The next-generation sphingosine-1 receptor modulator BAF312 (siponimod) improves cortical network functionality in focal autoimmune encephalomyelitis

Targeting Pathways and Integrated Approaches to Treat Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a chronic symmetrical systemic disorder that not only affects joints but also other organs such as heart, lungs, kidney, and liver. Approximately there is 0.5%-1% of the total population affected by RA. RA pathogenesis still remains unclear due to which its appropriate treatment is a challenge. Further, multitudes of factors have been reported to affect its progression i.e. genetic factor, environmental factor, immune factor, and oxidative factor. Therapeutic approaches available for the treatment of RA include NSAIDs, DMARDs, enzymatic, hormonal, and gene therapies. But most of them provide the symptomatic relief without treating the core of the disease. This makes it obligatory to explore and reach the molecular targets for cure and long-term relief from RA. Herein, we attempt to provide extensive overlay of the new targets for RA treatment such as signaling pathways, proteins, and receptors affecting the progression of the disease and its severity. Precise modification in these targets such as suppressing the notch signaling pathway, SIRT 3 protein, Sphingosine-1-phosphate receptor and stimulating the neuronal signals particularly efferent vagus nerve and SIRT 1 protein may offer long term relief and potentially diminish the chronicity. To target or alter the novel molecules and signaling pathway a specific delivery system is required such as liposome, nanoparticles and micelles and many more. Present review paper discusses in detail about novel targets and delivery systems for treating RA.

Assessing neuroprotective effects of diroximel fumarate and siponimod via modulation of pacemaker channels in an experimental model of remyelination

Cuprizone (CPZ)-induced alterations in axonal myelination are associated with a period of neuronal hyperexcitability and increased activity of hyperpolarization-activated and cyclic nucleotide-gated (HCN) channels in the thalamocortical (TC) system. Substances used for the treatment of multiple sclerosis (MS) have been shown to normalize neuronal excitability in CPZ-treated mice. Therefore, we aimed to examine the effects of diroximel fumarate (DRF) and the sphingosine 1-phospate receptor (S1PR) modulator siponimod on action potential firing and the inward current (Ih) carried by HCN ion channels in naive conditions and during different stages of de- and remyelination. Here, DRF application reduced Ih current density in ex vivo patch clamp recordings from TC neurons of the ventrobasal thalamic complex (VB), thereby counteracting the increase of Ih during early remyelination. Siponimod reduced Ih in VB neurons under control conditions but had no effect in neurons of the auditory cortex (AU). Furthermore, siponimod increased and decreased AP firing properties of neurons in VB and AU, respectively. Computational modeling revealed that both DRF and siponimod influenced thalamic bursting during early remyelination by delaying the onset and decreasing the interburst frequency. Thus, substances used in MS treatment normalize excitability in the TC system by influencing AP firing and Ih.

Investigating the Mitoprotective Effects of S1P Receptor Modulators Ex Vivo Using a Novel Semi-Automated Live Imaging Set-Up

In multiple sclerosis (MS), mitochondrial alterations appear to contribute to disease progression. The sphingosine-1-phosphate receptor modulator siponimod is approved for treating secondary progressive MS. Its preceding compound fingolimod was shown to prevent oxidative stress-induced alterations in mitochondrial morphology. Here, we assessed the effects of siponimod, compared to fingolimod, on neuronal mitochondria in oxidatively stressed hippocampal slices. We have also advanced the model of chronic organotypic hippocampal slices for live imaging, enabling semi-automated monitoring of mitochondrial alterations. The slices were prepared from B6.Cg-Tg(Thy1-CFP/COX8A)S2Lich/J mice that display fluorescent neuronal mitochondria. They were treated with hydrogen peroxide (oxidative stress paradigm) ± 1 nM siponimod or fingolimod for 24 h. Afterwards, mitochondrial dynamics were investigated. Under oxidative stress, the fraction of motile mitochondria decreased and mitochondria were shorter, smaller, and covered smaller distances. Siponimod partly prevented oxidatively induced alterations in mitochondrial morphology; for fingolimod, a similar trend was observed. Siponimod reduced the decrease in mitochondrial track displacement, while both compounds significantly increased track speed and preserved motility. The novel established imaging and analysis tools are suitable for assessing the dynamics of neuronal mitochondria ex vivo. Using these approaches, we showed that siponimod at 1 nM partially prevented oxidatively induced mitochondrial alterations in chronic brain slices.

The Benefits and Risks of Switching from Fingolimod to Siponimod for the Treatment of Relapsing-Remitting and Secondary Progressive Multiple Sclerosis

Multiple sclerosis (MS) is a chronic neurodegenerative disease that affects the central nervous system (CNS). Currently, MS treatment is limited to several Food and Drug Administration (FDA)- and European Medicines Agency (EMA)-approved medications that slow disease progression by immunomodulatory action. Fingolimod and siponimod have similar mechanisms of action, and consequently, their therapeutic effects may be comparable. However, while fingolimod is mainly used for relapsing-remitting MS (RRMS), siponimod, according to EMA label, is recommended for active secondary progressive MS (SPMS). Clinicians and scientists are analysing whether patients can switch from fingolimod to siponimod and identifying the advantages or disadvantages of such a switch from a therapeutic point of view. In this review, we aim to discuss the therapeutic effects of these two drugs and the advantages/disadvantages of switching treatment from fingolimod to siponimod in patients with the most common forms of MS, RRMS and SPMS.

