Stabilization of a hydrophobic recombinant cytokine by human serum albumin

Pharmaceutical proteins at the interfaces and the role of albumin

A critical measure of the quality of pharmaceutical proteins is the preservation of native conformations of the active pharmaceutical ingredients. Denaturation of the active proteins in any step before administration into patients could lead to loss of potency and/or aggregation, which is associated with an increased risk of immunogenicity of the products. Interfacial stress enhances protein instability as their adsorption to the air-liquid and liquid-solid interfaces are implicated in the formation of denatured proteins and aggregates. While excipients in protein formulations have been employed to reduce the risk of aggregation, the roles of albumin as a stabilizer have not been reviewed from practical and theoretical standpoints. The amphiphilic nature of albumin makes it accumulate at the interfaces. In this review, we aim to bridge the knowledge gap between interfacial instability and the influence of albumin as a surface-active excipient in the context of reducing the immunogenicity risk of protein formulations.

A Narrative Literature Review of the Established Safety of Human Serum Albumin Use as a Stabilizer in Aesthetic Botulinum Toxin Formulations Compared to Alternatives

Despite more than 80 years of use in a number of conditions, including in critically ill patients, comments have recently arisen regarding the safety and efficacy of human serum albumin (HSA) as a therapeutic product and stabilizer/excipient in botulinum neurotoxins. This review summarizes the literature on the safety of HSA. Beyond decades of safe use, the largest clinical dataset of HSA safety is a large meta-analysis of HSA supplier data, which found only an extremely remote risk of serious adverse events across millions of doses of therapeutic concentrations of HSA. There is a paucity of literature identifying HSA-specific adverse events when used as a stabilizer/excipient; however, studies of HSA-containing botulinum neurotoxins (BoNTs) suggest that adverse events are not related to HSA. Polysorbates, which are synthetically produced and not physiologically inert, are contained in pending or new-to-market BoNT formulations. In contrast to HSA, evidence exists to suggest that polysorbates (particularly PS20/PS80) can cause serious adverse events (e.g., hypersensitivity, anaphylaxis, and immunogenicity).

Stabilisation of Recombinant Human Basic Fibroblast Growth Factor (FGF-2) against Stressors Encountered in Medicinal Product Processing and Evaluation

Basic fibroblast growth factor (FGF-2) is a highly labile protein with strong potential for tissue engineering. The aim of this study was to develop FGF-2 formulations that are stable against physical stressors encountered in pharmaceutical processing and evaluation. Pharmaceutical excipients, alone or in combination, were added to aqueous FGF-2 (770 ng/mL) solution and the stability of the resulting solutions on storage at 4–37 °C was evaluated. Stability of the solutions to repeated freeze-thaw cycles and lyophilisation was also evaluated, as well as the stability of the lyophilised stabilised protein to storage at −4, 4 and 18 °C for up to 12 months. In all of these experiments FGF-2 was quantified by ELISA assay. The as-received FGF-2, when dissolved in water, was highly unstable, retaining only 50% of baseline protein content after 30 min at 37 °C or 1 h at 25 °C. By contrast, FGF-2 solutions prepared with 0.5% w/v methylcellulose (MC) and 20 mM alanine (formulation F5) or with 0.5% w/v MC and 1 mg/mL human serum albumin (HSA) (formulation F6) were highly stable, having residual FGF-2 content comparable to baseline levels even after 2 h at 37 °C and 5 h at 25 °C. F5 and F6 were also highly stable to repeated freeze-thaw cycles, with >99% of FGF-2 load remaining after the third cycle. In addition, F5 and F6 were stable to lyophilisation, and the lyophilised products could be stored at −4, 4 or 18 °C for at least 12 months, with less than 1% loss in mean FGF-2 content. Thus, FGF-2 solution is effectively stabilised against both thermal and processing stressors in the presence of MC and alanine (F5), or MC and HSA (F6). The resultant FGF-2 solutions may be applied as medicinal products or further processed into more advanced medicinal products, e.g., scaffolds, for wound healing and tissue regeneration.

