Size exclusion chromatography of biopharmaceutical products: From current practices for proteins to emerging trends for viral vectors, nucleic acids and lipid nanoparticles

The 21st century has been particularly productive for the biopharmaceutical industry, with the introduction of several classes of innovative therapeutics, such as monoclonal antibodies and related compounds, gene therapy products, and RNA-based modalities. All these new molecules are susceptible to aggregation and fragmentation, which necessitates a size variant analysis for their comprehensive characterization. Size exclusion chromatography (SEC) is one of the reference techniques that can be applied. The analytical techniques for mAbs are now well established and some of them are now emerging for the newer modalities. In this context, the objective of this review article is: i) to provide a short historical background on SEC, ii) to suggest some clear guidelines on the selection of packing material and mobile phase for successful method development in modern SEC; and iii) to highlight recent advances in SEC, such as the use of narrow-bore and micro-bore columns, ultra-wide pore columns, and low-adsorption column hardware. Some important innovations, such as recycling SEC, the coupling of SEC with mass spectrometry, and the use of alternative detectors such as charge detection mass spectrometry and mass photometry are also described. In addition, this review discusses the use of SEC in multidimensional setups and shows some of the most recent advances at the preparative scale. In the third part of the article, the possibility of SEC for the characterization of new modalities is also reviewed. The final objective of this review is to provide a clear summary of opportunities and limitations of SEC for the analysis of different biopharmaceutical products.

Considering the selectivity of pore size gradient size exclusion chromatography columns

One of the most significant performance determining variables of a size exclusion column is the pore size of its packing material. This is most definitely the case for assigning the suitability of a given column for differently sized analytes. As technologies for particle and column manufacturing continue to advance, it is worth contemplating the value of more finely controlled manipulation of this parameter. The change in a packing material's pores across the length of a size exclusion column was thus explored. A change in average pore diameter and pore size distribution was studied by means of theoretical modeling. These parameters were investigated for independent and combinatorial effects. From our predictions, versus tandem column chromatography, a gradient column apparatus does not yield sizable increases in monomer to dimer selectivity of any given critical pair. Instead, our modeling suggests it can yield more universally effective separations of multiple pairs of species at once, as is sometimes necessary when analyzing the high molecular weight components of highly aggregated drug substances.

Fast and efficient size exclusion chromatography of adeno associated viral vectors with 2.5 micrometer particle low adsorption columns

More and more transformative gene therapies (GTx) are reaching commercialization stage and many of them use Adeno Associated Viruses (AAVs) as their vector. Being larger than therapeutic antibodies, their size variant analysis poses an analytical challenge that must be addressed to speed up the development processes. Size exclusion chromatography (SEC) can provide critical information on the quality and purity of the product, but its full potential is not yet utilized by currently applied columns that are (i) packed with relatively large particles, (ii) prepared exclusively in large formats and (iii) built using metal hardware that is prone to secondary interactions. In this paper, we investigate the use of state-of-the-art sub-3 µm particles to address existing limitations. A prototype 2.5 µm column was found to deliver superior kinetic efficiency, significant reduction in run times and increased resolution of separations. No evidence for shear or sample sieving effects were found during comparisons with conventional 5 µm columns. Moreover, use of low adsorption hardware enabled the application of a wide range of mobile phase conditions and a chance to apply a more robust platform method for several AAV serotypes. The resulting method was tested for its reproducibility as well as utility for critical quality attribute assays, including multiangle light scattering based (MALS) measurements of size and molar mass. Thus, a new tool for higher resolution, higher throughput size variant analysis of AAVs has been described.

Improved sample introduction approach in hydrophilic interaction liquid chromatography to avoid breakthrough of proteins

When therapeutic proteins are analysed under hydrophilic interaction liquid chromatography (HILIC) conditions, there is an inherent mismatch between the sample diluent (proteins must be solubilised in aqueous media) and the mobile phase, which is mostly composed of aprotic solvent (acetonitrile). This difference in eluent strength between sample diluent and mobile phase is responsible for severe analyte breakthrough and peak distortion. As demonstrated with therapeutic proteins of different sizes (insulin of 6 kDa, anakinra of 17 kDa and rituximab subunits of 25 and 50 kDa), only very small volumes of 0.1-0.2 µL can be injected without breakthrough effects, when performing rapid analysis on short HILIC columns of 20-50 mm, leading to poor sensitivity. In order to avoid the undesired effect of the strong sample diluent, a special injection program should be preferred. This consists in the addition and automatic injection of a defined volume of weak solvent (acetonitrile) along with the sample to increase retention factors during sample loading. Various injection programs were tested, including the addition of a pre-injection or post-injection or both (bracketed injection) of acetonitrile plugs. Several weak to strong injection solvent ratios of 1:1, 1:2, 1:4 and 1:10 were tested. Our work proves that the addition of a pre-plug solvent with a weak vs. strong injection solvent ratio of 1:10 is a valuable strategy to inject relatively large volumes of proteins in HILIC, regardless of column dimensions, thus maximising sensitivity. No peak deformation or breakthrough was observed under these conditions. However, it is important to note that peak broadening (40 % larger peaks) was observed when the injection program increased the injection solvent ratio from 1:1 to 1:10. Finally, this strategy was applied to a wide range of therapeutic mAb products with different physico-chemical properties. In all cases, relatively large volumes can be successfully injected onto small volume HILIC columns using a purely aqueous sample diluent, as long as an appropriate (weak) solvent pre-injection is applied.

