A strategy for the identification of ecdysteroid receptor agonists and antagonists from plants

A strategy is described for receptor-based phytochemical screening of plant extracts for ecdysteroid agonists and antagonists. Milligram amounts of seed are methanol extracted. Lipids and pigments are removed by hexane partioning. Agonist and antagonist activities are detected with a microplate-based specific bioassay using the Drosophila melanogaster ecdysteroid-responsive BII cell line. Extracts are also screened with ecdysteroid-specific RIAs to identify extracts containing phytoecdysteroids. Over 1,700 species of plant have been screened in this way so far. Extracts are being sought which (i) contain large amounts of phytoecdysteroid, (ii) which contain novel phytoecdysteroids, (iii) which contain non-steroidal agonists and (iv) which contain antagonists. The aim of this paper is to describe the rationale behind the strategy, to describe its operation and to present, as an example, the results obtained with members of the Poaceae and of one genus, Briza, in particular. It is hoped that this approach will result in the identification of new sources of phytoecdysteroids, provide new phytoecdysteroid structures for structure/activity relationship studies, throw light on the phylogenetic distribution of phytoecdysteroids in the plant kingdom and provide useful agonists and antagonists for the investigation of ecdysteroid receptor function and as potential lead compounds for new classes of insect control agents.