STUDY OF THE APOPTOSIS INDUCED IN-VITRO BY ANTITUMORAL DRUGS ON LEUKEMIC-CELLS

A flow cytometric method for simultaneous apoptotic cell detection and cell cycle analysis was applied on the U937 cell line. Four antitumor al drugs currently used in the treatment of acute myeloid leukaemia we re studied in vitro: DNR, IDR, MITO and Ara-C. Our results show a diss ociation between the cytostatic effect (the block in the cell cycle ob served for low drug concentrations) and the cytotoxic effect (the indu ction of apoptosis induced by higher concentrations) for all the teste d molecules. Low concentrations of Ara-C induced a block in the S phas e while higher concentrations (> 10(-7) M) induced apoptosis at the G1 -S boundary. Low concentrations of anthracyclines (< 40 nM DNR and < 2 0 nM IDR) induced a block in G2 without apoptosis. Apoptosis was induc ed in G1 and/or early S phases by higher concentrations of anthracycli nes. The concentration inducing 50% apoptosis (IC50) was found to be, respectively, 200 and 40 nM for DNR and IDR. Analysis of MITO-treated cells showed a parallel increase in the percentages of S phase and apo ptotic cells. However, the bivariate analysis showed that apoptosis di d occur in a population with G1 DNA content. For two other drugs (CAM and COLC), apoptosis occurred for the same concentrations and in the s ame phase as the block (in S and G2M, respectively). The IC50 Of MITO was found to be 100 nM. Cotreatment of the cells with colchicin and ei ther Ara-C or IDR showed that the passage through mitosis was not nece ssary for the completion of apoptosis at the G1-S boundary. Short incu bations of U937 cells with high concentrations of anthracyclines were found to be efficient in inducing further apoptosis. We conclude that, for all the assayed molecules, the cytotoxic and/or cytostatic effect s of the antitumoral drugs tested greatly depend on the concentrations used and that, depending on their in vivo pharmacokinetics, the induc tion of apoptosis could be an important mechanism of action for some o f these drugs. (C) 1997 Published by Elsevier Science Ltd.