High-performance tryptic mapping of recombinant bovine somatotropin

Elucidating the Mechanism of Multispecific Antibody Aggregation through Subunit Analysis

Multispecific antibody constructs are quickly becoming more common constructs in biopharmaceuticals to improve specificity and efficacy. While the advent of this technology has led to improved therapeutics, its development has challenged the analytical tools through which these therapeutics are characterized. Moreover, new critical quality attributes, such as aggregation, have challenged the approaches to characterization even further. Herein, we describe a novel native subunit analysis using IdeS and IgdE analyzed by native size exclusion chromatography coupled with mass spectrometry to interrogate the mechanism of aggregation in a multispecific antibody. Digestion by IdeS and IdgE allows for the retention and detection of noncovalent interactions thereafter. Aggregation was localized to single-chain fragment variables (scFvs) wherein a domain swapping mechanism between VH1/VL2 and VH2/VL1 occurs.

High resolution fingerprinting of single and double-stranded RNA using ion-pair reverse-phase chromatography

The emergence of new sustainable approaches for insect management using RNA interference (RNAi) based insecticides has created the demand for high throughput analytical techniques to fully characterise and accurately quantify double stranded RNA (dsRNA) prior to downstream RNAi applications. In this study we have developed a method for the rapid characterisation of single stranded and double stranded RNA using high resolution RNase mapping in conjunction with ion-pair reverse-phase chromatography utilising a column with superficially porous particles. The high resolution oligoribonucleotide map provides an important 'fingerprint' for identity testing and bioprocess monitoring. Reproducible RNA mapping chromatograms were generated from replicate analyses. Moreover, this approach was used to provide a method to rapidly distinguish different RNA sequences of the same size, based on differences in the resulting chromatograms. Principal components analysis of the high resolution RNA mapping data enabled us to rapidly compare multiple HPLC chromatograms and distinguish two dsRNA sequences of different size which share 72% sequence homology. We used the high resolution RNase mapping method to rapidly fingerprint biomanufactured dsRNA across a number of different batches. The resulting chromatograms in conjunction with principal components analysis demonstrated high similarity in the dsRNA produced across the different batches highlighting the potential ability of this method to provide information for batch release in a high throughput manner.

Discrimination of recombinant and pituitary-derived bovine and porcine growth hormones by peptide mass mapping

Somatotropins, which are used in cattle for growth and lactating performances, are difficult to reliably detect because no direct method exists. Reversed-phase high-performance liquid chromatography (RP-HLC) coupled to electrospray ionization quadrupole mass spectrometry (ESI/MS) has been developed to separate and characterize the N-terminal peptides resulting from tryptic cleavage of natural and recombinant growth hormones from different species (bovine, porcine, and human) and suppliers. Conditions for tryptic digestion were optimized. This technique was found to be optimal to cleave efficiently the N-terminal peptide of the proteins without releasing too much noise from the matrix. Characterization of the peptides through ESI(+)-MS allowed natural and recombinant growth hormones from bovine and porcine species with N-terminal amino acid sequences differing from one amino acid residue to be discriminated. However, the studied human growth hormones had similar primary sequences that did not permit any discrimination between recombinant and natural forms, thus confirming the known identity of these hormones. Protein digestions with pepsin and chymotrypsin were also compared but were not conclusive due to the too small N-terminal peptides released after proteolysis.

Solid-state photodegradation of bovine somatotropin (bovine growth hormone): evidence for tryptophan-mediated photooxidation of disulfide bonds

Lyophilized recombinant bovine somatotropin (rbST; bovine growth hormone) is sensitive to photoinduced degradation. The underlying mechanisms of these processes are identified and presented. Lyophilized rbST was photolyzed with near-ultraviolet (UV) light between 305 and 410 nm, and the protein content was analyzed by various bioanalytical techniques, including tryptic mapping, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), amino acid analysis, and fluorescence, UV, Raman and Fourier transform infrared (FTIR) spectroscopy. The solid-state photodegradation of rbST by near-UV light exclusively targets the protein disulfide bonds. The reaction is initiated by photoionization of tryptophan (Trp) and one-electron reduction of the disulfide. However, in contrast to the behavior of other proteins in solution, rbST appears to undergo back electron transfer to restore Trp and yield a pair of cysteine (Cys) thiyL radicals, which add molecular oxygen and ultimately recombine to yield alpha-disulfoxide, thiosulfinate, and/or thiosulfonate. Photodegradation is strictly dependent on the presence of molecular oxygen, but does not involve singlet oxygen. Between 0.4 and 10%, residual moisture levels do not affect the rate of photodegradation. Our results show a novel mechanism for Trp-mediated photodegradation of protein disulfide bonds via formation of a pair of thiyL radicals followed by addition of molecular oxygen.

