Synthesis and evaluation of sphingosine analogues as inhibitors of sphingosine kinases

Alcoholic and Non-Alcoholic Liver Diseases: Promising Molecular Drug Targets and their Clinical Development

Alcoholic and non-alcoholic fatty liver diseases have become a serious concern worldwide. Both these liver diseases have an identical pathology, starting from simple steatosis to cirrhosis and, ultimately to hepatocellular carcinoma. Treatment options for alcoholic liver disease (ALD) are still the same as they were 50 years ago which include corticosteroids, pentoxifylline, antioxidants, nutritional support and abstinence; and for non-alcoholic fatty liver disease (NAFLD), weight loss, insulin sensitizers, lipid-lowering agents and anti-oxidants are the only treatment options. Despite broad research in understanding the disease pathophysiology, limited treatments are available for clinical use. Some therapeutic strategies based on targeting a specific molecule have been developed to lessen the consequences of disease and are under clinical investigation. Therefore, focus on multiple molecular targets will help develop an efficient therapeutic strategy. This review comprises a brief overview of the pathogenesis of ALD and NAFLD; recent molecular drug targets explored for ALD and NAFLD that may prove to be effective for multiple therapeutic regimens and also the clinical status of these promising drug targets for liver diseases.

Sphingosine kinase 1 regulates HMGB1 translocation by directly interacting with calcium/calmodulin protein kinase II-δ in sepsis-associated liver injury

Previously, we confirmed that sphingosine kinase 1 (SphK1) inhibition improves sepsis-associated liver injury. High-mobility group box 1 (HMGB1) translocation participates in the development of acute liver failure. However, little information is available on the association between SphK1 and HMGB1 translocation during sepsis-associated liver injury. In the present study, we aimed to explore the effect of SphK1 inhibition on HMGB1 translocation and the underlying mechanism during sepsis-associated liver injury. Primary Kupffer cells and hepatocytes were isolated from SD rats. The rat model of sepsis-associated liver damage was induced by intraperitoneal injection with lipopolysaccharide (LPS). We confirmed that Kupffer cells were the cells primarily secreting HMGB1 in the liver after LPS stimulation. LPS-mediated HMGB1 expression, intracellular translocation, and acetylation were dramatically decreased by SphK1 inhibition. Nuclear histone deacetyltransferase 4 (HDAC4) translocation and E1A-associated protein p300 (p300) expression regulating the acetylation of HMGB1 were also suppressed by SphK1 inhibition. HDAC4 intracellular translocation has been reported to be controlled by the phosphorylation of HDAC4. The phosphorylation of HDAC4 is modulated by CaMKII-δ. However, these changes were completely blocked by SphK1 inhibition. Additionally, by performing coimmunoprecipitation and pull-down assays, we revealed that SphK1 can directly interact with CaMKII-δ. The colocalization of SphK1 and CaMKII-δ was verified in human liver tissues with sepsis-associated liver injury. In conclusion, SphK1 inhibition diminishes HMGB1 intracellular translocation in sepsis-associated liver injury. The mechanism is associated with the direct interaction of SphK1 and CaMKII-δ.

Analysis of selective target engagement by small-molecule sphingosine kinase inhibitors using the Cellular Thermal Shift Assay (CETSA)

The recently renewed interest in scientific rigor and reproducibility is of critical importance for both scientists developing new targeted small-molecule inhibitors and those employing these molecule in cellular studies, alike. While off-target effects are commonly considered as limitations for any given small-molecule inhibitor, the ability of a given compound to distinguish between enzyme isoforms is often neglected when employing compounds in cellular studies. To call attention to this issue, we have compared the results of an assay for "direct target engagement", the Cellular Thermal Shift Assay (CETSA), to the published isoform selectivity of 12 commercially available sphingosine kinase 1 and 2 (SphK 1 and SphK2) inhibitors. Our results suggest that, at the concentrations commonly employed in cellular assay systems, none of the tested SKIs can be considered isoform selective. Thus, caution and complimentary assay strategies must be employed to fully discern isoform selectivity for the SphKs. Moreover, caution must be employed by the scientific community as a whole when designing experiments that aim to discern the effects of one enzyme isoform versus another to ensure that the concentration ranges used are able to distinguish isoform selectivity.

A Role of Sphingosine in the Intracellular Survival of Neisseria gonorrhoeae

Obligate human pathogenic Neisseria gonorrhoeae are the second most frequent bacterial cause of sexually transmitted diseases. These bacteria invade different mucosal tissues and occasionally disseminate into the bloodstream. Invasion into epithelial cells requires the activation of host cell receptors by the formation of ceramide-rich platforms. Here, we investigated the role of sphingosine in the invasion and intracellular survival of gonococci. Sphingosine exhibited an anti-gonococcal activity in vitro. We used specific sphingosine analogs and click chemistry to visualize sphingosine in infected cells. Sphingosine localized to the membrane of intracellular gonococci. Inhibitor studies and the application of a sphingosine derivative indicated that increased sphingosine levels reduced the intracellular survival of gonococci. We demonstrate here, that sphingosine can target intracellular bacteria and may therefore exert a direct bactericidal effect inside cells.

