Polymethoxylated flavones induce Ca(2+)-mediated apoptosis in breast cancer cells.
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.
Sergeev
Igor N
IN
Department of Nutrition, Food Science and Hospitality, South Dakota State University, Brookings, SD 57007, USA. igor.sergeev@sdstate.edu
Li
Shiming
S
Colby
Julie
J
Ho
Chi-Tang
CT
Dushenkov
Slavik
S
D017209:Apoptosis / Q000187:drug effects*; D001943:Breast Neoplasms / Q000188:drug therapy / Q000378:metabolism* / Q000473:pathology; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects*; D002154:Calpain / Q000378:metabolism; D053454:Caspase 12 / Q000378:metabolism; D045744:Cell Line, Tumor; D032084:Citrus sinensis / Q000737:chemistry; D004721:Endoplasmic Reticulum / Q000378:metabolism / Q000473:pathology; D004789:Enzyme Activation / Q000187:drug effects; D005260:Female; D006801:Humans; D007529:Isoflavones / Q000737:chemistry / Q000494:pharmacology* / Q000627:therapeutic use
D007529:Isoflavones; D002154:Calpain; D053454:Caspase 12; D002118:Calcium