Practical study on the impact of injection conditions in gradient elution mode for the analysis of therapeutic proteins when using very short columns

The impact of injected sample volume on apparent efficiency has been studied for very short columns in a systematic way. For large molecules such as therapeutic proteins, it was found that relatively large volumes can be injected onto ultra-short RPLC and IEX columns (i.e. L < 50 mm) without significantly affecting the quality of the separation. This favourable behavior is due to the on-off elution mechanism of large molecules and to the fact that therapeutic protein samples are formulated in aqueous-based media, which is the weakest solvent in RPLC and IEX. Therefore, their peak is strongly focused at the column inlet even when large volume is injected, and pre-column peak dispersion is compensated. However, ultra-short HILIC columns do not seem to be favorable, as they require for very low injection volume to avoid detrimental peak splitting and breakthrough effects. Such peak distortion is related to the inherent solvent mismatch between sample diluent (aqueous) and mobile phase strength (highly organic in HILIC). When studying mass load, the ranking of the elution modes was the same, and the largest relative mass could be injected onto IEX columns (as large as 10% sample to sorbent mass), without affecting the separation quality.

Separation of Plasmid DNA Topological Forms, Messenger RNA, and Lipid Nanoparticle Aggregates Using an Ultrawide Pore Size Exclusion Chromatography Column

Health authorities have highlighted the need to determine oligonucleotide aggregates. However, existing technologies have limitations that have prevented the reliable analysis of size variants for large nucleic acids and lipid nanoparticles (LNPs). In this work, nucleic acid and LNP aggregation was examined using prototype, low adsorption ultrawide pore size exclusion chromatography (SEC) columns. A preliminary study was conducted to determine the column's physicochemical properties. A large difference in aggregate content (17.8 vs 59.7 %) was found for a model messenger RNA (mRNA) produced by different manufacturers. We further investigated the nature of the aggregates via a heat treatment. Interestingly, thermal stress irreversibly decreased the amount of aggregates from 59.7 to 4.1% and increased the main peak area 3.3-fold. To the best of our knowledge, for the first time, plasmid DNA topological forms and multimers were separated by analytical SEC. The degradation trends were compared to the data obtained with an anion exchange chromatography method. Finally, unconjugated and fragment antigen-binding (Fab)-guided LNPs were analyzed and their elution times were plotted against their sizes as measured by DLS. Multi-angle light scattering (MALS) was coupled to SEC in order to gain further insights on large species eluting before the LNPs, which were later identified as self-associating LNPs. This study demonstrated the utility of ultrawide pore SEC columns in characterizing the size variants of large nucleic acid therapeutics and LNPs.

Ultra-short columns for the chromatographic analysis of large molecules

Today, reverse phase liquid chromatography (RPLC) analysis of proteins is almost exclusively performed on conventional columns (100-150 mm) in gradient elution mode. However, it was shown many years ago that large molecules present an on/off retention mechanism, and that only a very short inlet segment of the chromatographic column retains effectively the large molecules. Much shorter columns - like only a few centimetres or even a few millimetres - can therefore be used to efficiently analyse such macromolecules. The aim of this review is to summarise the historical and more recent works related to the use of very short columns for the analysis of model and therapeutic proteins. To this end, we have outlined the theoretical concepts behind the use of short columns, as well as the instrumental limitations and potential applications. Finally, we have shown that these very short columns were also possibly interesting for other chromatographic modes, such as ion exchange chromatography (IEX), hydrophilic interaction chromatography (HILIC) or hydrophobic interaction chromatography (HIC), as analyses in these chromatographic modes are performed in gradient elution mode.

[How could forensic psychiatry be made more attractive?]

INTRODUCTION

Decrease in the number of forensic psychiatric experts recently reached a critical level. Shortage of forensic experts caused difficulties in the health care as well as in the justice system.

OBJECTIVE

Surveying of how the field of forensic psychiatry and the forensic psychiatric expert work can be made more attractive.

METHOD

We performed an online survey among forensic psychiatric experts and specialists in psychiatry. We complied a questionnaire that beside demographic data contained questions in 4 areas. The first 2 areas of the questionnaire - simplifying the forensic psychiatry training (10 items), decreasing the cost of the forensic psychiatry training (5 items) - consisted of simple tatements. Responders had to indicate on a 10-point Likert scale their level of agreement. In the last 2 areas, participants were asked to describe in unstructured format whether they see any circumstance that makes forensic psychiatry attractive or unattractive. The questionnaire was sent out in electronic form to the forensic psychiatric experts on the mailing list of the Hungarian Forensic Expert Chamber, and all specialists in psychiatry on the mailing list of the Hungarian Medical Chamber.

