Production of saponins from in vitro cultures of Astragalus glycyphyllos and their antineoplastic activity

In the last decade the need of plant-derived cytotoxic compounds exceeds the possibilities for obtaining them from naturally grown sources. In vitro plant biotechnology offers a unique and often invaluable alternative for production of complex biologically active substances without harming the flora. Astragalus glycyphyllos L. (Fabaceae) is a plant native to Bulgaria that has been reported to contain triterpenoid saponins and flavonoids. It is used in folk medicine as an antihypertensive, diuretic, anti-inflammatory, anti-tumour, laxative, expectorant agent, etc. The aim was to study the saponin content of A. glycyphyllos cultures grown in vitro and their antiproliferative activity. Three types of cultures were developed: callus, shoot and suspension cultures. Murashige and Skoog’s, as well as other media, supplemented with various concentrations and combinations of plant growth regulators and different photoperiods were used. In all cultures the saponin content was determined by a novel liquid chromatography–mass spectrometry (LC-MS) method. Compared to the wild grown species, in vitro shoot cultures accumulated double the amount of the main saponin (225.00 ng/mg dw) found in the plant. Saponin-rich fractions obtained from shoot cultures were tested for cytotoxicity in a panel of various malignant human cells and half-maximal inhibitory concentration (IC₅₀) values were determined. Interestingly, the saponin-rich fractions showed higher efficacy against urinary bladder cancer cells with constitutive high expression level of the xenobiotic pump gp170 (MDR1). In vitro cultures of A. glycyphyllos could serve as an alternative way for production of saponins, with promising antineoplastic activity, which deserves further detailed characterization.