SpeB proteolysis with imaged capillary isoelectric focusing for the characterization of domain-specific charge heterogeneities of reference and biosimilar Rituximab

Development of a platform method for rapid detection and characterization of domain-specific post-translational modifications in bispecific antibodies

Charge heterogeneity is inherent to all therapeutic antibodies and arises from post-translational modifications (PTMs) and/or protein degradation events that may occur during manufacturing. Among therapeutic antibodies, the bispecific antibody (bsAb) containing two unique Fab arms directed against two different targets presents an additional layer of complexity to the charge profile. In the context of a bsAb, a single domain-specific PTM within one of the Fab domains may be sufficient to compromise target binding and could potentially impact the stability, safety, potency, and efficacy of the drug product. Therefore, characterization and routine monitoring of domain-specific modifications is critical to ensure the quality of therapeutic bispecific antibody products. We developed a Digestion-assisted imaged Capillary isoElectric focusing (DiCE) method to detect and quantitate domain-specific charge variants of therapeutic bispecific antibodies (bsAbs). The method involves enzymatic digestion using immunoglobulin G (IgG)-degrading enzyme of S. pyogenes (IdeS) to generate F(ab)2 and Fc fragments, followed by imaged capillary isoelectric focusing (icIEF) under reduced, denaturing conditions to separate the light chains (LCs) from the Fd domains. Our results suggest that DiCE is a highly sensitive method that is capable of quantitating domain-specific PTMs of a bsAb. In one case study, DiCE was used to quantitate unprocessed C-terminal lysine and site-specific glycation of Lys98 in the complementarity-determining region (CDR) of a bsAb that could not be accurately quantitated using conventional, platform-based charge variant analysis, such as intact icIEF. Quantitation of these PTMs by DiCE was comparable to results from peptide mapping, demonstrating that DiCE is a valuable orthogonal method for ensuring product quality. This method may also have potential applications for characterizing fusion proteins, antibody-drug conjugates, and co-formulated antibody cocktails.

Proteolytic Profiling of Streptococcal Pyrogenic Exotoxin B (SpeB) by Complementary HPLC-MS Approaches

Streptococcal pyrogenic exotoxin B (SpeB) is a cysteine protease expressed during group A streptococcal infection that represents a major virulence factor. Although subject to several studies, its role during infection is still under debate, and its proteolytic properties remain insufficiently characterized. Here, we revisited this protease through a set of complementary approaches relying on state of-the-art HPLC-MS methods. After conceiving an efficient protocol to recombinantly express SpeB, the zymogen of the protease and its activation were characterized. Employing proteome-derived peptide libraries, a strong preference for hydrophobic and aromatic residues at P2 alongside negatively charged amino acids at P3′ to P6′ was revealed. To identify relevant in vivo substrates, native proteins were obtained from monocytic secretome and plasma to assess their cleavage under physiological conditions. Besides corroborating our findings concerning specificity, more than 200 cleaved proteins were identified, including proteins of the extracellular matrix, proteins of the immune system, and proteins involved in inflammation. Finally, the cleavage of IgG subclasses was studied in detail. This study precisely depicts the proteolytic properties of SpeB and provides a library of potential host substrates, including their exact cleavage positions, as a valuable source for further research to unravel the role of SpeB during streptococcal infection.

Applications of capillary electrophoresis for biopharmaceutical product characterization

Capillary electrophoresis (CE), after being introduced several decades ago, has carved out a niche for itself in the field of analytical characterization of biopharmaceutical products. It does not only offer fast separation, high resolution in miniaturized format, but equally importantly represents an orthogonal separation mechanism to high-performance liquid chromatography. Therefore, it is not surprising that CE-based methods can be found in all major pharmacopoeias and are recommended for the analysis of biopharmaceutical products during process development, characterization, quality control, and release testing. Different separation formats of CE, such as capillary gel electrophoresis, capillary isoelectric focusing, and capillary zone electrophoresis are widely used for size and charge heterogeneity characterization as well as purity and stability testing of therapeutic proteins. Hyphenation of CE with MS is emerging as a promising bioanalytical tool to assess the primary structure of therapeutic proteins along with any impurities. In this review, we confer the latest developments in capillary electrophoresis, used for the characterization of critical quality attributes of biopharmaceutical products covering the past 6 years (2015-2021). Monoclonal antibodies, due to their significant share in the market, have been given prioritized coverage.

