Saponins extracted from by-product of Asparagus officinalis L. suppress tumour cell migration and invasion through targeting Rho GTPase signalling pathway

Background: The inedible bottom part (∼30-40%) of asparagus (Asparagus officinalis L.) spears is usually discarded as waste. However, since this by-product has been reported to be rich in many bioactive phytochemicals, it might be utilisable as a supplement in foods or natural drugs for its therapeutic effects. In this study it was identifed that saponins from old stems of asparagus (SSA) exerted potential inhibitory activity on tumour growth and metastasis. Results: SSA suppressed cell viability of breast, colon and pancreatic cancers in a concentration-dependent manner, with half-maximum inhibitory concentrations ranging from 809.42 to 1829.96μg mL^-1. However, SSA was more functional in blocking cell migration and invasion as compared with its cytotoxic effect, with an effective inhibitory concentration of 400μg mL^-1. A mechanistic study showed that SSA markedly increased the activities of Cdc42 and Rac1 and decreased the activity of RhoA in cancer cells. Conclusion: SSA inhibits tumour cell motility through modulating the Rho GTPase signalling pathway, suggesting a promising use of SSA as a supplement in healthcare foods and natural drugs for cancer prevention and treatment.