating glaucoma patients.

Therapeutic Potential of Targeting ß-Arrestin

ß-arrestins are multifunctional proteins that modulate heptahelical 7 transmembrane receptors, also known as G protein-coupled receptors (GPCRs), a superfamily of receptors that regulate most physiological processes. ß-arrestin modulation of GPCR function includes termination of G protein-dependent signaling, initiation of ß-arrestin-dependent signaling, receptor trafficking to degradative or recycling pathways, receptor transactivation, transcriptional regulation, and localization of second messenger regulators. The pleiotropic influence ß-arrestins exert on these receptors regulates a breadth of physiological functions, and additionally, ß-arrestins are involved in the pathophysiology of numerous and wide-ranging diseases, making them prime therapeutic targets. In this review, we briefly describe the mechanisms by which ß-arrestins regulate GPCR signaling, including the functional cellular mechanisms modulated by ß-arrestins and relate this to observed pathophysiological responses associated with ß-arrestins. We focus on the role for ß-arrestins in transducing cell signaling; a pathway that is complementary to the classical G protein-coupling pathway. The existence of these GPCR dual signaling pathways offers an immense therapeutic opportunity through selective targeting of one signaling pathway over the other. Finally, we will consider several mechanisms by which the potential of dual signaling pathway regulation can be harnessed and the implications for improved disease treatments.

CCL27/CCL28-CCR10 Chemokine Signaling Mediates Migration of Lymphatic Endothelial Cells

Metastasis via the lymphatic vasculature is an important step in cancer progression. The formation of new lymphatic vessels (lymphangiogenesis), or remodeling of existing lymphatics, is thought to facilitate the entry and transport of tumor cells into lymphatic vessels and on to distant organs. The migration of lymphatic endothelial cells (LEC) toward guidance cues is critical for lymphangiogenesis. While chemokines are known to provide directional navigation for migrating immune cells, their role in mediating LEC migration during tumor-associated lymphangiogenesis is not well defined. Here, we undertook gene profiling studies to identify chemokine-chemokine receptor pairs that are involved in tumor lymphangiogenesis associated with lymph node metastasis. CCL27 and CCL28 were expressed in tumor cells with metastatic potential, while their cognate receptor, CCR10, was expressed by LECs and upregulated by the lymphangiogenic growth factor VEGFD and the proinflammatory cytokine TNFα. Migration assays demonstrated that LECs are attracted to both CCL27 and CCL28 in a CCR10-dependent manner, while abnormal lymphatic vessel patterning in CCR10-deficient mice confirmed the significant role of CCR10 in lymphatic patterning. In vivo analyses showed that LECs are recruited to a CCL27 or CCL28 source, while VEGFD was required in combination with these chemokines to enable formation of coherent lymphatic vessels. Moreover, tumor xenograft experiments demonstrated that even though CCL27 expression by tumors enhanced LEC recruitment, the ability to metastasize was dependent on the expression of VEGFD. These studies demonstrate that CCL27 and CCL28 signaling through CCR10 may cooperate with inflammatory mediators and VEGFD during tumor lymphangiogenesis. SIGNIFICANCE: The study shows that the remodeling of lymphatic vessels in cancer is influenced by CCL27 and CCL28 chemokines, which may provide a future target to modulate metastatic spread.

Human stem cells home to and repair laser-damaged trabecular meshwork in a mouse model

Glaucoma is the leading cause of irreversible vision loss, and reducing elevated intraocular pressure is currently the only effective clinical treatment. The trabecular meshwork is the main resistance site for aqueous outflow that maintains intraocular pressure. In this study, we transplanted human trabecular meshwork stem cells (TMSCs) intracamerally into mice that received laser photocoagulation over a 180° arc of the trabecular meshwork. TMSCs preferentially homed and integrated to the laser-damaged trabecular meshwork region and expressed differentiated cell markers at 2 and 4 weeks. Laser-induced inflammatory and fibrotic responses were prevented by TMSC transplantation with simultaneous ultrastructure and function restoration. Cell affinity and migration assays and elevated expression of CXCR4 and SDF1 in laser-treated mouse trabecular meshwork suggest that the CXCR4/SDF1 chemokine axis plays an important role in TMSC homing. Our results suggest that TMSCs may be a viable candidate for trabecular meshwork refunctionalization as a novel treatment for glaucoma.

