The sulphorhodamine (SRB) assay and other approaches to testing plant extracts and derived compounds for activities related to reputed anticancer activity

Abstract

Since the major approach in searching for potential anticancer agents over the last 50 years has been based on selective cytotoxic effects on mammalian cancer cell lines, cell-based methods for cytotoxicity are described and compared. The sulphorhodamine B (SRB) assay is described in detail as the preferred method and also a novel approach has been developed which is based on the hypothesis that, in some circumstances, the naturally occurring compounds act as prodrugs rather than active compounds in their own right. Consequently, extracts or compounds are pre-incubated with systems modelling metabolic processes in the body before being tested. The methods have been validated using known compounds and Iris tectorum extracts have been shown to be more cytotoxic after treatment with beta-glucosidase. In addition bioassays based on mammalian cells involving antioxidant and upregulation of some cellular self-defence mechanisms are discussed which are related to prevention as well as treatment of cancer. Extracts of Alpinia officinarum induced glutathione-S-transferase (GST) activity in cultured hepatocytes and this was traced to the phenylpropanoids present, especially 1'-acetoxychavicol acetate.