Modification of sphingolipid metabolism by tamoxifen and N-desmethyltamoxifen in acute myelogenous leukemia--Impact on enzyme activity and response to cytotoxics.

Academic Article

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

  • Morad, Samy AF
  • Tan, Su-Fern
  • Feith, David J
  • Kester, Mark
  • Claxton, David F
  • Loughran, Thomas P
  • Barth, Brian
  • Fox, Todd E
  • Cabot, Myles C
  • Status

    Publication Date

  • July 2015
  • Keywords

  • Ceramide
  • Cytotoxins
  • Enzyme Activation
  • Estrogen Antagonists
  • HL-60 Cells
  • Humans
  • Leukemia
  • Leukemia, Myeloid, Acute
  • Lipid Metabolism
  • Phosphotransferases (Alcohol Group Acceptor)
  • Sphingolipid metabolism
  • Sphingolipids
  • Stilbenes
  • Tamoxifen
  • Triphenylethylenes
  • Tumor Cells, Cultured
  • Digital Object Identifier (doi)

    Start Page

  • 919
  • End Page

  • 928
  • Volume

  • 1851
  • Issue

  • 7