The supply of a plant-derived anti-cancer drug can finally meet global demand, according to a team of scientists from Denmark and the U.S. who engineered yeast (Saccharomyces cerevisiae) to produce the precursor molecules. Previously, these could only be obtained in trace concentrations in the native plant.

The researchers published their study “A microbial supply chain for production of the anti-cancer drug vinblastine” in Nature.

“Monoterpene indole alkaloids (MIAs) are a diverse family of complex plant secondary metabolites with many medicinal properties, including the essential anti-cancer therapeutics vinblastine and vincristine. As MIAs are difficult to chemically synthesize, the world’s supply chain for vinblastine relies on low-yielding extraction and purification of the precursors vindoline and catharanthine from the plant Catharanthus roseus, which is then followed by simple in vitro chemical coupling and reduction to form vinblastine at an industrial scale,” write the investigators.

A ball and stick molecular model of vinblastine showing its complex structure with many carbon rings. [Credit: MarinaVladivostok/Creative Commons]

“Here, we demonstrate the de novo microbial biosynthesis of vindoline and catharanthine using a highly engineered yeast, and in vitro chemical coupling to vinblastine. The study showcases a long biosynthetic pathway refactored into a microbial cell factory, including 30 enzymatic steps beyond the yeast native metabolites geranyl pyrophosphate and tryptophan to catharanthine and vindoline. In total, 56 genetic edits were performed, including expression of 34 heterologous genes from plants, as well as deletions, knock-downs, and overexpression of ten yeast genes to improve precursor supplies towards de novo production of catharanthine and vindoline, from which semisynthesis to vinblastine occurs.

“As the vinblastine pathway is one of the longest MIA biosynthetic pathways, this study positions yeast as a scalable platform to produce more than 3,000 natural MIAs and a virtually infinite number of new-to-nature analogues.”

“The yeast platform we developed will allow environmentally friendly and affordable production of vinblastine and the more than 3,000 other molecules that are in this family of natural products,” said project co-leader Jay Keasling, PhD, a senior faculty scientist at Lawrence Berkeley National Laboratory and scientific director at the Novo Nordisk Foundation Center for Biosustainability (DTU Biosustain). “In addition to vinblastine, this platform will enable production of anti-addiction and anti-malarial therapies as well as treatments for many other diseases.”

Keasling is a biochemical engineer whose team previously transferred the genetic pathway to produce an antimalarial drug, artemisinin, from an herb called sweet wormwood to E. coli. He is also a professor of chemical & biomolecular engineering at UC Berkeley.

Madagascar periwinkle (Catharanthus roseus) flower blooming in the garden
Madagascar periwinkle (Catharanthus roseus). [Sudhakar Bisen/Getty Images]
Vinblastine and another chemotherapy agent, vincristine, are both natural products of a pink-flowered plant called the Madagascar periwinkle. Their anti-cancer properties were first discovered in the 1950s, and in the decades since, they have become essential medicines. Vinblastine, which inhibits cell division, is used alongside other chemotherapy agents to treat multiple types of cancer, including lymphomas, testicular, ovarian, breast, bladder, and lung cancers. Vincristine inhibits white blood cell production and is a mainstay treatment for childhood lymphoblastic leukemia and non-Hodgkin lymphomas.

Monoterpenoid indole alkaloids (MIAs)

Vinblastine and vincristine belong to a group of botanical compounds called monoterpenoid indole alkaloids (MIAs) that have many useful medical applications. Unfortunately, this group is characterized by complicated atomic structures that are often impossible to replicate through synthetic chemistry.

So, much like the production of artemisinin before Keasling’s breakthrough, making vinblastine and vincristine requires growing and harvesting huge quantities of the native plant to extract precursor molecules. It takes 500 and 2,000 kilograms of dried Madagascar periwinkle leaves to produce one gram of vinblastine and vincristine, respectively.

A team lead by Keasling and Michael Jensen, PhD, a DTU Biosustain researcher, began exploring the possibility of engineering a microbe-based production process for MIAs in 2015. The first step was to develop the pathway for making strictosidine, the foundational molecule that all monoterpene indole alkaloids are built from.

For the new host organism, they turned to S. cerevisiae, a common yeast strain that Keasling and others have successfully engineered to make many other plant-derived compounds including opiates, cannabinoids, and other anti-cancer drugs.

After meeting their goal of making strictosidine, they set out to produce vinblastine. They chose to start with this particular MIA-based drug because it is one of the most commonly used chemotherapeutics worldwide and it has been in shortage multiple times in recent years.

Now that they have unlocked the process for strictosidine and vinblastine production, the team hopes to modify their yeast to tackle production of other valuable MIAs, including vincristine, irinotecan, and topotecan. All four medicines are chemotherapies on the World Health Organization’s essential medicines list.

“The pathway could also be augmented to produce new-to-nature MIAs, which may have improved pharmacological properties such as higher efficacy or fewer side effects,” pointed out first author Jie Zhang, PhD, a senior researcher at DTU Biosustain. “This will potentially enable us to explore the almost infinite chemical space with many new bioactivities.”

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