A comprehensive evaluation of mixed mode interactions of HEA and PPA HyperCel™ chromatographic media

Clear insight into complex multimodal resins and impurities to overcome recombinant protein purification challenges: A review

Increasing attention has been paid to the purity of therapeutic proteins imposing extensive costs and challenges to the downstream processing of biopharmaceuticals. One of the efforts, that has been exerted to overcome such limitations, was developing multimodal or mixed-mode chromatography (MMC) resins for launching selective, orthogonal, non-affinity purification platforms. Despite relatively extensive usage of MMC resins, their real potential and fulfillment have not been extensively reviewed yet. In this work, the explanation of practical and key aspects of downstream processing of recombinant proteins with or without MMC resins was debated, as being useful for further purification process development. This review has been written as a step-by-step guide to deconvolute both inherent protein purification and MMC complexities. Here, after complete elucidation of the potential of MMC resins, the effects of frequently used additives (mobile phase modifiers) and their possible interactions during the purification process, the critical characteristics of common product-related impurities (e.g., aggregates, charge variants, fragments), host-related impurities (e.g., host cell protein and DNA) and process related impurities (e.g., endotoxin, and viruses) with solved or unsolved challenges of traditional and MMC resins have been discussed. Such collective experiences which are reported in this study could be considered as an applied guide for developing successful downstream processing in challenging conditions by providing a clear insight into complex MMC resins and impurities.

Exploring preferred binding domains of IgG1 mAbs to multimodal adsorbents using a combined biophysics and simulation approach

In this work, we employ a recently developed biophysical technique that uses diethylpyrocarbonate (DEPC) covalent labeling and mass spectrometry for the identification of mAb binding patches to two multimodal cation exchange resins at different pH. This approach compares the labeling results obtained in the bound and unbound states to identify residues that are sterically shielded and thus located in the mAb binding domains. The results at pH 6 for one mAb (mAb B) indicated that while the complementarity determining region (CDR) had minimal interactions with both resins, the FC domain was actively involved in binding. In contrast, DEPC/MS data with another mAb (mAb C) indicated that both the CDR and FC domains were actively involved in binding. These results corroborated chromatographic retention data with these two mAbs and their fragments and helped to explain the significantly stronger retention of both the intact mAb C and its Fab fragment. In contrast, labeling results with mAb C at pH 7, indicated that only the CDR played a significant role in resin binding, again corroborating chromatographic data. The binding domains identified from the DEPC/MS experiments were also examined using protein surface hydrophobicity maps obtained using a recently developed sparse sampling molecular dynamics (MD) approach in concert with electrostatic potential maps. These results demonstrate that the DEPC covalent labeling/mass spectrometry technique can provide important information about the domain contributions of multidomain proteins such as monoclonal antibodies when interacting with multimodal resins over a range of pH conditions.

Fully automated minicolumn chromatography

Miniaturized chromatography columns (minicolumns) operated by automated liquid handlers are an integral part of bioprocess purification development. However, these systems can be limited in both their efficiency and accessibility. Because the minicolumn chromatography operation itself is higher throughput, the lower throughput pre- and post-operation activities become the bottleneck of the workflow. Additionally, method writing and operation of the systems while varying multiple parameters, using a design of experiments approach for example, can be error-prone and resource intensive. Here, we have developed a fully automated minicolumn chromatography system to both address these bottlenecks and improve the accessibility of these systems by allowing users to enter chromatography-relevant information through a simplified user interface. Methods have been developed to automate buffer preparation and protein solution titration leveraging modeling and integrated pH probes with feedback control. Chromatogram generation and fraction pooling has additionally been automated to improve the efficiency of post-chromatography operations. We have also demonstrated the flexibility of the system through an example run where both bind-and-elute chromatography and flowthrough chromatography experiments were performed in parallel. Additionally, all methodology and parameters to operate the system have been shared. We hope this will help interested parties improve the efficiency and accessibility of their minicolumn chromatography systems.

