CXCR4 Agonist Research Articles

Correction for O'Boyle et al., Chemokine receptor CXCR3 agonist prevents human T-cell migration in a humanized model of arthritic inflammation

Correction for O'Boyle et al., Chemokine receptor CXCR3 agonist prevents human T-cell migration in a humanized model of arthritic inflammation

Chemokine receptor CXCR3 agonist prevents human T-cell migration in a humanized model of arthritic inflammation

The recruitment of T lymphocytes during diseases such as rheumatoid arthritis is regulated by stimulation of the chemokine receptors expressed by these cells. This study was designed to assess the potential of a CXCR3-specific small-molecule agonist to inhibit the migration of activated human T cells toward multiple chemokines. Further experiments defined the molecular mechanism for this anti-inflammatory activity. Analysis in vitro demonstrated agonist induced internalization of both CXCR3 and other chemokine receptors coexpressed by CXCR3(+) T cells. Unlike chemokine receptor-specific antagonists, the CXCR3 agonist inhibited migration of activated T cells toward the chemokine mixture in synovial fluid from patients with active rheumatoid arthritis. A humanized mouse air-pouch model showed that intravenous treatment with the CXCR3 agonist prevented inflammatory migration of activated human T cells toward this synovial fluid. A potential mechanism for this action was defined by demonstration that the CXCR3 agonist induces receptor cross-phosphorylation within CXCR3-CCR5 heterodimers on the surface of activated T cells. This study shows that generalized chemokine receptor desensitization can be induced by specific stimulation of a single chemokine receptor on the surface of activated human T cells. A humanized mouse model was used to demonstrate that this receptor desensitization inhibits the inflammatory response that is normally produced by the chemokines present in synovial fluid from patients with active rheumatoid arthritis.

Label-free impedance responses of endogenous and synthetic chemokine receptor CXCR3 agonists correlate with Gi-protein pathway activation

The chemokine receptor CXCR3 is a G-protein-coupled receptor that signals through the Gαi class of heterotrimeric G-proteins. CXCR3 is highly expressed on activated T cells and has been proposed to be a therapeutic target in autoimmune disease. CXCR3 is activated by the chemokines CXCL9, CXCL10 and CXCL11. CXCR3 signaling properties in response to CXCL10, CXCL11 and the synthetic agonist VUF10661 have previously been evaluated using conventional endpoint assays.In the present study, label-free impedance measurements were used to characterize holistic responses of CXCR3-expressing cells to stimulation with chemokines and VUF10661 in real time and to compare these responses with both G-protein and non-G-protein (β-arrestin2) mediated responses. Differences in response kinetics were apparent between the chemokines and VUF10661. Moreover, CXCR3-independent effects could be distinguished from CXCR3-specific responses with the use of the selective CXCR3 antagonist NBI-74330 and the Gαi inhibitor pertussis toxin. By comparing the various responses, we observed that CXCL9 is a biased CXCR3 agonist, stimulating solely G-protein-dependent pathways. Moreover, CXCR3-mediated changes in cellular impedance correlated with G-protein signaling, but not β-arrestin2 recruitment.

Ubiquitin and Stromal Cell-Derived Factor-1α in Bronchoalveolar Lavage Fluid After Burn and Inhalation Injury

