Protein aggregation and its inhibition in biopharmaceutics

Influence of pH on heat-induced aggregation and degradation of therapeutic monoclonal antibodies

Monoclonal antibodies are widely used for the treatment of various diseases, and because therapeutic monoclonal antibodies are stored in an aqueous solution or in a lyophilized state, the preparation of a stabilizing formulation that prevents their deterioration (degradation and aggregation) is crucial. Given the structural similarities of the immunoglobulin G (IgG) framework regions and a diversity of only four subclasses, we aimed to find common conditions that stabilize many different antibodies. In this study, we analyzed the effect of pH (the most critical factor in establishing a stable formulation) on human monoclonal antibodies from subclasses IgG1, IgG2, and IgG4, all of which have been utilized in antibody therapeutics. We found that human IgGs are stable with minimal heat-induced degradation and aggregation at pH 5.0-5.5 irrespective of their subclass. We also found that IgG1 is more susceptible to fragmentation, whereas IgG4 is more susceptible to aggregation. This basic information emphasizing the influence of pH on IgG stability should facilitate the optimization of formulation conditions tailored to individual antibodies for specific uses.

Human embryonic stem cell-extracts inhibit the differentiation and function of monocyte-derived dendritic cells

Embryonic stem cells (ESC) possess inherent properties of immune privilege with the capacity to evade allogeneic immune responses. Moreover, ESCs have been shown to prevent immune activation in response to third party antigen presenting cells in vitro and have the capacity to promote allograft survival in vivo. However, clinical use of human ESCs to treat immunological disorders may risk teratoma or ectopic tissue formation. Here, we show that cellular extracts from both human and mouse ESCs retain the immune modulatory properties of intact cells. ESC-extracts that contained 12-24 μg of total protein effectively prevented T cell proliferation in allogeneic mixed lymphocyte reactions (MLR), whereas control fibroblast extracts did not affect proliferation. Cellular mechanisms underlying hESC extract-mediated immune modulation involve the maturation of monocyte derived dendritic cells (mDC). hESC extract-treated mDCs had reduced surface expression of co-stimulatory and maturation markers CD80, HLA-DR and CD83 and secreted lower levels of IL12p40. Accordingly, hESC extract-treated DCs were found to be poor stimulators of purified allogeneic T cells compared to those DCs treated with vehicle or fibroblast extracts. Our results demonstrate that ESC extracts retain the immune modulatory properties of ESCs and for the first time demonstrates that ESC derived factors can inhibit human mDC maturation and function.

Molecular level insights into thermally induced α-chymotrypsinogen A amyloid aggregation mechanism and semiflexible protofibril morphology

Understanding nonnative protein aggregation is critical not only to a number of amyloidosis disorders but also for the development of effective and safe biopharmaceuticals. In a series of previous studies [Weiss et al. (2007) Biophys. J. 93, 4392-4403; Andrews et al. (2007) Biochemistry 46, 7558-7571; Andrews et al. (2008) Biochemistry 47, 2397-2403], α-chymotrypsinogen A (aCgn) and bovine granulocyte colony stimulating factor (bG-CSF) have been shown to exhibit the kinetic and morphological features of other nonnative aggregating proteins at low pH and ionic strength. In this study, we investigated the structural mechanism of aCgn aggregation. The resultant aCgn aggregates were found to be soluble and exhibited semiflexible filamentous aggregate morphology under transmission electron microscopy. In addition, the filamentous aggregates were demonstrated to possess amyloid characteristics by both Congo red binding and X-ray diffraction. Peptide level hydrogen exchange (HX) analysis suggested that a buried native β-sheet comprised of three peptide segments (39-46, 51-64, and 106-114) reorganizes into the cross-β amyloid core of aCgn aggregates and that at least ∼50% of the sequence adopts a disordered structure in the aggregates. Furthermore, the equimolar, bimodal HX labeling distribution observed for three reported peptides (65-102, 160-180, and 229-245) suggested a heterogeneous assembly of two molecular conformations in aCgn aggregates. This demonstrates that extended β-sheet interactions typical of the amyloid are sufficiently strong that a relatively small fraction of polypeptide sequence can drive formation of filamentous aggregates even under conditions favoring colloidal stability.