Hongmin Yun et al. show that implanted human stem cells can accurately home to and repair damaged trabecular meshwork tissue in the mouse eye via a chemokine axis defined by CXCR4 and SDF1. The study suggests that stem cells from the trabecular meshwork could be used to refunctionalize the outflow pathway as a treatment for glaucoma.

Protease-Activated Receptor 1 as Therapeutic Target in Breast, Lung, and Ovarian Cancer: Pepducin Approach

The G-protein coupled receptors (GPCRs) belong to a large family of diverse receptors that are well recognized as pharmacological targets. However, very few of these receptors have been pursued as oncology drug targets. The Protease-activated receptor 1 (PAR1), which is a G-protein coupled receptor, has been shown to act as an oncogene and is an emerging anti-cancer drug target. In this paper, we provide an overview of PAR1’s biased signaling role in metastatic cancers of the breast, lungs, and ovaries and describe the development of PAR1 inhibitors that are currently in clinical use to treat acute coronary syndromes. PAR1 inhibitor PZ-128 is in a Phase II clinical trial and is being developed to prevent ischemic and thrombotic complication of patients undergoing cardiac catheterization. PZ-128 belongs to a new class of cell-penetrating, membrane-tethered peptides named pepducins that are based on the intracellular loops of receptors targeting the receptor G-protein interface. Application of PZ-128 as an anti-metastatic and anti-angiogenic therapeutic agent in breast, lung, and ovarian cancer is being reviewed.

Intracellular Receptor Modulation: Novel Approach to Target GPCRs

Recent crystal structures of multiple G protein-coupled receptors (GPCRs) have revealed a highly conserved intracellular pocket that can be used to modulate these receptors from the inside. This novel intracellular site partially overlaps with the G protein and β-arrestin binding site, providing a new manner of pharmacological intervention. Here we provide an update of the architecture and function of the intracellular region of GPCRs, until now portrayed as the signaling domain. We review the available evidence on the presence of intracellular binding sites among chemokine receptors and other class A GPCRs, as well as different strategies to target it, including small molecules, pepducins, and nanobodies. Finally, the potential advantages of intracellular (allosteric) ligands over orthosteric ligands are also discussed.

Circulating Progenitor Cell Response to Exercise in Wheelchair Racing Athletes

INTRODUCTION

Circulating progenitor cells (CPC) are a heterogeneous population of stem/progenitor cells in peripheral blood that participate in tissue repair. CPC mobilization has been well characterized in able-bodied persons but has not been previously investigated in wheelchair racing athletes. The purpose of this study was to characterize CPC and CPC subpopulation mobilization in elite wheelchair racing athletes in response to acute, upper-extremity aerobic exercise to determine whether CPC responses are similar to ambulatory populations.

METHODS

Eight participants (three females; age = 27.5 ± 4.0 yr, supine height = 162.5 ± 18.6 cm, weight = 53.5 ± 10.9 kg, V˙O2peak = 2.4 ± 0.62 L·min, years postinjury = 21.5 ± 6.2 yr) completed a 25-km time trial on a road course. Blood sampling occurred before and immediately after exercise for quantification of CPC (CD34), hematopoietic stem and progenitor cells (HSPC) (CD34/CD45), hematopoietic stem cells (HSC) (CD34/CD45/CD38), CD34 adipose tissue (AT)-derived mesenchymal stromal cells (MSC) (CD45/CD34/CD105/CD31), CD34 bone marrow (BM)-derived MSC (CD45/CD34/CD105/CD31), and endothelial progenitor cells (EPC) (CD45/CD34/VEGFR2) via flow cytometry. Blood lactate was measured before and after trial as an indicator of exercise intensity.

RESULTS

CPC concentration increased 5.7-fold postexercise (P = 0.10). HSPC, HSC, EPC, and both MSC populations were not increased postexercise. Baseline HSPC populations were significantly positively correlated to absolute V˙O2peak (rho = 0.71, P < 0.05) with HSC trending to positively correlate to V˙O2peak (rho = 0.62, P = 0.10). AT-MSC populations were trending to be negatively correlated to baseline V˙O2peak (rho = -0.62, P = 0.058). The change in CPC, EPC, and AT-MSC pre- and postexercise significantly positively correlated to the change in lactate concentrations (rho = 0.91 P = 0.002, 0.71 P = 0.047, 0.81 P = 0.02, respectively, all P < 0.05).

