Feasibility and physiological relevance of designing highly potent aminopeptidase-sparing leukotriene A4 hydrolase inhibitors

Leukotriene A4 Hydrolase (LTA4H) is a bifunctional zinc metalloenzyme that comprises both epoxide hydrolase and aminopeptidase activity, exerted by two overlapping catalytic sites. The epoxide hydrolase function of the enzyme catalyzes the biosynthesis of the pro-inflammatory lipid mediator leukotriene (LT) B4. Recent literature suggests that the aminopeptidase function of LTA4H is responsible for degradation of the tripeptide Pro-Gly-Pro (PGP) for which neutrophil chemotactic activity has been postulated. It has been speculated that the design of epoxide hydrolase selective LTA4H inhibitors that spare the aminopeptidase pocket may therefore lead to more efficacious anti-inflammatory drugs. In this study, we conducted a high throughput screen (HTS) for LTA4H inhibitors and attempted to rationally design compounds that would spare the PGP degrading function. While we were able to identify compounds with preference for the epoxide hydrolase function, absolute selectivity was not achievable for highly potent compounds. In order to assess the relevance of designing such aminopeptidase-sparing LTA4H inhibitors, we studied the role of PGP in inducing inflammation in different settings in wild type and LTA4H deficient (LTA4H KO) animals but could not confirm its chemotactic potential.  Attempting to design highly potent epoxide hydrolase selective LTA4H inhibitors, therefore seems to be neither feasible nor relevant.

Retinoic-acid-orphan-receptor-C inhibition suppresses Th17 cells and induces thymic aberrations

Retinoic-acid-orphan-receptor-C (RORC) is a master regulator of Th17 cells, which are pathogenic in several autoimmune diseases. Genetic Rorc deficiency in mice, while preventing autoimmunity, causes early lethality due to metastatic thymic T cell lymphomas. We sought to determine whether pharmacological RORC inhibition could be an effective and safe therapy for autoimmune diseases by evaluating its effects on Th17 cell functions and intrathymic T cell development. RORC inhibitors effectively inhibited Th17 differentiation and IL-17A production, and delayed-type hypersensitivity reactions. In vitro, RORC inhibitors induced apoptosis, as well as Bcl2l1 and BCL2L1 mRNA downregulation, in mouse and nonhuman primate thymocytes, respectively. Chronic, 13-week RORC inhibitor treatment in rats caused progressive thymic alterations in all analyzed rats similar to those in Rorc-deficient mice prior to T cell lymphoma development. One rat developed thymic cortical hyperplasia with preneoplastic features, including increased mitosis and reduced IKAROS expression, albeit without skewed T cell clonality. In summary, pharmacological inhibition of RORC not only blocks Th17 cell development and related cytokine production, but also recapitulates thymic aberrations seen in Rorc-deficient mice. While RORC inhibition may offer an effective therapeutic principle for Th17-mediated diseases, T cell lymphoma with chronic therapy remains an apparent risk.

Synthesis and Biological Evaluation of New Triazolo- and Imidazolopyridine RORγt Inverse Agonists

Retinoic-acid-related orphan receptor γt (RORγt) is a key transcription factor implicated in the production of pro-inflammatory Th17 cytokines, which drive a number of autoimmune diseases. Despite diverse chemical series having been reported, combining high potency with a good physicochemical profile has been a very challenging task in the RORγt inhibitor field. Based on available chemical structures and incorporating in-house knowledge, a new series of triazolo- and imidazopyridine RORγt inverse agonists was designed. In addition, replacement of the terminal cyclopentylamide metabolic soft spot by five-membered heterocycles was investigated. From our efforts, we identified an optimal 6,7,8-substituted imidazo[1,2-a]pyridine core system and a 5-tert-butyl-1,2,4-oxadiazole as cyclopentylamide replacement leading to compounds 10 ((S)-N-(8-((4-(cyclopentanecarbonyl)-3-methylpiperazin-1-yl)methyl)-7-methylimidazo[1,2-a]pyridin-6-yl)-2-methylpyrimidine-5-carboxamide) and 33 ((S)-N-(8-((4-(5-(tert-butyl)-1,2,4-oxadiazol-3-yl)-3-methylpiperazin-1-yl)methyl)-7-methylimidazo[1,2-a]pyridin-6-yl)-2-methylpyrimidine-5-carboxamide). Both derivatives showed good pharmacological potencies in biochemical and cell-based assays combined with excellent physicochemical properties, including low to medium plasma protein binding across species. Finally, 10 and 33 were shown to be active in a rodent pharmacokinetic/pharmacodynamic (PK/PD) model after oral gavage at 15 mg kg^-1 , lowering IL-17 cytokine production in ex vivo antigen recall assays.

