Seeking Innovative Affinity Approaches: A Performance Comparison between Magnetic Nanoparticle Agglomerates and Chromatography Resins for Antibody Recovery

Direct Affinity Ligand Immobilization onto Bare Iron Oxide Nanoparticles Enables Efficient Magnetic Separation of Antibodies

Magnetic separation is a promising alternative to chromatography for enhancing the downstream processing (DSP) of monoclonal antibodies (mAbs). However, there is a lack of efficient magnetic particles for successful application. Aiming to fill this gap, we demonstrate the suitability of bare iron oxide nanoparticles (BION) with physical site-directed immobilization of an engineered Protein A affinity ligand (rSpA) as an innovative magnetic material. The rSpA ligand contains a short peptide tag that enables the direct and stable immobilization onto the uncoated BION surface without commonly required laborious particle activation. The resulting BION@rSpA have beneficial characteristics outperforming conventional Protein A-functionalized magnetic particles: a simple, fast, low-cost synthesis, a particle size in the nanometer range with a large effective specific surface area enabling large immunoglobulin G (IgG) binding capacity, and a high magnetophoretic velocity advantageous for fast processing. We further show rapid interactions of IgG with the easily accessible rSpA ligands. The binding of IgG to BION@rSpA is thereby highly selective and not impeded by impurity molecules in perfusion cell culture supernatant. Regarding the subsequent acidic IgG elution from BION@rSpA@IgG, we observed a hampering pH increase caused by the protonation of large iron oxide surfaces after concentrating the particles in 100 mM sodium acetate buffer. However, the pH can be stabilized by adding 50 mM glycine to the elution buffer, resulting in recoveries above 85% even at high particle concentrations. Our work shows that BION@rSpA enable efficient magnetic mAb separation and could help to overcome emerging bottlenecks in DSP.

Supramolecular Mimotope Peptide Nanofibers Promote Antibody-Ligand Polyvalent and Instantaneous Recognition for Biopharmaceutical Analysis

Peptide-based supramolecules exhibit great potential in various fields due to their improved target recognition ability and versatile functions. However, they still suffer from numerous challenges for the biopharmaceutical analysis, including poor self-assembly ability, undesirable ligand-antibody binding rates, and formidable target binding barriers caused by ligand crowding. To tackle these issues, a "polyvalent recognition" strategy employing the CD20 mimotope peptide derivative NBD-FFVLR-GS-WPRWLEN (acting on the CDR domains of rituximab) was proposed to develop supramolecular nanofibers for target antibody recognition. These nanofibers exhibited rapid self-assembly within only 1 min and robust stability. Their binding affinity (179 nM) for rituximab surpassed that of the monomeric peptide (7 μM) by over 38-fold, highlighting that high ligand density and potential polyvalent recognition can efficiently overcome the target binding barriers of traditional supramolecules. Moreover, these nanofibers exhibited an amazing "instantaneous capture" rate (within 15 s), a high recovery (93 ± 3%), and good specificity for the target antibody. High-efficiency enrichment of rituximab was achieved from cell culture medium with good recovery and reproducibility. Intriguingly, these peptide nanofibers combined with bottom-up proteomics were successful in tracking the deamidation of asparagine 55 (from 10 to 16%) on the rituximab heavy chain after 21 day incubation in human serum. In summary, this study may open up an avenue for the development of versatile mimotope peptide supramolecules for biorecognition and bioanalysis of biopharmaceuticals.

A Review of the Use of Metallic Nanoparticles as a Novel Approach for Overcoming the Stability Challenges of Blood Products: A Narrative Review from 2011-2021

PURPOSE

To obtain safe and qualified blood products (e.g., platelets, plasma, and red blood cells), various limitations such as limited shelf life (especially for platelets) and stability must be addressed. In this review study, the most commonly used metal nanomaterials (e.g., gold, silver, iron, and magnetic) reported in the literature from 2011 to 2021 were discussed owing to their unique properties, which provide exciting approaches to overcome these limitations and improve the stability, safety, and quality of blood products. Novelty: This study reviews for the first time the results of studies (from 2011 to 2021) that consider the effects of various metallic nanoparticles on the different blood products.

