Cytotoxic and Natural Killer Cell Stimulatory Components of Phyllanthus songboiensis

The genus Phyllanthus is a large plant group containing over 600 species, of which many have been used in traditional medicine to treat human diseases and have been studied phytochemically. However, there are no previous reports on the chemical constituents of Phyllanthus songboiensis N. N. Thin (Phyllanthaceae). As part of a search for new natural product anticancer agents from diverse organisms, the aerial parts of P. songboiensis, collected in Vietnam, were found to be cytotoxic toward the HT-29 human colon cancer cell line. Using column chromatography guided by cytotoxicity to HT-29 cells, a new dichapetalin-type triterpenoid, a new dibenzylbutyrolactone-type lignan, and several known compounds were isolated from this plant. The structures of all compounds isolated were established from their IR, UV, NMR, and mass spectra, and the absolute configurations of these compounds were determined by analysis of their CD spectra. The cytotoxicity toward HT-29 cells of all isolates and the natural killer (NK) cell stimulation of some compounds were tested. Several compounds showed cytotoxicity toward HT-29 cells, and a sterol glycoside was found to stimulate NK cells in the presence of interleukin-12. This study describes for the first time the cancer cell cytotoxic and NK cell stimulatory constituents of Phyllanthus songboiensis.