Effective killing of CML cells by PEITC is associated with rapid increase of cellular ROS, depletion of glutathione and BCR-ABL degradation

3315 Chronic myelogenous leukemia (CML) is a myeloproliferative disorder that represents approximately 15-20% of all adult leukemia. The development of CML is clearly linked to the constitutively active tyrosine kinase of the chimeric protein BCR-ABL, which is encoded by the Bcr-Abl fusion gene due to chromosome 9/22 translocation or other aberrant cytogenetic events. Several recent studies and our findings suggested that the CML oncoprotein BCR-ABL could initiate cellular redox imbalance and promote persistent cellular oxidative stress. Cell adaptation to this redox alteration may promote CML cell survival and the development of this disease. Thus disrupting cellular redox system in CML cells is a possible strategy to kill the leukemia cells. Here we showed that β-phenylethyl isothiocyanate (PEITC), a natural compound found in edible vegetables, is effective in killing cultured human BCR-ABL positive CML cells by causing severe ROS stress and glutathione depletion. Importantly, we showed that CML cells harboring T315I-mutantation insensitive to the Bcr-Abl-targeted drug Gleevec remained sensitive to PEITC. The killing ability of PEITC was confirmed using CML cell lines and primary leukemia cells isolated from CML patients harboring T315I-mutant BCR-ABL. Treatment of CML cells expressing wild-type or T315I-mutant BCR-ABL with 10 μM PEITC resulted in a rapid increase of reactive oxygen species (ROS) stress, a severe depletion of cellular glutathione (GSH), and a redox-mediated degradation of the BCR-ABL protein, leading to massive cell death. Incubation with the GSH precursor antioxidant NAC attenuated the PEITC-induced oxidative stress in CML cells, and prevented the degradation of BCR-ABL, caspase-3 activation, and cell death. We further showed that the PEITC-induced degradation of BCR-ABL was mediated partially by caspase-3 and the proteasome pathway. Our results suggest that PEITC is a promising compound capable of killing both Gleevec-sensitive and -resistant CML cells through a ROS-mediated mechanism.