Bioavailable central nervous system disease-modifying therapies for multiple sclerosis

Disease-modifying therapies for relapsing multiple sclerosis reduce relapse rates by suppressing peripheral immune cells but have limited efficacy in progressive forms of the disease where cells in the central nervous system play a critical role. To our knowledge, alemtuzumab, fumarates (dimethyl, diroximel, and monomethyl), glatiramer acetates, interferons, mitoxantrone, natalizumab, ocrelizumab, ofatumumab, and teriflunomide are either limited to the periphery or insufficiently studied to confirm direct central nervous system effects in participants with multiple sclerosis. In contrast, cladribine and sphingosine 1-phosphate receptor modulators (fingolimod, ozanimod, ponesimod, and siponimod) are central nervous system-penetrant and could have beneficial direct central nervous system properties.

PET imaging of TREM1 identifies CNS-infiltrating myeloid cells in a mouse model of multiple sclerosis

Multiple sclerosis (MS) is an immune-mediated demyelinating disease of the central nervous system (CNS) that causes substantial morbidity and diminished quality of life. Evidence highlights the central role of myeloid lineage cells in the initiation and progression of MS. However, existing imaging strategies for detecting myeloid cells in the CNS cannot distinguish between beneficial and harmful immune responses. Thus, imaging strategies that specifically identify myeloid cells and their activation states are critical for MS disease staging and monitoring of therapeutic responses. We hypothesized that positron emission tomography (PET) imaging of triggering receptor expressed on myeloid cells 1 (TREM1) could be used to monitor deleterious innate immune responses and disease progression in the experimental autoimmune encephalomyelitis (EAE) mouse model of MS. We first validated TREM1 as a specific marker of proinflammatory, CNS-infiltrating, peripheral myeloid cells in mice with EAE. We show that the ⁶⁴Cu-radiolabeled TREM1 antibody-based PET tracer monitored active disease with 14- to 17-fold higher sensitivity than translocator protein 18 kDa (TSPO)-PET imaging, the established approach for detecting neuroinflammation in vivo. We illustrate the therapeutic potential of attenuating TREM1 signaling both genetically and pharmacologically in the EAE mice and show that TREM1-PET imaging detected responses to an FDA-approved MS therapy with siponimod (BAF312) in these animals. Last, we observed TREM1⁺ cells in clinical brain biopsy samples from two treatment-naïve patients with MS but not in healthy control brain tissue. Thus, TREM1-PET imaging has potential for aiding in the diagnosis of MS and monitoring of therapeutic responses to drug treatment.

The role of sphingosine 1-phosphate metabolism in brain health and disease

Lipids are essential structural and functional components of the central nervous system (CNS). Sphingolipids are ubiquitous membrane components which were discovered in the brain in the late 19^th century. In mammals, the brain contains the highest concentration of sphingolipids in the body. Sphingosine 1-phosphate (S1P) derived from membrane sphingolipids evokes multiple cellular responses which, depending on its concentration and localization, make S1P a double-edged sword in the brain. In the present review we highlight the role of S1P in brain development and focus on the often contrasting findings regarding its contributions to the initiation, progression and potential recovery of different brain pathologies, including neurodegeneration, multiple sclerosis (MS), brain cancers, and psychiatric illnesses. A detailed understanding of the critical implications of S1P in brain health and disease may open the door for new therapeutic options. Thus, targeting S1P-metabolizing enzymes and/or signaling pathways might help overcome, or at least ameliorate, several brain illnesses.

Therapeutic effect of combination vitamin D3 and siponimod on remyelination and modulate microglia activation in cuprizone mouse model of multiple sclerosis

Stimulation of remyelination is critical for the treatment of multiple sclerosis (MS) to alleviate symptoms and protect the myelin sheath from further damage. The current study aimed to investigate the possible therapeutic effects of combining vitamin D3 (Vit D3) and siponimod (Sipo) on enhancing remyelination and modulating microglia phenotypes in the cuprizone (CPZ) demyelination mouse model. The study was divided into two stages; demyelination (first 5 weeks) and remyelination (last 4 weeks). In the first 5 weeks, 85 mice were randomly divided into two groups, control (n = 20, standard rodent chow) and CPZ (n = 65, 0.3% CPZ mixed with chow for 6 weeks, followed by 3 weeks of standard rodent chow). At week 5, the CPZ group was re-divided into four groups (n = 14) for remyelination stages; untreated CPZ (0.2 ml of CMC orally), CPZ+Vit D3 (800 IU/kg Vit D3 orally), CPZ+Sipo (1.5 mg/kg Sipo orally), and CPZ+Vit D3 (800 IU/kg Vit D3) + Sipo (1.5 mg/kg Sipo orally). Various behavioral tasks were performed to evaluate motor performance. Luxol Fast Blue (LFB) staining, the expression level of myelin basic protein (MBP), and M1/M2 microglia phenotype genes were assessed in the corpus callosum (CC). The results showed that the combination of Vit D3 and Sipo improved behavioral deficits, significantly promoted remyelination, and modulated expression levels of microglia phenotype genes in the CC at early and late remyelination stages. These results demonstrate for the first time that a combination of Vit D3 and Sipo can improve the remyelination process in the cuprizone (CPZ) mouse model by attenuating the M1 microglia phenotype. This may help to improve the treatment of MS patients.

