Neuroprotective crosstalk from vitamin B12 and sphingolipid signaling pathways in therapy for multiple sclerosis.

Fingolimod (Gilenya) received regulatory approval from the US FDA in 2010 as the first-in-class sphingosine 1-phosphate (S1P) receptor (S1PR) modulator and was the first oral disease-modifying therapy (DMT) used for the treatment of the relapsing forms of multiple sclerosis (MS). Development of this new class of therapeutic compounds has continued to be a pharmacological goal of high interest in clinical trials for treatment of various autoimmune disorders, including MS. S1P is a physiologic signaling molecule that acts as a ligand for a group of cell surface receptors. S1PRs are expressed on various body tissues and regulate diverse physiological and pathological cellular responses involved in innate and adaptive immune, cardiovascular, and neurological functions. Subtype 1 of the S1PR (S1PR1) is expressed on the cell surface of lymphocytes, which are well known for their major role in MS pathogenesis and play an important regulatory role in the egress of lymphocytes from lymphoid organs to the lymphatic circulation. Thus, S1PR1-directed pharmacological interventions aim to modulate its role in immune cell trafficking through sequestration of autoreactive lymphocytes in the lymphoid organs to reduce their recirculation and subsequent infiltration into the central nervous system. Indeed, receptor subtype selectivity for S1PR1 is theoretically favored to minimize safety concerns related to interaction with other S1PR subtypes. Improved understanding of fingolimod's mechanism of action has provided strategies for the development of the more selective second-generation S1PR modulators. This selectivity serves to reduce the most important safety concern regarding cardiac-related side effects, such as bradycardia, which requires prolonged first-dose monitoring. It has led to the generation of smaller molecules with shorter half-lives, improved onset of action with no requirement for phosphorylation for activation, and preserved efficacy. The shorter half-lives of the second-generation agents allow for more rapid reversal of their pharmacological effects following treatment discontinuation. This may be beneficial in addressing further treatment-related complications in case of adverse events, managing serious or opportunistic infections such as progressive multifocal leukoencephalopathy, and eliminating the drug in pregnancies. In March 2019, a breakthrough in MS treatment was achieved with the FDA approval for the second S1PR modulator, siponimod (Mayzent), for both active secondary progressive MS and relapsing-remitting MS. This was the first oral DMT specifically approved for active forms of secondary progressive MS. Furthermore, ozanimod received FDA approval in March 2020 for treatment of relapsing forms of MS, followed by subsequent approvals from Health Canada and the European Commission. Other second-generation selective S1PR modulators that have been tested for MS, with statistically significant data from phase II and phase III clinical studies, include ponesimod (ACT-128800), ceralifimod (ONO-4641), and amiselimod (MT-1303). This review covers the available data about the mechanisms of action, pharmacodynamics and kinetics, efficacy, safety, and tolerability of the various S1PR modulators for patients with relapsing-remitting, secondary progressive, and, for fingolimod, primary progressive MS.

What is the cardiovascular effect of S1P receptor modulator therapy in multiple sclerosis? Sphingosine 1-phosphate (S1P) receptor (S1PR) modulators are among the most efficient therapies for multiple sclerosis. As small molecules, they are not only acting on the immune but on cardiovascular and nervous systems as well. Short-term effects of S1PR modulators on the cardiovascular system have already been extensively described, while long-term effects are less known. Our review describes the mechanisms of action and the short- and long-term effects of these therapeutic agents on the cardiovascular system in different clinical trials. We systematically reviewed the literature that had been published by January 2022. One hundred seven articles were initially identified by title and abstract using targeted keywords, and thirty-nine articles with relevance to cardiovascular effects of S1PR therapy in multiple sclerosis patients were thereafter considered, including their references for further accurate clarification. Studies on fingolimod, the first S1PR modulator approved for treating multiple sclerosis, primarily support the safety profile of this therapeutic class. The second-generation therapeutic agents along with a different treatment initiation approach helped mitigate several of the cardiovascular adverse effects that had previously been observed at the start of treatment. The heart rate may decrease when initiating S1PR modulators and, less commonly, the atrioventricular conduction may be prolonged, requiring cardiac monitoring for the first 6 h of medication. Continuous therapy with S1PR modulators can increase blood pressure values; therefore, the presence of arterial hypertension should be checked during long-term treatment. Periodic surveillance of the cardiovascular and autonomic functions can help predict cardiac outcomes and prevent possible adverse events in S1PR modulators treatment. Further studies with longer follow-ups are needed, especially for the second-generation of S1PR modulators, to confirm the safety profile of this therapeutic class.

