A novel sphingosine kinase inhibitor induces autophagy in tumor cells.
The sphingolipids ceramide, sphingosine, and sphingosine 1-phosphate (S1P) regulate cell signaling, proliferation, apoptosis, and autophagy. Sphingosine kinase-1 and -2 (SK1 and SK2) phosphorylate sphingosine to form S1P, shifting the balanced activity of these lipids toward cell proliferation. We have previously reported that pharmacological inhibition of SK activity delays tumor growth in vivo. The present studies demonstrate that the SK2-selective inhibitor 3-(4-chlorophenyl)-adamantane-1-carboxylic acid (pyridin-4-ylmethyl)amide (ABC294640) induces nonapoptotic cell death that is preceded by microtubule-associated protein light chain 3 cleavage, morphological changes in lysosomes, formation of autophagosomes, and increases in acidic vesicles in A-498 kidney carcinoma cells. ABC294640 caused similar autophagic responses in PC-3 prostate and MDA-MB-231 breast adenocarcinoma cells. Simultaneous exposure of A-498 cells to ABC294640 and 3-methyladenine, an inhibitor of autophagy, switched the mechanism of toxicity to apoptosis, but decreased the potency of the SK2 inhibitor, indicating that autophagy is a major mechanism for tumor cell killing by this compound. Induction of the unfolded protein response by the proteasome inhibitor N-(benzyloxycarbonyl)leucinylleucinylleucinal Z-Leu-Leu-Leu-al (MG-132) or the heat shock protein 90 inhibitor geldanamycin synergistically increased the cytotoxicity of ABC294640 in vitro. In severe combined immunodeficient mice bearing A-498 xenografts, daily administration of ABC294640 delayed tumor growth and elevated autophagy markers, but did not increase terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling-positive cells in the tumors. These data suggest that ABC294640 promotes tumor cell autophagy, which ultimately results in nonapoptotic cell death and a delay of tumor growth in vivo. Consequently, ABC294640 may effectively complement anticancer drugs that induce tumor cell apoptosis.
Beljanski
Vladimir
V
Drug Discovery Core, Hollings Cancer Center, Medical University of South Carolina, Charleston, South Carolina 29425, USA.
Knaak
Christian
C
Smith
Charles D
CD
D000218:Adamantane / Q000031:analogs & derivatives* / Q000494:pharmacology; D000225:Adenine / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D001343:Autophagy / Q000187:drug effects*; D015153:Blotting, Western; D002453:Cell Cycle / Q000187:drug effects; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D007976:Leupeptins / Q000494:pharmacology; D051379:Mice; D016513:Mice, SCID; D018613:Microscopy, Confocal; D008869:Microtubule-Associated Proteins / Q000187:drug effects / Q000502:physiology; D051336:Mitochondrial Membranes / Q000187:drug effects; D009368:Neoplasm Transplantation; D009374:Neoplasms, Experimental / Q000188:drug therapy* / Q000503:physiopathology; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000037:antagonists & inhibitors*; D016133:Polymerase Chain Reaction; D011725:Pyridines / Q000494:pharmacology*; D034741:RNA, Small Interfering / Q000235:genetics; D014407:Tumor Cells, Cultured; D056811:Unfolded Protein Response / Q000187:drug effects; D000099157:Sphingosine Kinase
D000218:Adamantane; D000225:Adenine; D007976:Leupeptins; D008869:Microtubule-Associated Proteins; D017853:Phosphotransferases (Alcohol Group Acceptor); D011725:Pyridines; D034741:RNA, Small Interfering; D000099157:Sphingosine Kinase; C025946:3-methyladenine; C548780:3-(4-chlorophenyl)-adamantane-1-carboxylic acid (pyridin-4-ylmethyl)amide; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde