Kirenol, a compound from Herba Siegesbeckiae, induces apoptosis in human chronic myeloid leukemia K562 cells

Kirenol is a biologically active substance isolated from Herba Siegesbeckiae. In the experiments, we explored a novel antitumor activity of kirenol. The data demonstrated that kirenol had strong cytotoxic effects to human chronic myeloid leukemia K562 cells, the 50% inhibitory concentration (IC50) for kirenol was 53.05 ig/ml, 18.19 pg/ml and 15.08 microg/ml for 24, 48 and 72 h, determined using the MTT assay. Further studies showed that kirenol treatment caused externalization of phosphatidylserine, accumulation of ROS (reactive oxygen species), alteration of mitochondrial membrane potential, release of cytochrome c, reduction in the level of the Bcl-2 protein and upregulation of Bax and tBid, kirenol induced cell apoptosis in a caspase-independent manner. Further studies indicated that kirenol treatment triggered the arrest of cell cycle S period which might resulted from the up-regulation of phosphorylation of p53 (Ser 6 and Ser 37) and expression of p21 protein. Our results indicated that kirenol possesses antitumor action on human chronic myeloid leukemia K562 cells in vitro. Kirenol may have therapeutic potential for the treatment of cancer that deserves further investigation.