Structure function differences in nonpeptide CCR1 antagonists for human and mouse CCR1

PET Imaging Radiotracers of Chemokine Receptors

Chemokines and chemokine receptors have been recognized as critical signal components that maintain the physiological functions of various cells, particularly the immune cells. The signals of chemokines/chemokine receptors guide various leukocytes to respond to inflammatory reactions and infectious agents. Many chemokine receptors play supportive roles in the differentiation, proliferation, angiogenesis, and metastasis of diverse tumor cells. In addition, the signaling functions of a few chemokine receptors are associated with cardiac, pulmonary, and brain disorders. Over the years, numerous promising molecules ranging from small molecules to short peptides and antibodies have been developed to study the role of chemokine receptors in healthy states and diseased states. These drug-like candidates are in turn exploited as radiolabeled probes for the imaging of chemokine receptors using noninvasive in vivo imaging, such as positron emission tomography (PET). Recent advances in the development of radiotracers for various chemokine receptors, particularly of CXCR4, CCR2, and CCR5, shed new light on chemokine-related cancer and cardiovascular research and the subsequent drug development. Here, we present the recent progress in PET radiotracer development for imaging of various chemokine receptors.

Identification of Amino Acid Residues in Human IgM Fc Receptor (FcµR) Critical for IgM Binding

Both non-immune “natural” and antigen-induced “immune” IgM are important for protection against infections and for regulation of immune responses to self-antigens. The roles of its Fc receptor (FcµR) in these IgM effector functions have begun to be explored. In the present study, by taking advantage of the difference in IgM-ligand binding of FcµRs of human (constitutive binding) and mouse (transient binding), we replaced non-conserved amino acid residues of human FcµR with mouse equivalents before establishment of cell lines stably expressing mutant or wild-type (WT) receptors. The resultant eight-different mutant FcµR-bearing cells were compared with WT receptor-bearing cells for cell-surface expression and IgM-binding by flow cytometric assessments using receptor-specific mAbs and IgM paraproteins as ligands. Three sites Asn66, Lys79-Arg83, and Asn109, which are likely in the CDR2, DE loop and CDR3 of the human FcµR Ig-like domain, respectively, were responsible for constitutive IgM binding. Intriguingly, substitution of Glu41 and Met42 in the presumed CDR1 with the corresponding mouse residues Gln and Leu, either single or more prominently in combination, enhanced both the receptor expression and IgM binding. A four-aa stretch of Lys24-Gly27 in the predicted A ß-strand of human FcµR appeared to be essential for maintenance of its proper receptor conformation on plasma membranes because of reduction of both receptor expression and IgM-binding potential when these were mutated. Results from a computational structural modeling analysis were consistent with these mutational data and identified a possible mode of binding of FcµR with IgM involving the loops including Asn66, Arg83 and Asn109 of FcµR interacting principally with the Cµ4 domain including Gln510 and to a lesser extent Cµ3 domain including Glu398, of human IgM. To our knowledge, this is the first experimental report describing the identification of amino acid residues of human FcµR critical for binding to IgM Fc.

Therapeutic potential of CCR1 antagonists for multiple myeloma

The chemokine receptor CCR1 has been the target of intensive research for nearly two decades. Small-molecule antagonists were first reported in 1998 and, since then, many inhibitors for CCR1 have been brought forth. Yet, with all the money and time spent, to date, no small-molecule antagonists have successfully moved past Phase II clinical trials. With the current advancement of CCR1 antagonists by Bristol-Myers Squibb and Chemocentrix, there has been renewed interest. In this review, we present an overview of CCR1, its activating ligands, methods of signaling, and downstream response. We discuss studies that indicate CCR1 plays an important role in multiple myeloma and the underlying molecular mechanisms. Finally, we present an overview of the clinical and preclinical compounds for CCR1. We address individual structures, discuss their pharmacological précis, and summarize the published evidence to assess their value for use in multiple myeloma.

