Morpholino Analogues of Fingolimod as Novel and Selective S1P1 Ligands with In Vivo Efficacy in a Mouse Model of Experimental Antigen-Induced Encephalomyelitis

Insight into modulators of sphingosine-1-phosphate receptor and implications for cardiovascular therapeutics

Cardiovascular disease is the leading cause of death worldwide, and it's of great importance to understand its underlying mechanisms and find new treatments. Sphingosine 1-phosphate (S1P) is an active lipid that exerts its effects through S1P receptors on the cell surface or intracellular signal, and regulates many cellular processes such as cell growth, cell proliferation, cell migration, cell survival, and so on. S1PR modulators are a class of modulators that can interact with S1PR subtypes to activate receptors or block their activity, exerting either agonist or functional antagonist effects. Many studies have shown that S1P plays a protective role in the cardiovascular system and regulates cardiac physiological functions mainly through interaction with cell surface S1P receptors (S1PRs). Therefore, S1PR modulators may play a therapeutic role in cardiovascular diseases. Here, we review five S1PRs and their functions and the progress of S1PR modulators. In addition, we focus on the effects of S1PR modulators on atherosclerosis, myocardial infarction, myocardial ischaemia/reperfusion injury, diabetic cardiovascular diseases, and myocarditis, which may provide valuable insights into potential therapeutic strategies for cardiovascular disease.

The emerging roles of sphingosine 1-phosphate and SphK1 in cancer resistance: a promising therapeutic target

Cancer chemoresistance is a problematic dilemma that significantly restrains numerous cancer management protocols. It can promote cancer recurrence, spreading of cancer, and finally, mortality. Accordingly, enhancing the responsiveness of cancer cells towards chemotherapies could be a vital approach to overcoming cancer chemoresistance. Tumour cells express a high level of sphingosine kinase-1 (SphK1), which acts as a protooncogenic factor and is responsible for the synthesis of sphingosine-1 phosphate (S1P). S1P is released through a Human ATP-binding cassette (ABC) transporter to interact with other phosphosphingolipids components in the interstitial fluid in the tumor microenvironment (TME), provoking communication, progression, invasion, and tumor metastasis. Also, S1P is associated with several impacts, including anti-apoptotic behavior, metastasis, mesenchymal transition (EMT), angiogenesis, and chemotherapy resistance. Recent reports addressed high levels of S1P in several carcinomas, including ovarian, prostate, colorectal, breast, and HCC. Therefore, targeting the S1P/SphK signaling pathway is an emerging therapeutic approach to efficiently attenuate chemoresistance. In this review, we comprehensively discussed S1P functions, metabolism, transport, and signaling. Also, through a bioinformatic framework, we pointed out the alterations of SphK1 gene expression within different cancers with their impact on patient survival, and we demonstrated the protein-protein network of SphK1, elaborating its sparse roles. Furthermore, we made emphasis on different machineries of cancer resistance and the tight link with S1P. We evaluated all publicly available SphK1 inhibitors and their inhibition activity using molecular docking and how SphK1 inhibitors reduce the production of S1P and might reduce chemoresistance, an approach that might be vital in the course of cancer treatment and prognosis.

S1P/S1PR signaling pathway advancements in autoimmune diseases

Sphingosine-1-phosphate (S1P) is a versatile sphingolipid that is generated through the phosphorylation of sphingosine by sphingosine kinase (SPHK). S1P exerts its functional effects by binding to the G protein-coupled S1P receptor (S1PR). This lipid mediator plays a pivotal role in various cellular activities. The S1P/S1PR signaling pathway is implicated in the pathogenesis of immune-mediated diseases, significantly contributing to the functioning of the immune system. It plays a crucial role in diverse physiological and pathophysiological processes, including cell survival, proliferation, migration, immune cell recruitment, synthesis of inflammatory mediators, and the formation of lymphatic and blood vessels. However, the full extent of the involvement of this signaling pathway in the development of autoimmune diseases remains to be fully elucidated. Therefore, this study aims to comprehensively review recent research on the S1P/S1PR axis in diseases related to autoimmunity.

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.

Topical Collection: New Insights on Sphingolipids in Health and Disease

The last two decades have boosted research on sphingolipids as bioactive and signaling molecules [...].

