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 IC50 value of RAW 264.7 cells for artesunate was determined to be 3.1 ± 0.7 lM. 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 NOrelated 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/b-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.
Abstract: Artesunate is a derivate of artemisinin, an antimalarial drug used for the treatment of malaria caused by Plasmodium falciparum and related parasites. Artesunate is hydrolized rapidly to dihydroartemisinin in vivo. It has been found that artemisinin and its derivatives may have neurotoxic effects. A method was developed to analyze human plasma samples for the contents of artesunate and dihydroartemisinin. The plasma samples are extracted with ethyl acetate, concentrated, and redissolved in water/acetonitrile. Analyses was performed with liquid chromatography–mass spectrometry using a binary gradient program with aquaeous formic acid and acetonitrile formic acid on a XTerra MS C18-column. The mass spectrometer was operated in the positive atmospheric pressure chemical ionization mode with single ion recording. The lower limits of detection were 10 and 25 ng/mL plasma for DHA and artesunate, respectively. The method was validated according to the guidelines for validation of bioanalytical methods.
Abstract: Artemisinin is a sesquiterpene compound of plant origin. It has a low molecular weight, and it contains five oxygen atoms, two in a lactone function, one is part of a seven membered ring system and two forms a peroxide function bridging over the seven-membered ring. It is a highly energetic molecule prone to lose its activity if circumstances permit. Reduction of its lactone function into dihydroartemisinin makes derivatization easy. Esterification and ether formation contribute to stability. Dihydroartemisinin exists preferably in a beta epimeric format but flip-flops with the alpha epimer. Solvation effects play a role. In doing so, open forms are created and they contribute to the instability, both of the peroxide and of the seven-membered ring. Artemisinins constitute a remarkable class of compounds which display instability both biologically and chemically due to the presence of various functional groups. Activity ranges from a wonderful action against a series of parasites, in particular malaria and schistosomiasis, to bacteria, fungi and selected viruses. The latest developments indicate a potential use in adjuvant cancer chemotherapy. The built-in chemical instability, necessary for biological action, causes serious pharmaceutical problems and only a restricted number of derivatives are useful. Problems are accelerated under tropical conditions and the basic active drug dihydroartemisinin cannot be used as such since it is prone to accelerated breakdown into a series of inactive products. The pitfalls of chemical instability and pharmaceutical stability are discussed in relation to the current uses of the drugs.
Abstract: Two types of dendritic nanoparticles were prepared, which contain (E)-stilbene chromophores in the terminal positions of the dendrons. The compounds showed a highly efficient photoreactivity in the course of which statistical CC bond formations led to a crosslinking of the particles. Finally, all stilbene chromophores reacted and the typical (E)-stilbene absorption and fluorescence disappeared completely.
Abstract: Small nanoparticles of defined three-dimensional structure can be formed through the programmed, sequence-specific assembly of short DNA strands. The extension of this concept to large nanoparticles of > 100 nm diameter, let alone macroscopic crystals has proven challenging. To date, no designed crystals, generated through base pairing between complementary nucleic acid strands have been reported. We have initiated a research program focused on the assembly of oligonucleotides covalently linked to organic core molecules. As a first example, we present DNA-based assemblies of sub-micrometer size that are generated through hybridization in aqueous buffer. These were characterized by electron microscopy and spectroscopic techniques. Another sequence was found to assemble into an insoluble solid upon cooling in aqueous solution.
