Screening methods for drug discovery from plants

Many drugs have been derived from bioactive components isolated from plants: while some have come from studies on traditionally used herbal medicines, others have come from leads found in screening campaigns. Phenotypic screening in model organisms has developed with the use of fruit flies (Drosophila melanogaster), nematode worms (Caenorhabditis elegans), and zebrafish (Danio rerio), and functional screens can also be conducted on cells in culture, either for studies on cell death and proliferation in cancer cell lines or for detection of more specific read-outs such as activation or inhibition of a particular biochemical pathway. Molecular assays based on target proteins are particularly suited for high throughput screening, but care needs to be taken when used with plant extracts to avoid non-specific interference, and the power of such assays also depends on their relevance to the disease that is the intended target: validation of the molecular target becomes a critical issue. Examples are given of assays that have been used for plant-based drug discovery in the areas of cancer, diabetes, inflammatory disease, and infectious diseases.