When seeking bacterial strains to manufacture vaccines or biologics, or for discovery and research projects, Pfenex scientists evaluate several hundred to one thousand production strains over five weeks. Screening includes robotics and running assays in 96-well plates.
The researchers are evaluating alternative approaches to screen thousands of strains in the same amount of time. Depending on the desired product, broader screens will provide gram quantities for lead-protein work or milligrams for earlier-stage work.
“Instead of looking for a single gene coding for a lead protein, we screen a thousand strains and look for five to ten genes that are potential lead proteins,” Lucy says. In the near future, Pfenex will increase throughput four- to fivefold by running assays in 384-well plates.
For example, in vaccine development, thousands of antigens are potential candidates against a pathogen, but only a few are formulated. When researchers try to express a likely candidate, the antigen is rejected if its expression is poor. “The antigen is thrown out strictly on the basis of whether it can be expressed and manufactured,” notes Lucy.
The Pfenex Expression Technology system improves the search by providing milligram amounts of several antigens for animal testing to narrow down the choice based on biological results. Starting with putative antigens, thousands of strains are screened to find ones that can make milligram batches of each antigen in small-scale fermentors.
“We leverage the Pfenex platform to express small amounts of a variety of antigens to enable partners to conduct animal testing faster. This allows discovery scientists to open up their pipeline and find more vaccines,” Lucy says. The same approach to expression-strain development is applied to protein-engineering projects as well.
Small molecule drugs, which are chemically designed to counterattack a protein in the body, are also identified by the Pfenex platform. Protein targets are often difficult to express, and researchers need milligrams of a target protein for further x-ray and crystallographic analysis to understand its biological function.
An additional advantage of the Pfenex Expression Technology is scalability. Traditional protein-expression systems, such as yeast or E. coli, sometimes produce small amounts of a protein for discovery yet fail during scale-up to make larger batches for clinical trials. Once Pfenex identifies a production strain, it can be used for discovery, preclinical and clinical testing, and large-scale fermentation.
“We are confident that our clients will not have to switch hosts in order to meet increasing demand as the product progresses through development and into commercialization,” says Lucy.
Pfenex has an internal pipeline of biosimilars, including human growth hormone and interferon beta-1b. These and many other biosimilars are manufactured inefficiently in traditional systems like E. coli, Lucy says. The expressed proteins are insoluble and do not fold like native proteins. In contrast, the high-quality biosimilars made in Pfenex host strains are soluble, active, and expressed at significantly higher levels than in E. coli, he adds.