Expanding the range of sub/supercritical fluid chromatography: Advantageous use of methanesulfonic acid in water-rich modifiers for peptide analysis

The aim of this work was to expand the applicability range of UHPSFC to series of synthetic and commercialized peptides. Initially, a screening of different column chemistries available for UHPSFC analysis was performed, in combination with additives of either basic or acidic nature. The combination of an acidic additive (13 mM TFA) with a basic stationary phase (Torus DEA and 2-PIC) was found to be the best for a series of six synthetic peptides possessing either acidic, neutral or basic isoelectric points. Secondly, methanesulfonic acid (MSA) was evaluated as a potential replacement for TFA. Due to its stronger acidity, MSA gave better performance than TFA at the same concentration level. Furthermore, the use of reduced percentages of MSA, such as 8 mM, yielded similar results to those observed with 15 mM of MSA. The optimized UHPSFC method was, then, used to compare the performance of UHPSFC against RP-UHPLC for peptides with different pI and with increasing peptide chain length. UHPSFC was found to give a slightly better separation of the peptides according to their pI values, in few cases orthogonal to that observed in UHPLC. On the other hand, UHPSFC produced a much better separation of peptides with an increased amino acidic chain compared to UHPLC. Subsequently, UHPSFC-MS was systematically compared to UHPLC-MS using a set of linear and cyclic peptides commercially available. The optimized UHPSFC method was able to generate at least similar, and in some cases even better performance to UHPLC with the advantage of providing complementary information to that given by UHPLC analysis. Finally, the analytical UHPSFC method was transferred to a semipreparative scale using a proprietary cyclic peptide, demonstrating excellent purity and high yield in less than 15 min.

New wide-pore superficially porous stationary phases with low hydrophobicity applied for the analysis of monoclonal antibodies

The article describes the development of new stationary phases for the analysis of proteins in reversed phase liquid chromatography (RPLC). The goal was to have columns offering high recovery at low temperature, low hydrophobicity and novel selectivity. For this purpose, three different ligands bound onto the surface of superficially porous silica-based particles were compared, including trimethyl-silane (C1), ethyl-dimethyl-silane (C2) and N-(trifluoroacetomidyl)-propyl-diisopropylsilane (ES-LH). These three phases were compared with two commercial RPLC phases. In terms of protein recovery, the new ES-LH stationary phase clearly outperforms the other phases for any type of biopharmaceutical sample, and can already be successfully used at a temperature of only 60°C. In terms of retention, the new ES-LH and C1 materials were the less retentive ones, requiring lower organic solvent in the mobile phase. However, it is important to mention that the stability of C1 phase was critical under acidic, high temperature conditions. Finally, some differences were observed in terms of selectivity, particularly for the ES-LH column. Besides the chemical nature of the stationary phase, it was found that the nature of organic modifier also plays a key role in selectivity.

Multi-dimensional LC-MS: the next generation characterization of antibody-based therapeutics by unified online bottom-up, middle-up and intact approaches

This review presents an overview of current analytical trends in antibody characterization by multidimensional LC-MS approaches.

Fast Afucosylation Profiling of Glycoengineered Antibody Subunits by Middle-Up Mass Spectrometry

Middle-up LC-MS antibody characterization workflows using reduction or IdeS digestion for a focused assessment of N-glycan profiling of three representative glycoengineered monoclonal antibodies (mAbs), namely, obinutuzumab (GlycomAb technology, Glycart/Roche), benralizumab (Potelligent Technology, BioWa, Kyowa Kirin) and mAb B (kifunensine) and compared to mAb A, produced in a common CHO cell line. In addition, EndoS or EndoS2 enzyme are used for quantitative determination of Fc-glycan core afucosylation and high mannose for these antibodies, as requested by health authorities for Fc-competent therapeutics mAbs critical quality attributes (CQAs).

Algorithms to optimize multi-column chromatographic separations of proteins

The goal of this work was to provide a technical solution for the automated optimization of multi-column systems for protein separation and fractionation. Both algorithm and a software that can be downloaded are provided. In this algorithm, the length and order of the individual column segments can be considered. Various solutions are provided by the algorithm, including i) to obtain uniform peak distribution, ii) to park the different species at the inlet of the individual column segments, and iii) to elute all species as a single peak. Two representative examples are presented, showing the possibility to obtain uniform selectivity between monoclonal antibody (mAb) sub-units, and the on-column fractioning of intact mAbs.