RESULTS

Altogether 171 persons filled in the questionnaire with a mean age of 57.26 ± 11.57 years. There were 122 (71.3%) females among the participants. The following proposals received the highest ratings from the forensic psychiatric experts as well as from the specialists in psychiatry: increasing the number of the training institutes; decreasing the costs of the training; making the Hungarian Forensic Expert Chamber course free of charge; and introducing a stipend to cover the costs of the training.

DISCUSSION

Results of the survey indicate that active forensic psychiatric experts and specialists in psychiatry representing a potential professional resource, concur that forensic psychiatry training can be made more attractive mainly with increasing the number of training institutes and decreasing the total costs of the training which is compiled from different constituents.

CONCLUSION

Due to the critical lack of necessary professionals, urgent action is needed to make forensic psychiatry more popular and the forensic psychiatry qualification easier to obtain. Orv Hetil. 2023; 164(35): 1373-1380.

High-Throughput Chromatographic Separation of Oligonucleotides: A Proof of Concept Using Ultra-Short Columns

Ion-pairing reversed-phase liquid chromatography (IP-RPLC) is the reference separation technique for characterizing oligonucleotides (ONs) and their related impurities. The aim of this study was to better understand the retention mechanism of ONs, evaluate the applicability of the linear solvent strength (LSS) retention model, and explore the potential of ultra-short columns having a length of only 5 mm for the separation of model ONs. First, the validity of the LSS model was evaluated for ONs having sizes comprised between 3 and 30 kDa, and the accuracy of retention time predictions was assessed. It was found that ONs in IP-RPLC conditions follow an "on-off" elution behavior, despite a molecular weight lower than that of proteins. For most linear gradient separation conditions, a column length between 5 and 35 mm was found to be appropriate. Ultra-short columns of only 5 mm were therefore explored to speed up separations by considering the impact of the instrumentation on the efficiency. Interestingly, the impacts of injection volume and post-column connection tubing on peak capacity were found to be negligible. Finally, it was demonstrated that longer columns would not improve selectivity or separation efficiency, but baseline separation of three model ONs mixtures was enabled in as little as 30 s on the 5 mm column. This proof-of-concept work paves the way for future investigations using more complex therapeutic ONs and their related impurities.

Investigation of several chromatographic approaches for untargeted profiling of central carbon metabolism

Monitoring the central carbon metabolism (CCM) network using liquid chromatography/mass spectrometry (LC-MS) analysis is hampered by the diverse chemical nature of its analytes, which are extremely difficult to analyze using single chromatographic conditions. Furthermore, CCM-related compounds present non-specific adsorption on metal surfaces, causing detrimental chromatographic effects and sensitivity loss. In this study, polar reversed-phase, mixed-mode (MMC), and zwitterionic hydrophilic interaction chromatography (HILIC) featuring low-adsorption hardware were investigated towards untargeted analysis of biological samples with a focus on energy metabolism-related analytes. Best results were achieved with sulfoalkylbetaine HILIC with different supports, where polymeric option featured the highest coverage and inert hybrid silica facilitated best throughput and kinetic performance at a cost of less selectivity for small carboxylic acids. MMC demonstrated excellent performance for strongly anionic analytes such as multiresidue phosphates. The obtained experimental data also suggested that an additional hydrophilic modulation might be necessary to facilitate better resolution of carboxylic acids in zHILIC mode, as found during the application of the developed method to study the effect of two different mutations on the energy metabolism of S. aureus.

Studying effective column lengths in liquid chromatography of large biomolecules

Based on their nature, large molecules tend to exhibit on-off elution such that only a small segment of a column bed participates in their separation. We were intrigued to investigate empirical data on this behavior and to apply a simple method to estimate the length of column bed that is needed to produce an effective separation. Models were derived by rearranging the linear solvent strength (LSS) model equations, and data sets from almost 100 different separation conditions were treated to illustrate effects for various types of solutes as separated by reversed phase (RP), ion-pair reversed phase (IP-RP), ion-exchange (IEX), hydrophobic interaction (HIC) and hydrophilic interaction (HILIC) chromatography. By empirically measuring S parameters (S is a solute dependent model parameter, it describes how sensitive is the solute retention to mobile phase composition), and calculating for an exit retention factor of 0.5, we have determined that there is little to no benefit to separating moderately sized solutes (5 - 10 kDa) with a column bed that is longer than 3 cm, particularly when a less than 20 min gradient is desired. Moreover, even shorter columns would be predicted to be adequate for 100 - 150 kDa molecules. Interpretations of this sort have become possible because there is some correlation between a solute's molecular weight and its S parameter. That is, empirical observations on retention behavior are not needed to select appropriate column lengths; molecular weight provides a sufficient approximation. With these insights, we suggest reconsidering the routine use of 5 - 15 cm long columns for >10 kDa biomolecule separations and instead propose that a new focus be placed on 1-2 cm long columns.