First in vivo fluorine-19 magnetic resonance imaging of the multiple sclerosis drug siponimod

Theranostic imaging methods could greatly enhance our understanding of the distribution of CNS-acting drugs in individual patients. Fluorine-19 magnetic resonance imaging (¹⁹F MRI) offers the opportunity to localize and quantify fluorinated drugs non-invasively, without modifications and without the application of ionizing or other harmful radiation. Here we investigated siponimod, a sphingosine 1-phosphate (S₁P) receptor antagonist indicated for secondary progressive multiple sclerosis (SPMS), to determine the feasibility of in vivo ¹⁹F MR imaging of a disease modifying drug. Methods: The ¹⁹F MR properties of siponimod were characterized using spectroscopic techniques. Four MRI methods were investigated to determine which was the most sensitive for ¹⁹F MR imaging of siponimod under biological conditions. We subsequently administered siponimod orally to 6 mice and acquired ¹⁹F MR spectra and images in vivo directly after administration, and in ex vivo tissues. Results: The ¹⁹F transverse relaxation time of siponimod was 381 ms when dissolved in dimethyl sulfoxide, and substantially reduced to 5 ms when combined with serum, and to 20 ms in ex vivo liver tissue. Ultrashort echo time (UTE) imaging was determined to be the most sensitive MRI technique for imaging siponimod in a biological context and was used to map the drug in vivo in the stomach and liver. Ex vivo images in the liver and brain showed an inhomogeneous distribution of siponimod in both organs. In the brain, siponimod accumulated predominantly in the cerebrum but not the cerebellum. No secondary ¹⁹F signals were detected from metabolites. From a translational perspective, we found that acquisitions done on a 3.0 T clinical MR scanner were 2.75 times more sensitive than acquisitions performed on a preclinical 9.4 T MR setup when taking changes in brain size across species into consideration and using equivalent relative spatial resolution. Conclusion: Siponimod can be imaged non-invasively using ¹⁹F UTE MRI in the form administered to MS patients, without modification. This study lays the groundwork for more extensive preclinical and clinical investigations. With the necessary technical development, ¹⁹F MRI has the potential to become a powerful theranostic tool for studying the time-course and distribution of CNS-acting drugs within the brain, especially during pathology.

Impact of Siponimod on Enteric and Central Nervous System Pathology in Late-Stage Experimental Autoimmune Encephalomyelitis

Multiple sclerosis (MS) is an autoimmune disease of the central nervous system (CNS). Although immune modulation and suppression are effective during relapsing-remitting MS, secondary progressive MS (SPMS) requires neuroregenerative therapeutic options that act on the CNS. The sphingosine-1-phosphate receptor modulator siponimod is the only approved drug for SPMS. In the pivotal trial, siponimod reduced disease progression and brain atrophy compared with placebo. The enteric nervous system (ENS) was recently identified as an additional autoimmune target in MS. We investigated the effects of siponimod on the ENS and CNS in the experimental autoimmune encephalomyelitis model of MS. Mice with late-stage disease were treated with siponimod, fingolimod, or sham. The clinical disease was monitored daily, and treatment success was verified using mass spectrometry and flow cytometry, which revealed peripheral lymphopenia in siponimod- and fingolimod-treated mice. We evaluated the mRNA expression, ultrastructure, and histopathology of the ENS and CNS. Single-cell RNA sequencing revealed an upregulation of proinflammatory genes in spinal cord astrocytes and ependymal cells in siponimod-treated mice. However, differences in CNS and ENS histopathology and ultrastructural pathology between the treatment groups were absent. Thus, our data suggest that siponimod and fingolimod act on the peripheral immune system and do not have pronounced direct neuroprotective effects.

Cladribine treatment improves cortical network functionality in a mouse model of autoimmune encephalomyelitis

Background

Cladribine is a synthetic purine analogue that interferes with DNA synthesis and repair next to disrupting cellular proliferation in actively dividing lymphocytes. The compound is approved for the treatment of multiple sclerosis (MS). Cladribine can cross the blood–brain barrier, suggesting a potential effect on central nervous system (CNS) resident cells. Here, we explored compartment-specific immunosuppressive as well as potential direct neuroprotective effects of oral cladribine treatment in experimental autoimmune encephalomyelitis (EAE) mice.

