z-Leucinyl-leucinyl-norleucinal induces apoptosis of human glioblastoma tumor-initiating cells by proteasome inhibition and mitotic arrest response

Mol Cancer Res. 2009 Nov;7(11):1822-34. doi: 10.1158/1541-7786.MCR-09-0225. Epub 2009 Oct 27.


Gamma-secretase inhibitors have been proposed as drugs able to kill cancer cells by targeting the NOTCH pathway. Here, we investigated two of such inhibitors, the Benzyloxicarbonyl-Leu-Leu-Nle-CHO (LLNle) and the N-[N-(3,5-difluorophenacetyl)-L-alanyl]-S-phenylglycine t-butyl ester (DAPT), to assess whether they were effective in killing human glioblastoma tumor-initiating cells (GBM TIC) in vitro. We found that only LLNle was able at the micromolar range to induce the death of GBM TICs by apoptosis. To determine the cellular processes that were activated in GBM TICs by treatment with LLNle, we analyzed the amount of the NOTCH intracellular domain and the gene expression profiles following treatment with LLNle, DAPT, and DMSO (vehicle). We found that LLNIe, beside inhibiting the generation of the NOTCH intracellular domain, also induces proteasome inhibition, proteolytic stress, and mitotic arrest in these cells by repressing genes required for DNA synthesis and mitotic progression and by activating genes acting as mitotic inhibitors. DNA content flow cytometry clearly showed that cells treated with LLNle undergo arrest in the G(2)-M phases of the cell cycle. We also found that DAPT and L-685,458, another selective Notch inhibitor, were unable to kill GBM TICs, whereas lactacystin, a pure proteasome inhibitor, was effective although at a much less extent than LLNle. These data show that LLNle kills GBM TIC cells by inhibiting the proteasome activity. We suggest that LLNle, being able to target two relevant pathways for GBM TIC survival, may have a potential therapeutic value that deserves further investigation in animal models.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amyloid Precursor Protein Secretases / antagonists & inhibitors
  • Amyloid Precursor Protein Secretases / genetics
  • Amyloid Precursor Protein Secretases / metabolism
  • Apoptosis / drug effects*
  • Apoptosis / genetics
  • Blotting, Western
  • Cell Cycle / drug effects
  • Cell Cycle / genetics
  • Cell Survival / drug effects
  • Dipeptides / pharmacology*
  • Enzyme Activation / genetics
  • Flow Cytometry
  • Gene Expression Profiling
  • Glioblastoma / drug therapy*
  • Glioblastoma / enzymology
  • Glioblastoma / genetics
  • Glioblastoma / pathology
  • HSP70 Heat-Shock Proteins / biosynthesis
  • HSP70 Heat-Shock Proteins / metabolism
  • Humans
  • Oligopeptides / pharmacology*
  • Proteasome Endopeptidase Complex / metabolism
  • Proteasome Inhibitors*
  • Receptors, Notch / antagonists & inhibitors
  • Ubiquitin / antagonists & inhibitors
  • Ubiquitin / metabolism


  • Dipeptides
  • HSP70 Heat-Shock Proteins
  • N-(N-(3,5-difluorophenacetyl)alanyl)phenylglycine tert-butyl ester
  • Oligopeptides
  • Proteasome Inhibitors
  • Receptors, Notch
  • Ubiquitin
  • benzyloxycarbonyl-leucyl-leucyl-norleucinal
  • Amyloid Precursor Protein Secretases
  • Proteasome Endopeptidase Complex