Biology of cell killing by 1-beta-D-arabinofuranosylcytosine and its relevance to molecular mechanisms of cytotoxicity.

Cells of the Chinese hamster ovary cell line were used to study the process of cell death induced by pulse treatment with 1-beta-D-arabinofuranosylcytosine (ara-C). Cells were synchronized by mitotic selection and pulse treated in early S phase with a concentration of ara-C (1 mM) which was sufficient to reduce plating efficiency to a few percentages of the control. The process of when and how the lethally damaged cells die was studied using a series of techniques in parallel. These included time-lapse microcinematography, flow microfluorimetry, and chromosome morphology in both anaphases/telophases and Colcemid-arrested metaphases. Most of the lethally damaged Chinese hamster ovary cells progressed through one, and many through two, cell cycles before death occurred. The cell death and abnormal divisions can be accounted for by the chromosome aberrations observed in Colcemid metaphases and anaphases/telophases. Death without any attempted division occurred between 3 and 9 normal cell cycle times after ara-C treatment. Chinese hamster ovary cells were also treated continuously with 1 mM ara-C. Under these conditions, cell death was still primarily division related. We argue that these data are not consistent with the actual incorporation of ara-C moieties into DNA being the primary cause of cell death. The data are discussed in relation to the postulated molecular mechanisms of toxicity of this drug.