Specificity of the G1 block induced by ethionine in human lymphocytes in vitro: a flow cytometric analysis.

Ethionine is the ethyl analogue of the amino acid methionine. The agent is well known to have a weak demethylating activity. In addition, its capacity to reversibly block the cell cycle progression in G1 human lymphocytes (HL) without interfering with blastic transformation has been reported. In order to better understand the mechanism by which the agent is able to induce cell cycle block, experiments have been performed by using flow cytometry, in HL. In particular the hypothesis of the involvement of a specific target at the G0/G1 boundary was tested by treating HL at different times after blastic transformation. Starting from the 40th hour after PHA stimulation, ethionine loses its blocking capacity in such a way that cells challenged by the agent do not differ from controls in any one of the tested cell cycle-related parameters. We suggest the agent exerts its blocking activity at a specific stage of the transformation pathway.