Miniaturized on-line proteolysis-capillary liquid chromatography-mass spectrometry for peptide mapping of lactate dehydrogenase

In this study, methodology was developed for on-line and miniaturized enzymatic digestion with liquid chromatographic (LC) separation and mass spectrometric (MS) detection. A packed capillary LC-MS system was combined with on-line trypsin cleavage of a model protein, lactate dehydrogenase, to provide an efficient system for peptide mapping. The protein was injected onto an enzymatic capillary reactor and the resulting peptides were efficiently trapped on a capillary trapping column. Different trapping columns were evaluated to achieve a high binding capacity for the peptides generated in the enzyme reactor. The peptides were further eluted from the pre-column and separated on an analytical capillary column by a buffer more suitable for the following an electrospray ionisation (ESI) MS process. An important aspect of the on-line approach was the desalting of peptides performed in the trapping column to avoid detrimental signal suppression in the ESI process. The developed on-line system was finally compared to a classical digestion in solution, with reference to peptide sequence coverage and sensitivity. It was shown that the on-line system gave more than 100% higher peptide sequence coverage than traditional digestion methods.

Characterization of the metal-binding site of bovine growth hormone through site-specific metal-catalyzed oxidation and high-performance liquid chromatography-tandem mass spectrometry

Metal-catalyzed oxidation was used to identify metal-binding His residues in bovine growth hormone (bGH), which has not been characterized well crystallographically due to a high propensity of bGH to aggregate. bGH was exposed to Cu(2+) and ascorbate (ascorbate/Cu(2+)/O(2)). 2-Oxo-His formation was identified by HPLC-tandem mass spectrometry (MS/MS) analysis of a tryptic digest. Two 2-oxo-His-containing fragments were detected, T2(O) (MH(2+)(2) = 748.8) and T20(O) (MH(+) = 528.3), both masses corresponding to the addition of only one oxygen atom (+16 amu) to the respective native fragments, T2 and T20. T2 contains (20)His and (22)His, and T20 contains (170)His. Quantitative HPLC-MS/MS analysis shows the following order of reactivity: (170)His >> (22)His > (20)His. Solvent-accessible surface area calculations determined (22)His and (170)His to be 26 and 35% solvent exposed, respectively, while (20)His is 65% solvent exposed. The presence of an analogous metal-binding site in human growth hormone, which is located in the hydrophobic core, and our experimental finding that oxidation was greatest for (22)His and (170)His in bGH suggests that (22)His and (170)His of bGH participate in metal binding. This result is supported by a previously predicted tertiary structure of bGH and compared with the location of metal-binding His residues of human growth hormone.

Molecular characterization and gene expression in the eye of the apolipophorin II/I precursor from Locusta migratoria

The transport of lipids via the circulatory system of animals constitutes a vital function that uses highly specialized lipoprotein complexes. In insects, a single lipoprotein, lipophorin, serves as a reusable shuttle for the transport of lipids between tissues. We have found that the two nonexchangeable apolipoproteins of lipophorin arise from a common precursor protein, apolipophorin II/I (apoLp-II/I). To examine the mechanisms of transport of lipids and liposoluble substances inside the central nervous system, this report provides the molecular cloning of a cDNA encoding the locust apoLp-II/I. We have recently shown that this precursor protein belongs to a superfamily of large lipid transfer proteins (Babin et al. [1999] J. Mol. Evol. 49:150-160). We determined that, in addition to its expression in the fat body, the locust apoLp-II/I is also expressed in the brain. Part of the signal resulted from fat body tissue associated with the brain; however, apoLp-II/I was strongly expressed and the corresponding protein detected, in pigmented glial cells of the lamina underlying the locust retina and in cells or cellular processes interspersed in the basement membrane. The latter finding strongly suggests an implication of apolipophorins in the transport of retinoids and/or fatty acids to the insect retina.

Statistical validation of reproducibility of HPLC peptide mapping for the identity of an investigational drug compound based on principal component analysis

Peptide mapping is a key analytical method for studying the primary structure of proteins. The sensitivity of the peptide map to even the smallest change in the covalent structure of the protein makes it a valuable "fingerprint" for identity testing and process monitoring. We recently conducted a full method validation study of an optimized reverse-phase high-performance liquid chromatography (RP-HPLC) tryptic map of a therapeutic anti-CD4 monoclonal antibody. We have used this method routinely for over a year to test production lots for clinical trials and to support bioprocess development. One of the difficulties in the validation of the peptide mapping method is the lack of proper quantitative measures of its reproducibility. A reproducibility study may include method and system precision study, ruggedness study, and robustness study. In this paper, we discuss the use of principal component analysis (PCA) to quantitate peptide maps properly using its projected scores on the reduced dimensions. This approach allowed us not only to summarize the reproducibility study properly, but also to use the method as a diagnostic tool to investigate any troubles in the reproducibility validation process.

