Krüppel-like factor 12 regulates aging ovarian granulosa cell apoptosis by repressing SPHK1 transcription and sphingosine-1-phosphate (S1P) production.

Oxidative stress triggered by aging, radiation, or inflammation impairs ovarian function by inducing granulosa cell (GC) apoptosis. However, the mechanism inducing GC apoptosis has not been characterized. Here, we found that ovarian GCs from aging patients showed increased oxidative stress, enhanced reactive oxygen species activity, and significantly decreased expression of the known antiapoptotic factor sphingosine-1-phosphate/sphingosine kinase 1 (SPHK1) in GCs. Interestingly, the expression of Krüppel-like factor 12 (KLF12) was significantly increased in the ovarian GCs of aging patients. Furthermore, we determined that KLF12 was significantly upregulated in hydrogen peroxide-treated GCs and a 3-nitropropionic acid-induced in vivo model of ovarian oxidative stress. This phenotype was further confirmed to result from inhibition of SPHK1 by KLF12. Interestingly, when endogenous KLF12 was knocked down, it rescued oxidative stress-induced apoptosis. Meanwhile, supplementation with SPHK1 partially reversed oxidative stress-induced apoptosis. However, this function was lost in SPHK1 with deletion of the binding region to the KLF12 promoter. SPHK1 reversed apoptosis caused by hydrogen peroxide-KLF12 overexpression, a result further confirmed in an in vitro ovarian culture model and an in vivo 3-nitropropionic acid-induced ovarian oxidative stress model. Overall, our study reveals that KLF12 is involved in regulating apoptosis induced by oxidative stress in aging ovarian GCs and that sphingosine-1-phosphate/SPHK1 can rescue GC apoptosis by interacting with KLF12 in negative feedback.

Targeting sphingosine kinase 1/2 by a novel dual inhibitor SKI-349 suppresses non-small cell lung cancer cell growth.

Sphingosine kinase 1 (SphK1) and sphingosine kinase (SphK2) are both important therapeutic targets of non-small cell lung cancer (NSCLC). SKI-349 is a novel, highly efficient and small molecular SphK1/2 dual inhibitor. Here in primary human NSCLC cells and immortalized cell lines, SKI-349 potently inhibited cell proliferation, cell cycle progression, migration and viability. The dual inhibitor induced mitochondrial depolarization and apoptosis activation in NSCLC cells, but it was non-cytotoxic to human lung epithelial cells. SKI-349 inhibited SphK activity and induced ceramide accumulation in primary NSCLC cells, without affecting SphK1/2 expression. SKI-349-induced NSCLC cell death was attenuated by sphingosine-1-phosphate and by the SphK activator K6PC-5, but was potentiated by the short-chain ceramide C6. Moreover, SKI-349 induced Akt-mTOR inactivation, JNK activation, and oxidative injury in primary NSCLC cells. In addition, SKI-349 decreased bromodomain-containing protein 4 (BRD4) expression and downregulated BRD4-dependent genes (Myc, cyclin D1 and Klf4) in primary NSCLC cells. At last, SKI-349 (10 mg/kg) administration inhibited NSCLC xenograft growth in nude mice. Akt-mTOR inhibition, JNK activation, oxidative injury and BRD4 downregulation were detected in SKI-349-treated NSCLC xenograft tissues. Taken together, targeting SphK1/2 by SKI-349 potently inhibits NSCLC cell growth in vitro and in vivo.

Synthesis, molecular docking, and biological evaluation of novel 1,2,4-triazole-isatin derivatives as potential Mycobacterium tuberculosis shikimate kinase inhibitors.

The issue of emerging resistance to antitubercular drugs has created a formidable barrier in the effective prevention and cure of tuberculosis globally. In an effort to search for new antimycobacterial agents, possibly comprising new pharmacophore, novel triazole-isatin derivatives were designed as Mycobacterium tuberculosis shikimate kinase inhibitors and synthesized by microwave-assisted method. The synthesized molecules were evaluated for their antimycobacterial activity by MABA assay against M. tuberculosis H37Rv. The molecule 5h demonstrated MIC of 0.8 µg/ml and good safety profile with higher selectivity index with HEK293 cell line. The antimycobacterial activity was further substantiated with molecular docking studies. The triazole-isatin derivatives showed significant binding interactions with amino acid residues in the active site of the enzyme. These studies revealed that molecule 5h could act as a potential lead molecule for further studies to find new target-directed molecules.

