Quantitative analysis of monoclonal antibodies by cation-exchange chromatofocusing

Separation of charge variants of a monoclonal antibody by overloaded ion exchange chromatography

A procedure for adjusting the content of charge variants of monoclonal antibody by ion exchange chromatography has been developed. The band splitting phenomenon was utilized to split the protein load into two parts, i.e., the flowthrough and bound fractions, which were either enriched or depleted with some of variants. The phenomenon was triggered by thermodynamic effects resulting from oversaturation of the resin binding sites at high column loadings as well as from kinetic effects arising from limited rates of mass transport. Cation exchange chromatography (CEX) and anion exchange chromatography (AEX) separations were examined, with the reverse order of the variant elution: acidic, main, basic in CEX, and basic, main, acidic in AEX, and the corresponding reverse enrichment tendency in the collected fractions. The separations were performed by pH gradient, whose course was simplified to two stages: isocratic loading and washing at mild pH to load and partly elute the protein, followed by a rapid pH change towards non-binding conditions to desorb the remains of the protein load. To improve yield of the operation, possibility of recycling of waste fractions was considered. To predict the process performance, a dynamic model was developed, which accounted for both adsorption kinetics and thermodynamics.

A case study of the mechanism of unfolding and aggregation of a monoclonal antibody in ion exchange chromatography

A mechanistic model for describing unfolding of a monoclonal antibody (mAb) in ion exchange chromatography has been developed. The model reproduced retention behavior characteristic for conformational changes of antibodies upon adsorption, including: multi-peak elution, aggregate formation, and recovery reduction. Two competitive paths in the adsorption mechanism of the unfolded protein were assumed: refolding in the adsorbed phase to the native form followed by its desorption, or direct desorption followed by instantaneous aggregation in the liquid phase. The reduction in recovery of the eluted protein was attributed to spreading of the unfolded protein on the adsorbent surface, which enhanced the binding affinity. The model was formulated based on the analysis of retention behavior of a model mAb that was eluted in pH gradients on a strong cation exchange resin. The pH profile was found to be distorted in the presence of the protein, which was ascribed to dissociation of ionizable groups of the protein in the adsorbed phase. Since the protein retention was strongly pH dependent, that phenomenon was also accounted for in mathematical modeling. A series of independent experiments was designed to evaluate the model parameters that quantified the process thermodynamics and kinetics: the Henry constants of the native, unfolded, spread and aggregated forms of the protein along with underlying kinetic coefficients. The model was efficient in reproducing the retention pattern of the protein and the aggregate content in eluting band profiles. After proper calibration, the model can potentially be used to quantify protein unfolding and elution in other ion exchange systems.

Performance Comparison of a Laterally-Fed Membrane Chromatography (LFMC) Device with a Commercial Resin Packed Column

The use of conventional membrane adsorbers such as radial flow devices is largely restricted to flow-through applications, such as virus and endotoxin removal, as they fail to give acceptable resolution in bind-and-elute separations. Laterally-fed membrane chromatography or LFMC devices have been specifically developed to combine high-speed with high-resolution. In this study, an LFMC device containing a stack of strong cation exchange membranes was compared with an equivalent resin packed column. Preliminary characterization experiments showed that the LFMC device had a significantly greater number of theoretical plates per metre than the column. These devices were used to separate a ternary model protein mixture consisting of ovalbumin, conalbumin and lysozyme. The resolution obtained with the LFMC device was better than that obtained with the column. For instance, the LFMC device could resolve lysozyme dimer from lysozyme monomer, which was not possible using the column. In addition, the LFMC device could be operated at lower pressure and at significantly higher flow rates. The devices were then compared based on an application case study, i.e., preparative separation of monoclonal antibody charge variants. The LFMC device gave significantly better separation of these variants than the column.