The objective of the study was to determine whether the CXC chemokine receptor (CXCR) 4 ligands ubiquitin and stromal cell-derived factor (SDF)-1α are detectable in bronchoalveolar lavage fluid (BALF) after burn and inhalation injury and whether their concentrations in BALF are associated with injury severity, physiological variables, or clinical outcomes. BALF was obtained on hospital admission from 51 patients (48 ± 18 years) with burn (TBSA: 23 ± 24%) and inhalation injury (controls: 10 healthy volunteers, 42 ± 8 years). BALF was analyzed for total protein and for ubiquitin and SDF-1α by enzyme-linked immunosorbent assay. Ubiquitin/SDF-1α levels were normalized to total BALF protein content. The extent of inhalation injury was determined during bronchoscopy using a standardized scoring system. Percent TBSA, Baux scores, revised Baux scores, and clinical variables were documented. Ubiquitin and SDF-1α were detectable in 40% of normal BALF specimens. After injury, ubiquitin was detectable in 90% (P < .01 vs control) and SDF-1α in 10% of the specimens (P < .05 vs control). While SDF-1α levels were reduced in patients (P < .01), ubiquitin levels were increased (P < .01). Ubiquitin concentrations correlated inversely with grade of inhalation injury, revised Baux scores, and resuscitation fluid requirements (Spearman correlation coefficients [r]: -.3, -.33, and -.45, respectively). Ubiquitin levels correlated positively with arterial oxygenation at the time of bronchoscopy (r: .35). BALF levels of CXCR4 agonists are differentially regulated after burn and inhalation injury. Increases in BALF ubiquitin after inhalation injury may maintain CXCR4-mediated lung protection and repair processes. The finding that BALF ubiquitin decreased with higher grades of inhalation injury may provide a biological correlate for an insufficient local inflammatory response after severe inhalation injury.

Structural Determinants of Ubiquitin-CXC Chemokine Receptor 4 Interaction

Ubiquitin, a post-translational protein modifier inside the cell, functions as a CXC chemokine receptor (CXCR) 4 agonist outside the cell. However, the structural determinants of the interaction between extracellular ubiquitin and CXCR4 remain unknown. Utilizing C-terminal truncated ubiquitin and ubiquitin mutants, in which surface residues that are known to interact with ubiquitin binding domains in interacting proteins are mutated (Phe-4, Leu-8, Ile-44, Asp-58, Val-70), we provide evidence that the ubiquitin-CXCR4 interaction follows a two-site binding mechanism in which the hydrophobic surfaces surrounding Phe-4 and Val-70 are important for receptor binding, whereas the flexible C terminus facilitates receptor activation. Based on these findings and the available crystal structures, we then modeled the ubiquitin-CXCR4 interface with the RosettaDock software followed by small manual adjustments, which were guided by charge complementarity and anticipation of a conformational switch of CXCR4 upon activation. This model suggests three residues of CXCR4 (Phe-29, Phe-189, Lys-271) as potential interaction sites. Binding studies with HEK293 cells overexpressing wild type and CXCR4 after site-directed mutagenesis confirm that these residues are important for ubiquitin binding but that they do not contribute to the binding of stromal cell-derived factor 1α. Our findings suggest that the structural determinants of the CXCR4 agonist activity of ubiquitin mimic the typical structure-function relationship of chemokines. Furthermore, we provide evidence for separate and specific ligand binding sites on CXCR4. As exogenous ubiquitin has been shown to possess therapeutic potential, our findings are expected to facilitate the structure-based design of new compounds with ubiquitin-mimetic actions on CXCR4.

The CXC Chemokine Receptor 4 Ligands Ubiquitin and Stromal Cell-derived Factor-1α Function through Distinct Receptor Interactions

Recently, we identified extracellular ubiquitin as an endogenous CXC chemokine receptor (CXCR) 4 agonist. However, the receptor selectivity and molecular basis of the CXCR4 agonist activity of ubiquitin are unknown, and functional consequences of CXCR4 activation with ubiquitin are poorly defined. Here, we provide evidence that ubiquitin and the cognate CXCR4 ligand stromal cell-derived factor (SDF)-1α do not share CXCR7 as a receptor. We further demonstrate that ubiquitin does not utilize the typical two-site binding mechanism of chemokine-receptor interactions, in which the receptor N terminus is important for ligand binding. CXCR4 activation with ubiquitin and SDF-1α lead to similar Gα(i)-responses and to a comparable magnitude of phosphorylation of ERK-1/2, p90 ribosomal S6 kinase-l and Akt, although phosphorylations occur more transiently after activation with ubiquitin. Despite the similarity of signal transduction events after activation of CXCR4 with both ligands, ubiquitin possesses weaker chemotactic activity than SDF-lα in cell migration assays and does not interfere with productive entry of HIV-1 into P4.R5 multinuclear activation of galactosidase indicator cells. Unlike SDF-1α, ubiquitin lacks interactions with an N-terminal CXCR4 peptide in NMR spectroscopy experiments. Binding and signaling studies in the presence of antibodies against the N terminus and extracellular loops 2/3 of CXCR4 confirm that the ubiquitin CXCR4 interaction is independent of the N-terminal receptor domain, whereas blockade of extracellular loops 2/3 prevents receptor binding and activation. Our findings define ubiquitin as a CXCR4 agonist, which does not interfere with productive cellular entry of HIV-1, and provide new mechanistic insights into interactions between CXCR4 and its natural ligands.