The use of native cation-exchange chromatography to study aggregation and phase separation of monoclonal antibodies

This study introduces a novel analytical approach for studying aggregation and phase separation of monoclonal antibodies (mAbs). The approach is based on using analytical scale cation-exchange chromatography (CEX) for measuring the loss of soluble monomer in the case of individual and mixed protein solutions. Native CEX outperforms traditional size-exclusion chromatography in separating complex protein mixtures, offering an easy way to assess mAb aggregation propensity. Different IgG1 and IgG2 molecules were tested individually and in mixtures consisting of up to four protein molecules. Antibody aggregation was induced by four different stress factors: high temperature, low pH, addition of fatty acids, and rigorous agitation. The extent of aggregation was determined from the amount of monomeric protein remaining in solution after stress. Consequently, it was possible to address the role of specific mAb regions in antibody aggregation by co-incubating Fab and Fc fragments with their respective full-length molecules. Our results revealed that the relative contribution of Fab and Fc regions in mAb aggregation is strongly dependent on pH and the stress factor applied. In addition, the CEX-based approach was used to study reversible protein precipitation due to phase separation, which demonstrated its use for a broader range of protein-protein association phenomena. In all cases, the role of Fab and Fc was clearly dissected, providing important information for engineering more stable mAb-based therapeutics.

Some observations on the effects of bioprocessing on biopolymer stability

A short review is given of some of the effects of the stresses encountered during bioprocessing of protein and carbohydrate-based macromolecular systems. This is of relevance to the effectiveness and safety of protein or peptide drugs themselves (such as insulin and monoclonal antibodies) and for the integrity of delivery systems (such as various carbohydrate-based hydrogel or mucoadhesive polymers). Some carbohydrate polymers are themselves bioactive or immunostimulatory and particular use is being made of polysaccharide and glycoconjugate vaccines whose effectiveness can be severely effected by chain degradation. Stability criteria include molecular weight and conformation and techniques ranging from simple viscomery measurements to sophisticated analytical ultracentrifuge and multi-angle light scattering coupled to size exclusion chromatography and precision viscometry measurements have been useful in this regard. We focus on some recent work on the degradation and aggregation of immunoglobulin G4-based monoclonal antibodies in response to repeated freezing and thawing and long-term storage, looking at the possible connection between conformation change and aggregation, the effects of storage conditions on the stability of chitosan mucoadhesive systems used for nasal and oral delivery. We look at the effects of sterilization conditions (thermal and irradiation) on the stability of a variety of other polysaccharides such as starches, κ-carrageenan, carboxymethylcellulose, alginate, low- and high-methoxy pectins, guar, and xyloglucans and consider the use of a relatively new method for the evaluation of the molecular weight distribution of glycoconjugate vaccines with molecular weights as high as 100 × 10(6) g/mol.

Impact of product-related factors on immunogenicity of biotherapeutics

All protein therapeutics have the potential to be immunogenic. Several factors, including patient characteristics, disease state, and the therapy itself, influence the generation of an immune response. Product-related factors such as the molecule design, the expression system, post-translational modifications, impurities, contaminants, formulation and excipients, container, closure, as well as degradation products are all implicated. However, a critical examination of the available data shows that clear unequivocal evidence for the impact of these latter factors on clinical immunogenicity is lacking. No report could be found that clearly deconvolutes the clinical impact of the product attributes on patient susceptibility. Aggregation carries the greatest concern as a risk factor for immunogenicity, but the impact of aggregates is likely to depend on their structure as well as on the functionality (e.g., immunostimulatory or immunomodulatory) of the therapeutic. Preclinical studies are not yet capable of assessing the clinically relevant immunogenicity potential of these product-related factors. Simply addressing these risk factors as part of product development will not eliminate immunogenicity. Minimization of immunogenicity has to begin at the molecule design stage by reducing or eliminating antigenic epitopes and building in favorable physical and chemical properties.

Sustained prolonged topical delivery of bioactive human insulin for potential treatment of cutaneous wounds

Skin damaged by heat, radiation, or chemical exposure is difficult to treat and slow to heal. Indeed full restoration of the tissue is difficult to obtain. Sub-dermal insulin injection was recently shown to stimulate wound healing of the skin by accelerating wound closure, stimulating angiogenesis and inducing a regenerative process of healing. We have developed a topical delivery vehicle that is capable of releasing therapeutic levels of bioactive insulin for several weeks with the potential to stimulate and sustain healing. By encapsulating the crystalline form of insulin within poly(d,l-lactide-co-glycolide) microspheres, we succeeded in stabilizing and then releasing bioactive insulin for up to 25 days. To measure bioactivity we used Rat L6 myofibroblasts, stimulated them with this slow release insulin and determined activation of the receptors on the cell surface by quantifying AKT phosphorylation. There was only a minor and gradual decrease in AKT phosphorylation over time. To determine whether the slow release insulin could stimulate keratinocyte migration, wounding was simulated by scratching confluent cultures of human keratinocytes (HaCaT). Coverage of the scratch "wounds" was significantly faster in the presence of insulin released from microspheres than in the insulin-free control. Extended and sustained topical delivery of active insulin from a stable protein crystal-based reservoir shows promise in promoting tissue healing.