HIV-1 Integrase: High-Level Production and Screening Assay for the Endonucleolytic Activity

The integration protein of the human immunodeficiency virus type 1 was purified from recombinant bacteria overproducing this enzyme. The final step of purification, namely chromatography on polyUsepharose, yielded a homogeneous protein preparation showing specific DNA cutting and joining activities. For a convenient assay of the endonuclease reaction, a 21-mer duplex oligonucleotide corresponding to the U5-LTR end of the viral DNA was radiolabeled at the dinucleotide that is removed by the enzyme. After the reaction, assay mixtures were passed through DEAE-cellulose filters which bind the substrate, but not the short radiolabeled product. Thus, an enzyme-dependent decrease of bound radioactivity was observed with time. Reaction rate was linearly dependent on enzyme concentration and the amount of substrate used was far below saturating concentrations. The reaction showed a pH-optimum at 7.5 and was strictly dependent on the presence of Mn2+. The presence of reducing agents like 2-mercaptoethanol was not essential for enzymatic activity. The assay was used to test selected compounds for their inhibitory potential against integrase. Typical inhibitors of DNA-topoisomerases did not inhibit the endonuclease reaction, with the exception of the intercalative agent actinomycin D which blocked the reaction with an IC50-value of 3 μM. Dextran sulphate inhibited the enzyme with an IC50 = 1.6 μg ml−1.

Potent and Orally Bioavailable HIV-1 Proteinase Inhibitors Containing the 2-aminobenzylstatine Moiety

In order to design HIV proteinase inhibitors which combine antiviral potency in HIV-infected cells with good oral bioavailability, new derivatives of 2-aminobenzylstatine containing HIV-1 proteinase inhibitors were synthesized. Compounds showing the desired profile emerged from a series of modifications at the P3′ moiety of the parent inhibitor [1], and are characterized by the presence of hydroxy or methoxy substituents at the C-terminal benzylamide. The most potent congeners, compounds [15] and [19], were evaluated in more detail and proved inhibitory to HIV-1 replication in primary T4 lymphocytes with EC90 = 2.2 and 2.7 nM, respectively. They also exhibited adequate oral bioavailability in the range of [13] to 42% in mice and rats. Thus, further investigation of this type of HIV proteinase inhibitor seems warranted.

Sphingosine 1-Phosphate Produced by Sphingosine Kinase 2 Intrinsically Controls Platelet Aggregation In Vitro and In Vivo

RATIONALE

Platelets are known to play a crucial role in hemostasis. Sphingosine kinases (Sphk) 1 and 2 catalyze the conversion of sphingosine to the bioactive metabolite sphingosine 1-phosphate (S1P). Although platelets are able to secrete S1P on activation, little is known about a potential intrinsic effect of S1P on platelet function.

OBJECTIVE

To investigate the role of Sphk1- and Sphk2-derived S1P in the regulation of platelet function.

METHODS AND RESULTS

We found a 100-fold reduction in intracellular S1P levels in platelets derived from Sphk2(-/-) mutants compared with Sphk1(-/-) or wild-type mice, as analyzed by mass spectrometry. Sphk2(-/-) platelets also failed to secrete S1P on stimulation. Blood from Sphk2-deficient mice showed decreased aggregation after protease-activated receptor 4-peptide and adenosine diphosphate stimulation in vitro, as assessed by whole blood impedance aggregometry. We revealed that S1P controls platelet aggregation via the sphingosine 1-phosphate receptor 1 through modulation of protease-activated receptor 4-peptide and adenosine diphosphate-induced platelet activation. Finally, we show by intravital microscopy that defective platelet aggregation in Sphk2-deficient mice translates into reduced arterial thrombus stability in vivo.

CONCLUSIONS

We demonstrate that Sphk2 is the major Sphk isoform responsible for the generation of S1P in platelets and plays a pivotal intrinsic role in the control of platelet activation. Correspondingly, Sphk2-deficient mice are protected from arterial thrombosis after vascular injury, but have normal bleeding times. Targeting this pathway could therefore present a new therapeutic strategy to prevent thrombosis.

Reduced Activity of Sphingosine-1-Phosphate Lyase Induces Podocyte-related Glomerular Proteinuria, Skin Irritation, and Platelet Activation

Sphingosine-1-phosphate (S1P) lyase is considered as a drug target in autoimmune diseases based on the protective effect of reducing activity of the enzyme in animal models of inflammation. Since S1P lyase deficiency in mice causes a severe, lethal phenotype, it was of interest to investigate any pathological alterations associated with only partially reduced activity of S1P lyase as may be encountered upon pharmacological inhibition. Both genetic reduction of S1P lyase activity in mice and inhibition of S1P lyase with a low-molecular-weight compound in rats consistently resulted in podocyte-based kidney toxicity, which is the most severe finding. In addition, skin irritation and platelet activation were observed in both instances. The similarity of the findings in both the genetic model and the pharmacological study supports the value of analyzing inducible partially target-deficient mice for safety assessment. If the findings described in rodents translate to humans, target-related toxicity, particularly podocyte dysfunction, may limit chronic systemic treatment of autoimmune diseases with S1P lyase inhibitors. Furthermore, partial deficiency or inhibition of S1P lyase appears to provide an in vivo rodent model to enable studies on the mechanism of podocyte dysfunction.

PIKfyve, a class III PI kinase, is the target of the small molecular IL-12/IL-23 inhibitor apilimod and a player in Toll-like receptor signaling

Toll-like receptor (TLR) signaling is a key component of innate immunity. Aberrant TLR activation leads to immune disorders via dysregulation of cytokine production, such as IL-12/IL-23. Herein, we identify and characterize PIKfyve, a lipid kinase, as a critical player in TLR signaling using apilimod as an affinity tool. Apilimod is a potent small molecular inhibitor of IL-12/IL-23 with an unknown target and has been evaluated in clinical trials for patients with Crohn's disease or rheumatoid arthritis. Using a chemical genetic approach, we show that it binds to PIKfyve and blocks its phosphotransferase activity, leading to selective inhibition of IL-12/IL-23p40. Pharmacological or genetic inactivation of PIKfyve is necessary and sufficient for suppression of IL-12/IL-23p40 expression. Thus, we have uncovered a phosphoinositide-mediated regulatory mechanism that controls TLR signaling.

