Cell proliferation and protein synthesis in human leukaemic myeloblasts after cytosine arabinoside therapy

The effect of a single intravenous bolus injection of cytosine arabinoside (ARA-C) on the cytokinetics and 3H-leucine uptake of leukaemic myeloblasts in bone marrow and blood was studied at intervals up to 96 h after ARA-C in five patients with previously untreated acute myelogenous leukaemia. An early decrease in mitotic index and in 3H-thymidine labelling was observed in four of five patients and pretreatment values were reached again within the observation period. Changes suggesting synchronization were not observed. ARA-C induced a marked decrease in protein synthesis in the leukaemic myeloblasts as estimated from either a decrease in the 3H-leucine labelling index or the mean grain count of 3H-leucine labelled cells. It is suggested that ARA-C is incorporated also by cell which are not in S-phase and has a prolonged biochemical effect on the leukaemic cells.