Rapid method for isolation of desiccation-tolerant strains and xeroprotectants

A novel biotechnological process has been developed for the isolation of desiccation-tolerant microorganisms and their xeroprotectants, i.e., compatible solutes involved in long-term stability of biomolecules in the dry state. Following exposure of soil samples to chloroform, we isolated a collection of desiccation-tolerant microorganisms. This collection was screened for the production of xeroprotectants by a variation of the bacterial milking (osmotic downshock) procedure and by a novel air-drying/rehydration ("dry milking") incubation method. The resultant solutes were shown to protect both proteins and living cells against desiccation damage, thereby validating them as xeroprotectants. Nuclear magnetic resonance (NMR) analytical studies were performed to identify the xeroprotectants; synthetic mixtures of these compounds were shown to perform similarly to natural isolates in drying experiments with proteins and cells. This new approach has biotechnological and environmental implications for the identification of new xeroprotectants of commercial and therapeutic value.

Investigating the effects of sodium dodecyl sulfate on the aggregative behavior of hen egg-white lysozyme at acidic pH

The research presented here is aimed at examining the effects of sodium dodecyl sulfate on the aggregative behavior of hen egg-white lysozyme at pH 2.0. Through various spectroscopic techniques, dynamic light scattering, and electron microscopy, we first demonstrated that SDS exhibited a biphasic effect on lysozyme fibrillation. The presence of SDS at higher concentrations (e.g., 0.25, 5.00, or 20.00 mM SDS) was found to suppress fibril formation of lysozyme whereas fibrillogenic lysozyme-SDS ensemble containing beta-sheet-rich conformation was observed upon the addition of lower concentrations of SDS (e.g., 0.00, 0.06, or 0.1mM SDS). Next, our equilibrium urea-unfolding data revealed that lysozyme samples with higher SDS concentrations showed superior thermodynamic stabilities over the ones with no or lower levels of SDS. Finally, the correlation between SDS concentration and lysozyme aggregative/fibrillogenic propensity and the underlying interacting mechanism were further explored using surface tensiometry and isothermal titration calorimetry. We believe the outcome from this work may not only help decipher the molecular mechanism of amyloid fibrillation, but also shed light on a rational design of potential therapeutic strategies for amyloid pathology.

Evaluation of a dual-wavelength size exclusion HPLC method with improved sensitivity to detect protein aggregates and its use to better characterize degradation pathways of an IgG1 monoclonal antibody

The evaluation of a dual wavelength size exclusion high performance liquid chromatography (DW-SE-HPLC) method with improved sensitivity to detect aggregates in a high concentration IgG1 monoclonal antibody formulation is presented. This technique utilizes ultraviolet detection at two different wavelengths to monitor the levels of monomer, aggregate, and fragments and was shown to have improved sensitivity for the detection aggregates and fragments compared to light scattering (LS) detection. After assay optimization including the use of column conditioning, the limit of quantitation for aggregates was determined to be 0.04% with essentially complete recovery of aggregates from the column (>99.5%). The DW-SE-HPLC method was used to evaluate the level of protein aggregates generated by different environmental conditions such as exposure to elevated temperatures/acidic pH or intense light. The detection and characterization of protein aggregates by DW-SE-HPLC was compared with an orthogonal biophysical technique (sedimentation velocity analytical ultracentrifugation, SV-AUC). A good overall correlation was observed for levels of monomer, aggregates (dimer and multimers), and fragments as measured by the two analytical techniques (e.g., 6.0% vs. 5.3% and 14% vs. 11% for dimeric aggregates generated by elevated temperature/acidic pH and light exposure, respectively). The stability profile of a high concentration IgG1 monoclonal antibody formulation was investigated under stressed storage conditions (40 degrees C over 3 months) using the DW-SE-HPLC method including the loss of monomeric species with the concomitant accumulation of both aggregates and fragments. The nature and composition of the aggregates (primarily noncovalent dimers) and fragments (primarily loss of Fab from an intact IgG1) formed during storage were further characterized by a combination of LS measurements and mass spectroscopy analysis of deglycosylated IgG1 samples isolated by preparative SE-HPLC. The combination of DW-SE-HPLC, SV-AUC, LS, and mass spectroscopy results provided a detailed overall understanding the monomer, aggregate, fragment degradation pathway(s) for a high concentration IgG1 monoclonal antibody formulation during storage.