Bone Morphogenetic Protein 2 (BMP-2) Aggregates Can be Solubilized by Albumin-Investigation of BMP-2 Aggregation by Light Scattering and Electrophoresis

Bone morphogenetic protein 2 (BMP-2) has a high tendency to aggregate at physiological pH and physiological ionic strength, which can complicate the development of growth factor delivery systems. The aggregation behavior in differently concentrated BMP-2 solutions was investigated using dynamic and static light scattering. It was found that at higher concentrations larger aggregates are formed, whose size decreases again with increasing dilution. A solubilizing effect and therefore less aggregation was observed upon the addition of albumin. Imaged capillary isoelectric focusing and the simulation of the surface charges of BMP-2 were used to find a possible explanation for the unusually low solubility of BMP-2 at physiological pH. In addition to hydrophobic interactions, attractive electrostatic interactions might be decisive in the aggregation of BMP-2 due to the particular distribution of surface charges. These results help to better understand the solubility behavior of BMP-2 and thus support future pharmaceutical research and the development of new strategies for the augmentation of bone healing.

Determination of Protein-Protein Interactions in a Mixture of Two Monoclonal Antibodies

The coformulation of monoclonal antibody (mAb) mixtures provides an attractive route to achieving therapeutic efficacy where the targeting of multiple epitopes is necessary. Controlling and predicting the behavior of such mixtures requires elucidating the molecular basis for the self- and cross-protein-protein interactions and how they depend on solution variables. While self-interactions are now beginning to be well understood, systematic studies of cross-interactions between mAbs in solution do not exist. Here, we have used static light scattering to measure the set of self- and cross-osmotic second virial coefficients in a solution containing a mixture of two mAbs, mAbA and mAbB, as a function of ionic strength and pH. mAbB exhibits strong association at a low ionic strength, which is attributed to an electrostatic attraction that is enhanced by the presence of a strong short-ranged attraction of nonelectrostatic origin. Under all solution conditions, the measured cross-interactions are intermediate self-interactions and follow similar patterns of behavior. There is a strong electrostatic attraction at higher pH values, reflecting the behavior of mAbB. Protein-protein interactions become more attractive with an increasing pH due to reducing the overall protein net charges, an effect that is attenuated with an increasing ionic strength due to the screening of electrostatic interactions. Under moderate ionic strength conditions, the reduced cross-virial coefficient, which reflects only the energetic contribution to protein-protein interactions, is given by a geometric average of the corresponding self-coefficients. We show the relationship can be rationalized using a patchy sphere model, where the interaction energy between sites i and j is given by the arithmetic mean of the i-i and j-j interactions. The geometric mean does not necessarily apply to all mAb mixtures and is expected to break down at a lower ionic strength due to the nonadditivity of electrostatic interactions.

Human Serum Albumin, a Suitable Candidate to Stabilize Freeze-Dried IgG in Combination with Trehalose: Central Composite Design

Freeze-dried immunoglobulin G (IgG) incorporating trehalose and human serum albumin (HSA) was statistically evaluated regarding the existence of synergism between additives on the stability profile. The levels of HSA (X₁) and trehalose (X₂) were independent variables. Aggregation following the process (Y₁), after 2 and 3 months at 40°C (Y₂) and (Y₃), respectively, along with the rate constant of aggregation (Y₄) were dependent variables. Aggregation and beta-sheet conformation were quantified through size-exclusion chromatography (SEC-HPLC) and Fourier transform infrared spectroscopy (FTIR). Central composite design (CCD) suggested the best formulation. The integrity and thermodynamic stability of optimized formulation were investigated through sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and differential scanning calorimetry (DSC). The calculated responses were Y₁, 0-0.90%; Y₂, 0.4-4.3%; Y₃, 2.10-13.46%; and Y₄, 0.16-0.69 1/month. The optimized formulation had 10 mg IgG, 86 mg trehalose, and 1 mg HSA with observed responses of Y₁, 0.01%; Y₂, 0.51%; Y₃, 3.08%; and Y₄, 0.33 1/month. The models were statistically well-fitted. The optimized formulation was amorphous during freeze-drying (FD), and no fragmentation was observed. Trehalose and HSA demonstrated statistical synergism. CCD was successfully employed to recommend the best ratio of stabilizers and achieve the maximum stabilization of IgG as a model freeze-dried antibody.

Stabilized Interleukin-4-Loaded Poly(lactic-co-glycolic) Acid Films Shift Proinflammatory Macrophages toward a Regenerative Phenotype in Vitro

Macrophages are immune cells involved in wound healing and tissue regeneration; however, the sustained presence of proinflammatory macrophages in wound sites impairs healing. In this study, we shifted peritoneal macrophage polarization away from a proinflammatory (M1) phenotype through exposure to stabilized interleukin-4 (IL-4) in poly(lactic-co-glycolic acid) films in combination with topographical guidance from electrospun poly-L-lactic acid fibers. To our knowledge, this was the first study to stabilize IL-4 with bovine serum albumin (BSA) within a biomaterial. When IL-4 was coloaded with BSA for stabilization, we saw increased IL-4 bioactivity compared to no added stabilization, trehalose stabilization, or murine serum albumin stabilization. We observed increased elongation of peritoneal macrophages, increased RNA expression of anti-inflammatory marker arginase-1, increased ratio of interleukin-10/interleukin- 12 p40 RNA, and decreased protein expression of proinflammatory markers (interleukin-12 p40 and RANTES) compared to controls. Taken together, these results suggest the macrophages were less proinflammatory and were a more pro-resolving phenotype. When stabilized with BSA, IL-4-loaded films effectively shift macrophage polarization state and are thus promising scaffolds to reduce inflammation within in vivo injury models.

