Above: Fruit and foliage of the Pacific Yew, taxus brevifolia (Jason Hollinger)
Your mother is probably always telling you to eat your vegetables. She knows that plants are an important source of food and nutrients. But plants can also be real lifesavers, providing treatments for deadly diseases.
Did you know? Yew trees can take 200 years to grow to their maximum height.
More than 50 years ago, the U.S. National Cancer Institute challenged botanists to find plants with anti-cancer properties. As a result, researchers collected bags of twigs, needles, bark, and flowers. In the lab, scientists tested these natural materials to see what they could do.
Success! A compound called taxol, derived from the bark of the Pacific yew tree, proved very useful in slowing cell growth. Taxol, now known as paclitaxel, is a mitotic inhibitor, which means it interferes with cell division. Since rapidly-dividing cells allow metastatic or invasive cancer to spread very quickly, chemotherapy drugs containing paclitaxel help patients battle the disease by slowing tumour growth.
The discovery of this drug was very exciting, but a major problem remained. All the bark from a single 12-metre tall Pacific yew tree only produces about 0.5 grams of paclitaxel. Forests could never meet the demand for yew bark without causing an environmental disaster.
Biotechnology to the rescue! Today, paclitaxel is produced using plant cell cultures. Cells from yew trees are grown in large tanks called fermentors with volumes of up to 75,000 litres. That's larger than some backyard swimming pools! The fermentors contain everything the cells need to grow.
Did you know? Paclitaxel is currently produced by Canadian-German biotech company Phyton Biotech.
So how is the drug extracted from the cells? Mixtures go through multiple rounds of purification until the final product is obtained through “crystallization.” This technique involves taking the mixture obtained from the final step in the purification process and dissolving it in a hot solvent. As solution cools, paclitaxel molecules stick together, forming a solid crystal of pure paclitaxel. The paclitaxel is then shipped to pharmaceutical companies which use it as an ingredient in various cancer-fighting drugs.
As researchers look for new ways to prevent and treat cancer, we can munch on some carrots, and wonder what other useful compounds are hiding in the trees and plants around us.
Jacoby, Mitch.(2005) “Taxol.” The Top Pharmaceuticals that Changed the World, Chemical and Engineering News. 83(25).
http://pubs.acs.org/cen/coverstory/83/8325/8325taxol.html Venkat K. (1998) “Paclitaxel production through plant cell culture: An exciting approach to harnessing biodiversity.” Pure Appl. Chem. 70: 2127