Cytotoxic activity of Hypericum perforatum L. on K562 erythroleukemic cells: differential effects between methanolic extract and hypericin

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Abstract
The influence of a methanolic extract of Hypericum perforatum L. and of purified hypericin has been comparatively tested on the growth of a human erythroleukemic cell line (K562). After 1 h exposure to increasing concentrations (as hypericin content) of both agents in the dark, leukemic cells were grown for 24 h and 48 h. The effects on cell growth were determined by viable cell count, flow cytometry analysis and fluorescence microscopy. Our data show that purified hypericin has only a weak inhibitory effect on cell growth and no effect in inducing apoptotic cell death. In contrast, the Hypericum flower extract shows a significant concentration‐dependent and long‐lasting inhibition of cell growth, and induces apoptotic cell death. This work confirms the interesting role of Hypericum perforatum L. in cancer therapy and strongly supports the hypothesis that agents, other than hypericin, present in the total extract can impair tumor cell growth acting separately or in a combined manner. Copyright © 2004 John Wiley & Sons, Ltd.