Orally active 7-substituted (4-benzylphthalazin-1-yl)-2-methylpiperazin-1-yl]nicotinonitriles as active-site inhibitors of sphingosine 1-phosphate lyase for the treatment of multiple sclerosis

Sphingosine 1-phosphate (S1P) lyase has recently been implicated as a therapeutic target for the treatment of multiple sclerosis (MS), based on studies in a genetic mouse model. Potent active site directed inhibitors of the enzyme are not known so far. Here we describe the discovery of (4-benzylphthalazin-1-yl)-2-methylpiperazin-1-yl]nicotinonitrile 5 in a high-throughput screen using a biochemical assay, and its further optimization. This class of compounds was found to inhibit catalytic activity of S1PL by binding to the active site of the enzyme, as seen in the cocrystal structure of derivative 31 with the homodimeric human S1P lyase. 31 induces profound reduction of peripheral T cell numbers after oral dosage and confers pronounced protection in a rat model of multiple sclerosis. In conclusion, this novel class of direct S1P lyase inhibitors provides excellent tools to further explore the therapeutic potential of T cell-targeted therapies in multiple sclerosis and other autoimmune and inflammatory diseases.

Second generation S1P pathway modulators: research strategies and clinical developments

Multiple Sclerosis (MS) is a chronic autoimmune disorder affecting the central nervous system (CNS) through demyelination and neurodegeneration. Until recently, major therapeutic treatments have relied on agents requiring injection delivery. In September 2010, fingolimod/FTY720 (Gilenya, Novartis) was approved as the first oral treatment for relapsing forms of MS. Fingolimod causes down-modulation of S1P1 receptors on lymphocytes which prevents the invasion of autoaggressive T cells into the CNS. In astrocytes, down-modulation of S1P1 by the drug reduces astrogliosis, a hallmark of MS, thereby allowing restoration of productive astrocyte communication with other neural cells and the blood brain barrier. Animal data further suggest that the drug directly supports the recovery of nerve conduction and remyelination. In human MS, such mechanisms may explain the significant decrease in the number of inflammatory markers on brain magnetic resonance imaging in recent clinical trials, and the reduction of brain atrophy by the drug. Fingolimod binds to 4 of the 5 known S1P receptor subtypes, and significant efforts were made over the past 5 years to develop next generation S1P receptor modulators and determine the minimal receptor selectivity needed for maximal therapeutic efficacy in MS patients. Other approaches considered were competitive antagonists of the S1P1 receptor, inhibitors of the S1P lyase to prevent S1P degradation, and anti-S1P antibodies. Below we discuss the current status of the field, and the functional properties of the most advanced compounds. This article is part of a Special Issue entitled New Frontiers in Sphingolipid Biology.

Partial deficiency of sphingosine-1-phosphate lyase confers protection in experimental autoimmune encephalomyelitis

Background

Sphingosine-1-phosphate (S1P) regulates the egress of T cells from lymphoid organs; levels of S1P in the tissues are controlled by S1P lyase (Sgpl1). Hence, Sgpl1 offers a target to block T cell-dependent inflammatory processes. However, the involvement of Sgpl1 in models of disease has not been fully elucidated yet, since Sgpl1 KO mice have a short life-span.

Methodology

We generated inducible Sgpl1 KO mice featuring partial reduction of Sgpl1 activity and analyzed them with respect to sphingolipid levels, T-cell distribution, and response in models of inflammation.

Principal Findings

The partially Sgpl1 deficient mice are viable but feature profound reduction of peripheral T cells, similar to the constitutive KO mice. While thymic T cell development in these mice appears normal, mature T cells are retained in thymus and lymph nodes, leading to reduced T cell numbers in spleen and blood, with a skewing towards increased proportions of memory T cells and T regulatory cells. The therapeutic relevance of Sgpl1 is demonstrated by the fact that the inducible KO mice are protected in experimental autoimmune encephalomyelitis (EAE). T cell immigration into the CNS was found to be profoundly reduced. Since S1P levels in the brain of the animals are unchanged, we conclude that protection in EAE is due to the peripheral effect on T cells, leading to reduced CNS immigration, rather than on local effects in the CNS.

Significance

The data suggest Sgpl1 as a novel therapeutic target for the treatment of multiple sclerosis.

A novel role of sphingosine 1-phosphate receptor S1pr1 in mouse thrombopoiesis

Sphingosine 1-phosphate guides the elongation of megakaryocytic proplatelet extensions and triggers their shedding.

