Study of the primary structure of recombinant tissue plasminogen activator by reversed-phase high-performance liquid chromatographic tryptic mapping

Physico-Chemical and Biological Properties of Biosimilar and Reference Tissue Plasminogen Activator Products

Recombinant tissue plasminogen activator (international nonproprietary name — alteplase) which was developed by «GENERIUM» (Russia) and received a marketing authorisation in Russia is completely analogous to Actilyse® which is used to treat medical conditions accompanied by thrombosis, such as acute myocardial infarction, pulmonary embolism, and ischemic stroke. The aim of the study was to carry out a comprehensive comparison of physico-chemical and biological properties of Revelyse® and the reference product Actilyse® in order to assess their biosimilarity. Materials and Methods: comparative peptide mapping and determination of comparability of chromatographic profiles of tryptic hydrolysates was performed using RP-HPLC and massspectrometry; the molecular weight distribution was determined by mass-spectrometry and polyacrylamide gel electrophoresis (Laemmli method). The purity and homogeneity of products as well as the content of related impurities (oligomers and fragments) were determined using gel filtration; N-glycosylation profile was analysed by hydrophilic HPLC, total sialic acid was quantified by the Svennerholm resorcinol method. Protein binding to fibrin and human fibrinogen was assessed by surface plasmon resonance, and the specific activity was compared by fibrin clot lysis. Results: the research demonstrated a complete overlap of the products’ peptide maps, which indicates the identity of аlteplase amino acid sequences in the two medicines being compared. The authors of the study also determined the molecular weight and the content of the intact single-stranded form of the protein, and quantified post-translational modifications, the content of sialic acids and neutral sugars. The analysis of the N-glycosylation profile revealed insignificant differences in the percentage of multiantenna complex glycans. The specificity of alteplase was evaluated by analysing the formation of protein complexes with natural alteplase ligands – fibrin and plasminogen activator inhibitor-1, but no significant differences were found. The comparison of specific activation of plasminogen fibrinolytic activity was performed based on the results of the assay analysing the fibrin clot lysis rate, and it demonstrated comparability of Revelyse® and Actilyse®. Conclusions: comparative experimental studies have shown no differences in the structure, charge distribution heterogeneity, impurities content, and specific activity of alteplase as a component of Revelyse® and the reference product Actilyse®, which leads to the conclusion that they are similar in terms of physicochemical and biological properties.

Structural and functional characterization of the trifunctional antibody catumaxomab

The Triomab family of trifunctional, bispecific antibodies that maintain an IgG-like shape are novel tumor targeting agents. These chimeras consist of two half antibodies, each with one light and one heavy chain, that originate from parental mouse IgG2a and rat IgG2b isotypes. This combination allows cost-effective biopharmaceutical manufacturing at an industrial scale since this specific mouse/rat isotype combination favors matching of corresponding antibody halves during production by means of quadroma technology. Whereas every Triomab family member is composed of an anti-CD3 rat IgG2b half antibody for T cell recognition, the antigen binding site presented by the mouse IgG2a isotype is exchangeable. Several Triomab antibodies have been generated that bind to tumor-associated antigens, e.g., EpCAM (catumaxomab), HER2/neu (ertumaxomab), CD20 (FBTA05), gangliosides GD2/GD3 (Ektomun), on appropriate tumor target cells associated with carcinomas, lymphomas or melanomas. Catumaxomab (Removab) was launched in Europe for treatment of malignant ascites in April 2009. Here, we report the structural and functional characterization of this product. Mass spectrometry revealed an intact mass of 150511 Dalton (Da) and 23717 Da, 24716 Da, 51957 Da and 52019 Da of the reduced and alkylated rat light chain, mouse light chain, rat heavy chain, mouse heavy chain chains, respectively. The observed masses were in agreement with the expected masses based on the amino acid sequence obtained from cDNA sequencing. The glycosylation profile was similar to other human IgG consisting of biantennary oligosaccharides with different numbers of terminal galactose. CD spectroscopy showed mainly beta-sheets secondary structure that is typical for IgG antibodies. Binding measurement revealed the unique trifunctional features of catumaxomab. Other analytical tools were used to evaluate characteristics of catumaxomab preparations, including the presence of isoforms and aggregates.