Glycosylation of therapeutic proteins: an effective strategy to optimize efficacy

During their development and administration, protein-based drugs routinely display suboptimal therapeutic efficacies due to their poor physicochemical and pharmacological properties. These innate liabilities have driven the development of molecular strategies to improve the therapeutic behavior of protein drugs. Among the currently developed approaches, glycoengineering is one of the most promising, because it has been shown to simultaneously afford improvements in most of the parameters necessary for optimization of in vivo efficacy while allowing for targeting to the desired site of action. These include increased in vitro and in vivo molecular stability (due to reduced oxidation, cross-linking, pH-, chemical-, heating-, and freezing-induced unfolding/denaturation, precipitation, kinetic inactivation, and aggregation), as well as modulated pharmacodynamic responses (due to altered potencies from diminished in vitro enzymatic activities and altered receptor binding affinities) and improved pharmacokinetic profiles (due to altered absorption and distribution behaviors, longer circulation lifetimes, and decreased clearance rates). This article provides an account of the effects that glycosylation has on the therapeutic efficacy of protein drugs and describes the current understanding of the mechanisms by which glycosylation leads to such effects.

Binding mode of Thioflavin T and other molecular probes in the context of amyloid fibrils-current status

Because understanding amyloid fibrillation in molecular detail is essential for development of strategies to control amyloid formation and overcome neurodegenerative disorders, increased understanding of present molecular probes as well as development of new probes are of utmost importance. To date, the binding modes of these molecular probes to amyloid fibrils are by no means adequately described or understood, and the large number of studies on Thioflavin T (ThT) and Congo Red (CR) binding have resulted in models that are incomplete and conflicting. Different types of binding sites are likely to be present in amyloid fibrils with differences in binding modes. ThT may bind in channels running parallel to the long axis of the fibril. In the channels, ThT may bind in either a monomeric or dimeric form of which the molecular conformation is likely to be planar. CR may bind in grooves formed along the β-sheets as a planar molecule in either a monomeric or supramolecular form.

Factors influencing antibody stability at solid-liquid interfaces in a high shear environment

A rotating disk shear device was used to study the effect of interfacial shear on the structural integrity of human monoclonal antibodies of IgG4 isotype. Factors associated with the solution conditions (pH, ionic strength, surfactant concentration, temperature) and the interface (surface roughness) were studied for their effect on the rate of IgG4 monomer loss under high shear conditions. The structural integrity of the IgG4 was probed after exposure to interfacial shear effects by SDS-PAGE, IEF, dynamic light scattering, and peptide mapping by LC-MS. This analysis revealed that the main denaturation pathway of IgG4 exposed to these effects was the formation of large insoluble aggregates. Soluble aggregation, breakdown in primary structure, and chemical modifications were not detected. The dominant factors found to affect the rate of IgG4 monomer loss under interfacial shear conditions were found to be pH and the nanometer-scale surface roughness associated with the solid-liquid interface. Interestingly, temperature was not found to be a significant factor in the range tested (15-45 degrees C). The addition of surfactant was found to have a significant stabilizing effect at concentrations up to 0.02% (w/v). Implications of these findings for the bioprocessing of this class of therapeutic protein are briefly discussed.

Amyloid fibrillation and cytotoxicity of insulin are inhibited by the amphiphilic surfactants

Amyloid fibrils have been associated with at least 25 different degenerative diseases. The 51-residue polypeptide hormone insulin, which is associated with type II diabetes, has been shown to self-assemble to form amyloid fibrils in vitro. With bovine insulin as a model, the research presented here explores the effects of two amphiphilic surfactants (1,2-dihexanoyl-sn-glycero-3-phosphocholine (di-C7-PC) and 1,2-diheptanoyl-sn-glycero-3-phosphocholine (di-C7-PC)) on the in vitro fibrillation process of bovine insulin at pH 2.0 and 55 degrees C. We demonstrated that insulin fibrillation may be inhibited by both surfactants in a dose-dependent fashion. The best inhibition of fibril formation is observed when insulin is incubated with 4mM di-C7-PC. Moreover, the addition of either surfactant at the concentrations studied attenuated insulin fibril-induced cytotoxicity in both PC12 and SH-SY5Y cell lines. The results from this work may contribute to the understanding of the molecular factors affecting amyloid fibrillation and the molecular mechanism(s) of the interactions between the membrane and amyloid proteins.