RESULTS

The results of this review study showed that some metallic nanoparticles are effective in improving the stability of plasma proteins. For this purpose, modified Fe₃O₄ magnetic nanoparticles and citrate-AuNPs protect albumin products against stressful situations. Also, SiO₂ microspheres and silicacoated magnetite nanoparticles are highly capable of improving IgG stability. ZnO nanoparticles also reduced thrombin production, and protein-coated GMNP nanoparticles prevented unwanted leakage of factor VIII through blood vessels. Furthermore, the stability and longevity of erythrocytes can be improved by AuNP nanoparticles and Zr-based organic nanoparticles. In addition, platelet storage time can be improved using PEGylated Au and functionalized iron oxide nanoparticles.

SUGGESTION

According to the results of this study, it is suggested that further research should be conducted on metal nanoparticles as the most promising candidates to prepare metal nanoparticles with improved properties to increase the stability of various blood products.

Competition at the Bio-nano Interface: A Protein, a Polysaccharide, and a Fatty Acid Adsorb onto Magnetic Nanoparticles

Magnetic nanoparticles are an attractive bioseparation tool due to their magnetic susceptibility and high adsorption capacity for different types of molecules. A major challenge for separation is to generate selectivity for a target molecule, or for a group of molecules in complex environments such as cell lysates. It is crucial to understand the factors that determine the targets' adsorption behavior in mixtures for triggering intended interactions and selectivity. Here we use a model system containing three molecules, each of them a common representative of the more abundant types of macromolecules in living systems: sodium oleate (SO), a fatty acid; bovine serum albumin (BSA), a protein; and dextran, a polysaccharide. Our results show that (a) the BSA adsorption capacity on the iron oxide material depends markedly on the pH, with the maximum capacity at the pI of the protein (0.39 g g_MNP^-1 ); (b) sodium oleate, a strongly negatively charged molecule, an organic anion, renders a maximum adsorption capacity of 0.40 g g_MNP^-1, even at pHs at which oleate as well as the nanoparticle surface are negatively charged; (c) the adsorbed masses of dextran, a neutral sugar, are lower than for the other two molecules, between 0.09 and 0.13 g g_MNP^-1, regardless of the system's pH. We observe an unexpected behavior in mixtures: SO completely prevents the adsorption of BSA, and dextran decreases the adsorption of the other competitors, SO and BSA, while adsorbing at the same capacities, unaffected by either the presence of the other two molecules or the pH. BSA does not decrease the oleate adsorption capacity. We demonstrate the essential role of pH in the adsorption of BSA (a protein) and SO (a fatty acid), as well as its impact in the structural organization of the oleate molecules in water. Moreover, we present exciting data on the adsorption of the molecules in competition, revealing the need to focus on interaction studies in more complex environments. This study attempts to open the scope of the current research of bio-nano interactions to not only proteins but also to mixtures, and generally to molecules with other physicochemical characteristics. Furthermore, we contribute to the understanding of multicomponent systems with the vision set in enhancing biomass exploitation and biofractionation processes.

Progress in affinity ligand-functionalized bacterial magnetosome nanoparticles for bio-immunomagnetic separation of HBsAg protein

