Abstract
Artemisinin is the active principle of the Chinese herb Artemisia annua L. In addition to its anti-malarial activity, artemisinin and its derivatives have been shown to exert profound anti-cancer activity. The endoperoxide moiety in the chemical structure of artemisinin is thought to be responsible for the bioactivity. Here, we analyzed the cytotoxicity and the ability of artemisinin, five of its derivatives, and two other endoperoxides to inhibit generation of nitric oxide (NO). In the RAW 264.7 mouse macrophage cell line, the well-established model cell line to analyze NO generation, artesunate revealed the highest ability to inhibit NO production among all compounds tested. In cytotoxicity assays (XTT assay), the IC(50) value of RAW 264.7 cells for artesunate was determined to be 3.1+/-0.7 microM. In order to associate the cytotoxic effects with specific alteration in gene expression related to NO metabolism and signaling, whole genome mRNA microarray analyses were conducted. RAW 264.7 cells were treated with artesunate using DMSO as vehicle control followed by microarray analysis. A total of 36 genes related to NO metabolism and signaling were found to be differentially expressed upon exposure to artesunate. Apart from NO-related genes, the expression of genes associated with other functional groups was also analyzed. Out of 24 functional groups, differential expression was most prominent in genes involved in cell-to-cell signaling and interactions. Further refinement of this analysis showed that the pathways for cAMP-mediated signaling and Wnt/beta-catenin signaling were most closely related to changes in mRNA expression. In conclusion, NO generation and signaling play a role in exhibiting cytotoxic activity of artesunate. In addition, other signaling pathways also contribute to the inhibitory effect of artesunate towards RAW 264.7 cells pointing to a multi-factorial mode of action of artesunate.