title: Sphingosine kinase activity is not required for tumor cell viability.
abstract: Sphingosine kinases (SPHKs) are enzymes that phosphorylate the lipid sphingosine, leading to the formation of sphingosine-1-phosphate (S1P). In addition to the well established role of extracellular S1P as a mitogen and potent chemoattractant, SPHK activity has been postulated to be an important intracellular regulator of apoptosis. According to the proposed rheostat theory, SPHK activity shifts the intracellular balance from the pro-apoptotic sphingolipids ceramide and sphingosine to the mitogenic S1P, thereby determining the susceptibility of a cell to apoptotic stress. Despite numerous publications with supporting evidence, a clear experimental confirmation of the impact of this mechanism on tumor cell viability in vitro and in vivo has been hampered by the lack of suitable tool reagents. Utilizing a structure based design approach, we developed potent and specific SPHK1/2 inhibitors. These compounds completely inhibited intracellular S1P production in human cells and attenuated vascular permeability in mice, but did not lead to reduced tumor cell growth in vitro or in vivo. In addition, siRNA experiments targeting either SPHK1 or SPHK2 in a large panel of cell lines failed to demonstrate any statistically significant effects on cell viability. These results show that the SPHK rheostat does not play a major role in tumor cell viability, and that SPHKs might not be attractive targets for pharmacological intervention in the area of oncology.
authors.affiliation: Oncology Research, Amgen Inc., Thousand Oaks, California, USA.
authors.forename: Karen
authors.initials: K
authors.lastname: Rex
authors.forename: Shawn
authors.initials: S
authors.lastname: Jeffries
authors.forename: Matthew L
authors.initials: ML
authors.lastname: Brown
authors.forename: Timothy
authors.initials: T
authors.lastname: Carlson
authors.forename: Angela
authors.initials: A
authors.lastname: Coxon
authors.forename: Flordeliza
authors.initials: F
authors.lastname: Fajardo
authors.forename: Brendon
authors.initials: B
authors.lastname: Frank
authors.forename: Darin
authors.initials: D
authors.lastname: Gustin
authors.forename: Alexander
authors.initials: A
authors.lastname: Kamb
authors.forename: Paul D
authors.initials: PD
authors.lastname: Kassner
authors.forename: Shyun
authors.initials: S
authors.lastname: Li
authors.forename: Yihong
authors.initials: Y
authors.lastname: Li
authors.forename: Kurt
authors.initials: K
authors.lastname: Morgenstern
authors.forename: Matthew
authors.initials: M
authors.lastname: Plant
authors.forename: Kim
authors.initials: K
authors.lastname: Quon
authors.forename: Astrid
authors.initials: A
authors.lastname: Ruefli-Brasse
authors.forename: Joanna
authors.initials: J
authors.lastname: Schmidt
authors.forename: Elissa
authors.initials: E
authors.lastname: Swearingen
authors.forename: Nigel
authors.initials: N
authors.lastname: Walker
authors.forename: Zhulun
authors.initials: Z
authors.lastname: Wang
authors.forename: J E Vivienne
authors.initials: JE
authors.lastname: Watson
authors.forename: Dineli
authors.initials: D
authors.lastname: Wickramasinghe
authors.forename: Mariwil
authors.initials: M
authors.lastname: Wong
authors.forename: Guifen
authors.initials: G
authors.lastname: Xu
authors.forename: Holger
authors.initials: H
authors.lastname: Wesche
mesh_terms: D000818:Animals; D002199:Capillary Permeability / Q000187:drug effects; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000737:chemistry / Q000493:pharmacokinetics / Q000494:pharmacology; D005260:Female; D055785:Gene Knockdown Techniques; D006801:Humans; D020128:Inhibitory Concentration 50; D051379:Mice; D009369:Neoplasms / Q000201:enzymology* / Q000235:genetics / Q000473:pathology; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D034622:RNA Interference; D047368:Tumor Burden / Q000187:drug effects; D014410:Tumor Stem Cell Assay; D042461:Vascular Endothelial Growth Factor A / Q000494:pharmacology; D023041:Xenograft Model Antitumor Assays; D000099157:Sphingosine Kinase
chemical_list: D004791:Enzyme Inhibitors; D017853:Phosphotransferases (Alcohol Group Acceptor); D042461:Vascular Endothelial Growth Factor A; D000099157:Sphingosine Kinase