Efficient Bio-immunomagnetic separation (BIMS) of recombinant hepatitis B surface antigen (rHBsAg) with high binding capacity was studied using affinity ligand immobilized bacterial magnetosome nanoparticles (Magnetospirillum gryphiswaldense strain MSR-1 bacteria) as an immunomagnetic sorbent. Our results showed immunomagnetic adsorption, acted by affinity interactions with the immobilized monoclonal antibody, offered higher antigen adsorption and desorption capacities as compared with the commercially available immunoaffinity sorbents. Four different ligand densities of the Hep-1 monoclonal antibody were examined during covalent immobilization on Pyridyl Disulfide-functionalized magnetosome nanoparticles for HBsAg immunomagnetic separation. The average of adsorption capacity was measured as 3 mg/ml in optimized immunomagnetic sorbent (1.056 mg rHBsAg/ml immunomagneticsorbent/5.5 mg of total purified protein) and 5mg/ml in immunoaffinity sorbent (0.876 mg rHBsAg/ml immunosorbent/5.5 mg total purified protein during 8 runs. Immunomagnetic sorbent demonstrated ligand leakage levels below 3 ng Mab/Ag rHBsAg during 12 consecutive cycles of immunomagnetic separation (IMS). The results suggest that an immunomagnetic sorbent with a lower ligand density (LD = 3 mg Mab/ml matrix) could be the best substitute for the immunosorbent used in affinity purification of r-HBsAg there are significant differences in the ligand density (98.59% (p-value = 0.0182)), adsorption capacity (97.051% (p-value = 0.01834)), desorption capacity (96.06% (p-value = 0.036)) and recovery (98.97% (p-value = 0.0231)). This study indicates that the immunosorbent approach reduces the cost of purification of Hep-1 protein up to 50% as compared with 5 mg Mab/ml immunoaffinity sorbent, which is currently used in large-scale production. As well, these results demonstrate that bacterial magnetosome nanoparticles (BMs) represent a promising alternative product for the economical and efficient immobilization of proteins and the immunomagnetic separation of Biomolecules, promoting innovation in downstream processing.

Protein Attachment Mechanism for Improved Functionalization of Affinity Monolith Chromatography (AMC)

This work aims at understanding the attachment mechanisms and stability of proteins on a chromatography medium to develop more efficient functionalization methodologies, which can be exploited in affinity chromatography. In particular, the study was focused on the understanding of the attachment mechanisms of bovine serum albumin (BSA), used as a ligand model, and protein G on novel amine-modified alumina monoliths as a stationary phase. Protein G was used to develop a column for antibody purification. The results showed that, at lower protein concentrations (i.e., 0.5 to 1.0 mg·mL⁻¹), protein attachment follows a 1st-order kinetics compatible with the presence of covalent binding between the monolith and the protein. At higher protein concentrations (i.e., up to 10 mg·mL⁻¹), the data preferably fit a 2nd-order kinetics. Such a change reflects a different mechanism in the protein attachment which, at higher concentrations, seems to be governed by physical adsorption resulting in a multilayered protein formation, due to the presence of ligand aggregates. The threshold condition for the prevalence of physical adsorption of BSA was found at a concentration higher than 1.0 mg·mL⁻¹. Based on this result, protein concentrations of 0.7 and 1.0 mg·mL⁻¹ were used for the functionalization of monoliths with protein G, allowing a maximum attachment of 1.43 mg of protein G/g of monolith. This column was then used for IgG binding–elution experiments, which resulted in an antibody attachment of 73.5% and, subsequently, elution of 86%, in acidic conditions. This proved the potential of the amine-functionalized monoliths for application in affinity chromatography.

Tag-mediated single-step purification and immobilization of recombinant proteins toward protein-engineered advanced materials

Background

The potential applications of protein-engineered functional materials are so wide and exciting that the interest in these eco-friendly advanced materials will further expand in the future. Tag-mediated protein purification/immobilization technologies have emerged as green and cost-effective approaches for the fabrication of such materials. Strategies that combine the purification and immobilization of recombinant proteins/peptides onto/into natural, synthetic or hybrid materials in a single-step are arising and attracting increasing interest.

Aim of Review

This review highlights the most significant advances of the last 5 years within the scope of tag-mediated protein purification/immobilization and elucidates their contributions for the development of efficient single-step purification and immobilization strategies. Recent progresses in the field of protein-engineered materials created using innovative protein-tag combinations and future opportunities created by these new technologies are also summarized and identified herein.