Negative gradient slope methods to improve the separation of closely eluting proteins

In the present work, we describe the fundamental and practical advantages of a new strategy to improve the resolution of very closely eluting peaks within therapeutic protein samples. This approach involves the use of multiple isocratic steps, together with the addition of a steep negative gradient segment (with a decrease in mobile phase strength) to "park" a slightly more retained peak somewhere along the column (at a given migration distance), while a slightly less retained compound can be eluted. First, some model calculations were performed to highlight the potential of this innovative approach. For this purpose, the retention parameters (logk₀ and S) for two case studies were considered, namely the analysis of a mixture of two therapeutic mAbs (simple to resolve sample) and separation of a therapeutic mAb from its main variant (challenging to resolve sample). The results confirm that the insertion of a negative segment into a multi-isocratic elution program can be a good tool to improve selectivity between critical peak pairs. However, it is also important to keep in mind that this approach only works with large solutes, which more or less follow an "on-off" type elution behavior. Two real applications were successfully developed to illustrate the practical advantage of this new approach, including the separation of a therapeutic mAb from its main variant possessing very close elution behavior, and the separation of a carrier protein from an intact mAb as might be encountered in a quantitative bioanalysis assay. These two examples demonstrate that improved selectivity can be achieved for protein RPLC through the inclusion of a negative gradient slope that selectively bifurcates the elution of two or more peaks of interest.

Supercritical fluid chromatography - Mass spectrometry in metabolomics: Past, present, and future perspectives

Metabolomics, which consists of the comprehensive analysis of metabolites within a biological system, has been playing a growing role in the implementation of personalized medicine in modern healthcare. A wide range of analytical approaches are used in metabolomics, notably mass spectrometry (MS) combined to liquid chromatography (LC), gas chromatography (GC), or capillary electrophoresis (CE). However, none of these methods enable a comprehensive analysis of the metabolome, due to its extreme complexity and the large differences in physico-chemical properties between metabolite classes. In this context, supercritical fluid chromatography (SFC) represents a promising alternative approach to improve the metabolome coverage, while further increasing the analysis throughput. SFC, which uses supercritical CO₂ as mobile phase, leads to numerous advantages such as improved kinetic performance and lower environmental impact. This chromatographic technique has gained a significant interest since the introduction of advanced instrumentation, together with the introduction of dedicated interfaces for hyphenating SFC to MS. Moreover, new developments in SFC column chemistry (including sub-2 µm particles), as well as the use of large amounts of organic modifiers and additives in the CO₂-based mobile phase, significantly extended the application range of SFC, enabling the simultaneous analysis of a large diversity of metabolites. Over the last years, several applications have been reported in metabolomics using SFC-MS - from lipophilic compounds, such as steroids and other lipids, to highly polar compounds, such as carbohydrates, amino acids, or nucleosides. With all these advantages, SFC-MS is promised to a bright future in the field of metabolomics.

Evaluation of Different Tandem MS Acquisition Modes to Support Metabolite Annotation in Human Plasma Using Ultra High-Performance Liquid Chromatography High-Resolution Mass Spectrometry for Untargeted Metabolomics

Ultra-high performance liquid chromatography coupled to high-resolution mass spectrometry (UHPLC-HRMS) is a powerful and essential technique for metabolite annotation in untargeted metabolomic applications. The aim of this study was to evaluate the performance of diverse tandem MS (MS/MS) acquisition modes, i.e., all ion fragmentation (AIF) and data-dependent analysis (DDA), with and without ion mobility spectrometry (IM), to annotate metabolites in human plasma. The influence of the LC separation was also evaluated by comparing the performance of MS/MS acquisition in combination with three complementary chromatographic separation modes: reversed-phase chromatography (RPLC) and hydrophilic interaction chromatography (HILIC) with either an amide (aHILIC) or a zwitterionic (zHILIC) stationary phase. RPLC conditions were first chosen to investigate all the tandem MS modes, and we found out that DDA did not provide a significant additional amount of chemical coverage and that cleaner MS/MS spectra can be obtained by performing AIF acquisitions in combination with IM. Finally, we were able to annotate 338 unique metabolites and demonstrated that zHILIC was a powerful complementary approach to both the RPLC and aHILIC chromatographic modes. Moreover, a better analytical throughput was reached for an almost negligible loss of metabolite coverage when IM-AIF and AIF using ramped instead of fixed collision energies were used.

