Developing plants as biofactories for re-engineered cyclic peptides

BJ Smithies, MA Jackson, YH Huang, EK Gilding and DJ Craik

Institute for Molecular Bioscience, The University of Queensland, Brisbane, 4072

For many therapeutic proteins, a plant-based production system offers a cost-effective and greener alternative to traditional synthesis methods. This was recently exemplified by the first plant-produced human therapeutic enzyme, taliglucerase alfa, which was FDA approved for the treatment of Gaucher's disease. In this study we aim to develop plants into biofactories for the production of valuable therapeutic peptides. Of particular interest is a class of natural plant-produced peptides termed cyclotides, which are post-translationally cyclized in planta and strengthened by a characteristic disulfide bond arrangement. Cyclotides are excellent scaffolds for stabilizing small peptides with therapeutic activity that would otherwise be unstable and unusable in a pharmaceutical sense. Recently, a cyclotide was re-engineered as a drug candidate for treatment of chronic myeloid leukemia (CML), a blood cancer prone to developing resistance to current treatments. Here, an engineered gene sequence encoding this cyclotide graft was transformed into the model plant Arabidopsis thaliana to establish the feasibility of plant-based production. Here, we present our progress in advances towards plants as biofactories for pharmaceutically relevant cyclic peptides. Analysis of peptide mass, cyclisation and yield was determined by MALDI-TOF-MS analysis and NMR. Our ultimate aim is to develop a flexible, costs effective, and scalable production option. This will require progression to commercially viable crop plants such as potatoes, which can then be used to take this biotechnology to people in the first and third world who can benefit from not only the medicines, but the ability to meet their own production needs.