Discovery and biological evaluation of biaryl acetamide derivatives as selective and in vivo active sphingosine kinase-2 inhibitors

Sphingosine kinase 2 (SphK2) has emerged as a promising target for cancer therapy due to its critical role in tumor growth. However, the lack of potent and selective inhibitors has hindered its clinical application. Herein, we report the design and synthesis of a series of novel SphK2 inhibitors, culminating in the identification of compound 12q as a highly selective and potent inhibitor of SphK2. Molecular dynamics simulations suggest that the incorporation of larger substitution groups facilitates a more effective occupation of the binding site, thereby stabilizing the complex. Compared to the widely used inhibitor ABC294640, compound 12q exhibits superior anti-proliferative activity against various cancer cells, inducing G2 phase arrest and apoptosis in liver cancer cells HepG2. Notably, 12q inhibited migration and colony formation in HepG2 and altered intracellular sphingolipid content. Moreover, intraperitoneal administration of 12q in mice resulted in decreased levels of S1P. 12q provides a valuable tool compound for exploring the therapeutic potential of targeting SphK2 in cancer.

A comprehensive measure of Golgi sphingolipid flux using NBD C6-ceramide: evaluation of sphingolipid inhibitors

Measurements of sphingolipid metabolism are most accurately performed by LC-MS. However, this technique is expensive, not widely accessible, and without the use of specific probes, it does not provide insight into metabolic flux through the pathway. Employing the fluorescent ceramide analogue NBD-C6-ceramide as a tracer in intact cells, we developed a comprehensive HPLC-based method that simultaneously measures the main nodes of ceramide metabolism in the Golgi. Hence, by quantifying the conversion of NBD-C6-ceramide to NBD-C6-sphingomyelin, NBD-C6-hexosylceramides, and NBD-C6-ceramide-1-phosphate (NBD-C1P), the activities of Golgi resident enzymes sphingomyelin synthase 1, glucosylceramide synthase, and ceramide kinase (CERK) could be measured simultaneously. Importantly, the detection of NBD-C1P allowed us to quantify CERK activity in cells, a usually difficult task. By applying this method, we evaluated the specificity of commonly used sphingolipid inhibitors and discovered that 1-phenyl-2-decanoylamino-3-morpholino-1-propanol, which targets glucosylceramide synthase, and fenretinide (4HPR), an inhibitor for dihydroceramide desaturase, also suppress CERK activity. This study demonstrates the benefit of an expanded analysis of ceramide metabolism in the Golgi, and it provides a qualitative and easy-to-implement method.

Sphingosine kinase 1-specific inhibitor PF543 reduces goblet cell metaplasia of bronchial epithelium in an acute asthma model

Sphingosine kinase 1 (SPHK1) has been shown to play a key role in the pathogenesis of asthma where SPHK1-generated sphingosine-1-phosphate (S1P) is known to mediate innate and adaptive immunity while promoting mast cell degranulation. Goblet cell metaplasia (GCM) contributes to airway obstruction in asthma and has been demonstrated in animal models. We investigated the role of PF543, a SPHK1-specific inhibitor, in preventing the pathogenesis of GCM using a murine (C57BL/6) model of allergen-induced acute asthma. Treatment with PF543 before triple allergen exposure (DRA: House dust mite, Ragweed pollen, and Aspergillus) reduced inflammation, eosinophilic response, and GCM followed by reduced airway hyperreactivity to intravenous methacholine. Furthermore, DRA exposure was associated with increased expression of SPHK1 in the airway epithelium which was reduced by PF543. DRA-induced reduction of acetylated α-tubulin in airway epithelium was associated with an increased expression of NOTCH2 and SPDEF which was prevented by PF543. In vitro studies using human primary airway epithelial cells showed that inhibition of SPHK1 using PF543 prevented an allergen-induced increase of both NOTCH2 and SPDEF. siRNA silencing of SPHK1 prevented the allergen-induced increase of both NOTCH2 and SPDEF. NOTCH2 silencing was associated with a reduction of SPDEF but not that of SPHK1 upon allergen exposure. Our studies demonstrate that inhibition of SPHK1 protected allergen-challenged airways by preventing GCM and airway hyperreactivity, associated with downregulation of the NOTCH2-SPDEF signaling pathway. This suggests a potential novel link between SPHK1, GCM, and airway remodeling in asthma.NEW & NOTEWORTHY The role of SPHK1-specific inhibitor, PF543, in preventing goblet cell metaplasia (GCM) and airway hyperreactivity (AHR) is established in an allergen-induced mouse model. This protection was associated with the downregulation of NOTCH2-SPDEF signaling pathway, suggesting a novel link between SPHK1, GCM, and AHR.

Second generation of pyrimidin-quinolone hybrids obtained from virtual screening acting as sphingosine kinase 1 inhibitors and potential anticancer agents

We report here the virtual screening design, synthesis and activity of eight new inhibitors of SphK1. For this study we used a pre-trained Graph Convolutional Network (GCN) combined with docking calculations. This exploratory analysis proposed nine compounds from which eight displayed significant inhibitory effect against sphingosine kinase 1 (SphK1) demonstrating a high level of efficacy for this approach. Four of these compounds also displayed anticancer activity against different tumor cell lines, and three of them (5), (6) and (7) have shown a wide inhibitory action against many of the cancer cell line tested, with GI50 below 5 µM, being (5) the most promising with TGI below 10 µM for the half of cell lines. Our results suggest that the three most promising compounds reported here are the pyrimidine-quinolone hybrids (1) and (6) linked by p-aminophenylsulfanyl and o-aminophenol fragments respectively, and (8) without such aryl linker. We also performed an exhaustive study about the molecular interactions that stabilize the different ligands at the binding site of SphK1. This molecular modeling analysis was carried out by using combined techniques: docking calculations, MD simulations and QTAIM analysis. In this study we also included PF543, as reference compound, in order to better understand the molecular behavior of these ligands at the binding site of SphK1.These results provide useful information for the design of new inhibitors of SphK1 possessing these structural scaffolds.

The shifting lipidomic landscape of blood monocytes and neutrophils during pneumonia

The lipidome of immune cells during infection has remained unexplored, although evidence of the importance of lipids in the context of immunity is mounting. In this study, we performed untargeted lipidomic analysis of blood monocytes and neutrophils from patients hospitalized for pneumonia and age- and sex-matched noninfectious control volunteers. We annotated 521 and 706 lipids in monocytes and neutrophils, respectively, which were normalized to an extensive set of internal standards per lipid class. The cellular lipidomes were profoundly altered in patients, with both common and distinct changes between the cell types. Changes involved every level of the cellular lipidome: differential lipid species, class-wide shifts, and altered saturation patterns. Overall, differential lipids were mainly less abundant in monocytes and more abundant in neutrophils from patients. One month after hospital admission, lipidomic changes were fully resolved in monocytes and partially in neutrophils. Integration of lipidomic and concurrently collected transcriptomic data highlighted altered sphingolipid metabolism in both cell types. Inhibition of ceramide and sphingosine-1-phosphate synthesis in healthy monocytes and neutrophils resulted in blunted cytokine responses upon stimulation with lipopolysaccharide. These data reveal major lipidomic remodeling in immune cells during infection, and link the cellular lipidome to immune functionality.

Therapeutic Potential for Sphingolipids in Inflammatory Bowel Disease and Colorectal Cancer

Inflammatory bowel disease (IBD), characterized by chronic inflammation in the intestinal tract, increases the risk for the development of colorectal cancer (CRC). Sphingolipids, which have been implicated in IBD and CRC, are a class of bioactive lipids that regulate cell signaling, differentiation, apoptosis, inflammation, and survival. The balance between ceramide (Cer), the central sphingolipid involved in apoptosis and differentiation, and sphingosine-1-phosphate (S1P), a potent signaling molecule involved in proliferation and inflammation, is vital for the maintenance of normal cellular function. Altered sphingolipid metabolism has been implicated in IBD and CRC, with many studies highlighting the importance of S1P in inflammatory signaling and pro-survival pathways. A myriad of sphingolipid analogues, inhibitors, and modulators have been developed to target the sphingolipid metabolic pathway. In this review, the efficacy and therapeutic potential for modulation of sphingolipid metabolism in IBD and CRC will be discussed.