Expanding Bedside Filtration-A Powerful Tool to Protect Patients From Protein Aggregates

Protein immunogenicity is intensively researched by academics, biopharmaceutical companies, and authorities as it can compromise the safety and efficacy of a biopharmaceutical drug. So far, the exact protein aggregate properties inducing immune responses are not known. Possible protein-related factors could be size, chemical modifications, or higher order structures. It is impossible to achieve an absolute absence of protein aggregates even for very stable formulations. The application of "bedside filtration," meaning filtration during the preparation or administration of the drug product immediately before injection, has the potential to increase the safety of every drug container and could prevent the undesired injection of particulate matter into the patient. In this study, the high efficiency of filtration for reducing the amount of protein particles was demonstrated with more than 19 stressed and nonstressed biopharmaceutical products which covered a broad concentration and molecular weight range. Furthermore, critical aspects regarding the usage of filters such as particle shedding from filters, protein loss as a result of protein adsorption, or the hold-up volume of the filters were assessed. Although differences between the filters were observed, no negative impact by the investigated filters could be found. A broader application of bedside filtration is therefore proposed.

Site-Specific Albumination as an Alternative to PEGylation for the Enhanced Serum Half-Life in Vivo

Polyethylene glycol (PEG) has been widely used as a serum half-life extender of therapeutic proteins. However, due to immune responses and low degradability of PEG, developing serum half-life extender alternatives to PEG is required. Human serum albumin (HSA) has several beneficial features as a serum half-life extender, including a very long serum half-life, good degradability, and low immune responses. In order to further evaluate the efficacy of HSA, we compared the extent of serum half-life extension of a target protein, superfolder green fluorescent protein (sfGFP), upon HSA conjugation with PEG conjugation side-by-side. Combination of site-specific incorporation of p-azido-l-phenylalanine into sfGFP and copper-free click chemistry achieved the site-specific conjugation of a single HSA, 20 kDa PEG, or 30 kDa PEG to sfGFP. These sfGFP conjugates exhibited the fluorescence comparable to or even greater than that of wild-type sfGFP (sfGFP-WT). In mice, HSA-conjugation to sfGFP extended the serum half-life 9.0 times compared to that of unmodified sfGFP, which is comparable to those of PEG-conjugated sfGFPs (7.3 times for 20 kDa PEG and 9.5 times for 30 kDa PEG). These results clearly demonstrated that HSA was as effective as PEG in extending the serum half-life of a target protein. Therefore, with the additional favorable features, HSA is a good serum half-life extender of a (therapeutic) protein as an alternative to PEG.

Spatially localized recruitment of anti-inflammatory monocytes by SDF-1α-releasing hydrogels enhances microvascular network remodeling

Tissue repair processes are characterized by the biphasic recruitment of distinct subpopulations of blood monocytes, including classical ("inflammatory") monocytes (IMs, Ly6C(hi)Gr1(+)CX3CR1(lo)) and non-classical anti-inflammatory monocytes (AMs, Ly6C(lo)Gr1(-)CX3CR1(hi)). Drug-eluting biomaterial implants can be used to tune the endogenous repair process by the preferential recruitment of pro-regenerative cells. To enhance recruitment of AMs during inflammatory injury, a novel N-desulfated heparin-containing poly(ethylene glycol) diacrylate (PEG-DA) hydrogel was engineered to deliver exogenous stromal derived factor-1α (SDF-1α), utilizing the natural capacity of heparin to sequester and release growth factors. SDF-1α released from the hydrogels maintained its bioactivity and stimulated chemotaxis of bone marrow cells in vitro. Intravital microscopy and flow cytometry demonstrated that SDF-1α hydrogels implanted in a murine dorsal skinfold window chamber promoted spatially-localized recruitment of AMs relative to unloaded internal control hydrogels. SDF-1α delivery stimulated arteriolar remodeling that was correlated with AM enrichment in the injury niche. SDF-1α, but not unloaded control hydrogels, supported sustained arteriogenesis and microvascular network growth through 7 days. The recruitment of AMs correlated with parameters of vascular remodeling suggesting that tuning the innate immune response by biomaterial SDF-1α release is a promising strategy for promoting vascular remodeling in a spatially controlled manner.