Click reactions with functional sphingolipids

Sphingolipids and glycosphingolipids can regulate cell recognition and signalling. Ceramide and sphingosine-1-phosphate are major players in the sphingolipid pathways and are involved in the initiation and regulation of signalling, apoptosis, stress responses and infection. Specific chemically synthesised sphingolipid derivatives containing small functionalities like azide or alkyne can mimic the biological properties of natural lipid species, which turns them into useful tools for the investigation of the highly complex sphingolipid metabolism by rapid and selective 'click chemistry' using sensitive tags like fluorophores. Subsequent analysis by various fluorescence microscopy techniques or mass spectrometry allows the identification and quantification of the corresponding sphingolipid metabolites as well as the research of associated enzymes. Here we present an overview of recent advances in the synthesis of ceramide and sphingosine analogues for bioorthogonal click reactions to study biosynthetic pathways and localization of sphingolipids for the development of novel therapeutics against lipid-dependent diseases.

The sphingosine kinase-1/sphingosine-1-phosphate axis in cancer: Potential target for anticancer therapy

Sphingolipid metabolites, such as ceramide, sphingosine and sphingosine-1-phosphate (S1P), play many important roles in cellular activities. Ceramide and sphingosine inhibit cell proliferation and induce cell apoptosis while S1P has the opposite effect. Maintaining a metabolic balance of sphingolipids is essential for growth and development of cells. Sphingosine kinase (SPHK) is an important regulator for keeping this balance. It controls the level of S1P and plays important roles in proliferation, migration, and invasion of cancer cells and tumor angiogenesis. There are two isoenzymes of sphingosine kinase, SPHK1 and SPHK2. SPHK1 is ubiquitously expressed in most cancers where it promotes survival and proliferation, while SPHK2 is restricted to only certain tissues and its functions are not well characterized. SPHK1 is currently considered as a novel target for the treatment of cancers. Targeting SPHK1 would provide new strategies for cancer treatment and improve the prognosis of cancer patients. Here we review and summarize the current research findings on the SPHK1-S1P axis in cancer from many aspects including structure, expression, regulation, mechanism, and potential inhibitors.

Sphingosine kinase AtSPHK1 functions in fumonisin B1-triggered cell death in Arabidopsis

The fungal toxin Fumonisin B1 (FB1) is a strong inducer to trigger plant hypersensitive responses (HR) along with increased long chain bases (LCB) and long chain base phosphates (LCBP) contents, though the regulatory mechanism of FB1 action and how the LCB/LCBP signalling cassette functions during the process is still not fully understood. Here, we report sphingosine kinase 1 (SPHK1) as a key factor in FB1-induced HR by modulating the salicylic acid (SA) pathway and reactive oxygen species (ROS) accumulation in Arabidopsis thaliana. Overexpression of SPHK1 increases the FB1-induced accumulations of ROS and SA. The double mutant that simultaneously overexpresses SPHK1 and suppresses the SPPASE or DPL1, two enzymes are mainly responsible for Phyto-sphingosine-1-phosphate (Phyto-S1P) removal, showed enhanced susceptibility to FB1 killing and FB1-induced SA activation than the plants overexpress SPHK1 alone. Exogenous sphingosine-1-phosphate (S1P) can modulate the transcription of the SA-responsive marker gene PR1 in a concentration-dependent biphasic manner. Suppression of SPHK1 decreases SA production whereas promotes jasmonic acid (JA) biosynthesis in response to FB1 applications. Our findings indicate a role of SPHK1 in modulating FB1-triggered cell death via SA and JA pathway interactions.

Sphingosine kinase 1 mediates AGEs-induced fibronectin upregulation in diabetic nephropathy

Activation of sphingosine kinase 1 (SphK1) signaling pathway mediates fibronectin (FN) upregulation in glomerular mesangial cells (GMCs) under high glucose (HG) condition. However, the roles of SphK1 in advanced glycation end products (AGEs)-induced DN have not been elucidated. Here we show that AGEs upregulated FN and SphK1 and SphK1 activity. Inhibition of SphK1 signaling attenuated AGEs-induced FN synthesis in GMCs. Inhibition of AGE receptor (RAGE) signaling reduced the upregulation of FN and SphK1 and SphK1 activity in GMCs induced by AGEs. Treatment of aminoguanidine ameliorates the renal injury and fibrosis in STZ-induced diabetic mice and attenuated SphK1 expression and activity in diabetic mouse kidneys. The renal injury and fibrosis in diabetic SphK1^-/- mice was significantly attenuated than WT mice. Furthermore, AGEs upregulated SphK1 by reducing its degradation and prolonging its half-life. Conclusion: SphK1 mediates AGEs-induced FN synthesis in GMCs and diabetic mice under hyperglycemic condition.

Enantioselective Addition of Alkynes to α,α-Dichlorinated Aldehydes

Enantioselective addition of terminal alkynes to α,α-dichlorinated aldehydes employing Zn(OTf)₂/NME is disclosed. The propargylic alcohols obtained are accessed in good yields and high enantioselectivity from easily accessible α,α-dichloroaldehydes. The method opens new strategic opportunities for the synthesis of chlorinated natural products, such as the chlorosulfolipids.

Classification of sphingosine kinase inhibitors using counter propagation artificial neural networks: A systematic route for designing selective SphK inhibitors

Accurate and robust classification models for describing and predicting the activity of 330 chemicals that are sphingosine kinase 1 (SphK1) and/or sphingosine kinase 2 (SphK2) inhibitors were derived. The classification models developed in this work assist in finding selective subspaces in chemical space occupied by particular groups of SphK inhibitors. A combination of a genetic algorithm (GA) and a counter propagation artificial neural network (CPANN) was utilized to select the most efficient subsets of the molecular descriptors. The optimized models in this work reasonably separate active inhibitors of SphK1 from active SphK2 inhibitors. Generally, the CPANN models in this work were used to classify the compounds according to their therapeutic targets and activities. The simplicity of the chosen descriptors and their relative importance sheds some light on the structural features necessary to induce selective inhibitory activity to the studied molecules. The areas under the receiver operating characteristic (ROC) curves for the GA-CPANN models in this work were 0.934 and 0.922 for active SphK1 and SphK2 inhibitors, respectively. Generally, the results in this work suggest some important molecular features and pharmacophores that could help medicinal chemists develop selective and potent SphK inhibitors.

