Apoptosis inducement of bigelovin from Inula helianthus-aquatica on human Leukemia U937 cells.

Inula helianthus-aquatica C. Y. Wu is a traditional medicinal plant used to treat some cancers in folk herbal medicine of Yunnan, China. Bigelovin, a sesquiterpene lactone isolated from this herb, potently inhibits the growth of a panel of eight cancer cell lines, especially in human monoblastic leukemia U937 cells with an IC(50) value of 0.47 microM. Characteristic morphological features of apoptosis were observed in U937 cells treated with bigelovin. Annexin V and nuclear DNA content distribution assays showed that the percentage of Annexin V positive cells increased to 8.86% (24 h) with 1 microM bigelovin treatment, and cells treated with bigelovin at this concentration apparently arrested at G(0)/G(1) phase compared with the control. These data suggested that cytotoxic effect of bigelovin on U937 cells involves induction of apoptosis, and the cell cycle is arrested at G(0)/G(1) phase.