Millions of platelets are produced each hour by bone marrow (BM) megakaryocytes (MKs). MKs extend transendothelial proplatelet (PP) extensions into BM sinusoids and shed new platelets into the blood. The mechanisms that control platelet generation remain incompletely understood. Using conditional mutants and intravital multiphoton microscopy, we show here that the lipid mediator sphingosine 1-phosphate (S1P) serves as a critical directional cue guiding the elongation of megakaryocytic PP extensions from the interstitium into BM sinusoids and triggering the subsequent shedding of PPs into the blood. Correspondingly, mice lacking the S1P receptor S1pr1 develop severe thrombocytopenia caused by both formation of aberrant extravascular PPs and defective intravascular PP shedding. In contrast, activation of S1pr1 signaling leads to the prompt release of new platelets into the circulating blood. Collectively, our findings uncover a novel function of the S1P–S1pr1 axis as master regulator of efficient thrombopoiesis and might raise new therapeutic options for patients with thrombocytopenia.

BZM055, an iodinated radiotracer candidate for PET and SPECT imaging of myelin and FTY720 brain distribution

FTY720 (fingolimod, Gilenya®) is a sphingosine 1-phosphate (S1P) receptor modulator that shows significant therapeutic efficacy after oral administration to patients of multiple sclerosis. Because FTY720 does not contain any atom whose PET or SPECT radioisotope would have a half-life compatible with its pharmacokinetic properties, it cannot be used directly for imaging. Instead, we propose BZM055 as a surrogate tracer to study its pharmacokinetics and organ distribution in patients and, given that FTY720 accumulates in myelin sheaths, for myelin imaging. BZM055 (2 a, 2-iodo-FTY720) can be easily radiolabeled with ¹²³I (for SPECT) or ¹²⁴I (for PET). Not only does it closely mimic the pharmacokinetics and organ distribution of FTY720, but also its affinity, selectivity for S1P receptors, phosphorylation kinetics, and overall physicochemical properties. [¹²³I]BZM055 is currently under development for clinical imaging.

Ovalbumin-induced plasma interleukin-4 levels are reduced in ceramide kinase-deficient DO11.10 RAG1-/- mice

Ceramide kinase (CERK) produces the bioactive lipid ceramide-1-phosphate (C1P) and is a key regulator of ceramide and dihydroceramide levels. It is likely that CERK and C1P play a role in inflammatory processes but the cells involved and the mechanisms used remain to be clarified. In particular, the impact of CERK on T-cell biology has not been studied so far. Here, we used Cerk-/- mice backcrossed with DO11.10/RAG1-/- mice to probe the effect of CERK ablation on T-cell activation. Levels of interleukin (IL)-2, IL-4, IL-5, IL-13, of tumor necrosis factor (TNF)-alpha, and of interferon (INF)-gamma were recorded following ovalbumin challenge in vivo and using ovalbumin-treated splenocytes ex- vivo. Absence of CERK led to a significant decrease in the production of IL-4, thus suggesting that CERK may polarize T cells towards the TH2 cell subtype. However, the importance of CERK to TH2 cell biology will have to be investigated further because in a model of asthma, which is TH2-cell driven, Cerk-/- mice responded like wild-type animals.

4,5,6-Trisubstituted piperidinones as conformationally restricted ceramide analogues: synthesis and evaluation as inhibitors of sphingosine and ceramide kinases and as NKT cell-stimulatory antigens

The conformationally based piperidinone sphingosine analogues 7, 8, 15, and 16 were synthesized from allylic alcohol 34 via lactams 31 and 32. The L-arabino diol 7 and the L-ribo diol 8 were transformed into the amino alcohols 17-24. The L-gluco ceramide analogues 43, 46a, and 47, and the L-altro ceramide analogues 51a and 52 were synthesized from either 31 or 32. The L-ribo diols 8 and 16, and the amino alcohols 19 and 20 inhibit sphingosine kinase 1 (SPHK1), while the L-arabino analogues 7, 15, 17, and 18 are inactive. The L-arabino and the L-ribo dimethylamines 21-24, the L-gluco ceramide analogues 43, 46a, and 47, and the L-altro ceramide analogues 51a and 52 did not block SPHK1. Neither the L-arabino diol 7 nor the L-ribo diol 8 inhibited SPHK2 or ceramide kinase. The L-arabino diols 7 and 15 stimulate invariant natural killer T (iNKT) cells when presented by living antigen-presenting cells (APC) and also by plate-bound human CD1d, whereas the L-ribo diols 8 and 16, the L-arabino amino alcohols 17-18, and the dimethylamines 21-22 did not activate iNKT cells. The L-gluco ceramide analogues 43, 46a, and 47 had strongly stimulatory effects on iNKT cells when presented by living APC and also by plate-bound human CD1d, whereas the L-altro ceramide analogue 52 activated only weakly. All activatory compounds induced preferentially the release of pro-inflammatory cytokines, indicating the formation of a stable CD1d--lipid--T-cell receptor complex.

Synthesis and evaluation of sphingolipid analogues: modification of the hydroxy group at C(1) of 7-oxasphingosine, and of the hydroxy group at C(1) and the amide group of 7-oxaceramides

The analogues 7-9 of 7-oxaceramide and 7-oxasphingosine were synthesized from the known azidosphingosine 21. The 1,4-disubstituted 1,2,3-triazole analogues 10-16 of ceramides were synthesized by the click reaction of the known azide 24. None of the analogues 7-15 was active as inhibitor of SPHK type 1 and of acid sphingomyelinase, whereas 16 is a weak inhibitor of SPHK1. Triazoles 10, 11, and 15 did not inhibit ceramide phosphorylation by CerK, and none of 7, 8, and 10-15 activated invariant natural killer T (iNKT) cell clones when presented by human CD1d-transfected antigen-presenting cells (APC) or by plate-bound human CD1d [55]. Triazoles 14 and 15 prevent binding of alpha-galactosylceramide (alpha-GalCer) to plate-bound human CD1d and subsequent T-cell response to alpha-GalCer. Only 15 reduced activation by alpha-GalCer significantly and independently of the cytokine measured.