Glycation of interferon-beta-1b and human serum albumin in a lyophilized glucose formulation. Part III: application of proteomic analysis to the manufacture of biological drugs

Glycation of interferon-beta-1b and human serum albumin was identified in a lyophilized glucose formulation by a sensitive LC-MS approach. The extent of glycation was measured by a label-free quantitation strategy. The glycation sites were determined by the accurate mass (FTICR MS) with MS/MS measurements on the corresponding tryptic peptides. The extent of glycation was measured by the ratio of the peak intensity between the glycated and the average value for three non-glycated peptides in the same run. Residues lysine 18 of interferon-beta-1b, and lysine 51, lysine 233, and lysine 545 of human serum albumin were more prone to be glycated than other sites in this lyophilized glucose formulation. Residues of lysine 51 and lysine 233 but not lysine 545 of human serum albumin are highly accessible to solvent as found in a solution storage study by Lapolla et al. The extent of glycation of both proteins and the number of glycation sites of human serum albumin were increased with the storage time at 25 degrees C. In total, two glycation sites of interferon beta-1b and 17 glycation sites of human serum albumin were identified in the lyophilized glucose formulation with a storage time at 25 degrees C of 35 days. Among the 17 glycation sites, only lysine 525 of human serum albumin has been found in vivo in diabetic patients by Shaklai et al. As expected, there was no glycation found on both interferon-beta-1b and human serum albumin in the control samples (similar lyophilized formulation but using mannitol instead of glucose).

Multiple enzymatic digestion for enhanced sequence coverage of proteins in complex proteomic mixtures using capillary LC with ion trap MS/MS

This study uses multiple enzyme digests to increase the sequence coverage of proteins identified by the shotgun sequencing approach to proteomic analysis. The enzymes used were trypsin, Lys-C, and Asp-N, which cleave at arginine and lysine residues, lysine, and aspartic acid residues, respectively. This approach was evaluated with the glycoprotein, tissue plasminogen activator, t-PA and gave enhanced sequence coverage, compared with a single enzymatic digest. The approach was then evaluated with a complex proteomic sample, namely plasma. It was found that trypsin and Lys-C were able to detect overlapping but distinct sets of proteins and a digital recombination of the data gave a significant increase in both the number of protein identifications as well as an increase in the number of peptides identified per protein (which improves the certainty of the assignment).

Effects of conformation on the chemical stability of pharmaceutically relevant polypeptides

Control of chemical instability in protein pharmaceuticals continues to be a critical issue in developing stable formulations. While the effects of pH, buffer composition, ionic strength and temperature remain the most effective methods for controlling hydrolysis and oxidation reactions, it appears that conformational control may also be important. Addition of excipients to maintain native structure and reduce the propensity of the protein to denature and/or aggregate is already a central theme in stabilizing proteins (Arakawa et al., 1993). The same additives have now been found to slow both deamidation and oxidation, whether in solution or in the solid state. What is emerging is an additional approach for producing protein pharmaceuticals that maintain native structure and activity during long-term storage.

Growth hormone abuse in the horse: preliminary assessment of a mass spectrometric procedure for IGF-1 identification and quantitation

Previous studies have shown that insulin-like growth factor 1 (IGF-1) is a promising marker for the detection of growth hormone (GH) abuse in the horse. The significant increases observed with GH administration in comparison to natural levels imply the possibility of setting a threshold level for IGF-1 that would be indicative of GH abuse. Although an immunoradiometric assay (IRMA) has been identified as a reliable screening method, a more specific IGF-1 quantification method needs to be developed for the prosecution of GH abuse by horseracing authorities. This study describes such an HPLC electrospray mass spectrometry (LC/ESI-MS) method that was developed and then assessed for the specific analysis of IGF-1 at the low levels encountered in serum. The structural identity of IGF-1 was confirmed by endoproteinase Asp-N digestion followed by LC/MS and LC/MS/MS characterisation. This was followed by quantification of IGF-1 as the intact molecule against an internal standard.

