The dietary phytochemical indole-3-carbinol is a natural elastase enzymatic inhibitor that disrupts cyclin E protein processing

Proc Natl Acad Sci U S A. 2008 Dec 16;105(50):19750-5. doi: 10.1073/pnas.0806581105. Epub 2008 Dec 8.


Indole-3-carbinol (I3C), a naturally occurring component of Brassica vegetables, such as broccoli, cabbage, and Brussels sprouts, induces a G(1) cell-cycle arrest of human breast cancer cells, although the direct cellular targets that mediate this process are unknown. Treatment of highly invasive MDA-MB-231 breast cancer cells with I3C shifted the stable accumulation of cyclin E protein from the hyperactive lower-molecular-mass 35-kDa form that is associated with cancer cell proliferation and poor clinical outcomes to the 50-kDa cyclin E form that typically is expressed in normal mammary tissue. An in vitro cyclin E processing assay, in combination with zymography, demonstrated that I3C, but not its natural dimer, 3,3'-diindolylmethane, disrupts proteolytic processing of the 50-kDa cyclin E into the lower-molecular-mass forms by direct inhibition of human neutrophil elastase enzymatic activity. Analysis of elastase enzyme kinetics using either cyclin E or N-methoxysuccinyl-Ala-Ala-Pro-Val-p-nitroanalide as substrates demonstrated that I3C acts as a noncompetitive inhibitor of elastase activity with an inhibitory constant of approximately 12 microM. Finally, siRNA ablation of neutrophil elastase protein production in MDA-MB-231 cells mimicked the I3C-disrupted processing of the 50-kDa cyclin E protein and the indole-induced cell-cycle arrest. Taken together, our results demonstrate that elastase is the first identified specific target protein for I3C and that the direct I3C inhibition of elastase enzymatic activity implicates the potential use of this indole, or related compounds, in targeted therapies of human breast cancers where high elastase levels are correlated with poor prognosis.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Antineoplastic Agents / pharmacology*
  • Brassica / chemistry
  • Breast Neoplasms / enzymology*
  • Cell Cycle / drug effects
  • Cells, Cultured
  • Cyclin E / metabolism*
  • Diet
  • Enzyme Inhibitors / pharmacology*
  • Humans
  • Indoles / pharmacology*
  • Oligopeptides / pharmacology
  • Pancreatic Elastase / antagonists & inhibitors*
  • Pancreatic Elastase / genetics
  • RNA, Small Interfering / genetics


  • Antineoplastic Agents
  • Cyclin E
  • Enzyme Inhibitors
  • Indoles
  • Oligopeptides
  • RNA, Small Interfering
  • N-methoxysuccinyl-alanyl-alanyl-prolyl-valine-4-nitroanilide
  • indole-3-carbinol
  • Pancreatic Elastase