Fanning the Flames of Endoplasmic Reticulum (ER) Stress: Can Sphingolipid Metabolism Be Targeted to Enhance ER Stress-Associated Immunogenic Cell Death in Cancer?

The three arms of the unfolded protein response (UPR) surveil the luminal environment of the endoplasmic reticulum (ER) and transmit information through the lipid bilayer to the cytoplasm to alert the cell of stress conditions within the ER lumen. That same lipid bilayer is the site of de novo synthesis of phospholipids and sphingolipids. Thus, it is no surprise that lipids are modulated by and are modulators of ER stress. Given that sphingolipids have both prosurvival and proapoptotic effects, they also exert opposing effects on life/death decisions in the face of prolonged ER stress detected by the UPR. In this review, we will focus on several recent studies that demonstrate how sphingolipids affect each arm of the UPR. We will also discuss the role of sphingolipids in the process of immunogenic cell death downstream of the protein kinase RNA-like endoplasmic reticulum kinase (PERK)/eukaryotic initiating factor 2α (eIF2α) arm of the UPR. Furthermore, we will discuss strategies to target the sphingolipid metabolic pathway that could potentially act synergistically with agents that induce ER stress as novel anticancer treatments. SIGNIFICANCE STATEMENT: This review provides the readers with a brief discussion of the sphingolipid metabolic pathway and the unfolded protein response. The primary focus of the review is the mechanism(s) by which sphingolipids modulate the endoplasmic reticulum (ER) stress response pathways and the critical role of sphingolipids in the process of immunogenic cell death associated with the ER stress response.

Targeting the SphK1/S1P/PFKFB3 axis suppresses hepatocellular carcinoma progression by disrupting glycolytic energy supply that drives tumor angiogenesis

BACKGROUND

Hepatocellular carcinoma (HCC) remains a leading life-threatening health challenge worldwide, with pressing needs for novel therapeutic strategies. Sphingosine kinase 1 (SphK1), a well-established pro-cancer enzyme, is aberrantly overexpressed in a multitude of malignancies, including HCC. Our previous research has shown that genetic ablation of Sphk1 mitigates HCC progression in mice. Therefore, the development of PF-543, a highly selective SphK1 inhibitor, opens a new avenue for HCC treatment. However, the anti-cancer efficacy of PF-543 has not yet been investigated in primary cancer models in vivo, thereby limiting its further translation.

METHODS

Building upon the identification of the active form of SphK1 as a viable therapeutic target in human HCC specimens, we assessed the capacity of PF-543 in suppressing tumor progression using a diethylnitrosamine-induced mouse model of primary HCC. We further delineated its underlying mechanisms in both HCC and endothelial cells. Key findings were validated in Sphk1 knockout mice and lentiviral-mediated SphK1 knockdown cells.

RESULTS

SphK1 activity was found to be elevated in human HCC tissues. Administration of PF-543 effectively abrogated hepatic SphK1 activity and significantly suppressed HCC progression in diethylnitrosamine-treated mice. The primary mechanism of action was through the inhibition of tumor neovascularization, as PF-543 disrupted endothelial cell angiogenesis even in a pro-angiogenic milieu. Mechanistically, PF-543 induced proteasomal degradation of the critical glycolytic enzyme 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 3, thus restricting the energy supply essential for tumor angiogenesis. These effects of PF-543 could be reversed upon S1P supplementation in an S1P receptor-dependent manner.

CONCLUSIONS

This study provides the first in vivo evidence supporting the potential of PF-543 as an effective anti-HCC agent. It also uncovers previously undescribed links between the pro-cancer, pro-angiogenic and pro-glycolytic roles of the SphK1/S1P/S1P receptor axis. Importantly, unlike conventional anti-HCC drugs that target individual pro-angiogenic drivers, PF-543 impairs the PFKFB3-dictated glycolytic energy engine that fuels tumor angiogenesis, representing a novel and potentially safer therapeutic strategy for HCC.

Mysterious sphingolipids: metabolic interrelationships at the center of pathophysiology

Metabolic pathways are complex and intertwined. Deficiencies in one or more enzymes in a given pathway are directly linked with genetic diseases, most of them having devastating manifestations. The metabolic pathways undertaken by sphingolipids are diverse and elaborate with ceramide species serving as the hubs of sphingolipid intermediary metabolism and function. Sphingolipids are bioactive lipids that serve a multitude of cellular functions. Being pleiotropic in function, deficiency or overproduction of certain sphingolipids is associated with many genetic and chronic diseases. In this up-to-date review article, we strive to gather recent scientific evidence about sphingolipid metabolism, its enzymes, and regulation. We shed light on the importance of sphingolipid metabolism in a variety of genetic diseases and in nervous and immune system ailments. This is a comprehensive review of the state of the field of sphingolipid biochemistry.

Opaganib (ABC294640) Induces Immunogenic Tumor Cell Death and Enhances Checkpoint Antibody Therapy

Antibody-based cancer drugs that target the checkpoint proteins CTLA-4, PD-1 and PD-L1 provide marked improvement in some patients with deadly diseases such as lung cancer and melanoma. However, most patients are either unresponsive or relapse following an initial response, underscoring the need for further improvement in immunotherapy. Certain drugs induce immunogenic cell death (ICD) in tumor cells in which the dying cells promote immunologic responses in the host that may enhance the in vivo activity of checkpoint antibodies. Sphingolipid metabolism is a key pathway in cancer biology, in which ceramides and sphingosine 1-phosphate (S1P) regulate tumor cell death, proliferation and drug resistance, as well as host inflammation and immunity. In particular, sphingosine kinases are key sites for manipulation of the ceramide/S1P balance that regulates tumor cell proliferation and sensitivity to radiation and chemotherapy. We and others have demonstrated that inhibition of sphingosine kinase-2 by the small-molecule investigational drug opaganib (formerly ABC294640) kills tumor cells and increases their sensitivities to other drugs and radiation. Because sphingolipids have been shown to regulate ICD, opaganib may induce ICD and improve the efficacy of checkpoint antibodies for cancer therapy. This was demonstrated by showing that in vitro treatment with opaganib increases the surface expression of the ICD marker calreticulin on a variety of tumor cell types. In vivo confirmation was achieved using the gold standard immunization assay in which B16 melanoma, Lewis lung carcinoma (LLC) or Neuro-2a neuroblastoma cells were treated with opaganib in vitro and then injected subcutaneously into syngeneic mice, followed by implantation of untreated tumor cells 7 days later. In all cases, immunization with opaganib-treated cells strongly suppressed the growth of subsequently injected tumor cells. Interestingly, opaganib treatment induced crossover immunity in that opaganib-treated B16 cells suppressed the growth of both untreated B16 and LLC cells and opaganib-treated LLC cells inhibited the growth of both untreated LLC and B16 cells. Next, the effects of opaganib in combination with a checkpoint antibody on tumor growth in vivo were assessed. Opaganib and anti-PD-1 antibody each slowed the growth of B16 tumors and improved mouse survival, while the combination of opaganib plus anti-PD-1 strongly suppressed tumor growth and improved survival (p < 0.0001). Individually, opaganib and anti-CTLA-4 antibody had modest effects on the growth of LLC tumors and mouse survival, whereas the combination of opaganib with anti-CTLA-4 substantially inhibited tumor growth and increased survival (p < 0.001). Finally, the survival of mice bearing B16 tumors was only marginally improved by opaganib or anti-PD-L1 antibody alone but was nearly doubled by the drugs in combination (p < 0.005). Overall, these studies demonstrate the ability of opaganib to induce ICD in tumor cells, which improves the antitumor activity of checkpoint antibodies.