The Role of Protein Excipient in Driving Antibody Responses to Erythropoietin

Human serum albumin (HSA) is an excipient present in formulations of several recombinant protein products that are approved for clinical use. We investigated the relative contributions of HSA and HSA particles to the generation of antibody responses against recombinant human erythropoietin (rhEPO) and the excipient HSA itself. Protein samples were characterized before injection for quantities of monomeric proteins, soluble protein aggregates, and nano- and micron-sized particles. rhEPO, containing various concentrations of HSA particles, were injected three times a week for 8 weeks into mice. Hematocrits and the production of anti-rhEPO and anti-HSA antibodies were determined at various time points. Levels of antibodies against rhEPO in mice injected with HSA-containing rhEPO were higher than those in mice treated with HSA-free rhEPO. Mice injected with formulations that contained particles of HSA produced strong anti-HSA antibody responses; whereas these responses were greatly reduced when particle-free formulations were administered. In contrast, anti-rhEPO antibody responses were not affected by the presence of particles.

Determination of supplier-to-supplier and lot-to-lot variability in glycation of recombinant human serum albumin expressed in Oryza sativa

The use of different expression systems to produce the same recombinant human protein can result in expression-dependent chemical modifications (CMs) leading to variability of structure, stability and immunogenicity. Of particular interest are recombinant human proteins expressed in plant-based systems, which have shown particularly high CM variability. In studies presented here, recombinant human serum albumins (rHSA) produced in Oryza sativa (Asian rice) (OsrHSA) from a number of suppliers have been extensively characterized and compared to plasma-derived HSA (pHSA) and rHSA expressed in yeast (Pichia pastoris and Saccharomyces cerevisiae). The heterogeneity of each sample was evaluated using size exclusion chromatography (SEC), reversed-phase high-performance liquid chromatography (RP-HPLC) and capillary electrophoresis (CE). Modifications of the samples were identified by liquid chromatography-mass spectrometry (LC-MS). The secondary and tertiary structure of the albumin samples were assessed with far U/V circular dichroism spectropolarimetry (far U/V CD) and fluorescence spectroscopy, respectively. Far U/V CD and fluorescence analyses were also used to assess thermal stability and drug binding. High molecular weight aggregates in OsrHSA samples were detected with SEC and supplier-to-supplier variability and, more critically, lot-to-lot variability in one manufactures supplied products were identified. LC-MS analysis identified a greater number of hexose-glycated arginine and lysine residues on OsrHSA compared to pHSA or rHSA expressed in yeast. This analysis also showed supplier-to-supplier and lot-to-lot variability in the degree of glycation at specific lysine and arginine residues for OsrHSA. Both the number of glycated residues and the degree of glycation correlated positively with the quantity of non-monomeric species and the chromatographic profiles of the samples. Tertiary structural changes were observed for most OsrHSA samples which correlated well with the degree of arginine/lysine glycation. The extensive glycation of OsrHSA from multiple suppliers may have further implications for the use of OsrHSA as a therapeutic product.

Particles in therapeutic protein formulations, Part 1: overview of analytical methods

The presence of particles is a major issue during therapeutic protein formulation development. Both proteinaceous and nonproteinaceous particles need to be analyzed not only due to the requirements of the Pharmacopeias but also to monitor the stability of the protein formulation. Increasing concerns about the immunogenic potential together with new developments in particle analysis make a comparative description of established and novel analytical methods useful. Our review aims to provide a comprehensive overview on analytical methods for the detection and characterization of visible and subvisible particles in therapeutic protein formulations. We describe the underlying theory, benefits, shortcomings, and illustrative examples for quantification techniques, as well as characterization techniques for particle shape, morphology, structure, and identity.

The use of flow cytometry for the detection of subvisible particles in therapeutic protein formulations

The amount, identity, and size distribution of particles in parenteral therapeutic protein formulations are of immense interest due to potential safety and efficacy-related implications. In this communication, we describe the use of a flow cytometer equipped with forward- and side-scattering as well as fluorescence detectors, to determine the number of subvisible particles in monoclonal antibody formulations. The method appears to detect particles of size 1 μ and larger, requiring relatively small sample volumes to estimate subvisible particle counts. Additionally, it facilitates differentiation of proteinaceous particles after staining with a fluorescent hydrophobic dye. The method is expected to be particularly well suited for pharmaceutical development, because it provides increased throughput due to the use of a 96-well autosampler.