Interaction between activated chemokine receptor 1 and FcepsilonRI at membrane rafts promotes communication and F-actin-rich cytoneme extensions between mast cells

Chemokines play important regulatory roles in immunity, but their contributions to mast cell function remain poorly understood. We examined the effects of FcepsilonRI-chemokine receptor (CCR) 1 co-stimulation on receptor localization and cellular morphology of bone marrow-derived mast cells. Whereas FcepsilonRI and CCR1 co-localized at the plasma membrane in unsensitized cells, sensitization with IgE promoted internalization of CCR1 molecules. Co-stimulation of FcepsilonRI and CCR1 with antigen and macrophage inflammatory protein-1alpha was more effective than FcepsilonRI stimulation alone in causing leading edge formation, flattened morphology, membrane ruffles and ganglioside (GM1(+)) lipid mediator release. Co-stimulation resulted in phalloidin-positive cytoneme-like cellular extensions, also known as tunneling nanotubes, which originated at points of calcium accumulation. This is the first report of cytoneme formation by mast cells. To determine the importance of lipid rafts for mast cell function, the cells were cholesterol depleted. Cholesterol depletion enhanced degranulation in resting, sensitized and co-stimulated cells, but not in FcepsilonRI-cross-linked cells, and inhibited formation of filamentous actin(+) cytonemes but not GM1(+) cytonemes. Treatment with latrunculin A to sequester globular-actin abolished cytoneme formation. The cytonemes may participate in intercellular communication during allergic and inflammatory responses, and their presence in the co-stimulated mast cells suggests new roles for CCRs in immunopathology.

Anti-chemokine small molecule drugs: a promising future?

IMPORTANCE OF THE FIELD

Chemokines have principally been associated with inflammation due to their role in the control of leukocyte migration, but just over a decade ago chemokine receptors were also identified as playing a pivotal role in the entry of the HIV virus into cells. Chemokines activate seven transmembrane G protein-coupled receptors, making them extremely attractive therapeutic targets for the pharmaceutical industry.

AREAS COVERED IN THIS REVIEW

Although there are now a large number of molecules targeting chemokines and chemokine receptors including neutralizing antibodies in clinical trials for inflammatory diseases, the results to date have not always been positive, which has been disappointing for the field. These failures have often been attributed to redundancy in the chemokine system. However, other difficulties have been encountered in drug discovery processes targeting the chemokine system, and these will be addressed in this review.

WHAT THE READER WILL GAIN

In this review, the reader will get an insight into the hurdles that have to be overcome, learn about some of the pitfalls that may explain the lack of success, and get a glimpse of the outlook for the future.

TAKE HOME MESSAGE

In 2007, the FDA approved maraviroc, an inhibitor of CCR5 for the prevention of HIV infection, the first triumph for a small-molecule drug acting on the chemokine system. The time to market, 11 years from discovery of CCR5, was fast by industry standards. A second small-molecule drug, a CXCR4 antagonist for hematopoietic stem cell mobilization, was approved by the FDA at the end of 2008. The results of a Phase III trial with a CCR9 inhibitor for Crohn's disease are also promising. This could herald the first success for a chemokine receptor antagonist as an anti-inflammatory therapeutic and confirms the importance of chemokine receptors as a target class for anti-inflammatory and autoimmune diseases.

Chemokines and Chemokine Receptors as Therapeutic Targets in Lupus Nephritis

Recruitment of leukocytes is a characteristic feature of tissue injury in systemic lupus erythematosus, including lupus nephritis. Locally secreted chemokines and their receptors are important mediators of leukocyte recruitment to the specific sites of immune complex injury, and contribute to renal inflammatory disease in the initiation and progression phase. Therefore, chemokines and chemokine receptors represent potential therapeutic targets in lupus nephritis. In this review we summarize available experimental and human data supporting their functional role in lupus nephritis. Moreover, interventional studies with chemokine and chemokine receptor antagonists that show the therapeutic potential of chemokine antagonists in experimental models of lupus nephritis and potentially in human renal disease are discussed.

Identification and structure-activity relationships of 1-aryl-3-piperidin-4-yl-urea derivatives as CXCR3 receptor antagonists

The synthesis and biological evaluation of a series of 1-aryl-3-piperidin-4-yl-urea derivatives as small-molecule CXCR3 antagonists is described. SAR studies resulted in significant improvement of potency and physicochemical properties and established the key pharmacophore of the series, and led to the identification of 9t, which exhibits an IC50 of 16 nM in the GTPgammaS35 functional assay.