CONCLUSION

These data suggest that CPC content in wheelchair racing athletes is related to cardiorespiratory fitness, and responses to exercise are positively related to exercise intensity.

Anti-fibrotic Effects of CXCR4-Targeting i-body AD-114 in Preclinical Models of Pulmonary Fibrosis

Idiopathic pulmonary fibrosis (IPF) is a chronic fibrotic lung disease that is prevalent in individuals >50 years of age, with a median survival of 3–5 years and limited therapeutic options. The disease is characterized by collagen deposition and remodeling of the lung parenchyma in a process that is thought to be driven by collagen-expressing immune and structural cells. The G-protein coupled C-X-C chemokine receptor 4, CXCR4, is a candidate therapeutic target for IPF owing to its role in the recruitment of CXCR4⁺ fibrocytes from the bone marrow to fibrotic lung tissue and its increased expression levels by structural cells in fibrotic lung tissue. We have engineered a novel fully human single domain antibody “i-body” called AD-114 that binds with high affinity to human CXCR4. We demonstrate here that AD-114 inhibits invasive wound healing and collagen 1 secretion by human IPF fibroblasts but not non-diseased control lung fibroblasts. Furthermore, in a murine bleomycin model of pulmonary fibrosis, AD-114 reduced the accumulation of fibrocytes (CXCR4⁺/Col1⁺/CD45⁺) in fibrotic murine lungs and ameliorated the degree of lung injury. Collectively, these studies demonstrate that AD-114 holds promise as a new biological therapeutic for the treatment of IPF.

Structure-inspired design of β-arrestin-biased ligands for aminergic GPCRs

Development of biased ligands targeting G protein-coupled receptors (GPCRs) is a promising approach for current drug discovery. Although structure-based drug design of biased agonists remains challenging even with an abundance of GPCR crystal structures, we present an approach for translating GPCR structural data into β-arrestin-biased ligands for aminergic GPCRs. We identified specific amino acid-ligand contacts at transmembrane helix 5 (TM5) and extracellular loop 2 (EL2) responsible for Gi/o and β-arrestin signaling, respectively, and targeted those residues to develop biased ligands. For these ligands, we found that bias is conserved at other aminergic GPCRs that retain similar residues at TM5 and EL2. Our approach provides a template for generating arrestin-biased ligands by modifying predicted ligand interactions that block TM5 interactions and promote EL2 interactions. This strategy could facilitate the structure-guided design of arrestin-biased ligands at other GPCRs, including polypharmacological biased ligands.

Odorant receptors can mediate axonal identity and gene choice via cAMP-independent mechanisms

Odorant receptors (ORs) control several aspects of cell fate in olfactory sensory neurons (OSNs), including singular gene choice and axonal identity. The mechanisms of OR-induced axon guidance have been suggested to principally rely on G-protein signalling. Here, we report that for a subset of OSNs, deleting G proteins or altering their levels of signalling does not affect axonal identity. Signalling-deficient ORs or surrogate receptors that are unable to couple to Gs/Golf still provide axons with distinct identities and the anterior–posterior targeting of axons does not correlate with the levels of cAMP produced by genetic modifications. In addition, we refine the models of negative feedback by showing that ectopic ORs can be robustly expressed without suppressing endogenous gene choice. In conclusion, our results uncover a new feature of ORs, showing that they can instruct axonal identity and regulate olfactory map formation independent of canonical G-protein signalling and cAMP production.