Efficient elimination of nonstoichiometric enzyme inhibitors from HTS hit lists

High-throughput screening often identifies not only specific, stoichiometrically binding inhibitors but also undesired compounds that unspecifically interfere with the targeted activity by nonstoichiometrically binding, unfolding, and/or inactivating proteins. In this study, the effect of such unwanted inhibitors on several different enzyme targets was assessed based on screening results for over a million compounds. In particular, the shift in potency on variation of enzyme concentration was used as a means to identify nonstoichiometric inhibitors among the screening hits. These potency shifts depended on both compound structure and target enzyme. The approach was confirmed by statistical analysis of thousands of dose-response curves, which showed that the potency of competitive and therefore clearly stoichiometric inhibitors was not affected by increasing enzyme concentration. Light-scattering measurements of thermal protein unfolding further verified that compounds that stabilize protein structure by stoichiometric binding show the same potency irrespective of enzyme concentration. In summary, measuring inhibitor IC(50) values at different enzyme concentrations is a simple, cost-effective, and reliable method to identify and eliminate compounds that inhibit a specific target enzyme via nonstoichiometric mechanisms.

Sphingosine kinase 1 is essential for proteinase-activated receptor-1 signalling in epithelial and endothelial cells

There is accumulating evidence that activation of sphingosine kinase 1 (SPHK1) is an important element in intracellular signalling cascades initiated by stimulation of multiple receptors, including certain growth factor, cytokine, and also G-protein coupled receptors. We here report that stimulation of the lung epithelial cell line A549 by thrombin leads to transient increase of SPHK1 activity and elevation of intracellular sphingosine-1-phosphate (S1P); abrogation of this stimulation by SPHK1-specific siRNA, pharmacological inhibition, or expression of a dominant-negative SPHK1 mutant blocks the response to thrombin, as measured by secretion of MCP-1, IL-6, IL-8, and PGE(2). Using selective stimulation of proteinase-activated receptors (PARs) a specific involvement of SPHK1 in the PAR-1 induced responses in A549 cell, including activation of NFkappaB, was evident, while PAR-2 and PAR-4 responses were independent of SPHK1. Moreover, PAR-1 or thrombin-induced cytokine production and adhesion factor expression of human umbilical vein endothelial cells was also seen to depend on SPHK1. Using dermal microvascular endothelial cells from SPHK1-deficient mice, we showed that absence of the enzyme abrogates MCP-1 production induced in these cells upon treatment with thrombin or PAR-1 activating peptide. We propose SPHK1 inhibition as a novel way to block PAR-1 mediated signalling, which could be useful in treatment of a number of diseases, in particular in atherosclerosis.

Neutropenia with impaired immune response to Streptococcus pneumoniae in ceramide kinase-deficient mice

In mammals, ceramide kinase (CerK)-mediated phosphorylation of ceramide is the only known pathway to ceramide-1-phosphate (C1P), a recently identified signaling sphingolipid metabolite. To help delineate the roles of CerK and C1P, we knocked out the gene of CerK in BALB/c mice by homologous recombination. All in vitro as well as cell-based assays indicated that CerK activity is completely abolished in Cerk-/- mice. Labeling with radioactive orthophosphate showed a profound reduction in the levels of de novo C1P formed in Cerk-/- macrophages. Consistently, mass spectrometry analysis revealed a major contribution of CerK to the formation of C16-C1P. However, the significant residual C1P levels in Cerk-/- animals indicate that alternative routes to C1P exist. Furthermore, serum levels of proapoptotic ceramide in these animals were significantly increased while levels of dihydroceramide as the biosynthetic precursor were reduced. Previous literature pointed to a role of CerK or C1P in innate immune cell function. Using a variety of mechanistic and disease models, as well as primary cells, we found that macrophage- and mast cell-dependent readouts are barely affected in the absence of CerK. However, the number of neutrophils was strikingly reduced in blood and spleen of Cerk-/- animals. When tested in a model of fulminant pneumonia, Cerk-/- animals developed a more severe disease, lending support to a defect in neutrophil homeostasis following CerK ablation. These results identify ceramide kinase as a key regulator of C1P, dihydroceramide and ceramide levels, with important implications for neutrophil homeostasis and innate immunity regulation.

Synthesis and immobilization of erythro-C14-omega-aminosphingosine-1-phosphate as a potential tool for affinity chromatography

A sphingosine-1-phosphate (S1P) analogue containing a terminal alkyl chain amino group is synthesized in a few steps via olefin cross-metathesis of an optically resolved intermediate and subsequent phosphorylation. Regioselective acylation of this intermediate at its N terminus in solution is demonstrated as a model reaction and provides a biologically active derivative. Finally, the omega-amino intermediate is immobilized on an affinity matrix. The choice of a UV-active phosphate protecting group allows for quantification of resin loading after cleavage which amounted to 66 %.

