Involvement of histone H3 phosphorylation via the activation of p38 MAPK pathway and intracellular redox status in cytotoxicity of HL-60 cells induced by Vitex agnus-castus fruit extract.

We have demonstrated that an extract from the ripe fruit of Vitex angus-castus (Vitex), might be a promising anticancer candidate. In order to further provide a molecular rationale for clinical development in anticancer therapy, a detailed mechanism underlying the efficacy of Vitex against HL-60 cells was investigated. Vitex induced a dose- and time-dependent decrease in cell viability associated with induction of apoptosis and G(2)/M cell cycle arrest, both of which were suppressed by the addition of SB203580, an inhibitor for p38 MAPK. Furthermore, SB203580 significantly suppressed Vitex-induced phosphorylation of histone H3, a downstream molecule of p38 MAPK known to be involved in apoptosis induction in tumor cells. Notably, Vitex induced upregulation of intracellular ATP, known to bind its binding pocket inside activated p38 MAPK and to be required for the activation of p38 MAPK pathway. These results, thus, suggest that upregulation of intracellular ATP and phosphorylation of histone H3 are closely associated with the activation of p38 MAPK pathway, consequently contributing to Vitex-mediated cytotoxicity. Intriguingly, a significant decrease of intracellular ROS levels and downregulation of expression level of gp91(phox), an important component of NADPH oxidase, were observed in Vitex-treated cells. A greater decline in ROS levels along with enhanced apoptosis was observed after treatment with Vitex in combination with SnPP, an inhibitor specific for HO-1. Since NADPH oxidase and HO-1 are closely correlated to redox status associated with intracellular ROS levels, the two enzymes are suggested to be implicated in Vitex-mediated cytotoxicity in HL-60 cells by regulating ROS generation. We also suggest that activation of the p38 MAPK pathway may be dependent on the alterations of intracellular ATP levels, rather than that of intracellular ROS levels. These results may have important implications for appropriate clinical uses of Vitex and provide novel insights into the interaction between Vitex and other conventional drugs capable of affecting intracellular redox status.

Cytotoxicity of Vitex agnus-castus fruit extract and its major component, casticin, correlates with differentiation status in leukemia cell lines.

We have demonstrated that an extract from the ripe fruit of Vitex agnus-castus (Vitex) exhibits cytotoxic activities against various types of solid tumor cells, whereas its effects on leukemia cells has not been evaluated to date. In this study, the effects of Vitex and its major component, casticin, on leukemia cell lines, HL-60 and U-937, were investigated by focusing on proliferation, induction of apoptosis and differentiation. Identification and quantitation by NMR spectroscopy showed that casticin accounted for approximate 1% weight of Vitex. Dose-dependent cytotoxicity of Vitex and casticin was observed in both cell lines, and HL-60 cells were more sensitive to the cytotoxicity of Vitex/casticin compared to U-937 cells. Furthermore, compared to unstimulated HL-60 cells, phorbol 12-myristate 13-acetate (PMA)- and 1,25-dihydroxyvitamin D3 (VD3)-differentiated HL-60 cells acquired resistance to Vitex/casticin based on the results from cell viability and apoptosis induction analysis. Since the HL-60 cell line is more immature than the U-937 cell line, these results suggested that the levels of cytotoxicity of Vitex/casticin were largely attributed to the degree of differentiation of leukemia cells; that is, cell lines with less differentiated phenotype were more susceptible than the differentiated ones. RT-PCR analysis demonstrated that PMA upregulated the expression of intercellular adhesion molecule-1 (ICAM-1) in HL-60 cells, and that anti-ICAM-1 monoclonal antibody not only abrogated PMA-induced aggregation and adhesion of the cells but also restored its sensitivity to Vitex. These results suggested that ICAM-1 plays a crucial role in the acquired resistance in PMA-differentiated HL-60 cells by contributing to cell adhesion. These findings provide fundamental insights into the clinical application of Vitex/casticin for hematopoietic malignancy.