Two distinct CXCR4 antagonists mobilize progenitor cells in mice by different mechanisms

Pharmacological mobilization of hematopoietic progenitor cells (HPCs) is used clinically to harvest HPCs for bone marrow transplants. It is now widely accepted that the CXCR4:CXCL12 chemokine axis plays a critical role in the retention of HPCs in the bone marrow, and CXCR4 antagonists have been developed for their mobilization. The first of this class of drugs to be US Food and Drug Administration-approved was the bicyclam AMD3100. In addition to mobilizing HPCs and leukocytes in naïve mice, AMD3100 has been shown to mobilize mesenchymal progenitor cells (MPCs) in vascular endothelial growth factor (VEGF-A) pretreated mice. AMD3100 binds to the transmembrane region of CXCR4 and is thought to mobilize HPCs by reversing the gradient of CXCL12 across the bone marrow endothelium. Consistent with this hypothesis, our data show that selective neutralization of CXCL12, with chalcone 4-phosphate (C4P), inhibited AMD3100-stimulated mobilization of HPCs and leukocytes in naïve mice and MPCs in VEGF-A pretreated mice. In contrast it is shown here that the CXCR4 antagonist KRH3955 that binds to the extracellular loop of CXCR4 does not reverse the CXCL12 chemokine gradient. However, this drug efficiently mobilizes HPCs, a response that is not inhibited by C4P. In contrast, KRH3955 does not mobilize MPCs in VEGF-A pretreated mice. These data suggest that CXCR4 antagonists that bind to distinct regions of the receptor mobilize progenitor cells by distinct molecular mechanisms.

Harnessing CXCR4 antagonists in stem cell mobilization, HIV infection, ischemic diseases, and oncology

CXCR4 antagonists (e.g., Plerixafor^TM ) have been successfully validated as stem cell mobilizers for peripheral blood stem cell transplantation. Applications of the CXCR4 antagonists have heralded the era of cell-based therapy and opened a potential therapeutic horizon for many unmet medical needs such as kidney injury, ischemic stroke, cancer, and myocardial infarction. In this review, we first introduce the central role of CXCR4 in diverse cellular signaling pathways and discuss its involvement in several disease progressions. We then highlight the molecular design and optimization strategies for targeting CXCR4 from a large number of case studies, concluding that polyamines are the preferred CXCR4-binding ligands compared to other structural options, presumably by mimicking the highly positively charged natural ligand CXCL12. These results could be further justified with computer-aided docking into the CXCR4 crystal structure wherein both major and minor subpockets of the binding cavity are considered functionally important. Finally, from the clinical point of view, CXCR4 antagonists could mobilize hematopoietic stem/progenitor cells with long-term repopulating capacity to the peripheral blood, promising to replace surgically obtained bone marrow cells as a preferred source for stem cell transplantation.

Membrane-lipid therapy: A historical perspective of membrane-targeted therapies - From lipid bilayer structure to the pathophysiological regulation of cells

Our current understanding of membrane lipid composition, structure and functions has led to the investigation of their role in cell signaling, both in healthy and pathological cells. As a consequence, therapies based on the regulation of membrane lipid composition and structure have been recently developed. This novel field, known as Membrane Lipid Therapy, is growing and evolving rapidly, providing treatments that are now in use or that are being studied for their application to oncological disorders, Alzheimer's disease, spinal cord injury, stroke, diabetes, obesity, and neuropathic pain. This field has arisen from relevant discoveries on the behavior of membranes in recent decades, and it paves the way to adopt new approaches in modern pharmacology and nutrition. This innovative area will promote further investigation into membranes and the development of new therapies with molecules that target the cell membrane. Due to the prominent roles of membranes in the cells' physiology and the paucity of therapeutic approaches based on the regulation of the lipids they contain, it is expected that membrane lipid therapy will provide new treatments for numerous pathologies. The first on-purpose rationally designed molecule in this field, minerval, is currently being tested in clinical trials and it is expected to enter the market around 2020. However, it seems feasible that during the next few decades other membrane regulators will also be marketed for the treatment of human pathologies. This article is part of a Special Issue entitled: Membrane Lipid Therapy: Drugs Targeting Biomembranes edited by Pablo V. Escribá.