Methods

In the current study, we compare immune cell frequencies and phenotypes in the periphery and CNS of EAE mice with distinct grey and white matter lesions (combined active and focal EAE) either orally treated with cladribine or vehicle, using flow cytometry. To evaluate potential direct neuroprotective effects, we assessed the integrity of the primary auditory cortex neuronal network by studying neuronal activity and spontaneous synaptic activity with electrophysiological techniques ex vivo.

Results

Oral cladribine treatment significantly attenuated clinical deficits in EAE mice. Ex vivo flow cytometry showed that cladribine administration led to peripheral immune cell depletion in a compartment-specific manner and reduced immune cell infiltration into the CNS. Histological evaluations revealed no significant differences for inflammatory lesion load following cladribine treatment compared to vehicle control. Single cell electrophysiology in acute brain slices was performed and showed an impact of cladribine treatment on intrinsic cellular firing patterns and spontaneous synaptic transmission in neurons of the primary auditory cortex. Here, cladribine administration in vivo partially restored cortical neuronal network function, reducing action potential firing. Both, the effect on immune cells and neuronal activity were transient.

Conclusions

Our results indicate that cladribine exerts a neuroprotective effect after crossing the blood–brain barrier independently of its peripheral immunosuppressant action.

Long-term efficacy and safety of siponimod in patients with secondary progressive multiple sclerosis: Analysis of EXPAND core and extension data up to >5 years

BACKGROUND

Siponimod significantly reduced the risk of confirmed disability progression (CDP), worsening in cognitive processing speed (CPS), relapses, and magnetic resonance imaging (MRI) measures of brain atrophy and inflammation versus placebo in secondary progressive multiple sclerosis (SPMS) patients in the Phase 3 EXPAND study.

OBJECTIVE

The aim of this study was to assess long-term efficacy and safety of siponimod 2 mg/day from the EXPAND study including the extension part, up to > 5 years.

METHODS

In the open-label extension part, participants receiving placebo during the core part were switched to siponimod (placebo-siponimod group) and those on siponimod continued the same treatment (continuous siponimod group).

RESULTS

Continuous siponimod reduced the risk of 6-month CDP by 22% (hazard ratio (HR) (95% confidence interval (CI)): 0.78 (0.66-0.92) p = 0.0026) and 6-month confirmed worsening in CPS by 23% (HR (95% CI): 0.77 (0.65-0.92) p = 0.0047) versus the placebo-siponimod group. Sustained efficacy on annualized relapse rate, total and regional brain atrophy, and inflammatory disease activity was also observed. No new, unexpected safety signals for siponimod were identified over the long term.

CONCLUSION

The sustained efficacy and consistent long-term safety profile of siponimod up to > 5 years support its clinical utility for long-term treatment of SPMS. Benefits in the continuous siponimod versus placebo-siponimod group highlight the significance of earlier treatment initiation.

TRIAL REGISTRATION NUMBER

NCT01665144.

The microbiome restrains melanoma bone growth by promoting intestinal NK and Th1 cell homing to bone

Bone metastases are frequent complications of malignant melanoma leading to reduced quality of life and significant morbidity. Regulation of immune cells by the gut microbiome influences cancer progression, but the role of the microbiome in tumor growth in bone is unknown. Using intracardiac or intratibial injections of B16-F10 melanoma cells into mice, we showed that gut microbiome depletion by broad-spectrum antibiotics accelerated intraosseous tumor growth and osteolysis. Microbiome depletion blunted melanoma-induced expansion of intestinal NK cells and Th1 cells and their migration from the gut to tumor-bearing bones. Demonstrating the functional relevance of immune cell trafficking from the gut to the bone marrow (BM) in bone metastasis, blockade of S1P-mediated intestinal egress of NK and Th1 cells, or inhibition of their CXCR3/CXCL9-mediated influx into the BM, prevented the expansion of BM NK and Th1 cells and accelerated tumor growth and osteolysis. Using a mouse model, this study revealed mechanisms of microbiota-mediated gut-bone crosstalk that are relevant to the immunological restraint of melanoma metastasis and tumor growth in bone. Microbiome modifications induced by antibiotics might have negative clinical consequences in patients with melanoma.

Hippocampal Cytokine Release in Experimental Epileptogenesis—A Longitudinal In Vivo Microdialysis Study

Background: Inflammation, particularly cytokine release, contributes to epileptogenesis by influencing the cerebral tissue remodeling and neuronal excitability that occurs after a precipitating epileptogenic insult. While several cytokines have been explored in this process, release kinetics are less well investigated. Determining the time course of cytokine release in the epileptogenic zone is necessary for precisely timed preventive or therapeutic anti-inflammatory interventions. Methods: Hippocampal extracellular levels of six cytokines and chemokines (IL-1β, IL-6, IL-10, CCL2, CCL3, and CCL5) were quantified at various time points during epileptogenesis in a rat model of mesial temporal lobe epilepsy with hippocampal sclerosis (mTLE-HS) using microdialysis (MD). Results: The analysis of microdialysates demonstrated consistent elevation at all time points during epileptogenesis for IL-1β and IL-10. IL-10 release was maximal on day 1, IL-1β release peaked at day 8. No correlation between local hippocampal IL-1β concentrations and IL-1β blood levels was found. Conclusion: The release kinetics of IL-1β are consistent with its established pro-epileptogenic properties, while the kinetics of IL-10 suggest a counter-regulatory effect. This proof-of-concept study demonstrates the feasibility of intraindividual longitudinal monitoring of hippocampal molecular inflammatory processes via repetitive MD over several weeks and sheds light on the kinetics of hippocampal cytokine release during epileptogenesis.