Dose-dependent reduction of lymphocyte count and heart rate after multiple administration of LC51-0255, a novel sphingosine-1-phosphate receptor 1 modulator, in healthy subjects

Aim: Sphingosine-1-phosphate receptor mediates the egress of lymphocytes from lymphoid organs, and its inhibition results in a decreased number of circulating lymphocytes. The aim of the current study was to investigate the safety and pharmacodynamic and pharmacokinetic characteristics of a novel sphingosine-1-phosphate receptor modulator, LC51-0255.

Methods: A phase 1 randomized, double-blind, placebo-controlled, multiple dosing, dose-escalation study was conducted on healthy Korean male subjects.

Results: After single and daily administration of LC51-0255 for 21 days, a dose-dependent decrease in lymphocyte count and heart rate was observed through 0.25–2 mg dose range of LC51-0255. The mean elimination half-life of LC51-0255 was 76–95 h. LC51-0255 was accumulated with a mean accumulation ratio of 5.17–6.64. During the study, LC51-0255 was generally well tolerated. The most common treatment-emergent adverse event was bradycardia. No clinically significant event of arrhythmia, including AV block, was observed. No clinically significant difference in blood pressure was observed between the dose groups. In other safety assessments, no clinically significant abnormalities were observed, except for bradycardia.

Conclusion: Daily administration of LC51-0255 in the range of 0.25–2 mg resulted in a dose-dependent reduction of lymphocyte counts and heart rate. LC51-0255 is generally safe and well tolerated in healthy volunteers.

Fingolimod-Conjugated Charge-Altering Releasable Transporters Efficiently and Specifically Deliver mRNA to Lymphocytes In Vivo and In Vitro

Charge-altering releasable transporters (CARTs) are a class of oligonucleotide delivery vehicles shown to be effective for delivery of messenger RNA (mRNA) both in vitro and in vivo. Here, we exploited the chemical versatility of the CART synthesis to generate CARTs containing the small-molecule drug fingolimod (FTY720) as a strategy to increase mRNA delivery and expression in lymphocytes through a specific ligand-receptor interaction. Fingolimod is an FDA-approved small-molecule drug that, upon in vivo phosphorylation, binds to the sphingosine-1-phosphate receptor 1 (S1P1), which is highly expressed on lymphocytes. Compared to its non-fingolimod-conjugated analogue, the fingolimod-conjugated CART achieved superior transfection of activated human and murine T and B lymphocytes in vitro. The higher transfection of the fingolimod-conjugated CARTs was lost when cells were exposed to a free fingolimod before transfection. In vivo, the fingolimod-conjugated CART showed increased mRNA delivery to marginal zone B cells and NK cells in the spleen, relative to CARTs lacking fingolimod. Moreover, fingolimod-CART-mediated mRNA delivery induces peripheral blood T-cell depletion similar to free fingolimod. Thus, we show that functionalization of CARTs with a pharmacologically validated small molecule can increase transfection of a cellular population of interest while conferring some of the targeting properties of the conjugated small molecule to the CARTs.

Sphingosylphosphorylcholine ameliorates experimental sjögren's syndrome by regulating salivary gland inflammation and hypofunction, and regulatory B cells

Sjögren syndrome (SS) is an autoimmune disease in which immune cells infiltrate the exocrine gland. Since SS is caused by a disorder of the immune system, treatments should regulate the immune response. Sphingosylphosphorylcholine (SPC) is a sphingolipid that mediates cellular signaling. In immune cells, SPC has several immunomodulatory functions. Accordingly, this study verifies the immunomodulatory ability and therapeutic effect of SPC in SS. To understand the function of SPC in SS, we treated SPC in female NOD/ShiJcl (NOD) mice. The mice were monitored for 10 weeks, and inflammation in the salivary glands was checked. After SPC treatment, we detected the expression of regulatory B (B_reg) cells in mouse splenocytes and the level of salivary secretion-related genes in human submandibular gland (HSG) cells. Salivary flow rate was maintained in the SPC-treated group compared to the vehicle-treated group, and inflammation in the salivary gland tissues was relieved by SPC. SPC treatment in mouse cells and HSG cells enhanced B_reg cells and salivary secretion markers, respectively. This study revealed that SPC can be considered as a new therapeutic agent against SS.