Targeting ceramide metabolism with a potent and specific ceramide kinase inhibitor

Ceramide kinase (CerK) produces the bioactive lipid ceramide-1-phosphate (C1P) and appears as a key enzyme for controlling ceramide levels. In this study, we discovered and characterized adamantane-1-carboxylic acid (2-benzoylamino-benzothiazol-6-yl)amide (NVP-231), a potent, specific, and reversible CerK inhibitor that competitively inhibits binding of ceramide to CerK. NVP-231 is active in the low nanomolar range on purified as well as cellular CerK and abrogates phosphorylation of ceramide, resulting in decreased endogenous C1P levels. When combined with another ceramide metabolizing inhibitor, such as tamoxifen, NVP-231 synergistically increased ceramide levels and reduced cell growth. Therefore, NVP-231 represents a novel and promising compound for controlling ceramide metabolism that may provide insight into CerK physiological function.

Binding of pimecrolimus and tacrolimus to skin and plasma proteins: implications for systemic exposure after topical application

Pimecrolimus and tacrolimus are calcineurin inhibitors used for the topical treatment of atopic dermatitis. Although structurally similar, they display specific differences including higher lipophilicity and lower skin permeation of pimecrolimus. The aim of the present study was to understand the reason for the differences in skin permeation; in addition, plasma protein binding of the two drugs was analyzed side by side as a basis for comparison of systemic exposure to free drug. Permeation of pimecrolimus and tacrolimus through a silicon membrane was found to be similar; therefore, we assumed that differences in skin permeation could be caused by differences in affinity to skin components. To test this hypothesis, we investigated binding of pimecrolimus and tacrolimus to a preparation of soluble human skin proteins. One binding protein of approximately 15 kDa, probably corresponding to macrophilin12, displayed a similar binding capacity for pimecrolimus and tacrolimus. However, less specific, nonsaturating binding to other proteins was approximately 3-fold higher for pimecrolimus. Because of the high local drug concentration after topical administration, the unspecific, high-capacity binding is probably dominating the permeation through skin. In plasma both drugs bound predominantly to lipoproteins, which may affect disposition differently from albumin binding. The unbound fraction of pimecrolimus in human plasma was approximately 9-fold lower compared with that of tacrolimus (0.4 +/- 0.1 versus 3.7 +/- 0.8%). In conclusion, these results provide an explanation for the observed lower systemic exposure to pimecrolimus than to tacrolimus after topical application and suggest that differences in systemic exposure to free drug might be even more pronounced.

Sphingolipid metabolizing enzymes as novel therapeutic targets

Pharmacological interference with sphingolipid metabolizing enzymes promises to provide novel ways to modulate cellular pathways relevant in multiple diseases. In this review, we focus on two sphingolipid signaling molecules, sphingosine-1-phosphate (S1P) and ceramide, as they are involved in cell fate decisions (survival vs. apoptosis) and in a wide range of pathophysiological processes. For S1P, we will discuss sphingosine kinases and S1P lyase as the enzymes which are crucial for its production and degradation, respectively, emphasizing the potential therapeutic usefulness of inhibitors of these enzymes. For ceramide, we will concentrate on acid sphingomyelinase, and critically review the substantial literature which implicates this enzyme as a worthwhile target for pharmacological inhibitors. It will become clear that the task to validate these enzymes as drug targets is not finished and many questions regarding the therapeutic usefulness of their inhibitors remain unanswered. Still this approach holds promise for a number of totally new therapies, and, on the way, detailed insight into sphingolipid signaling pathways can be gained.

Brain penetration of the oral immunomodulatory drug FTY720 and its phosphorylation in the central nervous system during experimental autoimmune encephalomyelitis: consequences for mode of action in multiple sclerosis

FTY720 [2-amino-2-[2-(4-octylphenyl) ethyl]propane-1,3-diol hydrochloride] is an oral sphingosine-1-phosphate receptor modulator under development for the treatment of multiple sclerosis (MS). The drug is phosphorylated in vivo by sphingosine kinase 2 to its bioactive form, FTY720-P. Although treatment with FTY720 is accompanied by a reduction of the peripheral lymphocyte count, its efficacy in MS and experimental autoimmune encephalomyelitis (EAE) may be due to additional, direct effects in the central nervous system (CNS). We now show that FTY720 localizes to the CNS white matter, preferentially along myelin sheaths. Brain trough levels of FTY720 and FTY720-P in rat EAE are of the same magnitude and dose dependently increase; they are in the range of 40 to 540 ng/g in the brain tissue at efficacious doses and exceed blood concentrations severalfold. In a rat model of chronic EAE, prolonged treatment with 0.03 mg/kg was efficacious, but limiting the dosing period failed to prevent EAE despite a significant decrease in blood lymphocytes. FTY720 effectiveness is likely due to a culmination of mechanisms involving reduction of autoreactive T cells, neuroprotective influence of FTY720-P in the CNS, and inhibition of inflammatory mediators in the brain.