Predictions of CCR1 chemokine receptor structure and BX 471 antagonist binding followed by experimental validation

A major challenge in the application of structure-based drug design methods to proteins belonging to the superfamily of G protein-coupled receptors (GPCRs) is the paucity of structural information (1). The 19 chemokine receptors, belonging to the Class A family of GPCRs, are important drug targets not only for autoimmune diseases like multiple sclerosis but also for the blockade of human immunodeficiency virus type 1 entry (2). Using the MembStruk computational method (3), we predicted the three-dimensional structure of the human CCR1 receptor. In addition, we predicted the binding site of the small molecule CCR1 antagonist BX 471, which is currently in Phase II clinical trials (4). Based on the predicted antagonist binding site we designed 17 point mutants of CCR1 to validate the predictions. Subsequent competitive ligand binding and chemotaxis experiments with these mutants gave an excellent correlation to these predictions. In particular, we find that Tyr-113 and Tyr-114 on transmembrane domain 3 and Ile-259 on transmembrane 6 contribute significantly to the binding of BX 471. Finally, we used the predicted and validated structure of CCR1 in a virtual screening validation of the Maybridge data base, seeded with selective CCR1 antagonists. The screen identified 63% of CCR1 antagonists in the top 5% of the hits. Our results indicate that rational drug design for GPCR targets is a feasible approach.

A novel, selective, and orally available antagonist for CC chemokine receptor 3

CC chemokine ligand 11 (CCL11/eotaxin) and other CC chemokine receptor 3 (CCR3) ligands (CCL24/eotaxin-2, CCL26/eotaxin-3, CCL13/monocyte chemotactic protein-4, etc.) play important roles in the chemotaxis and activation of eosinophils and other CCR3-expressing cells (basophils, mast cells, and CD4(+) T helper 2 cells) in allergic inflammation incidents, including asthma and rhinitis. A newly synthesized compound, N-{(3R)-1-[(6-fluoro-2-naphthyl)methyl]pyrrolidin-3-yl}-2-{1-[(5-hydroxy-3-methylpyridin-2-yl)carbonyl]piperidin-4-ylidene}-acetamide hemifumarate (YM-355179), inhibited the binding of CCL11 and CCL5/regulated on activation normal T cell expressed and secreted to CCR3-expressing B300-19 cells with IC(50) values of 7.6 and 24 nM, respectively. In contrast, YM-355179 did not affect the binding of CCL5 to CCR1 or CCR5. In functional assays, YM-355179 inhibited CCL11-induced, intracellular Ca(2+) influx, chemotaxis, and eosinophil degranulation with IC(50) values of 8.0, 24, and 29 nM, respectively. YM-355179 did not, however, affect any CC chemokine receptor (CCR1, CCR2, CCR4, or CCR5)-mediated Ca(2+) influx signals. Furthermore, oral administration of YM-355179 (1 mg/kg) inhibited CCL11-induced shape change of whole blood eosinophils in cynomolgus monkeys. Intravenous injection of YM-355179 (1 mg/kg) also inhibited eosinophil infiltration into airways of cynomolgus monkeys after segmental bronchoprovocation with CCL11. These results indicate that YM-355179 is a novel, selective, and orally available CCR3 antagonist with therapeutic potential for treating eosinophil-related allergic inflammatory diseases.

MIP-1α utilizes both CCR1 and CCR5 to induce osteoclast formation and increase adhesion of myeloma cells to marrow stromal cells

OBJECTIVES

Macrophage inflammatory protein-1alpha (MIP-1alpha), an osteoclast (OCL) stimulatory factor produced by primary multiple myeloma (MM) cells, increases bone destruction and tumor burden in murine models of MM. Several chemokine receptors (CCR1, CCR5, and CCR9) mediate the effects of MIP-1alpha. In this study, we determined which of these mediates the effects of MIP-1alpha on human OCL formation and myeloma cells.

METHODS

We employed RT-PCR analysis, neutralizing antibodies to CCR1 and CCR5 as well as a CCR1-specific antagonist and OCL formation assays to identify the MIP-1alpha receptors involved in MIP-1alpha's effects on myeloma cells and OCL formation.

RESULTS

RT-PCR analysis demonstrated that both CCR1 and CCR5 were expressed by highly purified human OCL precursors, myeloma cell lines, and purified marrow plasma cells from MM patients. Neutralizing antibodies to CCR1 or CCR5 inhibited MIP-1alpha-induced OCL formation. Furthermore, monocyte chemotactic protein-3 (MCP-3), which binds CCR1 but not CCR5 and the CCR1-specific antagonist, BX471, markedly inhibited OCL formation stimulated with MIP-1alpha. Anti-CCR1, anti-CCR5, or BX471 also inhibited the upregulation of beta1 integrin mRNA in myeloma cells induced by MIP-1alpha, as well as the adherence of myeloma cells to stromal cells and IL-6 production by stromal cells in response to myeloma cells.

