Drug-induced kinetic perturbations of the marrow blasts in acute leukemia. Effects of the daunorubicin, cytosine arabinoside and 6-thioguanine combination.

Cell kinetic changes induced in the marrow blasts by treatment with a triple cytotoxic regimen including daunorubicin, cytosine arabinoside and 6-thioguanine (DAT) were investigated in 6 previously untreated acute nonlymphocytic leukemia patients. A decrease in the labeling and mitotic indices was consistently observed 24 h after administration of daunorubicin, suggesting a G2 block and a preferential lytic effect on the S-phase cells operated by the drug. Conversely, cytosine arabinoside and 6-thioguanine in combination induced a series of kinetic perturbations variable from case to case; however, three principal patterns of kinetic response were recogized and discussed in detail. Useful information for the planning of a more rational antileukemic therapy can be drawn from a systematic study of the kinetic effects induced by drug combinations.