Sphingosine kinase 1 is required for TGF-β mediated fibroblastto- myofibroblast differentiation in ovarian cancer

Sphingosine kinase 1 (SPHK1), the enzyme that produces sphingosine 1 phosphate (S1P), is known to be highly expressed in many cancers. However, the role of SPHK1 in cells of the tumor stroma remains unclear. Here, we show that SPHK1 is highly expressed in the tumor stroma of high-grade serous ovarian cancer (HGSC), and is required for the differentiation and tumor promoting function of cancer-associated fibroblasts (CAFs). Knockout or pharmacological inhibition of SPHK1 in ovarian fibroblasts attenuated TGF-β-induced expression of CAF markers, and reduced their ability to promote ovarian cancer cell migration and invasion in a coculture system. Mechanistically, we determined that SPHK1 mediates TGF-β signaling via the transactivation of S1P receptors (S1PR2 and S1PR3), leading to p38 MAPK phosphorylation. The importance of stromal SPHK1 in tumorigenesis was confirmed in vivo, by demonstrating a significant reduction of tumor growth and metastasis in SPHK1 knockout mice. Collectively, these findings demonstrate the potential of SPHK1 inhibition as a novel stroma-targeted therapy in HGSC.

Visualizing red blood cell sickling and the effects of inhibition of sphingosine kinase 1 using soft X-ray tomography

Sickle cell disease is a destructive genetic disorder characterized by the formation of fibrils of deoxygenated hemoglobin, leading to the red blood cell (RBC) morphology changes that underlie the clinical manifestations of this disease. Using cryogenic soft X-ray tomography (SXT), we characterized the morphology of sickled RBCs in terms of volume and the number of protrusions per cell. We were able to identify statistically a relationship between the number of protrusions and the volume of the cell, which is known to correlate to the severity of sickling. This structural polymorphism allows for the classification of the stages of the sickling process. Recent studies have shown that elevated sphingosine kinase 1 (Sphk1)-mediated sphingosine 1-phosphate production contributes to sickling. Here, we further demonstrate that compound 5C, an inhibitor of Sphk1, has anti-sickling properties. Additionally, the variation in cellular morphology upon treatment suggests that this drug acts to delay the sickling process. SXT is an effective tool that can be used to identify the morphology of the sickling process and assess the effectiveness of potential therapeutics.

Therapeutic Strategies and Pharmacological Tools Influencing S1P Signaling and Metabolism

During the last two decades the study of the sphingolipid anabolic, catabolic, and signaling pathways has attracted enormous interest. Especially the introduction of fingolimod into market as first p.o. therapeutic for the treatment of multiple sclerosis has boosted this effect. Although the complex regulation of sphingosine-1-phosphate (S1P) and other catabolic and anabolic sphingosine-related compounds is not fully understood, the influence on different (patho)physiological states from inflammation to cytotoxicity as well as the availability of versatile pharmacological tools that represent new approaches to study these states are described. Here, we have summarized various aspects concerning the many faces of sphingolipid function modulation by different pharmacological tools up to clinical candidates. Due to the immense heterogeneity of physiological or pharmacological actions and complex cross regulations, it is difficult to predict their role in upcoming therapeutic approaches. Currently, inflammatory, immunological, and/or antitumor aspects are discussed.

Polydatin attenuates AGEs-induced upregulation of fibronectin and ICAM-1 in rat glomerular mesangial cells and db/db diabetic mice kidneys by inhibiting the activation of the SphK1-S1P signaling pathway

We previously demonstrated that activation of sphingosine kinase 1 (SphK1)- sphingosine 1- phosphate (S1P) signaling pathway by high glucose (HG) plays a pivotal role in increasing the expression of fibronectin (FN), an important fibrotic component, by promoting the DNA-binding activity of transcription factor activator protein 1 (AP-1) in glomerular mesangial cells (GMCs) under diabetic conditions. As a multi-target anti-oxidative drug, polydatin (PD) has been shown to have renoprotective effects on experimental diabetes. However, whether PD could resist diabetic nephropathy (DN) by regulating SphK1-S1P signaling pathway needs further investigation. Here, we found that PD significantly reversed the upregulated FN and ICAM-1 expression in GMCs exposed to AGEs. Simultaneously, PD dose-dependently inhibited SphK1 levels at the protein expression and kinase activity and attenuated S1P production under AGEs treatment conditions. In addition, PD reduced SphK activity in GMCs transfected with wild-type SphK(WT) plasmid and significantly suppressed SphK1-mediated increase of FN and ICAM-1 levels under normal conditions. Furthermore, we found that the AGEs-induced upregulation of phosphorylation of c-Jun at Ser63 and Ser73 and c-Fos at Ser32, DNA-binding activity and transcriptional activity of AP-1 were blocked by PD. In comparison with db/db model group, PD treatment suppressed SphK1 levels (mRNA, protein expression, and activity) and S1P production, reversed the upregulation of FN, ICAM-1, c-Jun, and c-Fos in the kidney tissues of diabetic mice, and finally ameliorated renal injury in db/db mice. These findings suggested that the downregulation of SphK1-S1P signaling pathway is probably a novel mechanism by which PD suppressed AGEs-induced FN and ICAM-1 expression and improved renal dysfunction of diabetic models.

