The Inhibitory Activity And QSAR Of Daphne Diterpene Esters Towards DNA Topoisomerase Ⅰ From Daphne Genkwa

The daphne diterpene esters, extracted from Daphne genkwa, a traditional Chinese medicine, has been found to show good antitumor activity, but the anticancer mechanism of these compounds has not been studied deeply. In this paper, a series of daphne diterpene esters were extracted from the bud of Daphne genkwa, the inhibitory activity and structure-activity relationship (QSAR) towards DNA topoisomerase I (topo I) of these compounds were studied, accordingly, the anticancer mechanism was discussed.A sample of the flower of D. genkwa was extracted with alcohol at room temperature to give a residue, this residue was subjected to silica-gel column chromatography and get a mixture. The further purification was performed by C₁₈ HPLC preparation chromatography to obtain four fractions: yuanhuacine, yuanhuadine, yuanhuagine and yuanhuapine, among them, yuanhuagine obtained from D. genkwa for the first time. Their structures were elucidated by a combination of UV, IR, MS and NMR spectra. In order to explore the QSAR, three derivatives of yuanhuacine were synthesized and characterized. The feasibility of Micheal addition reaction for yuanhuacine and glutathione was attempted, accordingly, it was deduced that daphne diterpene esters can not reacted with sulfydryl compound such as glutathione, it is also illuminated that these compounds nearly did not kill the normal cells. The inhibitory activities of above compounds against DNA topoisomerase I (topo I) were evaluated by agarose-gel electrophoresis experiments. The result manifested that all of these compounds except 8 exhibited potent inhibitory activities against topo I at IC50 levels of 11.1 53.4 μM. The QSAR study indicated that the orthoester group in daphne diterpene ester was necessary for the inhibitory activity against topo I, electron-donating groups can increase the inhibitory activity, and electron-withdrawing groups decrease the inhibitory activity.In summary, daphne diterpene esters are a new type of DNA topo I inhibitors bearing different structures compared with the known topo I inhibitors camptothecin and its analogues. The inhibitory activity against DNA topo I is probably one of the antitumor mechanisms of these daphne diterpene esters.