Effect of parallel feeding of oxidizing agent and protein on fed-batch refolding process of recombinant interferon beta-1b

Optimization of medium composition to increase the expression of recombinant human interferon-β using the Plackett-Burman and central composite design in E. coli SE1

Recombinant human interferon-β (rhIFN-β) is therapeutically important and new commercially viable approaches are needed for its increased production. In this study, a codon-optimized gene encoding for rhIFN-β_(C17S) protein was designed and expressed in E. coli SE1. As a first step of medium optimization, growth of E. coli as a function of different media components was studied. Subsequently, to optimize the media composition, a response surface methodology (RSM) was used. Our results show that optimized medium (15.0 g/L tryptone, 12.3 g/L meat extract, 1.0 g/L MgSO₄ and 0.5 g/L thiamine along with minimal medium) obtained in this study provide better growth of recombinant cells and the expression level of recombinant protein was ~ 1.7-fold more than Luria-Bertani medium. The optimized medium may be utilized for the large-scale production of rhIFN-β.

Advances in monitoring and control of refolding kinetics combining PAT and modeling

Overexpression of recombinant proteins in Escherichia coli results in misfolded and non-active protein aggregates in the cytoplasm, so-called inclusion bodies (IB). In recent years, a change in the mindset regarding IBs could be observed: IBs are no longer considered an unwanted waste product, but a valid alternative to produce a product with high yield, purity, and stability in short process times. However, solubilization of IBs and subsequent refolding is necessary to obtain a correctly folded and active product. This protein refolding process is a crucial downstream unit operation-commonly done as a dilution in batch or fed-batch mode. Drawbacks of the state-of-the-art include the following: the large volume of buffers and capacities of refolding tanks, issues with uniform mixing, challenging analytics at low protein concentrations, reaction kinetics in non-usable aggregates, and generally low re-folding yields. There is no generic platform procedure available and a lack of robust control strategies. The introduction of Quality by Design (QbD) is the method-of-choice to provide a controlled and reproducible refolding environment. However, reliable online monitoring techniques to describe the refolding kinetics in real-time are scarce. In our view, only monitoring and control of re-folding kinetics can ensure a productive, scalable, and versatile platform technology for re-folding processes. For this review, we screened the current literature for a combination of online process analytical technology (PAT) and modeling techniques to ensure a controlled refolding process. Based on our research, we propose an integrated approach based on the idea that all aspects that cannot be monitored directly are estimated via digital twins and used in real-time for process control. KEY POINTS: • Monitoring and a thorough understanding of refolding kinetics are essential for model-based control of refolding processes. • The introduction of Quality by Design combining Process Analytical Technology and modeling ensures a robust platform for inclusion body refolding.

Wanted: more monitoring and control during inclusion body processing

Inclusion bodies (IBs) are insoluble aggregates of misfolded protein in Escherichia coli. Against the outdated belief that the production of IBs should be avoided during recombinant protein production, quite a number of recombinant products are currently produced as IBs, which are then processed to give correctly folded and soluble product. However, this processing is quite cumbersome comprising IB wash, IB solubilization and refolding. To date, IB processing often happens rather uncontrolled and relies on empiricism rather than sound process understanding. In this mini review we describe current efforts to introduce more monitoring and control in IB processes, focusing on the refolding step, and thus generate process understanding and knowledge.

Antibiotic-free expression system for the production of human interferon-beta protein

Recombinant human interferon-β (rhIFN-β), a therapeutic protein, is produced using both prokaryotic and eukaryotic expression systems. However, instability of recombinant plasmid during cultivation of Escherichia coli results in low yield of the recombinant proteins. In addition, use of antibiotics during the cultivation imposes a major concern. In this study, we have compared the expression yield of rhIFN-β in E. coli BL21 (DE3) and E coli SE1 cells. Gene-encoding rhIFN-β was expressed in E. coli BL21 (DE3) and SE1 cells and the cultivation of recombinant E. coli cells was done in a laboratory scale bioreactor. Our results suggest that, compared to BL21(DE3) cells, the SE1 cells expressing rhIFN-β protein can be cultivated in the medium without antibiotic and provide increased stability of recombinant plasmid and higher expression yield of rhIFN-β protein. This system can be used for the production of rhIFN-β proteins for biomedical applications.

Effect of arginine on pre-nucleus stage of interferon beta-1b aggregation

Understanding the mechanism of aggregation of a therapeutic protein would not only ease the manufacturing processing but could also lead to a more stable finished product. Aggregation of recombinant interferon (IFNβ-1b) was studied by heating, oxidizing, or seeding of unformulated monomeric solution. The formation of aggregates was monitored by dynamic light scattering (DLS) and UV spectroscopy. The autocatalytic monomer loss model was used to fit the data on aggregation rates. The influence of pre-nucleation on aggregation step was demonstrated by inducing the liquid samples containing a monomer form of folded IFNβ-1b by heat and also an oxidizing agent. Results tend to suggest that the nucleus includes a single protein molecule which has been probably deformed. Seeding tests showed that aggregation of IFNβ-1b was probably initiated when 1.0% (w/w) of monomers converted to nucleus form. Chemiluminescence spectroscopy analysis of the sample indicated the generation of 3.0 μM of hydrogen peroxide (H2O2) during nucleation stage of IFNβ-1b aggregation. Arginine with a concentration of 200 mM was sufficient to suppress aggregation of IFNβ-1b by decreasing the rate of pre-nucleation step. We proposed the formation of pre-nucleus structures prior to nucleation as the mechanism of aggregation of IFNβ-1b. Furthermore, we have showed the positive anti-aggregation effect of arginine on pre-nucleation step.

A novel clot lysis assay for recombinant plasminogen activator

Recombinant plasminogen activator (r-PA, reteplase) is an engineered variant of alteplase. When expressed in E. coli, it appears as inclusion bodies that require refolding to recover its biological activity. An important step following refolding is to determine the activity of refolded protein. Current methods for enzymatic activity of thrombolytic drugs are costly and complex. Here a straightforward and low-cost clot lysis assay was developed. It quantitatively measures the activity of the commercial reteplase and is also capable of screening refolding conditions. As evidence for adequate accuracy and sensitivity of the current assay, r-PA activity measurements are shown to be comparable to those obtained from chromogenic substrate assay.