Agonists for the Chemokine Receptor CXCR4

The development of agonists for the chemokine receptor CXCR4 could provide promising therapeutic candidates. On the basis of previously forwarded two site model of chemokine–receptor interactions, we hypothesized that linking the agonistic N-terminus of SDF-1 to the T140 backbone would yield new high-affinity agonists of CXCR4. We developed chimeras with the agonistic SDF-1 N-terminus grafted to a T140 side chain and tested their binding affinity and chemotactic agonist activity. While chimeras with the peptide grafted onto position 12 of T140 remained high-affinity antagonists, those bearing the peptide on position 14 were in part agonists. One chimera was a full CXCR4 agonist with 25 nM affinity, and several chimeras showed low nanomolar affinities with partial agonist activity. Our results confirmed that we have developed high-affinity agonists of CXCR4.

The CXCL12/CXCR4 Axis as a Therapeutic Target in Cancer and HIV-1 Infection

The seven-spanning transmembrane G-protein coupled receptor CXCR4, which specifically binds to the chemokine CXCL12, is expressed on many cell types, including various types of tumour cells. CXCR4 plays a crucial role in organ-specific metastasis, directing migration of malignant cells expressing this receptor toward microenvironments where the cognate ligand is secreted. CXCL12 has a direct growth and survival-promoting effect for various cancer cells and enhances moreover tumour angiogenesis by recruiting endothelial progenitor cells to tumours. Drugs which modulate the CXCL12/CXCR4 axis are therefore promising candidates in anti-cancer therapies. CXCR4 is also a coreceptor for human immunodeficiency virus type 1 (HIV-1) X4 virus and, as such, plays an important role in virus entry into target cells. Hence, antiviral agents that bind to CXCR4 are expected to inhibit HIV-1 entry. Here we review the structure, mechanism of action and biological activity of the main CXCR4 antagonists (peptide inhibitors, non-peptide antagonists, neutralizing antibodies, modified analogues of CXCL12) and agonists (CXCL12 peptide analogues) and discuss the CXCL12/CXCR4 axis as an important target in development of anti-tumoral and anti-HIV-1 therapies.

Expression and agonist responsiveness of CXCR3 variants in human T lymphocytes

The chemokine receptor CXCR3 and its ligands CXCL9, CXCL10 and CXCL11 are involved in variety of inflammatory disorders including multiple sclerosis, rheumatoid arthritis, psoriasis and sarcoidosis. Two alternatively spliced variants of the human CXCR3-A receptor have been described, termed CXCR3-B and CXCR3-alt. Human CXCR3-B binds CXCL9, CXCL10, CXCL11 as well as an additional ligand CXCL4. In contrast, CXCR3-alt only binds CXCL11. We report that CXCL4 induces intracellular calcium mobilization as well as Akt and p44/p42 extracellular signal-regulated kinase phosphorylation, in activated human T lymphocytes. These responses have similar concentration dependence and time-courses to those induced by established CXCR3 agonists. Moreover, phosphorylation of Akt and p44/p42 is inhibited by pertussis toxin, suggesting coupling to Gα(i) protein. Surprisingly, and in contrast with the other CXCR3 agonists, stimulation of T lymphocytes with CXCL4 failed to elicit migratory responses and did not lead to loss of surface CXCR3 expression. Taken together, our findings show that, although CXCL4 is coupled to downstream biochemical machinery, its role in T cells is probably distinct from that of CXCR3-A agonists.

