No abstract

The knockdown of Pim-1 or inhibition of Pim-1 activity significantly increased c-H2A.X expression. The effect was correlated to apoptosis and was attributed to the inhibition of nonhomologous DNA-end-joining (NHEJ) repair activity supported by the following observations: (1) inhibition of ATM and DNA-PKcs activities, (2) down-regulation of Ku expression and nuclear localization and (3) decrease of DNA end-binding of both Ku70 and Ku80. The data suggest that Pim-1 plays a crucial role in the regula-tion of NHEJ repair. In the absence of Pim-1, the ability of DNA repair significantly decreases when exposed to paclitaxel, leading to severe DNA damage and apoptosis.

Data suggest that paclitaxel induces nuclear translocation and activation of PKC-δ, which in turn causes Golgi-Cdk1 activation, leading to Golgi associated DR5 up-regulation, and caspase-8 and 3 activation. Golgi mediated signaling cascades facilitate mitochondria involved apoptotic pathways and at least partly explain the anticancer activity of paclitaxel action.

No abstract

Microtubules are crucial targets for cancer chemotherapeutic drugs, and new microtubule-directed agents are of continued interest in drug development. A novel microtubule-directed agent, ethyl-2-[N-rho-chlorobenzyl-(2'-methoxy)]-anilino-4-oxo -4, 5-dihydro-furan-3-carboxylate, was identified. The compound, designated K2154, inhibited cell proliferation, with IC(50) values of 10.3, 15.3, 9.6, 11.2, 12.8 and 12.1 muM in prostate cancer PC-3, hepatocellular carcinoma Hep3B, non-small cell lung cancer A549, colorectal cancer HT29 and HCT116, and P-glycoprotein-rich breast cancer NCI/ADR-RES cells, respectively. Because NCI/ADR-RES cells were susceptible to inhibition by K2154, it indicated that this compound is a poor substrate for P-glycoprotein. In this study, PC-3 cells were used to identify the anticancer mechanisms of K2154. K2154 induced an arrest of the cell cycle at G2/M phase and a subsequent increase of hypodiploid phase in PC-3 cells, whereas it only induced a moderate level of G2/M arrest with little increase of hypodiploid phase in normal prostate cells. K2154 inhibited microtubule assembly in both in vitro turbidity assay and in vivo microtubule spin-down experiment. Immunochemical examination showed that K2154 caused formation of abnormal mitotic characteristics with bipolar spindles, particularly, in beta(II)- and beta(III)-tubulin staining. It also induced several pathways, including cyclin B1 up-regulation, dephosphorylation on Tyr(15) and phosphorylation on Thr(161) of Cdk1 and Cdc25C phosphorylation, and roscovitine (a Cdk1 inhibitor) significantly inhibited K2154-induced apoptosis, suggesting a pro-apoptotic role of Cdk1. Phosphorylation of Bcl-2 and Bcl-xL and cleavage of Mcl-1, together with activation of caspase-9 and -3, indicated that mitochondrial pathway played a central role in K2154-mediated apoptotic cell death. Additionally, AIF contributed to a late phase of K2154-induced apoptotic pathway. In conclusion, it is suggested that K2154 displays an anticancer activity through a target on microtubules and a subsequent signaling cascade on cell cycle regulation and apoptotic machinery.