Isotherm model discrimination for multimodal chromatography using mechanistic models derived from high-throughput batch isotherm data

In this work, we have examined an array of isotherm formalisms and characterized them based on their relative complexities and predictive abilities with multimodal chromatography. The set of isotherm models studied were all based on the stoichiometric displacement framework, with considerations for electrostatic interactions, hydrophobic interactions, and thermodynamic activities. Isotherm parameters for each model were first determined through twenty repeated fits to a set of mAb - Capto MMC batch isotherm data spanning a range of loading, ionic strength, and pH as well as a set of mAb - Capto Adhere batch data at constant pH. The batch isotherm data were used in two ways-spanning the full range of loading or consisting of only the high concentration data points. Predictive ability was defined through the model's capacity to capture prominent changes in salt gradient elution behavior with respect to pH for Capto MMC or unique elution patterns and yield losses with respect to gradient slope for Capto Adhere. In both cases, model performance was quantified using a scoring metric based on agreement in peak characteristics for column predictions and accuracy of fit for the batch data. These scores were evaluated for all twenty isotherm fits and their corresponding column predictions, thereby producing a statistical distribution of model performances. Model complexity (number of isotherm parameters) was then considered through use of the Akaike information criterion (AIC) calculated from the score distributions. While model performance for Capto MMC benefitted substantially from removal of low protein concentration data, this was not the case for Capto Adhere; this difference was likely due to the qualitatively different shapes of the isotherms between the two resins. Surprisingly, the top-performing (high accuracy with minimal number of parameters) isotherm model was the same for both resins. The extended steric mass action (SMA) isotherm (containing both protein-salt and protein-protein activity terms) accurately captured both the pH-dependent elution behavior for Capto MMC as well as loss in protein recovery with increasing gradient slope for Capto Adhere. In addition, this isotherm model achieved the highest median score in both resin systems, despite it lacking any explicit hydrophobic stoichiometric terms. The more complex isotherm models, which explicitly accounted for both electrostatic and hydrophobic interaction stoichiometries, were ill-suited for Capto MMC and had lower AIC model likelihoods for Capto Adhere due to their increased complexity. Interestingly, the ability of the extended SMA isotherm to predict the Capto Adhere results was largely due to the protein-salt activity coefficient, as determined via isotherm parameter sensitivity analyses. Further, parametric studies on this parameter demonstrated that it had a major impact on both binding affinity and elution behavior, therein fully capturing the impact of hydrophobic interactions. In summary, we were able to determine the isotherm formalisms most capable of consistently predicting a wide range of column behavior for both a multimodal cation-exchange and multimodal anion-exchange resin with high accuracy, while containing a minimized set of model parameters.

Evaluation of preferred binding regions on ubiquitin and IgG1 FC for interacting with multimodal cation exchange resins using DEPC labeling/mass spectrometry

There is significant interest in identifying the preferred binding domains of biological products to various chromatographic materials. In this work, we develop a biophysical technique that uses diethyl pyrocarbonate (DEPC) based covalent labeling in concert with enzymatic digestion and mass spectrometry to identify the binding patches for proteins bound to commercially available multimodal (MM) cation exchange chromatography resins. The technique compares the changes in covalent labeling of the protein in solution and in the bound state and uses the differences in this labeling to identify residues that are sterically shielded upon resin binding and, therefore, potentially involved in the resin binding process. Importantly, this approach enables the labeling of many amino acids and can be carried out over a pH range of 5.5-7.5, thus enabling the protein surface mapping at conditions of interest in MM cation exchange systems. The protocol is first developed using the model protein ubiquitin and the results indicate that lysine residues located on the front face of the protein show dramatic changes in DEPC labeling while residues present on other regions have minimal or no reductions. This indicates that the front face of ubiquitin is likely involved in resin binding. In addition, surface property maps indicate that the hypothesized front face binding region consists of overlapping positively charged and hydrophobic patches. The technique is then employed with an IgG1 F_C and the results indicate that residues on the C_H 2-C_H 3 interface and the hinge are significantly sterically shielded upon binding to the resin. Further, these regions are again associated with significant overlap of positively charged and hydrophobic patches. On the other hand, while, residues on the C_H 2 and the front face of the IgG1 F_C also exhibited some changes in DEPC labeling upon binding, these regions have less distinct charged and hydrophobic patches. Importantly, the hypothesized binding patches identified for both ubiquitin and F_C using this approach are shown to be consistent with previously reported NMR studies. In contrast to NMR, this new approach enables the identification of preferred binding regions without the need for isotopically labeled proteins or chemical shift assignments. The technique developed in this work sets the stage for the evaluation of the binding domains of a wide range of biological products to chromatographic surfaces, with important implications for designing biomolecules with improved biomanufacturability properties.