Sphingosine kinase 1 inhibition improves lipopolysaccharide/D-galactosamine-induced acute liver failure by inhibiting mitogen-activated protein kinases pathway

BACKGROUND

Sphingosine kinase 1 (SphK1)/sphingosine-1-phosphate (S1P)/sphingosine-1-phosphate receptors (S1PRs) signaling plays a key role in inflammatory responses. Lei et al. showed that SphK1 inhibition presented a hepatoprotective effect on acute liver damage via decreasing hepatic high-mobility group box 1 (HMGB1) cytoplasmic translocation.

OBJECTIVE

We aim to determine whether SphK1 or S1PRs inhibition improves lipopolysaccharide (LPS)/D-galactosamine (GalN)-induced acute liver failure by inhibiting the mitogen-activated protein kinases (MAPKs) pathway.

METHODS

A mouse model of acute liver failure was induced by LPS/GalN. Male C57BL/6J mice (6-8 weeks) were randomly distributed into five groups: control group, LPS/GalN group, SphK1 inhibition group (LPS/GalN+SKI-5c), S1PR1 inhibition group (LPS/GalN+W146), and S1PR3 inhibition group (LPS/GalN+CAY10444).

RESULTS

We confirmed the findings of Lei et al. that hepatic SphK1 expression was upregulated; serum transaminase activity (AST, ALT), as well as serum TNF-α and IL-6, were decreased by SphK1 inhibition. We further showed that the expression of S1PR1 and S1PR3 was augmented in response to LPS/GalN. SphK1 inhibition improves hepatic hemorrhage, and the activities of hepatic caspase-3 and myeloperoxidase (MPO). Furthermore, the activation of the MAPKs family (JNK, ERK and p38) was suppressed by SphK1 inhibition. However, S1PR1 or S1PR3 inhibition did not protect the mouse against liver damage, though S1PR1 or S1PR3 inhibition reduced serum TNF-α and IL-6, and partially attenuated the phosphorylation of the MAPKs signaling.

CONCLUSIONS

SphK1 inhibition improves LPS/GalN-induced liver injury by inhibiting activation of MAPKs signaling.

Estrogen regulates excitatory amino acid carrier 1 (EAAC1) expression through sphingosine kinase 1 (SphK1) transacting FGFR-mediated ERK signaling in rat C6 astroglial cells

Excitatory amino acid carrier 1 (EAAC1) is one important subtype of the excitatory amino acid transporters (EAATs), and its absence can increase the vulnerability to oxidative stress in neural tissue. Enhanced expression of EAAC1 can provide neuroprotection in multiple disorders, including ischemia and multiple sclerosis. However, the mechanism regulating EAAC1 expression is not fully understood. Using rat C6 astroglial cells, which specifically express EAAC1, we found that 17β-estradiol (E2) and (±)-1-[(3aR(∗),4S(∗),9bS(∗))-4-(6-bromo-1,3-benzodioxol-5-yl)-3a,4,5,9b-tetrahydro-3H-cyclopenta[c]quinolin-8-yl]-ethanone (G1), an agonist of the G-protein-coupled estrogen receptor (GPR30), strongly increased EAAC1 protein levels and protected cells from hydrogen peroxide (H2O2) toxicity. We further found that E2/G1 activated sphingosine kinase 1 (SphK1) via GPR30, resulting in the transcription of fibroblast growth factor 2 (FGF2), which stimulated its receptor (FGFR) and led to the phosphorylation of FGFR substrate 2α (FRS2α). This triggered downstream ERK1/2 signaling for the expression of EAAC1. Both the knockdown of FGF2 by siRNA and the pharmacological suppression of the FGFR-ERK cascade abolished the E2/G1 effect on EAAC1 expression. Overall, our work characterizes a signaling pathway by which E2 transactivates FGFR-ERK to induce EAAC1 expression in an FGF2-dependent manner. This occurs through SphK1 activation via GPR30 and leads to a resistance to H2O2 toxicity. This signal transduction pathway may provide novel insights into our understanding of the neuroprotective effects of E2 and may reveal new therapeutic targets or drugs for regulating the oxidative toxicity effects of various neurological diseases.

Identification and Characterization of FTY720 for the Treatment of Human African Trypanosomiasis

The screening of a focused library identified FTY720 (Fingolimod; Gilenya) as a potent selective antitrypanosomal compound active against Trypanosoma brucei gambiense and T. brucei rhodesiense, the causative agents of human African trypanosomiasis (HAT). This is the first report of trypanocidal activity for FTY720, an oral drug registered for the treatment of relapsing multiple sclerosis, and the characterization of sphingolipids as a potential new class of compounds for HAT.

SPHK1 regulates proliferation and survival responses in triple-negative breast cancer

Triple-negative breast cancer (TNBC) is characterized by unique aggressive behavior and lack of targeted therapies. Among the various molecular subtypes of breast cancer, it was observed that TNBCs express elevated levels of sphingosine kinase 1 (SPHK1) compared to other breast tumor subtypes. High levels of SPHK1 gene expression correlated with poor overall and progression- free survival, as well as poor response to Doxorubicin-based treatment. Inhibition of SPHK1 was found to attenuate ERK1/2 and AKT signaling and reduce growth of TNBC cells in vitro and in a xenograft SCID mouse model. Moreover, SPHK1 inhibition by siRNA knockdown or treatment with SKI-5C sensitizes TNBCs to chemotherapeutic drugs. Our findings suggest that SPHK1 inhibition, which effectively counteracts oncogenic signaling through ERK1/2 and AKT pathways, is a potentially important anti-tumor strategy in TNBC. A combination of SPHK1 inhibitors with chemotherapeutic agents may be effective against this aggressive subtype of breast cancer.

