Inhibitory effects of α-mangostin on mammalian DNA polymerase, topoisomerase, and human cancer cell proliferation

We found that the ethanol extract of mangosteen (Garcinia mangostana L.) fruit rind had a strong inhibitory effect on mammalian DNA polymerase (pol) activity and isolated alpha-mangostin as a potent pol inhibitor from the extract. In this study, the inhibitory activities against mammalian pols by alpha-mangostin and its related five compounds, 3-isomangostin, xanthone, 9,10-anthraquinone, 9-anthracenecarboxylic acid, and anthracene, were investigated. alpha-Mangostin was the most potent inhibitor of the mammalian pol species among the tested compounds, with IC50 values of 14.8-25.6 mu M. This compound also inhibited human DNA topoisomerases (topos) I and II activities with IC50 values of 15.0 and 7.5 mu M, respectively, but did not inhibit the activities of other DNA metabolic enzymes tested. alpha-Mangostin also did not directly bind to double-stranded DNA as determined by thermal transition analysis. alpha-Mangostin was found to suppress human colon HCT116 carcinoma cell proliferation with an LC50 of 18.5 mu M, inhibit the activity of cellular topos, halt cell cycle in the G2/M phase, and induce apoptosis. These results suggest that decreased proliferation by alpha-mangostin may be a result of the inhibition of cellular topos rather than pols, and alpha-mangostin might be an anticancer chemotherapeutic agent. (C) 2013 Elsevier Ltd. All rights reserved.