Pseudolaric acid B (PAB) is the primary biologically active compound isolated from the root bark of P. kaempferi Gordon. Previous studies have demonstrated that PAB arrests cells in G2/M phase in several cancer cell lines without significantly perturbing the G2/M transition-associated proteins. CylinB1, a marker for mitotic phase arrest, was up-regulated in cells treated with PAB. Therefore, we investigated whether PAB affects cell cycle progression at the mitotic phase. The mitotic index increased during a 24h treatment with PAB, suggesting that PAB arrested cell cycle progression at mitosis. In addition, after a prolonged mitotic arrest, the cells underwent mitotic catastrophe. After an extended treatment with PAB (longer than 24h), the protein levels of cylinB1 and cdc2 significantly decreased in both nuclear and cytosolic extracts. According to these results, we concluded that mitotic slippage could be due to the inactivation of the cylinB1-cdc2 complex resulting from prolonged treatment with PAB. The cells undergoing mitotic catastrophe died via apoptosis.
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