Simultaneous Monitoring of Monoclonal Antibody Variants by Strong Cation-Exchange Chromatography Hyphenated to Mass Spectrometry to Assess Quality Attributes of Rituximab-Based Biotherapeutics

Different manufacturing processes and storage conditions of biotherapeutics can lead to a significant variability in drug products arising from chemical and enzymatic post-translational modifications (PTMs), resulting in the co-existence of a plethora of proteoforms with different physicochemical properties. To unravel the heterogeneity of these proteoforms, novel approaches employing strong cation-exchange (SCX) high-performance liquid chromatography (HPLC) hyphenated to mass spectrometry (MS) using a pH gradient of volatile salts have been developed in recent years. Here, we apply an established SCX-HPLC-MS method to characterize and compare two rituximab-based biotherapeutics, the originator MabThera® and its Indian copy product Reditux™. The study assessed molecular differences between the two drug products in terms of C-terminal lysine variants, glycosylation patterns, and other basic and acidic variants. Overall, MabThera® and Reditux™ displayed differences at the molecular level. MabThera® showed a higher degree of galactosylated and sialylated glycoforms, while Reditux™ showed increased levels of oligomannose and afucosylated glycoforms. Moreover, the two drug products showed differences in terms of basic variants such as C-terminal lysine and N-terminal truncation, present in Reditux™ but not in MabThera®. This study demonstrates the capability of this fast SCX-HPLC-MS approach to compare different drug products and simultaneously assess some of their quality attributes.

Rituximab in combination with cyclophosphamide, doxorubicin, vincristine, and prednisone (R-CHOP) in diffuse large B-cell lymphoma

Background

Diffuse large B-cell lymphoma (DLBCL) is the most frequent non-Hodgkin lymphoma worldwide. The current standard of care is chemoimmunotherapy with an R-CHOP regimen. We aim to review the role of this regimen after two decades of being the standard of care.

Methods

A comprehensive literature review of DLBCL, including the epidemiology, trials defining R-CHOP as the standard of care, as well as dose intensification and dose reduction schemes. Additionally, we briefly review the development of rituximab biosimilars and the addition of targeted drugs to R-CHOP in clinical trials.

Discussion

R-CHOP cures approximately 70% of DLBCL patients. Dose-dense regimens do not show a benefit in response and increase toxicity. Dose reduction, particularly in elderly patients or with comorbidities, may be a treatment option. DLBCL constitutes a group of diseases that activate different biological pathways. Matching specific treatments to a defined genetic alteration is under development. Rituximab biosimilars have become available to a broader population, particularly in developing countries, where access to treatment is limited because of economic resources.

Conclusion

DLBCL landscape is heterogeneous. R-CHOP immunochemotherapy has been a standard of care for two decades and cures approximately 70% of cases. Molecular characterization of patients is evolving and may have critical therapeutic implications.

Analysis of Monoclonal Antibodies by Capillary Electrophoresis: Sample Preparation, Separation, and Detection

Therapeutic monoclonal antibodies (mAbs) are dominating the biopharmaceutical field due to the fact of their high specificity in the treatment of diverse diseases. Nevertheless, mAbs are very complex glycoproteins exhibiting several macro- and microheterogeneities that may affect their safety, quality, and efficacy. This complexity is very challenging for mAbs development, formulation, and quality control. To tackle the quality issue, a combination of multiple analytical approaches is necessary. In this perspective, capillary electrophoresis has gained considerable interest over the last decade due to the fact of its complementary features to chromatographic approaches. This review provides an overview of the strategies of mAbs and derivatives analysis by capillary electrophoresis hyphenated to ultraviolet, fluorescence, and mass spectrometry detection. The main sample preparation approaches used for mAb analytical characterization (i.e., intact, middle-up/down, and bottom-up) are detailed. The different electrophoretic modes used as well as integrated analysis approaches (sample preparation and separation) are critically discussed.

Intact and middle-down CIEF of commercial therapeutic monoclonal antibody products under non-denaturing conditions