The Peptidomimetic CXCR4 Antagonist TC14012 Recruits β-Arrestin to CXCR7: ROLES OF RECEPTOR DOMAINS

CXCR7 is an atypical chemokine receptor that signals through β-arrestin in response to agonists without detectable activation of heterotrimeric G-proteins. Its cognate chemokine ligand CXCL12 also binds CXCR4, a chemokine receptor of considerable clinical interest. Here we report that TC14012, a peptidomimetic inverse agonist of CXCR4, is an agonist on CXCR7. The potency of β-arrestin recruitment to CXCR7 by TC14012 is much higher than that of the previously reported CXCR4 antagonist AMD3100 and differs only by one log from that of the natural ligand CXCL12 (EC(50) 350 nM for TC14012, as compared with 30 nM for CXCL12 and 140 μM for AMD3100). Moreover, like CXCL12, TC14012 leads to Erk 1/2 activation in U373 glioma cells that express only CXCR7, but not CXCR4. Given that with TC14012 and AMD3100 two structurally unrelated CXCR4 antagonists turn out to be agonists on CXCR7, this likely reflects differences in the activation mechanism of the arrestin pathway by both receptors. To identify the receptor domain responsible for these opposed effects, we investigated CXCR4 and CXCR7 C terminus-swapping chimeras. Using quantitative bioluminescence resonance energy transfer, we find that the CXCR7 receptor core formed by the seven-transmembrane domains and the connecting loops determines the agonistic activity of both TC14012 and AMD3100. Moreover, we find that the CXCR7 chimera bearing the CXCR4 C-terminal constitutively associates with arrestin in the absence of ligands. Our data suggest that the CXCR4 and CXCR7 cores share ligand-binding surfaces for the binding of the synthetic ligands, indicating that CXCR4 inhibitors should be tested also on CXCR7.

Ubiquitin receptor binding and signaling in primary human leukocytes

Utilizing the human monocyte/macrophage cell line THP1, we recently identified extracellular ubiquitin as an endogenous agonist of the G protein-coupled receptor CXC chemokine receptor (CXCR) 4. Because receptor binding and signaling properties of extracellular ubiquitin have not been evaluated in primary human leukocytes, we analyzed its binding characteristics and subsequent Ca2+ signaling in freshly isolated human B-cells, T-cells and monocytes. Ubiquitin binding shows typical receptor binding characteristics and promotes intracellular Ca2+ flux within seconds in all three cell populations. The Kd for the ubiquitin receptor interaction in freshly isolated human monocytes is consistent with the affinity of the ubiquitin CXCR4 interaction that we reported for THP1 cells. As detected in THP1 cells previously, the ubiquitin induced Ca2+ flux can be attenuated with a phospholipase C inhibitor in all primary leukocyte cultures. Our observations further support the finding that ubiquitin is a CXCR4 agonist and demonstrate that extracellular ubiquitin induces physiological relevant signaling events in primary human leukocytes. Although the exact mechanism of the ubiquitin CXCR4 interaction, its receptor selectivity and subsequent signaling events remain to be determined, our findings identify a novel and unexpected biological role of extracellular ubiquitin as an endogenous immune modulator.

E0194 Src family kinase SFK is essential for recruitment of bonemarrow progenitor cells to the ischaemic myocardium

BackgroundThe G protein-coupled receptor CXCR4 and its ligand stromal–cell derived factor 1 (SDF-1) play an important role in directing progenitor cells (PC) homing to ischaemic tissue. The Src family protein...

Extracellular ubiquitin: immune modulator and endogenous opponent of damage-associated molecular pattern molecules