Increased Remyelination and Proregenerative Microglia Under Siponimod Therapy in Mechanistic Models

Background and Objectives

Siponimod is an oral, selective sphingosine-1-phosphate receptor-1/5 modulator approved for treatment of multiple sclerosis.

Methods

Mouse MRI was used to investigate remyelination in the cuprizone model. We then used a conditional demyelination Xenopus laevis model to assess the dose-response of siponimod on remyelination. In experimental autoimmune encephalomyelitis–optic neuritis (EAEON) in C57Bl/6J mice, we monitored the retinal thickness and the visual acuity using optical coherence tomography and optomotor response. Optic nerve inflammatory infiltrates, demyelination, and microglial and oligodendroglial differentiation were assessed by immunohistochemistry, quantitative real-time PCR, and bulk RNA sequencing.

Results

An increased remyelination was observed in the cuprizone model. Siponimod treatment of demyelinated tadpoles improved remyelination in comparison to control in a bell-shaped dose-response curve. Siponimod in the EAEON model attenuated the clinical score, reduced the retinal degeneration, and improved the visual function after prophylactic and therapeutic treatment, also in a bell-shaped manner. Inflammatory infiltrates and demyelination of the optic nerve were reduced, the latter even after therapeutic treatment, which also shifted microglial differentiation to a promyelinating phenotype.

Discussion

These results confirm the immunomodulatory effects of siponimod and suggest additional regenerative and promyelinating effects, which follow the dynamics of a bell-shaped curve with high being less efficient than low concentrations.

Abnormal oligodendrocyte function in schizophrenia explains the long latent interval in some patients

A puzzling feature of schizophrenia, is the long latency between the beginning of neuropathological changes and the clinical presentation that may be two decades later. Abnormalities in oligodendrocyte function may explain this latency, because mature oligodendrocytes produce myelination, and if myelination were abnormal from the outset, it would cause the synaptic dysfunction and abnormal neural tracts that are underpinning features of schizophrenia. The hypothesis is that latency is caused by events that occur in some patients as early as in-utero or infancy, because clones of abnormal, myelinating oligodendrocytes may arise at that time; their number doubles every ~2 years, so their geometric increase between birth and age twenty, when clinical presentation occurs, is about 1000-fold plus the effect of compounding. For those patients in particular, the long latency is because of a small but ongoing increase in volume of the resulting, abnormally myelinated neural tracts until, after a long latent interval, a critical mass is reached that allows the full clinical features of schizophrenia. During latency, there may be behavioral aberrancies because of abnormally myelinated neural tracts but they are insufficiently numerous for the clinical syndrome. The occurrence of behavioral symptoms during the long latent period, substantiates the hypothesis that abnormal oligodendrocytes explain the latency in some patients. Treatment with fingolimod or siponimod benefits both oligodendrocytes and neural tracts. Clinical trial would validate their potential benefit in appropriate patients with schizophrenia and, concurrently, would validate the hypothesis.

The Two Sides of Siponimod: Evidence for Brain and Immune Mechanisms in Multiple Sclerosis

Siponimod is a selective sphingosine 1-phosphate receptor subtype 1 (S1P₁) and 5 (S1P₅) modulator approved in the United States and the European Union as an oral treatment for adults with relapsing forms of multiple sclerosis (RMS), including active secondary progressive multiple sclerosis (SPMS). Preclinical and clinical studies provide support for a dual mechanism of action of siponimod, targeting peripherally mediated inflammation and exerting direct central effects. As an S1P₁ receptor modulator, siponimod reduces lymphocyte egress from lymph nodes, thus inhibiting their migration from the periphery to the central nervous system. As a result of its peripheral immunomodulatory effects, siponimod reduces both magnetic resonance imaging (MRI) lesion (gadolinium-enhancing and new/enlarging T2 hyperintense) and relapse activity compared with placebo. Independent of these effects, siponimod can penetrate the blood-brain barrier and, by binding to S1P₁ and S1P₅ receptors on a variety of brain cells, including astrocytes, oligodendrocytes, neurons, and microglia, exert effects to modulate neural inflammation and neurodegeneration. Clinical data in patients with SPMS have shown that, compared with placebo, siponimod treatment is associated with reductions in levels of neurofilament light chain (a marker of neuroaxonal damage) and thalamic and cortical gray matter atrophy, with smaller reductions in MRI magnetization transfer ratio and reduced confirmed disability progression. This review examines the preclinical and clinical data supporting the dual mechanism of action of siponimod in RMS.