Sphingosine kinase 1 is involved in triglyceride breakdown by maintaining lysosomal integrity in brown adipocytes

Sphingosine 1-phosphate (S1P) has been implicated in brown adipose tissue (BAT) formation and energy consumption; however, the mechanistic role of sphingolipids, including S1P, in BAT remains unclear. Here, we showed that, in mice, BAT activation by cold exposure upregulated mRNA and protein expression of the S1P-synthesizing enzyme sphingosine kinase 1 (SphK1) and S1P production in BAT. Treatment of wild-type brown adipocytes with exogenous S1P or S1P receptor subtype-selective agonists stimulated triglyceride (TG) breakdown only marginally, compared with noradrenaline. However, genetic deletion of Sphk1 resulted in hypothermia and diminished body weight loss upon cold exposure, suggesting that SphK1 is involved in thermogenesis through mechanisms different from receptor-mediated, extracellular action of S1P. In BAT of wild-type mice, SphK1 was localized largely in the lysosomes of brown adipocytes. In the brown adipocytes of Sphk1-/- mice, the number of lysosomes was reduced and lysosomal function, including proteolytic activity, acid esterase activity, and motility, was impaired. Concordantly, nuclear translocation of transcription factor EB, a master transcriptional regulator of lysosome biogenesis, was reduced, leading to decreased mRNA expression of the lysosome-related genes in Sphk1-/- BAT. Moreover, BAT of Sphk1-/- mice showed greater TG accumulation with dominant larger lipid droplets in brown adipocytes. Inhibition of lysosomes with chloroquine resulted in a less extent of triglyceride accumulation in Sphk1-/- brown adipocytes compared with wild-type brown adipocytes, suggesting a reduced lysosome-mediated TG breakdown in Sphk1-/- mice. Our results indicate a novel role of SphK1 in lysosomal integrity, which is required for TG breakdown and thermogenesis in BAT.

Sphingosine kinase 1/S1P receptor signaling axis is essential for cellular uptake of Neisseria meningitidis in brain endothelial cells

Invasion of brain endothelial cells (BECs) is central to the pathogenicity of Neisseria meningitidis infection. Here, we established a key role for the bioactive sphingolipid sphingosine-1-phosphate (S1P) and S1P receptor (S1PR) 2 in the uptake process. Quantitative sphingolipidome analyses of BECs infected with N. meningitidis revealed elevated S1P levels, which could be attributed to enhanced expression of the enzyme sphingosine kinase 1 and its activity. Increased activity was dependent on the interaction of meningococcal type IV pilus with the endothelial receptor CD147. Concurrently, infection led to increased expression of the S1PR2. Blocking S1PR2 signaling impaired epidermal growth factor receptor (EGFR) phosphorylation, which has been shown to be involved in cytoskeletal remodeling and bacterial endocytosis. Strikingly, targeting S1PR1 or S1PR3 also interfered with bacterial uptake. Collectively, our data support a critical role of the SphK/S1P/S1PR axis in the invasion of N. meningitidis into BECs, defining a potential target for adjuvant therapy.

Sphingosine 1-phosphate signaling during infection and immunity

Sphingolipids are essential components of all eukaryotic membranes. The bioactive sphingolipid molecule, Sphingosine 1-Phosphate (S1P), regulates various important biological functions. This review aims to provide a comprehensive overview of the role of S1P signaling pathway in various immune cell functions under different pathophysiological conditions including bacterial and viral infections, autoimmune disorders, inflammation, and cancer. We covered the aspects of S1P pathways in NOD/TLR pathways, bacterial and viral infections, autoimmune disorders, and tumor immunology. This implies that targeting S1P signaling can be used as a strategy to block these pathologies. Our current understanding of targeting various components of S1P signaling for therapeutic purposes and the present status of S1P pathway inhibitors or modulators in disease conditions where the host immune system plays a pivotal role is the primary focus of this review.

Targeting sphingosine kinase 1 in p53KO thymic lymphoma

Sphingosine kinase 1 (SK1) is a key sphingolipid enzyme that is upregulated in several types of cancer, including lymphoma which is a heterogenous group of malignancies. Treatment for lymphoma has improved significantly by the introduction of new therapies; however, subtypes with tumor protein P53 (p53) mutations or deletion have poor prognosis, making it critical to explore new therapeutic strategies in this context. SK1 has been proposed as a therapeutic target in different types of cancer; however, the effect of targeting SK1 in cancers with p53 deletion has not been evaluated yet. Previous work from our group suggests that loss of SK1 is a key event in mediating the tumor suppressive effect of p53. Employing both genetic and pharmacological approaches to inhibit SK1 function in Trp53KO mice, we show that targeting SK1 decreases tumor growth of established p53KO thymic lymphoma. Inducible deletion of Sphk1 or its pharmacological inhibition drive increased cell death in tumors which is accompanied by selective accumulation of sphingosine levels. These results demonstrate the relevance of SK1 in the growth and maintenance of lymphoma in the absence of p53 function, positioning this enzyme as a potential therapeutic target for the treatment of tumors that lack functional p53.

Integrative roles of sphingosine kinase in liver pathophysiology

Bioactive sphingolipids and enzymes that metabolize sphingolipid-related substances have been considered as critical messengers in various signaling pathways. One such enzyme is the crucial lipid kinase, sphingosine kinase (SphK), which mediates the conversion of sphingosine to the potent signaling substance, sphingosine-1-phosphate. Several studies have demonstrated that SphK metabolism is strictly regulated to maintain the homeostatic balance of cells. Here, we summarize the role of SphK in the course of liver disease and illustrate its effects on both physiological and pathological conditions of the liver. SphK has been implicated in a variety of liver diseases, such as steatosis, liver fibrosis, hepatocellular carcinoma, and hepatic failure. This study may advance the understanding of the cellular and molecular foundations of liver disease and establish therapeutic approaches via SphK modulation.

PF543-like compound, a promising sphingosine kinase 1 inhibitor: Structure-based virtual screening and molecular dynamic simulation approaches

Sphingosine kinase 1 (SphK1) has been widely recognized as a significant contributor to various types of cancer, including breast, lung, prostate, and hematological cancers. This research aimed to find a potential SphK1 inhibitor through a step-by-step virtual screening of PF543 (a known SphK1 inhibitor)-like compounds obtained from the PubChem library with the Tanimoto threshold of 80 %. The virtual screening process included several steps, namely physicochemical and ADMET evaluation, PAINS filtering, and molecular docking, followed by molecular dynamics (MD) simulation and principal component analysis (PCA). The results showed that compound CID:58293960 ((3R)-1,1-dioxo-2-[[3-[(4-phenylphenoxy)methyl]phenyl]methyl]-1,2-thiazolidine-3-carboxylic acid) demonstrated high potential as SphK1 inhibitor. All-atom MD simulations were performed for 100 ns to evaluate the stability and structural changes of the docked complexes in an aqueous environment. The analysis of the time evolution data of structural deviations, compactness, PCA, and free energy landscape (FEL) indicated that the binding of CID:58293960 with SphK1 is relatively stable throughout the simulation. The results of this study provide a platform for the discovery and development of new anticancer therapeutics targeting SphK1.

Therapeutic potential of the sphingosine kinase 1 inhibitor, PF-543

PF-543 is a sphingosine kinase 1（SPHK1）inhibitor developed by Pfizer and is currently considered the most potent selective SPHK1 inhibitor. SPHK1 catalyses the production of sphingosine 1-phosphate (S1P) from sphingosine. It is the rate-limiting enzyme of S1P production, and there is substantial evidence to support a very important role for sphingosine kinase in health and disease. This review is the first to summarize the role and mechanisms of PF-543 as an SPHK1 inhibitor in anticancer, antifibrotic, and anti-inflammatory processes, providing new therapeutic leads and ideas for future research and clinical trials.

