N-(β-Elemene-13-yl)tryptophan methyl ester induces apoptosis in human leukemia cells and synergizes with arsenic trioxide through a hydrogen peroxide dependent pathway

β-Elemene is an active component of herb medicine Curcuma Wenyujin and N-(β-elemene-13-yl)tryptophan methyl ester (ETME) was synthesized for increasing its antitumor activity. ETME induced apoptosis in human leukemia HL-60 and NB4 cells at concentrations less than 40 μM. The apoptosis induction ability of ETME was associated with the production of hydrogen peroxide (H2O2), the decrease of mitochondrial membrane potential, and the activation of caspase-3 that was blocked by catalase. ETME in combination with arsenic trioxide (As2O3), an agent used to treat acute promyelocytic leukemia, synergistically induced apoptosis in both cell lines by enhanced production of H2O2. These data suggest that ETME induces apoptosis and synergizes with As2O3 in leukemia cells through a H2O2-dependent pathway.