Inhibitors of sphingosine-1-phosphate metabolism (sphingosine kinases and sphingosine-1-phosphate lyase)

Sphingolipids (SLs) are essential structural and signaling molecules of eukaryotic cells. Among them, sphingosine 1 phosphate (S1P) is a recognized promoter of cell survival, also involved, inter alia, in inflammation and tumorigenesis processes. The knowledge and modulation of the enzymes implicated in the biosynthesis and degradation of S1P are capital to control the intracellular levels of this lipid and, ultimately, to determine the cell fate. Starting with a general overview of the main metabolic pathways involved in SL metabolism, this review is mainly focused on the description of the most relevant findings concerning the development of modulators of S1P, namely inhibitors of the enzymes regulating S1P synthesis (sphingosine kinases) and degradation (sphingosine 1 phosphate phosphatase and lyase). In addition, a brief overview of the most significant agonists and antagonists at the S1P receptors is also addressed.

Sphingosine kinase 1 mediates neuroinflammation following cerebral ischemia

Sphingosine kinases (Sphks) are the rate-limiting kinases in the generation of sphingosine-1-phosphate, which is a well-established intracellular pro-survival lipid mediator. Sphk2 has been reported to be protective following experimental stroke. We investigated the role of Sphk1 in cerebral ischemia using a mouse middle cerebral artery occlusion (MCAO) model and an in vitro glucose-oxygen deprivation (OGD) model. Sphk expression and activity were assessed in the ischemic brain with quantitative PCR (qPCR), Western blot, immunohistochemistry and enzyme-linked immunosorbent assay (ELISA). Pharmacological and gene knockdown approaches were utilized to investigate the effects of Sphk1 on stroke outcomes. The expression of Sphk1 but not that of Sphk2 was rapidly induced in the cortical penumbra over 96h after MCAO, and the microglia were one of the major cellular sources of Sphk1 induction. Consistently, Sphk activity was enhanced in the cortical penumbra. In contrast to the protective role of Sphk2, pharmacological inhibition and cortical knockdown of Sphk1 reduced infarction at 24 and 96h after reperfusion. Additionally, the Sphk1 inhibitor improved the neurological deficits at 96h after reperfusion. Mechanistically, Sphk1 inhibition and knockdown significantly attenuated MCAO-induced expression of inflammatory mediators in the cortical penumbra. Moreover, using a conditioned medium transfer approach, we demonstrated that OGD-treated neurons induced the expression of Sphk1 and pro-inflammatory mediators in primary microglia, and the microglial induction of pro-inflammatory mediators by ischemic neurons was blunted by Sphk1 inhibition. Taken together, our results indicate that Sphk1 plays an essential role in mediating post-stroke neuroinflammation.

Characterization of phytochemicals and evaluation of anti-cancer potential of Blumea eriantha DC

The aim of the present study was to evaluate the in vitro anti-cancer and anti-oxidant potential of methanol extract of Blumea eriantha as well as its phytochemical characterization. The in vitro cytotoxic and antiproliferative activities of B. eriantha methanolic extract of leaves were evaluated using MTT assay on HeLa and B16F10 cell lines, and wound scratch and colony formation assays on B16F10 cell lines. The expressions of p53 and Bcl-2 genes were also determined by reverse transcriptase-polymerase chain reaction to establish apoptosis. Isolation and identification of chemical constituents were carried out by various chromatographic and spectroscopic analytical techniques including HPTLC and LC-MS. The methanol extract of the leaves of B. eriantha showed potent in vitro antioxidant and anticancer properties. Moreover, the extract showed significant loss of wound healing, thus suggesting that it could prevent a possible metastasis. Hence, B. eriantha could be explored as a potential anticancer plant with antimetastatic properties.

Synthesis of aromatic sphingosine analogues by diastereoselective amination of enantioenriched trans-γ,δ-unsaturated β-hydroxyesters

An effective route to N-Boc-protected aromatic sphingosine analogues is accomplished. The strategy is based on the diastereoselective amination of enantioenriched trans-γ,δ-unsaturated β-hydroxyesters to establish anti,N-Boc-α-hydrazino-β-hydroxyesters. Nonreductive E1cB elimination is essential for the successful N-N bond cleavage of hydrazine while preserving the trans double bond. Either the (3R,2S) and (3S,2R) enantiomer of N-Boc-protected sphingosine analogues has been synthesized in five steps with excellent optical purity with ∼99% ee and >99% de.

Sphingosine kinase 1 promotes malignant progression in colon cancer and independently predicts survival of patients with colon cancer by competing risk approach in South asian population

OBJECTIVES

Sphingosine kinase 1 (SphK1) phosphorylates the membrane sphingolipid, sphingosine, to sphingosine-1-phosphate (S1P), an oncogenic mediator, which drives tumor cell growth and survival. Although SphK1 has gained increasing prominence as an oncogenic determinant in several cancers, its potential as a therapeutic target in colon cancer remains uncertain. We investigated the clinical relevance of SphK1 expression in colon cancer as well as its inhibitory effects in vitro.

METHODS

SphK1 expression in human colon tumor tissues was determined by immunohistochemistry and its clinicopathological significance was ascertained in 303 colon cancer cases. The effects of SphK1 inhibition on colon cancer cell viability and the phosphoinositide 3-kinase (PI3K)/Akt cell survival pathway were investigated using a SphK1-selective inhibitor-compound 5c (5c). The cytotoxicity of a novel combination using SphK1 inhibition with the chemotherapeutic drug, 5-fluorouracil (5-FU), was also determined.

