Next-generation expression systems
Advances in molecular control of gene expression are also expanding the opportunities for protein expression systems. As drug manufacturers look for cheaper ways to express new biologic drugs, next-gen expression systems are gaining traction. Currently, the standard expression system is mammalian Chinese hamster ovary (CHO) cell lines. However, the limitations of CHO cells—such as high cost and comparatively slow doubling times—make the next-gen systems worth considering for expressing new biopharmaceuticals, especially to help reduce the costs of important medicines.
For example, the SoluPro protein expression platform from AbSci can generate soluble, properly folded proteins at extremely high titers, currently 4g/L of full-length antibody and >20g/L of other complex products, using Escherichia coli expression. Typically, some human proteins can’t be expressed in E. coli, and require mammalian cell lines for proper folding. AbSci’s technology includes two innovations that make it possible to produce such proteins in E. coli, while taking advantage of the simplicity and lower costs of this expression system.
One creation is a semioxidized cytoplasm that produces soluble, disulfide-linked proteins. “Cytoplasmic production, which traditionally is limited by inclusion body formation, is desirable because it has significantly higher capacity than the periplasm, places no restrictions on protein size, and achieves dramatically shorter production cycles of one to two days, compared to secretion-based expression systems,” says Sean McClain, AbSci’s founder and CEO. The second innovation is SoluPro’s dual inducible promoters, which can be independently controlled. This enables “tuning” of protein production rates by optimizing for the best protein-folding and titer.
“The SoluPro system’s ability to properly fold proteins overcomes a large majority of the limitations found with traditional E. coli expression,” says McClain. “We have successfully produced novel antibody scaffolds as well as IgG1 and IgG4 molecules where effector function is not desirable.” Many of these novel antibody scaffolds, which are gaining increasing traction in development pipelines, are challenging to produce in CHO cells. “AbSci is keenly focused on these hard-to-produce next-generation antibody scaffolds, including bispecifics, Fc [fragment crystallizable]-fusion proteins, and other multispecific products, which SoluPro is ideally suited to manufacture efficiently,” he says.