Sphk1 and Sphk2 Differentially Regulate Erythropoietin Synthesis in Mouse Renal Interstitial Fibroblast-like Cells

Erythropoietin (Epo) is a crucial hormone regulating red blood cell number and consequently the hematocrit. Epo is mainly produced in the kidney by interstitial fibroblast-like cells. Previously, we have shown that in cultures of the immortalized mouse renal fibroblast-like cell line FAIK F3-5, sphingosine 1-phosphate (S1P), by activating S1P₁ and S1P₃ receptors, can stabilize hypoxia-inducible factor (HIF)-2α and upregulate Epo mRNA and protein synthesis. In this study, we have addressed the role of intracellular iS1P derived from sphingosine kinases (Sphk) 1 and 2 on Epo synthesis in F3-5 cells and in mouse primary cultures of renal fibroblasts. We show that stable knockdown of Sphk2 in F3-5 cells increases HIF-2α protein and Epo mRNA and protein levels, while Sphk1 knockdown leads to a reduction of hypoxia-stimulated HIF-2α and Epo protein. A similar effect was obtained using primary cultures of renal fibroblasts isolated from wildtype mice, Sphk1−/−, or Sphk2−/− mice. Furthermore, selective Sphk2 inhibitors mimicked the effect of genetic Sphk2 depletion and also upregulated HIF-2α and Epo protein levels. The combined blockade of Sphk1 and Sphk2, using Sphk2−/− renal fibroblasts treated with the Sphk1 inhibitor PF543, resulted in reduced HIF-2α and Epo compared to the untreated Sphk2−/− cells. Exogenous sphingosine (Sph) enhanced HIF-2α and Epo, and this was abolished by the combined treatment with the selective S1P₁ and S1P₃ antagonists NIBR-0213 and TY52156, suggesting that Sph was taken up by cells and converted to iS1P and exported to then act in an autocrine manner through S1P₁ and S1P₃. The upregulation of HIF-2α and Epo synthesis by Sphk2 knockdown was confirmed in the human hepatoma cell line Hep3B, which is well-established to upregulate Epo production under hypoxia. In summary, these data show that sphingolipids have diverse effects on Epo synthesis. While accumulation of intracellular Sph reduces Epo synthesis, iS1P will be exported to act through S1P₁₊₃ to enhance Epo synthesis. Furthermore, these data suggest that selective inhibition of Sphk2 is an attractive new option to enhance Epo synthesis and thereby to reduce anemia development in chronic kidney disease.

Molecular Pharmacology and Novel Potential Therapeutic Applications of Fingolimod

Fingolimod is a well-tolerated, highly effective disease-modifying therapy successfully utilized in the management of multiple sclerosis. The active metabolite, fingolimod-phosphate, acts on sphingosine-1-phosphate receptors (S1PRs) to bring about an array of pharmacological effects. While being initially recognized as a novel agent that can profoundly reduce T-cell numbers in circulation and the CNS, thereby suppressing inflammation and MS, there is now rapidly increasing knowledge on its previously unrecognized molecular and potential therapeutic effects in diverse pathological conditions. In addition to exerting inhibitory effects on sphingolipid pathway enzymes, fingolimod also inhibits histone deacetylases, transient receptor potential cation channel subfamily M member 7 (TRMP7), cytosolic phospholipase A2α (cPLA2α), reduces lysophosphatidic acid (LPA) plasma levels, and activates protein phosphatase 2A (PP2A). Furthermore, fingolimod induces apoptosis, autophagy, cell cycle arrest, epigenetic regulations, macrophages M1/M2 shift and enhances BDNF expression. According to recent evidence, fingolimod modulates a range of other molecular pathways deeply rooted in disease initiation or progression. Experimental reports have firmly associated the drug with potentially beneficial therapeutic effects in immunomodulatory diseases, CNS injuries, and diseases including Alzheimer's disease (AD), Parkinson's disease (PD), epilepsy, and even cancer. Attractive pharmacological effects, relative safety, favorable pharmacokinetics, and positive experimental data have collectively led to its testing in clinical trials. Based on the recent reports, fingolimod may soon find its way as an adjunct therapy in various disparate pathological conditions. This review summarizes the up-to-date knowledge about molecular pharmacology and potential therapeutic uses of fingolimod.

