Enantioselective synthesis of the phosphate esters of the immunosuppressive lipid FTY720

Enantioselective desymmetrization of FTY720

A method for enantioselective desymmetrization of N-Ac and N-Boc-FTY720 by nonenzymatic asymmetric acylation was developed. Effective enantioselective monobenzoylation using benzoyl chloride in the presence of the tetraphenylbisoxazoline (L2)-CuCl2 complex gave the desired products 3a and 3b in 52-62% yield with 64% ee.

Fingolimod (FTY720): a recently approved multiple sclerosis drug based on a fungal secondary metabolite

Fingolimod (Gilenya; FTY720), a synthetic compound based on the fungal secondary metabolite myriocin (ISP-I), is a potent immunosuppressant that was approved (September 2010) by the U.S. FDA as a new treatment for multiple sclerosis (MS). Fingolimod was synthesized by the research group of Tetsuro Fujita at Kyoto University in 1992 while investigating structure-activity relationships of derivatives of the fungal metabolite ISP-I, isolated from Isaria sinclairii. Fingolimod becomes active in vivo following phosphorylation by sphingosine kinase 2 to form fingolimod-phosphate, which binds to extracellular G protein-coupled receptors, sphingosine 1-phosphates, and prevents the release of lymphocytes from lymphoid tissue. Fingolimod is orally active, which is unique among current first-line MS therapies, and it has the potential to be used in the treatment of organ transplants and cancer. This review highlights the discovery and development of fingolimod, from an isolated lead natural product, through synthetic analogues, to an approved drug.

FTY720 and (S)-FTY720 vinylphosphonate inhibit sphingosine kinase 1 and promote its proteasomal degradation in human pulmonary artery smooth muscle, breast cancer and androgen-independent prostate cancer cells

Sphingosine kinase 1 (SK1) is an enzyme that catalyses the phosphorylation of sphingosine to produce the bioactive lipid sphingosine 1-phosphate (S1P). We demonstrate here that FTY720 (Fingolimod) and (S)-FTY720 vinylphosphonate are novel inhibitors of SK1 catalytic activity and induce the proteasomal degradation of this enzyme in human pulmonary artery smooth muscle cells, MCF-7 breast cancer cells and androgen-independent LNCaP-AI prostate cancer cells. Proteasomal degradation of SK1 in response to FTY720 and (S)-FTY720 vinylphosphonate is associated with the down-regulation of the androgen receptor in LNCaP-AI cells. (S)-FTY720 vinylphosphonate also induces the apoptosis of these cells. These findings indicate that SK1 is involved in protecting LNCaP-AI from apoptosis. This protection might be mediated by so-called 'inside-out' signalling by S1P, as LNCaP-AI cells exhibit increased expression of S1P(2/3) receptors and reduced lipid phosphate phosphatase expression (compared with androgen-sensitive LNCaP cells) thereby potentially increasing the bioavailability of S1P at S1P(2/3) receptors.

Characterization of sphingosine-1-phosphate lyase activity by electrospray ionization-liquid chromatography/tandem mass spectrometry quantitation of (2E)-hexadecenal

Sphingosine-1-phosphate (S1P) is a sphingolipid signaling molecule crucial for cell survival and proliferation. S1P-mediated signaling is largely controlled through its biosynthesis and degradation, and S1P lyase (S1PL) is the only known enzyme that irreversibly degrades sphingoid base-1-phosphates to phosphoethanolamine and the corresponding fatty aldehydes. S1PL-mediated degradation of S1P results in the formation of (2E)-hexadecenal, whereas hexadecanal is the product of dihydrosphingosine-1-phosphate (DHS1P) degradation. Fatty aldehydes can undergo biotransformation to fatty acids and/or alcohols, making them elusive and rendering the task of fatty aldehyde quantitation challenging. We have developed a simple, highly sensitive, and high-throughput protocol for (2E)-hexadecenal quantitation as a semicarbazone derivative by liquid chromatography-electrospray ionization-tandem mass spectrometry. The approach was applied to determining S1PL activity in vitro with the ability to use as low as 0.25μg of microsomal protein per assay. The method is also applicable to the use of total tissue homogenate as the source of S1PL. A correction for (2E)-hexadecenal disappearance due to its biotransformation during enzymatic reaction is required, especially at higher protein concentrations. The method was applied to confirm FTY720 as the inhibitor of S1PL with an IC₅₀ value of 52.4μM.

