Oxidative protein refolding on size exclusion chromatography: From batch single-column to multi-column counter-current continuous processing

Mechanistic Modeling of Size Exclusion Chromatography-Assisted In Vitro Refolding of the Recombinant Biosimilar Teriparatide (PTH-34)

In vitro protein refolding is one of the critical unit operations in manufacturing recombinant peptides expressed using Escherichia coli as host cells. This study is focused on designing size exclusion chromatography-assisted in vitro refolding process for biosimilar recombinant parathyroid hormone. Inclusion bodies (IBs) of recombinant parathyroid hormone were solubilized at higher pH, and in vitro refolding was performed using size exclusion chromatography. In the first part of the investigation, DoE-based empirical optimization was performed to achieve a higher refolding yield for a biosimilar recombinant parathyroid hormone. The effect of solubilized inclusion body (IB) feed volume, concentration of IBs, and residence time on in vitro refolding of recombinant teriparatide was studied using the Box-Behnken design. Size exclusion chromatography (SEC)-assisted in vitro refolding was performed at 8 °C at pH 10.5 by using 20 mM Tris buffer. The maximum refolding yield of 98.12% was achieved at feed volume (12.5% of CV) and 20 mg/mL inclusion body (IB) concentration with a residence time of 50 min and a purity of 66.1% based on densitometric analysis using SDS-PAGE. In the latter part of the investigation, the general rate mechanistic model framework for size exclusion chromatography was developed and validated with the experimental results. The developed model helped in the accurate prediction of the elution volumes and product yield. The developed model also helps to predict the elution performance of a scalable column a priori. Post in vitro refolding, the formation of the native peptide structure was examined using various orthogonal analytical tools to study the protein's primary, secondary, and tertiary structures. The developed hybrid process development approach is a valuable tool toachieve high-yield, scalable refolding conditions for recombinant proteins without disulfide bonds.

Refolding in the modern biopharmaceutical industry

Inclusion bodies (IBs) often emerge upon overexpression of recombinant proteins in E. coli. From IBs, refolding is necessary to generate the native protein that can be further purified to obtain pure and active biologicals. This work focusses on refolding as a significant process step during biopharmaceutical manufacturing with an industrial perspective. A theoretical and historical background on protein refolding gives the reader a starting point for further insights into industrial process development. Quality requirements on IBs as starting material for refolding are discussed and further economic and ecological aspects are considered with regards to buffer systems and refolding conditions. A process development roadmap shows the development of a refolding process starting from first exploratory screening rounds to scale-up and implementation in manufacturing plant. Different aspects, with a direct influence on yield, such as the selection of chemicals including pH, ionic strength, additives, etc., and other often neglected aspects, important during scale-up, such as mixing, and gas-fluid interaction, are highlighted with the use of a quality by design (QbD) approach. The benefits of simulation sciences (process simulation and computer fluid dynamics) and process analytical technology (PAT) for seamless process development are emphasized. The work concludes with an outlook on future applications of refolding and highlights open research inquiries.

Mechanistic Study of Protein Adsorption on Mesoporous TiO2 in Aqueous Buffer Solutions

Protein adsorption is of fundamental importance for bioseparation engineering applications. In this work, a series of mesoporous TiO₂ with various geometric structures and different aqueous buffer solutions were prepared as platforms to investigate the effects of the surface geometry and ionic strength on the protein adsorptive behavior. The surface geometry of the TiO₂ was found to play a dominant role in the protein adsorption capacity when the ionic strength of buffer solutions is very low. With the increase in ionic strength, the effect of the geometric structure on the protein adsorption capacity reduced greatly. The change of ionic strength has the highest significant effect on the mesoporous TiO₂ with large pore size compared with that with small pore size. The interaction between the protein and TiO₂ measured with atomic force microscopy further demonstrated that the adhesion force induced by the surface geometry reduced with the increase in the ionic strength. These findings were used to guide the detection of the retention behavior of protein by high-performance liquid chromatography, providing a step forward toward understanding the protein adsorption for predicting and controlling the chromatographic separation of proteins.

β-Cyclodextrin-Modified Magnetic Nanoparticles Immobilized on Sepharose Surface Provide an Effective Matrix for Protein Refolding

In this article, we propose an impressive and facile strategy to improve protein refolding using solid phase artificial molecular chaperones consisting of the surface-functionalized magnetic nanoparticles. Specifically, monotosyl-β-cyclodextrin connected to the surface of 3-aminopropyltriethoxysilane (APES)-modified magnetic nanoparticles is immobilized on the sepharose surface to promote interaction with exposed hydrophobic surfaces of partially folded (intermediates) and unfolded states of proteins. Their efficiencies were investigated by circular dichroism spectroscopy and photoluminescence spectroscopy of the protein. Although the mechanism of this method is based on principles of hydrophobic chromatography, this system is not only purging the native protein from inactive inclusion bodies but also improving the protein refolding process. We chose β-cyclodextrin (β-CD) considering multiple reports in the literature about its efficiency in protein refolding and its biocompatibility. To increase the surface area/volume ratio of the sepharose surface by nanoparticles, more β-CD molecules are connected to the sepharose surface to make a better interaction with proteins. We suppose that proteins are isolated in the nanospace created by bound cyclodextrins on the resin surface so intermolecular interactions are reduced. The architecture of nanoparticles was characterized by Fourier transform infrared spectra, X-ray diffraction, scanning electron microscopy images, energy dispersive X-ray spectroscopy, nuclear magnetic resonance (¹H NMR and ¹³C NMR), and dynamic light scattering.