Sample preparation for peptide mapping--A pharmaceutical quality-control perspective

In quality control of therapeutic proteins peptide mapping is used for confirmation of primary structure and detection of posttranslational modifications. The demands put on the experimental procedure are therefore different than in the case of determination of an unknown protein structure. It is here recognized that a peptide-mapping method for quality control of proteins should be inert (not induce or revert modifications), general, robust, and allow a high sample throughput. The steps prior to the separation of the generated peptides are identified as crucial for meeting these demands. This includes denaturation, reduction, alkylation, buffer exchange, solubilization, and digestion. A critical review of the literature regarding these steps is presented. Relevant options in all steps are experimentally evaluated. Novel approaches are developed for many of the steps. The result is a sample preparation procedure that essentially meets the stated demands.

The glycosylation heterogeneity of recombinant human IFN-gamma

The cloning of the cDNA for human interferon-gamma (IFN-gamma) has resulted in its expression in Escherichia coli, baculovirus-infected insect cells, Chinese hamster ovary (CHO) cells, and the mammary gland of transgenic mice. Large quantities of highly purified recombinant IFN-gamma have been generated, aided by the use of highly specific neutralizing monoclonal antibodies, with a view to its production as a human therapeutic protein. The primary source of structural heterogeneity for IFN-gamma during its production in mammalian expression systems is glycosylation, which can profoundly affect the three-dimensional structure of a glycoprotein and its biological function. A number of analytical approaches have been developed recently to allow a detailed analysis of the carbohydrate structures associated with IFN-gamma, the principal advances being in the areas of capillary electrophoresis and mass spectrometry. The implementation of these high-resolution analytical tools to determine the glycosylation profile of IFN-gamma makes it one of the best characterized recombinant glycoproteins. Recombinant human IFN-gamma acts as a model secretory glycoprotein, typifying the intrinsic glycosylation processing events associated with production of a potential therapeutic glycoprotein.

The use of sequential high-performance liquid chromatography and capillary zone electrophoresis to separate the glycosylated peptides from recombinant tissue plasminogen activator to a detailed level of microheterogeneity

The advantage of using the two-dimensional separation method was demonstrated by the separation of the complex tryptic peptides of recombinant human tissue plasminogen activator (rt-PA) glycoprotein. This method hybridizes two analytical methods where fractions containing glycopeptides are collected from reversed-phase high-performance liquid chromatography (RP-HPLC) and separated by capillary zone electrophoresis (CZE). CZE readily resolved carbohydrate structural variants, based on sialic acid content and branching, on the same peptide. Nonglycosylated peptides incidentally collected in the same RP-HPLC fraction were well resolved from the glycopeptides. This combination of RP-HPLC and CZE was able to uniquely resolve all of the peptides and glycopeptide variants in rt-PA. Confirmation of the specific peaks in the CZE was made by matrix-assisted laser-induced ionization time-of-flight mass spectrometry. The advantages and disadvantages of the existing methods for carbohydrate characterization in the biotech industry were compared. The advantage of this approach is to provide a simple extension of the existing tryptic digest protocols to include carbohydrate analysis to a detailed level of microheterogeneity.

Analysis of monoclonal antibody and immunoconjugate digests by capillary electrophoresis and capillary liquid chromatography

Comparative peptide mapping of a monoclonal antibody chimeric BR96 and corresponding doxorubicin (DOX) immunoconjugate was performed using capillary electrophoresis (CE) and capillary liquid chromatography (CLC). A unique, highly sensitive and selective approach combined with both UV absorbance and laser-induced fluorescence (LIF) detection has been developed and applied to studies including enzymatic digests of antibody and conjugate and related drug and conjugation linker substances. The analytical methodology has been established based on the unique characteristic of the anticancer drug DOX which yields native fluorescence. With an excitation wavelength of 488 nm from argon-ion laser, DOX conjugated to the monoclonal antibody using a hydrazone linker can be determined with a detection limit at the attomole level. Approaches were developed based on the successful conjugation and analysis of a model peptide conjugate. Enzymatic digests of the monoclonal antibody BR96 and its immunoconjugate were mapped by CE and CLC with on-line UV and LIF detection, which results in a unique fingerprint for structural analysis. With a two-dimensional LC-CE approach, conjugated peptide-DOX species from LC were further analyzed by CE with LIF detection. The drug-containing peptide fragments in the mixture were readily detected, which can be further characterized using other complementary analytical techniques.

