Discovery of a Potent and Selective Sphingosine Kinase 1 Inhibitor through the Molecular Combination of Chemotype-Distinct Screening Hits

Sphingosine
kinase (SphK) is the major source of the lipid mediator
and G protein-coupled receptor agonist sphingosine-1-phosphate (S1P).
S1P promotes cell growth, survival, and migration and is a key regulator
of lymphocyte trafficking. Inhibition of S1P signaling has been proposed
as a strategy for treatment of inflammatory diseases and cancer. Two
different formats of an enzyme-based high-throughput screen yielded
two attractive chemotypes capable of inhibiting S1P formation in cells.
The molecular combination of these screening hits led to compound 22a (PF-543) with 2 orders of magnitude improved potency.
Compound 22a inhibited SphK1 with an IC50 of
2 nM and was more than 100-fold selective for SphK1 over the SphK2
isoform. Through the modification of tail-region substituents, the
specificity of inhibition for SphK1 and SphK2 could be modulated,
yielding SphK1-selective, potent SphK1/2 dual, or SphK2-preferential
inhibitors.