Signaling through the S1P-S1PR Axis in the Gut, the Immune and the Central Nervous System in Multiple Sclerosis: Implication for Pathogenesis and Treatment

Sphingosine 1-phosphate (S1P) is a signaling molecule with complex biological functions that are exerted through the activation of sphingosine 1-phosphate receptors 1–5 (S1PR1–5). S1PR expression is necessary for cell proliferation, angiogenesis, neurogenesis and, importantly, for the egress of lymphocytes from secondary lymphoid organs. Since the inflammatory process is a key element of immune-mediated diseases, including multiple sclerosis (MS), S1PR modulators are currently used to ameliorate systemic immune responses. The ubiquitous expression of S1PRs by immune, intestinal and neural cells has significant implications for the regulation of the gut–brain axis. The dysfunction of this bidirectional communication system may be a significant factor contributing to MS pathogenesis, since an impaired intestinal barrier could lead to interaction between immune cells and microbiota with a potential to initiate abnormal local and systemic immune responses towards the central nervous system (CNS). It appears that the secondary mechanisms of S1PR modulators affecting the gut immune system, the intestinal barrier and directly the CNS, are coordinated to promote therapeutic effects. The scope of this review is to focus on S1P−S1PR functions in the cells of the CNS, the gut and the immune system with particular emphasis on the immunologic effects of S1PR modulation and its implication in MS.

Deconstructing the Pharmacological Contribution of Sphingosine-1 Phosphate Receptors to Mouse Models of Multiple Sclerosis Using the Species Selectivity of Ozanimod, a Dual Modulator of Human Sphingosine-1 Phosphate Receptor Subtypes 1 and 5

Ozanimod, a sphingosine-1 phosphate (S1P) receptor modulator that binds with high affinity selectively to S1P receptor subtypes 1 (S1P₁) and 5 (S1P₅), is approved for the treatment of relapsing multiple sclerosis (MS) in multiple countries. Ozanimod profiling revealed a species difference in its potency for S1P₅ in mouse, rat, and canine compared with that for human and monkey. Site-directed mutagenesis identified amino acid alanine at position 120 to be responsible for loss of activity for mouse, rat, and canine S1P₅ and mutation back to threonine as in human/monkey S1P₅ restored activity. Radioligand binding analysis performed with mouse S1P₅ confirmed the potency loss is a consequence of a loss of affinity of ozanimod for mouse S1P₅ and was restored with mutation of alanine 120 to threonine. Study of ozanimod in preclinical mouse models of MS can now determine the S1P receptor(s) responsible for observed efficacies with receptor engagement as measured using pharmacokinetic exposures of free drug. Hence, in the experimental autoimmune encephalomyelitis model, ozanimod exposures sufficient to engage S1P₁, but not S1P₅, resulted in reduced circulating lymphocytes, disease scores, and body weight loss; reduced inflammation, demyelination, and apoptotic cell counts in the spinal cord; and reduced circulating levels of the neuronal degeneration marker, neurofilament light. In the demyelinating cuprizone model, ozanimod prevented axonal degradation and myelin loss during toxin challenge but did not facilitate enhanced remyelination post-intoxication. Since free drug levels in this model only engaged S1P_1, we concluded that S1P₁ activation is neuroprotective but does not appear to affect remyelination. Significance Statement Ozanimod, a selective human S1P_1/5 modulator, displays reduced potency for rodent and dog S1P₅ compared with human, which results from mutation of threonine to alanine at position 120. Ozanimod can thus be used as a selective S1P₁ agonist in mouse models of multiple sclerosis to define efficacies driven by S1P₁ but not S1P₅ Based on readouts for experimental autoimmune encephalomyelitis and cuprizone intoxication, S1P₁ modulation is neuroprotective but S1P₅ activity may be required for remyelination.

The Role of Distinct Subsets of Macrophages in the Pathogenesis of MS and the Impact of Different Therapeutic Agents on These Populations

Multiple sclerosis (MS) is a demyelinating inflammatory disorder of the central nervous system (CNS). Besides the vital role of T cells, other immune cells, including B cells, innate immune cells, and macrophages (MФs), also play a critical role in MS pathogenesis. Tissue-resident MФs in the brain’s parenchyma, known as microglia and monocyte-derived MФs, enter into the CNS following alterations in CNS homeostasis that induce inflammatory responses in MS. Although the neuroprotective and anti-inflammatory actions of monocyte-derived MФs and resident MФs are required to maintain CNS tolerance, they can release inflammatory cytokines and reactivate primed T cells during neuroinflammation. In the CNS of MS patients, elevated myeloid cells and activated MФs have been found and associated with demyelination and axonal loss. Thus, according to the role of MФs in neuroinflammation, they have attracted attention as a therapeutic target. Also, due to their different origin, location, and turnover, other strategies may require to target the various myeloid cell populations. Here we review the role of distinct subsets of MФs in the pathogenesis of MS and different therapeutic agents that target these cells.

[Disease-modifying treatment of secondary progressive multiple sclerosis]

BACKGROUND

Multiple sclerosis (MS) is a disease continuum from a clinically isolated syndrome through relapsing remitting MS to secondary progressive MS (SPMS). There are numerous therapeutic approaches with proven efficacy on relapse and focal inflammatory disease aspects, whereas treatment of secondary progression and associated neuropathological aspects continues to be a challenge.