RESULTS

High SphK1 expression correlated with advanced tumor stages (AJCC classification). Using a competing risk analysis model to take into account disease recurrence, we found that SphK1 is a significant independent predictor for mortality in colon cancer patients. In vitro, the inhibition of SphK1 induced cell death in colon cancer cell lines and attenuated the serum-dependent PI3K/Akt signaling. Inhibition of SphK1 also enhanced the sensitivity of colon cancer cells to 5-FU.

CONCLUSION

Our findings highlight the impact of SphK1 in colon cancer progression and patient survival, and provide evidence supportive of further development in combination strategies that incorporate SphK1 inhibition with current chemotherapeutic agents to improve colon cancer outcomes.

A review of ceramide analogs as potential anticancer agents

Ceramide serves as a central mediator in sphingolipid metabolism and signaling pathways, regulating many fundamental cellular responses. It is referred to as a 'tumor suppressor lipid', since it powerfully potentiates signaling events that drive apoptosis, cell cycle arrest, and autophagic responses. In the typical cancer cell, ceramide levels and signaling are usually suppressed by overexpression of ceramide-metabolizing enzymes or downregulation of ceramide-generating enzymes. However, chemotherapeutic drugs as well as radiotherapy increase intracellular ceramide levels, while exogenously treating cancer cells with short-chain ceramides leads to anticancer effects. All evidence currently points to the fact that the upregulation of ceramide levels is a promising anticancer strategy. In this review, we exhibit many anticancer ceramide analogs as downstream receptor agonists and ceramide-metabolizing enzyme inhibitors.

3-Ketone-4,6-diene ceramide analogs exclusively induce apoptosis in chemo-resistant cancer cells

Multidrug-resistance is a major cause of cancer chemotherapy failure in clinical treatment. Evidence shows that multidrug-resistant cancer cells are as sensitive as corresponding regular cancer cells under the exposure to anticancer ceramide analogs. In this work we designed five new ceramide analogs with different backbones, in order to test the hypothesis that extending the conjugated system in ceramide analogs would lead to an increase of their anticancer activity and selectivity towards resistant cancer cells. The analogs with the 3-ketone-4,6-diene backbone show the highest apoptosis-inducing efficacy. The most potent compound, analog 406, possesses higher pro-apoptotic activity in chemo-resistant cell lines MCF-7TN-R and NCI/ADR-RES than the corresponding chemo-sensitive cell lines MCF-7 and OVCAR-8, respectively. However, this compound shows the same potency in inhibiting the growth of another pair of chemo-sensitive and chemo-resistant cancer cells, MCF-7 and MCF-7/Dox. Mechanism investigations indicate that analog 406 can induce apoptosis in chemo-resistant cancer cells through the mitochondrial pathway. Cellular glucosylceramide synthase assay shows that analog 406 does not interrupt glucosylceramide synthase in chemo-resistant cancer cell NCI/ADR-RES. These findings suggest that due to certain intrinsic properties, ceramide analogs' pro-apoptotic activity is not disrupted by the normal drug-resistance mechanisms, leading to their potential use for overcoming cancer multidrug-resistance.

Garner's aldehyde as a versatile intermediate in the synthesis of enantiopure natural products

Since its introduction to the synthetic community in 1984, Garner's aldehyde has gained substantial attention as a chiral intermediate for the synthesis of numerous amino alcohol derivatives. This review presents some of the most successful carbon chain elongation reactions, namely carbonyl alkylations and olefinations. The literature is reviewed with particular attention on understanding how to avoid the deleterious epimerization of the existing stereocenter in Garner's aldehyde.

Curcumin ameliorates diabetic nephropathy by inhibiting the activation of the SphK1-S1P signaling pathway

Curcumin, a major polyphenol from the golden spice Curcuma longa commonly known as turmeric, has been recently discovered to have renoprotective effects on diabetic nephropathy (DN). However, the mechanisms underlying these effects remain unclear. We previously demonstrated that the sphingosine kinase 1-sphingosine 1-phosphate (SphK1-S1P) signaling pathway plays a pivotal role in the pathogenesis of DN. This study aims to investigate whether the renoprotective effects of curcumin on DN are associated with its inhibitory effects on the SphK1-S1P signaling pathway. Our results demonstrated that the expression and activity of SphK1 and the production of S1P were significantly down-regulated by curcumin in diabetic rat kidneys and glomerular mesangial cells (GMCs) exposed to high glucose (HG). Simultaneously, SphK1-S1P-mediated fibronectin (FN) and transforming growth factor-beta 1 (TGF-β1) overproduction were inhibited. In addition, curcumin dose dependently reduced SphK1 expression and activity in GMCs transfected with SphK(WT) and significantly suppressed the increase in SphK1-mediated FN levels. Furthermore, curcumin inhibited the DNA-binding activity of activator protein 1 (AP-1), and c-Jun small interference RNA (c-Jun-siRNA) reversed the HG-induced up-regulation of SphK1. These findings suggested that down-regulation of the SphK1-S1P pathway is probably a novel mechanism by which curcumin improves the progression of DN. Inhibiting AP-1 activation is one of the therapeutic targets of curcumin to modulate the SphK1-S1P signaling pathway, thereby preventing diabetic renal fibrosis.

