Background: Regarding the strong differentiation and anti-leukemic activity of Dendrostellera lessertii extract, an active agent with similar capabilities was isolated from the crude extract of the plant leaves. The aim of this study was to determine whether the anti-proliferative effect observed for this compound, is differentiation-dependent among the drug-treated cells, using U937 cells. Methods: Monocyte differentiation was evaluated by Wright-Giemsa staining, latex particle assay and flow cytometry. Induction of apoptosis was analyzed by Annexin-PI double staining. Results: The new compound, at 0.5-2.5 µg/ml inhibited proliferation of U937 cells by more than 70% and their viabilities were decreased by 47 ± 2.1% after 72 h of treatments. In addition, we found that the effect of the new compound on U937 cells was associated with differentiation toward monocyte/macrophage lineage based on nitroblue tetrazolium reduction assay, morphology change, phagocytic activity and expression of cell surface markers (CD14 and CD11b) as analyzed by flow cytometry. Moreover, our results indicated that the treatment of U937 cells with the new compound for 3 to 4 days induced apoptosis as assayed qualitatively by acridine orange/ethidium bromide and Annexin-V/PI double staining technique using flow cytometry. Conclusion: Based on these observations, it is concluded that the anti-proliferative function of the new compound is exerted through differentiation-dependent apoptosis among the treated cells, similar to the function of 3-hydrogenkwadaphnin previously characterized from D. lessertii crude extract.

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