Sphingosine Kinases Promote Ebola Virus Infection and Can Be Targeted to Inhibit Filoviruses, Coronaviruses, and Arenaviruses Using Late Endocytic Trafficking to Enter Cells

Entry of enveloped viruses in host cells requires the fusion of viral and host cell membranes, a process that is facilitated by viral fusion proteins protruding from the viral envelope. These viral fusion proteins need to be triggered by host factors, and for some viruses, this event occurs inside endosomes and/or lysosomes. Consequently, these 'late-penetrating viruses' must be internalized and delivered to entry-conducive intracellular vesicles. Because endocytosis and vesicular trafficking are tightly regulated cellular processes, late-penetrating viruses also depend on specific host proteins for efficient delivery to the site of fusion, suggesting that these could be targeted for antiviral therapy. In this study, we investigated a role for sphingosine kinases (SKs) in viral entry and found that chemical inhibition of sphingosine kinase 1 (SK1) and/or SK2 and knockdown of SK1/2 inhibited entry of Ebola virus (EBOV) into host cells. Mechanistically, inhibition of SK1/2 prevented EBOV from reaching late-endosomes and lysosomes that contain the EBOV receptor, Niemann Pick C1 (NPC1). Furthermore, we present evidence that suggests that the trafficking defect caused by SK1/2 inhibition occurs independently of sphingosine-1-phosphate (S1P) signaling through cell-surface S1P receptors. Lastly, we found that chemical inhibition of SK1/2 prevents entry of other late-penetrating viruses, including arenaviruses and coronaviruses, and inhibits infection by replication-competent EBOV and SARS-CoV-2 in Huh7.5 cells. In sum, our results highlight an important role played by SK1/2 in endocytic trafficking, which can be targeted to inhibit entry of late-penetrating viruses and could serve as a starting point for the development of broad-spectrum antiviral therapeutics.

Host-Erythrocytic Sphingosine-1-Phosphate Regulates Plasmodium Histone Deacetylase Activity and Exhibits Epigenetic Control over Cell Death and Differentiation

The evolution of resistance to practically all antimalarial drugs poses a challenge to the current malaria elimination and eradication efforts. Given that the epigenome of Plasmodium falciparum governs several crucial parasite functions, pharmaceutical interventions with transmission-blocking potential that target epigenetic molecular markers and regulatory mechanisms are likely to encounter drug resistance. In the malaria parasite, histone deacetylases (HDACs) are essential epigenetic modulators that regulate cellular transcriptional rearrangements, notably the molecular mechanisms underlying parasite proliferation and differentiation. We establish "lipid sequestration" as a mechanism by which sphingolipids, specifically Sphingosine-1-Phosphate (S1P) (a metabolic product of Sphingosine Kinase 1 [SphK-1]), regulate epigenetic reprogramming in the parasite by interacting with, and modulating, the histone-deacetylation activity of PfHDAC-1, thereby regulating Plasmodium pathogenesis. Furthermore, we demonstrate that altering host S1P levels with PF-543, a potent and selective Sphk-1 inhibitor, dysregulates PfHDAC-1 activity, resulting in a significant increase in the global histone acetylation signals and, consequently, transcriptional modulation of genes associated with gametocytogenesis, virulence, and proliferation. Our findings point to a hitherto unrecognized functional role for host S1P-mediated sphingolipid signaling in modulating PfHDAC-1's enzymatic activity and, as a result, the parasite's dynamic genome-wide transcriptional patterns. The epigenetic regulation of parasite proliferation and sexual differentiation offers a novel approach for developing host-targeted therapeutics to combat malaria resistance to conventional regimens. IMPORTANCE Sphingolipid is an 18-carbon amino-alcohol-containing lipid with a sphingosine backbone, which when phosphorylated by sphingosine kinase 1 (SphK-1), generates sphingosine-1-phosphate (S1P), an essential lipid signaling molecule. Dysregulation of S1P function has been observed in a variety of pathologies, including severe malaria. The malaria parasite Plasmodium acquires a host S1P pool for its growth and survival. Here, we describe the molecular attuning of histone deacetylase-1 (PfHDAC-1), a crucial epigenetic modulator that contributes to the establishment of epigenetic chromatin states and parasite survival, in response to S1P binding. Our findings highlight the host lipid-mediated epigenetic regulation of malaria parasite key genes.

FTY720 Reduces Lipid Accumulation by Upregulating ABCA1 through Liver X Receptor and Sphingosine Kinase 2 Signaling in Macrophages

Formation of foam cells as a result of excess lipid accumulation by macrophages is a pathological hallmark of atherosclerosis. Fingolimod (FTY720) is an immunosuppressive agent used in clinical settings for the treatment of multiple sclerosis and has been reported to inhibit atherosclerotic plaque development. However, little is known about the effect of FTY720 on lipid accumulation leading to foam cell formation. In this study, we investigated the effects of FTY720 on lipid accumulation in murine macrophages. FTY720 treatment reduced lipid droplet formation and increased the expression of ATP-binding cassette transporter A1 (ABCA1) in J774 mouse macrophages. FTY720 also enhanced the expression of liver X receptor (LXR) target genes such as FASN, APOE, and ABCG1. In addition, FTY720-induced upregulation of ABCA1 was abolished by knockdown of sphingosine kinase 2 (SphK2) expression. Furthermore, we found that FTY720 treatment induced histone H3 lysine 9 (H3K9) acetylation, which was lost in SphK2-knockdown cells. Taken together, FTY720 induces ABCA1 expression through SphK2-mediated acetylation of H3K9 and suppresses lipid accumulation in macrophages, which provides novel insights into the mechanisms of action of FTY720 on atherosclerosis.

Pathogenic Role of the Sphingosine 1-Phosphate (S1P) Pathway in Common Gynecologic Disorders (GDs): A Possible Novel Therapeutic Target

Sphingosine 1-phosphate (S1P) is a bioactive sphingolipid, noteworthy for its involvement both in the modulation of various biological processes and in the development of many diseases. S1P signaling can be either pro or anti-inflammatory, and the sphingosine kinase (SphK)–S1P–S1P receptor (S1PR) axis is a factor in accelerating the growth of several cells, including endometriotic cells and fibrosis. Gynecologic disorders, including endometriosis, adenomyosis, and uterine fibroids are characterized by inflammation and fibrosis. S1P signaling and metabolism have been shown to be dysregulated in those disorders and they are likely implicated in their pathogenesis and pathophysiology. Enzymes responsible for inactivating S1P are the most affected by the dysregulation of S1P balanced levels, thus causing accumulation of sphingolipids within these cells and tissues. The present review highlights the past and latest evidence on the role played by the S1P pathways in common gynecologic disorders (GDs). Furthermore, it discusses potential future approaches in the regulation of this signaling pathway that could represent an innovative and promising therapeutical target, also for ovarian cancer treatment.

S1P/S1PR1 signaling differentially regulates the allogeneic response of CD4 and CD8 T cells by modulating mitochondrial fission

Graft-versus-host disease (GVHD) significantly contributes to patient morbidity and mortality after allogeneic hematopoietic cell transplantation (allo-HSCT). Sphingosine-1-phosphate (S1P) signaling is involved in the biogenetic processes of different immune cells. In the current study, we demonstrated that recipient sphingosine kinase 1 (Sphk1), but not Sphk2, was required for optimal S1PR1-dependent donor T-cell allogeneic responses by secreting S1P. Using genetic and pharmacologic approaches, we demonstrated that inhibition of Sphk1 or S1PR1 substantially attenuated acute GVHD (aGVHD) while retaining the graft-versus-leukemia (GVL) effect. At the cellular level, the Sphk1/S1P/S1PR1 pathway differentially modulated the alloreactivity of CD4+ and CD8+ T cells; it facilitated T-cell differentiation into Th1/Th17 cells but not Tregs and promoted CD4+ T-cell infiltration into GVHD target organs but was dispensable for the CTL activity of allogeneic CD8+ T cells. At the molecular level, the Sphk1/S1P/S1PR1 pathway augmented mitochondrial fission and increased mitochondrial mass in allogeneic CD4+ but not CD8+ T cells by activating the AMPK/AKT/mTOR/Drp1 pathway, providing a mechanistic basis for GVL maintenance when S1P signaling was inhibited. For translational purposes, we detected the regulatory efficacy of pharmacologic inhibitors of Sphk1 and S1PR1 in GVHD induced by human T cells in a xenograft model. Our study provides novel mechanistic insight into how the Sphk1/S1P/S1PR1 pathway modulates T-cell alloreactivity and validates Sphk1 or S1PR1 as a therapeutic target for the prevention of GVHD and leukemia relapse. This novel strategy may be readily translated into the clinic to benefit patients with hematologic malignancies and disorders.