Key Scientific Concepts of Review

Protein purification/immobilization tags present a remarkable ability to establish specific non-covalent/covalent interactions between solid materials and biological elements, which prompted the creation of tailor-made and advanced functional materials, and of next-generation hybrid materials. Affinity tags can bind to a wide range of materials (of synthetic, natural or hybrid nature), being most suitable for protein purification. Covalently binding tags are most suitable for long-term protein immobilization, but can only bind naturally to protein-based materials. Hybrid affinity-covalently binding tags have allowed efficient one-step purification and immobilization of proteins onto different materials, as well as the development of innovative protein-engineered materials. Self-aggregating tags have been particularly useful in combination with other tags for generating protein-engineered materials with self-assembling, flexible and/or responsive properties. While these tags have been mainly explored for independent protein purification, immobilization or functionalization purposes, efficient strategies that combine tag-mediated purification and immobilization/functionalization in a single-step will be essential to guarantee the sustainable manufacturing of advanced protein-engineered materials.

Magnetic Nanoparticles with Surface Nanopockets for Highly Selective Antibody Isolation

Monoclonal antibodies (mAbs) are key components of revolutionary disease immunotherapies and are also essential for medical diagnostics and imaging. The impact of cost is illustrated by a price >$200,000 per year per patient for mAb-based cancer therapy. Purification represents a major issue in the final cost of these immunotherapy drugs. Protein A (PrA) resins are widely used to purify antibodies, but resin cost, separation efficiency, reuse, and stability are major issues. This paper explores a synthesis strategy for low-cost, reusable, stable PrA-like nanopockets on core-shell silica-coated magnetic nanoparticles (NPs) for IgG antibody isolation. Mouse IgG_2a, a strong PrA binder, was used as a template protein, first attaching it stem-down onto the NP surface. The stem-down orientation of IgG_2a on the NP surface before polymerization is critical for designing the films to bind IgGs. Following this, 1-tetraethoxysilane and four organosilane monomers with functional groups capable of mimicking binding interactions of proteins with IgG antibody stems were reacted to form a thin polymer coating on the NPs. After blocking nonspecific binding sites, removal of the mouse IgG_2a provided nanopockets on the core-shell NPs that showed binding characteristics for antibodies remarkably similar to PrA. Both smooth and rough core-shell NPs were used, with the latter providing much larger binding capacities for IgGs, with an excellent selectivity slightly better than that of commercial PrA magnetic beads. This paper is the first report of IgG-binding NPs that mimic PrA selectivity. These nanopocket NPs can be used for at least 15 regeneration cycles, and cost/use was 57-fold less than a high-quality commercial PrA resin.

Magnetically Induced Aggregation of Iron Oxide Nanoparticles for Carrier Flotation Strategies

On the nanoscale, iron oxides can be used for multiple applications ranging from medical treatment to biotechnology. We aimed to utilize the specific properties of these nanoparticles for new process concepts in flotation. Magnetic nanoparticles were synthesized by alkaline coprecipitation, leading to a primary particle size of 9 nm, and coated with oleate. The nanomaterial was characterized for its superparamagnetism and its colloidal stability at different ionic strengths, with and without an external magnetic field. The nanomaterial was used for model experiments on magnetic carrier flotation of microplastic particles, based on magnetically induced heteroagglomeration. We were able to demonstrate the magnetically induced aggregation of the nanoparticles which allows for new flotation strategies. Since the nanomaterial has zero remanent magnetization, the agglomeration is reversible which facilitates the process control. Magnetic carrier flotation based on iron oxide nanoparticles can pave the way to promising new recycling processes for microplastic wastes.

Recent trends in sorbents for bioaffinity chromatography

Isolation or enrichment of biological molecules from complex biological samples is mostly a prerequisite in proteomics, genomics, and glycomics. Different techniques have been used to advance the efficiency of the purification of biological molecules. Bioaffinity chromatography is one of the most powerful technique that plays an important role in the isolation of target biological molecules by the specific interactions with ligands that are immobilized on different support materials. This review examines the recent developments in bioaffinity chromatography particularly over the past 5 years in the literature. Also properties of supports, immobilization techniques, types of binding agents, and methods used in bioaffinity chromatography applications are summarized.