Cellular Kinetics in Acute Leukemia

Abstract

In most patients with acute leukemia, the generation time of leukemic cells is about (10 hours, longer than for normal cells. Approximate times for the phases of the cell cycle are: DNA synthesis (S), 20 hours; mitosis (M), 2 hours; and the post-synthesis and postmitosis rest phases (G2 and Gi), 2 and 36 hours, respectively. A most important finding has been that a variable proportion of leukemic cells are out of cycle, that is, are in a resting or Go state. These resting cells are in equilibrium with the dividing cells, and some, as yet unknown, control mechanism for leukemic-cell growth controls the flow of cells from one compartment to the other. A critical feature of the resting cells is that they are relatively resistant to cycle-dependent chemotherapeutic agents. Much information has been obtained concerning the effects of drugs on the proliferative characteristics of leukemic cells. This information provides the basis for designing regimens with better timing of drug administration and advantageous use of combined chemotherapy.