Inhibition of SDF-1 receptors CXCR4 and CXCR7 attenuates acute pulmonary inflammation via the adenosine A2B-receptor on blood cells

Acute pulmonary inflammation is characterized by migration of polymorphonuclear neutrophils into the different compartments of the lung. Recent studies showed evidence that the chemokine stromal cell-derived factor (SDF)-1 and its receptors CXCR4 and CXCR7 influence migration of immune cells and their activity was linked to adenosine concentrations. We investigated the particular role of CXCR4- and CXCR7-inhibition and the potential link to the adenosine A_2B-receptor, which plays an important anti-inflammatory role in the lung. After LPS-inhalation for 45 minutes, administration of the CXCR4-inhibitor (AMD3100) decreased transendothelial and transepithelial migration, whereas CXCR7-antagonism influenced epithelial migration exclusively. In A_2B−/− mice, no anti-inflammatory effects were detectible through either one of the agents. Using chimeric mice, we identified A_2B on hematopoietic cells to be crucial for these anti-inflammatory effects of CXCR4/7-inhibition. Both inhibitors decreased TNFα, IL6, CXCL1 and CXCL2/3 levels in the bronchoalveolar lavage of wild type mice, while not influencing the chemokine release in A_2B−/− mice. Inflammation augmented the expression of both receptors and their inhibition increased A_2B-levels upon inflammation. In vitro assays with human epithelium/endothelium confirmed our in vivo findings. During inflammation, inhibition of CXCR4- and CXCR7-receptors prevented microvascular permeability in wild type but not in A_2B−/− mice, highlighting the pivotal role of an active A_2B-receptor in this setting. The combination of both inhibitors had a synergistic effect in preventing capillary leakage. In conclusion, we determined the pivotal role of CXCR4- and CXCR7-inhibition in acute pulmonary inflammation, which depended on A_2B-receptor signalling.

WITHDRAWN: Membrane-lipid therapy: A historical perspective of membrane-targeted therapies-From lipid bilayer structure to the pathophysiological regulation of cells

The Publisher regrets that this article is an accidental duplication of an article that has already been published, http://dx.doi.org/10.1016/j.bbamem.2017.05.017. The duplicate article has therefore been withdrawn. The full Elsevier Policy on Article Withdrawal can be found at https://www.elsevier.com/about/our-business/policies/article-withdrawal.

G Protein-Coupled Receptor Kinase 3 and Protein Kinase C Phosphorylate the Distal C-Terminal Tail of the Chemokine Receptor CXCR4 and Mediate Recruitment of β-Arrestin

Phosphorylation of G protein-coupled receptors (GPCRs) is a key event for cell signaling and regulation of receptor function. Previously, using tandem mass spectrometry, we identified two phosphorylation sites at the distal C-terminal tail of the chemokine receptor CXCR4, but were unable to determine which specific residues were phosphorylated. Here, we demonstrate that serines (Ser) 346 and/or 347 (Ser-346/7) of CXCR4 are phosphorylated upon stimulation with the agonist CXCL12 as well as a CXCR4 pepducin, ATI-2341. ATI-2341, a Gα_iβγ heterotrimer-biased CXCR4 agonist, induced more robust phosphorylation of Ser-346/7 compared with CXCL12. Knockdown of G protein-coupled receptor kinase (GRK) 2, GRK3, or GRK6 reduced CXCL12-induced phosphorylation of Ser-346/7 with GRK3 knockdown having the strongest effect, while inhibition of the conventional protein kinase C (PKC) isoforms, particularly PKCα, reduced phosphorylation of Ser-346/7 induced by either CXCL12 or ATI-2341. The loss of GRK3- or PKC-mediated phosphorylation of Ser-346/7 impaired the recruitment of β-arrestin to CXCR4. We also found that a pseudo-substrate peptide inhibitor for PKCζ effectively inhibited CXCR4 phosphorylation and signaling, most likely by functioning as a nonspecific CXCR4 antagonist. Together, these studies demonstrate the role Ser-346/7 plays in arrestin recruitment and initiation of receptor desensitization and provide insight into the dysregulation of CXCR4 observed in patients with various forms of WHIM syndrome.