Theoretical study on solute migration and band broadening occurring in pressure-enhanced liquid chromatography

Upon recently studying the use of pressure gradients during liquid chromatography (LC), it was noted that pressure differentials across a column can have a significant impact on peak shape, not just retention as has been noted several times before. Theoretical models and thought experiments were performed here to more carefully study these effects. Two situations have been elucidated. The first is one that reflects a protein reversed phase separation wherein solute retention increases with pressure. In this condition, it has been found that a positive pressure gradient will result in band broadening while a negative pressure gradient will help yield sharper peaks. The second case that has come to be better appreciated is when solute retention decreases with pressure, which can occur in protein ion exchange (IEX) and hydrophobic interaction chromatography (HIC). In this situation, a positive pressure gradient will conversely result in peak sharpening, and a negative pressure gradient will introduce band broadening. These observations have facilitated making new fundamental understandings on pressurized separations which has in turn made it possible to begin envisioning new ways of and reasons for applying pressure enhanced LC methods.

Challenges and emerging trends in liquid chromatography-based analyses of mRNA pharmaceuticals

Lipid encapsulated messenger RNA (LNP mRNA) has garnered a significant amount of interest from the pharmaceutical industry and general public alike. This attention has been catalyzed by the clinical success of LNP mRNA for SARS-CoV-2 vaccination as well as future promises that might be fulfilled by the biotechnology pipeline, such as the in vivo delivery of a CRISPR/Cas9 complex that can edit patient cells to reduce levels of low-density lipoprotein. LNP mRNAs are comprised of various chemically diverse molecules brought together in a sophisticated intermolecular complex. This can make it challenging to achieve thorough analytical characterization. Nevertheless, liquid chromatography is becoming an increasingly relied upon technique for LNP mRNA analyses. Although there have been significant advances in all types of LNP mRNA analyses, this review focuses on recent developments and the possibilities of applying anion exchange (AEX) and ion pairing reversed phase (IP-RP) liquid chromatography for intact mRNAs as well as techniques for oligo mapping analysis, 5' endcap testing and lipid compositional assays.

Ultra-Fast Middle-Up Reversed Phase Liquid Chromatography Analysis of Complex Bispecific Antibodies Obtained in Less Than One Minute

This work illustrates the benefits and limitations of using ultra-short reversed phase liquid chromatography (RPLC) columns for the characterization of various complex bispecific antibodies after prolonged thermal stress at the middle-up level of analysis. First, we have demonstrated that alternative organic modifiers, such as isopropanol, can be used in RPLC mode without generating excessive pressure, thanks to the prototype 10 × 2.1 mm, 2.7 µm particle column. However, compared to acetonitrile, the selectivity was not improved, at least for the selected biopharmaceutical products. Importantly, very fast separations (sub-1 min) of high quality were systematically obtained for the different samples when using a spectroscopic detector, but a severe loss of performance was observed with mass spectrometry (MS) detection due to dispersion effects. Based on these results, there is a clear need to improve the interfacing between LC and MS (shorter/thinner tubing) to mitigate band broadening.

Studying the possibilities of dual stationary phase gradients to explore alternative selectivities in liquid chromatography

Previous studies on stationary phase gradients have inspired a new phase of theoretical work and an expansion of the concept to include multiple retention mechanisms. The theoretical work presented here corroborates previous reports that a stationary phase gradient can produce selectivity in a separation as effectively as careful adjustments to a mobile phase gradient program, especially when such column is operated in mobile phase gradient elution mode. In reality, no column is singularly based on one type of interaction mechanism, and many columns are nowadays designed to solicit multiple solute to stationary phase interactions. These mixed-mode columns inspired us to give more careful consideration to the idea of dual stationary phase gradients. With the theory applied here, it is suggested that the modulation of two unique interaction mechanisms across a chromatographic column has the potential to open up previously unseen selectivities. With the increasing prevalence of mixed-mode columns, we believe there will be ample opportunity to explore these new concepts in experimental work.

