Lijing Sun

Comparison of site-specific PEGylations of the N-terminus of interferon beta-1b: selectivity, efficiency, and in vivo/vitro activity.

PEGylation, including nonspecific and site-directed approaches, is a well-established and validated strategy to increase the stability, in vivo plasma retention time, and efficacy of protein pharmaceutics together with a reduction in immunogenicity and hydrophobicity. Site-directed conjugation by PEG-aldehyde is the most widely used method for N-terminal modification; however, the generation of multimodified products is inevitable because of lysine chemistry, which always leads to difficulties in purification and quantification. In this study, we developed a specific PEGylation strategy through the periodation of the N-terminus of interferon beta-1b (IFN-β-1b) followed by the coupling of PEG-hydrazide. The prolonged elimination half-life and significantly diminished immunogenicity of the PEG-hydrazide-modified protein indicated the development of an effective process for improving the pharmacology and immunogenicity of IFN-β-1b. We further conducted comparisons on the selectivity, velocity, yield, and pharmacokinetics of the two methods. The results demonstrated that the hydrazide-based conjugation was a highly specific coupling reaction that only produced homogeneous N-terminal mono-PEGylated conjugate but also generated heterogeneous multimodified products in the aldehyde-based process. In addition, a better PEGylation yield was found for the hydrazide conjugation compared with that of the aldehyde strategy. These investigations supply a practical approach for the site-specific modification of proteins with an N-terminal serine or threonine to achieve improved homogeneity of the conjugates as well as enhanced pharmacological properties.

Efficient separation of homologous α-lactalbumin from transgenic bovine milk using optimized hydrophobic interaction chromatography

Transgenic bovine milk could be a rich source of recombinant human proteins. However, the co-presence of bovine and human homologous proteins can be a challenge for product purification. In this study, the average surface hydrophobicity and electric potential of human alpha-lactalbumin (HLA) and bovine alpha-lactalbumin (BLA) were analyzed and compared through the exposure area calculation of different amino acids. Based on the analysis, calcium independent hydrophobic interaction chromatography was selected for separation of recombinant human alpha-lactalbumin (rHLA) from BLA in transgenic bovine milk. The operating conditions for the best separation of two proteins were predicted by fluorescence data. Three commercially available HIC resins (Butyl Sepharose 4 FF, Octyl Sepharose 4 FF, Phenyl Sepharose 6 FF) were compared. The transgenic milk was skimmed and treated by pH adjustment to remove a large quantity of casein protein. The supernatant was loaded on the hydrophobic interaction chromatographic matrix. The correct elution fraction was further treated with gel filtration chromatography. The overall recovery of rHLA was up to 67.1% with the purity greater than 95%. Circular dichroism spectroscopy (CD) and mass spectrogram (MS) confirmed the native state and glycosylated form of the purified rHLA.

Konjac glucomannan microspheres for low-cost desalting of protein solution

In this study, low-cost konjac glucomannan (KGM) microspheres used for desalting were developed by an inverse dispersion method. High concentration of KGM was pretreated to reduce viscosity by acid hydrolysis method under the condition of high temperature and pressure. The selectivity of the obtained cross-linked KGM gels with different degree of crosslinking was studied by constructing calibration curves (K(av)) of standard molecular weight substances. The stability of the gels was investigated, which showed that the KGM microspheres are tolerant to a wide range of pH and stable in all commonly used aqueous buffers, and insensitive to autoclaving as well. Furthermore, protein-desalting performances of GM-1250, a cross-linked KGM microsphere, were evaluated with two proteins, bovine serum albumin and filamentous hemagglutinin, which turned out that GM-1250 is comparable to the widely used commercial product--Sephadex G25 Fine. From economic considerations, KGM gel is a prospective alternative for dextran gels in protein desalting process.

Reversible protection of Cys-93(β) by PEG alters the structural and functional properties of the PEGylated hemoglobin.

As a potential hemoglobin (Hb)-based oxygen carrier (HBOC), the PEGylated Hb has received much attention for its non-nephrotoxicity. However, PEGylation can adversely alter the structural and functional properties of Hb. The site of PEGylation is an important factor to determine the structure and function of the PEGylated Hb. Thus, protection of some sensitive residues of Hb from PEGylation is of great significance to develop the PEGylated Hb as HBOC. Here, Cys-93(β) of Hb was conjugated with 20 kDa polyethylene glycol (PEG20K) through hydrazone and disulfide bonds. Then, the conjugate was modified with PEG5K succinimidyl carbonate (PEG5K-SC) using acylation chemistry, followed by removal of PEG20K Hb with hydrazone hydrolysis and disulfide reduction. Reversible conjugation of PEG20K at Cys-93(β) can protect Lys-95(β), Val-1(α) and Lys-16(α) of Hb from PEGylation with PEG5K-SC. The autoxidation rate, oxygen affinity, structural perturbation and tetramer instability of the PEGylated Hb were significantly decreased upon protection with PEG20K. The present study is expected to improve the efficacy of the PEGylated Hb as an oxygen therapeutic.

PEGylation of G-CSF in organic solvent markedly increase the efficacy and reactivity through protein unfolding, hydrolysis inhibition and solvent effect.