Pharmacological Targeting of Sphingosine Kinases Impedes HIV-1 Infection of CD4 T Cells through SAMHD1 Modulation.

Sphingosine-1-phosphate (S1P) is a sphingolipid modulator of a myriad of cellular processes, and therapeutic targeting of S1P signaling is utilized clinically to treat multiple sclerosis. We have previously shown that functional antagonism of S1P receptors reduces cell-free, cell-to-cell, and latent HIV-1 infection in primary CD4 T cells. In this work, we examined whether targeting sphingosine kinase 1 or 2 (SPHK1/2) to inhibit S1P production would prevent infection using multiple HIV-1 primary isolates and infectious molecular clones. SPHK inhibition reduced HIV transmission between primary CD4 T cells in both cell-to-cell transmission and pretreatment coculture models. Mechanistically, pharmacological inhibition of SPHK reduced susceptibility to infection primarily by downregulating phosphorylated SAMHD1 (pSAMHD1), enhancing the activity of this innate HIV-1 restriction factor. Furthermore, genetic disruption of either SPHK1 or SPHK2 by CRISPR/Cas9 reduced phosphorylation of SAMHD1, demonstrating the role of these kinases in modulation of SAMHD1 activity. The effect of SPHK inhibition on limiting HIV-1 infection in CD4 T cells was observed irrespective of the biological sex or age of the donor, with neither variable significantly influencing the effectiveness of SPHK inhibition. Our results demonstrate that targeting SPHK inhibits transmission of HIV-1 via modulation of SAMHD1 phosphorylation to decrease permissiveness to infection in CD4 T cells and suggests that therapeutic targeting of this pathway early in infection enables development of strategies to prevent establishment of infection and hinder cell-to-cell transmission of HIV-1. IMPORTANCE HIV-1 infection, once established, requires lifelong treatment due to the ability of the virus to maintain latent infection in its host and become reactivated during an interruption in antiretroviral treatment (ART). Although preventing transmission and acquisition of HIV is an important goal, no ART thus far have exploited harnessing a component of the host immune system to combat transmission of the virus. We have previously shown that inhibition of sphingosine-1-phosphate (S1P) receptors, a component of S1P signaling, reduces HIV-1 infection in human CD4 T cells. We therefore investigated inhibition of sphingosine kinases, another element of this signaling system, in this work. We found that inhibition of sphingosine kinases 1 and 2 (SPHK1/2) could reduce HIV-1 transmission, both among CD4 T cells and between macrophages and CD4 T cells. Our research therefore suggests that therapeutic targeting of SPHK or S1P receptors may aid in the development of strategies to prevent establishment and transmission of HIV-1 infection among immune cells.

Development of Selective Phosphatidylinositol 5-Phosphate 4-Kinase γ Inhibitors with a Non-ATP-competitive, Allosteric Binding Mode.

Phosphatidylinositol 5-phosphate 4-kinases (PI5P4Ks) are emerging as attractive therapeutic targets in diseases, such as cancer, immunological disorders, and neurodegeneration, owing to their central role in regulating cell signaling pathways that are either dysfunctional or can be modulated to promote cell survival. Different modes of binding may enhance inhibitor selectivity and reduce off-target effects in cells. Here, we describe efforts to improve the physicochemical properties of the selective PI5P4Kγ inhibitor, NIH-12848 (1). These improvements enabled the demonstration that this chemotype engages PI5P4Kγ in intact cells and that compounds from this series do not inhibit PI5P4Kα or PI5P4Kß. Furthermore, the first X-ray structure of PI5P4Kγ bound to an inhibitor has been determined with this chemotype, confirming an allosteric binding mode. An exemplar from this chemical series adopted two distinct modes of inhibition, including through binding to a putative lipid interaction site which is 18 Å from the ATP pocket.

