Short communicationTarget-directed discovery and production of pharmaceuticals in transgenic mutant plant cells

•We discovered a novel inhibitor of dopamine transport in Lobelia cardinalis.•We functionally expressed the Human dopamine transporter in L. cardinalis plant cells.•Next a Gain-of-function mutant transgenic population was generated from these cells, in presence of a neurotoxin accumulated by the transporter.•The resulting toxin-resistant population was highly enriched in mutants with increased inhibitory activity on the transporter.•Some toxin-resistant mutants overproduce the known active metabolite from wild-type.•Many others contain other active metabolites including some not readily detectable in the wild-type plant.

Plants are a source of complex bioactive compounds, with value as pharmaceuticals, or leads for synthetic modification. Many of these secondary metabolites have evolved as defenses against competing organisms and their pharmaceutical value is “accidental”, resulting from homology between target proteins in these competitors, and human molecular therapeutic targets. Here we show that it is possible to use mutation and selection of plant cells to re-direct their “evolution” toward metabolites that interact with the therapeutic target proteins themselves. This is achieved by expressing the human target protein in plant cells, and selecting mutants for survival based on the interaction of their metabolome with this target. This report describes the successful evolution of hairy root cultures of a Lobelia species toward increased biosynthesis of metabolites that inhibit the human dopamine transporter protein. Many of the resulting selected mutants are overproducing the active metabolite found in the wild-type plant, but others overproduce active metabolites that are not readily detectable in non-mutants. This technology can access the whole genomic capability of a plant species to biosynthesize metabolites with a specific target. It has potential value as a novel platform for plant drug discovery and production, or as a means of optimizing the therapeutic value of medicinal plant extracts.