FTY720-phosphate is dephosphorylated by lipid phosphate phosphatase 3

FTY720 is a novel immunomodulatory drug efficacious in the treatment of multiple sclerosis. The drug is converted in vivo to the monophosphate, FTY720-P, by sphingosine kinase 2. This conversion is incomplete, suggesting opposing actions of kinase and phosphatase activities. To address which of the known lipid phosphatases might dephosphorylate FTY720-P, we overexpressed the broad specificity lipid phosphatases LPP1-3, and the specific S1P phosphatases (SPP1 and 2) in HEK293 cells, and performed in vitro assays using lysates of transfected cells. Among LPPs, only LPP3 was able to dephosphorylate FTY720-P; among SPPs, only SPP1 showed activity against FTY720-P. On intact cells, LPP3 acted as an ecto-phosphatase or FTY720-P, thus representing the major phosphatase involved in the equilibrium between FTY720 and FTY720-P observed in vivo.

FTY720, an immunomodulatory sphingolipid mimetic: translation of a novel mechanism into clinical benefit in multiple sclerosis

FTY720 (fingolimod; 2-amino-2[2-(4-octylphenyl)ethyl]-1,3-propanediol, Novartis) is the prototype of a new generation of immunomodulators. The drug is the result of extensive chemical derivatisation based on the natural product myriocin, isolated from the ascomycete Isaria sinclairii. FTY720 bears structural similarity to sphingosine, a naturally occurring sphingolipid. As with sphingosine, FTY720 is effectively phosphorylated by sphingosine kinases in vivo and the phosphorylated drug targets G-protein-coupled receptors for sphingosine-1-phosphate (S1P). Gene deletion and reverse pharmacology studies have shown that FTY720 acts at S1P1 receptors on lymphocytes and the endothelium, thereby inhibiting the egress of T- and B cells from secondary lymphoid organs into the blood and their recirculation to inflamed tissues. Animal studies suggest that this novel mechanism translates into effective treatments for several autoimmune diseases and a recently completed Phase II clinical trial highlighted FTY720 as a potential therapy for relapsing-remitting multiple sclerosis.

Normal neutrophil functions in sphingosine kinase type 1 and 2 knockout mice

Sphingosine kinase (SPHK) has been implicated as an important element in neutrophil responses to diverse stimulatory agents. To get more insight into the role of the type 1 and 2 isoforms of SPHK in neutrophil functions, we made use of the respective SPHK knockout mice. Neutrophils isolated from the bone marrow of these mice showed normal increase of intracellular Ca(2+) when stimulated in vitro by fMLP, platelet-activating factor, the anaphylatoxin C5a, or ATP, and normal migration towards fMLP and C5a. Also, recruitment of neutrophils into the peritoneum towards the chemokines KC and MIP-2 or to LPS, and into the peripheral blood after fMLP injection was similar in SPHK knockout strains and wild-type animals. An in vivo model of bacterial lung infection revealed an accelerated progression of disease in SPHK2 (but not SPHK1) knockout mice as compared to wild-type controls. However, effector functions of SPHK-deficient neutrophils, such as superoxide production, beta-glucuronidase release and their capacity to kill bacteria were unchanged as compared to wild-type cells. To conclude, the data derived from SPHK knockout mice do not support the hypothesis that any of the two lipid kinases plays a crucial role in signalling downstream of various neutrophil stimuli; SPHKs appear not to be essential for neutrophil recruitment and effector functions.

Synthesis of Borondipyrromethene (BODIPY)-Labeled Sphingosine Derivatives by Cross-metathesis Reaction

A new efficient and flexible synthesis of fluorescently labeled sphingosine derivatives from commercially available Garner aldehyde (8) is described. For this, appropriate alkenylated borondipyrromethene (BODIPY) dyes were synthesized and used for the first time in a cross-metathesis reaction, the key step of the approach. The labeled sphingosines with appropriate chain length were accepted as substrates by sphingosine kinases (SPHKs), yielding the corresponding phosphorylated products. One of these derivatives (11d) was identified as the first reported selective substrate for SPHK-1.

Constrained azacyclic analogues of the immunomodulatory agent FTY720 as molecular probes for sphingosine 1-phosphate receptors

Constrained azacyclic analogues of FTY720 were prepared starting with d- and l-pyroglutamic acids. One enantiomer was shown to be a substrate for sphingosine kinase 2, being phosphorylated 4-fold more efficiently than FTY720. Among the corresponding phosphates, two were found to have unusual specificity in binding to S1P receptors: while being inactive on S1P1 and S1P3, they acted as potent agonists on S1P4 and S1P5. The phosphates may be useful to explore the biology and binding site of these receptors.

Drug evaluation: apilimod, an oral IL-12/IL-23 inhibitor for the treatment of autoimmune diseases and common variable immunodeficiency

Apilimod is a small molecule that inhibits IL-12 and IL-23 production - cytokines that are involved in autoimmune diseases - through the prevention of nuclear translocation of c-Rel. Synta Pharmaceuticals Corp is developing apilimod for the potential treatment of Crohn's disease (CD) and other autoimmune diseases. Preclinical studies demonstrated the successful inhibition of IL-12 and IL-23 production by the drug. In the clinical setting, apilimod has been generally well tolerated, with mild-to-moderate side effects reported, including headaches and nausea. Patients with CD responded within 14 days of treatment with apilimod and, after 28 days, the drug significantly reduced the Crohn's disease activity index (CDAI). Apilimod is currently in phase II clinical trials for rheumatoid arthritis, common variable immunodeficiency and CD. From the data available to date, apilimod appears to be a promising treatment for CD, and the oral formulation of this compound provides an advantage for apilimod over injectable therapies.