Cyclical and Dose-Dependent Responses of Adult Human Mature Oligodendrocytes to Fingolimod

Editor's evaluation: Transmembrane protein CD69 acts as an S1PR1 agonist

Immunosuppressant drugs such as cyclosporin have allowed widespread organ transplantation, but their utility remains limited by toxicities, and they are ineffective in chronic management of autoimmune diseases such as multiple sclerosis. In contrast, the immune modulating drug FTY720 is efficacious in a variety of transplant and autoimmune models without inducing a generalized immunosuppressed state and is effective in human kidney transplantation. FTY720 elicits a lymphopenia resulting from a reversible redistribution of lymphocytes from circulation to secondary lymphoid tissues by unknown mechanisms. Using FTY720 and several analogs, we show now that FTY720 is phosphorylated by sphingosine kinase; the phosphorylated compound is a potent agonist at four sphingosine 1-phosphate receptors and represents the therapeutic principle in a rodent model of multiple sclerosis. Our results suggest that FTY720, after phosphorylation, acts through sphingosine 1-phosphate signaling pathways to modulate chemotactic responses and lymphocyte trafficking.

Decision letter: The signaling lipid sphingosine 1-phosphate regulates mechanical pain

Sphingosine 1-phosphate (S1P) receptors (nomenclature as agreed by the NC-IUPHAR Subcommittee on Lysophospholipid receptors [96]) are activated by the endogenous lipid sphingosine 1-phosphate (S1P). Originally cloned as orphan members of the endothelial differentiation gene (edg) family [16, 123], the receptors are currently designated as S1P1R through S1P5R [73, 16, 123]. Their gene nomenclature has been codified as human S1PR1, S1PR2, etc. (HUGO Gene Nomenclature Committee, HGNC) and S1pr1, S1pr2, etc. for mice (Mouse Genome Informatics Database, MGI) to reflect species and receptor function. All S1P receptors (S1PRs) have been knocked-out in mice constitutively and in some cases, conditionally. S1PRs, particularly S1P1, are expressed throughout all mammalian organ systems. Ligand delivery occurs via two known carriers (or "chaperones"): albumin and HDL-bound apolipoprotein M (ApoM), the latter of which elicits biased agonist signaling by S1P1 in multiple cell types [18, 53]. The five S1PRs, two chaperones, and active cellular metabolism have complicated analyses of receptor ligand binding in native systems. Signaling pathways and physiological roles have been characterized through radioligand binding in heterologous expression systems, targeted deletion of the different S1PRs, and most recently, mouse models that report in vivo S1P1R activation [101, 103]. The structures of S1P1 [180, 69, 108, 184], S1P2 [32], S1P3[116, 187], and S1P5 [110, 185] are solved, and confirmed aspects of ligand binding, specificity, and receptor activation, determined previously through biochemical and genetic studies [69, 17]. fingolimod (FTY720), the first FDA-approved drug to target any of the lysophospholipid receptors, binds as a phosphorylated metabolite to four of the five S1PRs, and was the first oral therapy for multiple sclerosis (MS) [35]. Second-generation S1PR modulators siponimod, ozanimod, and ponesimod that target S1P1 and S1P5 are also FDA approved for the treatment of various MS forms [16, 123]. In 2021, ozanimod became the first S1PR modulator to be FDA approved for the treatment of ulcerative colitis [145]. The mechanisms of action of fingolimod and other S1PR-modulating drugs now in development include binding S1PRs in multiple organ systems, e.g., immune and nervous systems, although the precise nature of their receptor interactions requires clarification [141, 37, 63, 64].

Molecular and neuroimmune pharmacology of S1P receptor modulators and other disease-modifying therapies for multiple sclerosis

Fingolimod: Direct CNS effects of sphingosine 1-phosphate (S1P) receptor modulation and implications in multiple sclerosis therapy

FTY720 (Fingolimod) is the first of a new immunomodulator class: sphingosine 1-phosphate (S1P) receptor modulator. We have found FTY720 by chemical modification of a natural product, myriocin derived from Isaria sinclairii, a kind of vegetative wasp. FTY720 is orally active and is highly effective in various autoimmune disease models including experimental autoimmune encephalomyelitis (EAE), adjuvant- or collagen-induced arthritis, and lupus nephritis. Particularly, oral administration of FTY720 shows marked therapeutic effects on EAE in mice with a significant reduction of demyelination and T cell infiltration in the central nervous system. A most striking feature of FTY720 is the induction of a marked decrease in peripheral blood lymphocytes at doses that show immunomodulating effects. It is revealed that the reduction of circulating lymphocytes by FTY720 is due to sequestration of lymphocytes into secondary lymphoid organs. FTY720 is rapidly converted to FTY720-phosphate (FTY720-P) by sphingosine kinases. FTY720-P acts as a potent agonist at S1P receptor type 1 (S1P1), internalizes S1P1 on lymphocytes, and inhibits migration of lymphocytes toward S1P. It is highly likely that immunomodulating effects of FTY720 are caused by inhibition of S1P/S1P1-dependent lymphocyte egress from secondary lymphoid organs. Moreover, it is suggested that direct effects of FTY720-P on neural cells via S1P receptors promote neuroprotection. Since FTY720 possesses a novel mechanism of action and is highly effective in relapsing remitting multiple sclerosis patients, it is presumed that oral FTY720 provides a new therapeutic approach for autoimmune diseases including multiple sclerosis.