Kinetics of circulating progenitor cell mobilization during submaximal exercise

Circulating progenitor cells (CPCs) are a heterogeneous population of stem/progenitor cells in peripheral blood that includes hematopoietic stem and progenitor cells (HSPCs and HSCs), endothelial progenitor cells (EPCs), and mesenchymal stem cells (MSCs) that are involved in tissue repair and adaptation. CPC mobilization during exercise remains uncharacterized in young adults. The purpose of this study was to investigate the kinetics of CPC mobilization during and after submaximal treadmill running and their relationship to mobilization factors. Seven men [age = 25.3 ± 2.4 yr, body mass index = 23.5 ± 1.0 kg/m2, peak O2uptake (V̇o2peak) = 60.9 ± 2.74 ml·kg−1·min−1] ran on a treadmill for 60 min at 70% V̇o2peak. Blood sampling occurred before (Pre), during [20 min (20e), 40 min (40e), 60 min (60e)], and after exercise [15 min (15p), 60 min (60p), 120 min (120p)] for quantification of CPCs (CD34+), HSPCs (CD34+/CD45low), HSCs (CD34+/CD45low/CD38−), CD34+MSCs (CD45−/CD34+/CD31−/CD105+), CD34−MSCs (CD45−/CD34−/CD31−/CD105+), and EPCs (CD45−/CD34+/CD31+) via flow cytometry. CPC concentration increased compared with Pre at 20e and 40e (2.7- and 2.4-fold, respectively, P < 0.05). HSPCs and HSCs increased at 20e compared with 60p (2.7- and 2.8-fold, respectively, P < 0.05), whereas EPCs and both MSC populations did not change. CXC chemokine ligand (CXCL) 12 (1.5-fold; P < 0.05) and stem cell factor (1.3-fold; P < 0.05) were increased at 40e and remained elevated postexercise. The peak increase in CPCs was positively correlated to concentration of endothelial cells during exercise with no relationship to CXCL12 and SCF. Our data show the kinetics of progenitor cell mobilization during exercise that could provide insight into cellular mediators of exercise-induced adaptations, and have implication for the use of exercise as an adjuvant therapy for CPC collection in hematopoietic stem cell transplant.

NEW & NOTEWORTHY Using a comprehensive evaluation of circulating progenitor cells (CPCs), we show that CPC mobilization during exercise is related to tissue damage, and not plasma concentrations of CXC chemokine ligand 12 and stem cell factor. These data have implications for the use of exercise interventions as adjuvant therapy for CPC mobilization in the context of hematopoietic stem cell transplant and also support the role of mobilized progenitor cells as cellular mediators of systemic adaptations to exercise.

Intracellular allosteric antagonism of the CCR9 receptor

Chemokines and their G-protein-coupled receptors play a diverse role in immune defence by controlling the migration, activation and survival of immune cells. They are also involved in viral entry, tumour growth and metastasis and hence are important drug targets in a wide range of diseases. Despite very significant efforts by the pharmaceutical industry to develop drugs, with over 50 small-molecule drugs directed at the family entering clinical development, only two compounds have reached the market: maraviroc (CCR5) for HIV infection and plerixafor (CXCR4) for stem-cell mobilization. The high failure rate may in part be due to limited understanding of the mechanism of action of chemokine antagonists and an inability to optimize compounds in the absence of structural information. CC chemokine receptor type 9 (CCR9) activation by CCL25 plays a key role in leukocyte recruitment to the gut and represents a therapeutic target in inflammatory bowel disease. The selective CCR9 antagonist vercirnon progressed to phase 3 clinical trials in Crohn's disease but efficacy was limited, with the need for very high doses to block receptor activation. Here we report the crystal structure of the CCR9 receptor in complex with vercirnon at 2.8 Å resolution. Remarkably, vercirnon binds to the intracellular side of the receptor, exerting allosteric antagonism and preventing G-protein coupling. This binding site explains the need for relatively lipophilic ligands and describes another example of an allosteric site on G-protein-coupled receptors that can be targeted for drug design, not only at CCR9, but potentially extending to other chemokine receptors.

Macrophage Migration Inhibitory Factor-CXCR4 Receptor Interactions: EVIDENCE FOR PARTIAL ALLOSTERIC AGONISM IN COMPARISON WITH CXCL12 CHEMOKINE

