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.