Cucurbitacin B inhibits STAT3 and the Raf/MEK/ERK pathway in leukemia cell line K562

Cucurbitacin B is a natural anti-cancer compound found in Cucurbitaceae. Although the anti-cancer activity of cucurbitacin B in human leukemia cells has been reported, the underlining mechanism is still unclear. To clarify its anti-cancer activity and the mechanism of action, five different leukemia cell lines (CCRF-CEM, K562, MOLT-4, RPMI-8226 and SR) of the National Cancer Institute panel were treated with cucurbitacin B. Leukemia cell growth was inhibited by cucurbitacin B with GI50 ranged from 15.6 nM to 35.3 nM and the growth inhibition effect was attributable to G2/M phase arrest and apoptosis. Western blotting analysis of cell signaling molecules indicated that cucurbitacin B inhibits STAT3 activation and the Raf/MEK/ERK pathway in the K562 cells.