Flow cytometry: a promising technique for the study of silicone oil-induced particulate formation in protein formulations

Subvisible particles in formulations intended for parenteral administration are of concern in the biopharmaceutical industry. However, monitoring and control of subvisible particulates can be complicated by formulation components, such as the silicone oil used for the lubrication of prefilled syringes, and it is difficult to differentiate microdroplets of silicone oil from particles formed by aggregated protein. In this study, we demonstrate the ability of flow cytometry to resolve mixtures comprising subvisible bovine serum albumin (BSA) aggregate particles and silicone oil emulsion droplets with adsorbed BSA. Flow cytometry was also used to investigate the effects of silicone oil emulsions on the stability of BSA, lysozyme, abatacept, and trastuzumab formulations containing surfactant, sodium chloride, or sucrose. To aid in particle characterization, the fluorescence detection capabilities of flow cytometry were exploited by staining silicone oil with BODIPY 493/503 and model proteins with Alexa Fluor 647. Flow cytometric analyses revealed that silicone oil emulsions induced the loss of soluble protein via protein adsorption onto the silicone oil droplet surface. The addition of surfactant prevented protein from adsorbing onto the surface of silicone oil droplets. There was minimal formation of homogeneous protein aggregates due to exposure to silicone oil droplets, although oil droplets with surface-adsorbed trastuzumab exhibited flocculation. The results of this study demonstrate the utility of flow cytometry as an analytical tool for monitoring the effects of subvisible silicone oil droplets on the stability of protein formulations.

Aggregated recombinant human interferon Beta induces antibodies but no memory in immune-tolerant transgenic mice

Purpose

To study the influence of protein aggregation on the immunogenicity of recombinant human interferon beta (rhIFNβ) in wild-type mice and transgenic, immune-tolerant mice, and to evaluate the induction of immunological memory.

Methods

RhIFNβ-1b and three rhIFNβ-1a preparations with different aggregate levels were injected intraperitoneally in mice 15× during 3 weeks, and the mice were rechallenged with rhIFNβ-1a. The formation of binding (BABs) and neutralizing antibodies (NABs) was monitored.

Results

Bulk rhIFNβ-1a contained large, mainly non-covalent aggregates and stressed rhIFNβ-1a mainly covalent, homogeneous (ca. 100 nm) aggregates. Reformulated rhIFNβ-1a was essentially aggregate-free. All products induced BABs and NABs in wild-type mice. Immunogenicity in the transgenic mice was product dependent. RhIFNβ-1b showed the highest and reformulated rhIFNβ-1a the lowest immunogenicity. In contrast with wild-type mice, transgenic mice did not show NABs, nor did they respond to the rechallenge.

Conclusions

The immunogenicity of the products in transgenic mice, unlike in wild-type mice, varied. In the transgenic mice, neither NABs nor immunological memory developed. The immunogenicity of rhIFNβ in a model reflecting the human immune system depends on the presence and the characteristics of aggregates.

Trimeric coiled-coil domain of human pulmonary surfactant protein D enhances zinc-binding ability and biologic activity of soluble TRAIL

Unlike other TNF ligand family members, the homotrimeric tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) contains a buried zinc atom coordinated by three Cys230 residues from each subunit. The bound zinc ion is essential for maintaining the structure stability and bioactivity of TRAIL. To improve characteristics of TRAIL by modification to enhance its zinc-binding ability, we constructed a new variant of TRAIL in which the extracellular region of the ligand was N-terminally fused with a trimeric coiled-coil domain derived from human pulmonary surfactant-associated protein D (ST), and compared its characteristics with that of native TRAIL. Circular dichroism (CD) studies and metal assays showed that two versions of TRAIL folded as predicted into secondary and tertiary structures, and contained stoichiometric Zn(2+) through optimizing bacterial expression and purification. The addition of the human trimeric coiled-coil domain, however, significantly increased the antitumor activity of soluble TRAIL in vitro and in vivo. The accelerated thermal stability studies demonstrated that human serum album (HSA) promoted the aggregation and degradation of native TRAIL, but not ST, and the addition of ZnSO(4) to the solution of native TRAIL with HSA partially inhibited its aggregation, suggesting ST is more difficult to lose its bound zinc ion than native TRAIL. The issue was further confirmed by dialysis assess. This is the first example of modified TRAIL with enhanced zinc-binding ability.