Anti-plasmodial polyvalent interactions in Artemisia annua L. aqueous extract--possible synergistic and resistance mechanisms.

Artemisia annua hot water infusion (tea) has been used in in vitro experiments against P. falciparum malaria parasites to test potency relative to equivalent pure artemisinin. High performance liquid chromatography (HPLC) and mass spectrometric analyses were employed to determine the metabolite profile of tea including the concentrations of artemisinin (47.5±0.8 mg L(-1)), dihydroartemisinic acid (70.0±0.3 mg L(-1)), arteannuin B (1.3±0.0 mg L(-1)), isovitexin (105.0±7.2 mg L(-1)) and a range of polyphenolic acids. The tea extract, purified compounds from the extract, and the combination of artemisinin with the purified compounds were tested against chloroquine sensitive and chloroquine resistant strains of P. falciparum using the DNA-intercalative SYBR Green I assay. The results of these in vitro tests and of isobologram analyses of combination effects showed mild to strong antagonistic interactions between artemisinin and the compounds (9-epi-artemisinin and artemisitene) extracted from A. annua with significant (IC50 <1 µM) anti-plasmodial activities for the combination range evaluated. Mono-caffeoylquinic acids, tri-caffeoylquinic acid, artemisinic acid and arteannuin B showed additive interaction while rosmarinic acid showed synergistic interaction with artemisinin in the chloroquine sensitive strain at a combination ratio of 1:3 (artemisinin to purified compound). In the chloroquine resistant parasite, using the same ratio, these compounds strongly antagonised artemisinin anti-plasmodial activity with the exception of arteannuin B, which was synergistic. This result would suggest a mechanism targeting parasite resistance defenses for arteannuin B's potentiation of artemisinin.

Antiproliferative and antimalarial anthraquinones of Scutia myrtina from the Madagascar forest.

Bioassay-guided fractionation of an ethanol extract of a Madagascar collection of the bark of Scutia myrtina led to the isolation of three new anthrone-anthraquinones, scutianthraquinones A, B and C (1-3), one new bisanthrone-anthraquinone, scutianthraquinone D (4), and the known anthraquinone, aloesaponarin I (5). The structures of all compounds were determined using a combination of 1D and 2D NMR experiments, including COSY, TOCSY, HSQC, HMBC, and ROESY sequences, and mass spectrometry. All the isolated compounds were tested against the A2780 human ovarian cancer cell line for antiproliferative activities, and against the chloroquine-resistant Plasmodium falciparum strains Dd2 and FCM29 for antiplasmodial activities. Compounds 1, 2 and 4 showed weak antiproliferative activities against the A2780 ovarian cancer cell line, while compounds 1-4 exhibited moderate antiplasmodial activities against P. falciparum Dd2 and compounds 1, 2, and 4 exhibited moderate antiplasmodial activities against P. falciparum FCM29.

Overcoming drug resistance to heme-targeted antimalarials by systematic side chain variation of 7-chloro-4-aminoquinolines.

Systematic variation of the branching and basicity of the side chain of chloroquine yielded a series of new 7-chloro-4-aminoquinoline derivatives exhibiting high in vitro activity against four different strains of P. falciparum. Many of the compounds tested showed excellent potency against chloroquine sensitive and resistant strains. In particular 4b, 5a, 5b, 5d, 17a, and 17b were found to be significantly more potent than chloroquine against the resistant strains Dd2 and FCB.

Novel, rapid, and inexpensive cell-based quantification of antimalarial drug efficacy.

We report on the development of a new SYBR Green I-based plate assay for analyzing the activities of antimalarial drugs against intraerythrocytic Plasmodium falciparum. This assay is considerably faster, less labor-intensive, and less expensive than conventional radiotracer (e.g., [3H]hypoxanthine and [3H]ethanolamine)-based assays or P. falciparum lactate dehydrogenase activity-based assays. The assay significantly improves the pace at which antimalarial drug discovery efforts may proceed.