Separation of the Isoforms of a Monoclonal Antibody by Gel Isoelectric Focusing, High Performance Liquid Chromatography and Capillary Isoelectric Focusing

Charge heterogeneity of a therapeutic monoclonal antibody conjugated with a cytotoxic antitumor antibiotic, calicheamicin

A robust and highly reproducible capillary isoelectric focusing (cIEF) method for the evaluation of charge heterogeneity of monoclonal antibody (mAb) pharmaceutical which contains covalently bound antitumor compounds was developed using a combination of commercially available dimethylpolysiloxane-coated capillary and carrier ampholyte. In order to optimize major analytical parameters for robust mobilization, experimental responses from three pI markers were selected. The optimized method gave excellent repeatability and intermediate precision in estimated pI values of charge variants with relative standard deviations (RSDs) of not more than 0.06% and 0.95%, respectively, when using IgG(4) as a model. Furthermore, RSDs of charge variant compositions were less than 5.0%. These results suggest that the proposed method can be a powerful tool for reproducible evaluation of charge variants of both naked mAbs and their conjugates with high resolution, and it is applicable to quality testing and detailed characterization in the pharmaceutical industry. In addition, it should be noticed that the method provided non-linear pH gradient within the tested ranges, from pI 9.50 to 3.78, and the pH gradient caused the inconsistency of estimated pI ranges between cIEF and gel IEF. This result indicates that selecting appropriate pI markers based on the target pI ranges of charge variants for each mAb related pharmaceutical is highly recommended for the precise determination of pI values.

Regulation of cathepsin B activity by 2A2 monoclonal antibody

Cathepsin B (EC 3.4.22.1) is a lysosomal cysteine protease with both endopeptidase and exopeptidase activity. The former is associated with the degradation of the extracellular matrix proteins, which is a process required for tumour cell invasion and metastasis. In the present study, we show that 2A2 monoclonal antibody, raised by our group, is able to regulate cathepsin B activity. The EPGYSP sequence, located between amino acid residues 133-138 of cathepsin B in the proximity of the occluding loop, was determined to be the epitope for 2A2 monoclonal antibody using SPOT analysis. By surface plasmon resonance, an equilibrium dissociation constant (Kd) of 4.7 nM was determined for the interaction between the nonapeptide CIAEPGYSP, containing the epitope sequence, and 2A2 monoclonal antibody. 2A2 monoclonal antibody potentiated cathepsin B exopeptidase activity with a activation constant (Ka) of 22.3 nM, although simultaneously inhibiting its endopeptidase activity. The median inhibitory concentration values for the inhibition of hydrolysis of protein substrates, BODIPY FL casein and DQ-collagen IV were 761 and 702 nM, respectively. As observed by native gel electrophoresis and gel filtration, the binding of 2A2 monoclonal antibody to the cathepsin B/cystatin C complex caused the dissociation of cystatin C from the complex. The results obtained in the present study suggest that, upon binding, the 2A2 monoclonal antibody induces a conformational change in cathepsin B, stabilizing its exopeptidase conformation and thus disabling its harmful action associated with its endopeptidase activity.

Peak identification in capillary isoelectric focusing using the concept of relative peak position as determined by two isoelectric point markers

In CIEF analysis, sample peaks can be identified by their relative peak positions (RPP) that are determined using only two internal pI markers. The two internal pI marker peaks should bracket, as close as possible, the sample peaks. The RPP values of the sample peaks are then calculated using the pI values, peak positions of the two pI markers, and peak position of the sample. Use of this method can effectively compensate for pH gradient distortions that often occur as a result of salts. Also, as shown by the results of this paper, regardless of the linearity of the pH gradient established by the given carrier ampholytes, sample peaks can be identified within an SD of 0.1 pH unit in RPP (<2% RSD) as long as the sample is run using the same carrier ampholytes and maintaining salt concentrations in the range of 0-15 mM.

Separation and quantitation of monoclonal antibodies in cell growth medium using capillary zone electrophoresis

IgG1 is separated from its impurities in cell growth medium under simple CZE conditions without specific sample pretreatment. Linearity, limit of quantitation, limit of detection, precision and accuracy for the method are demonstrated. The quantitation for IgG1 in the cell growth medium is obtained by generating a calibration curve and by using standard additions. This CE method can offer a good alternative to conventional HPLC methods. Attempts are also made to separate the heterogeneous species in monoclonal antibodies using both CZE and MECC.

