Mara Rossi

Degradation of an Fc-Fusion Recombinant Protein by Host Cell Proteases: Identification of a CHO Cathepsin D Protease

A host‐cell‐related proteolytic activity was identified in a recombinant Fc‐fusion protein production process. This report describes the strategy applied to characterize and isolate the enzyme responsible for this degradation by combining cell culture investigation and dedicated analytical tools. After isolation and sequencing of the clipped fragment generated in post‐capture material, enzymatic activity was traced in different culture conditions, allowing identification of viable CHO cells as the source of protease. Inhibitors and pH screenings showed that the enzyme belongs to an aspartic protease family and is preferably active at acidic pH. The protease was isolated by purification on a pepstatin A column and characterized as a protein related to cathepsin D. An additional metallo‐protease inhibited by EDTA was identified with an optimum activity at neutral pH. This study is an example of how quality and stability of therapeutic recombinant molecules are strongly influenced by cell culture parameters. Biotechnol. Bioeng. 2009; 104: 1132–1141.

High resolution TOF MS coupled to CE for the analysis of isotopically resolved intact proteins

Intact protein analysis by mass spectrometry is of great interest for the characterisation of biotechnological products. Exact mass measurement in combination with isotopic resolution allows the detection of modifications leading to small mass changes like deamidation or reduction of disulfide bonds directly on the level of the intact protein. Here, a concept is presented based on time-of-flight mass spectrometry. A bench top TOF MS and a high resolution TOF MS were used to resolve the isotopes of intact recombinant human growth hormone and intact human erythropoietin, respectively. Thus, these 22 and around 30kDa large proteins can be characterised sensitively in great detail and along with capillary electrophoretic separation unambiguous identification of minor protein modifications like deamidation is possible.

Subvisible (2–100 μm) Particle Analysis During Biotherapeutic Drug Product Development: Part 1, Considerations and Strategy

Measurement and characterization of subvisible particles (defined here as those ranging in size from 2 to 100 μm), including proteinaceous and nonproteinaceous particles, is an important part of every stage of protein therapeutic development. The tools used and the ways in which the information generated is applied depends on the particular product development stage, the amount of material, and the time available for the analysis. In order to compare results across laboratories and products, it is important to harmonize nomenclature, experimental protocols, data analysis, and interpretation. In this manuscript on perspectives on subvisible particles in protein therapeutic drug products, we focus on the tools available for detection, characterization, and quantification of these species and the strategy around their application.

Characterisation of a novel growth hormone variant comprising a thioether link between Cys182 and Cys189.

A novel variant of recombinant human growth hormone (r‐hGH), isolated from biopharmaceutical preparations produced in E. coli, was identified and characterised. This variant contains a nonreducible thioether bridge near the C terminus between Cys182 and Cys189 and was characterised using various analytical techniques. As previous work by Cunningham and Wells (1993) highlighted the involvement of several residues in this part of the sequence in the binding and affinity of the molecule to its receptor, the presence of this modified intramolecular link may have important implications with regard to the biological behaviour of the molecule. Furthermore, as the conversion of a disulfide into a thioether was previously reported for a therapeutic monoclonal antibody (Tous et al., 2005), this may imply that disulfide bridges located in this part of the molecule have a generic susceptibility to thioether formation. This in turn is relevant to the biopharmaceutical industry for monitoring the integrity of disulfide bridges near the protein C terminus. The present study exhibits a state of the art physicochemical investigation for the unequivocal elucidation of a novel structure involving peptide mapping with mass spectrometry and de novo peptide sequencing. Changes in the higher order structure of the molecule were highlighted by near UV circular dichroism and molecular modelling.

Subvisible (2–100 μm) particle analysis during biotherapeutic drug product development: Part 2, experience with the application of subvisible particle analysis

Measurement and characterization of subvisible particles (including proteinaceous and non-proteinaceous particulate matter) is an important aspect of the pharmaceutical development process for biotherapeutics. Health authorities have increased expectations for subvisible particle data beyond criteria specified in the pharmacopeia and covering a wider size range. In addition, subvisible particle data is being requested for samples exposed to various stress conditions and to support process/product changes. Consequently, subvisible particle analysis has expanded beyond routine testing of finished dosage forms using traditional compendial methods. Over the past decade, advances have been made in the detection and understanding of subvisible particle formation. This article presents industry case studies to illustrate the implementation of strategies for subvisible particle analysis as a characterization tool to assess the nature of the particulate matter and applications in drug product development, stability studies and post-marketing changes.

Heterogeneity of commercial recombinant human growth hormone (r-hGH) preparations containing a thioether variant

The objective of the present study was to assess (I) the potential presence of a recently discovered thioether variant in commercially available recombinant human growth hormone (r-hGH) preparations, and (II) the impact of the thioether modification on the in-vivo bioactivity and the receptor binding kinetics. Samples were tested employing European (EP) and US Pharmacopeia (USP) Somatropin monograph and mass spectrometry methods. None of the international standards contained this variant. All products conformed to EP specifications but six out of eight lots contained the variant. An artificially enriched thioether sample exhibited a significantly reduced in vivo biopotency and altered receptor-binding properties compared with a control. The absence of the variant in the pituitary hGH standard, and the possibility to generate it artificially suggests that it is not naturally occurring and that it may arise from an uncontrolled manufacturing process. Controlled studies may be required to assess its clinical efficacy and safety. EP and USP methods may need to be adapted to reliably detect the presence of the variant.

