title: Modification of sphingolipid metabolism by tamoxifen and N-desmethyltamoxifen in acute myelogenous leukemia--Impact on enzyme activity and response to cytotoxics.
abstract: The triphenylethylene antiestrogen, tamoxifen, can be an effective inhibitor of sphingolipid metabolism. This off-target activity makes tamoxifen an interesting ancillary for boosting the apoptosis-inducing properties of ceramide, a sphingolipid with valuable tumor censoring activity. Here we show for the first time that tamoxifen and metabolite, N-desmethyltamoxifen (DMT), block ceramide glycosylation and inhibit ceramide hydrolysis (by acid ceramidase, AC) in human acute myelogenous leukemia (AML) cell lines and in AML cells derived from patients. Tamoxifen (1-10 μM) inhibition of AC in AML cells was accompanied by decreases in AC protein expression. Tamoxifen also depressed expression and activity of sphingosine kinase 1 (SphK1), the enzyme-catalyzing production of mitogenic sphingosine 1-phosphate (S1-P). Results from mass spectroscopy showed that tamoxifen and DMT (i) increased the levels of endogenous C16:0 and C24:1 ceramide molecular species, (ii) nearly totally halted production of respective glucosylceramide (GC) molecular species, (iii) drastically reduced levels of sphingosine (to 9% of control), and (iv) reduced levels of S1-P by 85%, in vincristine-resistant HL-60/VCR cells. The co-administration of tamoxifen with either N-(4-hydroxyphenyl)retinamide (4-HPR), a ceramide-generating retinoid, or a cell-deliverable form of ceramide, C6-ceramide, resulted in marked decreases in HL-60/VCR cell viability that far exceeded single agent potency. Combination treatments resulted in synergistic apoptotic cell death as gauged by increased Annexin V binding and DNA fragmentation and activation of caspase-3. These results show the versatility of adjuvant triphenylethylene with ceramide-centric therapies for magnifying therapeutic potential in AML. Such drug regimens could serve as effective strategies, even in the multidrug-resistant setting.
authors.affiliation: Department of Biochemistry and Molecular Biology, Brody School of Medicine, East Carolina Diabetes and Obesity Institute, East Carolina University, Greenville, NC 27834, USA.
authors.forename: Samy A F
authors.initials: SA
authors.lastname: Morad
authors.affiliation: Department of Medicine, Hematology/Oncology, University of Virginia, Charlottesville, VA 22908-0716, USA.
authors.forename: Su-Fern
authors.initials: SF
authors.lastname: Tan
authors.affiliation: Department of Medicine, Hematology/Oncology, University of Virginia, Charlottesville, VA 22908-0716, USA; University of Virginia Cancer Center, Charlottesville, VA 22908-0716, USA.
authors.forename: David J
authors.initials: DJ
authors.lastname: Feith
authors.affiliation: University of Virginia Cancer Center, Charlottesville, VA 22908-0716, USA.
authors.forename: Mark
authors.initials: M
authors.lastname: Kester
authors.affiliation: Penn State Hershey Cancer Institute, Hershey, PA 17033, USA.
authors.forename: David F
authors.initials: DF
authors.lastname: Claxton
authors.affiliation: Department of Medicine, Hematology/Oncology, University of Virginia, Charlottesville, VA 22908-0716, USA; University of Virginia Cancer Center, Charlottesville, VA 22908-0716, USA.
authors.forename: Thomas P
authors.initials: TP
authors.lastname: Loughran
authors.affiliation: Penn State Hershey Cancer Institute, Hershey, PA 17033, USA.
authors.forename: Brian M
authors.initials: BM
authors.lastname: Barth
authors.affiliation: Department of Pharmacology, University of Virginia, Charlottesville, VA 22908-0001, USA.
authors.forename: Todd E
authors.initials: TE
authors.lastname: Fox
authors.affiliation: Department of Biochemistry and Molecular Biology, Brody School of Medicine, East Carolina Diabetes and Obesity Institute, East Carolina University, Greenville, NC 27834, USA. Electronic address: cabotm@ecu.edu.
authors.forename: Myles C
authors.initials: MC
authors.lastname: Cabot
mesh_terms: D003603:Cytotoxins / Q000494:pharmacology*; D004789:Enzyme Activation / Q000187:drug effects; D004965:Estrogen Antagonists / Q000494:pharmacology; D018922:HL-60 Cells; D006801:Humans; D015470:Leukemia, Myeloid, Acute / Q000378:metabolism* / Q000473:pathology; D050356:Lipid Metabolism / Q000187:drug effects; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000187:drug effects / Q000378:metabolism*; D013107:Sphingolipids / Q000378:metabolism*; D013267:Stilbenes / Q000494:pharmacology; D013629:Tamoxifen / Q000031:analogs & derivatives* / Q000494:pharmacology*; D014407:Tumor Cells, Cultured; D000099157:Sphingosine Kinase
chemical_list: D003603:Cytotoxins; D004965:Estrogen Antagonists; D017853:Phosphotransferases (Alcohol Group Acceptor); D013107:Sphingolipids; D013267:Stilbenes; D013629:Tamoxifen; D000099157:Sphingosine Kinase; C028787:N-desmethyltamoxifen; C037749:triphenylethylene
keywords: Ceramide; Leukemia; Sphingolipid metabolism; Tamoxifen; Triphenylethylenes