NBD-labeled derivatives of the immunomodulatory drug FTY720 as tools for metabolism and mode of action studies

FTY720-induced endocytosis of yeast and human amino acid transporters is preceded by reduction of their inherent activity and TORC1 inhibition

FTY720 is a sphingoid base analog that acts as an anticancer agent in animal models. Its effect on tumor cells stems largely from its ability to trigger endocytosis of several nutrient transporters. The observation that FTY720 similarly stimulates downregulation of amino acid permeases in yeast suggests that the cellular mechanisms it targets, which are still poorly characterized, are evolutionarily conserved. We here report that adding FTY720 to yeast cells results in rapid inhibition of the intrinsic activity of multiple permeases. This effect is associated with inhibition of the TORC1 kinase complex, which in turn promotes ubiquitin-dependent permease endocytosis. Further analysis of the Gap1 permease showed that FTY720 elicits its ubiquitylation via the same factors that promote this modification when TORC1 is inhibited by rapamycin. We also show that FTY720 promotes endocytosis of the LAT1/SLC7A5 amino acid transporter in HeLa cells, this being preceded by loss of its transport activity and by mTORC1 inhibition. Our data suggest that in yeast, TORC1 deactivation resulting from FTY720-mediated inhibition of membrane transport elicits permease endocytosis. The same process seems to occur in human cells even though our data and previous reports suggest that FTY720 promotes transporter endocytosis via an additional mechanism insensitive to rapamycin.

Synthesis and immobilization of erythro-C14-omega-aminosphingosine-1-phosphate as a potential tool for affinity chromatography

A sphingosine-1-phosphate (S1P) analogue containing a terminal alkyl chain amino group is synthesized in a few steps via olefin cross-metathesis of an optically resolved intermediate and subsequent phosphorylation. Regioselective acylation of this intermediate at its N terminus in solution is demonstrated as a model reaction and provides a biologically active derivative. Finally, the omega-amino intermediate is immobilized on an affinity matrix. The choice of a UV-active phosphate protecting group allows for quantification of resin loading after cleavage which amounted to 66 %.

Synthesis and spectral properties of cholesterol- and FTY720-containing boron dipyrromethene dyes

Two analogues (1, 2) of free cholesterol and one analogue (3) of the immunosuppressive sphingolipid FTY720 containing a boron dipyrromethene chromophore (BODIPY) were synthesized. The synthetic routes involved preparation of boron dipyrromethene moieties (5, 11), bearing a phenylethynyl group at different positions of the chromophore, and lipids (13, 20) bearing an azido group. The dye was tethered to the lipid via a 1,2,3-triazole in the linker by the click reaction. Analogues derived from 11 [in which an (E)-styrylethynyl moiety is bonded to C-5 of BODIPY] exhibited a marked red shift (approximately 70-80 nm) compared with those derived from 5 (in which a phenylethynyl moiety is bonded to C-8 of BODIPY).

FTY720-phosphate is dephosphorylated by lipid phosphate phosphatase 3

FTY720 is a novel immunomodulatory drug efficacious in the treatment of multiple sclerosis. The drug is converted in vivo to the monophosphate, FTY720-P, by sphingosine kinase 2. This conversion is incomplete, suggesting opposing actions of kinase and phosphatase activities. To address which of the known lipid phosphatases might dephosphorylate FTY720-P, we overexpressed the broad specificity lipid phosphatases LPP1-3, and the specific S1P phosphatases (SPP1 and 2) in HEK293 cells, and performed in vitro assays using lysates of transfected cells. Among LPPs, only LPP3 was able to dephosphorylate FTY720-P; among SPPs, only SPP1 showed activity against FTY720-P. On intact cells, LPP3 acted as an ecto-phosphatase or FTY720-P, thus representing the major phosphatase involved in the equilibrium between FTY720 and FTY720-P observed in vivo.

Essential requirement for sphingosine kinase 2 in a sphingolipid apoptosis pathway activated by FTY720 analogues

The clinical immunosuppressant FTY720 is a sphingosine analogue that, once phosphorylated by sphingosine kinase 2 (Sphk2), is an agonist of multiple receptor subtypes for sphingosine 1-phosphate. Short exposures to FTY720 afford long term protection in lymphoproliferative and autoimmune disease models, presumably by inducing apoptosis in subsets of cells essential for pathogenesis. Sphingosine itself is pro-apoptotic, and apoptosis induced with FTY720 or sphingosine is thought to proceed independently of their phosphorylation. Following chemical mutagenesis of Jurkat cells we isolated mutants that are selectively resistant to FTY720 analogue AAL(R), as well as natural sphingolipid bases, including sphingosine. Cells lacking functional Sphk2 were resistant to apoptosis induced with AAL(R), indicating that apoptosis proceeds through AAL(R) phosphorylation. Phosphorylation of AAL(R) was also required for induction of lymphocyte apoptosis in mice, as apoptosis was not induced with the non-phosphorylatable chiral analogue, AAL(S). Apoptosis was induced in the spleen but not the thymus of mice administered 1 mg/kg AAL(R), correlating with levels of AAL(R)-phosphate (AFD(R)) in organ extracts. AFD(R) did not induce apoptosis when added to the cell culture medium, indicating that it induces apoptosis through an intracellular target. NBD-labeled AAL(R) localized to the endoplasmic reticulum, and AAL(R) treatment resulted in elevated cytosolic calcium, Bax redistribution from cytosol to mitochondrial and endoplasmic reticulum membranes, and caspase-independent mitochondrial permeabilization in Jurkat cells. We therefore describe an apoptotic pathway triggered by intracellular accumulation of sphingolipid base phosphates and suggest that sphingoid base substrates for Sphk2 acting intracellularly could be useful in the treatment of lymphoproliferative diseases.

Constrained azacyclic analogues of the immunomodulatory agent FTY720 as molecular probes for sphingosine 1-phosphate receptors

Constrained azacyclic analogues of FTY720 were prepared starting with d- and l-pyroglutamic acids. One enantiomer was shown to be a substrate for sphingosine kinase 2, being phosphorylated 4-fold more efficiently than FTY720. Among the corresponding phosphates, two were found to have unusual specificity in binding to S1P receptors: while being inactive on S1P1 and S1P3, they acted as potent agonists on S1P4 and S1P5. The phosphates may be useful to explore the biology and binding site of these receptors.