Doramectin

Codexis, Inc. (Redwood City, CA, a subsidiary of Maxygen, Inc., www.codexis. com) has entered into a multiyear collaboration with Pfizer (New York, NY, www.pfizer.com) to develop biocatalysts to improve manufacturing efficiencies for several small-molecule drugs. Codexis carries out genetic engineering to create new enzymes (biocatalysts) that can be used in fermentation processes to synthesize small-molecule drugs with fewer process steps and less waste than in fermentation using wild-type enzymes or in conventional chemical synthesis.

Under the new agreement, Pfizer has the option to license Codexis's technology for application to several drugs in Phase I and Phase II development. Previously, however, Codexis helped Pfizer increase the manufacturing efficiency of a product already on the market--doramectin, a veterinary antiparasitic drug. Before working with Codexis, Pfizer manufactured the active pharmaceutical ingredient (API) using a wildtype biocatalyst in a fermentation process with Streptomyces avermitilis. The original process, however, generated lower quantities of the desired molecule (B1) than of a byproduct (B2), in a ratio of 0.6 to 1. A year later, Codexis produced a genetically engineered biocatalyst that reversed that proportion, producing the API and by-product in a ratio of 2.5 to 1. Another six months of work increased the production ratio to 15 to 1. According to Tassos Gianakakos, vice-president of corporate development at Codexis, the increased efficiency allowed Pfizer to reduce the cost of goods by more than 10%, and free up several months' worth of plant capacity per year to manufacture other products.

Creating new biocatalysts is an iterative genetic engineering process (see Figure 1). When presented with a new molecule to be produced through biocatalysis, Codexis' teams of chemical process development and molecular biology specialists first look for a suitable enzyme in the company's library. If none is available, the team selects organisms (usually genetically engineered Escherichia coli, yeast, or fungus) that possess genes they think will be good "parent genes?' Those sets of genes, and sometimes whole genomes, are then recombined through sexual reproduction of the microorganisms in proprietary processes the company calls "Molecular Breeding" and "DNAShuffling." The resulting library of gene variations is then put into an expression system and screened for the desired enzymatic expression. The best sets are chosen as parent genes for the next round of crossing and the results of that round are then screened again. The process is repeated until a suitable enzyme is produced.

"The main difference between the way Codexis carries out its directed evolution processes and what other companies do" says Gianakakos, "is that Codexis has harnessed sexual reproduction and mitosis. This makes our processes more efficient." Codexis researchers also use bioinformatics tools that increase evolutionary speed by predicting points where beneficial crossover recombination is likely to occur. "Our processes produce highly active, intact proteins" Gianakakos says. "The viability rate is high." Once Codexis identifies the desired genetic sequence, the company usually outsources the DNA production, because it has outstripped internal capacity.

The process also received an internal corporate award at Pfizer for green manufacturing processes, Gianakokis says. "By reducing by-products and the use of harsh chemical reagents, the application of our technology generally results in environmentally friendly manufacturing," he explains, adding that increased manufacturing efficiency can also reduce capital expenses such as heating and cooling.

In addition to Pfizer, Codexis has partnerships with various other pharmaceutical manufacturers to use DNAShuffling and Molecular Breeding to produce small-molecule intermediates and APIs. Partners include Eli Lilly, Novozymes, Sandoz, and Gist-brocades NV, a subsidiary of DSM. Another DSM subsidiary, DSM Pharma Chemicals, does similar development work with biocatalysts (see Pharmaceutical Technology, March 2004, p. 17). Codexis's technology is currently used in five commercialized processes.

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