Ubiquitin is a post-translational protein modifier and plays essential roles in all aspects of biology. Although the discovery of ubiquitin introduced this highly conserved protein as a molecule with extracellular actions, the identification of ubiquitin as the ATP-dependent proteolysis factor 1 has focused subsequent research on its important intracellular functions. Little attention has since been paid to its role outside of the cell. During recent years, multiple observations suggest that extracellular ubiquitin can modulate immune responses and that exogenous ubiquitin has therapeutic potential to attenuate exuberant inflammation and organ injury. These observations have not been integrated into a comprehensive assessment of its possible role as an endogenous immune modulator. This review recapitulates the current knowledge about extracellular ubiquitin and discusses an emerging facet of its role in biology during infectious and noninfectious inflammation. The synopsis of these data along with the recent identification of ubiquitin as a CXCR4 agonist suggest that extracellular ubiquitin may have pleiotropic roles in the immune system and functions as an endogenous opponent of DAMPs. Functions of extracellular ubiquitin could constitute an evolutionary conserved control mechanism aimed to balance the immune response and prevent exuberant inflammation. Further characterization of its mechanism of action and cellular signaling pathways is expected to provide novel insights into the regulation of the innate immune response and opportunities for therapeutic interventions.

The chemotactic effects of stromal cell derived factor-1 on neural stem cells

Objective To investigate the effect of stromal cell derived factor-1 ( SDF-1) on the regulation of neural stem cells (NSCs) migration. Methods NSCs were obtained from the cerebral cortex of embryonic GFP transgenic rats. After cell cultured in vitro, CXCR4, specific receptor of SDF-1, was detected by fluorescence immunocytochemistry. Using Blind-Well chambers, the chemotactic effects of SDF-1 was investigated by counting the cells which had crossed 8μm pore membrane and adhered to the superficies inferia of the membrane when confronted with varying concentrations of SDF-1α (0, 1, 10, 50, 100, 500 and 1000 μg/L) and the agonist or antagonist of CXCR4. Results Neurospheres were formed, which expressed GFP and were capable of differentiating into neurons (β-tubulin + ) and astrocytes (GFAP + ) in media without mitogens. Fluorescence immunocytochemistry showed that CXCR4 and Nestin were co-expressed in NSCs. SDF-1 showed great chemotaxis to NSCs, and the amount of cells migrating through the membrane in 500 μg/L SDF-1 group was more than that in other groups (P < 0. 05). The number of cells crossing the membrane could be augmented and diminished by the agonist and antagonist of CXCR4 respectively. Conclusion SDF-1 binding to its specific receptor CXCR4 was capable of inducing NSCs migrating directionally to the source of SDF-1. Key words: Neural stem cells; Chemotaxis; Stromal cell derived factor-1

Evidence for PI3K-dependent CXCR3 agonist-induced degranulation of human cord blood-derived mast cells

The chemokine receptor CXCR3, which has three known variants (CXCR3-A, CXCR3-B and CXCR3-Alt), has been implicated in the recruitment of mast cells to tissues in many different chronic diseases with its agonists found in elevated levels in several pulmonary diseases. All three variants of CXCR3 were detected in cord blood-derived mast cells at the mRNA level. Using an antibody that is unable to distinguish individual CXCR3 isoforms, we detected a marked down-regulation of intracellular protein during maturation from progenitor cells, with no concomitant changes in the modest surface expression of CXCR3. The known CXCR3 agonists CXCL9, CXCL10 and CXCL11 as well as the reported CXCR3-B agonist CXCL4, were able to induce Akt and ERK1/2 phosphorylation, as well as partial degranulation. Responses to all agonists were inhibited by pre-treatment with selective CXCR3 antagonists and pertussis toxin. Use of novel isoform-selective inhibitors, indicates that the p110γ isoform of PI3K is required for degranulation and signaling responses to CXCR3 agonists.

CXC Chemokine Receptor 4 Is a Cell Surface Receptor for Extracellular Ubiquitin

Ubiquitin is one of the most highly conserved proteins in eukaryotes and plays major biological roles as a post-translational protein modifier. Ubiquitin is also a natural constituent of plasma, and several lines of evidence suggest that extracellular ubiquitin is an immune modulator with anti-inflammatory properties. In addition, ubiquitin treatment has been shown to limit inflammation and reduce organ injury in various disease models and species in vivo. However, its mechanism of action is unknown. Here we show that extracellular ubiquitin is a natural CXC chemokine receptor 4 (CXCR4 and CD184) agonist. Extracellular ubiquitin promotes intracellular Ca(2+) flux and reduces cAMP levels through a G protein-coupled receptor that signals via a Galpha(i/o) protein in THP1 cells. Toll-like receptor 4 stimulation reduces ubiquitin-binding sites, which enabled identification of four Galpha(i/o) PCRs as ubiquitin receptor candidates. Overexpression of candidate genes in HEK293 cells, gene silencing in THP1 cells, competition binding, and signaling studies with the CXCR4 agonist stromal cell-derived factor-1alpha (chemokine (CXC motif) ligand 12) and inhibitor AMD3100 identify CXCR4 as a functional ubiquitin receptor. Our finding uncovers a fundamentally new aspect of the role of ubiquitin in biology, has implications for the understanding of CXCR4-mediated events, and is expected to facilitate development of new therapeutic avenues for a variety of diseases.