CRISPR screens uncover protective effect of PSTK as a regulator of chemotherapy-induced ferroptosis in hepatocellular carcinoma.

BACKGROUND: Hepatocellular carcinoma (HCC) is among the most common forms of cancer and is associated with poor patient outcomes. The emergence of therapeutic resistance has hampered the efficacy of targeted treatments employed to treat HCC patients to date. In this study, we conducted a series of CRISPR/Cas9 screens to identify genes associated with synthetic lethality capable of improving HCC patient clinical responses. METHODS: CRISPR-based loss-of-function genetic screens were used to target 18,053 protein-coding genes in HCC cells to identify chemotherapy-related synthetic lethal genes in these cells. Synergistic effects were analyzed through in vitro and in vivo analyses, while related mechanisms were explored through RNA-seq and metabolomics analyses. Potential inhibitors of identified genetic targets were selected through high-throughput virtual screening. RESULTS: The inhibition of phosphoseryl-tRNA kinase (PSTK) was found to increase HCC cell sensitivity to chemotherapeutic treatment. PSTK was associated with the suppression of chemotherapy-induced ferroptosis in HCC cells, and the depletion of PSTK resulted in the inactivation of glutathione peroxidative 4 (GPX4) and the disruption of glutathione (GSH) metabolism owing to the inhibition of selenocysteine and cysteine synthesis, thus enhancing the induction of ferroptosis upon targeted chemotherapeutic treatment. Punicalin, an agent used to treat hepatitis B virus (HBV), was identified as a possible PSTK inhibitor that exhibited synergistic efficacy when applied together with Sorafenib to treat HCC in vitro and in vivo. CONCLUSIONS: These results highlight a key role for PSTK as a mediator of resistance to targeted therapeutic treatment in HCC cells that functions by suppressing ferroptotic induction. PSTK inhibitors may thus represent ideal candidates for overcoming drug resistance in HCC.

Identification and optimization of a novel series of selective PIP5K inhibitors.

Phosphatidyl inositol (4,5)-bisphosphate (PI(4,5)P2) plays several key roles in human biology and the lipid kinase that produces PI(4,5)P2, PIP5K, has been hypothesized to provide a potential therapeutic target of interest in the treatment of cancers. To better understand and explore the role of PIP5K in human cancers there remains an urgent need for potent and specific PIP5K inhibitor molecules. Following a high throughput screen of the AstraZeneca collection, a novel, moderately potent and selective inhibitor of PIP5K, 1, was discovered. Detailed exploration of the SAR for this novel scaffold resulted in the considerable optimization of both potency for PIP5K, and selectivity over the closely related kinase PI3Kα, as well as identifying several opportunities for the continued optimization of drug-like properties. As a result, several high quality in vitro tool compounds were identified (8, 20 and 25) that demonstrate the desired biochemical and cellular profiles required to aid better understanding of this complex area of biology.

Resensitising proteasome inhibitor-resistant myeloma with sphingosine kinase 2 inhibition.

The introduction of the proteasome inhibitor bortezomib into treatment regimens for myeloma has led to substantial improvement in patient survival. However, whilst bortezomib elicits initial responses in many myeloma patients, this haematological malignancy remains incurable due to the development of acquired bortezomib resistance. With other patients presenting with disease that is intrinsically bortezomib resistant, it is clear that new therapeutic approaches are desperately required to target bortezomib-resistant myeloma. We have previously shown that targeting sphingolipid metabolism with the sphingosine kinase 2 (SK2) inhibitor K145 in combination with bortezomib induces synergistic death of bortezomib-naïve myeloma. In the current study, we have demonstrated that targeting sphingolipid metabolism with K145 synergises with bortezomib and effectively resensitises bortezomib-resistant myeloma to this proteasome inhibitor. Notably, these effects were dependent on enhanced activation of the unfolded protein response, and were observed in numerous separate myeloma models that appear to have different mechanisms of bortezomib resistance, including a new bortezomib-resistant myeloma model we describe which possesses a clinically relevant proteasome mutation. Furthermore, K145 also displayed synergy with the next-generation proteasome inhibitor carfilzomib in bortezomib-resistant and carfilzomib-resistant myeloma cells. Together, these findings indicate that targeting sphingolipid metabolism via SK2 inhibition may be effective in combination with a broad spectrum of proteasome inhibitors in the proteasome inhibitor resistant setting, and is an approach worth clinical exploration.