Thermal stability studies of immunoglobulins using capillary isoelectric focusing and capillary zone electrophoretic methods

The affinity of an antibody towards its antigen is highly specific to its conformation, in order to have optimal antibody-antigen interaction. The increase of temperature might cause changes in antibody conformations. The change of structure conformations may be reflected in the isoelectric points (pI values), peak shape and absorbance of the antibody. In this study, a monoclonal antibody was heated over a period of time. Capillary isoelectric focusing (cIEF) and capillary zone electrophoresis (CZE) were used to monitor the change in the antibody. The longer the heating period, the lower the pI values were under cIEF conditions. CZE also showed changes in peak shapes and decreases in absorbance of the antibody with heating.

Validation of a capillary isoelectric focusing method for the recombinant monoclonal antibody C2B8

A capillary isoelectric focusing (cIEF) method has been developed for the purpose of determining the identity and charge distribution of mouse/human chimeric antibody to human CD20 antigen (C2B8). The assay was validated in accordance with ICH guidelines in order to demonstrate that it is suitable for its intended purpose and so that it may be performed as a lot release test for bulk and final product. As a result of the validation process the assay was found to be linear over the concentration range of 2-356 micrograms ml-1 with recovery of 125I-labeled C2B8 at the target sample concentration of 125 micrograms ml-1 equal to 99%. The repeatability and intermediate precision relative standard deviations of the four major peaks for migration time, peak area, and peak area percent ranged from 0.9-4.4%. The specificity of the assay was demonstrated by baseline resolution of the C2B8 main peak from product excipients, and other Genentech monoclonal antibodies. The results of this validation demonstrate that the cIEF assay for the determination of identity and charge distribution of C2B8 is accurate, precise, linear, and highly specific. The assay is rapid and suitably rugged.

Affinity mode of capillary isoelectric focusing for the characterization of the biotin-binding protein actinavidin

Different modes of capillary isoelectric focusing (CIEF) with salt mobilization and zwitterionic additive to cathodic mobilizer were applied to characterize the biotin-binding protein actinavidin and its affinity properties. The analysis is performed in a neutral coated capillary with completely eliminated electroosmotic flow. Synthetic pI standards with absorption in the visible region were used in all runs and pI determinations were based on a fitted nonlinear calibration graph. CIEF of highly purified actinavidin in native conditions was revealed in about 12 peaks in pI range 6.2-7.5, with three major forms having pI 6.80, 6.86, 6.90. CIEF of a mixture of actinavidin and increasing concentrations of two affinity ligands (biotin and biotinylated oligonucleotide) demonstrated drastic changes in the number of protein isoforms. In the latter case it resulted in only one peak (pI 5.05) when the ligand was in excess. This method, which can be named affinity CIEF, was found to be well-suited for studying structural changes, occurring in receptor proteins upon binding with a ligand. CIEF of the protein, performed under denaturing conditions (6 M urea in a solution of carrier ampholytes) is also reported. It was revealed in three isoforms with a pI more acidic than that of native actinavidin. It is demonstrated that careful selection of denaturing conditions was necessary for the reproducible results.

Qualitative and quantitative analysis of hemoglobin variants by capillary isoelectric focusing

We developed two capillary isoelectric focusing (CIEF) assays, in narrow pH gradients, with the aim of routinely separating and quantitating normal and abnormal hemoglobins (Hbs): a one-step CIEF assay where residual electroosmotic flow mobilizes the proteins during focalization, and a two-step CIEF assay where focused Hbs are mobilized by low pressure by maintaining high-voltage. The resolution of 0.10 pH unit obtained with the one-step assay allowed the separation of the Hbs A, F, S and C; but Hb A2, which represents about 2-3% of whole Hb, could not be quantitated. The better resolution of 0.02 pH unit obtained with the two-step assay allowed the separation of some Hb variants of very close isoelectric points. The reproducibility of retention times was satisfactory (C.V.<5%). Moreover, in this configuration quantitation of Hb A2, Hb F and Hb S led to a standard deviation of less than 5%, allowing the diagnosis of thalassemias. The one-step assay could be useful only for the detection of abnormal variants, while the two-step assay could be applied to the routine analysis of Hbs, with quantitation of minor fractions and presumptive identification of variants.