Previous studies demonstrated that hydrophobic proteins could be PEGylated in organic phase rather than water phase. It is still not known what the difference is for a hydrophilic proteins PEGylation in these two different phases. In this study, granulocyte colony stimulating factor (G-CSF) was dissolved in neat dimethyl sulfoxide (DMSO) and was PEGylated. In comparison with the PEGylation in water solution, the PEGylation degree in the organic solvent increased by 33% and 42% for PEG-maleimide (MAL-PEG) and PEG-succinimidyl carbonate (SC-PEG) respectively. Structure analysis revealed that the protein was unfolded in DMSO, which could make the PEGylated sites of G-CSF easily accessible. The hydrolysis half-life in water solution was 40min and 9h for SC-PEG and MAL-PEG respectively. However, in DMSO solvent, PEGs were very stable and no hydrolysis could be detected. Stopped-flow demonstrated that the conjugation speed of G-CSF by MAL-PEG and SC-PEG in DMSO were 1.6×10(4) and 2×10(2) times faster than those in aqueous solution. The remarkable acceleration could mainly be attributed to an increase of protein nucleophilicity in DMSO. The results of this study could be referential to industrial application where the cost of PEG reagents and the speed of reaction on large scale are very important.

CO binding improves the structural, functional, physical and anti-oxidation properties of the PEGylated hemoglobin

Abstract Context: PEGylated hemoglobin (Hb) is a promising oxygen therapeutic agent for clinical application. However, it suffered from structural perturbation, functional instability and methemoglobin (metHb) formation. Objective: To improve the structural, functional, physical and anti-oxidation properties of the PEGylated Hb. Materials and methods: PEGylation of Hb with CO binding (HbCO) was conducted using maleimide and acylation chemistry, respectively. Physical and chemical parameters were measured for Hb samples. The circular dichroism spectra, dynamic light scattering and analytical ultracentrifugation were used to investigate the structure and conformation of PEGylated HbCO. Results: CO binding can inhibit the autoxidation of the PEGylated Hb, structurally stabilize its tetramer and improve its thermal and pH stability. Importantly, the circular dichroism spectra showed that CO binding can decrease the structural perturbation of Hb induced by PEGylation. The PEGylated HbCO with CO release showed slightly higher oxygen-delivery capacity than the PEGylated Hb. The PEGylated HbCO did not show metHb formation after 30-day storage at 4°C. Discussion and conclusion: CO binding structurally stabilized the PEGylated Hb, abolished its metHb formation, and significantly increased its physical stability. In particular, it also avoided the perturbation of PEG chains on the heme microenvironment. The functional property of the PEGylated HbCO can be maintained during its long-term storage, which is of great significance for field transfusion.

Stabilization study of inactivated foot and mouth disease virus vaccine by size-exclusion HPLC and differential scanning calorimetry

The inactivated foot and mouth disease virus (FMDV), which has a sedimentation coefficient of 146S, is crucial to the efficacy of vaccine preparations, but extremely unstable in vitro. It is prone to dissociate into smaller particles referred to as 12S with a concomitant decrease in immunogenicity; therefore, it is of great importance to find the best condition for stabilizing the FMDV. In the present work, the effects of solution pH and temperature on the dissociation of 146S was investigated and potential stabilizers were screened, with aid of high-performance size-exclusion chromatography (HPSEC) for rapid and quantitative determination of 146S, together with differential scanning calorimetry (DSC) technology for thermal stability analysis. The most stable pH was found between 7.5 and 8.0. Among excipients tested, sucrose and glycerol provided the best protection, such that the half-life of 146S in solution at 45°C could be prolonged from less than 30min to more than 3days by adding 20% sucrose. The stabilization mechanism was confirmed using DSC analysis, which showed that the transition temperature related to 146S dissociation was increased by 5.4°C in the presence of 20% sucrose. The physical stabilization effects afforded by these stabilizers would allow for the retaining of effective 146S antigens during transportation and storage under relative harsh condition.

A Simple and Rapid Procedure for Purification of Haptoglobin from Human Plasma Fraction IV

Abstract Human plasma fraction IV is an intermediate precipitate during the production of human serum albumin using cold ethanol method. Haptoglobin locates in this fraction can be purified for various applications. A new process integration of polyethylene glycol (PEG) precipitation and ion-exchange chromatography (IEC) was developed for purification of haptoglobin, which could effectively purify the haptoglobin from 16.6% to 95%. The recovery of the new process was 58.2% in comparison to 30.3% of the conventional affinity chromatography. Furthermore, 175 mg haptoglobin production in a scaled-up process showed the method to be simple, fast, and low-cost.

Effect of solution environment on the purification of pertussis toxin

The low recovery of pertussis toxin (PT) and the low resolving efficiency of chromatography, due to the instability of PT in low salt condition, are the main challenges for its purification. We aplied 2 mol/L urea to prevent the aggregation and disassociation of PT during the purification by ion-exchange chromatography (IEC) and gel filtration chromatography (GFC). The effect of urea on the purification of PT was studied by ELISA assay and non-reduced SDS-PAGE. The activity recoveries of PT and filamentous hemagglutinin (FHA) in IEC and GFC, the resolution efficiency in GFC and the purities of PT and FHA were improved obviously by adding 2 mol/L urea in the mobile phase. The results highlight the potential application of urea in the acellular pertussis vaccine (APV) manufacture procedure.

Comparison of Adsorbent with Varying Spacer Arm Length and Ligand Density for the Purification of Recombinant Hepatitis B Virus Surface Antigen

Novel hydrophobic absorbents were synthesized by immobilizing butyl derivative onto the highly cross-linked agarose beads manufatured in China, which are used as matrix. The effect of the spacer arm length (3C, 8C and 10C) and ligand density (from 13 to 45 micromol/mL) on the hydrophobicity were investigated using purified Hepatitis B surface antigen (HBsAg) expressed by CHO cell lines. Also considering the effects of salt concentration and pH on HBsAg recovery and purification factor, orthogonal experiment design method was used to evaluated the absorbents. The results showed the butyl-S absorbent with the spacer arm length of C8, the ligand density of 22 micromol/mL gel showed the best performance for the separation of HBsAg. Approximately 100% HBsAg recovery and 60 as purification fold were achieved by this media under the operating condition of pH 7.0 and 9% of salt concentrateion.