Validation of a peptide mapping method for a therapeutic monoclonal antibody: what could we possibly learn about a method we have run 100 times?

Peptide mapping is a key analytical method for studying the primary structure of proteins. The sensitivity of the peptide map to even the smallest change in the covalent structure of the protein makes it a valuable 'finger-print' for identity testing and process monitoring. We recently conducted a full method validation study of an optimised reverse-phase high-performance liquid chromatography (RP-HPLC) tryptic map of a therapeutic anti-CD4 IgG1 monoclonal antibody. We have used this method routinely for over 1 year to support bioprocess development and test production lots for clinical trials. Herein we summarize the precision and ruggedness of the testing procedure and the main findings with respect to 'coverage of amino acid sequence' and limits-of-detection for various hypothetical structural variants. We also describe, in more detail, two unanticipated insights into the method gained from the validation study. The first of these is a potentially troublesome side-product arising during the reduction/alkylation step. Once the cause of this side-product was identified, it was easily prevented. We also report on subtle changes to the peptide map upon extended storage of the digest in the autosampler. These findings helped us to develop a 'robust' method for implementation in a quality control laboratory.

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.

Mapping of recombinant hemoglobin using immobilized trypsin cartridges

A tryptic mapping procedure has been developed for a recombinant hemoglobin (rHb1.1) using an immobilized trypsin cartridge. Apohemoglobin is passed through the trypsin cartridge and the products of the digestion are captured directly onto an in-line C18 reversed-phase column. The peptides are then separated using a gradient elution. This new procedure is rapid and reproducible and can be fully automated. The total time of analysis is less than 2 h. The mapping of apohemoglobins produced an unexpected isomerization of two peptides: beta8,9 (K66-K82) and alpha8,9 (K61-K90). It appears that the isomerization may occur through transpeptidation followed by proteolysis at a newly generated site next to the site of ligation. This mapping procedure can be a useful tool for research and routine analysis of proteins.

Evaluation of genetic stability of recombinant human factor VIII by peptide mapping and on-line mass spectrometric analysis

PURPOSE

The genetic stability of a recombinant human factor VIII (rhFVIII) product expressed in Chinese hamster ovary cells (Recombinate) has been evaluated through comparisons of the protein produced at the beginning, middle and end of a typical production campaign.

METHODS

Recombinant human factor VIII was incubated with thrombin, the resulting four polypeptides were isolated by RP-HPLC, subjected to proteolysis with trypsin, and the peptide mixtures were resolved by RP-HPLC. Tryptic peptide mixtures were subjected to online mass spectrometric analysis using an electrospray ionization source interfaced to a quadrupole mass analyzer scanning from 1950-200 amu, and the peptide ion data were compared for three lots produced from the beginning, middle and end of a production campaign.

RESULTS

The UV elution profiles for each of the rhFVIIIa polypeptides were highly similar for factor VIII isolated from the beginning, middle and end of production. Total ion data from the peptide maps derived from three lots of rhFVIII were compared by MH1+ values as a function of scan range. A total of 918 ions were analyzed for the four polypeptides of rhFVIII produced at the beginning, middle and end of a production campaign. The ions were detected at the same relative retention times, as indicated by the similar scan numbers for the three lots.

CONCLUSIONS

These observations support that rhFVIII preparations produced from the beginning, middle and end of a production campaign were highly similar, and demonstrate genetic stability in the manufacturing process of Recombinate.

Validation of a peptide map for recombinant porcine growth hormone and application to stability assessment

A reverse-phase HPLC method for the analysis of tryptic digests of recombinant porcine growth hormone (pGH) has been developed and validated. Digestion was performed at 4 degrees C for a 20-hr period with TPCK-treated trypsin at a 1:20 (w/w) trypsin:pGH ratio. Gradient elution HPLC, using an Aquapore RP300 C8 column, was incorporated for separation of the digestion products and peak identification was carried out by mass spectrometry (MS). The digestion procedure and subsequent chromatography were linear in the initial concentration range of 4.55-45.46 microM (100 to 1000 micrograms/mL) pGH. The variability in the fragment retention times was low and the normalized peak area variability was less than 5% for all but three of the fragments. The utility of the trypsin digestion and chromatography procedures has been demonstrated by assessing chemical changes in pGH induced by incubation at elevated pH. Upon incubation of pGH in 0.2 M Tris buffer at pH 9 (ionic strength adjusted to 0.5 with NaCl) and 37 degrees C over a period of 400 hr, significant degradation in the regions corresponding to the digestion fragments T23-T25 (residues 181-182 linked by a disulfide bond to residues 184-191), T9 (residues 96-108), and T5-T18 (residues 43-64 linked by a disulfide bond to residues 158-166) was observed. The disappearance of the peaks corresponding to fragments T23-T25 and T9 both displayed apparent first-order degradation kinetics over the time period investigated with half-lives of 131 and 154 hr, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)