Mitotic arrest induced by XK469, a novel antitumor agent, is correlated with the inhibition of cyclin B1 ubiquitination

XK469 (NSC 697887) is a novel antitumor agent with broad activity against a variety of tumors. Previous studies suggest that XK469 is a topoisomerase lip poison with functional activity similar to that of 4'- (9-acridinylamin o) methanesulfon-m-anisidide (m-AMSA). The goal of our study was to investi gate its mechanism of action further using a human HCT-116 (H116) colon tum or cell model. Concentration-survival curves with continuous exposure indic ated that XK469 had low cytotoxic activity against H116 cells. Cell cycle a nalysis revealed that XK469 is a phase-specific cell cycle blocker that is associated with increased levels of cyclin BI, cyclin A and p53 but not CDK I (cdc2) or cyclin E. In contrast, treatment of H116 cells with m-AMSA caus ed a total degradation of both cyclin A and BI but enhanced expression of c yclin E and p53. Accumulation of cyclin BI in XK469-treated cells was corre lated with the inhibition of cyclin BI ubiquitination, a metabolic process mandatory for proteasome-mediated protein turnover. However, no inhibition of cyclin BI ubiquitination was detected in cells treated with rn-AMSA or c olchicine, a known mitotic inhibitor. Furthermore, unlike rn-AMSA, XK469 di d not induce caspase activation or apoptotic cell death in H116 cells. Our results suggest that XK469 is a phase-specific cell cycle inhibitor with a unique mechanism of action that is correlated with the inhibition of cyclin BI ubiquitination and its accumulation at early M phase. (C) 2002 Wiley-Li ss, Inc.