A selective sphingosine kinase 1 inhibitor integrates multiple molecular therapeutic targets in human leukemia

Abstract

The potent bioactive sphingolipid mediator, sphingosine-1-phosphate (S1P), is produced by 2 sphingosine kinase isoenzymes, SphK1 and SphK2. Expression of SphK1 is up-regulated in cancers, including leukemia, and associated with cancer progression. A screen of sphingosine analogs identified (2R,3S,4E)-N-methyl-5-(4-pentylphenyl)-2-aminopent-4-ene-1,3-diol, designated SK1-I (BML-258), as a potent, water-soluble, isoenzymespecific inhibitor of SphK1. In contrast to pan-SphK inhibitors, SK1-I did not inhibit SphK2, PKC, or numerous other protein kinases. SK1-I decreased growth and survival of human leukemia U937 and Jurkat cells, and enhanced apoptosis and cleavage of Bcl-2. Lethality of SK1-I was reversed by caspase inhibitors and by expression of Bcl-2. SK1-I not only decreased S1P levels but concomitantly increased levels of its proapoptotic precursor ceramide. Conversely, S1P protected against SK1-I-induced apoptosis. SK1-I also induced multiple perturbations in activation of signaling and survival-related proteins, including diminished phosphorylation of ERK1/2 and IntroductionSphingosine-1-phosphate (S1P), a potent lipid mediator produced from sphingosine by sphingosine kinases (SphKs), regulates many processes important for cancer progression, including cell growth and survival. 1 In contrast to S1P, its precursors, sphingosine and ceramide, are associated with growth arrest and induction of apoptosis. 2 Thus, the balance between these interconvertible sphingolipid metabolites has been viewed as a cellular rheostat determining cell fate. 3 Numerous studies have shown that perturbations in the S1P/ceramide rheostat are involved in the regulation of resistance to chemotherapy and radiation therapy of neoplastic cells, including those of hematopoietic origin. 2,4,5 Two SphK isoenzymes, SphK1 and SphK2, have been described that, although sharing many features, 6,7 exhibit distinct functions. SphK1 promotes cell growth and survival, [8][9][10][11] whereas SphK2, when overexpressed, has opposite effects. 12,13 SphK1 is a key enzyme that regulates the S1P/ceramide rheostat. 12,14,15 Indeed, S1P and SphK1 have long been implicated in resistance of both primary leukemic cells and leukemia cell lines to apoptosis induced by commonly used cytotoxic agents. 3,[16][17][18] Non-isoenzyme-specific inhibitors of SphKs, such as L-threo-dihydrosphingosine (safingol) and N,N-dimethylsphingosine (DMS), are cytotoxic to leukemia cells. 18,19 Interestingly, multidrugresistant HL-60 myelogenous leukemia cells were more sensitive to DMS than the parental cells. 18 Moreover, SphK1 activity was lower in HL-60 cells sensitive to doxorubicin or etoposide than in MDR (multidrug resistance protein)-1-or MRP1 (multidrug resistance protein 1)-positive HL-60 cells. Enforced expression of SphK1 in sensitive HL-60 cells blocked apoptosis, whereas down-regulation of SphK1 overcame chemoresistance by inducing mitochondria-dependent apoptosis. 10 These observations take on added significance in light of evidence that MDR expression is a strong p...

Expressions of Sphingosine-1-phosphate (S1P) Receptors, Sphingosine Kinases in Malignant Bone and Soft Tissue Tumors, and The role of Sphingosine Kinase-1 in Growth of MFH Cell Lines

“…SPHK1 is frequently overexpressed in a varietly of solid tumors, suggesting a potential oncogenic function and an important role in human tumorigenesis. Recently SPHK1 inhibitors have shown to decrease proliferation of cancer cell lines [32][33][34][35][36]. In the current study, we could confirm that all MFH cell lines expressed SPHK1 proteins by Western blotting.…”

Reduction in sphingosine kinase 1 influences the susceptibility to dengue virus infection by altering antiviral responses

“…3b). Similarly, pre-treatment of HEK293 cells with an SK1-specific inhibitor, SK1-I [1,2, 4-trideoxy-4-(methylamino)-1-(4-pentylphenyl)-D-eythro-pent-1-enitol hydrochloride; Paugh et al, 2008], also reduced infectious virus release (Fig. 3c), with approximately a 1-2 log reduction in DENV infectious virus release at 24 h p.i.…”

Sphingosine 1-phosphate chemical biology

“…Further, a set of sphingosine analogs that contained numerous SPHK2 inhibitors was nearly devoid of SPHK1 inhibitors [65]. However, very recently a D-threo-sphingosine analog (SK1-I ((2R,3S,4E)-N-methyl-5-(4'-pentylphenyl)-2-aminopent-4-ene-1,3-diol)) was reported to be a selective human SPHK1 inhibitor (Ki ≈ 10 µM) [66]. In using SPHK-directed compounds, it is important to realize that there exists a wide variation in activity of SPHK substrates and inhibitors at mouse vs. human SPHK2 receptors.…”