Monoclonal antibody heterogeneity analysis and deamidation monitoring with high-performance cation-exchange chromatofocusing using simple, two component buffer systems

Ultra-short ion-exchange columns for fast charge variants analysis of therapeutic proteins

The purpose of this work was to study the potential of recently developed ultra-short column hardware for ion exchange chromatography (IEX). Various prototype and commercial columns having lengths of 5, 10, 15, 20 and 50 mm and packed with non-porous 3 µm particles were systematically compared. Both pH and salt gradient modes of elution were evaluated. Similarly, what has been previously reported for reversed phase liquid chromatography (RPLC) mode, an "on-off" retention mechanism was observed in IEX for therapeutic proteins and their fragments (25-150 kDa range). Because of the non-porous nature of the IEX packing material, the column porosity was relatively low (ε = 0.42) and therefore the volumes of ultra-short columns were very small. Based on this observation, it was important to reduce as much as possible all the sources of extra-column volumes (i.e. injection volume, extra-bed volume, detector cell volume and connector tubing volume), to limit peak broadening. With a fully optimized UHPLC system, very fast separations of intact and IdeS digested mAb products were successfully performed in about 1 min using an IEX column with dimensions of 15 × 2.1 mm. This column was selected for high-throughput separations, since it probably offers the best compromise between efficiency and analysis time. For such ultra-fast separations, PEEK tubing was applied to bypass the column oven (column directly connected) to the optical detector via a zero dead volume connection.

Characterization of therapeutic proteins by cation exchange chromatography-mass spectrometry and top-down analysis

Recently, cation exchange chromatography (CEX) using aqueous volatile buffers was directly coupled with mass spectrometry (MS) and applied for intact analysis of therapeutic proteins and antibodies. In our study, chemical modifications responsible for charge variants were identified by CEX-UV-MS for a monoclonal antibody (mAb), a bispecific antibody, and an Fc-fusion protein. We also report post-CEX column addition of organic solvent and acid followed by mixing at elevated temperatures, which unfolded proteins, increased ion intensity (sensitivity) and facilitated top-down analysis. mAb stressed by hydrogen peroxide oxidation was used as a model system, which produced additional CEX peaks. The on-line CEX-UV-MS top-down analysis produced gas-phase fragments containing one or two methionine residues. Oxidation of some methionine residues contributed to earlier (acidic), some to later (basic) eluting peaks, while oxidation of other residues did not change CEX elution. The abundance of the oxidized and non-oxidized fragment ions also allowed estimation of the oxidation percentage of different methionine residues in stressed mAb. CEX-UV-MS measurement revealed a new intact antibody proteoform at 5% that eluted as a basic peak and included paired modifications: high-mannose glycosylation and remaining C-terminal lysine residue (M5/M5 + K). This finding was confirmed by peptide mapping and on-column disulfide reduction coupled with reversed-phase liquid chromatography - top-down MS analysis of the collected basic peak. Overall, our results demonstrate the utility of the on-line method in providing site-specific structural information of charge modifications without fraction collection and laborious peptide mapping.

Recent advancements, challenges, and practical considerations in the mass spectrometry-based analytics of protein biotherapeutics: A viewpoint from the biosimilar industry

The extensive analytical characterization of protein biotherapeutics, especially of biosimilars, is a critical part of the product development and registration. High-resolution mass spectrometry became the primary analytical tool used for the structural characterization of biotherapeutics. Its high instrumental sensitivity and methodological versatility made it possible to use this technique to characterize both the primary and higher-order structure of these proteins. However, even by using high-end instrumentation, analysts face several challenges with regard to how to cope with industrial and regulatory requirements, that is, how to obtain accurate and reliable analytical data in a time- and cost-efficient way. New sample preparation approaches, measurement techniques and data evaluation strategies are available to meet those requirements. The practical considerations of these methods are discussed in the present review article focusing on hot topics, such as reliable and efficient sequencing strategies, minimization of artefact formation during sample preparation, quantitative peptide mapping, the potential of multi-attribute methodology, the increasing role of mass spectrometry in higher-order structure characterization and the challenges of MS-based identification of host cell proteins. On the basis of the opportunities in new instrumental techniques, methodological advancements and software-driven data evaluation approaches, for the future one can envision an even wider application area for mass spectrometry in the biopharmaceutical industry.