Chiral vinylphosphonate and phosphonate analogues of the immunosuppressive agent FTY720

The first enantioselective synthesis of chiral isosteric phosphonate analogues of FTY720 is described. One of these analogues, FTY720-(E)-vinylphosphonate (S)-5, but not its R enantiomer, elicited a potent antiapoptotic effect in intestinal epithelial cells, suggesting that it exerts its action via the enantioselective activation of a receptor. (S)-5 failed to activate the sphingosine 1-phosphate type 1 (S1P(1)) receptor.

FTY720 inhibits ceramide synthases and up-regulates dihydrosphingosine 1-phosphate formation in human lung endothelial cells

Novel immunomodulatory molecule FTY720 is a synthetic analog of myriocin, but unlike myriocin FTY720 does not inhibit serine palmitoyltransferase. Although many of the effects of FTY720 are ascribed to its phosphorylation and subsequent sphingosine 1-phosphate (S1P)-like action through S1P(1,3-5) receptors, studies on modulation of intracellular balance of signaling sphingolipids by FTY720 are limited. In this study, we used stable isotope pulse labeling of human pulmonary artery endothelial cells with l-[U-(13)C, (15)N]serine as well as in vitro enzymatic assays and liquid chromatography-tandem mass spectrometry methodology to characterize FTY720 interference with sphingolipid de novo biosynthesis. In human pulmonary artery endothelial cells, FTY720 inhibited ceramide synthases, resulting in decreased cellular levels of dihydroceramides, ceramides, sphingosine, and S1P but increased levels of dihydrosphingosine and dihydrosphingosine 1-phosphate (DHS1P). The FTY720-induced modulation of sphingolipid de novo biosynthesis was similar to that of fumonisin B1, a classical inhibitor of ceramide synthases, but differed in the efficiency to inhibit biosynthesis of short-chain versus long-chain ceramides. In vitro kinetic studies revealed that FTY720 is a competitive inhibitor of ceramide synthase 2 toward dihydrosphingosine with an apparent K(i) of 2.15 microm. FTY720-induced up-regulation of DHS1P level was mediated by sphingosine kinase (SphK) 1, but not SphK2, as confirmed by experiments using SphK1/2 silencing with small interfering RNA. Our data demonstrate for the first time the ability of FTY720 to inhibit ceramide synthases and modulate the intracellular balance of signaling sphingolipids. These findings open a novel direction for therapeutic applications of FTY720 that focuses on inhibition of ceramide biosynthesis, ceramide-dependent signaling, and the up-regulation of DHS1P generation in cells.

The immunomodulator FTY720 has a direct cytoprotective effect in oligodendrocyte progenitors

The immunomodulator 2-amino-2-[2-(4-octylphenyl)ethyl]-1,3-propanediol (FTY720) has promising therapeutic effects in multiple sclerosis (MS), a degenerative disease in which demyelination of the central nervous system is accompanied by death of oligodendrocytes (OLGs), the myelin-producing cells. In vivo phosphorylation of FTY720 generates an agonist for G protein-coupled receptors for sphingosine-1-phosphate, a lipid mediator that plays a crucial role in the stimulation of OLG survival by neurotrophin-3 (NT-3). The mechanisms underlying the action of FTY720 in MS are not clearly understood, although the effects of this drug in autoimmune diseases are thought to stem from its ability to reduce lymphocyte infiltration and inflammation. Interestingly, we now found that FTY720 also has a direct effect on OLG progenitors. Treatment of these cells with FTY720 causes activation of extracellular signal-regulated kinase 1/2 and Akt, accompanied by protection from apoptosis. However, FTY720 also arrested OLG differentiation. Importantly, this effect was counteracted by NT-3, which not only enhanced the survival of OLG progenitors induced by FTY720 but also stimulated their maturation. Altogether, these observations suggest that in addition to its immunosuppressive functions, FTY720 could also have a beneficial effect in MS by direct action on OLG progenitors. However, the finding that FTY720 blocks the differentiation of these cells raises the question of whether MS therapies with FTY720 should include the use of differentiation-enhancing factors such as NT-3. This approach would ensure both protection of existing OLG progenitor pools against immune-mediated insults as well as stimulation of remyelination by enhancing the maturation of these cells.