CONCLUSION

These data demonstrate that MIP-1alpha utilizes either CCR1 or CCR5 for its effects on OCL formation and myeloma cells, and that blocking either CCR1 or CCR5 inhibits OCL formation and myeloma cell adhesion to stromal cells.

Structure-based Drug Discovery Using GPCR Homology Modeling: Successful Virtual Screening for Antagonists of the Alpha1A Adrenergic Receptor

In this paper, we describe homology modeling of the alpha1A receptor based on the X-ray structure of bovine rhodopsin. The protein model has been generated by applying ligand-supported homology modeling, using mutational and ligand SAR data to guide the protein modeling procedure. We performed a virtual screening of the company's compound collection to test how well this model is suited to identify alpha1A antagonists. We applied a hierarchical virtual screening procedure guided by 2D filters and three-dimensional pharmacophore models. The ca. 23,000 filtered compounds were docked into the alpha1A homology model with GOLD and scored with PMF. From the top-ranked compounds, 80 diverse compounds were tested in a radioligand displacement assay. 37 compounds revealed K(i) values better than 10 microM; the most active compound binds with 1.4 nM to the alpha1A receptor. Our findings suggest that rhodopsin-based homology models may be used as the structural basis for GPCR lead finding and compound optimization.

Site-directed mutagenesis of CC chemokine receptor 1 reveals the mechanism of action of UCB 35625, a small molecule chemokine receptor antagonist

The chemokine receptor CCR1 and its principal ligand, CCL3/MIP-1alpha, have been implicated in the pathology of several inflammatory diseases including rheumatoid arthritis, multiple sclerosis, and asthma. As such, these molecules are the focus of much research with the ultimate aim of developing novel therapies. We have described previously a non-competitive small molecule antagonist of CCR1 (UCB 35625), which we hypothesized interacted with amino acids located within the receptor transmembrane (TM) helices (Sabroe, I., Peck, M. J., Jan Van Keulen, B., Jorritsma, A., Simmons, G., Clapham, P. R., Williams, T. J., and Pease, J. E. (2000) J. Biol. Chem. 275, 25985-25992). Here we describe an approach to identifying the mechanism by which the molecule antagonizes CCR1. Thirty-three point mutants of CCR1 were expressed transiently in L1.2 cells, and the cells were assessed for their capacity to migrate in response to CCL3 in the presence or absence of UCB 35625. Cells expressing the mutant constructs Y41A (TM helix 1, or TM1), Y113A (TM3), and E287A (TM7) were responsive to CCL3 but resistant to the antagonist, consistent with a role for the TM helices in CCR1 interactions with UCB 35625. Subsequent molecular modeling successfully docked the compound with CCR1 and suggests that the antagonist ligates TM1, 2, and 7 of CCR1 and severely impedes access to TM2 and TM3, a region thought to be perturbed by the chemokine amino terminus during the process of receptor activation. Insights into the mechanism of action of these compounds may facilitate the development of more potent antagonists that show promise as future therapeutic agents in the treatment of inflammatory disease.

Chemokine-receptor interactions: GPCRs, glycosaminoglycans and viral chemokine binding proteins

A key feature of the immune system is the migration of leukocytes throughout the organism in an effort to patrol for infectious pathogens, tissue damage, and other physiological insults. This remarkable surveillance system is controlled by a family of proteins called chemokines (chemoattractant cytokines), and their respective receptors. Originally discovered because of their role in cell recruitment during inflammation, it is now well recognized that chemokines are also involved in other diverse processes including lymphocyte development and homing, organogenesis, and neuronal communication. While chemokines have evolved largely for host protection, their ability to induce cell damage and inappropriate cell recruitment, can lead to disease. Thus, there is considerable interest in developing antagonists. In this review we emphasize what is known about the structural biology of chemokines, chemokine receptors, and interactions with cell surface glycosaminoglycans. We also briefly describe their role in certain diseases and strategies for interfering with chemokine function that have emerged from mechanistic and structural understanding of their function. Finally we discuss viral mechanisms for sabotaging or manipulating the chemokine system, in part to illustrate the level of molecular mimicry that viruses have achieved and the evolutionary pressure imposed on the immune system by these pathogens.