title: Methoxyflavone derivatives modulate the effect of TRAIL-induced apoptosis in human leukemic cell lines.
abstract: BACKGROUND
  Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) induces apoptosis in various tumor cells, but does not affect normal cells or human leukemic cells, such as MOLT-4 and U937 cells, which are relatively resistant to TRAIL. Three flavonoids extracted from the rhizome of K. parviflora were 5,7-dimethoxyflavone (DMF), 5,7,4'-trimethoxyflavone (TMF) and 3,5,7,3',4'-pentamethoxyflavone (PMF), and synthetic flavonoids including 5-methoxyflavone (5-MF) and 2'-methoxyflavone (2"-MF) were chosen for testing in this study. The aims of this study were to examine whether the treatment of TRAIL-resistant leukemia MOLT-4 and U937 cells, with methoxyflavone derivatives could enhance the apoptotic response and to identify the mechanism involved.
  
  
  METHODS
  The cytotoxic effect of methoxyflavone (MF) derivatives in MOLT-4, U937 and peripheral blood mononuclear cells (PBMCs) was analyzed by the MTT assay. The induction of apoptosis and the reduction of mitochondrial transmembrane potential (ΔΨm) after staining with annexin V FITC and propidium iodide (PI), and 3,3'-dihexyloxacarbocyanine iodide (DiOC(6)), respectively, were performed using flow cytometry. ROS production was determined by staining with 2',7'-dichlorofluorescin diacetate and processed with a flow cytometer. DR4, DR5, cFLIP, Mcl-1, BAX and Bid expression were demonstrated by immunoblotting. Caspase-8 and -3 activities were determined by using IETD-AFC and DEVD-AFC substrates and the fluorescence intensity was measured.
  
  
  RESULTS
  All methoxyflavone derivatives were cytotoxic to MOLT-4, U937 cells and PBMCs, except DMF, TMF and PMF were not toxic to PBMCs. All MF derivatives induced human leukemic MOLT-4 cell apoptosis, but not in U937 cells. Percentage of MOLT-4 cells with (ΔΨm) was increased when treated with DMF, TMF, PMF, 5-MF and 2'-MF in the presence of TRAIL. 5-MF and 2'-MF enhanced TRAIL-induced apoptosis through the up-regulation of both DRs and the down-regulation of cFLIP and Mcl-1. Bid was cleaved and BAX was up-regulated, followed by the activation of caspase-8 and -3. Oxidative stress was also increased. 2'-MF gave the same result compared with 5-MF but with a less effect.
  
  
  CONCLUSIONS
  Methoxyflavone derivatives enhanced TRAIL-induced apoptosis in human leukemic MOLT-4 cells through the death receptors and mitochondrial pathways.
authors.affiliation: Department of Biochemistry, Faculty of Medicine, Chiang Mai University, Chiang Mai 50200, Thailand.
authors.forename: Benjawan
authors.initials: B
authors.lastname: Wudtiwai
authors.forename: Bungorn
authors.initials: B
authors.lastname: Sripanidkulchai
authors.forename: Prachya
authors.initials: P
authors.lastname: Kongtawelert
authors.forename: Ratana
authors.initials: R
authors.lastname: Banjerdpongchai
mesh_terms: D017209:Apoptosis / Q000187:drug effects; D018929:Cell Culture Techniques; D045744:Cell Line, Tumor; D004347:Drug Interactions; D047309:Flavones / Q000302:isolation & purification / Q000494:pharmacology*; D006801:Humans; D007938:Leukemia / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D008564:Membrane Potentials / Q000187:drug effects; D008928:Mitochondria / Q000187:drug effects; D054198:Precursor Cell Lymphoblastic Leukemia-Lymphoma / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D053221:TNF-Related Apoptosis-Inducing Ligand / Q000494:pharmacology*; D020298:U937 Cells
chemical_list: D047309:Flavones; D053221:TNF-Related Apoptosis-Inducing Ligand