Abstract
To find fractions from Spatholobi caulis with cytotoxic effects on cancer cell lines, screening tests were carried out using the SRB assay on the HL60 cell line. Further investigation with HL60 and another four human cancer cell lines (KB, K562, MCF-7 and Hep G2), revealed a dose-dependent response. High-performance liquid chromatography coupled with electrospray ionization-tandem mass spectrometry (HPLC- ESI-MSn) was used to isolate and identify the active constituents from the active fraction. Three fractions (F-IV, F-V and F-VII) showed in vitro cytotoxicity. F-V inhibited the growth of cancer cells in a dose-dependent manner. The IC50 values for KB, K562 and HL60 cells were 17.6, 8.3 and 9.7 μg/mL, respectively. The dominating constituents of F-V were either identified or tentatively characterized as nine phenolic compounds, eight isoflavones and 9-methoxycoumestrol. The isoflavones 7-hydroxy-3′,4′-dimethoxy isoflavone, 7-hydroxy-6,2′,4′-trimethoxy isoflavone and 3′-hydroxy-7,4′-dimethoxy isoflavone are reported for the first time for Spatholobi caulis. The results suggest that these compounds contribute to the cytotoxic effect of Spatholobi caulis.