Breakthroughs in Biotechnology

As the pathway is so long and complex, the approach taken has been to work on it ‘in pieces’, Smolke explains. Since her group started working on it a decade ago, most of the pieces have been engineered. In 2008, Smolke’s group reported a yeast strain that could produce reticuline – an important intermediate – from norlaudosoline, a commercially available chemical. Other sections of the pathway, converting reticuline to thebaine and other opioids have also been achieved. And in a major breakthrough earlier this year a team led by John Dueber of the University of California, Berkeley, US, completed the early part of the pathway by incorporating a tyrosine hydroxylase enzyme into a yeast strain, allowing it to produce reticuline from glucose. ‘[In May] we predicted that assembling the complete pathway was just around the corner, ’ says Vincent Martin, a bioengineer from Concordia University in Canada who worked with Dueber.

To get the pathway to go from a sugar on opioid thebaine, Smolke’s team needed to put most of the pieces together and integrate 21 enzyme-controlled steps into just one strain. ‘There tend to be a lot of challenges associated with getting the enzymes becoming useful – getting all of them correctly creased and prepared and localised, ’ says Smolke. After effectively making thebaine, these people were in a position to include another two enzymes that converted it to hydrocodone, another opioid painkiller.

The team has shown that thebaine are converted to drugs including morphine various other modified strains, so theoretically it would be feasible to increase the pathway even more, although this isn’t presently feasible with such little yields.

Scaling up

‘What has to be done now … will be increase the yield through the strain utilizing standard metabolic manufacturing tools and fermentation tricks, ’ Martin states. Current yields are extremely reasonable, because of the multitude of steps. Utilizing this certain stress it would simply take a huge number of litres of fermentation broth to create one 5mg dose of hydrocodone.

But Smolke is hopeful so it might only just take another couple of years to optimise the process adequate to make it commercially viable. ‘A lot of understanding was gathered within the last few years about performing industrial fermentations with fungus to produce high value substances, ’ she claims.

Although current low yields tend to be an important challenge to commercialisation, they should in addition calm any instant problems about ‘home-brew heroin’, Smolke adds. ‘There’s no danger of that with these fungus strains. You Have Access To a lot more of these substances from poppy seeds.’ The concept ought to be revisited as yields improve, she adds, as it's simple to do experiments to determine if it is feasible getting important manufacturing in a non-optimal ‘home-brew’ environment.

In the long run, the expect this technology is the fact that it can be applied to other biosynthetic pathways to make brand-new medications.

‘I think this is an important milestone in terms of the complexity of a biosynthetic pathway we can put into an organism like yeast and actually get it to work, ’ says Smolke. ‘It indicates we could commence to do this with substances beyond the opioids.’