Rapid high-performance isoelectric focusing of monoclonal antibodies in uncoated fused-silica capillaries

Rapid (< 5 min) high-performance isoelectric focusing was performed in uncoated fused-silica capillaries to resolve isoforms of monoclonal antibodies and to determine their isoelectric points (pI). The methodology involved the use of a 32 cm (effective length 9 cm) x 50 microns I.D. uncoated capillary. (Hydroxypropyl)methyl cellulose was used as an additive to suppress analyte-wall interaction and to precisely control electroosmotic flow so that focusing and mobilization of focused zones past detector occur simultaneously. Urea was included in the separation medium to solubilize the antibodies that precipitated at their point of focusing. The methods with and without urea used ampholytes pH 5-8 to generate a demonstrate linear gradient between pH 5.4 and pH 7.2, based on the separation of various protein standards. Reproducibility [< 2% (R.S.D.)] of the migration times (corresponding to the detectable isoforms of the antibodies) was obtained by using two sets of reagents and capillaries on three consecutive days. pI values determined from day-to-day with a reference standard were shown to vary by only 0.01 pH unit. The described capillary isoelectric focusing methods provided a rapid, simple and reproducible way of monitoring micro-heterogeneity and pI of the murine monoclonal antibodies investigated.

HPCE methods for the identification and quantitation of antibodies, their conjugates and complexes

We review here much of the existing literature that deals with analysis, resolution, characterization, and (at times) quantitation of antibodies in capillary electrophoresis modes. Each major mode of CE shown applicable to antibody analysis is described, along with the major applications of that mode for antibodies. Discussions are presented as to the mechanisms of antibody resolution in CE, interactions of various buffer components with the proteins leading to resolution, and methods of quantitation for antibodies. The literature is critically reviewed with regard to true application of CE for antibody analysis, limitations, information possible, information implied, and which samples have actually been assayed by CE modes. The literature is critically reviewed up to and including 1996, both for the scientific and commercial literature, especially vendor applications and real world applications possible.

Capillary isoelectric focusing and high-performance cation-exchange chromatography compared for qualitative and quantitative analysis of hemoglobin variants

We have developed two assays for complete analysis of hemoglobins (Hbs) in the field of hemoglobinopathies: a high-performance cation-exchange liquid chromatography (HPLC) assay on the weak cation-exchanger Poly Cat A and a two-step capillary isoelectric focusing (CIEF) assay on the neutral-coated capillary from Beckman in a narrow pH gradient. The resolution was satisfactory for both HPLC and CIEF and allowed separation of normal and common abnormal Hbs, i.e., Hb A, Hb F, Hb A2, Hb S, Hb C, and Hb E; slight differences were shown for the resolution of unusual variants such as Hb C-Harlem and Hb D-Punjab. The reproducibility of retention times was satisfactory as well for HPLC (CV 3.3%) and CIEF (CV 4.9%). The imprecision of quantification of Hb A2, evaluated at two concentrations, and of Hb F and Hb S was &lt;5%, except for low concentrations of Hb A2quantified by CIEF. Quantitative data obtained for these three Hb forms were highly correlated between the two assays. These results suggest that the new CIEF assay can be competitive with HPLC for complete routine analysis of Hb variants.

Capillary isoelectric focusing and sodium dodecyl sulfate-capillary gel electrophoresis of recombinant humanized monoclonal antibody HER2

Capillary isoelectric focusing (cIEF) and IEF of recombinant humanized monoclonal antibody HER2 (rhuMAbHER2) show five charged isoforms with estimated pI values ranging from 8.6-9.1. The cIEF assay demonstrated good precision with relative standard deviations (R.S.D.) 0.7-3.7% and 0.4-4.2% for intra and interassay analysis, respectively. The method was linear for the area of the main peak over the concentration range 2-250 micrograms/ml with a Pearson correlation coefficient > 0.99. The limit of detection for the main peak was determined to be 2 ppm. With both sodium dodecyl sulfate-capillary gel electrophoresis (SDS-CGE) and SDS-polyacrylamide gel electrophoresis, the nonreduced rhuMAbHER2 migrated as a single major peak with minor peaks in the aggregate and clip regions. After reduction, the electropherogram and the slab gel showed the expected heavy chain and light chain fragments with minor peaks in the aggregate and clip regions. The SDS-CGE assay showed good precision with R.S.D. values of 0.1-7.8% and 0.1-8.1% for intra and interassay analysis, respectively. The Pearson correlation coefficient for the area of the main peak was > 0.99 demonstrating linearity for the concentration range 0.5-500 micrograms/ml. The limit of detection for intact rhuMAbHER2 was determined to be 0.5 ppm. The data presented demonstrates the feasibility of replacing the slab gel techniques with capillary electrophoresis in a quality control environment.