An emerging number of non-chemokine mediators are found to bind to classical chemokine receptors and to elicit critical biological responses. Macrophage migration inhibitory factor (MIF) is an inflammatory cytokine that exhibits chemokine-like activities through non-cognate interactions with the chemokine receptors CXCR2 and CXCR4, in addition to activating the type II receptor CD74. Activation of the MIF-CXCR2 and -CXCR4 axes promotes leukocyte recruitment, mediating the exacerbating role of MIF in atherosclerosis and contributing to the wealth of other MIF biological activities. Although the structural basis of the MIF-CXCR2 interaction has been well studied and was found to engage a pseudo-ELR and an N-like loop motif, nothing is known about the regions of CXCR4 and MIF that are involved in binding to each other. Using a genetic strain of Saccharomyces cerevisiae that expresses a functional CXCR4 receptor, site-specific mutagenesis, hybrid CXCR3/CXCR4 receptors, pharmacological reagents, peptide array analysis, chemotaxis, fluorescence spectroscopy, and circular dichroism, we provide novel molecular information about the structural elements that govern the interaction between MIF and CXCR4. The data identify similarities with classical chemokine-receptor interactions but also provide evidence for a partial allosteric agonist compared with CXCL12 that is possible due to the two binding sites of CXCR4.

Targeting chemokine receptor CXCR4 for treatment of HIV-1 infection, tumor progression, and metastasis

The chemokine receptor CXCR4 is required for the entry of human immunodeficiency virus type 1 (HIV-1) into target cells and for the development and dissemination of various types of cancers, including gastrointestinal, cutaneous, head and neck, pulmonary, gynecological, genitourinary, neurological, and hematological malignancies. The T-cell (T)-tropic HIV-1 strains use CXCR4 as the entry coreceptor; consequently, multiple CXCR4 antagonistic inhibitors have been developed for the treatment of acquired immune deficiency syndrome (AIDS). However, other potential applications of CXCR4 antagonists have become apparent since its discovery in 1996. In fact, increasing evidence demonstrates that epithelial and hematopoietic tumor cells exploit the interaction between CXCR4 and its natural ligand, stromal cellderived factor (SDF)-1α, which normally regulates leukocyte migration. The CXCR4 and/or SDF-1α expression patterns in tumor cells also determine the sites of metastatic spread. In addition, the activation of CXCR4 by SDF-1α promotes invasion and proliferation of tumor cells, enhances tumor-associated neoangiogenesis, and assists in the degradation of the extracellular matrix and basement membrane. As such, the evaluation of CXCR4 and/or SDF-1α expression levels has a significant prognostic value in various types of malignancies. Several therapeutic challenges remain to be overcome before the use of CXCR4 inhibitors can be translated into clinical practice, but promising preclinical data demonstrate that CXCR4 antagonists can mobilize tumor cells from their protective microenvironments, interfere with their metastatic and tumorigenic potentials, and/or make tumor cells more susceptible to chemotherapy.

From biased signalling to polypharmacology: unlocking unique intracellular signalling using pepducins

For over a decade, pepducins have been utilized to develop unique pharmacological profiles that have been particularly challenging for traditional drug discovery methods. It is becoming increasingly clear that these cell-penetrating lipopeptides can access receptor conformations that are currently not accessible through orthosteric targeting. This review addresses the emerging concepts in the development of pepducins including the elicitation of biased signalling, pepducin polypharmacology and recent insight into their mechanism of action.

Exercise as an Adjuvant Therapy for Hematopoietic Stem Cell Mobilization

Hematopoietic stem cell transplant (HSCT) using mobilized peripheral blood hematopoietic stem cells (HSPCs) is the only curative strategy for many patients suffering from hematological malignancies. HSPC collection protocols rely on pharmacological agents to mobilize HSPCs to peripheral blood. Limitations including variable donor responses and long dosing protocols merit further investigations into adjuvant therapies to enhance the efficiency of HSPCs collection. Exercise, a safe and feasible intervention in patients undergoing HSCT, has been previously shown to robustly stimulate HSPC mobilization from the bone marrow. Exercise-induced HSPC mobilization is transient limiting its current clinical potential. Thus, a deeper investigation of the mechanisms responsible for exercise-induced HSPC mobilization and the factors responsible for removal of HSPCs from circulation following exercise is warranted. The present review will describe current research on exercise and HSPC mobilization, outline the potential mechanisms responsible for exercise-induced HSPC mobilization, and highlight potential sites for HSPC homing following exercise. We also outline current barriers to the implementation of exercise as an adjuvant therapy for HSPC mobilization and suggest potential strategies to overcome these barriers.