Cytotoxic and pro-apoptotic activities of cynaropicrin, a sesquiterpene lactone, on the viability of leukocyte cancer cell lines

Cynaropicrin, a sesquiterpene lactone from Saussurea lappa, has been reported to possess immunomodulatory effects on cytokine release, nitric oxide production and immunosuppressive effects. In this study, we have examined cytotoxic effect of cynaropicrin against several types of cell lines such as macrophages, eosinophils, fibroblasts and lymphocytes. Cynaropicrin potently inhibited the proliferation of leukocyte cancer cell lines, such as U937, Eol-1 and Jurkat T cells, but some other cells such as Chang liver cells and human fibroblast cell lines were not strongly suppressed by cynaropicrin treatment. The cytotoxic effect of cynaropicrin was due to inducing apoptosis and cell cycle arrest at G1/S phase, according to flow-cytometric, DNA fragmentation and morphological analyses using U937 cells. Evidence that combination treatment with L-cysteine and N-acetyl-L-cysteine, reactive oxygen species scavengers, or rottlerin (1-[6-[(3-acetyl-2,4,6-trihydroxy-5-methylphenyl)methyl]-5,7- dihydroxy-2, 2-dimethyl-2H-1-benzopyran-8-yl]-3-phenyl-2-propen-1-one), a specific protein kinase (PK) Cδ inhibitor, abolished cynaropicrin-mediated cytotoxicity and morphological change, and that cynaropicrin-induced proteolytic cleavage of PKCδ suggests that reactive oxygen species and PKCδ may play an important role in mediating pro-apoptotic activity by cynaropicrin. Taken together, these results indicate that cynaropicrin may be a potential anticancer agent against some leukocyte cancer cells such as lymphoma or leukemia, through pro-apoptotic activity.