Targeted biosynthesis of pharmaceutically relevant triterpenoids

Triterpenoids with more than 14,000 known compounds within the plant kingdom is one of the largest group of secondary metabolites. Isoprene substrates give rise to more than 100 different triterpene scaffolds during biosynthesis, which undergo further modifications and thus lead to the enormous structural diversity. Of particular interest are cyclic triterpenoids. For numerous plant species, these metabolites have been described to exhibit highly versatile bioactive functions. The potential includes antimicrobial, antioxidant, anticarcinogenic, and antiallergic effects, making them attractive for agricultural and pharmaceutical applications.

In the framework program "National Research Strategy Bioeconomy 2030", a consortium of SMEs and research institutions has joined forces for the project "ASPIRANT" with the aim of the targeted biosynthesis of pharmaceutically relevant triterpenoids in yeasts. The consortium, coordinated by the Fraunhofer IME, combines expertise from the fields of chemistry, biology, process engineering and pharmacy and pursues the entire value chain in a system-oriented manner. The focus lies, among other things, on the production and pharmaceutical evaluation of new substances.

Following a knowledge-based selection of suitable triterpenoids, the enzymes required for their biosynthesis were identified and introduced into yeasts. Plant oxidosqualene cyclases form the desired triterpenoid from 2,3-oxidosqualene, which occurs naturally in yeast. Further enzymatic modification such as oxidation or incorporation of sugar residues change its chemical properties and bioactivity. A yeast strain with an MVA pathway optimized at Fraunhofer IME in Münster is used for this purpose. In this strain, a key regulator is switched off. In its active form, the regulator inhibits the transcription of the MVA synthesis genes and thus prevents the formation of the necessary enzymes. In a further step, the researchers overexpressed genes that are essential for the production of the precursor molecules to increase their quantity. Furthermore, they modified a side branch that also converts the precursor in yeast allowing it to be turned on and off in a controlled manner.
The implementation of this yeast platform increased the overall productivity and redirected the metabolic flux toward the desired triterpenoid. The success is reflected in a drastically increased yield. The extracted triterpenoids exhibit high purity and consistent quality. In vitro, these substances showed positive effects on inflammatory parameters. The iterative optimization of the modification of competitive metabolic pathways enables production in economically relevant quantities. The yeast platform is being further expanded and is now available for the synthesis of additional terpenoids.