The role of the sphingosine axis in immune regulation: A dichotomy in the anti-inflammatory effects between sphingosine kinase 1 and sphingosine kinase 2-dependent pathways.

Background: Sphingosine kinase has been identified as playing a central role in the immune cascade, being a common mediator in the cellular response to a variety of signals. The different effects of sphingosine kinase 1 and 2 (SphK1 and SphK2, respectively) activity have not been completely characterized. Aim: To determine the different roles played by SphK1 and SphK2 in the regulation of immune-mediated disorders. Methods: Nine groups of mice were studied. Concanavalin A (ConA) injection was used to induce immune-mediated hepatitis. Mice were treated with SphK1 inhibitor (termed SphK-I) and SphK2 inhibitor (termed ABC294640), prior to ConA injection, and effects of treatment on liver enzymes, subsets of T lymphocytes, and serum levels of cytokines were observed. Results: While liver enzyme elevation was ameliorated by administration of SphK1 inhibitor, SphK2 inhibitor-treated mice did not show this tendency. A marked decrease in expression of CD25+ T-cells and Foxp+ T-cells was observed in mice treated with a high dose of SphK1 inhibitor. Alleviation of liver damage was associated with a statistically significant reduction of serum IFNγ levels in mice treated with SphK1 inhibitor and not in those treated with SphK2 inhibitor. Conclusions: Early administration of SphK1 inhibitor in a murine model of immune-mediated hepatitis alleviated liver damage and inflammation with a statistically significant reduction in IFN-γ levels. The data support a dichotomy in the anti-inflammatory effects of SphK1 and SphK2, and suggests that isoenzyme-directed therapies can improve the effect of targeting these pathways.

Finding the First Potential Inhibitors of Shikimate Kinase from Methicillin Resistant Staphylococcus aureus through Computer-Assisted Drug Design.

Methicillin-resistant Staphylococcus aureus (MRSA) is an important threat as it causes serious hospital and community acquired infections with deathly outcomes oftentimes, therefore, development of new treatments against this bacterium is a priority. Shikimate kinase, an enzyme in the shikimate pathway, is considered a good target for developing antimicrobial drugs; this is given because of its pathway, which is essential in bacteria whereas it is absent in mammals. In this work, a computer-assisted drug design strategy was used to report the first potentials inhibitors for Shikimate kinase from methicillin-resistant Staphylococcus aureus (SaSK), employing approximately 5 million compounds from ZINC15 database. Diverse filtering criteria, related to druglike characteristics and virtual docking screening in the shikimate binding site, were performed to select structurally diverse potential inhibitors from SaSK. Molecular dynamics simulations were performed to elucidate the dynamic behavior of each SaSK-ligand complex. The potential inhibitors formed important interactions with residues that are crucial for enzyme catalysis, such as Asp37, Arg61, Gly82, and Arg138. Therefore, the compounds reported provide valuable information and can be seen as the first step toward developing SaSK inhibitors in the search of new drugs against MRSA.

The Sphingosine Kinase 2 Inhibitor ABC294640 Restores the Sensitivity of BRAFV600E Mutant Colon Cancer Cells to Vemurafenib by Reducing AKT-Mediated Expression of Nucleophosmin and Translationally-Controlled Tumour Protein.

