According to Keasling, the team carefully considered the efficiency of every step in the pathway, in order to keep the production costs as low as possible. One of the most crucial modifications was blocking a pathway for making a cholesterol–like substance. This pathway uses the same precursors as artemisinin, and would therefore divert some of the organism’s drug-making capabilities. “We turned down that pathway so the yeast made just enough of the [cholesterol-like molecule] to live,” says Keasling. “That increased the yield tenfold.”
Scientists still need to make the process 50 to 100 times more efficient to lower the price enough so that those in poor countries can afford the treatment (estimated at about 22 cents a dose). Keasling projects that it will take another year and a half to achieve this level of efficiency.
Eventually, the yeast will be cultivated in bioreactors, to make huge amounts of the drug precursor. In 2004, Keasling won a $42.6 million grant from the Bill and Melinda Gates Foundation to develop the technology for pharmaceutical use. The grant will support Amyris Biotechnologies, a company founded by Keasling and colleagues to ramp up the technology for industrial-scale production, as well as the nonprofit pharmaceutical company, OneWorld Health, which will work on regulatory approval for the drug.
Keasling also plans to produce other drugs using some of the same technologies developed to make artemisinic acid. His next project will be the anti-HIV drug prostratin, which also comes from a plant.