Effects of genistein on growth and differentiation of NB4 human acute promyelocytic leukemia cells

AIM: To investigate the possible actions of isoflavone genistein in inducing apoptosis and differentiation of NB4 leukemia cells. METHODS: NBT dye reduction ability was used as the biomarker of differentiation of NB4 cells. Apoptosis was assayed through genomic DNA gel electrophoresis. Expression of bcl-2 gene and DNA topoisomerase II activity were examined with Northern blot analysis and plasmid DNA breakage analysis, respectively. RESULTS: Genistein (40 μmol·L^-1) significantly suppressed the growth of NB4 cells, while a large amount of cells died with the prolongation of the drug exposure time. At concentration larger than 40 μmol·L^-1, genistein induced condensation of chromatin, breakage of nucleus, and appearance of DNA ladder after agarose electrophoresis in NB4 cells. In consistent with the induction of apoptosis, genistein inhibited expression of bcl-2 gene. At 10 ∼ 200 μmol·L^-1, genistein stimulated the topoisomerase II-mediated DNA breakage. On the other hand, genistein induced increase of NBT positive cell number, but the positive rates were lower than 50%. CONCLUSION: Genistein inhibited the growth of NB4 cells through induction of apoptosis and cell death. The mechanism of action might be associated with suppression of DNA topoisomerase II activity. Induction of differentiation may contribute little to the therapeutic activities of genistein in leukemia cells.