Induction of apoptosis by Cordyceps militaris fraction in human chronic myeloid leukemia K562 cells involved with mitochondrial dysfunction

Background: Cordyceps militaris is widely used for various ethno medical conditions including cancer and inflammation complications in traditional Chinese medicine. Objective: To investigate the in vitro antitumor activity of Cordyceps militaris fraction (CMF) and the molecular mechanism underlying the apoptosis it induces in human chronic myeloid leukemia K562 cells. Materials and Methods: CMF was prepared according to our previous report. Cell viability was assessed by MTT assay. The rate of apoptosis, distribution of cell cycle and loss of mitochondrial membrane potential were measured by flow cytometry. Caspase activities were analyzed by Western blot and oxygen consumption rate was recorded using the Oxytherm system. Results: The results demonstrated that CMF triggered growth inhibition in K562 cells with only minor toxicity on a normal human cell line and inhibited the proliferation of K562 cells in a dose- and time-dependent manner with IC50 value of 34.1 +/- 2.0 mu g/ml after 48 h incubation. This most likely resulted from cell cycle arrest at the S phase and the induction of apoptosis. In addition, CMF induced activation of caspase-3 and subsequent cleavage of poly ADP-ribose polymerase (PARP). The caspase signals may originate from mitochondrial dysfunction, which was supported by the finding of decreased mitochondria transmembrance potential and the lower oxygen consumption rate. Conclusion: CMF possessed the in vitro antitumor effect on K562 cells and CMF-induced apoptosis might be involved by the mitochondrial dysfunction and valuable to research and develop as a potential antitumor agency.