Aim:To investigate the effects of 2-methoxyestradiol (2-ME) on 2 myeloid leuke-mia cell lines HL-60 and U937,and to explore its mechanisms.Methods:Humanmyeloid leukemia cells HL-60 and U937 were used.Measurement of mitochondrialmembrane potential (Dym) was performed using 5,5’,6,6’-Tetrachloro-1,1’,3,3’-tetraethylbenzimidazolylcarbocyanine iodide (JC-1).Apoptosis and cellular nitricoxide (NO) were detected by flow cytometry using Annexin V and NO sensor dye.Superoxide anion was measured with a fluorescent plate reader by dihydroethidium(DHE).Cytotoxicity was analyzed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium assay.Results:2-ME resulted in viability decrease in a dose-depen-dent manner.2-ME treatment also generated reactive oxygen species (ROS),including NO and superoxide anions,which resulted in mitochondria damage.2-ME-induced apoptosis was correlated with an increase in ROS.The quenchingof ROS with N-acetyl-L-cysteine protected leukemia cells from 2-ME cytotoxicityand prevented apoptosis induction by 2-ME.Furthermore,the addition ofmanumycin,a farnesyltransferase inhibitor,significantly enhanced apoptosis in-duced by 2-ME.Conclusion:Cellular ROS generation plays an important role inthe cytotoxic effect of 2-ME.It is possible to use ROS generation agents,such asmanumycin,to enhance the antileukemic effect.The combination strategy needsfurther in vivo justification and may have potential clinical application. Aim: To investigate the effects of 2-methoxyestradiol (2-ME) on 2 myeloid leuke-mia cell lines HL-60 and U937, and to explore its mechanisms. Methods: Human myeloid leukemia cells HL-60 and U937 were used. Measurement of mitochondrialmembrane potential (Dym) was performed using 5,5 ’, 6,6’-Tetrachloro-1,1’, 3,3’-tetraethylbenzimidazolylcarbocyanine iodide (JC- using Annexin V and NO sensor dye. Superoxide anion was measured with a fluorescent plate reader by dihydroethidium (DHE). Cytotoxicity was analyzed by 3- (4,5-dimethylthiazol-2-yl) -2,5-diphenyl- tetrazolium assay. Results: 2-ME resulted in viability decrease in a dose-dependent-dent manner.2-ME treatment also generated reactive oxygen species (ROS), including NO and superoxide anions, which resulted in mitochondria damage.2-ME-induced apoptosis was correlated with an increase in ROS. quenching of ROS with N-acetyl-L-cysteine ​​protected leukemia cells from 2-ME cytotoxicityand regulated apoptosis induction by 2-ME. Future addition, the addition of manumycin, a farnesyltransferase inhibitor, significantly enhanced apoptosis in-duced by 2-ME. Conlusion: Cellular ROS generation plays an important role in the cytotoxic effect of 2-ME.It is possible to use ROS generation agents, such as asmanumycin, to enhance the antileukemic effect. The combination strategy needs further in vivo justification and may have potential clinical application.