Synthetic triterpenoids activate a pathway for apoptosis in AML cells involving downregulation of FLIP and sensitization to TRAIL

Leukemia. 2003 Nov;17(11):2122-9. doi: 10.1038/sj.leu.2403112.

Abstract

Acute myelogenous leukemia (AML) remains a deadly disease for most adult patients, due primarily to the emergence of chemoresistant cells. Defects in apoptosis pathways make important contributions to chemoresistance, suggesting a need to restore apoptosis sensitivity or to identify alternative pathways for apoptosis induction. Triterpenoids represent a class of naturally occurring and synthetic compounds with demonstrated antitumor activity, including 2-cyano-3,12-dioxoolean-1,9-dien-28-oic acid (CDDO) and its methyl ester (CDDO-m). We explored the effects of CDDO and CDDO-m in vitro on established AML cell lines (HL-60, U937, AML-2) and on freshly isolated AML blasts. CDDO and CDDO-m reduced the viability of all AML cell lines tested in a dose-dependent manner, with effective doses for killing 50% of cells (ED(50)) within 48 h of approximately 1 and 0.5 muM, respectively. CDDO or CDDO-m also induced substantial increases in cell death in five out of 10 samples of primary AML blasts. Cell death induced by CDDO and CDDO-m was attributed to apoptosis, based on characteristic cell morphology and evidence of caspase activation. Immunoblot analysis demonstrated proteolytic processing of caspase-3, -7, and -8, but not caspase-9, suggesting the involvement of the 'extrinsic' pathway, linked to apoptosis induction by TNF-family death receptors. Accordingly, CDDO and CDDO-m induced concentration-dependent reductions in the levels of FLIP protein, an endogenous antagonist of caspase-8, without altering the levels of several other apoptosis-relevant proteins. Reductions in FLIP were rapid, detectable within 3 h after exposure of AML cell lines to CDDO or CDDO-m. CDDO and CDDO-m also sensitized two of four leukemia lines to TRAIL, a TNF-family death ligand. The findings suggest that synthetic triterpenoids warrant further investigation in the treatment of AML, alone or in combination with TRAIL or other immune-based therapies.

MeSH terms

  • Antineoplastic Agents / pharmacology*
  • Apoptosis / drug effects*
  • Apoptosis Regulatory Proteins
  • CASP8 and FADD-Like Apoptosis Regulating Protein
  • Carrier Proteins / genetics*
  • Cell Survival / drug effects
  • Gene Expression Regulation, Neoplastic / drug effects
  • Gene Expression Regulation, Neoplastic / genetics*
  • HL-60 Cells
  • Humans
  • Intracellular Signaling Peptides and Proteins*
  • Membrane Glycoproteins / pharmacology*
  • Oleanolic Acid / analogs & derivatives*
  • Oleanolic Acid / pharmacology*
  • Protease Inhibitors / pharmacology*
  • TNF-Related Apoptosis-Inducing Ligand
  • Tumor Cells, Cultured
  • Tumor Necrosis Factor-alpha / pharmacology*
  • U937 Cells

Substances

  • 2-cyano-3,12-dioxoolean-1,9-dien-28-oic acid
  • Antineoplastic Agents
  • Apoptosis Regulatory Proteins
  • CASP8 and FADD-Like Apoptosis Regulating Protein
  • CFLAR protein, human
  • Carrier Proteins
  • Intracellular Signaling Peptides and Proteins
  • Membrane Glycoproteins
  • Protease Inhibitors
  • TNF-Related Apoptosis-Inducing Ligand
  • TNFSF10 protein, human
  • Tumor Necrosis Factor-alpha
  • Oleanolic Acid
  • methyl 2-cyano-3,12-dioxoolean-1,9-dien-28-oate