Vemurafenib (PLX4032), small-molecule inhibitor of mutated BRAFV600E protein, has emerged as a potent anti-cancer agent against metastatic melanoma harboring BRAFV600E mutation. Unfortunately, the effect of PLX4032 in the treatment of metastatic BRAF mutated colorectal cancer (CRC) is less potent due to high incidence of fast-developing chemoresistance. It has been demonstrated that sphingolipids are important mediators of chemoresistance to various therapies in colon cancer. In this study, we will explore the role of major regulators of sphingolipid metabolism and signaling in the development of resistance to vemurafenib in BRAF mutant colon cancer cells. The obtained data revealed significantly increased expression levels of activated sphingosine kinases (SphK1 and SphK2) in resistant cells concomitant with increased abundance of sphingosine-1-phosphate (S1P) and its precursor sphingosine, which was accompanied by increased expression levels of the enzymes regulating the ceramide salvage pathway, namely ceramide synthases 2 and 6 and acid ceramidase, especially after the exposure to vemurafenib. Pharmacological inhibition of SphK1/SphK2 activities or modulation of ceramide metabolism by exogenous C6-ceramide enhanced the anti-proliferative effect of PLX4032 in resistant RKO cells in a synergistic manner. It is important to note that the inhibition of SphK2 by ABC294640 proved effective at restoring the sensitivity of resistant cells to vemurafenib at the largest number of combinations of sub-toxic drug concentrations with minimal cytotoxicity. Furthermore, the obtained findings revealed that enhanced anti-proliferative, anti-migratory, anti-clonogenic and pro-apoptotic effects of a combination treatment with ABC294640 and PLX4032 relative to either drug alone were accompanied by the inhibition of S1P-regulated AKT activity and concomitant abrogation of AKT-mediated cellular levels of nucleophosmin and translationally-controlled tumour protein. Collectively, our study suggests the possibility of using the combination of ABC294640 and PLX4032 as a novel therapeutic approach to combat vemurafenib resistance in BRAF mutant colon cancer, which warrants additional preclinical validation studies.

Discovery and Characterization of the Potent and Highly Selective 1,7-Naphthyridine-Based Inhibitors BAY-091 and BAY-297 of the Kinase PIP4K2A.

PIP4K2A is an insufficiently studied type II lipid kinase that catalyzes the conversion of phosphatidylinositol-5-phosphate (PI5P) into phosphatidylinositol 4,5-bisphosphate (PI4,5P2). The involvement of PIP4K2A/B in cancer has been suggested, particularly in the context of p53 mutant/null tumors. PIP4K2A/B depletion has been shown to induce tumor growth inhibition, possibly due to hyperactivation of AKT and reactive oxygen species-mediated apoptosis. Herein, we report the identification of the novel potent and highly selective inhibitors BAY-091 and BAY-297 of the kinase PIP4K2A by high-throughput screening and subsequent structure-based optimization. Cellular target engagement of BAY-091 and BAY-297 was demonstrated using cellular thermal shift assay technology. However, inhibition of PIP4K2A with BAY-091 or BAY-297 did not translate into the hypothesized mode of action and antiproliferative activity in p53-deficient tumor cells. Therefore, BAY-091 and BAY-297 serve as valuable chemical probes to study PIP4K2A signaling and its involvement in pathophysiological conditions such as cancer.

The alleviating effect of sphingosine kinases 2 inhibitor K145 on nonalcoholic fatty liver.

Sphingosine kinase 2 (SphK2) inhibitors are developed for tumor therapy as considering its anti-tumor effect. Many studies also explored SphK2 modulated glucose and lipid homeostasis, which extended its potential function for metabolic diseases therapy. In this study, we discovered a significant reduction of hepatic lipid accumulation as well as recovery of liver function in ob/ob mice with intraperitoneal injection of K145. Also, db/db mice received K145 showed improvement of both NALFD and hyperglycemia. We furtherly analyzed the genes associated with lipid metabolism and found a remarkable decreased expression of lipogenic genes including FAS, ACC1 and SREBP1c whereas elevated mitochondrial fatty acid ß-oxidation (FAO) related genes expression including CPT1A, MCAD, LCAD, PPAR-α, UCP2. Consistent to in vivo study, in vitro study also confirmed the role of K145 in decreasing lipid accumulation in human HL7702 cells, while inhibiting FAS, ACC1 and SREBP1c mRNA expression. It indicated a possible mechanism of K145 induced improvement of hepatic lipid accumulation partly via inhibition of lipigenesis. Our study suggested a promising role of K145 in drug development for NAFLD and diabetes therapy.

