RT Journal Article
SR Electronic
T1 Elimination of a Hydroxyl Group in FTY720 Dramatically Improves the Phosphorylation Rate
JF Molecular Pharmacology
JO Mol Pharmacol
FD American Society for Pharmacology and Experimental Therapeutics
SP 685
OP 692
DO 10.1124/mol.110.064873
VO 78
IS 4
A1 Eve Jary
A1 Thomas Bee
A1 Scott R. Walker
A1 Sung-Kee Chung
A1 Kyung-Chang Seo
A1 Jonathan C. Morris
A1 Anthony S. Don
YR 2010
UL http://molpharm.aspetjournals.org/content/78/4/685.abstract
AB The new immunosuppressant FTY720 (fingolimod), an analog of the endogenous lipid sphingosine, induces transient lymphopenia through the sequestration of lymphocytes in secondary lymphoid organs. Phosphorylation of FTY720 by sphingosine kinase 2 (SphK2) yields the active metabolite FTY720-phosphate (FTY-P), which induces lymphopenia through agonism of the sphingosine 1-phosphate receptor S1P1 on endothelial cells and lymphocytes. Dephosphorylation of circulating FTY-P creates an equilibrium between FTY720 and its phosphate, and results with human patients indicate that phosphorylation of FTY720 could be rate limiting for efficacy. We report that the FTY720 derivative 2-amino-4-(4-heptyloxyphenyl)-2-methylbutanol [AAL(R)] is phosphorylated much more rapidly than FTY720 in cultured human cells and whole blood. The Kcat for AAL(R) with recombinant SphK2 is 8-fold higher than for FTY720, whereas the Km for the two substrates is very similar, indicating that the increased rate of phosphorylation results from faster turnover by SphK2 rather than a higher binding affinity. Consequently, treating cells with AAL(R), but not FTY720, triggers an apoptotic pathway that is dependent on excessive intracellular accumulation of long-chain base phosphates. In agreement with the in vitro results, phosphorylation of AAL(R) is more complete than that of FTY720 in vivo (mice), and AAL(R) is a more potent inducer of lymphopenia. These differences may be magnified in humans, because phosphorylation of FTY720 is much less efficient in humans compared with rodents. Our results suggest that AAL(R) is a better tool than FTY720 for in vivo studies with S1P analogs and would probably be a more effective immunosuppressant than FTY720.