As more and more biopharmaceuticals move along the torturous process of development, clinical evaluation, and approval, dealing with changes to these complex protein molecules becomes increasingly paramount. A number of meetings and symposia have examined this question lately, and it’s clear that the technology is ramping up to successfully add or delete whole classes of changes when necessary.
Gary Walsh, Ph.D., associate professor at the University of Limerick in Ireland, foresees a wave of advances in fundamental post-translational modification (PTM) engineering technologies as new protein therapeutics work their way through the research lab and into the marketplace. With more than 2,000 biopharmaceuticals in clinical and preclinical development, there will be a pressing need for platforms that can successfully address the upscaling of highly modified protein therapeutics.
Dr. Walsh believes that biosimilars will become increasingly important and the issue of achieving their appropriate post-translational modification profile will constitute a major challenge in coming years. The EMA has already approved six biosimilars, and many more are being evaluated.
Whereas glycosylation is the major concern of post-translational engineers, there are many other alterations in protein molecules that may be required for appropriate performance. These include acetylation, ADP-ribosylation, acylation, phosphorylation, disulfide bond formation, proteolytic processing, γ-carboxylation, β-hydroxylation, amidation, and sulphation.
A major component of research in this area is concerned with the redesign of production systems to move post-translational modifications forward on an industrial scale, according to Dr. Walsh. As an example, cell lines are being engineered for improved glycosylation production by inactivating glycosylation enzymes that are problematic. One of these is the Potelligent cell line, in which fucosyltransferase is knocked out from the CHO parent cell. This allows the stable production of fucose-free antibodies, which show dramatically enhanced ADCC in vitro and ex vivo, and improved in vivo activity.
Another engineering accomplishment eliminates the problem of hypermannosylation in yeast. GlycoFi has radically engineered Pichia pastoris, knocking out four genes while at the same time introducing 14 others.
Yet another protein-production platform that has received relatively little notice is plant systems, which may generate hyperglycosylated products containing α-1,3-fucose and β-1,2-xylose. Greenovation Biotech working with moss, and Biolex which is based on the exploitation of duckweed, have engineered around this problem.
“Choosing an expression system capable of generating an appropriate post-translational product profile remains one of the most crucial decisions drug developers must make,” says Dr. Walsh.
The moss Physcomitrella patens offers unique opportunities for bioengineering, according to Andreas Schaaf, Ph.D., head of R&D at Greenovation. All green plants use photons of light to produce energy, so they thrive in simple media while retaining the ability to produce complex, post-translationally modified proteins at the same time.
Mosses are different from more advanced plants in that they are haploid through most of their life cycle and can be easily engineered to avoid plant-specific xylose and fucose glycosylation steps, for instance.
“Our facilities are capable of producing 500 liter batches of high-quality, fully glycosylated proteins within a time frame of 6 to 10 weeks,” Dr. Schaaf explains. Because the product is secreted into a medium containing only a simple mineral constituency, downstream processing is much simpler than is the case with mammalian cells. “The purity of protein secreted into the medium is approximately 80%, and after moss removal the medium is ready for generic downstream processing.”
Finally, as a fully contained, whole plant production system, bryotechnology enjoys several regulatory advantages, according to Dr. Schaaf. The culture medium is free of any animal-derived compounds, and there is no chance of inadvertent passage of viruses or prions in the products.