VT-ME6 is a potent and selective sphingosine kinase 2 inhibitor. VT-ME6, contained a quaternary ammonium group as a warhead and established that a positively charged moiety is necessary for engaging key amino acid residues in the enzyme binding pocket.13,14 This compound is moderately potent (Ki = 8 lM) and displays three-fold selectivity for SphK2 over SphK1. Sphingosine-1-phosphate (S1P) is a ubiquitous, endogenous small molecule that is synthesized by two isoforms of sphingosine kinase (SphK1 and 2). Intervention of the S1P signaling pathway has attracted significant attention because alteration of S1P levels is linked to several disease states including cancer, fibrosis, and sickle cell disease.