Microfluorimetric evaluation of cell kill kinetics with 1-beta-D-arabinofuranosylcytosine.

Abstract

The effect of different concentrations of 1-β-d-arabinofuranosylcytosine (ara-C) on the progression of an established cell line of human lymphoid cells through the cell cycle was studied using a fluorescent DNA-specific Feulgen-type staining technique and a flow microfluorimeter. In addition to the distribution analysis of the relative DNA content, the number of intact cells, the percentage of incorporation of thymidine-3H, and the mitotic activity were determined after different periods of treatment. At a low ara-C concentration (10-6 m), the cells were transiently synchronized and the DNA-inhibitory effect was expressed as a slowing of the growth rate. At all effective concentrations, there was a blocking effect of the cells in S phase; most cells continued to enter S phase at a near-normal rate and were blocked immediately upon entrance. This blocking effect was only partial and was reversible at low ara-C concentrations if the cells were exposed to the drug for short periods of time (cytostatic effect), whereas it was more complete and irreversible at high concentrations even after short exposure times (cytocidal effect). The cells that completed S phase at low ara-C concentrations accumulated in G2, and the cells blocked in G1 and G2 remained relatively protected from further drug action. A minor proportion of cells, representing about 10% of the whole population, was blocked in G1 during the entire period of continuous exposure to the drug and remained in G1 for a considerable time after its removal. Some of these G1 cells can survive at least 5 to 7 days of treatment with high ara-C concentrations and eventually resume normal growth after drug removal.