Microfluidics as a high-throughput solution for chromatographic process development - The complexity of multimodal chromatography used as a proof of concept

High-throughput technologies are fundamental to expedite the implementation of novel purification platforms. The possibility of performing process development within short periods of time while saving consumables and biological material are prime features for any high-throughput screening device. In this work, a microfluidic device is evaluated as high-throughput solution for a complete study of chromatographic operation conditions on ten different multimodal resins. The potential of this class of purification solutions is generally hindered by its complexity. Taking this into consideration, the microfluidic platform was herein applied and assessed as a tool for high-throughput applications. The commercially available multimodal ligands were studied for the binding of three antibody-based biomolecules (polyclonal mixture of whole antibodies, Fab and Fc fragments) at different pH and salt conditions, in a total of 450 experiments. The results obtained with the microfluidic device were comparable to a standard 96-well filtering microplate high-throughput tool. Additionally, five of the ten multimodal ligands tested were packed into a bench-scale column to perform a final validation of the microfluidic results obtained. All the data acquired in this work using different screening protocols corroborate each other, showing that microfluidic chromatography is a valuable tool for the fast implementation of a new purification step, particularly, if the goal is to narrow the downstream possibilities by being a first point of decision.

A framework for calculating orthogonal selectivities in multimodal systems directly from cell culture fluid

This paper presents a straightforward approach for measuring and quantifying orthogonality directly in complex cell culture fluids (CCFs) without the requirement for tracking the retention behaviors of large sets of proteins. Null-producing CCFs were fractionated using linear salt gradients at constant pH on a set of multimodal resins. Fractions were then analyzed by ultraperformance-reversed phase liquid chromatography and the resulting chromatograms provided host cell protein (HCP) "fingerprints." Using these fingerprints, an inner product vector-based approach was employed to quantify the degree of orthogonality between pairs of resins and operating conditions for these large HCP protein sets. To compare resin orthogonality behavior in different expression systems, the Chinese hamster ovary and Pichia pastoris null-producing CCFs were examined. Orthogonality in multimodal systems was found to strongly depend on the expression system and the HCPs being screened. We also identified several unexpected pairs of multimodal resins within the same family that exhibited significant orthogonality. Furthermore, "self-orthogonality" was evaluated between resins operated at different pHs, and important operating regimes were identified for maximizing orthogonal selectivities. The framework developed in this paper for calculating orthogonality without the need for labor-intensive HCP tracking has important implications for efficient process development and resin/operating condition selection for both monoclonal antibody (mAb) polishing steps and non-mAb processes. In addition, this study provides a tool to unlock the untapped potential of multimodal resins by aiding in their rational selection and incorporation. Finally, the orthogonality framework here can facilitate the development of sets of next-generation multimodal resins specifically designed to provide highly orthogonal and efficient separations tailored for different expression systems.

Benzotriazole-5-carboxylic as a mixed-mode ligand for chromatographic separation of antibody with enhanced adsorption capacity

Mixed-mode chromatography provides a promising strategy for industrial protein purification for its potential merit of balancing efficiency and cost-effectiveness. However, mixed-mode media with satisfactory selectivity and binding capacity towards antibody are still urgently needed. A new type of mixed-mode chromatography resin was prepared using benzotriazole-5-carboxylicas as ligand (BTA MM), and its application in antibody separation was explored. A typical pH-dependent protein binding was observed, and the neutral condition was favorable for antibody adsorption. Dynamic binding capacity of human immunoglobulin G (hIgG) was 57.7 mg/mL at pH 7.4 (10 mM phosphate buffer, containing 150 mM NaCl), while elution with acidic solutions (pH 3-4) could achieve a recovery of more than 85%. Protein adsorption on the resin showed a salt-independent manner, thus it could work under physiological solution conditions, with satisfied antibody selectivity. One-step purification of antibody components from human serum samples could obtain a product with the purity more than 84%. Satisfied performance was also observed when the adsorbent was used for purifying a IgG1-type monoclonal antibody (mAb) from cell culture supernatant. In addition, the benzotriazole adsorbent has been found stable enough to withstand autoclave sterilization and other harsh conditions, including 1 M NaOH, 1 M HCl, and 75% ethanol. The results proved the potential of this type of mixed-mode chromatography medium for industrial antibody purification.