Strategies to increase the reproducibility of protein fibrillization in plate reader assays

There is great interest in developing reproducible high-throughput screens to identify small molecular inhibitors of protein fibrillization and aggregation for possible therapy against deposition diseases such as Alzheimer's and Parkinson's (PD). We have made a methodical analysis of factors increasing the reproducibility of the fibrillization of alpha-synuclein (alphaSN), a 140-amino-acid protein implicated in PD and notorious for its erratic fibrillization behavior. Salts and polyanionic polymers do not significantly improve the quality of the assay. However, an orbital agitation mode in the plate reader is a crucial first step toward reproducible alphaSN fibrillization. Higher reproducibility is achieved by the addition of glass beads, as evaluated by the percentage standard deviation of the nucleation and elongation rate constants and the end-stage fluorescence intensity of the fibril-binding dye thioflavin T (ThT). The highest reproducibility is obtained by either seeding the solution with preformed fibrils or by adding submicellar amounts of sodium dodecyl sulfate (SDS), where we obtain percentage standard deviations of 3-4% on the end ThT level. We conclude that there are multiple ways to achieve satisfactory levels of reproducibility, although the different conditions used to induce aggregation may lead to different fibrillization pathways.

Stability of protein pharmaceuticals: an update

In 1989, Manning, Patel, and Borchardt wrote a review of protein stability (Manning et al., Pharm. Res. 6:903-918, 1989), which has been widely referenced ever since. At the time, recombinant protein therapy was still in its infancy. This review summarizes the advances that have been made since then regarding protein stabilization and formulation. In addition to a discussion of the current understanding of chemical and physical instability, sections are included on stabilization in aqueous solution and the dried state, the use of chemical modification and mutagenesis to improve stability, and the interrelationship between chemical and physical instability.

The protein kingdom extended: ordered and intrinsically disordered proteins, their folding, supramolecular complex formation, and aggregation

The native state of a protein is usually associated with a compact globular conformation possessing a rigid and highly ordered structure. At the turn of the last century certain studies arose which concluded that many proteins cannot, in principle, form a rigid globular structure in an aqueous environment, but they are still able to fulfill their specific functions--i.e., they are native. The existence of the disordered regions allows these proteins to interact with their numerous binding partners. Such interactions are often accompanied by the formation of complexes that possess a more ordered structure than the original components. The functional diversity of these proteins, combined with the variability of signals related to the various intra- and intercellular processes handled by these proteins and their capability to produce multi-variant and multi-directional responses allow them to form a unique regulatory net in a cell. The abundance of disordered proteins inside the cell is precisely controlled at the synthesis and clearance levels as well as via interaction with specific binding partners and post-translational modifications. Another recently recognized biologically active state of proteins is the functional amyloid. The formation of such functional amyloids is tightly controlled and therefore differs from the uncontrolled formation of pathogenic amyloids which are associated with the pathogenesis of several conformational diseases, the development of which is likely to be determined by the failures of the cellular regulatory systems rather than by the formation of the proteinaceous deposits and/or by the protofibril toxicity.

Elution behavior of insulin on high-performance size exclusion chromatography at neutral pH

The pharmacopoeia protocol for HP-SEC of insulin, using an acidic non-physiological eluent, does not represent insulin's association state in the formulation. This study aimed to evaluate insulin's elution behavior in HP-SEC in a "physiological" (aqueous, neutral pH) eluent, using on-line UV absorption and multi-angle laser light scattering detection. The effect of insulin concentration and association state in the formulation (monitored by circular dichroism) and eluent composition (zinc ion, arginine) on its elution behavior was assessed. We showed that the elution behavior of insulin in "physiological" HP-SEC is affected by both dynamic association-dissociation of insulin molecules and insulin-column interactions. Insulin molecules re-equilibrated in the HP-SEC eluent, making its elution behavior practically insensitive to the association state of insulin in the formulation. Zinc ions in the eluent promoted association of insulin to hexamers, whereas arginine overruled the effect of zinc ions and induced on-column dissociation of insulin to dimers and monomers. Combined results from "physiological" and compendial HP-SEC were shown to provide a better view of the aggregation state of heat-stressed insulin than either of the single methods. The insights obtained with this study are crucial for a proper evaluation of HP-SEC data of insulin.