FTY720 Story. Its Discovery and the following Accelerated Development of Sphingosine 1-Phosphate Receptor Agonists as Immunomodulators Based on Reverse Pharmacology

Fingolimod (FTY720) is the first of a novel class: sphingosine 1-phosphate (S1P) receptor modulator and is currently in phase 3 clinical trials for multiple sclerosis (MS). FTY720 was first synthesized in 1992 by chemical modification of an immunosuppressive natural product, ISP-I (myriocin). ISP-I was isolated from the culture broth of Isaria sinclairii, a type of vegetative wasp that was an ‘eternal youth’ nostrum in traditional Chinese medicine. ISP-I is an amino acid having three successive asymmetric centers and some functionalities. We simplified the structure drastically to find a nonchiral symmetric 2-substitued-2-aminopropane-1,3-diol framework for an in vivo immunosuppressive activity (inhibition of rat skin allograft rejection test or prolonging effect on rat skin allograft survival) and finally discovered FTY720. During the course of the lead optimization process, we encountered an unexpected dramatic change of the mechanism of action with an in vivo output unchanged. Since it proved that FTY720 did not inhibit serine palmitoyltransferase that is the target enzyme of ISP-I, reverse pharmacological approaches have been preformed to elucidate that FTY720 is mainly phosphorylated by sphingosine kinease 2 in vivo and the phosphorylated drug acts as a potent agonist of four of the five G protein coupled receptors for S1P: S1P1, S1P3, S1P4 and S1P5. Evidence has accumulated that immunomodulation by FTY720-P is based on agonism at the S1P1 receptor. Medicinal chemistry targeting S1P1 receptor agonists is currently in progress. The FTY720 story provides a methodology where in vivo screens rather than in vitro screens play important roles in the lead optimization. Unlike recent drug discovery methodologies, such a strategy as adopted by the FTY720 program would more likely meet serendipity.

Sphingosine‐1‐phosphate and the immunosuppressant, FTY720‐phosphate, regulate detrusor muscle tone

Overactive bladder syndrome (OBS) results from disturbances of bladder function. Bladder smooth muscle (detrusor) exhibits spontaneous rhythmic activity (tone) independent of neurogenic control, which is enhanced in patients with OBS. We have now uncovered a prominent role for the bioactive sphingolipid metabolite, sphingosine-1-phosphate (S1P), in regulating rabbit detrusor smooth muscle tone and contraction. S1P-induced contraction of detrusor muscle was dependent on stretch and intracellular calcium. Although detrusor expresses the S1P receptors S1P1 and S1P2, only S1P2 appeared to be involved in S1P-induced contraction, since SEW2871 (S1P1 agonist) and dihydro-S1P (potent agonist for all S1P receptors except S1P2) were poor contractile agents. In agreement, the S1P2 antagonist JTE013 inhibited S1P-induced contraction. The fast, transient muscle contraction (phasic) mediated by S1P was dependent on phospholipase C (PLC) whereas the slower, sustained contraction (tonic) was not. Surprisingly, the immunosuppressant FTY720-phosphate, an agonist for all S1P receptors except S1P2, had distinct contractile properties and also induced slow, sustained contraction. Thus, FTY720-phosphate and/or S1P may regulate calcium channels in an S1P receptor-independent manner. Collectively, our results demonstrate that S1P may regulate detrusor smooth muscle tone and suggest that dysregulation of complex S1P signaling might contribute to OBS.