Many drugs consist of biomolecules from plants, but getting plants to make enough of the desired substances is often difficult. Scientists have now developed a method to induce yeast to produce large quantities of novel monoterpenoid indole alkaloids (MIAs) that may be useful as medicine.
Many of the drugs used today to treat people with cancer, malaria and mental disorders derive from plants.
For example, the chemotherapeutic drug vinblastine comes from Catharanthus roseus, a plant that produces MIAs and grows in Madagascar.
The problem with these valuable drugs, however, is that they are complex molecules that are difficult to make synthetically or require huge quantities of Catharanthus roseus leaves to produce.
For example, between 500 and 2,000 kg of Catharanthus roseus leaves are needed to make one gram of vinblastine.
However, there may be another way to acquire these plant molecules.
A major project has now shown that researchers can not only get yeast to produce the valuable MIAs but can also get the yeast to make variants of these biomolecules that may be potentially more effective or have fewer side-effects.
“Plants do not produce MIAs for human use; they just happen to be able to be used in this way. New variants of these biomolecules might be more potent or have fewer side-effects. We can now not only get yeast to produce the MIAs but also get them to make completely new-to-nature variants,” explains a researcher behind the study, Samuel Bradley, Research Assistant, Novo Nordisk Foundation Center for Biosustainability, Technical University of Denmark, Kongens Lyngby.
The research has been published in Nature Chemical Biology.
Biomolecules for treating people with cancer, malaria and mental disorders
The researchers wanted to determine whether yeast can produce variants of existing MIAs with therapeutic potential.
They focused on two MIAs: alstonine and serpentine, which have therapeutic properties in numerous diseases, including cancer, malaria and mental disorders.
The researchers extracted the genes for the signalling pathways to produce alstonine and serpentine from their respective plants and inserted them into baker’s yeast, inducing the yeast to produce the two molecules in large quantities in yeast tanks rather than having to harvest the leaves from the plants.
Induced yeast to make new-to-nature MIAs
However, the aim was not only to get yeast to make serpentine and alstonine as they exist in nature but also to make new-to-nature variants.
The researchers therefore acquired various indoles: the substrates that the synthetic pathway in the yeast or plant must use to make the two MIAs.
The idea was that the yeast would then convert a panel of fluorinated, chlorinated and brominated indoles into different halogenated MIAs.
Halogens are often an active part of many of the MIAs present in drugs.
About 25% of biomedicines are organohalogens containing chlorine, bromine or fluorine.
This showed that the yeast could make serpentine and alstonine with different halogens, potentially new therapeutic properties.
Refactoring biosynthetic pathways from bacteria
However, the researchers continued, inserting a synthetic pathway from a bacterium into the yeast since working with halogens can be toxic.
However, this synthetic pathway enables the bacteria to add halogens to tryptophan which, after indoles, is the next step in the biosynthetic pathway for producing serpentine and alstonine.
Inserting the synthetic pathway into the yeast enables it to handle the process independently because it no longer depends on a haloindole substrate for producing the new-to-nature haloserpentine and haloalstonine analogues.
The researchers fed the yeasts with table salt containing the relevant halogens and then indoles without halogens.
“We got the yeast to produce 19 of the 36 possible serpentines and alstonines. These new-to-nature MIAs may have potential therapeutic effects – and we induced yeast to produce them,” says Samuel Bradley.
Investigations required to test effectiveness
The researchers’ next step is to investigate whether these potentially useful molecules also have useful therapeutic properties.
The researchers need to produce enough serpentine and alstonine analogues to carry out relevant experiments. The top priority therefore is scaling up the procedure so that the researchers can induce the yeast to produce the MIAs in large tanks.
Then they have to test these new-to-nature MIAs on cells and animals to determine whether they might be more effective antipsychotic or antimalarial drugs than naturally produced molecules or have fewer side effects.
“There is enormous potential. Within MIAs alone, more than 3,000 substances have been identified that may be useful as drugs. With this technology, we can expand that repertoire with many more useful substances. The 19 identified molecules are just a small appetiser and a proof of concept that yeast can be induced to produce these new-to-nature halogenated MIAs,” explains Samuel Bradley.
Co-author Michael Krogh Jensen, Senior Researcher, Novo Nordisk Foundation Center for Biosustainability, says that based on their discoveries, the researchers have established a biotechnology company called Biomia ApS to try to develop and manufacture new drugs based on the innovative technology for biosynthesising halogenated plant MIAs.
“At Biomia, we are determined to leverage this platform for treatment for pain and mental disorders. In continuation of this study, we consider Biomia a unique opportunity for developing and producing new variants of alstonine that can ameliorate the side-effects of current psychopharmaceuticals such as reduced immunity and weight gain. In addition, they can constitute more effective treatments for the many people with mental disorders such as schizophrenia, anxiety and depression. Our goal is that the technology behind the biosynthesis of halogenated MIAs will be able to bring new alstonines to clinical trials within three years,” concludes Michael Krogh Jensen.
