A wide variety of drug classes, as well as other high-value compounds, are (or are derived from) plant natural products.
Many are plant secondary metabolites (compounds produced by the plant that are not directly involved in growth and development; often involved in protecting the plants from pests and disease)
But successful development of a natural-product drug can rapidly lead to issues around supply and sustainability:
Taxol – significant issues with supply of yew bark in early years. Ultimately solved by semi-synthesis and an integrated cultivation program.
QS-21 – pressure growing on Quillaja supply chain after launch of first vaccine (several more products in the pipeline)
Vincristine/vinblastine – low yield (approx. 3 tonnes of leaf material processed per gram vincristine)
The QS-21 adjuvant precursor, quillaic acid (QA), has been produced in Nicotiana by using transiently-expressed, known enzymes from a variety of plant species to convert the common precursor, β-amyrin, into QA.
Remarkably, none of the enzymes were from Quillaja, which is the natural source of QS-21.