ST-2191, an Anellated Bismorpholino Derivative of Oxy-Fingolimod, Shows Selective S1P1 Agonist and Functional Antagonist Potency In Vitro and In Vivo

Sphingosine 1-phosphate (S1P) is an extensively studied signaling molecule that contributes to cell proliferation, survival, migration and other functions through binding to specific S1P receptors. The cycle of S1P₁ internalization upon S1P binding and recycling to the cell surface when local S1P concentrations are low drives T cell trafficking. S1P₁ modulators, such as fingolimod, disrupt this recycling by inducing persistent S1P₁ internalization and receptor degradation, which results in blocked egress of T cells from the secondary lymphoid tissues. The approval of these compounds for the treatment of multiple sclerosis has placed the development of S1PR modulators in the focus of pharmacological research, mostly for autoimmune indications. Here, we report on a novel anellated bismorpholino derivative of oxy-fingolimod, named ST-2191, which exerts selective S1P₁ agonist and functional antagonist potency. ST-2191 is also effective in reducing the lymphocyte number in mice, and this effect is not dependent on phosphorylation by sphingosine kinase 2 for activity. These data show that ST-2191 is a novel S1P₁ modulator, but further experiments are needed to analyze the therapeutic impact of ST-2191 in animal models of autoimmune diseases.

The immune regulatory effects of tetrahedral framework nucleic acid on human T cells via the mitogen-activated protein kinase pathway

OBJECTIVES

Autoimmune diseases are a heterogeneous group of diseases which lose the immunological tolerance to self-antigens. It is well recognized that irregularly provoked T cells participate in the pathological immune responses. As a novel nanomaterial with promising applications, tetrahedral framework nucleic acid (TFNA) nanostructure was found to have immune regulatory effects on T cells in this study.

MATERIALS AND METHODS

To verify the successful fabrication of TFNA, the morphology of TFNA was observed by atomic force microscopy (AFM) and dynamic light scattering. The regulatory effect of TFNA was evaluated by flow cytometry after cocultured with CD3+ T cells isolated from healthy donors. Moreover, the associated signaling pathways were investigated. Finally, we verified our results on the T cells from patients with neuromyelitis optica spectrum disorder (NMOSD), which is a typical autoimmune disease induced by T cells.

RESULTS

We revealed the alternative regulatory functions of TFNA in human primary T cells with steady status via the JNK signaling pathway. Moreover, by inhibiting both JNK and ERK phosphorylation, TFNA exhibited significant suppressive effects on IFNγ secretion from provoking T cells without affecting TNF secretion. Similar immune regulatory effects of TFNA were also observed in autoreactive T cells from patients with NMOSD.

CONCLUSIONS

Overall, our results revealed a potential application of TFNA in regulating the adaptive immune system, as well as shed a light on the treatment of T cell-mediated autoimmune diseases.

Novel compounds with dual S1P receptor agonist and histamine H3 receptor antagonist activities act protective in a mouse model of multiple sclerosis

The sphingosine 1-phosphate (S1P) receptor 1 (S1P₁) has emerged as a therapeutic target for the treatment of multiple sclerosis (MS). Fingolimod (FTY720) is the first functional antagonist of S1P₁ that has been approved for oral treatment of MS. Previously, we have developed novel butterfly derivatives of FTY720 that acted similar to FTY720 in reducing disease symptoms in a mouse model of experimental autoimmune encephalomyelitis (EAE). In this study, we have synthesized a piperidine derivative of the oxazolo-oxazole compounds, denoted ST-1505, and its ring-opened analogue ST-1478, and characterised their in-vitro and in-vivo functions. Notably, the 3-piperidinopropyloxy moiety resembles a structural motif of pitolisant, a drug with histamine H₃R antagonistic/inverse agonist activity approved for the treatment of narcolepsy. Both novel compounds exerted H₃R affinities, and in addition, ST-1505 was characterised as a dual S1P₁₊₃ agonist, whereas ST-1478 was a dual S1P₁₊₅ agonist. Both multitargeting compounds were also active in mice and reduced the lymphocyte numbers as well as diminished disease symptoms in the mouse model of MS. The effect of ST-1478 was dependent on SK-2 activity suggesting that it is a prodrug like FTY720, but with a more selective S1P receptor activation profile, whereas ST-1505 is a fully active drug even in the absence of SK-2. In summary, these data suggest that the well soluble piperidine derivatives ST-1505 and ST-1478 hold promise as novel drugs for the treatment of MS and other autoimmune or inflammatory diseases, and by their H₃R antagonist potency, they might additionally improve cognitive impairment during disease.