Helenalin triggers a CD95 death receptor-independent apoptosis that is not affected by overexpression of Bcl-x(L) or Bcl-2

Cancer Res. 2001 Aug 1;61(15):5817-23.


Apoptosis is required for proper tissue homeostasis. Defects in apoptosis signaling pathways, thus, contribute to carcinogenesis and chemoresistance. A major goal in chemotherapy is, therefore, to find cytotoxic agents that restore the ability of tumor cells to undergo apoptosis. We show here that the sesquiterpene lactone helenalin (10-50 microM) induces apoptosis in leukemia Jurkat T cells even if they lack the CD95 death receptor or overexpress the antiapoptotic proteins Bcl-x(L) or Bcl-2. Activated peripheral blood mononuclear cells, however, are not affected (10-50 microM helenalin). Helenalin led to a time-dependent (0-24 h) cleavage of the specific caspase-3-like substrate Asp-Glu-Val-Asp-7-amino-4-trifluoromethylcoumarin as well as to the proteolytic processing of procaspase-3 and -8. Caspase activation was a necessary requirement for apoptosis because the broad-spectrum caspase inhibitor benzyloxycarbonyl-Val-Ala-Asp(OMe)-fluoromethylketone (zVAD-fmk, 50 microM) completely abrogated helenalin-induced DNA fragmentation as well as phosphatidylserin translocation. Although the initiator caspase-8 was activated, the helenalin-induced signaling pathway did not require the CD95 death receptor as shown using cells without or with an antibody (ZB4)-blocked CD95 receptor. Helenalin also did not induce CD95 or CD95-ligand expression. On the other hand, helenalin was found to induce the release of cytochrome c from mitochondria that was not inhibited by the caspase inhibitor zVAD-fmk, which indicated that cytochrome c release precedes caspase activation. Cytochrome c release was accompanied by dissipation of the mitochondrial transmembrane potential (DeltaPsi(m)), which was partly inhibited by zVAD-fmk, which suggests that caspases are involved in loss of DeltaPsi(m). Most importantly, overexpression of the mitochondria protecting proteins Bcl-x(L) or Bcl-2 failed to confer resistance to helenalin-induced apoptosis, although the data presented here suggest that helenalin induces a mitochondria-dependent pathway. Thus, helenalin is a promising experimental cytotoxic agent that possibly points to new strategies to overcome apoptosis resistance attributable to overexpression of antiapoptotic Bcl-2 proteins.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antineoplastic Agents, Phytogenic / pharmacology*
  • Apoptosis / drug effects*
  • Apoptosis / physiology
  • Caspase 3
  • Caspase 8
  • Caspase 9
  • Caspases / metabolism
  • Enzyme Activation
  • Enzyme Induction / drug effects
  • Fas Ligand Protein
  • Humans
  • Jurkat Cells / drug effects*
  • Jurkat Cells / metabolism
  • Jurkat Cells / pathology
  • Matrix Metalloproteinases / biosynthesis
  • Membrane Glycoproteins / physiology
  • Proto-Oncogene Proteins c-bcl-2 / biosynthesis*
  • Proto-Oncogene Proteins c-bcl-2 / physiology
  • Sesquiterpenes / pharmacology*
  • Sesquiterpenes, Guaiane
  • bcl-X Protein
  • fas Receptor / physiology*


  • Antineoplastic Agents, Phytogenic
  • BCL2L1 protein, human
  • FASLG protein, human
  • Fas Ligand Protein
  • Membrane Glycoproteins
  • Proto-Oncogene Proteins c-bcl-2
  • Sesquiterpenes
  • Sesquiterpenes, Guaiane
  • bcl-X Protein
  • fas Receptor
  • helenalin
  • CASP3 protein, human
  • CASP8 protein, human
  • CASP9 protein, human
  • Caspase 3
  • Caspase 8
  • Caspase 9
  • Caspases
  • Matrix Metalloproteinases