Different effects of two cyclic chalcone analogues on cell cycle of Jurkat T cells

Abstract

It has been previously shown that the cyclic chalcone analogues E-2-(4′-methoxybenzylidene)- ( 2) and E-2-(4′-methylbenzylidene)-1-benzusuberone ( 3) inhibited proliferation of various murine and human tumor cells. In order to gain new insights into the cytotoxic mechanism of the two compounds detection of apoptosis and necrosis of Jurkat T cells exposed to 2 and 3 were performed by flow cytometry using the Annexin V-FITC and propidium iodide double staining method. Analysis of the DNA histograms at 8, 24 and 48 h exposure times showed that near equitoxic doses of 2 and 3 had different effects on the cell cycle of the exposed cells. The immediate (8 h) effect of 2 was a remarkable decrease of cells in the G 0/G 1 phase and increase in the G 2/M phase. This effect could also be seen in the histogram of cells at the 24 h time point. On the contrary, such an effect of 3 could not be observed. At the 24 and 48 h time points accumulation of sub-G 0 (apoptotic and necrotic) and hyperdiploid cells could be detected after both treatments. Incubation of 2 and 3 with reduced glutathione under cell-free conditions indicated spontaneous conjugation (non-redox) reaction at pH 7.4 and pH 9.0. Analyzing the mechanism of action the total thiol content of the cells exposed to compounds 2 and 3 was determined. Compound 2 showed to reduce the total cellular thiol level both under nutrient-free and nutrient-supplemented conditions. Under the latter conditions an increase of the total thiol level of the cells exposed to 3 for 4 h could be observed. The different effect of the two compounds on the cellular thiol status might contribute to the different tumor cytotoxicity of the cyclic chalcone analogues 2 and 3. Investigation of antioxidant capacity of the compounds by monitoring time course of the Fenton-reaction initiated in vitro degradation of 2-deoxyribose indicated that both compounds displayed hydroxyl radical scavenger activity. The experiments provide further details of dual – cytotoxic and cytoprotective (chemopreventive) – effects of the compounds.