Expediting the chromatographic analysis of COVID-19 antibody therapeutics with ultra-short columns, retention modeling and automated method development

The COVID-19 pandemic necessitated the emergency use authorization (EUA) of several new therapeutics and vaccines. Several monoclonal antibodies (mAbs) were among those authorized for use, and they have served a purpose to provide passive immunity and to help minimize dangerous secondary effects in at-risk and hospitalized patients infected with SARS-CoV-2. With an EUA submission, scientific data on a drug candidate is often collected near simultaneously alongside drug development. In such a situation, there is little time to allow misguided method development nor time to wait on traditional turnaround times. We have taken this dilemma as a chance to propose new means to expediting the chromatographic characterization of protein therapeutics. To this end, we have combined the use of automated, systematic modeling and ultrashort LC columns to quickly optimize high throughput RP, IEX, HILIC and SEC separations for two COVID-19-related mAbs. The development and verification of these four complementary analytical methods required only 2 days of experimental work. In the end, one chromatographic analysis can be performed with a sub-2 min run time such that it is feasible to comprehensively characterize a COVID-19 mAb cocktail by 4 different profiling techniques within a 1-hour turnaround time.

Internet Use Related to Suicidal Thoughts and Help-Seeking – Preliminary Results of a Study with Depressive Patients

Introduction

Suicide-related Internet use is becoming more common, and many research study its potential risks and benefits.

Objectives

Data on suicidal thoughts and Internet use of patients with depressive disorders were collected to assess their suicide-related Internet use and its relation to help-seeking preferences.

Methods

Semi-structured interviews were completed to assess Internet use patterns and suicidal thoughts among patients treated with depressive disorders, and preferred forms of help-seeking were also examined.

Results

113 patients completed the interviews, most of them spend more hours a day using the Internet. More than 80% came across suicide-related contents while browsing, a quarter reported specific search for suicidal contents. In case of suicidal thoughts, three-quarters of depressed patients would seek help from a mental health professional, two-thirds from their partners, half from friends, and nearly one-third from parents, other relatives or from GPs. Most patients would prefer offline (personal) help for their psychological problems and suicidal thoughts, online methods were less preferred, with only one-fifth choosing these options. However, a third of them also considered it probable that they would not ask anyone for help.

Conclusions

Despite of the frequent use of the Internet, online help-seeking is less common in depressive patients. However, in the times of pandemic, online help facilities may provide an opportunity to prevent suicidal behavior for those, who have suicidal thoughts and use the Internet regularly, especially searching for suicide-related contents. In the future, further research is needed to develop more effective online suicide prevention programs and applications.

Disclosure

No significant relationships.

Pressure-Enhanced Liquid Chromatography, a Proof of Concept: Tuning Selectivity with Pressure Changes and Gradients

Many chromatographers have observed that the operating pressure can dramatically change the chromatographic retention of solutes. Small molecules show observables changes, yet even more sizable effects are encountered with large biomolecules. With this work, we have explored the use of pressure as a method development parameter to alter the reversed-phase selectivity of peptide and protein separations. An apparatus for the facile manipulation of column pressure was assembled through a two-pump system and postcolumn flow restriction. The primary pump provided an eluent flow through the column, while the secondary pump provided a pressure-modulating flow at a tee junction after the column but ahead of a flow restrictor. Using this setup, we were able to quickly program various constant pressure changes and even pressure gradients. It was reconfirmed that pressure changes impact the retention of large molecules to a much greater degree than small molecules, making it especially interesting to consider the use of pressure to selectively separate solutes of different sizes. The addition of pressure to bring the column operating pressure beyond 500 bar was enough to change the elution order of insulin (a peptide hormone) and cytochrome C (a small serum protein). Moreover, with the proposed setup, it was possible to combine eluent and pressure gradients in the same analytical run. This advanced technique was applied to improve the separation of insulin from one of its forced degradation impurities. We have referred to this method as pressure-enhanced liquid chromatography and believe that it can offer unseen selectivity, starting with peptide and protein reversed-phase separations.

Improving Selectivity in the Chromatographic Analysis of Monoclonal Antibodies (mAbs) Through the Use of Multi-Isocratic Elution Mode

When characterizing monoclonal antibodies (mAbs) with reversed-phase liquid chromatography (RPLC), it is often challenging to attain sufficient selectivity between mAbs and their related variants. A new strategy, referred to as multi-isocratic elution mode, has recently been developed. It is based on setting a series of consecutive isocratic steps and very short steep gradient segments at solute elution. This elution mode offers several advantages compared to the usually applied linear gradient mode. Large biomolecules can benefit the most because of their “on/off” elution behavior. Arbitrary selectivity can be set between closely related protein variants while maintaining sharp peaks because of the strong band compression effects occurring at elution within the steep gradient segments.