Capillary electrophoresis with pulsed amperometric detection of carbohydrates and glycopeptides

The utility of capillary electrophoresis with pulsed amperometric detection (CE-PAD) for the analysis of carbohydrate-containing samples from a variety of biological sources is described. CE-PAD was used to separate a mixture of oligosaccharides obtained from bovine fetuin and to monitor the desialylation process used in the characterization of the oligosaccharides. Additionally, the high resolving power of the system was demonstrated using a series of glycopeptides obtained from recombinant coagulation factor VIIa, which possess the same decapeptide core but differ in the extent of sialylation. Deglycosylation of these glycopeptides for characterization purposes resulted in a mixture of carbohydrates and peptides. Unlike CE with UV detection, this system gave good responses for all analytes, demonstrating the unique ability of PAD to respond to the electrochemical features of diverse classes of biomolecules such as carbohydrates and peptides. Finally, CE-PAD was applied to the analysis of a tryptic digest of recombinant tissue plasminogen activator. The use of different detection potentials in sequential runs on a sample gave structural information about the peptides, such as glycosylation. A brief review of prior applications of CE-PAD to the analysis of standard mixtures of simple saccharides is also presented.

Posttranslational processing of recombinant human interferon-gamma in animal expression systems

We have characterized the heterogeneity of recombinant human interferon-gamma (IFN-gamma) produced by three expression systems: Chinese hamster ovary cells, the mammary gland of transgenic mice, and baculovirus-infected Spodopera frugiperda (Sf9) insect cells. Analyses of whole IFN-gamma proteins by electrospray ionization-mass spectrometry (ESI-MS) from each recombinant source revealed heterogeneous populations of IFN-gamma molecules resulting from variations in N-glycosylation and C-terminal polypeptide cleavages. A series of more specific analyses assisted interpretation of maximum entropy deconvoluted ESI-mass spectra of whole IFN-gamma proteins; MALDI-MS analyses of released, desialylated N-glycans and of deglycosylated IFN-gamma polypeptides were combined with analyses of 2-aminobenzamide labeled sialylated N-glycans by cation-exchange high-performance liquid chromatography. These analyses enabled identification of specific polypeptide cleavage sites and characterization of associated N-glycans. Production of recombinant IFN-gamma in the mammalian expression systems yielded polypeptides C-terminally truncated at dibasic amino acid sites. Mammalian cell derived IFN-gamma molecules displayed oligosaccharides with monosaccharide compositions equivalent to complex, sialylated, or high-mannose type N-glycans. In contrast, IFN-gamma derived from baculovirus-infected Sf9 insect cells was truncated further toward the C-terminus and was associated with neutral (nonsialylated) N-glycans. These data demonstrate the profound influence of host cell type on posttranslational processing of recombinant proteins produced in eukaryotic systems.

Application of capillary high-performance liquid chromatography to biotechnology, with reference to the analysis of recombinant DNA-derived human growth hormone

Using capillary HPLC, femtomole amounts of recombinant DNA-derived human growth hormone (rhGH) have been successfully detected from solutions at nanomolar concentrations. The separation used capillaries of 15 cm x 320 microns I.D. and detection was with a UV absorbance detector containing a capillary Z-shaped flow-cell. A sample of rhGH that was recovered from rat serum was analyzed by capillary reversed-phase HPLC, using both acidic- and neutral-pH mobile phases, as well as by capillary ion-exchange chromatography. When compared to HPLC separations performed at flow-rates of 1 ml/min, the sensitivity of the detection was increased 200 times, without any loss in resolution. Sub-microgram amounts of rhGH were also analyzed by tryptic mapping using capillary HPLC and peptides were identified by capillary LC-MS.

