Project Description
A little history about Paclitaxel manufacturing
The discovery of Paclitaxel in the 1960s ignited intense scientific efforts to characterise its structure and fully synthesise the molecule for use in cancer treatment. However, problems existed in how it was produced - it required the logging and debarking of fully-grown Yew trees, which take close to 100 years to mature. Despite these hindrances, the benefits of the molecule’s anticancer activity far outweighed the unsustainable nature of production and provided sufficient motivation to continue the pursuit for the drug’s clinical development. The demand for the molecule increased as it was approved for clinical use, but the limited supply remained a problem.
The current problem with Paclitaxel Manufacturing
A semi-synthetic route was achieved in the early 2000s when it was realised that Paclitaxel could be produced using a precursor found at very low amounts in the needles of the Yew tree species.
These precursors; 10-deacetylbaccatin III (10-DAB) and Bacccatin III undergo a series of chemical transformations to be converted into Paclitaxel. While this semi-synthesis method still relies on the collection of plant material, it comes from a more renewable resource, and reduces logging of the Yew tree. However, it is clear that this pathway is unsustainable long term:
- Precursors used to produce Paclitaxel are rare. (0.0005%-0.1% of Yew tree leaves)
- Chemical semi-synthesis produces high racemeric content, reducing the efficiency of products.
- It's significantly more expensive than direct extraction of Paclitaxel from the Yew Tree bark as semi-synthesis methods involve many complex steps.
- Many other potential precursors are discarded as waste
- It requires the use of many environment harming solvents and reagents.
- And as such the direct extraction method is still commonly used, and preferred by certain producers. This has resulted in exploitation of the Yew Tree species, and driven some to endangerment (Taxus Contorta, Taxus Wallichiana).
Taxus Contorta, Taxus Wallichiana
Local and Global inspirations
Cancer is the second biggest killer in Australia, which has the highest rates of cancer cases globally, second place are our neighbours New Zealand. As the global and local population ages, the demand for Paclitaxel is expected to increase with more cancer patients requiring the drug.
There is a strong need for addressing unsustainable harvesting of natural resources and finding more efficient production methods for Paclitaxel. These problems, and their local relevance to Australia, inspired us to use synthetic biology to help provide a solution.
OUR PROJECT GOALS
Our team created two formative goals for our project:
- Improve biochemical manufacturing processes
- Create a more sustainable and efficient manufacturing process for Paclitaxel
Biosynthetic Paclitaxel Manufacturing
We believe the future of Paclitaxel manufacturing needs to be completely biosynthetic. There are many benefits to this, beyond just addressing the issues presented above. It's significantly more environmentally friendly, and can help meet Paclitaxel demands more sustainably. It improves upon inefficiencies in chemical synthesis, preventing the usage of hazardous chemicals, and as a result, is a cheaper production method.
We've worked to move Paclitaxel production towards biosynthesis through the scaffolding of rate limiting enzymes; PAM and TycA. This method produces the Paclitaxel side-chain with no racemers, increasing the efficiency of the overall current semi-synthetic pathway.
Next generation Paclitaxel Manufacturing from XDT, a sustainable alternative.
During our investigation of discarded natural resources from Yew tree harvesting, we discovered a molecule called 7-beta-Xylosyl-10-deacetyltaxol (XDT) that can be enzymatically converted to Paclitaxel. This analogue is found at much a higher concentration than current precursors, and presents a more sustainable way to produce Paclitaxel. It could also encourage the industrial move away from both direct extraction of Paclitaxel and its chemical semi-synthesis.
XDT can be converted into Paclitaxel when it undergoes de-glycosylation into DT and acetylation into Paclitaxel. However to commercially realise this pathway, the conversion of XDT to DT will need to be more efficient.
We believe that Assemblase can provide the solution to solve this problem. Assemblase can be used to co-localise the enzymes (7-beta-xyloxidase and 10-beta-acetyltransferase) which catalyse the conversion of XDT to Paclitaxel. This would improve the overall efficiency of the 10 DT synthesis pathway, bringing it one step closer to commercial viability.
Moreover, a by-product of this reaction is CoA-SH, which is a cofactor for our first pathway. Overall, our work presents 2 sustainable Paclitaxel production pathways that can occur in conjunction, maximising Paclitaxel production from natural resources. We hope this will help move industry production of Paclitaxel towards more sustainable and efficient methods.
Overall project with pathways 1 and 2
WHY SYNTHETIC BIOLOGY
Our protein scaffold has been applied to this problem as it is compatible with the biochemical manufacturing process. Traditional chemical synthesis often creates racemic mixtures, decreasing the net yield of favoured enantiomers. Our approach using Synthetic Biology removes this problem as enzymes are stereoselective ensuring optimal yield.