A Dansyl-Modified Sphingosine Kinase Inhibitor DPF-543 Enhanced De Novo Ceramide Generation.

Sphingosine-1-phosphate (S1P) synthesized by sphingosine kinase (SPHK) is a signaling molecule, involved in cell proliferation, growth, differentiation, and survival. Indeed, a sharp increase of S1P is linked to a pathological outcome with inflammation, cancer metastasis, or angiogenesis, etc. In this regard, SPHK/S1P axis regulation has been a specific issue in the anticancer strategy to turn accumulated sphingosine (SPN) into cytotoxic ceramides (Cers). For these purposes, there have been numerous chemicals synthesized for SPHK inhibition. In this study, we investigated the comparative efficiency of dansylated PF-543 (DPF-543) on the Cers synthesis along with PF-543. DPF-543 deserved attention in strong cytotoxicity, due to the cytotoxic Cers accumulation by ceramide synthase (CerSs). DPF-543 exhibited dual actions on Cers synthesis by enhancing serine palmitoyltransferase (SPT) activity, and by inhibiting SPHKs, which eventually induced an unusual environment with a high amount of 3-ketosphinganine and sphinganine (SPA). SPA in turn was consumed to synthesize Cers via de novo pathway. Interestingly, PF-543 increased only the SPN level, but not for SPA. In addition, DPF-543 mildly activates acid sphingomyelinase (aSMase), which contributes a partial increase in Cers. Collectively, a dansyl-modified DPF-543 relatively enhanced Cers accumulation via de novo pathway which was not observed in PF-543. Our results demonstrated that the structural modification on SPHK inhibitors is still an attractive anticancer strategy by regulating sphingolipid metabolism.

SPHK1 contributes to cisplatin resistance in bladder cancer cells via the NONO/STAT3 axis.

Sphingosine­1­phosphate (S1P) serves an important role in various physiological and pathophysiological processes, including the regulation of cell apoptosis, proliferation and survival. Sphingosine kinase 1 (SPHK1) is a lipid kinase that phosphorylates sphingosine to generate S1P. S1P has been proven to be positively correlated with chemotherapy resistance in breast cancer, colorectal carcinoma and non­small cell lung cancer. However, whether SPHK1 is involved in the development of cisplatin resistance remains to be elucidated. The present study aimed to identify the association between SPHK1 and chemoresistance in bladder cancer cells and to explore the therapeutic implications in patients with bladder cancer. Bladder cancer cell proliferation and apoptosis were determined using Cell Counting Kit­8 assays and flow cytometry, respectively. Apoptosis­related proteins were detected via western blotting. The results revealed that SPHK1 was positively correlated with cisplatin resistance in bladder cancer cells, exhibiting an antiapoptotic effect that was reflected by the downregulation of apoptosis­related proteins (Bax and cleaved caspase­3) and the upregulation of an antiapoptotic protein (Bcl­2) in SPHK1­overexpression cell lines. Suppression of SPHK1 by small interfering RNA or FTY­720 significantly reversed the antiapoptotic effect. A potential mechanism underlying SPHK1­induced cisplatin resistance and apoptosis inhibition may be activation of STAT3 via binding non­POU domain containing octamer binding. In conclusion, the present study suggested that SPHK1 displayed significant antiapoptotic effects in cisplatin­based treatment, thus may serve as a potential novel therapeutic target for the treatment for bladder cancer.

Mechanism of BIP-4 mediated inhibition of InsP3Kinase-A.

