The selection and the establishment of suitable bioassay methods have to be considered in any development programme related to the search for new biologically active compounds from plants. For example, the recent discovery of paclitaxel, as an anticancer agent, was linked to the use of bioassay methods. The approach we have developed for the detection of new bioactive taxoids from Taxus baccata stem bark extracts, was based on the use of two biological tools that are complimentary: antibodies (anti-paclitaxel and anti-10-deacetylbaccatin III) and naturally occurring receptor(s) for taxoids (complex of tubulin-microtubule). The immunoenzymatic methods (ELISA) combined with the tubulin assay were successfully applied to the bioassay guided fractionation of crude extracts. In addition, the high sensitivity and specificity of both assays allowed the screening of alternative sources of bioactive taxoids including Taxus tissue cultures and microorganisms, such as fungus and bacteria.
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