Sphingosine kinase type 1 inhibition reveals rapid turnover of circulating sphingosine 1-phosphate

S1P (sphingosine 1-phosphate) is a signalling molecule involved in a host of cellular and physiological functions, most notably cell survival and migration. S1P, which signals via a set of five G-protein-coupled receptors (S1P1-S1P5), is formed by the action of two SphKs (sphingosine kinases) from Sph (sphingosine). Interfering RNA strategies and SphK1 (sphingosine kinase type 1)-null (Sphk1-/-) mouse studies implicate SphK1 in multiple signalling cascades, yet there is a paucity of potent and selective SphK1 inhibitors necessary to evaluate the effects of rapid onset inhibition of this enzyme. We have identified a set of submicromolar amidine-based SphK1 inhibitors and report using a pair of these compounds to probe the cellular and physiological functions of SphK1. In so doing, we demonstrate that our inhibitors effectively lower S1P levels in cell-based assays, but we have been unable to correlate SphK1 inhibition with changes in cell survival. However, SphK1 inhibition did diminish EGF (epidermal growth factor)-driven increases in S1P levels and Akt (also known as protein kinase B)/ERK (extracellular-signal-regulated kinase) phosphorylation. Finally, administration of the SphK1 inhibitor to wild-type, but not Sphk1-/-, mice resulted in a rapid decrease in blood S1P levels indicating that circulating S1P is rapidly turned over.

Inhibition of sphingosine 1-phosphate receptor 2 protects against renal ischemia-reperfusion injury

Activation of the sphingosine 1-phosphate receptor 1 (S1P(1)R) protects against renal ischemia-reperfusion (IR) injury and inflammation, but the role of other members of this receptor family in modulating renal IR injury is unknown. We found that a selective S1P(2)R antagonist protected against renal IR injury in a dose-dependent manner. Consistent with this observation, both S1P(2)R-deficient mice and wild-type mice treated with S1P(2)R small interfering RNA had reduced renal injury after IR. In contrast, a selective S1P(2)R agonist exacerbated renal IR injury. The S1P(2)R antagonist increased sphingosine kinase-1 (SK1) expression via Rho kinase signaling in renal proximal tubules; the S1P(2)R agonist decreased SK1. S1P(2)R antagonism failed to protect the kidneys of SK1-deficient mice or wild-type mice pretreated with an SK1 inhibitor or an S1P(1)R antagonist, suggesting that the renoprotection conferred by S1P(2)R antagonism results from pathways involving activation of S1P(1)R by SK1. In cultured human proximal tubule (HK-2) cells, the S1P(2)R antagonist selectively upregulated SK1 and attenuated both H(2)O(2)-induced necrosis and TNF-α/cycloheximide-induced apoptosis; the S1P(2)R agonist had the opposite effects. In addition, increased nuclear hypoxia inducible factor-1α was critical in mediating the renoprotective effects of S1P(2)R inhibition. Finally, induction of SK1 and S1P(2)R in response to renal IR and S1P(2)R antagonism occurred selectively in renal proximal tubule cells but not in renal endothelial cells. Taken together, these data suggest that S1P(2)R may be a therapeutic target to attenuate the effects of renal IR injury.

Pharmacological relevance and potential of sphingosine 1-phosphate in the vascular system

Sphingosine-1-phosphate (S1P) was identified as a crucial molecule for regulating immune responses, inflammatory processes as well as influencing the cardiovascular system. S1P mediates differentiation, proliferation and migration during vascular development and homoeostasis. S1P is a naturally occurring lipid metabolite and is present in human blood in nanomolar concentrations. S1P is not only involved in physiological but also in pathophysiological processes. Therefore, this complex signalling system is potentially interesting for pharmacological intervention. Modulation of the system might influence inflammatory, angiogenic or vasoregulatory processes. S1P activates G-protein coupled receptors, namely S1P(1-5) , whereas only S1P(1-3) is present in vascular cells. S1P can also act as an intracellular signalling molecule. This review highlights the pharmacological potential of S1P signalling in the vascular system by giving an overview of S1P-mediated processes in endothelial cells (ECs) and vascular smooth muscle cells (VSMCs). After a short summary of S1P metabolism and signalling pathways, the role of S1P in EC and VSMC proliferation and migration, the cause of relaxation and constriction of arterial blood vessels, the protective functions on endothelial apoptosis, as well as the regulatory function in leukocyte adhesion and inflammatory responses are summarized. This is followed by a detailed description of currently known pharmacological agonists and antagonists as new tools for mediating S1P signalling in the vasculature. The variety of effects influenced by S1P provides plenty of therapeutic targets currently under investigation for potential pharmacological intervention.

Sphingosine kinase 1 protects against renal ischemia-reperfusion injury in mice by sphingosine-1-phosphate1 receptor activation

The roles of sphingosine kinases SK1 and SK2 in ischemia-reperfusion injury have not been fully elucidated since studies have found beneficial effects of SK1 while others showed no role in this injury. To help resolve this, we used SK1 or SK2 knockout mice and confirmed that renal ischemia-reperfusion injury induced SK1, but not SK2, in the kidneys. Furthermore, knockout or pharmacological inhibition of SK1 increased injury after renal ischemia-reperfusion injury. In contrast, lack of SK2 conferred renal protection following injury. In addition, we used lentiviral gene delivery to selectively express enhanced green fluorescent protein (EGFP) or human SK1 coexpressed with EGFP (EGFP-huSK1) in the kidney. Mice with kidney-specific overexpression of EGFP-huSK1 had significantly improved renal function with lower plasma creatinine, renal necrosis, apoptosis, and inflammation. Moreover, EGFP-huSK1 overexpression in cultured human proximal tubule (HK-2) cells protected against peroxide-induced necrosis. Selective overexpression of EGFP-huSK1 led to increased HSP27 mRNA and protein expression in vivo and in vitro. Functional protection as well as induction of HSP27 with EGFP-huSK1 overexpression in vivo was blocked with sphingosine-1-phosphate-1 receptor(1) (S1P(1)) antagonism. Thus, our findings suggest that SK1 is renoprotective by S1P(1) activation and perhaps HSP27 induction. Kidney-specific expression of SK1 through lentiviral delivery may be a viable therapeutic option to attenuate renal ischemia-reperfusion injury.