The CXCR4 Antagonist AMD3100 Has Dual Effects on Survival and Proliferation of Myeloma CellsIn Vitro

PurposeAMD3100, an antagonist of the CXCR4 chemokine receptor is soon to be used clinically for the peripheral mobilization of hematopoietic stem cells (HSCs) in patients with multiple myeloma. AMD3100 has been shown to activate a G protein coupled with CXCR4 and thus acts as a partial CXCR4 agonist in vitro. Thus, we explored whether AMD3100 affected the survival and proliferation of myeloma cells in vitro.Materials and MethodsThe effects of AMD3100 on survival and proliferation of two myeloma cell lines (RPMI8226 and U266) as well as CD138+ cells obtained from several patients with multiple myeloma were analyzed by flow cytometry using annexin V and a colorimetric cell proliferation assay (CCK-8 assay).ResultsAMD3100, but not T140, another CXCR4 antagonist, stimulated the proliferation of myeloma cell lines and CD138+ primary human myeloma cells (-2-fold increase) in a dose-dependent manner in serum-free culture for up to 5 days, which was inhibited by pretreating the cells with pertussis toxin. AMD3100 enhanced the proliferation of U266 cells induced by interleukin-6 and partially reversed AG490-mediated growth inhibition and apoptosis induced by serum deprivation in RPMI8226 cells. AMD3100 induced the phosphorylation of Akt and MAPK p44/p42 in U266 cells and MAPK p44/p42 in RPMI8226 cells. In contrast, AMD3100 markedly increased the cell apoptosis and reduced the number of RPMI8226 cells after 5 to 7 days of culture under serum-free conditions.ConclusionAMD3100 exerts dual effects, initially enhancing and subsequently inhibiting the survival and proliferation of myeloma cells, signaling via CXCR4 in vitro.

The CXCR4 Antagonist AMD3100 Has Dual Effects, Initially Enhancing and Later Inhibiting Survival and Proliferation, in Myeloid Leukemia Cells in Vitro.

Abstract 1721Poster Board I-747AMD3100, a small bicyclam antagonist for chemokine receptor CXCR4, induces the peripheral mobilization of hematopoietic stem cells. It also induces the segregation of leukemia cells in the bone marrow microenvironment, which should enhance the chemosensitivity of the cells. Based on these observations, AMD3100 is being considered for clinical use. However, AMD3100 activates G-protein coupled with CXCR4 and acts as a partial CXCR4 agonist. In this study, we explored whether AMD3100 affects the proliferation and survival of myeloid leukemia cells. As demonstrated previously, both AMD3100 and T140, another CXCR4 antagonist, markedly inhibited stromal cell-derived factor-1 (SDF-1)-induced chemotaxis and induced the internalization of CXCR4 in myeloid leukemia cell lines (U937, HL-60, MO7e, KG1a, and K562 cells) and CD34+ primary human acute myeloid leukemia (AML) cells. SDF-1 alone did not stimulate the proliferation of these leukemia cells, nor did it rescue the cells from apoptosis induced by serum deprivation. By contrast, AMD3100, but not T140, stimulated the proliferation of all five leukemia cell lines and primary AML cells in a dose-dependent manner in serum-free conditions for up to 5 days (∼ 2-fold increases at a concentration of 10-5M), which was abrogated by pretreating the cells with pertussis toxin. AMD3100 binds to CXCR7, another SDF-1 receptor, and all of the cells examined in this study expressed CXCR4 on the cell surface to some extent. The proliferation-enhancing effects of AMD3100 were not changed by knocking-down CXCR7 using the siRNA technique, whereas knocking-down CXCR4 significantly delayed the enhanced proliferation induced by AMD3100. Neither AMD3100 nor T140 induced the phosphorylation of Akt, Stat3, MAPK p44/p42, or MAPK p38, which are involved in SDF-1 signaling. In extended cultures of these cells for up to 14 days, AMD3100, but not T140, induced a marked decrease in the number of cells, compared to the control, after incubation for 5-7 days. Adding SDF-1 at the beginning and middle of the incubation did not affect the early increase or later decrease in the number of cells. AMD3100 reduced the apoptosis of these cells to a modest degree over the first 5-7 days and then markedly increased it. Consistent with the proliferation assay, AMD3100 increased the number of leukemia cell colonies during the early period of the assay, while it markedly decreased the number and size of the colonies in the later period of the assay. In conclusion, AMD3100 exerts dual effects, initially enhancing and subsequently inhibiting the survival and proliferation, in myeloid leukemia cells in vitro. DisclosuresNo relevant conflicts of interest to declare.