Investigating the use of unconventional temperatures in supercritical fluid chromatography

The use of unorthodox temperatures, ranging from -5 °C up to 80 °C, have been thoroughly investigated in supercritical fluid chromatography. To this purpose, an initial evaluation of the kinetic and thermodynamic performance has been made with a set of 4 analytes eluting at different percentages of organic co-solvent in the mobile phase (3%-10% - 45%-80%). The van Deemter plots have demonstrated how, at low organic modifier presence, the use of low temperatures did not necessarily translate into worse performance, while high temperatures could pose more issues due to the poor handling of the super/subcritical mobile phase by the chromatographic system. With important percentages of co-solvent, however, high temperatures were fundamental in ensuring better profiles of the van Deemter plots, compared to low temperatures. Pressure plots have demonstrated that gradients reaching elevated percentages of organic modifiers can also be used on stationary phases packed with sub 2 μm silica particles if high temperatures are employed. The thermodynamic evaluation, made via the analysis of van't Hoff plots, indicates the presence of three retention behaviors happening in UHPSFC when switching from high to low temperatures, depending on the co-solvent percentage needed to elute one analyte. Finally, an assessment of the stationary phase stability at high temperatures was performed: the retention times variabilities recorded were minimal (RSD < 2.5%), as well as the peak widths and inlet column pressures were somewhat constant throughout the analyses. In the second part of this study, a focus on potential applications benefiting from such unconventional temperatures has been made. A series of challenging analytes have experienced better chromatographic resolution at either high or low temperatures, providing therefore a potentially interesting tool to analysts during the chromatographic method development process. In conclusion, the UV sensitivity at different temperatures was also taken into consideration, with no significant impact on the quality of the UV signal under any condition.

Therapeutic Fc-fusion proteins: Current analytical strategies

Fc-Fusion proteins represent a successful class of biopharmaceutical products, with already 13 drugs approved in the European Union and United States as well as three biosimilar versions of etanercept. Fc-Fusion products combine tailored pharmacological properties of biological ligands, together with multiple functions of the fragment crystallizable domain of immunoglobulins. There is a great diversity in terms of possible biological ligands, including the extracellular domains of natural receptors, functionally active peptides, recombinant enzymes, and genetically engineered binding constructs acting as cytokine traps. Due to their highly diverse structures, the analytical characterization of Fc-Fusion proteins is far more complex than that of monoclonal antibodies and requires the use and development of additional product-specific methods over conventional generic/platform methods. This can be explained, for example, by the presence of numerous sialic acids, leading to high diversity in terms of isoelectric points and complex glycosylation profiles including multiple N- and O-linked glycosylation sites. In this review, we highlight the wide range of analytical strategies used to fully characterize Fc-fusion proteins. We also present case studies on the structural assessment of all commercially available Fc-fusion proteins, based on the features and critical quality attributes of their ligand-binding domains.

Impact of the column on effluent pH in cation exchange pH gradient chromatography, a practical study

In ionexchange chromatography, the pH gradient mode becomes more and more popular today for the analysis of therapeutic proteins as this mode can provide higher or alternative selectivity to the commonly used salt gradient mode. Ideally, a linear pH response is expected when performing linear gradients. However up to now, only a very few buffer systems have been developed and are commercially available which can perform nearly linear pH responses when flowing through a given column. It is also known that a selected buffer system (mobile phase) can work well on one column but can fail on other column. The goal of this study was to practically evaluate the effects that ionexchange columns (weak and strong exchangers) might have on effluent pH, when performing linear pH gradient separations of therapeutic monoclonal antibodies. To attain this objective, the pH was monitored on-line at the column outlet using a specific setup. To make comprehensive observations of the phenomenon, four different mobile phase conditions and five cation exchange columns (weak and strong exchangers) were employed. The obtained pH responses were systematically compared to responses measured in the absence of the columns. From this work, it has become clear that both the column and mobile phase can have significant effects on pH gradient chromatography and that their combination must be considered when developing a new method. Phase systems (column + mobile phase) providing linear pH responses are indeed the most suitable for separating mAbs with different isoelectric points and, with them, it is possible to elute mAbs across wide retention time ranges and with high selectivity.

