Polymethoxylated flavones induce Ca(2+)-mediated apoptosis in breast cancer cells

Life Sci. 2006 Dec 23;80(3):245-53. doi: 10.1016/j.lfs.2006.09.006. Epub 2006 Sep 15.


Flavonoids, polyphenolic phytochemicals which include flavones and isoflavones, are present in the common human diet. It has been suggested that these compounds may exert anticancer activity; however, the mechanisms involved remain unknown. We have recently shown (Sergeev, 2004, Biochem Biophys Res Commun 321: 462-467) that isoflavones can activate the novel apoptotic pathway mediated by cellular Ca(2+). Here, we report that polymethoxyflavones (PMFs) derived from sweet orange (Citrus sinensis L.) inhibit growth of human breast cancer cells via Ca(2+)-dependent apoptotic mechanism. The treatment of MCF-7 breast cancer cells with 5-hydroxy-3,6,7,8,3',4'-hexamethoxyflavone (5-OH-HxMF) and 3'-hydroxy-5,6,7,4'-tetramethoxyflavone (3'-OH-TtMF) induced a sustained increase in concentration of intracellular Ca(2+) ([Ca(2+)](i)) resulting from both depletion of the endoplasmic reticulum Ca(2+) stores and Ca(2+) influx from the extracellular space. This increase in [Ca(2+)](i) was associated with the activation of the Ca(2+)-dependent apoptotic proteases, mu-calpain and caspase-12, as evaluated with the calpain and caspase-12 peptide substrates and antibodies to active (cleaved) forms of the enzymes. Corresponding non-hydroxylated PMFs, 3,5,6,7,8,3',4'-heptamethoxyflavone (HpMF) and 5,6,7,3',4'-pentamethoxyflavone (PtMF), were dramatically less active in inducing Ca(2+)-mediated apoptosis. Our results strongly suggest that the cellular Ca(2+) modulating activity of flavonoids underlies their apoptotic mechanism and that hydroxylation of PMFs is critical for their ability to induce an increase in [Ca(2+)](i) and, thus, activate Ca(2+)-dependent apoptotic proteases.

Publication types

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

MeSH terms

  • Apoptosis / drug effects*
  • Breast Neoplasms / drug therapy
  • Breast Neoplasms / metabolism*
  • Breast Neoplasms / pathology
  • Calcium / metabolism*
  • Calcium Signaling / drug effects*
  • Calpain / metabolism
  • Caspase 12 / metabolism
  • Cell Line, Tumor
  • Citrus sinensis / chemistry
  • Endoplasmic Reticulum / metabolism
  • Endoplasmic Reticulum / pathology
  • Enzyme Activation / drug effects
  • Female
  • Humans
  • Isoflavones / chemistry
  • Isoflavones / pharmacology*
  • Isoflavones / therapeutic use


  • Isoflavones
  • Calpain
  • Caspase 12
  • Calcium