Therapeutic drug monitoring in children and adolescents with schizophrenia and other psychotic disorders using risperidone

Risperidone is commonly used to treat different psychiatric disorders worldwide. Knowledge on dose–concentration relationships of risperidone treatment in children and adolescents with schizophrenia or other psychotic disorders is, however, scarce and no age-specific therapeutic ranges have been established yet. Multicenter data of a therapeutic drug monitoring service were analyzed to evaluate the relationship between risperidone dose and serum concentration of the active moiety (risperidone (RIS) plus its main metabolite 9-hydroxyrisperidone (9-OH-RIS)) in children and adolescents with psychotic disorders. Patient characteristics, doses, serum concentrations and therapeutic outcomes were assessed by standardized measures. The study also aimed to evaluate whether the therapeutic reference range for adults (20–60 ng/ml) is applicable for minors. In the 64 patients (aged 11–18 years) included, a positive correlation between daily dose and the active moiety (RIS_am) concentration was found (r_s = 0.49, p = 0.001) with variation in dose explaining 24% (r_s² = 0.240) of the variability in serum concentrations. While the RIS_am concentration showed no difference, RIS as well 9-OH-RIS concentrations and the parent to metabolite ratio varied significantly in patients with co-medication of a CYP2D6 inhibitor. Patients with extrapyramidal symptoms (EPS) had on average higher RISam concentrations than patients without (p = 0.05). Considering EPS, the upper threshold of the therapeutic range of RIS_am was determined to be 33 ng/ml. A rough estimation method also indicated a possibly decreased lower limit of the preliminary therapeutic range in minors compared to adults. These preliminary data may contribute to the definition of a therapeutic window in children and adolescents with schizophrenic disorders treated with risperidone. TDM is recommended in this vulnerable population to prevent concentration-related adverse drug reactions.

Direct coupling of size exclusion chromatography and mass spectrometry for the characterization of complex monoclonal antibody products

The present study describes the possibilities offered by an innovative bioinert size exclusion chromatography column for size variant characterization of complex monoclonal antibody products. This size exclusion chromatography column includes a novel column hardware surface. The column was prepared from metallic hardware components that were treated to have prototype hydrophilically modified hybrid organic–inorganic silica surfaces called hybrid surface technology. This provides a significant reduction in nondesired hydrophobic and electrostatic interactions that can occur between column and analyte when performing size exclusion chromatography analysis with volatile mobile phase.

Compared to a reference stainless‐steel column packed with the same batch of packing material, peak tailing, band broadening, and above all recovery of high molecular weight species were distinctly improved for all types of monoclonal antibody products. Based on our observations, we found that 50 mM ammonium acetate in water was a suitable mobile phase offering good compromise in terms of liquid chromatography performance and mass spectrometry sensitivity. In addition, method repeatability (intra‐ and interday relative standard deviations) on elution times and high molecular weight species peak areas were found to be excellent.

By using this innovative size exclusion chromatography material, the low and high molecular weight species contained in various stressed and nonstressed monoclonal antibody products were successfully characterized with mass spectrometry detection.

Size Exclusion and Ion Exchange Chromatographic Hardware Modified with a Hydrophilic Hybrid Surface

Certain biomolecules have proven to be difficult to analyze by liquid chromatography (LC), especially under certain chromatographic conditions. The separation of proteins in aqueous mobile phases is one such example because there is the potential for both hydrophobic and ionic secondary interactions to occur with chromatographic hardware to the detriment of peak recovery, peak shape, and the overall sensitivity of the LC analysis. To decrease non-specific adsorption and undesired secondary interactions between column hardware and biomolecules, we have developed and applied a new hydrophilically modified hybrid surface (h-HST) for size exclusion chromatography (SEC) and anion exchange (AEX) separations of proteins and nucleic acids. This surface incorporates additional oxygen and carbon atoms onto an ethylene bridge hybrid siloxane polymer. As a result, it exhibits reduced electrostatic properties and hydrophilicity that facilitates challenging aqueous separations. Flow injection tests with a phosphate buffer showed superior protein recovery from an h-HST frit when compared to unmodified ethylene-bridged hybrid HST, titanium, stainless steel, and PEEK frits. When applied to SEC of rituximab, ramucirumab, and trastuzumab emtansine with a 50 mM ammonium acetate buffer, this new hydrophilic chromatographic hardware yielded improved monomer and aggregate recovery, higher plate numbers, and more symmetrical peaks. AEX columns also benefited from h-HST hardware. An acidic mAb (eculizumab) showed improved recovery, more stable retention, and a sharper peak when eluted from an h-HST versus SS column. Moreover, AEX separations of intact mRNA samples (Cas9 and EPO mRNA) were improved, where it was seen that h-HST column hardware provided higher sensitivity and more repeatable peak areas from injection to injection. As such, there is significant potential in the use of h-HST chromatographic hardware to facilitate more robust and more sensitive analyses for a multitude of challenging separations and analytes.

