XK469, a novel antitumor agent, inhibits signaling by the MEK/MAPK signaling pathway.

PURPOSE

XK469 (NSC 697887) is a novel antitumor agent with broad activity against a variety of tumors including drug-resistant tumors. Previous studies have indicated that XK469 is an antiproliferative agent with a low cytotoxic effect in human H116 tumor cells. In this study, we sought to determine the signaling pathways involved in mediating its antiproliferative activity.

METHODS

The antiproliferative activity of XK469 was tested using human U-937 leukemia cells in culture. XK469-induced cell cycle arrest was determined using flow cytometric analysis. Phosphorylation/activation of MEK and MAPK was analyzed using immunoblot analyses with specific antibodies against p-MEK and p-MAPK.

RESULTS

Cell cycle analysis revealed that XK469 arrested U-937 cells at the G(2)/M phase. Compared with conventional anticancer agents, XK469 showed very low, if any, cytotoxic or proapoptotic effect against U-937 cells. In contrast, treatment of U-937 cells with vinblastine, doxorubicin and m-AMSA resulted in extensive cell death through apoptotic pathways. XK469, but not other agents, potently inhibited the phosphorylation/activation of MEK in U-937 cells cultured in serum-containing medium. XK469 was also able to block the activation of MEK by serum addition in starved U-937 cells. Exposure of cells to XK469 for 1 h was sufficient to inhibit the activation of MEK and its downstream kinase, MAPK. The antiproliferative response to XK469 was correlated with a steady accumulation of cyclins B1 and A, which appeared to be a direct result of G(2)/M arrest.

CONCLUSIONS

Our findings suggest that the antiproliferative effect of XK469 is mediated by inhibiting the MEK/MAPK signaling pathways in U-937 human leukemia cells.