Assessing genetic heterogeneity in production cell lines: detection by peptide mapping of a low level Tyr to Gln sequence variant in a recombinant antibody

A recombinant antibody directed against the human epidermal growth factor receptor-2 extracellular domain was subjected to detailed structural characterization. Heterogeneity in the heavy chain was demonstrated by recovery of two forms of a tryptic peptide, with either glutamine or the expected tyrosine at residue 376. Subsequent experiments indicated that the Y376Q variant developed during transfection of the antibody heavy and light chain genes into Chinese hamster ovary cells. Levels of the Y376Q variant (range: 27% to 1%) in the purified antibody were inversely proportional to cell age. The established cell line was subcloned and found to be heterogeneous by polymerase chain reaction analysis of cell extracts and protein analysis of the purified antibody. Ten percent of subclones produced high levels of the Y376Q variant while 90% of the subclones produced antibody with only the expected heavy chain sequence. This report demonstrates the utility of peptide mapping as a sensitive tool for assessing genetic heterogeneity of recombinant cell lines.

Identification and structural analysis of the tetrasaccharide NeuAc alpha(2-->6)Gal beta(1-->4)GlcNAc beta(1-->3)Fuc alpha 1-->O-linked to serine 61 of human factor IX

O-Linked fucose has been found attached to Thr/Ser residues within the sequence Cys-X-X-Gly-Gly-Thr/Ser-Cys in the N-terminal EGF domains of several coagulation/fibrinolytic proteins. Carbohydrate composition and mass spectrometric analyses of tryptic and thermolytic peptides containing the corresponding site (Ser-61) in the first EGF domain of human factor IX indicated the presence of a tetrasaccharide containing one residue each of sialic acid, galactose, N-acetylglucosamine, and fucose. The Ser-61 tetrasaccharide was not susceptible to alpha-fucosidase digestion. Fragments generated during mass spectrometric analysis indicated that fucose was the attachment sugar residue. The involvement of fucose in the carbohydrate-peptide linkage was confirmed by two-dimensional 1H NMR spectroscopic analysis of the glycopeptide containing factor IX residues 57-65. The complete structure of the tetrasaccharide was obtained by methylation analysis and two-dimensional 1H TOCSY and ROESY experiments as NeuAc alpha(2-->6)Gal beta(1-->4)GlcNAc beta(1-->3)Fuc alpha 1-->O-Ser61.

Peptide mapping on HIV polypeptides expressed in Escherichia coli. Quality control of different batches and identification of tryptic fragments containing residues of aromatic amino acids or cysteine

Peptide mapping was used for the quality control of different batches of the recombinant HIV proteins p24 core and p24-gp41, expressed in Escherichia coli. These proteins comprise gag and env region polypeptides of the virus and may serve as suitable components in the diagnosis of HIV infections. The proteins were digested with trypsin and the mixtures were subjected to peptide mapping to prove batch equivalence of p24-gp41 and to isolate fragments of the p24-gp41 digest that differ from those of the p24 core digest. The proteins were reduced with dithiothreitol and the cysteine residues were derivatized by addition of 4-vinylpyridine. Peptide mapping was performed by means of reversed-phase high-performance liquid chromatography. Batch equivalence was proved by comparison of the maps. Peaks present in one map but not in the other were considered to be due to sequence differences or variability in digestion.

Factors influencing the performance of peptide mapping by reversed-phase high-performance liquid chromatography

Factors controlling the performance of peptide mapping on reversed-phase columns were systematically evaluated. Performance criteria included resolution (peak capacity and selectivity), system reproducibility, sensitivity and analysis speed. Column configuration, characteristics of packing materials, mobile phase composition, operating variables and instrumental designs were found to influence the performance of peptide mapping. Considerations for peptide identification techniques are discussed.