c-FLIP downregulation contributes to apoptosis induction by the novel synthetic triterpenoid methyl-2-cyano-3, 12-dioxooleana-1, 9-dien-28-oate (CDDO-Me) in human lung cancer cells

Cancer Biol Ther. 2007 Oct;6(10):1614-20. doi: 10.4161/cbt.6.10.4763. Epub 2007 Jul 19.


The novel synthetic triterpenoid methyl-2-cyano-3, 12-dioxooleana-1, 9-dien-28-oate (CDDO-Me) induces apoptosis of cancer cells, enhances tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis, and exhibits potent anticancer activity in animal models with a favorable pharmacokinetic profile. Thus, CDDO-Me is being tested in Phase I clinical trials. In an effort to understand the mechanism by which CDDO-Me induces apoptosis, particularly in human lung cancer cells, we previously demonstrated that CDDO-Me induces apoptosis involving c-Jun N-terminal kinase (JNK)-dependent upregulation of death receptor 5 (DR5) expression. In the current work, we determined the modulatory effects of CDDO-Me on the levels of c-FLIP, a major inhibitor of death receptor-mediated caspase-8 activation, and its impact on CDDO-Me-induced apoptosis and enhancement of TRAIL-induced apoptosis in human lung cancer cells. CDDO-Me rapidly and potently decreased c-FLIP levels including both long (FLIP(L)) and short (FLIP(S)) forms of c-FLIP in multiple human lung cancer cell lines. The presence of the proteasome inhibitor MG132, but not the JNK inhibitor SP600125, prevented CDDO-Me-induced c-FLIP reduction. Moreover, CDDO-Me increased ubiquitination of c-FLIP. Thus, CDDO-Me induces ubiquitin/proteasome-dependent c-FLIP degradation independently of JNK activation. Importantly, overexpression of c-FLIP (e.g., FLIP(L)) protected cells not only from CDDO-Me-induced apoptosis, but also from induction of apoptosis by the combination of CDDO-Me and TRAIL. Accordingly, silencing of c-FLIP with c-FLIP siRNA sensitized cancer cells to CDDO-Me. Collectively, these results indicate that c-FLIP downregulation contributes to CDDO-Me-initiated apoptosis and also to enhancement of TRAIL-induced apoptosis by CDDO-Me.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Antineoplastic Agents / pharmacology*
  • Apoptosis
  • CASP8 and FADD-Like Apoptosis Regulating Protein / antagonists & inhibitors*
  • Carcinoma, Non-Small-Cell Lung / metabolism*
  • Cell Line, Tumor
  • Down-Regulation
  • Humans
  • Lung Neoplasms / metabolism*
  • MAP Kinase Kinase 4 / metabolism
  • Oleanolic Acid / analogs & derivatives*
  • Oleanolic Acid / pharmacology
  • Proteasome Endopeptidase Complex / metabolism
  • TNF-Related Apoptosis-Inducing Ligand / pharmacology
  • Terpenes / pharmacology*
  • Ubiquitin / metabolism


  • Antineoplastic Agents
  • CASP8 and FADD-Like Apoptosis Regulating Protein
  • CFLAR protein, human
  • TNF-Related Apoptosis-Inducing Ligand
  • Terpenes
  • Ubiquitin
  • Oleanolic Acid
  • bardoxolone methyl
  • MAP Kinase Kinase 4
  • Proteasome Endopeptidase Complex