Overexpression of the neuronal InsP3kinase-A increases malignancy of different tumor types. Since InsP3kinase-A highly selectively binds Ins(1,4,5)P3, small molecules competing with Ins(1,4,5)P3 provide a promising approach for the therapeutic targeting of InsP3kinase-A. Based on this consideration, we analyzed the binding mechanism of BIP-4 (2-[3,5-dimethyl-1-(4-nitrophenyl)-1H-pyrazol-4-yl]-5, 8-dinitro-1H-benzo[de]isoquinoline-1,3(2H)-dione), a known competitive small-molecule inhibitor of Ins(1,4,5)P3. We tested a total of 80 BIP-4 related compounds in biochemical assays. The results of these experiments revealed that neither the nitrophenyl nor the benzisochinoline group inhibited InsP3kinase-A activity. Moreover, none of the BIP-4 related compounds competed for Ins(1,4,5)P3, demonstrating the high selectivity of BIP-4. To analyze the inhibition mechanism of BIP-4, mutagenesis experiments were performed. The results of these experiments suggest that the nitro groups attached to the benzisochinoline ring compete for binding of Ins(1,4,5)P3 while the nitrophenyl group is associated with amino acids of the ATP-binding pocket. Our results now offer the possibility to optimize BIP-4 to design specific InsP3Kinase-A inhibitors suitable for therapeutic targeting of the enzyme.

Sphingosine-1-phosphate modulates PAR1-mediated human platelet activation in a concentration-dependent biphasic manner.

Sphingosine 1-phosphate (S1P) is a bioactive signalling sphingolipid that is increased in diseases such as obesity and diabetes. S1P can modulate platelet function, however the direction of effect and S1P receptors (S1PRs) involved are controversial. Here we describe the role of S1P in regulating human platelet function and identify the receptor subtypes responsible for S1P priming. Human platelets were treated with protease-activated receptor 1 (PAR-1)-activating peptide in the presence or absence of S1P, S1PR agonists or antagonists, and sphingosine kinases inhibitors. S1P alone did not induce platelet aggregation but at low concentrations S1P enhanced PAR1-mediated platelet responses, whereas PAR1 responses were inhibited by high concentrations of S1P. This biphasic effect was mimicked by pan-S1PR agonists. Specific agonists revealed that S1PR1 receptor activation has a positive priming effect, S1PR2 and S1PR3 have no effect on platelet function, whereas S1PR4 and S1PR5 receptor activation have an inhibitory effect on PAR-1 mediated platelet function. Although platelets express both sphingosine kinase 1/2, enzymes which phosphorylate sphingosine to produce S1P, only dual and SphK2 inhibition reduced platelet function. These results support a role for SphK2-mediated S1P generation in concentration-dependent positive and negative priming of platelet function, through S1PR1 and S1PR4/5 receptors, respectively.

Blocking SphK1/S1P/S1PR1 Signaling Pathway Alleviates Lung Injury Caused by Sepsis in Acute Ethanol Intoxication Mice.

Acute ethanol intoxication increases the risk of sepsis and aggravates the symptoms of sepsis and lung injury. Therefore, this study aimed to explore whether sphingosine kinase 1 (SphK1)/sphingosine-1-phosphate (S1P)/S1P receptor 1 (S1PR1) signaling pathway functions in lung injury caused by acute ethanol intoxication-enhanced sepsis, as well as its underlying mechanism. The acute ethanol intoxication model was simulated by intraperitoneally administering mice with 32% ethanol solution, and cecal ligation and puncture (CLP) was used to construct the sepsis model. The lung tissue damage was observed by hematoxylin-eosin (H&E) staining, and the wet-to-dry (W/D) ratio was used to evaluate the degree of pulmonary edema. Inflammatory cell counting and protein concentration in bronchoalveolar lavage fluid (BALF) were, respectively, detected by hemocytometer and bicinchoninic acid (BCA) method. The levels of tumor necrosis factor (TNF)-α, interleukin (IL)-6, IL-1ß, and IL-18 in BALF were detected by their commercial enzyme-linked immunosorbent assay (ELISA) kits. The myeloperoxidase (MPO) activity and expression of apoptosis-related proteins and SphK1/S1P/S1PR1 pathway-related proteins were, respectively, analyzed by MPO ELISA kit and Western blot analysis. The cell apoptosis in lung tissues was observed by TUNEL assay. Acute ethanol intoxication (EtOH) decreased the survival rate of mice and exacerbated the lung injury caused by sepsis through increasing pulmonary vascular permeability, neutrophil infiltration, release of inflammatory factors, and cell apoptosis. In addition, EtOH could activate the SphK1/S1P/S1PR1 pathway in CLP mice. However, PF-543, as a specific inhibitor of SphK1, could partially reverse the deleterious effects on lung injury of CLP mice. PF-543 alleviated lung injury caused by sepsis in acute ethanol intoxication rats by suppressing the SphK1/S1P/S1PR1 signaling pathway.