OBJECTIVE

Overview of the current options for disease-modifying treatment of SPMS.

MATERIAL AND METHODS

Results of randomized clinical trials are presented and evaluated on a substance-specific basis.

RESULTS

Randomized SPMS trials showed inconsistent results regarding disability progression for beta interferons and negative results for natalizumab. Oral cladribine and ocrelizumab reduced disability progression in relapsing MS but have not been specifically studied in an SPMS population. Positive results for mitoxantrone are only partially applicable to current SPMS patients. For siponimod, a substance that crosses the blood-brain barrier, the EXPAND trial demonstrated a significant reduction in the risk of disability progression in typical SPMS. Subgroup analyses suggest a higher efficacy of siponimod in younger patients with active SPMS.

CONCLUSION

There is limited evidence for the use of previously available disease-modifying treatment in SPMS. Siponimod represents a new therapeutic option for active SPMS, defined by relapses or focal inflammatory MRI activity. To establish the therapeutic indications for siponimod, early detection of relapse-independent progression as well as differentiation of active SPMS from inactive disease are of critical importance.

Sphingosine 1-phosphate Receptor Modulator Therapy for Multiple Sclerosis: Differential Downstream Receptor Signalling and Clinical Profile Effects

Lysophospholipids are a class of bioactive lipid molecules that produce their effects through various G protein-coupled receptors (GPCRs). Sphingosine 1-phosphate (S1P) is perhaps the most studied lysophospholipid and has a role in a wide range of physiological and pathophysiological events, via signalling through five distinct GPCR subtypes, S1PR1 to S1PR5. Previous and continuing investigation of the S1P pathway has led to the approval of three S1PR modulators, fingolimod, siponimod and ozanimod, as medicines for patients with multiple sclerosis (MS), as well as the identification of new S1PR modulators currently in clinical development, including ponesimod and etrasimod. S1PR modulators have complex effects on S1PRs, in some cases acting both as traditional agonists as well as agonists that produce functional antagonism. S1PR subtype specificity influences their downstream effects, including aspects of their benefit:risk profile. Some S1PR modulators are prodrugs, which require metabolic modification such as phosphorylation via sphingosine kinases, resulting in different pharmacokinetics and bioavailability, contrasting with others that are direct modulators of the receptors. The complex interplay of these characteristics dictates the clinical profile of S1PR modulators. This review focuses on the S1P pathway, the characteristics and S1PR binding profiles of S1PR modulators, the mechanisms of action of S1PR modulators with regard to immune cell trafficking and neuroprotection in MS, together with a summary of the clinical effectiveness of the S1PR modulators that are approved or in late-stage development for patients with MS. Sphingosine 1-phosphate receptor modulator therapy for multiple sclerosis: differential downstream receptor signalling and clinical profile effects (MP4 65540 kb).

Siponimod and Cognition in Secondary Progressive Multiple Sclerosis: EXPAND Secondary Analyses

OBJECTIVE

To investigate the effects of siponimod on cognitive processing speed in patients with secondary progressive (SP) multiple sclerosis (MS), by means of a predefined exploratory and post hoc analysis of the Exploring the Efficacy and Safety of Siponimod in Patients With Secondary Progressive Multiple Sclerosis (EXPAND) study, a randomized controlled trial comparing siponimod and placebo.

METHODS

EXPAND was a double-blind, placebo-controlled phase 3 trial involving 1,651 patients with SPMS randomized (2:1) to either siponimod 2 mg/d or placebo. Cognitive function was assessed with the Symbol Digit Modalities Test (SDMT), Paced Auditory Serial Addition Test (PASAT), and Brief Visuospatial Memory Test-Revised (BVMT-R) administered at baseline, 6-month intervals, and end of treatment.

RESULTS

Between-group differences in mean change from baseline in SDMT scores were significantly better in siponimod- vs placebo-treated patients at month 12 (difference 1.08 [95% confidence interval 0.23-1.94]; p = 0.0132), month 18 (1.23 [0.25-2.21); p = 0.0135), and month 24 (2.30 [1.11-3.50]; p = 0.0002). Siponimod-treated patients were at significantly lower risk for having a 4-point sustained decrease in SDMT score (hazard ratio [HR] 0.79 [0.65-0.96]; p = 0.0157), while their chance for having a 4-point sustained increase in SDMT score was higher (HR 1.28 [1.05-1.55]; p = 0.0131). PASAT and BVMT-R scores did not differ significantly between the 2 treatment groups (all p > 0.28).

CONCLUSION

Siponimod had a significant benefit on SDMT in patients with SPMS. Siponimod-treated patients were at significantly lower risk for having a ≥4-point decrease in SDMT score and had a significantly higher chance for having a ≥4-point increase in SDMT score, a magnitude of change accepted as clinically meaningful.

CLINICALTRIALSGOV IDENTIFIER

NCT01665144.

CLASSIFICATION OF EVIDENCE

This study provides Class II evidence that, for patients with SPMS, siponimod had a significant benefit on cognitive processing speed.