Prevalence and correlates of aggressive behavior in psychiatric inpatient populations

Aggressive behavior in patients with psychiatric disorders is attracting increasing research interest. One reason for this is that psychiatric patients are generally considered more likely to be aggressive, which raises a related question of whether diagnoses of psychiatric disorders predict the prevalence of aggressive behavior. Predicting aggression in psychiatric wards is crucial, because aggressive behavior not only endangers the safety of both patients and staff, but it also extends the hospitalization times. Predictions of aggressive behavior also need careful attention to ensure effective treatment planning. This literature review explores the relationship between aggressive behavior and psychiatric disorders and syndromes (dementia, psychoactive substance use, acute psychotic disorder, schizophrenia, bipolar affective disorder, major depressive disorder, obsessive-compulsive disorder, personality disorders and intellectual disability). The prevalence of aggressive behavior and its underlying risk factors, such as sex, age, comorbid psychiatric disorders, socioeconomic status, and history of aggressive behavior are discussed as these are the components that mostly contribute to the increased risk of aggressive behavior. Measurement tools commonly used to predict and detect aggressive behavior and to differentiate between different forms of aggressive behavior in both research and clinical practice are also reviewed. Successful aggression prevention programs can be developed based on the current findings of the correlates of aggressive behavior in psychiatric patients.

Ultra-short ion-exchange columns for fast charge variants analysis of therapeutic proteins

The purpose of this work was to study the potential of recently developed ultra-short column hardware for ion exchange chromatography (IEX). Various prototype and commercial columns having lengths of 5, 10, 15, 20 and 50 mm and packed with non-porous 3 µm particles were systematically compared. Both pH and salt gradient modes of elution were evaluated. Similarly, what has been previously reported for reversed phase liquid chromatography (RPLC) mode, an "on-off" retention mechanism was observed in IEX for therapeutic proteins and their fragments (25-150 kDa range). Because of the non-porous nature of the IEX packing material, the column porosity was relatively low (ε = 0.42) and therefore the volumes of ultra-short columns were very small. Based on this observation, it was important to reduce as much as possible all the sources of extra-column volumes (i.e. injection volume, extra-bed volume, detector cell volume and connector tubing volume), to limit peak broadening. With a fully optimized UHPLC system, very fast separations of intact and IdeS digested mAb products were successfully performed in about 1 min using an IEX column with dimensions of 15 × 2.1 mm. This column was selected for high-throughput separations, since it probably offers the best compromise between efficiency and analysis time. For such ultra-fast separations, PEEK tubing was applied to bypass the column oven (column directly connected) to the optical detector via a zero dead volume connection.

Towards a simple on-line coupling of ion exchange chromatography and native mass spectrometry for the detailed characterization of monoclonal antibodies

This work describes the direct hyphenation of cation exchange chromatography (CEX) with a compact, easy-to-use benchtop Time of Flight mass spectrometer (ToF/MS) for the analytical characterization of monoclonal antibodies (mAbs). For this purpose, a wide range of commercial mAb products (including expired samples and mAb biosimilars) were selected to draw reliable conclusions. From a chromatographic point of view, various buffers and column dimensions were tested. When considering pH response, buffer stability over time and MS compatibility, the best compromise is represented by the following recipe: 50 mM ammonium acetate, titrated to pH 5.0 (mobile phase A) and 160 mM ammonium acetate, titrated to pH 8.5 (mobile phase B). Despite the broader peaks observed with the 2.1 mm i.d. CEX column, this was preferentially selected for CEX-MS operation, since the efficiency loss (caused by extra-column dispersion) was still acceptable while MS compatibility was strongly enhanced (thanks to low flow rate). In terms of MS, it was important to avoid the use of glass-bottled mobile phases, laboratory glassware and glass vials to minimize loss of MS resolution, sensitivity, and mass accuracy due to metal contaminants. With this new CEX-MS setup, straightforward and rapid analysis (in less than 10 min) of charge variants was possible, allowing the separation and identification of several charge variants.

Development of a Fast and Robust UHPLC Method for Apixaban In-Process Control Analysis

In-process control (IPC) is an important task during chemical syntheses in pharmaceutical industry. Despite the fact that each chemical reaction is unique, the most common analytical technique used for IPC analysis is high performance liquid chromatography (HPLC). Today, the so-called “Quality by Design” (QbD) principle is often being applied rather than “Trial and Error” approach for HPLC method development. The QbD approach requires only for a very few experimental measurements to find the appropriate stationary phase and optimal chromatographic conditions such as the composition of mobile phase, gradient steepness or time (tG), temperature (T), and mobile phase pH. In this study, the applicability of a multifactorial liquid chromatographic optimization software was studied in an extended knowledge space. Using state-of-the-art ultra-high performance liquid chromatography (UHPLC), the analysis time can significantly be shortened. By using UHPLC, it is possible to analyse the composition of the reaction mixture within few minutes. In this work, a mixture of route of synthesis of apixaban was analysed on short narrow bore column (50 × 2.1 mm, packed with sub-2 µm particles) resulting in short analysis time. The aim of the study was to cover a relatively narrow range of method parameters (tG, T, pH) in order to find a robust working point (zone). The results of the virtual (modeled) robustness testing were systematically compared to experimental measurements and Design of Experiments (DoE) based predictions.