Hetero-oligomerization of CCR2, CCR5, and CXCR4 and the Protean Effects of “Selective” Antagonists

Chemokine receptors constitute an attractive family of drug targets in the frame of inflammatory diseases. However, targeting specific chemokine receptors may be complicated by their ability to form dimers or higher order oligomers. Using a combination of luminescence complementation and bioluminescence resonance energy transfer assays, we demonstrate for the first time the existence of hetero-oligomeric complexes composed of at least three chemokine receptors (CCR2, CCR5, and CXCR4). We show in T cells and monocytes that negative binding cooperativity takes place between the binding pockets of these receptors, demonstrating their functional interaction in leukocytes. We also show that specific antagonists of one receptor (TAK-779 or AMD3100) lead to functional cross-inhibition of the others. Finally, using the air pouch model in mice, we show that the CCR2 and CCR5 antagonist TAK-779 inhibits cell recruitment promoted by the CXCR4 agonist SDF-1 alpha, demonstrating that cross-inhibition by antagonists also occurs in vivo. Thus, antagonists of the therapeutically important chemokine receptors regulate the functional properties of other receptors to which they do not bind directly with important implications for the use of these agents in vivo.

Anti‐inflammatory therapy by intravenous delivery of non‐heparan sulfate‐binding CXCL12

Interaction between chemokines and heparan sulfate (HS) is essential for leukocyte recruitment during inflammation. Previous studies have shown that a non-HS-binding mutant form of the inflammatory chemokine CCL7 can block inflammation produced by wild-type chemokines. This study examined the anti-inflammatory mechanism of a non-HS-binding mutant of the homeostatic chemokine CXCL12. Initial experiments demonstrated that mutant CXCL12 was an effective CXCR4 agonist. However, this mutant chemokine failed to promote transendothelial migration in vitro and inhibited the haptotactic response to wild-type CCL7, CXCL12, and CXCL8, and naturally occurring chemoattractants in synovial fluid from the rheumatoid synovium, including CCL2, CCL7, and CXCL8. Notably, intravenous administration of mutant CXCL12 also inhibited the recruitment of leukocytes to murine air pouches filled with wild-type CXCL12. Following intravenous administration, wild-type CXCL12 was cleared from the circulation rapidly, while the mutant chemokine persisted for >24 h. Chronic exposure to mutant CXCL12 in the circulation reduced leukocyte-surface expression of CXCR4, reduced the chemotactic response of these cells to CXCL12, and inhibited normal chemokine-mediated induction of adhesion between the α4β1 integrin, VLA-4, and VCAM-1. These data demonstrate that systemic administration of non-HS-binding variants of CXCL12 can mediate a powerful anti-inflammatory effect through chemokine receptor desensitization.—O’Boyle, G., Mellor, P., Kirby, J. A., Ali, S. Anti-inflammatory therapy by intravenous delivery of non-heparan sulfate-binding CXCL12.