Examination of capillary zone electrophoresis, capillary isoelectric focusing and sodium dodecyl sulfate capillary electrophoresis for the analysis of recombinant tissue plasminogen activator

The microscale techniques of CZE, cIEF and SDS capillary electrophoresis have been evaluated for the analysis of a complex glycoprotein, recombinant tissue plasminogen activator (rtPA). A series of omega-amino acid buffers (pH approximately 5) was found suitable for the CZE separation of rtPA on coated capillaries. rtPA could be resolved into a series of major and minor peaks in an epsilon-aminocaproic acid buffer containing 0.01% (v/v) Tween 80. For cIEF, a two step method with pressure mobilization was utilized. Using a commercial instrument, either a polymer solution with a 50 microns I.D. capillary or narrow bore capillaries without a polymer solution (25 microns I.D.) were employed. rtPA was resolved into at least eight species within a pI range of 6.4-9.2 using Ampholine 3.5-10. Migration time precision for the major peaks ranged from 0.2% for CZE to < or = 2-3% R.S.D. for cIEF. Total recovery of rtPA from the capillary was also demonstrated for both methods. Analysis of rtPA, rtPA Type I, rtPA Type II and the desialylated forms resulted in the expected elution profiles. Finally, the potential of SDS capillary electrophoresis using a coated capillary for an rtPA Type I/Type II purity assay was shown.

Capillary isoelectric focusing as a tool in the examination of antibodies, peptides and proteins of pharmaceutical interest

This paper describes the recent history and development of capillary isoelectric focusing (cIEF), as it has evolved over the past 10 years forming a distinct mode of high-performance capillary electrophoresis (HPCE). The theory, equations, fundamentals and basics of cIEF are discussed and described, including modes of focusing and mobilization, coated vs uncoated capillaries, different detection schemes, resolutions possible, peak capacity possible and final commercialized approaches now available. Then, the applications of the technique are emphasized, as applied to smaller peptides, larger proteins and still larger antibodies and antibody-protein complexes. The emphasis has been on the application of capillary electromigration techniques in drug analysis. Throughout, attempts have been made to emphasize the potential applications and uses of cIEF methods, and how these might be successfully utilized in drug analysis and assays for larger biopolymers.

Application of capillary isoelectric focusing with absorption imaging detection to the quantitative determination of human hemoglobin variants

The capillary isoelectric focusing (CIEF)-absorption imaging detector is a multicapillary separation instrument. Several protein samples can be separated and detected in a single run. The analysis time for one run is only 3 min. Because an imaging detector is used, the mobilization process of conventional CIEF is not necessary, eliminating such drawbacks as long analysis time and poor reproducibility in mobilization speed. Human hemoglobin variants were quantitatively determined using the instrument. The peak areas of the analytes were proportional to their concentrations in the concentration range of 0-200 micrograms/mL. Hemoglobin variant A2, which only comprises 2% of the whole hemoglobin, can be quantitatively determined with a standard deviation of less than 10%. For the high concentration variants, such as variant S, the deviation is less than 1%.

Fast analysis of proteins by isoelectric focusing performed in capillary array detected with concentration gradient imaging system

Isoelectric focusing of several protein samples is performed simultaneously in an array of 2-4 short capillaries (4-10 cm long). The separated proteins are detected by either an on-line concentration gradient imaging detection system, or a single point concentration gradient detector which requires a mobilization step following the focusing process. The application of the capillary array increases the throughput of the capillary isoelectric focusing (CIEF) technique, and makes the technique comparable in sample throughput to the gel slab isoelectric focusing technique, but with much faster speed of separation and quantitation. The analysis is completed in 2-3 min with the imaging detection system, which is about 100 times faster than the conventional gel slab isoelectric focusing and 10 times faster compared to conventional CIEF. The resolution of the separation is 0.02 pH units or better. All separated proteins in the capillary array are detected by the universal concentration gradient detector, which eliminates the need for sample derivatization. The concentration limit of detection for the inexpensive instrument described in this work is about 30 micrograms/mL and can be reduced by using higher quality components in the system, such as a more stable laser, higher optical quality capillaries and a faster computer A/D board. The sample consumption is 400 nL for the 4 cm long, 100 microns ID square capillary. The isoelectric point (pI) values of the samples can be directly determined without internal pI markers from their positions inside the capillary after focusing when the imaging detection system is used.

Isoelectric focusing by free solution capillary electrophoresis

A reproducible, quantitative isoelectric focusing method using capillary electrophoresis that exhibits high resolution and linearity over a wide pH gradient was developed. RNase T1 and RNase ba are two proteins that have isoelectric points (pI's) at the two extremes of a pH 3-10 gradient. Site-directed mutants of the former were separated from the wild-type form and pI's determined in the same experiment. The pI's of RNase T1 wild-type, its three mutants, and RNase ba were determined for the first time as 2.9, 3.1, 3.1, 3.3, and 9.0, respectively. The paper describes the protocol for isoelectric focusing by capillary electrophoresis, as well as presenting data describing the linearity, resolution, limits of mass loading, and reproducibility of the method.