Sphingosine-1-Phosphate Receptor Modulators and Oligodendroglial Cells: Beyond Immunomodulation

Multiple sclerosis (MS) is an autoimmune inflammatory disease characterized by demyelination, axonal loss, and synaptic impairment in the central nervous system (CNS). The available therapies aim to reduce the severity of the pathology during the early inflammatory stages, but they are not effective in the chronic stage of the disease. In this phase, failure in endogenous remyelination is associated with the impairment of oligodendrocytes progenitor cells (OPCs) to migrate and differentiate into mature myelinating oligodendrocytes. Therefore, stimulating differentiation of OPCs into myelinating oligodendrocytes has become one of the main goals of new therapeutic approaches for MS. Different disease-modifying therapies targeting sphingosine-1-phosphate receptors (S1PRs) have been approved or are being developed to treat MS. Besides their immunomodulatory effects, growing evidence suggests that targeting S1PRs modulates mechanisms beyond immunomodulation, such as remyelination. In this context, this review focuses on the current understanding of S1PR modulators and their direct effect on OPCs and oligodendrocytes.

Protective Effects of Leukadherin1 in a Rat Model of Targeted Experimental Autoimmune Encephalomyelitis (EAE): Possible Role of P47phox and MDA Downregulation

Background

Reactive oxygen and nitrogen species (ROS and RNS) are involved in pathologic mechanisms underlying demyelination and exacerbation in multiple sclerosis (MS) lesions. P47phox is the most important subunit of an ROS-producing enzyme (NADPH oxidase) which is reportedly upregulated in MS plaques due to the intense activity of infiltrated immune cells and resident microglia. Leukadherin1 is a specific CD11b/CD18 agonist that inhibits signaling and transmigration of inflammatory cells to sites of injury. Based on this mechanism, we evaluated therapeutic effects of leukadherin1 in an animal model of targeted experimental autoimmune encephalomyelitis (EAE) through focal injection of inflammatory cytokines to the spinal cord.

Methods

For model induction, Lewis rats were first immunized with 15µg MOG 1–125 emulsion. Twenty days later, animals were subjected to stereotaxic injection of IFNγ and TNFα to the specific spinal area (T8). One day after injection, all animals presented EAE clinical signs, and their behaviors were monitored for eight days through open-field locomotion and grid-walking tests. Leukadherin1-treated animals received daily intraperitoneal injections of 1mg/kg of the drug. The specific spinal tissues were extracted on day 5 in order to measure nitric oxide (NO), malon di-aldehyde (MDA), and TNFα concentrations alongside P47phox real-time PCR analysis. In addition, spinal sections were prepared for immunohistochemical (IHC) observation of infiltrated leukocytes and activated microglia.

Results

Leukadherin1 exhibited promising improvements in EAE clinical scores and behavioral tests. Demyelination, CD45+ leukocyte infiltration, and Iba1+ microglia activation were reduced in spinal tissues of leukadherin1-treated animals. Furthermore, P47phox expression levels, MDA, and NO amounts were decreased in treated animals. However, TNFα concentrations did not differ following treatment.

Conclusion

Based on our results, we suggest that leukadherin1 may be used as a novel therapeutic agent in tackling the clinical challenge of multiple sclerosis, especially during the acute phase of the disease. This effect was possibly mediated through decreased leukocyte infiltration and oxidative stress.

Does Siponimod Exert Direct Effects in the Central Nervous System?

The modulation of the sphingosine 1-phosphate receptor is an approved treatment for relapsing multiple sclerosis because of its anti-inflammatory effect of retaining lymphocytes in lymph nodes. Different sphingosine 1-phosphate receptor subtypes are expressed in the brain and spinal cord, and their pharmacological effects may improve disease development and neuropathology. Siponimod (BAF312) is a novel sphingosine 1-phosphate receptor modulator that has recently been approved for the treatment of active secondary progressive multiple sclerosis (MS). In this review article, we summarize recent evidence suggesting that the active role of siponimod in patients with progressive MS may be due to direct interaction with central nervous system cells. Additionally, we tried to summarize our current understanding of the function of siponimod and discuss the effects observed in the case of MS.

Sphingosine-1-phosphate (S1P) receptors: Promising drug targets for treating bone-related diseases

Sphingosine-1-phosphate (S1P) is a natural bioactive lipid molecule and a common first or second messenger in the cardiovascular and immune systems. By binding with its receptors, S1P can serve as mediator of signalling during cell migration, differentiation, proliferation and apoptosis. Although the predominant role of S1P in bone regeneration has been noted in many studies, this role is not as well-known as its roles in the cardiovascular and immune systems. In this review, we summarize previous research on the role of S1P receptors (S1PRs) in osteoblasts and osteoclasts. In addition, S1P is regarded as a bridge between bone resorption and formation, which brings hope to patients with bone-related diseases. Finally, we discuss S1P and its receptors as therapeutic targets for treating osteoporosis, inflammatory osteolysis and bone metastasis based on the biological effects of S1P in osteoclastic/osteoblastic cells, immune cells and tumour cells.