Sphingosine kinase type 2 inhibition elevates circulating sphingosine 1-phosphate

SIP (sphingosine 1-phosphate) is a pleiotropic lipid mediator involved in numerous cellular and physiological functions. Of note among these are cell survival and migration, as well as lymphocyte trafficking. SIP, which exerts its effects via five GPCRs (G-protein-coupled receptors) (S1P1-S1P5), is formed by the action of two SphKs (sphingosine kinases). Although SphK1 is the more intensively studied isotype, SphK2 is unique in it nuclear localization and has been reported to oppose some of the actions ascribed to SphK1. Although several scaffolds of SphK1 inhibitors have been described, there is a scarcity of selective SphK2 inhibitors that are necessary to evaluate the downstream effects of inhibition of this isotype. In the present paper we report a cationic amphiphilic small molecule that is a selective SphK2 inhibitor. In the course of characterizing this compound in wild-type and SphK-null mice, we discovered that administration of the inhibitor to wild-type mice resulted in a rapid increase in blood SIP, which is in contrast with our SphK I inhibitor that drives circulating SIP levels down. Using a cohort of F2 hybrid mice, we confirmed, compared with wild-type mice, that circulating SIP levels were higher in SphK2-null mice and lower in SphK1-null mice. Thus both SphK I and SphK2 inhibitors recapitulate the blood SIP levels observed in the corresponding null mice. Moreover, circulating SIP levels mirror SphK2 inhibitor levels, providing a convenient biomarker of target engagement.