Cytotoxic Xanthone Constituents of the Stem Bark of Garcinia mangostana (Mangosteen)

Bioassay-guided fractionation of a chloroform-soluble extract of Garcinia mangostana stem bark, using the HT-29 human colon cancer cell line and an enzyme-based ELISA NF-κB assay, led to the isolation of a new xanthone, 11-hydroxy-3-O-methyl-1-isomangostin (1). The structure of 1 was elucidated by spectroscopic data analysis. In addition, 10 other known compounds, 11-hydroxy-1-isomangostin (2), 11α-mangostanin (3), 3-isomangostin (4), α-mangostin (5), β-mangostin (6), garcinone D (7), 9-hydroxycalabaxanthone (8), 8-deoxygartanin (9), gartanin (10), and cratoxyxanthone (11), were isolated. Compounds 4−8 exhibited cytotoxicity against the HT-29 cell line with ED₅₀ values of 4.9, 1.7, 1.7, 2.3, and 9.1 μM, respectively. In an ELISA NF-κB assay, compounds 5−7, 9, and 10 inhibited p65 activation with IC₅₀ values of 15.9, 12.1, 3.2, 11.3, and 19.0 μM, respectively, and 6 showed p50 inhibitory activity with an IC₅₀ value of 7.5 μM. α-Mangostin (5) was further tested in an in vivo hollow fiber assay, using HT-29, LNCaP, and MCF-7 cells, but it was found to be inactive at the highest dose tested (20 mg/kg).