Evaluation of cytarabine-induced apoptosis in leukemic cell lines; utility of annexin V method

Apoptosis is a morphologically and biochemically distinct form of cell death that occurs under a variety of physiological and pathological conditions. In the present study, using leukemic cell lines, time course of cytarabine-induced apoptosis was examined morphologically, using annexin V method, TUNEL method and fluorometric assay for caspase-3 activity. Morphological changes characteristic of apoptosis were observed in U937 and HL60 cells after 4-hour incubation with cytarabine and progressively evident until 48-hour incubation, but rarely found in K562 cells. In annexin V method and assay for caspase-3 activity, changes accompanied by apoptosis could also be detected at 4-hour incubation with cytarabine, but in TUNEL method, they were not found until 24-hour incubation. The advantage of annexin V method which detects phosphatidylserine emerging on cell surface during the early course of apoptosis included simplicity and rapidity of the procedure and short time requirement for apoptosis to appear after incubation with cytarabine. Usefulness of annexin V method in a study of clinical samples was discussed.