title: Polymethoxylated flavones induce Ca(2+)-mediated apoptosis in breast cancer cells.
abstract: 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.
authors.affiliation: Department of Nutrition, Food Science and Hospitality, South Dakota State University, Brookings, SD 57007, USA. igor.sergeev@sdstate.edu
authors.forename: Igor N
authors.initials: IN
authors.lastname: Sergeev
authors.forename: Shiming
authors.initials: S
authors.lastname: Li
authors.forename: Julie
authors.initials: J
authors.lastname: Colby
authors.forename: Chi-Tang
authors.initials: CT
authors.lastname: Ho
authors.forename: Slavik
authors.initials: S
authors.lastname: Dushenkov
mesh_terms: 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
chemical_list: D007529:Isoflavones; D002154:Calpain; D053454:Caspase 12; D002118:Calcium