High-capacity multimodal anion-exchange membranes for polishing of therapeutic proteins

This contribution reports on a study using Purexa™-MQ multimodal anion-exchange (AEX) membranes for protein polishing at elevated solution conductivities. Dynamic binding capacities (DBC₁₀ ) of bovine serum albumin (BSA), human immunoglobulins, and salmon sperm DNA (ss-DNA) are reported for various salt types, salt concentrations, flowrates, and pH. Using 1 mg/ml BSA, DBC₁₀ values for Purexa™-MQ were >90 mg/ml at conductivities up to 15 mS/cm. The membranes maintained a high, salt-tolerant BSA DBC₁₀ of 89.8 ± 2.7 (SD) over the course of 100 bind-elute cycles. Polishing studies with acidic and basic monoclonal antibodies at >2 kg/L loads showed that Purexa™-MQ had higher clearance of host cell proteins and aggregate species at high conductivity (13 mS/cm) and in the presence of phosphate than other commercial AEX media. Purexa™-MQ also had a high ss-DNA DBC₁₀ of 50 mg/ml at conductivities up to 15 mS/cm, markedly outperforming other commercial products. In addition to the effectiveness of Purexa™-MQ for protein polishing at elevated solution conductivities, its unusually high binding capacity for ss-DNA indicates potential applications for plasmid DNA purification.

Protein Solvent Interaction: Transition of Protein-solvent Interaction Concept from Basic Research into Solvent Manipulation of Chromatography

Previously, we have reviewed in this journal (Arakawa, T., Kita, Y., Curr. Protein Pept. Sci., 15, 608-620, 2014) the interaction of arginine with proteins and various applications of this solvent additive in the area of protein formulations and downstream processes. In this special issue, we expand the concept of protein-solvent interaction into the analysis of the effects of solvent additives on various column chromatography, including mixed-mode chromatography. Earlier in our research, we have studied the interactions of such a variety of solvent additives as sugars, salts, amino acids, polymers and organic solvents with a variety of proteins, which resulted in mechanistic understanding on their protein stabilization and precipitation effects, the latter known as Hofmeister series. While such a study was then a pure academic research, rapid development of genetic engineering technologies and resultant biotechnologies made it a valuable knowledge in fully utilizing solvent additives in manipulation of protein solution, including column chromatography.

Exploring the separation power of mixed-modal resins for purification of recombinant osteopontin from clarified Escherichia coli lysates

Osteopontin (OPN) is a structural protein with potential value in therapeutic and diagnostic applications. Low titer, acidic isoelectric point, and the lack of well-defined secondary and tertiary structure were some of the challenges that complicated purification development of OPN from recombinant Escherichia coli lysates. Reported processes for OPN recovery from recombinant sources use nonorthogonal unit operations and often suffer from low yield. In this work, we expanded the search for an optimal OPN purification method by including mixed-modal resins with both ionic and hydrophobic properties (Capto adhere, HEA HyperCel, and PPA HyperCel). Plate-based high-throughput screening (HTS) platform revealed useful information about the interactions between the three different ligands and OPN as function of pH and ionic strength. The HTS data allowed the selection of OPN adsorption and elution conditions that were tested and optimized in a batch mode. In terms of purification factor and yield, HEA HyperCel performed significantly better than the other two mixed-modal resins. Pairing HEA HyperCel with a strong anion exchange step (Capto Q) resulted in a two-step purification process that achieved 45-fold purification of OPN with a final purity of 95% and 44% overall yield. The orthogonality provided by mixed-modal and ion exchange steps resulted in higher yield in fewer unit operations than reported processes. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 35: e2722, 2019.