n-n-dimethylsphingenine and Leukemia

We evaluated the cytotoxicity of dimethylsphingosine (DMS) against four human leukemia cell lines: two acute (HL60 and a multi-drug resistance MDR-positive derivative HL60-dox) and two blast crisis chronic myelogenous leukemias (JFP1, from a treatment refractory patient and K562), and against blasts isolated from 11 leukemia patients. Cell line viability decreased proportionally to DMS concentration and treatment time (P<0.001). HL60-dox and JFP1 were the most sensitive, indicating DMS efficacy against human leukemia MDR. Importantly, leukemia samples showed a similar sensitivity to DMS as that of the cell lines, firstly demonstrating PKC-independent sphingolipid activity against fresh human tumor specimens. DMS-based chemotherapy may improve leukemia treatment.

Topics: Antineoplastic Agents; Blast Crisis; Bone Marrow Cells; Cell Division; Cell Survival; Drug Resistance, Neoplasm; Enzyme Inhibitors; HL-60 Cells; Humans; K562 Cells; Leukemia; Leukemia, Myelogenous, Chronic, BCR-ABL Positive; Sphingosine; Tumor Cells, Cultured; Tumor Stem Cell Assay

Topics: Apoptosis; Enzyme Inhibitors; Humans; Leukemia; Phosphotransferases (Alcohol Group Acceptor); Sphingosine

Sphingosine 1-phosphate (S-1P) has been implicated as a second messenger preventing apoptosis by counteracting activation of executioner caspases. Here it is reported that S-1P prevents apoptosis and executioner caspase-3 activation by inhibiting the translocation of cytochrome c and Smac/DIABLO from mitochondria to the cytosol induced by anti-Fas, tumor necrosis factor-alpha (TNF-alpha), serum deprivation, and cell-permeable ceramides in the human acute leukemia Jurkat, U937, and HL-60 cell lines. Furthermore, the tumor promoter 12-O-tetradecanoyl-phorbol-13-acetate, which stimulates sphingosine kinase, the enzyme responsible for S-1P production, also inhibits cytochrome c and Smac/DIABLO release. In contrast, dimethylsphingosine (DMS), a specific inhibitor of sphingosine kinase, sensitizes cells to cytochrome c and Smac/DIABLO release triggered by anti-Fas, TNF-alpha, serum deprivation, or ceramide. DMS-induced mitochondrial apoptogenic factor leakage can likewise be overcome by S-1P cotreatment. Hence, S-1P, likely generated through a protein kinase C- mediated activation of sphingosine kinase, inhibits the apoptotic cascade upstream of the release of the mitochondrial apoptogenic factors, cytochrome c, and Smac/DIABLO in human acute leukemia cells.

Topics: Apoptosis; Apoptosis Regulatory Proteins; Carrier Proteins; Ceramides; Culture Media, Serum-Free; Cytochrome c Group; HL-60 Cells; Humans; Intracellular Signaling Peptides and Proteins; Jurkat Cells; Leukemia; Lysophospholipids; Mitochondria; Mitochondrial Proteins; Protein Transport; Receptors, Tumor Necrosis Factor; Sphingosine; Tetradecanoylphorbol Acetate; U937 Cells