S1P/S1PR1 signaling differentially regulates the allogeneic response of CD4 and CD8 T cells by modulating mitochondrial fission

Graft-versus-host disease (GVHD) significantly contributes to patient morbidity and mortality after allogeneic hematopoietic cell transplantation (allo-HSCT). Sphingosine-1-phosphate (S1P) signaling is involved in the biogenetic processes of different immune cells. In the current study, we demonstrated that recipient sphingosine kinase 1 (Sphk1), but not Sphk2, was required for optimal S1PR1-dependent donor T-cell allogeneic responses by secreting S1P. Using genetic and pharmacologic approaches, we demonstrated that inhibition of Sphk1 or S1PR1 substantially attenuated acute GVHD (aGVHD) while retaining the graft-versus-leukemia (GVL) effect. At the cellular level, the Sphk1/S1P/S1PR1 pathway differentially modulated the alloreactivity of CD4⁺ and CD8⁺ T cells; it facilitated T-cell differentiation into Th1/Th17 cells but not Tregs and promoted CD4⁺ T-cell infiltration into GVHD target organs but was dispensable for the CTL activity of allogeneic CD8⁺ T cells. At the molecular level, the Sphk1/S1P/S1PR1 pathway augmented mitochondrial fission and increased mitochondrial mass in allogeneic CD4⁺ but not CD8⁺ T cells by activating the AMPK/AKT/mTOR/Drp1 pathway, providing a mechanistic basis for GVL maintenance when S1P signaling was inhibited. For translational purposes, we detected the regulatory efficacy of pharmacologic inhibitors of Sphk1 and S1PR1 in GVHD induced by human T cells in a xenograft model. Our study provides novel mechanistic insight into how the Sphk1/S1P/S1PR1 pathway modulates T-cell alloreactivity and validates Sphk1 or S1PR1 as a therapeutic target for the prevention of GVHD and leukemia relapse. This novel strategy may be readily translated into the clinic to benefit patients with hematologic malignancies and disorders.

Regulatory Role of Sphingosine-1-Phosphate and C16:0 Ceramide, in Immunogenic Cell Death of Colon Cancer Cells Induced by Bak/Bax-Activation

We recently identified the sphingosine kinases (SphK1/2) as key intracellular regulators of immunogenic cell death (ICD) in colorectal cancer (CRC) cells. To better understand the mechanism by which SphK inhibition enhances ICD, we focused on the intracellular signaling pathways leading to cell surface exposure of calreticulin (ectoCRT). Herein, we demonstrate that ABT-263 and AZD-5991, inhibitors of Bcl-2/Bcl-XL and Mcl-1, respectively, induce the production of ectoCRT, indicative of ICD. Inhibition of SphK1 significantly enhanced ABT/AZD-induced ectoCRT production, in a caspase 8-dependent manner. Mechanistically, we demonstrate that ABT/AZD-induced Bak/Bax activation stimulates pro-survival SphK1/sphingosine-1-phosphate (S1P) signaling, which attenuates ectoCRT production. Additionally, we identified a regulatory role for ceramide synthase 6 (CerS6)/C16:0 ceramide in transporting of ectoCRT to the cell surface. Together, these results indicate that the sphingolipid metabolic regulators of the sphingolipid rheostat, S1P and C16:0 ceramide, influence survival/death decisions of CRC cells in response to ICD-inducing chemotherapeutic agents. Importantly, SphK1, which produces S1P, is a stress-responsive pro-survival lipid kinase that suppresses ICD. While ceramide, produced by the inhibition of SphK1 is required for production of the cell surface marker of ICD, ectoCRT. Thus, inhibition of SphK1 represents a means to enhance the therapeutic efficacy of ICD-inducing agents.

Monolithic Silica Microbands Enable Thin-Layer Chromatography Analysis of Single Cells

A picoliter thin-layer chromatography (pTLC) platform was developed for analyzing extremely miniature specimens, such as assay of the contents of a single cell of 1 picoliter volume. The pTLC chip consisted of an array of microscale bands made from highly porous monolithic silica designed to accept picoliter-scale volume samples. pTLC bands were fabricated by combining sol-gel chemistry and microfabrication technology. The width (60-80 μm) and depth (13 μm) of each band is comparable to the size of single cells and acted to reduce the lateral diffusion and confine the movement of compounds along the microbands. Ultrasmall volumes (tens of pL) of model fluorescent compounds were spotted onto the microband by a piezoelectric microdispenser and successfully separated by pTLC. The separation resolution and analyte migration were dependent on the macropore size (ranging from 0.3 to 2.3 μm), which was adjustable by changing the porogen concentration during the sol-gel process. For a 0.3 μm macropore size, attomoles of analyte were detectable by fluorescence using standard microscopy methods. The separation resolution, theoretical plate number, and separation times ranged from 1.3 to 2.1, 4 to 357, and 2 to 8 min, respectively, for the chosen model biological lipids. To demonstrate the capability of pTLC for separating analytes from single mammalian cells, cells loaded with fluorescent lipophilic dyes or sphingosine kinase reporter were spotted on microbands, and the single-cell contents separated by pTLC were detected from their fluorescence. These results demonstrate the potential of pTLC for applications in many areas where miniature specimens and high-throughput parallel analyses are needed.

Geniposide inhibits SphK1 membrane targeting to restore macrophage polarization balance in collagen-induced arthritis mice

Imbalance of macrophage polarization plays a critical role in the progression of rheumatoid arthritis (RA). Geniposide (GE) has been shown to exert anti-inflammatory effects. However, the effect of GE on macrophage polarization remains unclear. Here, we investigated the regulation of GE on the imbalance of macrophage polarization in RA and how it functions. We established a mouse model of collagen-induced arthritis (CIA) and isolated bone marrow-derived macrophages (BMDMs). The results confirmed that pro-inflammatory M1 macrophages were dominant in CIA mice, but the polarization imbalance of macrophages was restored to a certain extent after GE treatment. Furthermore, the membrane targeting of sphingosine kinase 1 (SphK1) was increased in BMDMs of CIA mice, as manifested by increased membrane and cytoplasmic expression of p-SphK1 and high secretion level of sphingosine-1-phosphate (S1P). RAW264.7 cells were stimulated with lipopolysaccharide (LPS)-interferon (IFN)-γ or interleukin (IL)-4 to induce M1 or M2 phenotype, respectively, to revalidate the results obtained in BMDMs. The results again observed SphK1 membrane targeting in LPS-IFN-γ-stimulated RAW264.7 cells. Selective inhibition of SphK1 by PF543 or inhibition of the S1P receptors by FTY720 both restored the proportion of M1 and M2 macrophages in LPS-IFN-γ-stimulated RAW264.7 cells, confirming that SphK1 membrane targeting mediated a proportional imbalance in M1 and M2 macrophage polarization. In addition, GE inhibited SphK1 membrane targeting and kinase activity. Taken together, results confirmed that the inhibition of SphK1 membrane targeting by GE was responsible for restoring the polarization balance of macrophages in CIA mice.

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 of PP2A-Activating PF-543 Derivatives and Investigation of Their Inhibitory Effects on Pancreatic Cancer Cells

Sphingosine kinase (SK) is involved in the growth of cells, including cancer cells. However, which of its two isotypes—SK1 and SK2—is more favorable for cancer growth remains unclear. Although PF-543 strongly and selectively inhibits SK1, its anticancer effect is not high, and the underlying reason remains difficult to explain. We previously determined that the tail group of PF-543 is responsible for its low metabolic stability (MS). In this study, compounds containing aromatic or aliphatic tails in the triazole group were synthesized, and changes in the SK-inhibitory effect and anticancer activity of PF-543 were assessed using pancreatic cancer cells. The compounds with aliphatic tails showed high inhibitory effects on pancreatic cancer cells but slightly lower selectivity for SK1. A compound with an introduced aliphatic tail activated protein phosphatase 2A (PP2A), showing an effect similar to that of FTY720. Molecular docking analysis revealed that the PP2A-binding form of this newly synthesized compound was different from that noted in the case of FTY720. This compound also improved the MS of PF-543. These results indicate that the tail structure of PF-543 influences MS.