Interlaboratory and Interplatform Study of Steroids Collision Cross Section by Traveling Wave Ion Mobility Spectrometry

Collision cross section (CCS) databases based on single-laboratory measurements must be cross-validated to extend their use in peak annotation. This work addresses the validation of the first comprehensive ^TWCCS_N2 database for steroids. First, its long-term robustness was evaluated (i.e., a year and a half after database generation; Synapt G2-S instrument; bias within ±1.0% for 157 ions, 95.7% of the total ions). It was further cross-validated by three external laboratories, including two different TWIMS platforms (i.e., Synapt G2-Si and two Vion IMS QToF; bias within the threshold of ±2.0% for 98.8, 79.9, and 94.0% of the total ions detected by each instrument, respectively). Finally, a cross-laboratory ^TWCCS_N2 database was built for 87 steroids (142 ions). The cross-laboratory database consists of average ^TWCCS_N2 values obtained by the four TWIMS instruments in triplicate measurements. In general, lower deviations were observed between ^TWCCS_N2 measurements and reference values when the cross-laboratory database was applied as a reference instead of the single-laboratory database. Relative standard deviations below 1.5% were observed for interlaboratory measurements (<1.0% for 85.2% of ions) and bias between average values and ^TWCCS_N2 measurements was within the range of ±1.5% for 96.8% of all cases. In the context of this interlaboratory study, this threshold was also suitable for ^TWCCS_N2 measurements of steroid metabolites in calf urine. Greater deviations were observed for steroid sulfates in complex urine samples of adult bovines, showing a slight matrix effect. The implementation of a scoring system for the application of the CCS descriptor in peak annotation is also discussed.

Applicability of Supercritical fluid chromatography-Mass spectrometry to metabolomics. II-Assessment of a comprehensive library of metabolites and evaluation of biological matrices

In this work, the impact of biological matrices, such as plasma and urine, was evaluated under SFCHRMS in the field of metabolomics. For this purpose, a representative set of 49 metabolites were selected. The assessment of the matrix effects (ME), the impact of biological fluids on the quality of MS/MS spectra and the robustness of the SFCHRMS method were each taken into consideration. The results have highlighted a limited presence of ME in both plasma and urine, with 30% of the metabolites suffering from ME in plasma and 25% in urine, demonstrating a limited sensitivity loss in the presence of matrices. Subsequently, the MS/MS spectra evaluation was performed for further peak annotation. Their analyses have highlighted three different scenarios: 63% of the tested metabolites did not suffer from any interference regardless of the matrix; 21% were negatively impacted in only one matrix and the remaining 16% showed the presence of matrix-belonging compounds interfering in both urine and plasma. Finally, the assessment of retention times stability in the biological samples, has brought into evidence a remarkable robustness of the SFCHRMS method. Average RSD (%) values of retention times for spiked metabolites were equal or below 0.5%, in the two biological fluids over a period of three weeks. In the second part of the work, the evaluation of the Sigma Mass Spectrometry Metabolite Library of Standards containing 597 metabolites, under SFCHRMS conditions was performed. A total detectability of the commercial library up to 66% was reached. Among the families of detected metabolites, large percentages were met for some of them. Highly polar metabolites such as amino acids (87%), nucleosides (85%) and carbohydrates (71%) have demonstrated important success rates, equally for hydrophobic analytes such as steroids (78%) and lipids (71%). On the negative side, very poor performance was found for phosphorylated metabolites, namely phosphate-containing compounds (14%) and nucleotides (31%).

Non-invasive targeted iontophoretic delivery of cetuximab to skin

Background: Cetuximab (CTX) is a glycosylated anti-EGFR monoclonal antibody of great interest in the treatment of non-melanoma skin cancers. Its intravenous administration is associated with severe side effects. This is the first report on the noninvasive iontophoretic-targeted topical delivery of CTX to skin.Methods: Iontophoretic transport of CTX (0.5 mA/cm²) was studied as a function of formulation pH (4, 5.5 and 7) and duration of current application (2, 4 and 8 h). CTX cutaneous biodistribution was determined; electrotransport mechanisms and penetration pathways were investigated.Results: Electrophoretic mobility measurements of CTX isoforms and co-iontophoresis of acetaminophen at each pH demonstrated that CTX electrotransport was due to electroosmosis: despite an ~8-fold reduction in charge, CTX skin deposition was greater at pH 7 than pH 4 (8.974 ± 1.952 and 0.482 ± 0.165 μg/mm³) - consistent with the increased electroosmotic flow at pH 7. Iontophoresis of an Alex488-CTX conjugate showed that skin penetration occurred by the intercellular and follicular routes. Therapeutic concentrations of CTX in the viable epidermis, upper dermis and lower dermis were achieved following iontophoresis for 2, 4 and 8 h, respectively.Conclusion: The results demonstrate the topical delivery of a 152 kDa monoclonal antibody into skin in a targeted, controlled and entirely noninvasive manner.