Flavones and flavonols exert cytotoxic effects on a human oesophageal adenocarcinoma cell line (OE33) by causing G2/M arrest and inducing apoptosis

Dietary flavonoids have been shown to exert specific cytotoxicity towards some cancer cells, but the precise molecular mechanisms are still not completely understood. In our study, cytotoxic effects of structurally related flavones and flavonols on a human oesophageal adenocarcinoma cell line (OE33) were compared, and the molecular mechanisms responsible for their cytotoxic effects were explored. The results of MTT assay showed that flavones (luteolin, apigenin, chrysin) and flavonols (quercetin, kaempferol, myricetin) were all able to induce cytotoxicity in OE33 cells in a dose- and time-dependent manner, and the cytotoxic potency of these compounds was in the order of quercetin > luteolin > chrysin > kaempferol > apigenin > myricetin. Flow cytometry and DNA fragmentation analysis indicated that the cytotoxicity induced by flavones and flavonols was mediated by G2/M cell cycle arrest and apoptosis. Furthermore, the expression of genes related to cell cycle arrest and apoptosis was assessed by oligonucleotide microarray, real-time RT-PCR and Western blot. It was found that the treatment of OE33 cells with flavones and flavonols caused G2/M arrest through up-regulation of GADD45β and 14-3-3σ and down-regulation of cyclin B1 at the mRNA and protein levels, and induced p53-independent mitochondrial-mediated apoptosis through up-regulation of PIG3 and cleavage of caspase-9 and caspase-3. The results of western blot analysis further showed that increases of p63 and p73 protein translation or stability might be contribute to the regulation of GADD45β, 14-3-3σ, cyclin B1 and PIG3.