Targeting Sphingolipid Metabolism as a Therapeutic Strategy in Cancer Treatment

Sphingolipids are bioactive molecules that have key roles in regulating tumor cell death and survival through, in part, the functional roles of ceramide accumulation and sphingosine-1-phosphate (S1P) production, respectively. Mechanistic studies using cell lines, mouse models, or human tumors have revealed crucial roles of sphingolipid metabolic signaling in regulating tumor progression in response to anticancer therapy. Specifically, studies to understand ceramide and S1P production pathways with their downstream targets have provided novel therapeutic strategies for cancer treatment. In this review, we present recent evidence of the critical roles of sphingolipids and their metabolic enzymes in regulating tumor progression via mechanisms involving cell death or survival. The roles of S1P in enabling tumor growth/metastasis and conferring cancer resistance to existing therapeutics are also highlighted. Additionally, using the publicly available transcriptomic database, we assess the prognostic values of key sphingolipid enzymes on the overall survival of patients with different malignancies and present studies that highlight their clinical implications for anticancer treatment.

Ceramide-induced integrated stress response overcomes Bcl-2 inhibitor resistance in acute myeloid leukemia

Enhancing cellular ceramide levels in AML activates protein kinase R to induce the integrated stress response.

The ISR induces the BH3-only protein Noxa, causing degradation of Mcl-1 and sensitization of AML to Bcl-2 inhibition.

Inducing cell death by the sphingolipid ceramide is a potential anticancer strategy, but the underlying mechanisms remain poorly defined. In this study, triggering an accumulation of ceramide in acute myeloid leukemia (AML) cells by inhibition of sphingosine kinase induced an apoptotic integrated stress response (ISR) through protein kinase R–mediated activation of the master transcription factor ATF4. This effect led to transcription of the BH3-only protein Noxa and degradation of the prosurvival Mcl-1 protein on which AML cells are highly dependent for survival. Targeting this novel ISR pathway, in combination with the Bcl-2 inhibitor venetoclax, synergistically killed primary AML blasts, including those with venetoclax-resistant mutations, as well as immunophenotypic leukemic stem cells, and reduced leukemic engraftment in patient-derived AML xenografts. Collectively, these findings provide mechanistic insight into the anticancer effects of ceramide and preclinical evidence for new approaches to augment Bcl-2 inhibition in the therapy of AML and other cancers with high Mcl-1 dependency.

Novel Sphingosine Kinase 1 Inhibitor Suppresses Growth of Solid Tumor and Inhibits the Lung Metastasis of Triple-Negative Breast Cancer

Targeting sphingosine kinase 1 (SphK1) has become a novel strategy for the treatment of inflammatory bowel disease and cancer via the SphK1/S1P signaling pathway. However, exploration of SphK1 inhibitor therapeutic applications has been hampered by the poor pharmacokinetic properties of these SphK1 inhibitors. Herein, we report the structural optimization and structure-activity relationship studies of a series of novel SphK1 inhibitors. The novel compound 28 selectively inhibits SphK1 and exhibits higher anti-proliferative activity compared to the positive compound PF-543 in various cancer cells, which is associated with the induction of G0/G1 phase arrest and apoptosis; besides, it could also inhibit the cell migration. Further, compound 28 can suppress in vivo growth of both colon tumor and triple-negative breast tumor and inhibits the lung metastasis of triple-negative breast cancer with higher potency compared with that of PF-543. Collectively, compound 28 represents a promising lead compound for the treatment of solid tumor and the metastasis.

Tumor Necrosis Factor-α Induces a Preeclamptic-like Phenotype in Placental Villi via Sphingosine Kinase 1 Activation

Preeclampsia (PE) involves inadequate placental function. This can occur due to elevated pro-inflammatory tumor necrosis factor-α (TNF-α). In other tissues, TNF-α signals via sphingosine kinase 1 (SphK1). SphK1 hinders syncytial formation. Whether this occurs downstream of TNF-α signaling is unclear. We hypothesized that placental SphK1 levels are higher in PE and elevated TNF-α decreases syncytial function, increases syncytial shedding, and increases cytokine/factor release via SphK1 activity. Term placental biopsies were analyzed for SphK1 using immunofluorescence and qRT-PCR. Term placental explants were treated after 4 days of culture, at the start of syncytial regeneration, with TNF-α and/or SphK1 inhibitors, PF-543. Syncytialization was assessed by measuring fusion and chorionic gonadotropin release. Cell death and shedding were measured by lactate dehydrogenase release and placental alkaline phosphatase-positive shed particles. Forty-two cytokines were measured using multiplex assays. Placental SphK1 was increased in PE. Increased cell death, shedding, interferon-α2, IFN-γ-induced protein 10, fibroblast growth factor 2, and platelet-derived growth factor-AA release induced by TNF-α were reversed upon SphK1 inhibition. TNF-α increased the release of 26 cytokines independently of SphK1. TNF-α decreased IL-10 release and inhibiting SphK1 reversed this effect. Inhibiting SphK1 alone decreased TNF-α release. Hence, SphK1 partially mediates the TNF-α-induced PE placental phenotype, primarily through cell damage, shedding, and specific cytokine release.

The anti-osteosarcoma cell activity by the sphingosine kinase 1 inhibitor SKI-V

Sphingosine kinase 1 (SphK1) expression and activity are elevated in human osteosarcoma (OS) and is a promising target of therapy. SKI-V is a non-competitive and highly-efficient non-lipid SphK1 inhibitor. The potential anti-OS cell activity by the SphK1 inhibitor was studied here. In primary OS cells and immortalized cell lines, SKI-V robustly suppressed cell survival, growth and proliferation as well as cell mobility, and inducing profound OS cell death and apoptosis. The SphK1 inhibitor was however non-cytotoxic nor pro-apoptotic in human osteoblasts. SKI-V robustly inhibited SphK1 activation and induced accumulation of ceramides, without affecting SphK1 expression in primary OS cells. The SphK1 activator K6PC-5 or sphingosine-1-phosphate partially inhibited SKI-V-induced OS cell death. We showed that SKI-V concurrently blocked Akt-mTOR activation in primary OS cells. A constitutively-active Akt1 (ca-Akt1, S473D) construct restored Akt-mTOR activation and mitigated SKI-V-mediated cytotoxicity in primary OS cells. In vivo, daily injection of SKI-V potently suppressed OS xenograft tumor growth in nude mice. In SKI-V-administrated OS xenograft tissues, SphK1 inhibition, ceramide increase and Akt-mTOR inhibition were detected. Together, SKI-V exerts significant anti-OS activity by inhibiting SphK1 and Akt-mTOR cascades in OS cells.