Design, synthesis, and biological evaluation of novel benzimidazole derivatives as sphingosine kinase 1 inhibitor.

Sphingosine kinase 1 (SphK1) has emerged as an attractive drug target for different diseases. Recently, discovered SphK1 inhibitors have been recommended in cancer therapeutics; however, selectivity and potency are great challenges. In this study, a novel series of benzimidazoles was synthesized and evaluated as SphK1 inhibitors. Our design strategy is twofold: It aimed first to study the effect of replacing the 5-position of the benzimidazole ring with a polar carboxylic acid group on the SphK1-inhibitory activity and cytotoxicity. Our second aim was to optimize the structures of the benzimidazoles through the elongation of the chain. The enzyme inhibition potentials against all the synthesized compounds toward SphK1 were evaluated, and the results revealed that most of the studied compounds inhibited SphK1 effectively. The binding affinity of the benzimidazole derivatives toward SphK1 was measured by fluorescence binding and molecular docking. Compounds 33, 37, 39, 41, 42, 43, and 45 showed an appreciable binding affinity. Therefore, the SphK1-inhibitory potentials of compounds 33, 37, 39, 41, 42, 43, and 45 were studied and IC50 values were determined, to reveal high potency. The study showed that these compounds inhibited SphK1 with effective IC50 values. Among the studied compounds, compound 41 was the most effective one with the lowest IC50 value and a high cytotoxicity on a wide spectrum of cell lines. Molecular docking revealed that most of these compounds fit well into the ATP-binding site of SphK1 and form hydrogen bond interactions with catalytically important residues. Overall, the findings suggest the therapeutic potential of benzimidazoles in the clinical management of SphK1-associated diseases.

Sphingosine kinase inhibitor, SKI-II confers protection against the ionizing radiation by maintaining redox homeostasis most likely through Nrf2 signaling.

Exposure to ionizing radiation (IR) set a series of deleterious events causing acute radiation syndrome and mortality, posing the need for a potent and safe radio-protective drug. IR induces cell death predominantly by causing oxidative stress and macromolecular damage. The pre-existing antioxidant defence machinery of the cellular system plays a crucial role in protecting the cells against oxidative stress by activation of Nrf2. The current study was undertaken to investigate the radio-protective potential of sphingosine kinase inhibitor (SKI-II), which was demonstrated to activate Nrf2 signaling. The safety and efficacy of SKI-II were evaluated with cell cytotoxicity, proliferation index, and clonogenic survival assays in different cell lines, namely Raw 264.7, INT-407, IEC-6 and NIH/3T3 cell lines. A safe dose of SKI-II was found radio-protective in all the cell lines linked with the activated antioxidant defence system, thereby resulting in the amelioration of IR induced oxidative stress. SKI-II pretreatment also significantly reduced DNA damage, micronuclei expression, and accelerated DNA repair kinetics as compared to IR exposed cells. Reduced oxidative stress and enhanced DNA repair significantly reduced apoptosis and suppressed the pro-death signaling associated with IR exposure. Furthermore, the in-vitro observation was verified in the in-vivo model (C57 BL/6). The Intra-peritoneal (IP) administration of SKI-II, 2 h before a lethal dose of IR exposure (7.5 Gy) resulted in 75% survival. These results imply that SKI-II ameliorates IR-induced oxidative stress and cell death by inducing anti-oxidant defence system and DNA repair pathways, thus strengthening its potential to be used as radiation countermeasure.