Diallyl Trisulfide-induced Apoptosis in Human Cancer Cells Is Linked to Checkpoint Kinase 1-Mediated Mitotic Arrest

Growth suppressive effect of diallyl trisulfide (DATS), a promising cancer chemopreventive constituent of garlic, against cultured human cancer cells correlates with checkpoint kinase 1 (Chk1)-mediated mitotic arrest, but the fate of the cells arrested in mitosis remains elusive. Using LNCaP and HCT-116 human cancer cells as a model, we now demonstrate that the Chk1-mediated mitotic arrest resulting from DATS exposure leads to apoptosis. The DATS exposure resulted in G(2) phase and mitotic arrest in both LNCaP and HCT-116 cell lines. The G(2) arrest was accompanied by downregulation of cyclin-dependent kinase 1 (Cdk1), cell division cycle (Cdc) 2513, and Cdc25C leading to Tyr15 phosphorylation of Cdk1 (inactivation). The DATS-mediated mitotic arrest correlated with inactivation of anaphase-promoting complex/cyclosome as evidenced by accumulation of its substrates cyclinB1 and securin. The DATS treatment increased activating phosphorylation of Chk1 (Ser317) and transient transfection with Chk1-targeted siRNA conferred significant protection against DATS-induced mitotic arrest in both cell lines. The Chk1 protein knockdown also afforded partial yet statistically significant protection against apoptotic DNA fragmentation and caspase-3 activation resulting from DATS exposure in both LNCaP and HCT-116 cells. Even though DATS treatment resulted in stabilization and Ser15 phosphorylation of p53, the knockdown of p53 protein failed to rescue DATS-induced mitotic arrest. In conclusion, the results of the present study indicate that Chk1 dependence of DATS-induced mitotic arrest in human cancer cells is not influenced by the p53 status and cells arrested in mitosis upon DATS exposure are driven to apoptotic DNA fragmentation. (C) 2009 Wiley-Liss, Inc.