Determining the Anticancer Activity of Sphingosine Kinase Inhibitors Containing Heteroatoms in Their Tail Structure

Sphingosine kinase (SK) enzyme, a central player of sphingolipid rheostat, catalyzes the phosphorylation of sphingosine to the bioactive lipid mediator sphingosine 1 phosphate (S1P), which regulates cancer cell proliferation, migration, differentiation, and angiogenesis through its extracellular five G protein-coupled S1P receptors (S1PR_1–5). Recently, several research studies on SK inhibitors have taken place in order use them for the development of novel anticancer-targeted therapy. In this study, we designed and synthesized analog derivatives of known SK1 inhibitors, namely RB005 and PF-543, by introducing heteroatoms at their tail structure, as well as investigated their anticancer activities and pharmacokinetic parameters in vitro. Compounds 1–20 of RB005 and PF-543 derivatives containing an aliphatic chain or a tail structure of benzenesulfonyl were synthesized. All compounds of set 1 (1–10) effectively reduced cell viability in both HT29 and HCT116 cells, whereas set 2 derivatives (11–20) showed poor anticancer effect. Compound 10, having the highest cytotoxic effect (48 h, HT29 IC₅₀ = 6.223 µM, HCT116 IC₅₀ = 8.694 µM), induced HT29 and HCT116 cell death in a concentration-dependent manner through the mitochondrial apoptotic pathway, which was demonstrated by increased annexin V-FITC level, and increased apoptotic marker cleaved caspase-3 and cleaved PARP. Compound 10 inhibited SK1 by 20%, and, thus, the S1P level decreased by 42%. Unlike the apoptosis efficacy, the SK1 inhibitory effect and selectivity of the PF-543 derivative were superior to that of the RB005 analog. As a result, compounds with an aliphatic chain tail exhibited stronger apoptotic effects. However, this ability was not proportional to the degree of SK inhibition. Compound 10 increased the protein phosphatase 2A (PP2A) activity (1.73 fold) similar to FTY720 (1.65 fold) and RB005 (1.59 fold), whereas compounds 11 and 13 had no effect on PP2A activation. Since the PP2A activity increased in compounds with an aliphatic chain tail, it can be suggested that PP2A activation has an important effect on anticancer and SK inhibitory activities.

GRAND: a database of gene regulatory network models across human conditions

Gene regulation plays a fundamental role in shaping tissue identity, function, and response to perturbation. Regulatory processes are controlled by complex networks of interacting elements, including transcription factors, miRNAs and their target genes. The structure of these networks helps to determine phenotypes and can ultimately influence the development of disease or response to therapy. We developed GRAND (https://grand.networkmedicine.org) as a database for computationally-inferred, context-specific gene regulatory network models that can be compared between biological states, or used to predict which drugs produce changes in regulatory network structure. The database includes 12 468 genome-scale networks covering 36 human tissues, 28 cancers, 1378 unperturbed cell lines, as well as 173 013 TF and gene targeting scores for 2858 small molecule-induced cell line perturbation paired with phenotypic information. GRAND allows the networks to be queried using phenotypic information and visualized using a variety of interactive tools. In addition, it includes a web application that matches disease states to potentially therapeutic small molecule drugs using regulatory network properties.

Sphingosine kinase 1 regulates lysyl oxidase through STAT3 in hyperoxia-mediated neonatal lung injury

INTRODUCTION

Neonatal lung injury as a consequence of hyperoxia (HO) therapy and ventilator care contribute to the development of bronchopulmonary dysplasia (BPD). Increased expression and activity of lysyl oxidase (LOX), a key enzyme that cross-links collagen, was associated with increased sphingosine kinase 1 (SPHK1) in human BPD. We, therefore, examined closely the link between LOX and SPHK1 in BPD.

METHOD

The enzyme expression of SPHK1 and LOX were assessed in lung tissues of human BPD using immunohistochemistry and quantified (Halo). In vivo studies were based on Sphk1^-/- and matched wild type (WT) neonatal mice exposed to HO while treated with PF543, an inhibitor of SPHK1. In vitro mechanistic studies used human lung microvascular endothelial cells (HLMVECs).

RESULTS

Both SPHK1 and LOX expressions were increased in lungs of patients with BPD. Tracheal aspirates from patients with BPD had increased LOX, correlating with sphingosine-1-phosphate (S1P) levels. HO-induced increase of LOX in lungs were attenuated in both Sphk1^-/- and PF543-treated WT mice, accompanied by reduced collagen staining (sirius red). PF543 reduced LOX activity in both bronchoalveolar lavage fluid and supernatant of HLMVECs following HO. In silico analysis revealed STAT3 as a potential transcriptional regulator of LOX. In HLMVECs, following HO, ChIP assay confirmed increased STAT3 binding to LOX promoter. SPHK1 inhibition reduced phosphorylation of STAT3. Antibody to S1P and siRNA against SPNS2, S1P receptor 1 (S1P₁) and STAT3 reduced LOX expression.

CONCLUSION

HO-induced SPHK1/S1P signalling axis plays a critical role in transcriptional regulation of LOX expression via SPNS2, S1P₁ and STAT3 in lung endothelium.

Loss of E-Cadherin Leads to Druggable Vulnerabilities in Sphingolipid Metabolism and Vesicle Trafficking

Simple Summary

Germline loss of the CDH1 gene is the primary genetic basis for hereditary diffuse gastric cancer, a disease resulting in elevated risk of both diffuse gastric cancer and lobular breast cancer. Current preventative treatment consists of prophylactic total gastrectomy, a therapy with several associated long-term morbidities. To address the lack of targeted molecular therapies for hereditary diffuse gastric cancer, we have utilized a synthetic lethal approach to identify candidate compounds that can specifically kill CDH1-null cells. Inhibitors of sphingolipid metabolism and vesicle trafficking pathways were identified as promising candidate compounds in a cell line model of CDH1 loss, then further validated in murine-derived organoid models of hereditary diffuse gastric cancer. With further research, these findings may lead to the development of novel chemoprevention strategies for the treatment of hereditary diffuse gastric cancer.

Abstract

Germline inactivating variants of CDH1 are causative of hereditary diffuse gastric cancer (HDGC), a cancer syndrome characterized by an increased risk of both diffuse gastric cancer and lobular breast cancer. Because loss of function mutations are difficult to target therapeutically, we have taken a synthetic lethal approach to identify targetable vulnerabilities in CDH1-null cells. We have previously observed that CDH1-null MCF10A cells exhibit a reduced rate of endocytosis relative to wildtype MCF10A cells. To determine whether this deficiency is associated with wider vulnerabilities in vesicle trafficking, we screened isogenic MCF10A cell lines with known inhibitors of autophagy, endocytosis, and sphingolipid metabolism. Relative to wildtype MCF10A cells, CDH1^−/− MCF10A cells showed significantly greater sensitivity to several drugs targeting these processes, including the autophagy inhibitor chloroquine, the endocytosis inhibitors chlorpromazine and PP1, and the sphingosine kinase 1 inhibitor PF-543. Synthetic lethality was confirmed in both gastric and mammary organoid models of CDH1 loss, derived from CD44-Cre/Cdh1^fl/fl/tdTomato mice. Collectively, these results suggest that both sphingolipid metabolism and vesicle trafficking represent previously unrecognised druggable vulnerabilities in CDH1-null cells and may lead to the development of new therapies for HDGC.

aPC/PAR1 confers endothelial anti-apoptotic activity via a discrete, β-arrestin-2-mediated SphK1-S1PR1-Akt signaling axis

Endothelial dysfunction is associated with vascular disease and results in disruption of endothelial barrier function and increased sensitivity to apoptosis. Currently, there are limited treatments for improving endothelial dysfunction. Activated protein C (aPC), a promising therapeutic, signals via protease-activated receptor-1 (PAR1) and mediates several cytoprotective responses, including endothelial barrier stabilization and anti-apoptotic responses. We showed that aPC-activated PAR1 signals preferentially via β-arrestin-2 (β-arr2) and dishevelled-2 (Dvl2) scaffolds rather than G proteins to promote Rac1 activation and barrier protection. However, the signaling pathways utilized by aPC/PAR1 to mediate anti-apoptotic activities are not known. aPC/PAR1 cytoprotective responses also require coreceptors; however, it is not clear how coreceptors impact different aPC/PAR1 signaling pathways to drive distinct cytoprotective responses. Here, we define a β-arr2-mediated sphingosine kinase-1 (SphK1)-sphingosine-1-phosphate receptor-1 (S1PR1)-Akt signaling axis that confers aPC/PAR1-mediated protection against cell death. Using human cultured endothelial cells, we found that endogenous PAR1 and S1PR1 coexist in caveolin-1 (Cav1)-rich microdomains and that S1PR1 coassociation with Cav1 is increased by aPC activation of PAR1. Our study further shows that aPC stimulates β-arr2-dependent SphK1 activation independent of Dvl2 and is required for transactivation of S1PR1-Akt signaling and protection against cell death. While aPC/PAR1-induced, extracellular signal-regulated kinase 1/2 (ERK1/2) activation is also dependent on β-arr2, neither SphK1 nor S1PR1 are integrated into the ERK1/2 pathway. Finally, aPC activation of PAR1-β-arr2-mediated protection against apoptosis is dependent on Cav1, the principal structural protein of endothelial caveolae. These studies reveal that different aPC/PAR1 cytoprotective responses are mediated by discrete, β-arr2-driven signaling pathways in caveolae.