A two‐step CIEF with chemical mobilization was developed for charge profiling of the therapeutic mAb rituximab under non‐denaturing separation conditions. CIEF of the intact mAb was combined with a middle‐down approach analyzing Fc/2 and F(ab´)₂ fragments after digest with a commercial cysteine protease (IdeS). CIEF methods were optimized separately for the intact mAb and its fragments due to their divergent pIs. Best resolution was achieved by combining Pharmalyte (PL) 8–10.5 with PL 3–10 for variants of intact rituximab and of F(ab´)₂ fragments, respectively, whereas PL 6.7–7.7 in combination with PL 3–10 was used for Fc/2 variants. Charge heterogeneity in Fc/2 dominates over F(ab´)₂. In addition, a copy product of rituximab, and adalimumab were analyzed. Both mAbs contain additional alkaline C‐terminal lysine variants as confirmed by digest with carboxypeptidase B. The optimized CIEF methods for intact mAb and Fc/2 were tested for their potential as platform approaches for these mAbs. The CIEF method for Fc/2 was slightly adapted in this process. The pI values for major intact mAb variants were determined by adjacent pI markers resulting in 9.29 (rituximab) and 8.42 (adalimumab). In total, seven to eight charge variants could be distinguished for intact adalimumab and rituximab, respectively.

Rituximab biosimilars for lymphoma in Europe

Introduction: The approval of rituximab, a monoclonal antibody targeting CD20, revolutionized the treatment of B-cell non-Hodgkin lymphomas and became an undisputed standard of care. However, as with all biologic medicines, the complex development and manufacturing process for rituximab have meant that the medicine attracts high treatment costs. Approved rituximab biosimilars have been comprehensively demonstrated to match the reference medicine. With the potential to increase access to biologic therapy, they have a key role in helping to improve patient outcomes in lymphoma care. Areas covered: In this review, we discuss the role of rituximab in the treatment of lymphoma. We explore development and regulatory requirements for biosimilar development and the potential impact of these medicines on access and sustainability. Focusing on biosimilars of rituximab, we examine in detail the evidence for biosimilarity for the two rituximab biosimilars that are approved in Europe and provide an overview of rituximab biosimilars currently in development. Expert opinion: We foresee a wider uptake of biosimilar medicines for lymphoma treatment over the next 5 years. The associated cost savings should be invested in broadening patient access to biological therapies, enabling wider use of more expensive treatment strategies and driving innovation in cancer care.

Proteoform-Resolved FcɤRIIIa Binding Assay for Fab Glycosylated Monoclonal Antibodies Achieved by Affinity Chromatography Mass Spectrometry of Fc Moieties

Fcɤ receptors (FcɤR) mediate key functions in immunological responses. For instance, FcɤRIIIa is involved in antibody-dependent cell-mediated cytotoxicity (ADCC). FcɤRIIIa interacts with the fragment crystallizable (Fc) of immunoglobulin G (IgG). This interaction is known to be highly dependent on IgG Fc glycosylation. Thus, the impact of glycosylation features on this interaction has been investigated in several studies by numerous analytical and biochemical techniques. FcɤRIIIa affinity chromatography (AC) hyphenated to mass spectrometry (MS) is a powerful tool to address co-occurring Fc glycosylation heterogeneity of monoclonal antibodies (mAbs). However, MS analysis of mAbs at the intact level may provide limited proteoform resolution, for example, when additional heterogeneity is present, such as antigen-binding fragment (Fab) glycosylation. Therefore, we investigated middle-up approaches to remove the Fab and performed AC-MS on the IgG Fc to evaluate its utility for FcɤRIIIa affinity assessment compared to intact IgG analysis. We found the protease Kgp to be particularly suitable for a middle-up FcɤRIIIa AC-MS workflow as demonstrated for the Fab glycosylated cetuximab. The complexity of the mass spectra of Kgp digested cetuximab was significantly reduced compared to the intact level while affinity was fully retained. This enabled a reliable assignment and relative quantitation of Fc glycoforms in FcɤRIIIa AC-MS. In conclusion, our workflow allows a functional separation of differentially glycosylated IgG Fc. Consequently, applicability of FcɤRIIIa AC-MS is extended to Fab glycosylated IgG, i.e., cetuximab, by significantly reducing ambiguities in glycoform assignment vs. intact analysis.

A three-point identity criteria tool for establishing product identity using icIEF method

Product identity is one of the release testing requirements that needs to be established to ensure that there is no misidentification of drugs. Here, we demonstrated the challenges that can come across while establishing a product identity method for monoclonal antibody (mAb) and mAb-related products using icIEF method. A unique three-point identity criteria tool (visual comparison, pI of individual peaks and ΔpIs) was applied to distinguish mAb1 from the other in-house mAbs. A reduction approach followed by icIEF showed higher potential for establishing identity for mAb1 product as compared to native and enzymatic digestion approach. In general, icIEF method lacks specificity required to unequivocally establish the identity for mAbs, therefore, risk analysis is recommended before implementing icIEF as a stand-alone identity method for monoclonal antibodies.