Reciprocal Translocation Observed in End-of-Production Cells of a Commercial CHO-Based Process.

During the validation of an additional working cell bank derived from a validated master cell bank to support the commercial production continuum of a recombinant protein, we observed an unexpected chromosomal location of the gene of interest in some end-of-production cells. This event—identified by fluorescence in situ hybridization and multicolour chromosome painting as a reciprocal translocation involving a chromosome region containing the gene of interest with its integral coding and flanking sequences—was unique, occurred probably during or prior to multicolour chromosome painting establishment, and was transmitted to the descending generations. Cells bearing the translocation had a transient and process-independent selective advantage, which did not affect process performance and product quality. However, this first report of a translocation affecting the gene of interest location in Chinese Hamster Ovary cells used for producing a biotherapeutic indicates the importance of the demonstration of the integrity of the gene of interest in end-of-production cells. LAY ABSTRACT: The expression of recombinant therapeutic proteins in mammalian cells depends on the establishment of a cell line with the gene of interest integrated in the host genome and stably expressed over time. Before being used for commercial production, cell lines are submitted to a qualification program in order to ensure their phenotypic and genotypic characteristics and the efficacy and safety of the product. During the production life cycle of a therapeutic protein, additional cells banks have to be validated after exhaustion of the current qualified cell bank in order to support the commercial production continuum of the recombinant protein. It is during the validation of an additional working cell bank derived from a validated master cell bank that we detected a different chromosome bearing the gene of interest in a portion of cells at the end of the upstream production phase. In our case, this event did not affect the process performance, the product quality, or its safety profile, but it highlights the need to characterize the integrity of the gene of interest in end-of-production cells when producing recombinant proteins for human use.

In vitro biological characterization of IFN-β-1a major glycoforms

Recombinant human interferon β-1a (IFN-β-1a) is extensively used as the first-line treatment of relapsing forms of multiple sclerosis. Its glycosylation is recognized as having a complex impact on a wide range of molecule characteristics and functions. The present study reports the enrichment of IFN-β-1a glycoforms and their physicochemical and biological characterization by means of electrospray ionization-mass spectrometry, sialic acid content, thermal denaturation and various in vitro bioassays (antiproliferative, antiviral, immunomodulatory and reporter gene assay). The glycoforms were fractionated by means of cation-exchange chromatography using recombinant IFN-β-1a derived from Chinese Hamster Ovary cell culture as starting material. The obtained fractions contained bi- and higher-antennarity glycans as described in the European Pharmacopoeia monograph (Nr. 1639E, Interferon beta 1a concentrated solution). The in vitro bioassay responses revealed a correlation mainly with the glycan antennarity. It is therefore suggested that all glycoforms have biological activity and play a role in modulating the overall IFN-β biological activity with higher-antennarity glycoforms being able to better sustain IFN-β-1a bioactivity over time. These data indicate the role of IFN-β-1a glycosylation in vivo and shed new light on the role of the glycosylation heterogeneity, in particular with regard to antennarity, on biological properties of glycoproteins.

A deamidated interferon-β variant binds to integrin αvβ3

HIGHLIGHTSInterferon‐beta contains a sequence motif prone to deamidation.Deamidation generates the DGR and iso‐DGR motifs.Deamidated interferon‐beta binds integrin &agr;v&bgr;3 with nanomolar affinity. ABSTRACT Human type I interferons are a family of pleiotropic cytokines with antiviral, anti‐proliferative and immunomodulatory activities. They signal through the same cell surface receptors IFNAR1 and IFNAR2 yet evoking markedly different physiological effects. One differentiating factor of interferon‐beta (IFN‐&bgr;) from other type I interferons is the presence of the Asn‐Gly‐Arg (NGR) sequence motif, which, upon deamidation, converts to Asp‐Gly‐Arg (DGR) and iso‐Asp‐Gly‐Arg (iso‐DGR) motifs. In other proteins, the NGR and iso‐DGR motifs are reported as CD13‐ and &agr;v&bgr;3, &agr;v&bgr;5, &agr;v&bgr;6, &agr;v&bgr;8 and &agr;5&bgr;1 integrin‐binding motifs, respectively. The scope of this study was to perform exploratory surface plasmon resonance (SPR) experiments to assess the binding properties of a deamidated IFN‐&bgr; variant to integrins. For this purpose, integrin &agr;v&bgr;3 was selected as a reference model within the iso‐DGR‐ integrin binding members. The obtained results show that deamidated IFN‐&bgr; binds integrin &agr;v&bgr;3 with nanomolar affinity and that the response was dependent on the deamidation extent. Based on these results, it can be expected that deamidated IFN‐&bgr; also binds to other integrin family members that are able to bind to the iso‐DGR binding motif. The novel binding properties could help elucidate specific IFN‐&bgr; attributes that under physiological conditions may be modulated by the deamidation.