Thymoquinone up-regulates PTEN expression and induces apoptosis in doxorubicin-resistant human breast cancer cells

Mutat Res. 2011 Jan 10;706(1-2):28-35. doi: 10.1016/j.mrfmmm.2010.10.007. Epub 2010 Oct 30.


The use of innocuous naturally occurring compounds to overcome drug resistance and cancer recalcitrance is now in the forefront of cancer research. Thymoquinone (TQ) is a bioactive constituent of the volatile oil derived from seeds of Nigella sativa Linn. TQ has shown promising anti-carcinogenic and anti-tumor activities through different mechanisms. However, the effect of TQ on cell signaling and survival pathways in resistant cancer cells has not been fully delineated. Here, we report that TQ greatly inhibits doxorubicin-resistant human breast cancer MCF-7/DOX cell proliferation. TQ treatment increased cellular levels of PTEN proteins, resulting in a substantial decrease of phosphorylated Akt, a known regulator of cell survival. The PTEN expression was accompanied with elevation of PTEN mRNA. TQ arrested MCF-7/DOX cells at G2/M phase and increased cellular levels of p53 and p21 proteins. Flow cytometric analysis and agarose gel electrophoresis revealed a significant increase in Sub-G1 cell population and appearance of DNA ladders following TQ treatment, indicating cellular apoptosis. TQ-induced apoptosis was associated with disrupted mitochondrial membrane potential and activation of caspases and PARP cleavage in MCF-7/DOX cells. Moreover, TQ treatment increased Bax/Bcl2 ratio via up-regulating Bax and down-regulating Bcl2 proteins. More importantly, PTEN silencing by target specific siRNA enabled the suppression of TQ-induced apoptosis resulting in increased cell survival. Our results reveal that up-regulation of the key upstream signaling factor, PTEN, in MCF-7/DOX cells inhibited Akt phosphorylation, which ultimately causes increase in their regulatory p53 levels affecting the induction of G2/M cell cycle arrest and apoptosis. Overall results provide mechanistic insights for understanding the molecular basis and utility of the anti-tumor activity of TQ.

Publication types

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

MeSH terms

  • Apoptosis / drug effects*
  • Benzoquinones / chemistry
  • Benzoquinones / pharmacology*
  • Blotting, Western
  • Breast Neoplasms / genetics
  • Breast Neoplasms / metabolism
  • Breast Neoplasms / pathology
  • Caspases / metabolism
  • Cell Division / drug effects
  • Cell Line, Tumor
  • Cell Proliferation / drug effects
  • Cell Survival / drug effects
  • DNA Fragmentation / drug effects
  • Dose-Response Relationship, Drug
  • Doxorubicin / pharmacology
  • Drug Resistance, Neoplasm / drug effects*
  • Female
  • G2 Phase / drug effects
  • Humans
  • Molecular Structure
  • PTEN Phosphohydrolase / genetics
  • PTEN Phosphohydrolase / metabolism*
  • Poly(ADP-ribose) Polymerases / metabolism
  • Proto-Oncogene Proteins c-bcl-2 / metabolism
  • RNA Interference
  • Reverse Transcriptase Polymerase Chain Reaction
  • Tumor Suppressor Protein p53 / metabolism
  • Up-Regulation / drug effects
  • bcl-2-Associated X Protein / metabolism


  • Benzoquinones
  • Proto-Oncogene Proteins c-bcl-2
  • Tumor Suppressor Protein p53
  • bcl-2-Associated X Protein
  • Doxorubicin
  • Poly(ADP-ribose) Polymerases
  • PTEN Phosphohydrolase
  • Caspases
  • thymoquinone