Evaluation of chromatofocusing as a capture method for monoclonal antibody products

Chromatofocusing is investigated as an alternative to protein A chromatography for the initial capture step in a purification process for several monoclonal antibodies and antibody fusion products. For comparison, this work also investigates the use of ion-exchange chromatography with either pH or salt gradient elution as additional alternatives to protein A chromatography. The specific conditions employed for the capture step for the case of chromatofocusing were selected on a rational basis using a computer-aided design method implemented in the form of a Microsoft Excel spreadsheet. Alternative operating conditions were compared experimentally with regard to the product yield achieved as well as the removal of total host cell proteins (HCPs) and of a specific HCP major component. Results from this study indicate that both chromatofocusing and ion-exchange chromatography are useful alternatives to a protein A chromatography capture step in many practical cases. This is especially true for the case of chromatofocusing when it is possible to exploit the ability of the method to create complex gradient shapes that are self-forming inside the column and to simultaneous focus and separate proteins inside the column.

Role of Buffers in Protein Formulations

Buffers comprise an integral component of protein formulations. Not only do they function to regulate shifts in pH, they also can stabilize proteins by a variety of mechanisms. The ability of buffers to stabilize therapeutic proteins whether in liquid formulations, frozen solutions, or the solid state is highlighted in this review. Addition of buffers can result in increased conformational stability of proteins, whether by ligand binding or by an excluded solute mechanism. In addition, they can alter the colloidal stability of proteins and modulate interfacial damage. Buffers can also lead to destabilization of proteins, and the stability of buffers themselves is presented. Furthermore, the potential safety and toxicity issues of buffers are discussed, with a special emphasis on the influence of buffers on the perceived pain upon injection. Finally, the interaction of buffers with other excipients is examined.

Oxidation in the complementarity-determining regions differentially influences the properties of therapeutic antibodies

Therapeutic antibodies can undergo a variety of chemical modification reactions in vitro. Depending on the site of modification, either antigen binding or Fc-mediated functions can be affected. Oxidation of tryptophan residues is one of the post-translational modifications leading to altered antibody functionality. In this study, we examined the structural and functional properties of a therapeutic antibody construct and 2 affinity matured variants thereof. Two of the 3 antibodies carry an oxidation-prone tryptophan residue in the complementarity-determining region of the V_L domain. We demonstrate the differences in the stability and bioactivity of the 3 antibodies, and reveal differential degradation pathways for the antibodies susceptible to oxidation.

Ion-exchange chromatography for the characterization of biopharmaceuticals

Ion-exchange chromatography (IEX) is a historical technique widely used for the detailed characterization of therapeutic proteins and can be considered as a reference and powerful technique for the qualitative and quantitative evaluation of charge heterogeneity. The goal of this review is to provide an overview of theoretical and practical aspects of modern IEX applied for the characterization of therapeutic proteins including monoclonal antibodies (Mabs) and antibody drug conjugates (ADCs). The section on method development describes how to select a suitable stationary phase chemistry and dimensions, the mobile phase conditions (pH, nature and concentration of salt), as well as the temperature and flow rate, considering proteins isoelectric point (pI). In addition, both salt-gradient and pH-gradient approaches were critically reviewed and benefits as well as limitations of these two strategies were provided. Finally, several applications, mostly from pharmaceutical industries, illustrate the potential of IEX for the characterization of charge variants of various types of biopharmaceutical products.

Detailed mass analysis of structural heterogeneity in monoclonal antibodies using native mass spectrometry

The molecular complexity of biopharmaceuticals puts severe demands on the bioanalytical techniques required for their comprehensive structural characterization. Mass spectrometry (MS) has gained importance in the analysis of biopharmaceuticals, taking different complementary approaches ranging from peptide-based sequencing to direct analysis of intact proteins and protein assemblies. In this protocol, we describe procedures optimized to perform the analysis of monoclonal antibodies (mAbs) at the intact protein level under pseudo-native conditions, using native MS. Some of the strengths of native MS in the analysis of biopharmaceuticals are its analysis speed, sensitivity and specificity: for most experiments, the whole protocol requires one working day, whereby tens of samples can be analyzed in a multiplexed manner, making it suitable for high-throughput analysis. This method can be used for different applications such as the analysis of mixtures of mAbs, drug-antibody conjugates and the analysis of mAb post-translational modifications, including the qualitative and quantitative analysis of mAb glycosylation.

Highly linear pH gradients for analyzing monoclonal antibody charge heterogeneity in the alkaline range

Recombinant antibodies with high isoelectric point are frequent since most of them are constructed from the same framework. Classically, cation exchange chromatography is used as a standard method for the determination of antibody charge heterogeneity. In contrast, in this study highly linear pH gradients were achieved by keeping the buffering capacity over the length of the gradient constant. The buffering compounds were selected to be unretained on the column and their respective concentration was adjusted in the start and end buffer of the pH gradient to achieve constant buffering capacity. This helps conserve linearity and stability of the gradient. The method allows quantification of charge variant distribution and the determination of chromatographic isoelectric point. To demonstrate the effectiveness of this novel method, a ProPac WCX-10 column was used to separate isoforms of trastuzumab biosimilar antibodies. Effects of pH gradient linearity and of varying the analytical amount of sample on the separation are shown.