Sustained exposure to the DNA demethylating agent, 2′-deoxy-5- azacytidine, leads to apoptotic cell death in chronic myeloid leukemia by promoting differentiation, senescence, and autophagy

In addition to its demethylating properties, 2′-deoxy-5-azacytidine (DAC) induces cell cycle arrest, differentiation, cell sensitization to chemotherapy, and cell death. However, the mechanisms by which DAC induces antiproliferation via these processes and how they are interconnected remain unclear. In this study, we found that a clinically relevant concentration of DAC triggered erythroid and megakaryocytic differentiation in the human chronic myeloid leukemia (CML) K-562 and MEG-01 cell lines, respectively. In addition, cells showed a marked increase in cell size in both cell lines and a more adhesive cell profile for MEG-01. Furthermore, DAC treatment induced cellular senescence and autophagy as shown by β-galactosidase staining and by autophagosome formation, respectively. After prolonged DAC treatment, phosphatidyl serine exposure, nuclear morphology analysis, and caspase cleavage revealed an activation of mitochondrial-dependent apoptosis in CML cells. This activation was accompanied by a decrease of anti-apoptotic proteins and an increase of calpain activity. Finally, we showed that combinatory treatment of relatively resistant CML with DAC and either conventional apoptotic inducers or with an histone deacetylase inhibitor increased synergistically apoptosis. We therefore conclude that induction of differentiation, senescence, and autophagy in CML are a key in cell sensitization and DAC-induced apoptosis.