A critical beta6-beta7 loop in the pleckstrin homology domain of ceramide kinase

CerK (ceramide kinase) produces ceramide 1-phosphate, a sphingophospholipid with recognized signalling properties. It localizes to the Golgi complex and fractionates essentially between detergent-soluble and -insoluble fractions; however, the determinants are unknown. Here, we made a detailed mutagenesis study of the N-terminal PH domain (pleckstrin homology domain) of CerK, based on modelling, and identified key positively charged amino acid residues within an unusual motif in the loop interconnecting beta-strands 6 and 7. These residues are critical for CerK membrane association and polyphosphoinositide binding and activity. Their mutagenesis results in increased thermolability, sensitivity to proteolysis, reduced apparent molecular mass as well as propensity of the recombinant mutant protein to aggregate, indicating that this loop impacts the overall conformation of the CerK protein. This is in contrast with most PH domains whose function strongly relies on charges located in the beta1-beta2 loop.

Effects of ceramide-1-phosphate on cultured cells: dependence on dodecane in the vehicle

Ceramide-1-phosphate (C1P), the product of ceramide kinase, is a sphingophospholipid with recently recognized signaling properties. In particular, it was reported to be mitogenic and capable of direct stimulation of cytosolic phospholipase A(2alpha). Much of the present knowledge has relied on the use of C1P of various acyl chain lengths, together with diverse protocols to deliver it to cultured cells. A mixture of ethanol (or methanol) with dodecane, as the vehicle, has become popular. However, the contribution of this solvent to the observed effects of C1P has not been documented. Here, we show that addition of C1P in ethanol-dodecane to culture medium leads to irreversible cytotoxic effects. These culminate in mitochondrial swelling, vacuole formation, and cell death. Not only the toxicity of C1P, but also its ability to trigger prostaglandin E2 release, is fully dependent upon addition of a premade C1P-dodecane mixture. Furthermore, we show that these effects are not restricted to C1P. They result from the capacity of dodecane to interact with phospholipids; hence, they go undetected with a vehicle control. This study should raise awareness about the use of dodecane for phospholipid delivery and, in turn, help in unraveling C1P signaling, which is still poorly understood.

Sphingosine 1-phosphate phosphatase 2 is induced during inflammatory responses

Sphingosine 1-phosphate (S1P) levels in cells and, consequently, its bioactivity as a signalling molecule are controlled by the action of enzymes responsible for its synthesis and degradation. In the present report, we examined alterations in expression patterns of enzymes involved in S1P-metabolism (sphingosine kinases including their splice variants, sphingosine 1-phosphate phosphatases, and sphingosine 1-phosphate lyase) under certain inflammatory conditions. We found that sphingosine kinase type 1 (SPHK1) mRNA could be triggered in a cell type-specific manner; individual SPHK1 splice variants were induced with similar kinetics. Remarkably, expression and activity of S1P phosphatase 2 (SPP2) was found to be highly upregulated by inflammatory stimuli in a variety of cells (e.g., neutrophils, endothelial cells). Bandshift analysis using oligonucleotides spanning predicted NFkappaB sites within the SPP2 promoter and silencing of NFkappaB/RelA via RelA-directed siRNA demonstrated that SPP2 is an NFkappaB-dependent gene. Silencing of SPP2 expression in endothelial cells, in turn, led to a marked reduction of TNF-alpha-induced IL-1beta mRNA and protein and to a partial reduction of induced IL-8, suggesting a pro-inflammatory role of SPP2. Notably, up-regulation of SPP2 was detected in samples of lesional skin of patients with psoriasis, an inflammatory skin disease. This study provides detailed insights into the regulation of SPP2 gene expression and suggests that SPP2 might be a novel player in pro-inflammatory signalling.

NBD-labeled derivatives of the immunomodulatory drug FTY720 as tools for metabolism and mode of action studies

Fluorescently labeled chiral analogs of the immunomodulatory drug FTY720 and its corresponding phosphates with variable aliphatic spacers between the aromatic ring and the NBD label have been synthesized. Determining the influence of the spacer on the in vitro phosphorylation rate by SPHK1 and 2 resulted in the identification of NBD-(R)-AAL 1c,d which are phosphorylated with an efficiency comparable to that of the unlabeled FTY720 analog (R)-AAL. Furthermore, the NBD-(R)-AAL phosphates 10c,d were proven to be a functional S1P receptor agonist.

Sphingosine kinase type 2 is essential for lymphopenia induced by the immunomodulatory drug FTY720

FTY720, a potent immunomodulatory drug in phase 2/3 clinical trials, induces rapid and reversible sequestration of lymphocytes into secondary lymphoid organs, thereby preventing their migration to sites of inflammation. As prerequisite for its function, phosphorylation of FTY720 to yield a potent agonist of the sphingosine-1-phosphate receptor S1P(1) is required in vivo, catalyzed by an as-yet-unknown kinase. Here, we report on the generation of sphingosine kinase 2 (SPHK2) knockout mice and demonstrate that this enzyme is essential for FTY720 phosphate formation in vivo. Consequently, administration of FTY720 does not induce lymphopenia in SPHK2-deficient mice. After direct dosage of FTY720 phosphate, lymphopenia is only transient in this strain, indicating that SPHK2 is constantly required to maintain FTY720 phosphate levels in vivo.