Sept. 30, 2022 -- An incredibly old way of making drugs is now an incredible new way to make drugs. Scientists have genetically reengineered a yeast fermentation process in order to produce chemotherapy compounds instead of beer.
Vinblastine is the most complex compound produced with engineered yeast so far, the researchers say. Its naturally occurring ingredients are normally harvested from an endangered plant in Madagascar, and the chemotherapeutic is on the World Health Organization's essential medications list. Synthetic production of vinblastine could eliminate supply problems, lower costs, and save lives.
Getting it right took 7 years.
"It's like getting an orchestra to play in tune, because all of those steps have to work together in order to get to that final product," article co-author Jay Keasling, PhD, says. "If you feed yeast sugar, it produces beer and wine. In this case, we've replaced the ethanol pathway with pathways to produce these natural products."
Genetically engineered yeast (along with E coli) is a key microorganism used in biopharmaceutical production. Yeast has been redesigned to produce other naturally occurring compounds, such as cannabinoids and the antimalarial drug artemisinin. The process involves removing a sequence of biochemical reactions, or metabolic pathway, from a plant cell and reconstructing it inside a yeast cell.
The Holy Grail of Compounds
Vinblastine is part of a family of more than 3,000 plant-produced molecules called monoterpene indole alkaloids (MIAs), several of which have the FDA has approved as therapeutics. Each MIA comes from a different plant, some of which are rare or in danger of extinction from overharvesting, according to Keasling.
"Engineering a yeast to produce these molecules would enable their production in a simple platform, fermentation, rather than having to grow individual plants or harvest them from the wild," Keasling says. "We've essentially co-opted this age-old method for producing beer and wine to produce these other important products."
The international team of researchers, led by the Technical University of Denmark, wanted to prove that they could synthetically manufacture all kinds of MIAs, so they started with the most complex one they knew of: vinblastine.
Vinblastine has something like 30,000 genes. The researchers first had to identify a 31-step sequence. It is the longest biosynthetic pathway ever removed from a plant and inserted into a microbe, according to the researchers.
Until now, vinblastine could only be produced by using two active ingredients, vindoline and catharanthine, harvested from the leaves of the Madagascar periwinkle plant. It can take more than 4000 pounds of dried leaves to produce a single gram of vinblastine. Supply delays resulted in an international shortage of the drug from the summer of 2019 until 2021.
Although the researchers couldn't produce vinblastine directly in yeast, they succeeded in genetically engineering yeast to produce vindoline and catharanthine. These compounds were then purified and coupled chemically to form vinblastine.
Reconstructing vinblastine's metabolic pathway required 56 genetic edits, according to the researchers. Biochemical reactions that occur at each step along the pathway require enzymes ― so the researchers had to ensure that enzymes were produced in the correct amount.
"You can't have one step working significantly better than all the other steps, or one step that doesn't work very well at all," said Keasling. The enzymes also depend on other factors, such as vitamins and minerals, which also had to be inserted into the sequence.
The researchers produced only a very small amount of vinblastine, but the technique opens the door for production of numerous other naturally occurring compounds, including an antiaddiction molecule that's expensive to manufacture because it's produced by plants in small quantities.
"This molecule we chose is kind of like a holy grail. It's a big molecule, it's really challenging to produce in any other way," Keasling said. "And so, if we can do this molecule, that means that the other ones are definitely doable."