The structure and function of the S1P1 receptor

Ozanimod, a sphingosine 1-phosphate (S1P) receptor modulator, binds with high affinity selectively to S1P receptor subtypes 1 (S1P1) and 5 (S1P5), and is approved in multiple countries for treating adults with relapsing forms of multiple sclerosis (MS) or moderately to severely active ulcerative colitis (UC). Other S1P receptor modulators have been approved for the treatment of MS or are in clinical development for MS or UC, but it is unknown whether these compounds bind competitively with each other to S1P1 or S1P5. We developed a competitive radioligand binding assay using tritiated ozanimod and demonstrate full displacement of ozanimod by S1P (endogenous ligand), suggesting that ozanimod binds to the S1P1 and S1P5 orthosteric binding sites. S1P receptor modulators FTY720-p, siponimod, etrasimod, ponesimod, KRP-203-p, and amiselimod-p also completely displacing radiolabeled ozanimod; thus, on a macroscopic level, all bind to the same site. Molecular docking studies support these results and predict the binding of each molecule to the orthosteric site of the receptors, creating similar interactions within S1P1 and S1P5. The absolute free energy perturbation method further validated key proposed binding modes. Functional potency tightly aligned with binding affinities across S1P1 and S1P5 and all compounds elicited S1P1-mediated β-arrestin recruitment. Since all the S1P modulators included in this study display similar receptor pharmacology and compete for binding at the same site, they can be considered interchangeable with one another. The choice of any one particular agent should therefore be made on the basis of overall therapeutic profile, and patients can be offered the opportunity to switch S1P medications without the potential concern of additive S1P pharmacology.

Viral infections may have an important role in the precipitation or relapse of multiple sclerosis (MS) and its treatment. This review describes the normal immune response to viral infection, the possible associations between viral infections and MS therapy, and the impact of sphingosine 1-phosphate (S1P) receptor (S1PR) modulation with fingolimod (FTY720) on the immune responses to viral infection. The physiologic immune response to viral infection involves lymphocyte activation and control of the circulation of subsets of lymphocytes with different functions between the lymph nodes, vascular system, and tissues, under the control of the S1P/S1PR signaling mechanism. In MS, it has been postulated that viral infections may play a role in triggering MS relapses, with virus-specific T cells being responsible for the demyelinating lesions within the CNS. Fingolimod-an S1PR modulator approved for the treatment of relapsing MS in some countries-is thought to act by downmodulating lymphatic S1P subtype 1 receptors. This retains naïve T cells and central memory T cells, but not effector memory T cells, within the lymph nodes and prevents their circulation to the CNS. Evidence from infection models supports that the selective effects of fingolimod on T cell subsets allows key immune responses to be preserved during therapy. However, in patients, long-term observation is important as both the risk of cancer and infection is potentially increased by the use of any immunomodulatory agent.

Sphingosine 1-phosphate (S1P) receptor modulators possess a unique mechanism of action as disease-modifying therapy for multiple sclerosis (MS). Subtype 1 S1P receptors are expressed on the surfaces of lymphocytes and are important in regulating egression from lymph nodes. The S1P receptor modulators indirectly antagonize the receptor's function and sequester lymphocytes in lymph nodes. Fingolimod was the first S1P agent approved in the USA in 2010 for relapsing MS after two phase III trials (FREEDOMS and TRANSFORMS) demonstrated potent efficacy, and good safety and tolerability. Post-marketing experience, as well as a third phase III trial (FREEDOMS II), also showed favorable results. More selective S1P receptor agents-ponesimod (ACT128800), siponimod (BAF312), ozanimod (RPC1063), ceralifimod (ONO-4641), GSK2018682, and MT-1303-are still in relatively early stages of development, but phase I and II trials showed promising efficacy and safety. However, these observations have yet to be reproduced in phase III clinical trials.

Until recently, all approved multiple sclerosis (MS) disease treatments were administered parenterally. Oral fingolimod was approved in September 2010 by the US Food and Drug Administration to reduce relapses and disability progression in relapsing forms of MS. In the clinical trials that led to approval, fingolimod reduced not only acute relapses and magnetic resonance imaging lesion activity but also disability progression and brain volume loss, suggesting preservation of tissue. Fingolimod's mechanism of action in MS is not known with certainty. Its active form, fingolimod-phosphate (fingolimod-P), is a sphingosine 1-phosphate receptor (S1PR) modulator that inhibits egress of lymphocytes from lymph nodes and their recirculation, potentially reducing trafficking of pathogenic cells into the central nervous system (CNS). Fingolimod also readily penetrates the CNS, and fingolimod-P formed in situ may have direct effects on neural cells. Fingolimod potently inhibits the MS animal model, experimental autoimmune encephalomyelitis, but is ineffective in mice with selective deficiency of the S1P₁ S1PR subtype on astrocytes despite normal expression in the immune compartment. These findings suggest that S1PR modulation by fingolimod in both the immune system and CNS, producing a combination of beneficial anti-inflammatory and possibly neuroprotective/reparative effects, may contribute to its efficacy in MS. In clinical trials, fingolimod was generally safe and well tolerated. Its interaction with S1PRs in a variety of tissues largely accounts for the reported adverse effects, which were seen more frequently with doses 2.5 to 10x the approved 0.5 mg dose. Fingolimod's unique mechanism of action distinguishes it from all other currently approved MS therapies.