Development of amidine-based sphingosine kinase 1 nanomolar inhibitors and reduction of sphingosine 1-phosphate in human leukemia cells

Sphingosine 1-phosphate (S1P) is a bioactive lipid that has been identified as an accelerant of cancer progression. The sphingosine kinases (SphKs) are the sole producers of S1P, and thus, SphK inhibitors may prove effective in cancer mitigation and chemosensitization. Of the two SphKs, SphK1 overexpression has been observed in a myriad of cancer cell lines and tissues and has been recognized as the presumptive target over that of the poorly characterized SphK2. Herein, we present the design and synthesis of amidine-based nanomolar SphK1 subtype-selective inhibitors. A homology model of SphK1, trained with this library of amidine inhibitors, was then used to predict the activity of additional, more potent, inhibitors. Lastly, select amidine inhibitors were validated in human leukemia U937 cells, where they significantly reduced endogenous S1P levels at nanomolar concentrations.

A rapid assay for assessment of sphingosine kinase inhibitors and substrates

Sphingosine kinases (SphKs) catalyze the transfer of phosphate from adenosine triphosphate (ATP) to sphingosine to generate sphingosine 1-phosphate (S1P), an important bioactive lipid molecule that mediates a diverse range of cell signaling processes. The conventional assay of SphK enzymatic activity uses [γ-(32)P]ATP and sphingosine as substrates, with the radiolabeled S1P product recovered by organic extraction, displayed by thin layer chromatography, and quantified by liquid scintillation counting. Although this assay is sensitive and accurate, it is slow and labor-intensive; thus, it precludes the simultaneous screening of more than a few inhibitor compounds. Here we describe a 96-well assay for SphKs that is rapid and reproducible. Our method, which takes advantage of the limited solubility of S1P, detects radioactive S1P adhering to the plate by scintillation proximity counting. Our procedure obviates extraction into organic solvents, postreaction transfers, and chromatography. Furthermore, our assay enables assessment of both inhibitors and substrates, and it can detect endogenous SphK activity in cell and tissue extracts. The SphK kinetic parameter, K(m), and the K(i) values of inhibitors determined with our assay and the conventional assay were indistinguishable. These results document that our assay is well-suited for the screening of chemical libraries of SphK inhibitors.

Sphingosine-1-phosphate and immune regulation: trafficking and beyond

Sphingosine-1-phosphate (S1P) is a bioactive lipid with important functions in the immune system. S1P levels are regulated by the balance between its synthesis through sphingosine kinases and its degradation by S1P lyase. S1P signals through plasma membrane G-protein-coupled receptors (S1PR1-S1PR5) or acts directly on intracellular targets. Although it has long been known that the S1P-S1PR1 axis mediates T cell egress from lymphoid organs, recent studies have revealed intrinsic functions of S1P and its receptors in both innate and adaptive immune systems that are independent of immune cell trafficking. Here I summarize recent advances in understanding of the roles of S1P and S1P receptors in inflammatory and allergic responses and lymphocyte differentiation, which directly contribute to the regulation of inflammatory and autoimmune diseases. I also describe strategies to target S1P and S1P receptors for immune-mediated diseases, particularly the immunosuppressant FTY720 (fingolimod), which has recently become the first oral therapy for relapsing multiple sclerosis.

Sphingosine 1-phosphate and cancer

There is substantial evidence that sphingosine 1-phosphate (S1P) is involved in cancer. S1P regulates processes such as inflammation, which can drive tumorigenesis; neovascularization, which provides cancer cells with nutrients and oxygen; and cell growth and survival. This occurs at multiple levels and involves S1P receptors, sphingosine kinases, S1P phosphatases and S1P lyase. This Review summarizes current research findings and examines the potential for new therapeutics designed to alter S1P signalling and function in cancer.

RETRACTED: SphK1 regulates proinflammatory responses associated with endotoxin and polymicrobial sepsis

During sepsis, activation of phagocytes leads to the overproduction of proinflammatory cytokines, causing systemic inflammation. Despite substantial information regarding the underlying molecular mechanisms that lead to sepsis, several elements in the pathway remain to be elucidated. We found that the enzyme sphingosine kinase 1 (SphK1) is up-regulated in stimulated human phagocytes and in peritoneal phagocytes of patients with severe sepsis. Blockade of SphK1 inhibited phagocyte production of endotoxin-induced proinflammatory cytokines. We observed protection against sepsis in mice treated with a specific SphK1 inhibitor that was enhanced by treatment with a broad-spectrum antibiotic. These results demonstrated a critical role for SphK1 in endotoxin signaling and sepsis-induced inflammatory responses and suggest that inhibition of SphK1 is a potential therapy for septic shock.

Discovery, biological evaluation, and structure-activity relationship of amidine based sphingosine kinase inhibitors

Sphingosine 1-phosphate (S1P), a potent phospholipid growth and trophic factor, is synthesized in vivo by two sphingosine kinases. Thus these kinases have been proposed as important drug targets for treatment of hyperproliferative diseases and inflammation. We report here a new class of amidine-based sphingosine analogues that are competitive inhibitors of sphingosine kinases exhibiting varying degrees of enzyme selectivity. These inhibitors display K(I) values in the submicromolar range for both sphingosine kinases and, in cultured vascular smooth muscle cells, decrease S1P levels and initiate growth arrest.