Advances in liquid formulations of parenteral therapeutic proteins

Liquid formulation of therapeutic proteins is a maturing technology. Demand for products that are easy to use in the clinic or that are amenable to self-administration make a ready to use liquid formulation desirable. Most modern liquid formulations have a simple composition; comprising a buffer, a tonicity modifier, a surfactant, sometimes a stabiliser, the therapeutic protein and water. Recent formulations of monoclonal antibodies often use histidine or acetate as the buffer, sucrose or trehalose as the tonicity modifier and polysorbate 20 or 80 as the surfactant with a pH of 5.7 +/- 0.4. The mechanisms for the behaviour of excipients is still debated by academics so formulation design is still a black art. Fortunately, a statistical approach like design of experiment is suitable for formulation development and has been successful when combined with accelerated stability experimentation. The development of prefilled syringes and pens has added low viscosity and shear resistance to the quality attributes for a successful formulation. To achieve patient compliance for self-administration, formulations that cause minimal pain and tissue damage is also desirable.

Microheterogeneity of therapeutic monoclonal antibodies is governed by changes in the surface charge of the protein

It has previously been shown for individual antibodies, that the microheterogenity pattern can have a significant impact on various key characteristics of the product. The aim of this study to get a more generalized understanding of the importance of microheterogeneity. For that purpose, the charge variant pattern of various different commercially available therapeutic mAb products was compared using Cation-Exchange Chromatography with linear pH gradient antigen affinity, Fc-receptor affinity, antibody dependent cellular cytotoxicity (ADCC) and conformational stability. For three of the investigated antibodies, the basic charge variants showed a stronger binding affinity towards FcγRIIIa as well as an increased ADCC response. Differences in the conformational stability of antibody charge variants and the corresponding reference samples could not be detected by differential scanning calorimetry. The different biological properties of the mAb variants are therefore governed by changes in the surface charge of the protein and not by an altered structure. This can help to identify aspects of microheterogeneity that are critical for product quality and can lead to further improvements in the development and production of therapeutic antibody products.

Computer assisted liquid chromatographic method development for the separation of therapeutic proteins

This review summarizes the use of computer assisted liquid chromatographic method development for the analytical characterization of protein biopharmaceuticals.

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.

Highly linear pH gradients for analyzing monoclonal antibody charge heterogeneity in the alkaline range: Validation of the method parameters

Cation exchange chromatography has been routinely used for the quantification of monoclonal antibody (mAb) charge heterogeneity. A previously developed method utilizing pH gradients for the elution instead of salt gradients was validated according to current guidelines proposed by the ICH. The linearity, stability, accuracy, precision and the lower limit of quantification have been determined, using pure charge variant standards. The method is valid for the quantification of mAb samples with a charge heterogeneity between 1% and 50%. Three different approaches to obtaining pure standard material for the validation of bio-analytical methods for the quantification of charge heterogeneity of IgG are presented. These methods are based on salt gradient elution, pH gradient elution and displacement in cation exchange chromatography.

Ion exchange-high-performance liquid chromatography (IEX-HPLC)

The ion exchange-high-performance liquid chromatography is a high-throughput analytical method that allows to determine the charge profile of purified antibodies. Here, we describe the preparation of the samples, chromatographic conditions to be used (buffer preparation, salt gradient, quantity injected, flow rate, run time, column suitability, etc.), validity of the analysis, and integration of the chromatogram in order to calculate the proportion of the different isoforms.

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.

Electrostatic interactions of monoclonal antibodies with subcutaneous tissue

AIM

The majority of the subcutaneously injected monoclonal antibodies already on the market achieve 50-65% bioavailability, yet the fate of the portion that is lost remains unknown. This consistently incomplete systemic absorption affects the efficacy, safety and overall cost of the drug product. There are many potential factors that might influence the absorption, such as charge, hydrophobicity, formulation variables and the depth and volume of the injection.

MATERIALS & METHODS

To explore the possibility that the charge of the injected protein and/or formulation components is partially responsible for drug retention at the subcutaneous site, an ex vivo study, where the monoclonal antibodies were exposed to homogenized rat subcutaneous tissue, was performed.

RESULTS & CONCLUSION

It was found that positively charged monoclonal antibodies bind to subcutaneous tissue in a manner that is dependent on ionic strength and pH, suggesting the electrostatic nature of the interaction. As expected, saturation of both nonspecific and electrostatic subcutaneous binding sites was observed after incubation with highly concentrated monoclonal antibody solutions. Additionally, it was demonstrated using model proteins that electrostatic effects of buffer components depend on ionic strength of ions bearing opposite charge rather than total ionic strength of the solution. These results suggest that electrostatic interactions may play a role in absorption processes of positively charged therapeutic proteins after subcutaneous administration.