Though medicines are often thought of as purely synthetic compounds, nature is a vital source of many of the medications we rely on. The challenge in working with these compounds comes from harvesting them in ways that are environmentally sustainable and economically scalable to meet pharmaceutical needs.
Research being led by Shanteri Singh, an assistant professor in the Department of Chemistry and Biochemistry, Dodge Family College of Arts and Sciences at the University of Oklahoma, is taking a new approach to solving these complex issues. Her method forgoes growing whole plants and animals by co-opting their enzymes – the biological machinery responsible for performing chemical reactions – for direct compound synthesis.
“What nature is already doing in plants, animals and microorganisms, we want to recreate in the lab,” said Singh, who is a member of the Institute for Natural Products Applications and Research Technologies as well as a member of the Oklahoma Center of Biomedical Research Excellence in Structural Biology. “We’re using enzymes, nature’s chemists, added together in a sustainable host like E. coli to try to synthesize it, because growing plants take years.”
In contrast to the months needed to grow, harvest and extract compounds from plants, E. coli – a common host for microbiological experimentation – multiplies rapidly. Each cell replicates in just 20 minutes.
“If we put the enzymes in E. coli, we can get huge amounts of them within a day; it’s exponential growth,” she said. “Then we purify them and use them to perform reactions that convert simple starting materials into valuable compounds.”
Funded by a $1.4 million, five-year R01 grant from the National Institutes of Health, Singh is using this unique method to synthesize a class of organic compounds called isoprenoids, a large class of natural products that are isolated from plants and microorganisms.
“Most of the drugs we have today originated from natural products,” Singh said. “If a natural product comes from a plant, you would have to cut down a lot of plants in order to isolate a small amount of it. But these natural products and other potential drug compounds are biosynthesized by a set of enzymes which we can generate outside of the plant for our own uses.”
“What my lab does is study these enzymes to understand how they behave,” she added. “We engineer these enzymes to make natural as well as non-natural compounds which can be used as potential drug molecules.”
For this project, Singh’s lab is developing a multi-enzyme platform that can create diverse molecules. They are specifically testing the development of two important compound classes, cannabinoids and squalenes.
Cannabinoids are the molecules produced by the plant Cannabis sativa, of which CBD and THC are the most well known. THC is the psychoactive component of marijuana, whereas CBD is non-psychoactive.
“The combination of THC and CBD gives rise to several different drugs that have implications in a number of neurodegenerative diseases,” Singh said. “People are investigating their potential roles in treating Alzheimer’s Disease, Parkinson’s Disease and epilepsy.”
The research mentioned by Singh hit a major milestone in 2018, as the FDA approved a CBD-based drug, called Epidiolex, to treat seizures caused by a rare, severe form of epilepsy.
“Normally, Cannabis sativa produces a tiny amount of the necessary compounds, so we wanted to know how we can sustainably produce large quantities of the cannabinoids,” she said. “Using our platform, we are hoping to produce a good amount of not only the natural cannabinoids but novel cannabinoid analogs, which can be tested as potential drug compounds.”
The other compound that Singh’s research group is investigating is squalene, a compound found in certain fish oils and most commonly extracted from shark livers. Several influenza vaccines use squalene as adjuvants, which are widely administered in conjunction with these vaccines to enhance the immune response and strengthen protection against disease.
“It’s been seen that using squalene as a vaccine adjuvant has very good advantages. It has good immunological properties, generating large amounts of antibodies and a good immune response,” Singh said. “Even now, there are studies investigating using squalene as an adjuvant in COVID-19 vaccines, which would require a lot of squalene and would require killing even more sharks.
“Furthermore, the squalene obtained from sharks can contain a lot of environmental contaminants because the oceans have a lot of pollutants,” she added. “Purifying those contaminants from squalene is not easy.”
The promise of Singh’s research is a platform to synthesize large quantities of these beneficial compounds in a sustainable and economic manner.
Ann West, associate vice president for research development at the University of Oklahoma, said of the project, “Dr. Singh’s platform is a clever engineered approach to making better drugs, and the potential environmental and health benefits are significant.”