Plants Could Be Used to Grow Medicines in Space, Study Shows

“With plants, you can grow complex therapeutic compounds using light, water and soil,” said study senior author Nicole Steinmetz, the Leo and Trude Szilard Chancellor's Endowed Chair in the Aiiso Yufeng Li Family Department of Chemical and Nano Engineering at the UC San Diego Jacobs School of Engineering.

That’s a big advantage over current pharmaceutical manufacturing systems that require giant tanks and sterile environments. Plus, plants are already cultivated in space and can help recycle air and water aboard spacecraft.

Producing an Experimental Drug from Plants

Steinmetz and colleagues demonstrated the idea using an experimental therapeutic compound that they have been studying for more than a decade: a plant virus called cowpea mosaic virus (CPMV). While CPMV is more commonly known for infecting legumes, Steinmetz’s team knows it for its ability to stimulate the immune system to attack cancer cells. CPMV has shown strong anti-tumor effects in preclinical mouse models and in clinical studies in canine cancer patients.

To make CPMV, Steinmetz’s team uses Nicotiana benthamiana and black-eyed pea plants. “Growing the compound in these plants is simple,” said study first author Patrick Opdensteinen, a postdoctoral researcher in Steinmetz’s lab. “They can produce a whole lot of biomass in a short amount of time, and more biomass equals more product. The main difficulty now is figuring out how to get the product out of the plants.”

Extracting CPMV — and other pharmaceutical products — from plants typically involves picking the leaves and grinding them in a blender. “You end up with something that looks like a smoothie, and you can imagine getting your product out of that smoothie is challenging,” Opdensteinen said. “The equipment that we use to do this fills our entire lab. You can’t fit all that on a spacecraft.”

The new study focused on simplifying that step.

The team was inspired by an approach used with bacterial and mammalian cells in pharmaceutical manufacturing: product secretion. “Basically, the product comes out of these cells,” Opdensteinen said. “This is possible in plants, too.” Plants secrete products into a compartment inside the leaves called the apoplast, which is a network of interconnected spaces outside of the plasma membrane.

The researchers found that they can draw CPMV out of the apoplast while keeping the leaves intact. First, the leaves are submerged in a buffer solution and placed in a sealed vessel. Vacuum is applied, which floods the apoplast with fluid. The saturated leaves are then placed in vials and gently spun in a centrifuge to draw the liquid — which contains CPMV particles — back out. The resulting liquid is purified through a filter that separates the larger CPMV particles from smaller unwanted plant material.

The method is easy to scale up. Researchers were able to harvest and purify CPMV particles from more than 50 plants in under two hours. And because the leaves remain intact, the plants can continue to grow and potentially be harvested over and over again. The team envisions adapting the process to entire living plants rather than just the leaves.

Testing Drug Production in Space Conditions

The team also tested the method on plants grown under simulated space conditions.

To mimic microgravity, Steinmetz’s lab collaborated with the lab of Maziar Ghazinejad, professor in the Department of Mechanical and Aerospace Engineering at the UC San Diego Jacobs School of Engineering, to custom build a random positioning machine, which continually rotates the plants to effectively cancel out gravity. Ghazinejad’s lab normally uses these machines to study how materials would behave in space. Steinmetz and Ghazinejad saw an opportunity to adapt this approach for plant studies.

The plants were also exposed to temperature fluctuations and oxidative stress to mimic the effects of space radiation. In some cases, the stressors slightly increased CPMV yields. The researchers hypothesize that the effect may be linked to the nature of CPMV as a plant virus. “Plants become more susceptible to disease when stressed, which is usually a disadvantage,” Opdensteinen said. “But since our product is derived from a plant virus, we can use that stress response to increase yields.”

The team’s ultimate goal is to have their method tested on actual space missions. Before that can happen, the team still has more work ahead. They will continue studying how space conditions affect plant processes such as water and nutrient uptake. They will also be working with the Rocket Propulsion Laboratory at UC San Diego to test how rocket launches affect plant seeds and the genetic materials used in the process.

Full study: “Streamlined molecular farming of plant virus therapeutics for space flight and other low-resource environments”

This work was supported in part by the National Institutes of Health (grant R01CA274640) and the Translational Research Institute for Space Health (TRISH) through NASA Cooperative Agreement NNX16AO69A.

Disclosures: Nicole Steinmetz is a co-founder and CEO of, and has equity in, PlantiosX Inc. Steinmetz is a co-founder of and has equity in Mosaic ImmunoEngineering Inc. Steinmetz is a co-founder and manager of Pokometz Scientific LLC, under which she is a paid consultant to Ring Therapeutics, Inc. The other authors declare no potential COI.