Empirical correction of non-linear pH gradients and a tool for application to protein ion exchange chromatography

This concept article reports a practical solution to improve the linearity of effluent pH response as observed in pH gradient cation exchange chromatography (CEX). When performing pH gradient CEX, it is not easy to develop buffer systems that will universally provide pH response proportional with the mobile phase (buffer) composition. It is an especially challenging pursuit when exploring MS compatible buffers (e.g. ammonium-acetate, ammonium-carbonate). In addition to "non-proportional" behavior from the mobile phase composition, the chromatographic column itself will sometimes impose an unpredictable impact on the effluent pH. Here, we propose a simple approach based on the on-line measurement of effluent pH response, conversion of pH to mobile phase volume fraction (φ) and then generation of the inverse response function in the time domain. In the end, when setting the inverse function as the gradient program instead of a linear gradient, an improved - ideally linear - pH response can be produced. A simple Excel tool was developed to assist analysts with this correction procedure, and it has been made available by download for public use.

Defining Material Used in Biopharmaceutical Analysis

There is a need to use more descriptive and precise terms to describe some of the properties of the products used for biopharmaceutical analysis. It is probably more correct to say “low adsorption” and “corrosion-resistant” systems.

Using 1.5 mm internal diameter columns for optimal compatibility with current liquid chromatographic systems

This article describes the use of a new prototype column hardware made with 1.5 mm internal diameter (i.d.) and demonstrates some benefits over the 1.0 mm i.d. micro-bore column. The performance of 2.1, 1.5 and 1.0 mm i.d. columns were systematically compared. With the 1.5 mm i.d. column, the loss of apparent column efficiency can be significantly reduced compared to 1.0 mm i.d. columns in both isocratic and gradient elution modes. In the end, the 1.5 mm i.d. column is almost comparable to 2.1 mm i.d. column from a peak broadening point of view. The advantages of the 1.5 mm i.d. hardware vs 2.1 mm i.d. narrow-bore columns are the lower sample and solvent consumption, and reduced frictional heating effects due to decreased operating flow rates.

Aptamer-based immunoaffinity LC-MS using an ultra-short column for rapid attomole level quantitation of intact mAbs

Quantification of proteins in biofluids has largely involved either traditional ligand binding assays or "bottom-up" mass spectrometry. Recently, top-down mass spectrometry using reversed-phase liquid chromatography (RPLC) paired with high-resolution mass spectrometry (HRMS) has emerged as a promising technique, due to the potential of better identification of post-translational modifications (PTMs), lack of downstream interferences, and less time-consuming sample preparation and analysis times. However, it can be difficult with this approach to robustly obtain high-fidelity MS data, especially when pushing for low limits of detection. To address these issues, we developed a chromatographic device with an optimized form factor and stationary phase to improve protein recovery, while reducing run times. We have observed that by using this device, it is possible to achieve attomole quantitation of mAbs without the addition of carrier proteins and with over three-fold higher throughput than columns employed in previous studies. Moreover, we have devised a novel affinity capture method, based on repurposing a unique aptamer ligand that can give 93% recovery of mAb using only a 2 h incubation. When hyphenated together, these two technologies greatly improve the ability to analyze proteins in complex matrices.

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.

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.

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.

Updating the European Pharmacopoeia impurity profiling method for terazosin and suggesting alternative columns

This work was motivated by the demand of European Directorate for the Quality of Medicines and HealthCare (EDQM). A new liquid chromatographic (LC) method was developed for terazosin impurity profiling to replace the old European Pharmacopoeia (Ph. Eur.) method. This new method is published as part of the new Ph. Eur. monograph proposal of terazosin in Pharmeuropa issue 32.2. The aim of the method renewal was to cut the analysis time from 90 min (2 × 45 min) down to below 20 min. The Ph. Eur. monograph method is based on two different chromatographic separations to analyze the specified impurities of terazosin. The reason for the two methods is that two of the impurities are not sufficiently retained in reversed phase (RP) conditions, not even with 100% water as eluent. Therefore, next to RP, an ion-pair (IP) chromatographic method has to be applied to analyze those two impurities. With our new proposed method it was possible to appropriately increase the retention of the two critical compounds using alternative stationary phases (instead of a C18 phase which is suggested by the Ph. Eur. method). Applying a pentafluoro-phenyl (PFP) stationary phase, it was feasible to separate and adequately retain all the impurities. The detection wavelength was also changed compared to the Ph. Eur. method and is now appropriate for the detection and quantification of all impurities using perchloric acid in the mobile phase at low pH. Another goal of the present study was to develop a generic workflow and to evaluate the chromatographic resolution in a wide range of method variables and suggest some replacement columns for terazosin impurity profiling. Retention modeling was applied to study the chromatographic behavior of the compounds of interest and visualize resolution for the different columns, where a given criterion is fulfilled. A zone (set of chromatographic conditions) of a robust space could be then quickly identified by the overlay of the individual response surfaces (resolution maps). It was also demonstrated that two columns from different providers (Kinetex F5 and SpeedCore PFP) can be used as replacement columns, providing sufficient resolution at the same working point and a high degree of robustness.