Therapeutic Potential of SphK1 Inhibitors Based on Abnormal Expression of SphK1 in Inflammatory Immune Related-Diseases

Sphingosine kinase 1(SphK1) a key enzyme that catalyzes the conversion of sphingosine (Sph) to sphingosine 1-phosphate (S1P), so as to maintain the dynamic balance of sphingolipid-rheostat in cells and participate in cell growth and death, proliferation and migration, vasoconstriction and remodeling, inflammation and metabolism. The normal expression of SphK1 maintains the balance of physiological and pathological states, which is reflected in the regulation of inflammatory factor secretion, immune response in traditional immune cells and non-traditional immune cells, and complex signal transduction. However, abnormal SphK1 expression and activity are found in various inflammatory and immune related-diseases, such as hypertension, atherosclerosis, Alzheimer’s disease, inflammatory bowel disease and rheumatoid arthritis. In view of the therapeutic potential of regulating SphK1 and its signal, the current research is aimed at SphK1 inhibitors, such as SphK1 selective inhibitors and dual SphK1/2 inhibitor, and other compounds with inhibitory potency. This review explores the regulatory role of over-expressed SphK1 in inflammatory and immune related-diseases, and investigate the latest progress of SphK1 inhibitors and the improvement of disease or pathological state.

The unfolding role of ceramide in coordinating retinoid-based cancer therapy

Sphingolipid-mediated regulation in cancer development and treatment is largely ceramide-centered with the complex sphingolipid metabolic pathways unfolding as attractive targets for anticancer drug discovery. The dynamic interconversion of sphingolipids is tightly controlled at the level of enzymes and cellular compartments in response to endogenous or exogenous stimuli, such as anticancer drugs, including retinoids. Over the past two decades, evidence emerged that retinoids owe part of their potency in cancer therapy to modulation of sphingolipid metabolism and ceramide generation. Ceramide has been proposed as a 'tumor-suppressor lipid' that orchestrates cell growth, cell cycle arrest, cell death, senescence, autophagy, and metastasis. There is accumulating evidence that cancer development is promoted by the dysregulation of tumor-promoting sphingolipids whereas cancer treatments can kill tumor cells by inducing the accumulation of endogenous ceramide levels. Resistance to cancer therapy may develop due to a disrupted equilibrium between the opposing roles of tumor-suppressor and tumor-promoter sphingolipids. Despite the undulating effect and complexity of sphingolipid pathways, there are emerging opportunities for a plethora of enzyme-targeted therapeutic interventions that overcome resistance resulting from perturbed sphingolipid pathways. Here, we have revisited the interconnectivity of sphingolipid metabolism and the instrumental role of ceramide-biosynthetic and degradative enzymes, including bioactive sphingolipid products, how they closely relate to cancer treatment and pathogenesis, and the interplay with retinoid signaling in cancer. We focused on retinoid targeting, alone or in combination, of sphingolipid metabolism nodes in cancer to enhance ceramide-based therapeutics. Retinoid and ceramide-based cancer therapy using novel strategies such as combination treatments, synthetic retinoids, ceramide modulators, and delivery formulations hold promise in the battle against cancer.

Sphingosine Kinase Inhibition Enhances Dimerization of Calreticulin at the Cell Surface in Mitoxantrone-Induced Immunogenic Cell Death

Agents that induce immunogenic cell death (ICD) alter the cellular localization of calreticulin (CRT), causing it to become cell surface-exposed within the plasma membrane lipid raft microdomain [cell surface-exposed CRT (ectoCRT)] where it serves as a damage associated-molecular pattern that elicits an antitumor immune response. We have identified the sphingolipid metabolic pathway as an integral component of the process of ectoCRT exposure. Inhibition of the sphingosine kinases (SphKs) enhances mitoxantrone-induced production of hallmarks of ICD, including ectoCRT production, with an absolute mean difference of 40 MFI (95% CI: 19-62; P = 0.0014) and 1.3-fold increase of ATP secretion with an absolute mean difference of 87 RLU (95% CI: 55-120; P < 0.0001). Mechanistically, sphingosine kinase inhibition increases mitoxantrone-induced accumulation of ceramide species, including C16:0 ceramide 2.8-fold with an absolute mean difference of 1.390 pmol/nmol Pi (95% CI: 0.798-1.983; P = 0.0023). We further examined the localization of ectoCRT to the lipid raft microdomain and demonstrate that ectoCRT forms disulfide-bridged dimers. Together, our findings suggest that ceramide accumulation impinges on the homeostatic function of the endoplasmic reticulum to induce ectoCRT exposure and that structural alterations of ectoCRT may underlie its immunogenicity. Our findings further suggest that inhibition of the SphKs may represent a means to enhance the therapeutic immunogenic efficacy of ICD-inducing agents while reducing overt toxicity/immunosuppressive effects by allowing for the modification of dosing regimens or directly lowering the dosages of ICD-inducing agents employed in therapeutic regimens. SIGNIFICANCE STATEMENT: This study demonstrates that inhibition of sphingosine kinase enhances the mitoxantrone-induced cell surface exposure of a dimeric form of the normally endoplasmic reticulum resident chaperone calreticulin as part of the process of a unique form of regulated cell death termed immunogenic cell death. Importantly, inhibition of sphingosine kinase may represent a means to enhance the therapeutic efficacy of immunogenic cell death-inducing agents, such as mitoxantrone, while reducing their overt toxicity and immunosuppressive effects, leading to better therapeutic outcomes for patients.

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.

Integrated transcriptomic analysis of human tuberculosis granulomas and a biomimetic model identifies therapeutic targets

Tuberculosis (TB) is a persistent global pandemic, and standard treatment for it has not changed for 30 years. Mycobacterium tuberculosis (Mtb) has undergone prolonged coevolution with humans, and patients can control Mtb even after extensive infection, demonstrating the fine balance between protective and pathological host responses within infected granulomas. We hypothesized that whole transcriptome analysis of human TB granulomas isolated by laser capture microdissection could identify therapeutic targets, and that comparison with a noninfectious granulomatous disease, sarcoidosis, would identify disease-specific pathological mechanisms. Bioinformatic analysis of RNAseq data identified numerous shared pathways between TB and sarcoidosis lymph nodes, and also specific clusters demonstrating TB results from a dysregulated inflammatory immune response. To translate these insights, we compared 3 primary human cell culture models at the whole transcriptome level and demonstrated that the 3D collagen granuloma model most closely reflected human TB disease. We investigated shared signaling pathways with human disease and identified 12 intracellular enzymes as potential therapeutic targets. Sphingosine kinase 1 inhibition controlled Mtb growth, concurrently reducing intracellular pH in infected monocytes and suppressing inflammatory mediator secretion. Immunohistochemical staining confirmed that sphingosine kinase 1 is expressed in human lung TB granulomas, and therefore represents a host therapeutic target to improve TB outcomes.

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.

S1P signaling, its interactions and cross-talks with other partners and therapeutic importance in colorectal cancer

Sphingosine-1-Phosphate (S1P) plays an important role in normal physiology, inflammation, initiation and progression of cancer. Deregulation of S1P signaling causes aberrant proliferation, affects survival, leads to angiogenesis and metastasis. Sphingolipid rheostat is crucial for cellular homeostasis. Discrepancy in sphingolipid metabolism is linked to cancer and drug insensitivity. Owing to these diverse functions and being a potent mediator of tumor growth, S1P signaling might be a suitable candidate for anti-tumor therapy or combination therapy. In this review, with a focus on colorectal cancer we have summarized the interacting partners of S1P signaling pathway, its therapeutic approaches along with the contribution of S1P signaling to various cancer hallmarks.